Review of literature

2. Review of literature

2.1. Growth parameters

Eucalyptus species are not consistent in their growth and the variation is considerable

depending upon the conditions under which they are grown. Therefore depending upon the site,

selection of species and their provenances the actual yields have varied considerably.

Phanuel Oballa et al., (2005) studied the growth performance of different Eucalyptus

clones and the seedlings and reported that, all the clones performed equally well at this site as

compared to the local landraces, clone GC14 had a height of 17.15 m while the local landraces E.

camaldulensis and E. tereticornis had the lowest height of 11.99 m and 11.58 m respectively. In

the case of DBH, there were significant differences in DBH in year three at p < 0.001. The best

performing clones and species at this site are GC15, GC581, GC14 and GC642. E. camaldulensis

and E. tereticornis did not perform well at this site, as they are more adapted to low and warmer

sites.

The varied growth trends in the different sites showed a strong environment-by-clone interaction,

an observation supported by Wamalwa et al., (2007).

Balozi Kirongo et al., (2010) reported that, the potential of Eucalyptus clones to

outperform local Eucalyptus species. However, the trial results for the local Eucalyptus species

recorded the mean height of 18.40 m (i.e. E. camaldulensis, E. tereticornis and E.urophylla)

were much poorer especially for E. urophylla with a mean height of 12.05 m compared to clones

in height and girth parameters.

Height of Eucalyptus differed significantly among different Eucalyptus species. E. hybrid

recorded significantly higher height (11.25 m) followed by E. grandis (10.90 m) and E.

tereticornis (10.35 m). Lowest height was recorded in E. pelleta (9.10 m). Height increment was

significantly higher in E. hybrid followed by E. tereticornis and E. grandis throughout the

growing season. The maximum height increments of 2.36 and 2.18 m were observed during 2005

in E. teriticornis and E. hybrid respectively. E. hybrid recorded significantly higher DBH (20.18

cm) followed by E. tereticornis (18.60 cm) and lowest diameter was observed in E. pelleta

(12.14 cm) and the clone selected from Dandeli (10.86 cm). Current annual increment in dbh was

significantly higher in E. tereticornis and E. hybrid and lowest was observed in E. pelleta. Mean

annual increment in DBH was significantly higher in E. tereticornis (2.33 cm) and E. hybrid

(2.52 cm) as compared to the clone selected from Dandeli (1.36 cm) (Patil et al., 2012).

Similarly significant differences in different Eucalyptus species have been reported by

various workers. Lal (2005) conducted a study to assess the comparative growth performance of

various Eucalyptus species. Kumar and Bangawa (2006) observed significant differences for

growth attributes among seven species of Eucalyptus species. Maximum MAI for diameter at

breast height was recorded in E. tereticornis and E. hybrid.

Patil et al., (2012) revealed that, among the Eucalyptus species maximum variation was

observed in E. tereticornis for all the characters under this study. Significantly higher values

were observed in current annual increment of total height, clear bole height and diameter

increment in E. tereticornis and E. hybrid. These results are in confirmation with results of

Gomes and Correia (1995) and Kumar and Bangarwa (2006).

Significant differences were observed between G×N hybrid clones in both growth and

snow tolerance. The top-performing clones significantly outperformed both pure species controls

in terms of growth and snow tolerance. Early results indicate that G×N hybrids may be better

suited to high-potential, mid-altitude sites exposed to light snow risk than the currently

recommended pure species (Iain Thompson, 2013).

Evaluation of Provenances of E. camaldulensis and clones of E. camaldulensis and E.

tereticornis at contrasting sites in Southern India by Varghese et al., (2008) revealed that,

interaction of provenance performance with site was significant. Within-provenance individual-

tree heritabilities for height and diameter at breast height (dbh) were low at the three individual

sites, ranging from 0.08 ± 0.05 to 0.19 ± 0.05 for height and 0.10 ± 0.05 to 0.19 ± 0.04 for dbh.

Across-site heritabilities, 0.07 ± 0.02 for both height and dbh, were lower than those at

individual sites.

Wei Zhongmian et al., (2009) evaluated the growth comparison of eight year old

Eucalyptus clones (Eucalyptus urophylla × E. grandis clones 3229, 30-1 and E. urophylla clone

U6) and revealed that, Eucalyptus clones showed high growth rate during the first three years.

There were significant differences amongst the 3 Eucalyptus clones in plant height, diameter and

volume growth. These indexes were positively correlated with the increasing age. Clone 3229

showed best growth followed by 30-1, while the U6 grew worst.

2.2. Biomass and Productivity

The general term ‘productivity’ may be considered as the rate of net primary production. Mean

annual net primary productivity is obtained by averaging the biomass over the age of the stand. The

production by a plant community is the reflection of its capacity to assimilate solar energy under some set

of environmental conditions.

Wood production varies substantially with resource availability, and the variation in

wood production can result from several mechanisms: increased photosynthesis, and changes in

partitioning of photosynthesis to wood production, belowground flux, foliage production or

respiration.

Different plant communities have different rates of biomass production, based on their efficiency.

High producing forest plantations in Europe generally attain a biomass of approximately 350X103 kg ha

-1

at about 50 years of age.

Vijay Rawat and Negi (2004) reported that, Eucalyptus plantations raised from seed

origin, produced the biomass range from 11.9 t ha-1

in three year old plantation to 146 t ha-1

than

in 9 year old plantation in moist regions. In dry tropical region it varied from 5.65 t ha-1

in 5 year

plantation to 135.5 t ha-1

in 9 year old plantation. In dry tropical regions biomass accumulation

was more in cooler areas as compared to warmer areas. Where water is not the limiting factor,

comparatively higher mean annual temperature of around 25 °C seems to produce higher

biomass. A higher share of leaf biomass was observed in dry region. Prabhakar (1998) reported

that, under eight year rotation, the mean annual growth of Eucalyptus per hectare, is about 8

cubic metres (cu. m.), though has been known to reach as much as 40 cu. m, while for

indigenous trees, the average is 0.50 cu. m.

Very short rotation (2 to 6 years) clonal eucalypt plantations are producing very high

volumes (40-80 m3 ha

-1 yr

-1), MAIs of 60 m

3 ha

-1 yr

-1 have been reported in Brazil (Laércio

Couto et al., 2011). E. grandis has an MAI range from about 20-47 m3 ha

-1 yr

-1, with optimum

rotation of 7-10 years in Uganda (Dennis Alder et al., 2003). Reyna Perez-Sandoval et al.,

(2012) reported that mean annual increments (MAI) of E. urophylla and E. grandis were

comparable to other regions of the world reaching 49 m3

ha−1

yr−1

across a range of low to high

soil fertility gradient (15 to 80 m3 ha

−1 yr

−1) in Mexico.

Overall biomass produced by the Eucalyptus was 2-8 folds higher than native species

while water use [transpiration] was 2-3 folds. Translating this into transpiration coefficient (TC)

and WUE, Eucalyptus growth performance was better than native species. Data showed that

Eucalyptus was very efficient water users with TC of 739 L kg-1

as compared to Acacia, Albizzia,

and Azadirachta which used 1042 L, 872 L and 1951 L of water to produce one kg of biomass

(Din Muhammad Zahid et al., 2010). It was reported by Kallarackal and Somen, (1997) that

under low relative humidity and without supply of nutrients the TC becomes higher.

Eucalyptus shows a broad productivity response depending on species, clones and soils

factors (Onyekwelu et al., 2011). Eucalyptus sp. has some of the highest net primary productivity

rates up to 49 m3

ha–1

yr–1

. Mean annual increments of clone plantations of Eucalyptus sp. with

no fertilization, with fertilization and fertilization combined with irrigation are 33, 46 and 62 m3

ha–1

yr–1

, respectively (Stape et al., 2010).

Eucalyptus hybrids plantations (E. urophylla × E. grandis) in South America recorded

productivity ranging from 15 - 60 m3

ha–1

yr–1

. Rodríguez et al., (2009) reported MAI in

plantations of E. nitens in Chile ranging from 47 to 52 m3

ha–1

yr–1

. Under intensive management

practices, genetic improvement and high productivity sites, Eucalyptus Clonal Forestry

Plantation (CFP) produced 60 m3

ha–1

yr–1

in MAI (Stape et al., 2010).

Eucalyptus plantations in Brazil in 1970 typically grew at rates of about 15 m3 ha

-1 yr

-1.

Over the next 35 years, intensive research and improved operations tripled the average yields

across almost 4 million ha, through improved silviculture (site preparation, fertilization and

control of leaf cutting ants and weeds), improved seed selection, and the development of clonal

propagation (Queiroz and Barrichelo, 2008).

The relationship between soil texture and soil water is key factor to consider in the

establishment of forest plantations of Eucalyptus in South-east Mexico. Aluminum saturation is

not negatively related to the productivity of E. urophylla but a negative relationship was seen for

E. grandis. Soil phosphorus availability showed positive correlation with the productivity of E.

urophylla but not with that of E. grandis (Stape et al., 2010). Jose Luiz Stape et al., (2010)

revealed that, Eucalyptus plantations yields 33 m3 ha

-1 yr

-1 under rainfed conditions and about 62

m3

ha-1

yr-1

under irrigated conditions in Brazil.

Herwitz and Gutterman (1990) revealed that, Eucalyptus salubris was considered to have

the most efficient water use, with highest annual productivity (1169 kg ha-1

) and lowest

transpiration rates. Eucalyptus torquata was slightly less efficient than E. salubris. E.

woodwardii was comparable in terms of productivity, but transpired at much higher rates.

Eucalyptus socialis and E. grossa were the least efficient in water use, with significantly lower

annual productivity (<660 kg ha-1

).

Singh and Toky (1995) revealed that, Leucaena leucocephala showed fairly high net primary

productivity (33 t ha−1

yr−1

) closely followed by E. tereticornis (29 t ha−1

yr−1

) and the standing

biomass after 4 years was 112 t ha−1

in L. leucocephala, 96 t ha−1

in E. tereticornis and 52 t ha−1

in

A. nilotica. Prasad et al., (2011) reported that, marketable biomass productivity was higher with

Leucaena (95 Mg ha−1

) in comparison to Eucalyptus (87 Mg ha−1

).

Comparative production of Acacia auriculiformis and C. equisetifolia was studied by

Kushalapa (1987) in high rainfall areas of Karnataka, and the study revealed that above ground

biomass (AGB) of C. equisetifolia was 108.3 t ha-1

at the age of 9 years. Jayaraman et al., (1992)

reported that C. equisetifolia plantations growing in the West Coast areas of Kerala are highly

productive and can produce biomass of 190 t ha-1

at the age of 4.5 years. Swaminath (1988)

studied the response of fast growing forest species grown for biomass production under irrigation

and found that, C. equisetifolia produced biomass of 26.97 t ha-1

yr-1

under irrigated condition

compared to 17.95 t ha-1

yr-1

under normal. Biomass production in accordance with different

spacing was also reported in Tectona grandis by Adams (1993) and in Leucaena leucocephala

by Mishra et al., (1986).

Eucalyptus is the dominant hardwood planted and the mean annual increment of managed

forests has increased from 12 m3 ha

−1 year

-1 in the 1960s to 20–60 m

3 ha

−1 yr

-1 as a result of

improved genetics and silviculture (Santana et al., 2000). Hunter (2001) reported that, two

Eucalyptus species had a total dry weight averaging 45.3 t ha-1

while the Dalbergia had an

average dry weight of only 7.6 tonnes. There were no interactions between species and

treatments. Irrigation increased dry weight linearly across treatments and by 74% in the highest

irrigation rate. The two eucalyptus had accumulated a stem volume of 60 m3

ha-1

at a rate of 20

m3 ha

−1 yr

-1.

Stand parameters indicate that soils in the study area can potentially reach high levels of

mean annual increment (MAI) with values from 23 to 49 m3

ha–1

yr–1

. This productivity falls in

the range of that of some eucalyptus hybrids plantations (E. urophylla × E. grandis) in South

America with MAI from 15 - 60 m3

ha–1

yr–1

. Rodríguez et al., (2009) reported MAI in

plantations of E. nitens in Chile ranging from 47 to 52 m3

ha–1

yr–1

. Under intensive management

practices, genetic improvement and high productivity sites, Eucalyptus CFP produced 60 m3

ha–1

yr–1

in MAI (Stape et al., 2010).

Piare Lal (2006) evaluated different Eucalyptus clones (E. camaldulensis, E. tereticornis

and E. hybrid) for yield and productivity in Punjab and reported that, the most productive clones

(2070, 285, 316, 288, 498, 286 and 2045) in clonal testing area (CTA-1) were ranging with MAI

from 24 to 30 m3

ha-1

yr-1

at 4 years age. The most productive clones (413, 407, 285, 290, 105 and

72) in CTA-2 were ranging with MAI 30-36 m3

ha-1

yr-1

. The clone 413 performed significantly

superior among all other clones at 4 years of age.

George (1986) concluded that the organic matter and exchangeable potassium are

depleted in the soil under Eucalyptus plantation than in wood lands, but no difference in calcium

and magnesium was observed. Hopmans et al., (1990) studied the Growth, biomass production

and nutrient accumulation by seven tree species irrigated with municipal effluent and reported

that, Height and diameter growth varied significantly between species. At the age of four years,

mean dominant height of E. grandis, E. saligna and Populus deltoides × P. nigra ranged from

14.3 to 15.0 m compared with 6.6 to 9.8 m for Casuarina cunninghamiana, E. camaldulensis, P.

deltoides and Pinus radiata. Wood production of the faster-growing species (E. grandis and E.

saligna) was approximately 130 m3 ha

−1 or around 32 m

3 ha

−1 year

−1 over a 4-year period. This

was nearly three-fold the production of the other native species and twice that of P. radiata.

Volume growth of P. deltoides × P. nigra (85 m3 ha

−1) was significantly greater than that of P.

deltoides (42 m3 ha

−1).

2.3. Biomass distribution

Mineral capital and its distribution within wood land ecosystems changes as a result of

the balance between the various factors, both internal and external, affecting the circulation of

chemical elements.

Fabio et al., (1995) revealed that, the proportion of the below ground biomass relative to

the total tree biomass and the root/shoot ratio were higher in C at early growth periods. The

average aboveground biomass of E. globulus increased with age from 79.23 t ha-1

at 6 years to

112.04 t ha-1

at 9 years. This increase of biomass was allocated to stem-wood and stem-bark.

Stem-wood was the major component and its biomass was comprised between 69% and 77% of

total aboveground biomass (Cole and Rapp, 1980).

Biomass partitioning to the bole was high in case of Leucaena ranged from 83% in 2.5-5

cm diameter at breast height (DBH) trees to 89% in 12.5-15 cm DBH trees and in eucalyptus

clones the corresponding values were 71% in 2.5-5 cm DBH trees and 83% in 12.5-15 cm DBH

trees (Prasad et al., 2011).

Allocation to the bole-wood in E. urophylla changed from 46 to 36%, in E.

camaldulensis from 37 to 32%, and E. pellita from 31–34% at 3x1.5 vs. 4x3 m spacing,

respectively. Allocation to the root system in E. urophylla changed from 23–30%, in E.

camaldulensis from 34–45%, and E. pellita from 37–33% at 3x1.5 vs. 4x3 m spacing,

respectively (Alberto L. Bernardo et al., 1998). Poggiani and Couto (1983) revealed that the

Biomass distribution in the E. grandis plantation recorded that, among the components of the

stand is about 9% leaves, 7% limbs and 83% stems. However nutrients content in the stand

biomass are about 37% in the leaves, 10% in the limbs and 53% in the stems.

Sara Bastien-Henri et al., (2010) studied the biomass distribution among tropical tree

species grown under differing regional climates and the results showed that, 18 species

accumulated greater total biomass at the humid site than at the dry site over a two-year period.

Species-specific biomass partitioning among leaves, branches and trunks was observed.

2.4. Physiological Parameters

2.4.1. Photosynthesis

Plant productivity is ultimately dependent on the rate of photosynthesis, but it is well

known that it is the amount rather than the activity of the photosynthetic tissues that usually

determines plant productivity.

Gratani et al., (1998) studied the relationship between the photosynthetic activity and

chlorophyll content in Oak trees and found that, discordances between chlorophyll content and

PN over the year influenced the regression analysis, which although positive did not show very

high correlation coefficients (r = 0.7). The high Chl (a+b) content during most of the year

indicated that the photosynthetic apparatus remained basically intact also during stress periods.

Enhanced transpiration and stomatal conductance were beneficial to the photosynthesis

for higher productivity. According to Novak et al., (2005) reliable estimates of plant

transpiration rates are essential to predict the water flow and crop growth and thus, the rate of

transpiration depends on various properties of the continuum soil-plant-atmosphere.

Novriyanti et al., (2012) reported that, relative to the Eucalyptus, Acacias had lower leaf

net photosynthetic nitrogen use efficiency, higher water use efficiency, higher LMA and higher

leaf nitrogen per unit area.

Morphological and physiological parameters which correlate with growth rate were

sought as early indicators of field performance. The physiological basis of vigorous growth of

faster-growing genotypes has been correlated with gibberellin levels water use efficiency and, in

some studies, net photosynthesis (i.e., photosynthesis minus respiration). However, correlations

between morphological and physiological parameters and growth in the field are often poor. The

influence of plant water status and growth rate appears to have received little study. However,

the authors revealed that, faster growing hybrids had a greater ability to limit transpirational

water loss compared with slower-growing clones, resulting in a higher water use efficiency – i.e.,

they fixed more carbon in photosynthesis per unit of water transpired. (Blake and Yeatman,

1989).

2.4.2. Stomatal conductance

The stomata are not only the entry route for gas exchanges for CO2, but also the outflow

of water in vapor form, from the inside to the outside of the leaf. In order to absorb CO2 from the

outside, the plant inexorably loses water and when this loss decreases, it also restricts the intake

of CO2. This interdependence was recognized long ago and numerically expressed by the ratio

between total assimilation and water consumption.

It is often assumed that species with high WUE would be favoured in dry environments,

but there may be a physiological cost for this. Models of stomatal conductance (gs) are based on

coupling between gs and CO2 assimilation (Anet), and it is often assumed that the slope of this

relationship (‘g1’) is constant across species. A decrease in stomatal conductance causes a

proportionally larger decrease in transpiration than in carbon assimilation, with the net result of a

higher WUE.

The maintenance of high WUE, by maintaining stomata partially closed, also decreases

the rate of carbon assimilation, thus reducing growth (De Lucia and Heckathorn, 1989).

Therefore, the main role of this stomatal response may be related to the control of water loss,

rather in the sense of preventing tissue damage so as to maximise carbon assimilation in the

prevailing circumstances than in the sense of conserving water (Grace, 1993).

The efficiency of water use (WUE) represents the ability that vegetation has to absorb

carbon while limiting water loss through the stomata. Stomatal control or a reduction in leaf area

will almost certainly lead to a significant reduction in productivity. Differences among clones in

transpiration were related to differences in leaf area under optimum conditions. Because yield is

correlated with transpiration and the relationship between transpiration and leaf area confirms the

importance of early leaf development for maximizing productivity (Turner and Jones, 1980).

The authors also found that Eucalyptus have efficient stomatal control on transpiration

during the dry season. The decline in WUEi, results from a reduction in stomatal conductance,

which affects more the photosynthetic rate than the rate of leaf transpiration.

Roberts and Rosier (1993) used evaporation from leaf replicas of E. camaldulensis and E.

tereticornis to estimate gb for individual leaves ranging from 0.8 to 2.6 mol m-2

s-1

at low (0.5 m

s-1

) and high (4 m s-1

) wind speeds, respectively. These values were consistently higher than

those for gs, which reached a maximum value of 700 m mol m-2

s-1

in early-morning conditions

during the monsoon period. Values of gs were substantially lower than this later in the day and at

other times in the year.

Based on measurements made with E. grandis leaves, Leuning (1995) showed that a

hyperbolic relationship best explained the response of gs to air saturation deficit (D), though it is

often described by an exponential decay function. The slopes of exponential functions in E.

globulus and E. nitens (-0.63) and E. grandis (-0.61 in summer) were commensurate with 50 and

90% reductions in gs at D = 1:1 and 3.7 kPa, respectively, an indication that gs can be quite

sensitive to D in some Eucalyptus species. Stomatal conductance in E. grandis was less sensitive

to D in summer (slope -0.30) but a 50% reduction in gs was still observed at D = 2:3 kPa (Dye

and Olbrich, 1993).

2.4.3. Transpiration

According to Novak et al., (2005) reliable estimates of plant transpiration rates are

essential to predict the water flow and crop growth and thus, the rate of transpiration depends on

various properties of the continuum soil-plant-atmosphere.

Pilar Pita and Rose Pardos (2001) studied the transpiration, tissue water relations,

changes in leaf size and specific leaf area in rooted cuttings of selected clones of E. globulus and

found that there was a significant clone x treatment interactions in transpiration.

Hybrids of E. urophylla x E. grandis and E. urophylla x E. tereticornis, with high

photosynthesis and transpiration rate grew faster than E. urophylla x E. camalduensis and E.

urophylla (Zhaohua Lu et al., 2001).

Terry Blake and Eddie Bevilacqua (1990) reported that, clonal differences were observed

in physiological parameters, with cv. 79 and cv. 33 having significantly higher gwv, T, and Pn

compared to cv. 93.

Prabhakar (1998) stated that the transpiration of Eucalyptus is high under conditions of

high soil moisture, termed ‘luxury consumption’, and under conditions of water stress, stomatal

closure occurs, which restricts water loss from the plant. Greenwood et al., (1985) measured and

compared transpiration from two species of Eucalyptus, and grassland, and annual average

transpiration rates were found to be 2700 mm and 390 mm respectively. However, another study

indicated that plantations of E. tereticornis and E. camaldulensis use no greater quantity of water

than degraded indigenous forest on adjacent sites.

Mana Gharun et al., (2013) studied the canopy transpiration in the E. radiate and E.

goniocalyx and revealed that, there was a stronger relationship between average daily

transpiration (0.71 mm day−1

) and daily minimum relative humidity (R2 = 0.71), than between

average daily transpiration and daily maximum temperature (R2 = 0.65).

Din Muhammad Zahid and Aamir Nawaz (2007) found significant variation between two

species was observed for WUE and transpiration coefficient (TC). WUE and TC of Shisham

were 0.89 and 7.94 g L-1

as compared to that of Eucalyptus, which were 0.93 and 4.06 g L-1

,

respectively. However, evaporation losses were higher (0.99 g L-1

) for shisham than for

Eucalyptus (0.84 g L-1

).

Water consumption by one year old Eucalyptus (149.27 L) was almost twice that of by

Albizia (82.84 L) and more than three times that of by Acacia (58.30 L), and Azadirachta (51.57

L). Significant variation between the species was observed for biomass produced. When this was

translated into water use efficiency, it was found as 0.32 g L-1

, 0.48 g L-1

, 0.16 g L-1

and 0.77 g

L-1

while transpiration coefficient was 1042 L kg-1

, 872 L kg-1

, 1951 L kg-1

and 739 L kg-1

for

Acacia, Albizzia, Azadirachta and Eucalyptus respectively. It is important to control evaporation

losses (44-69% of total irrigation) which may be much higher than transpiration (Zahid et al.,

2010).

Dunn and Connor (1993) measured sap flow in E. regnans trees of different ages and

estimated maximum transpiration rates of 1.9 and 0.8 mm per day for 50- and 230-year-old trees,

respectively. In annual terms, this amounted to a difference of 383 mm, which would be

observed as an increase in water yield. Sap velocity was the same in trees of different ages and

the decline in transpiration with increasing age was attributed to decreases in sapwood

conducting area, and thus leaf area (Hatton et al., 1995) of the older stands.

Zahid et al., (2010) reported that the transpiration efficiency (g L-1

) alternatively called

Aboveground Net Primary Productivity ANPP (kg m-3

) of Acacia, Albizzia, Azadirachta and

Eucalyptus was 0.63, 0.51, 0.13 and 0.68 respectively. Stoneman et al., (1996) reported a quite

high ANPP (3.21 kg m-3

) of E. tereticornis plantation with added nitrogen fertilizer in tropical

soils having high fertility and high rainfall.

2.5. Water Use Efficiency:

Water Use Efficiency (WUE) is an indicator of the relationship between the amount of

water required for a particular purpose and the amount of water used or delivered. WUE is

traditionally defined as the ratio of dry matter accumulation to water consumption over a season.

The term "water use efficiency" originates in the economic concept of productivity. Water use

efficiency studies are very limited in tree species and particularly at the level of clones. This is

one of the important physiological parameters for ranking the clones for better water use

efficiency and higher productivity under varied site conditions. Water productivity might be

measured by the volume of water taken into a plant to produce a unit of the output. In general,

the lower the resource input requirement per unit, the higher the efficiency.

Increasing WUE could theoretically affect plant growth. When water is limited, plants

that use a finite water supply more efficient would grow more rapidly, in this case, high WUE

would positively affect plant productivity. Another way to increase WUE is to close stomata

partially, thus restricting photosynthesis relative to plants whose stomata are fully open, this

strategy would result in a negative correlation between WUE and plant productivity (Richards

and Condon, 1993).

Reduced water use, which is reflected in higher WUE, is generally achieved by plant

traits and environmental responses that reduce yield potential. Improved WUE on the basis of

reduced water use is expressed in improved yield under water-limited conditions only when there

is need to balance crop water use against a limited and known soil moisture reserve. However,

under most dry land situations where crops depend on unpredictable seasonal rainfall, the

maximization of soil moisture use is a crucial component of drought resistance (avoidance),

which is generally expressed in lower WUE.

The strength and direction of the relationship between water-use efficiency and plant

performance can illustrate interspecific differences in drought tolerance strategies, ranging from

stress tolerance to stress avoidance (Aranda et al., 2012; Chaves et al., 2002 and Nicotra et al.,

2010) for a more complete discussion of tree responses to drought). Stress tolerance is associated

with higher water use efficiency, lower photosynthetic rates, slower growth, and higher survival,

while stress avoidance is associated with lower water-use efficiency, higher photosynthetic rates,

faster growth, and lower survival (Chaves et al., 2002).

Plant water-use efficiency, the amount of water used per carbon gain, explicitly links

plant performance with water availability. At the leaf level, intrinsic water-use efficiency is

expressed as the balance between photosynthetic carbon fixation (A) and stomatal conductance

(gs), which is correlated with the ratio of intercellular to ambient CO2 partial pressures (Ci/Ca) in

C3 plants. Therefore, time-integrated, intrinsic water-use efficiency can be inferred using stable

carbon isotope ratios (d13

C) of plant tissues given its inverse linear relationship with Ci/Ca,

whereby high water use efficiency is indicated by less negative d13

C and low Ci/Ca and vice

versa (Dawson et al. 2002; Farquhar et al., 1982; Farquhar and Richards, 1984).

Water use efficiency varies significantly among Eucalyptus clones (for the same age and

site). Evidence of this was presented by Olbrich et al., (1993) who found significant clonal

differences in WUE between four E. grandis clones growing on a high quality site. In a lysimeter

study, Le Roux et al., (1996) investigated variation in WUE among six Eucalyptus clones up to

the age of 16 months and found significant clonal variation in WUE as well as patterns of growth

allocation to roots, stems, branches, and leaves.

Stape et al., (2004) concluded that water use efficiency of Eucalyptus species was 3.8 kg

m-3

in irrigated plots in wet year and 1.8 kg m-3

in control during normal year (low rainfall).

The amount of water use by Eucalyptus plantation is a relevant ecological question

worldwide. Eucalyptus actually appears to be more efficient in water use than other ‘useful’

native trees. The study showed that Eucalyptus consumed 0.48 litres of water to produce a gram

of wood, compared to 0.55, 0.77, 0.50 and 0.88 litre per gram for siris, shisham, jamun and kanji

respectively (Prabhakar, 1998). Chaturvedi et al., (1988) reported that of ten species tested for

water consumption, E. tereticornis was found to be the most efficient in biomass production per

litre of water consumed, but also found to consume most water overall, given its high

productivity.

Pryor (1976) stated that Eucalyptus has ‘an ability to extract water from the soil even

though soil moisture tension is higher than that at which more mesophytic plants can extract

water.

Productivity of fast-growing species, such as poplars, is highly dependent on water

availability (Tschaplinski et al., 1994). Inter- and intraspecific differences in WUE, defined as

the ratio between plant biomass accumulation and plant transpiration, have been reported

(Condon et al., 2002). Inter-genotypic variability in WUE is mainly controlled by diversity in

stomatal conductance, whereas a positive relationship indicates that WUE is controlled mainly

by photosynthetic capacity (Farquhar et al., 1989).

Debbie Le Roux et al., (1996) reported that water use efficiencies differed significantly

between Eucalyptus clones. Chunying Yin (2005) found that there were significant inter-specific

differences in early growth, dry matter allocation, and WUE between two sympatric Populus

species under well-watered and water-stressed treatments.

In nature, the WUE is influenced not only by water, but also by climatic conditions

(Tonello and Filho, 2013). Similar situations were reported by several authors in different

cultures, including several genera of Eucalyptus sp (Whitehead and Beadle, 2004 and Poni et al.,

2009).

Poni et al., (2009) clearly showed that regardless of the stress level in the soil, the

intrinsic WUE tends to increase with increasing VPD, while instantaneous WUE usually shows

an opposite tendency.

Studies conducted at the Institute of Forest Genetics and Tree Breeding, Coimbatore

revealed considerable variation with respect to physiological parameters including water use

efficiency in 33 Casuarina equisetifolia clones (Kannan, et al., 2007). Water use efficiency

studies have been conducted especially in Eucalyptus species at Kerala Forest Research Institute

(Kallarackal and Somen, 1997).

2.6. Carbon isotope discrimination

WUE is defined in agronomic terms as the ratio of dry matter production to water use

(Boyer, 1996) or, in physiological terms, as the ratio between the rate of carbon fixed and the

rate of water transpired. Farquhar and Richards (1984) described the relationship between WUE

and carbon isotope discrimination in C3 plants. The discrimination against the heavier carbon

isotope, 13

C (d13

C), is calculated as the 13

C/12

C ratio in plant material relative to the value of the

same ratio in the air assimilated by plants. Carbon isotope discrimination has been proposed by

several authors as an indirect selection criterion for yield under drought (Condon et al., 2002). It

has been shown that d13

C is related to WUE in wheat genotypes (Farquhar and Richards,1984).

Thus, the smaller the CO2 partial pressure inside the plant in comparison to the partial pressure in

the atmosphere, the less the plants discriminate between the two isotopes (d13

C more positive)

and the greater the WUE (Ehlers and Goss, 2003). This theory is corroborated by a large volume

of literature (Wright et al., 1988; Hall et al., 1992) but also contradicted by other authors (Austin

et al., 1990; Ngugi et al., 1996). Moreover, except for the studies published by Johnson and

Tieszen (1994) and Ray et al. (2004), there are no clear data for this WUE/d13

C relationship in

alfalfa genotypes.

The isotopic ratio of 13

C to 12

C in plant tissue is less than the isotopic ratio of 13

C to 12

C

in the atmosphere, indicating that plants discriminate against 13

C during photosynthesis.

Variation in discrimination against 13

C during photosynthesis is due to both stomatal limitations

and enzymatic processes. Theoretical and empirical studies have demonstrated that carbon

isotope discrimination is highly correlated with plant water use efficiency. Analysis of carbon

isotope discrimination has conceptual and practical advantages over measuring water use

efficiency by instantaneous measurements of gas exchange or whole-plant harvests. Carbon

isotope discrimination provides an integrated measure of water-use efficiency.

The isotopic ratio of 13

C to 12

C in C3 plants (d13

C) varies mainly due to discrimination

during diffusion and enzymatic processes. The rate of diffusion of 13

CO2 across the stomatal pore

is lower than that of 12

CO2 by a factor of 4.4%. Additionally, there is an isotope effect caused by

the preference of ribulose bisphosphate carboxylase (Rubisco) for 12

CO2 over 13

CO2 (by a factor

of ~27‰). In both cases, the processes discriminate against the heavier isotope, 13

C (Farquhar et

al. 1989). Based on the work of Farquhar the linkage between discrimination against 13

C during

photosynthesis and water use efficiency may be demonstrated by the following relationships.

The stable isotope ratio (d13

C) is expressed as the 13

C/12

C ratio relative to a standard (Pee Dee

Belemnite) (Craig, 1957). The resulting d13

C value may be used to estimate isotope

discrimination (D) as:

D= (da – dp)/(1+ dp).

Where dp is the isotopic composition of the plant material and da is that of the air (assumed to be

8%). As CO2 assimilation (A) increases or stomatal conductance (gs) decreases, intercellar

CO2 decreases resulting in decreased discrimination against 13

C. The relationship between Ci and

D is represented by the model of Farquhar et al., (1982).

Carbon isotope discrimination has several conceptual and logistical advantages to

screening for drought tolerance based on TE or WUEi. Carbon isotope discrimination

integrates ci/ca over the time the sampled tissue was formed. In contrast, WUEi measured by gas

exchange provides ‘snapshots’ of A/g or A/E and may not be representative of overall WUE.

Measurements of D are much less time and labor intensive than calculation of whole plant water

use and dry weight data needed to calculate TE.

This water use efficiency will be measured in directly through the ‘Stable Isotope Mass

Spectrophotometer’ based on the carbon isotope discrimination expressed as stable isotope ratio

(d13

C) which is the ratio of 13

C to 12

C. Water and nutrient supplies are the main abiotic factors

affecting plantation growth in the tropics (Fisher and Binkley, 2000) and evaluation of these

supplies is important for zoning plantation potential and for establishing silvicultural methods for

site preparation, fertilization and control of competition. Rapid forest growth rates are generally

coupled with the high use of site resources, which raises questions regarding both the ecological

impacts of plantations and the sustainability of wood production (Wang et al., 1991; Lima,

1993).

Recently the relationships between d13

C and dry mass accumulation and WUE have

been explored in woody shrub and tree species. Negative correlations between d13

C of leaf tissue

and tree height were demonstrated in 13-month old commercial clones of E. grandis, implying

that more water-use-efficient trees were more productive (Bond and Stock, 1990).

Similarly, growing season WUE and d13

C were positively correlated in western larch and

E. globulus seedlings (Zhang and Marshall 1993, Osório and Pereira 1994). Genetic variation in

WUE and d13

C was also reported for both tree and shrub species (Hubick and Gibson 1993,

Zhang and Marshall 1993, Donovan and Ehleringer, 1994). Although clonal variation in d13

C

was shown in a study of four-year-old clones of Eucalyptus grandis (Olbrich et al., 1993), a poor

relationship was found between d13

C and WUE in the production of harvestable stems (i.e., the

water cost of wood production) suggesting that the relationship between d13

C and WUE in leaves

may change when scaling up to stems, shoots and whole trees.

Variation in allocation patterns in trees could result in simultaneous changes in

harvestable stem coupled with changes in WUE. Individuals allocating a high proportion of dry

mass to stems could have a high WUE when expressed on harvestable stem basis but have a low

WUE at the whole-plant level. A strong correlation between isotope discrimination and water use

efficiency has been reported for numerous crop and tree species. Greenwood and Beresford

(1979) reported that, considerable variation exists in WUE between species at different sites in

Australia. Kallarackal and Soman (1997) reported that, the relation between the net

photosynthesis and stomatal conductance was almost linear in six Eucalyptus species and better

water use efficiency was recorded in E. urophylla, E. camaldulensis, E. brassiana and E. pellita

compared to E. degulpta and E. tereticornis.

2.7. Nutrient in the standing biomass:

Mineral capital and its distribution within wood land ecosystems changes as result of the

balance between the various factors, both external and internal, affecting the circulation of

chemical elements. The buildup of the plant mass results in a progressive accumulation of

minerals which are effectively removed from the active circulatory systems. Brans et al., (2000)

reported that, in mature plantations of Eucalyptus globulus (6-18 years old), the total quantities

of P, K, Ca and Mg in tree biomass were higher than available quantities of P, K, Ca and Mg in

the soil.

Nutrient concentrations varied considerably among tree components and according to

position within the tree canopy. Nitrogen, P and K concentrations were highest in foliage

whereas Mg and Ca concentrations were highest in stem-bark. The high Ca concentration in bark

(28.21 mg g-1

) is similar to that reported for other Eucalyptus species (Spangenberg et al., 1996).

Stem-wood had the lowest concentrations of all those nutrients for other Eucalyptus species

reported for different forest species. Nitrogen and P concentrations in foliage decreased from the

top to the bottom of the canopy and this variation may be attributed to the withdrawal of these

elements, as has been reported for several Eucalyptus species (Attiwill and Leeper, 1987).

George and Varghese (1990) reported that, in Eucalyptus globulus, the contribution of

bgb to total biomass was 18 per cent and the accumulation of various nutrients ranged from 22 to

28 %. Similar observation was also reported by Negi et al., (1990) in Tectona grandis.

Harvesting of Eucalyptus wood would cause an export of about 224 kg ha-1

of N, 19 kg

ha-1

of P, 106 kg ha-1

of K and 110 kg ha-1

of Ca. These quantities represent 43% of N, 39% of P,

49% of K and 24% of Ca contained in aboveground tree biomass in Brazil (José Leonardo de

Moraes Gonçalves et al., 1998).

Qureshi et al., (1967) reported that in C. equisetifolia, the needles contain highest (1.95

per cent) concentration of Ca and lowest of P (0.16 per cent). Wang et al., (1991) revealed that

in C. equisetifolia, concentration of most nutrients followed the order, leaves > bark > small

branches > wood of stem.

During growth and development of trees, nutrients will be accumulated in biomass

components. Malhotra et al., (1987) reported that in Pinus patula plantations, maximum amount

of nutrients are accumulated in needles in younger stands but as the stand matures, accumulation

occurs in the boles. Similar observation was also reported by Tandon et al., (1996) in Eucalyptus

hybrid and Negi and Tandon (1997) in Populus elliotii. Wang et al., (1991) reported that in C.

equisetifolia, among various nutrients, Ca accumulated maximum (940 kg ha-1

) and P the

minimum (119 kg ha-1

) at age of 5.5 years.

Verma et al., (1987) revealed that, in C. equisetifolia, nutrient accumulation in agb

increases with increase in age. Increasing trend of nutrient contents with plantations age was

largely in the order of N > K > Ca > Mg > P (Kadeba, 1991). Similar observation in the

accumulation of nutrients with stand age was also reported by Pande et al., (1987) in Eucalyptus

hybrid; Tandon et al., (1988) in Eucalyptus grandis and Singh (1994) in Cryptomeria japoica.

Negi et al., (1990) reported that in Gmelina arborea, BGB accumulates 32% of N, 44%

of P, 13% of Ca and 25% of Mg and accumulation of K exceeds the total accumulation of K in

agb.

After 3-year growth, E. globulus stands irrigated with effluent accumulated 72 oven dry

t/ha of above-ground total biomass with a total of 651 kg N, 55 kg P, 393 kg K, 251 kg Ca, 35 kg

Mg and 67 kg Mn. Effluent irrigation increased the accumulation of biomass, N, P, K and Mn,

but tended to reduce the leaf area index and leaf biomass, and decreased the accumulation of Ca

and Mg (Guo et al., 2002).

Xue (1996) also reported that in Cunninghamia lanceolata, among different nutrients, Ca

constituted highest concentration (0.07 per cent to 1.37 per cent) and P the least (0.005 to 0.08

per cent). Similar observation in C. equisetifolia was reported by Verma et al., (1987) and

Jamaludheen (1994) and George (1985) in Eucalyptus hybrid.

Nutrient concentration varies considerably with age. Queshi et al., (1967) and Vadiraj

(1993) reported that in Casuarina equisetifolia, there was a general increase in nutrient

percentage in aerial components with increase in stand age. Singh (1994) made similar

observation in Cryptomeria japonica and by Singh (1982) in Pinus patula. Concentration of

certain nutrients shows a definite trend with increase in age. Ovington and Madgwick (1959)

reported that in Betula verrucosa, Mg concentration in the needle increases with age. Wright and

Will (1958) reported that Scots and Crosican pine growing on sand dunes exhibited decreasing

pattern of some nutrients with age.

2.8. Nutrient use efficiency

The annual increment in above-ground biomass, and the corresponding nutrient content

of eucalypt plantations growing in nine different sites, were evaluated by Santana et al., (2000)

and reported that, the nutrient content in the stem was highest in the most productive sites,

showing a close relationship with biomass production. At three of the sites, the amount of

nutrients in the stem decreased in the order nitrogen > calcium > potassium > magnesium > and

phosphorus. However, calcium exceeded nitrogen at the other six sites. Nutrient use efficiency

(NUE) for stem and above-ground biomass production was significantly different among sites.

On average, the values of NUE for both stem and above-ground biomass decreased in the order

phosphorus > magnesium > potassium > nitrogen > calcium. Although bark constitutes only 10%

of the above-ground dry matter, it contains large amounts of nutrients (73% of the calcium in the

stem, 65% of the magnesium, 46% of the phosphorus, 41% of the potassium, and 24% of the

nitrogen).

Anthony A. Kimaro et al., (2007) studied the above ground use efficiency for N (P =

0.0035), P (P < 0.0001), K (P < 0.0001), Ca (P = 0.001), and Mg (P = 0.0081) varied

significantly among the tree species. In general, A. crassicarpa was the most efficient for all

nutrients except for N and Mg, exemplifying that this species produced the highest above ground

biomass at lowest nutrient ‘‘costs’’. Its K-use efficiency was four times higher than that of G.

sepium while P-use efficiency was three times as high as that of A. nilotica. Similar results were

also observed for nutrient use efficiency based on wood production. Overall, nutrient use

efficiency of wood was consistently higher than that of whole-tree biomass except for K, Ca, and

Mg in A. polyacantha, and for P and Ca in A. nilotica.

Although some fluxes of nutrients have been studied intensively (mainly litter fall and

nutrient content of the trees), studies quantifying the dynamics of the main fluxes of the

biological cycle of nutrients during stand development are scarce for Eucalyptus plantations

(Bargali et al., 1992; Goncalves et al., 1997; Parrotta, 1999). For a production of 92 t ha-1

ligneous aerial dry matter of 7 year old Eucalyptus stand, immobilization in the ligneous

components of the trees amounted to 235 kg ha-1

of N, 47 kg ha-1

of P, 59 kg ha-1

of K, 68 kg ha-1

of Ca and 49 kg ha-1

of Mg (Jean Paul Laclau et al., 2003).

Also reported that nutrient return of 159 kg N ha-1

yr-1

, 9 kg P ha-1

yr-1

, 28 kg K ha-1

yr-1

,

125 kg Ca ha-1

yr-1

and 22 kg Mg ha-1

yr-1

under the 3 year rotation of three Eucalyptus short

rotation forest species.

Nutrient concentration controls the biochemical as well as biogeochemical cycles.

Bargali et al., (1992), George and Verghese (1991) and Lodhiyal (1990) have reported that leaf

contains highest concentration of nutrients in eucalypt, teak and poplar plantations, respectively.

Present investigation agrees to these reports only to the extent that only nitrogen concentration is

highest in the leaves while phosphorus is highest in roots. However, magnitude of concentration

of N and P is 1.51% and 0.16%, respectively. This is comparable to the reports of George and

Verghese (1991) where N and P concentration is 1.60% and 0.11%, respectively.

Final output of nutrient cycling is standing state of nutrients that has been defined as

quantity of nutrient storage at a given time in a unit area. Standing state of nutrients increased

with increase in age of the plantation and at the age of thirty years teak stored 586.6 kg/ha N and

208.8 kg/ha P. This kind of age versus storage relationship was also found in poplar (Bargali et

al., 1992) and Eucalyptus (Lodhiyal, 1990) in the same locality.

Magnitude of primary productivity is directly proportional to nutrient uptake. Since

annual productivity was not affected by the age of stands nutrient uptake also did not show any

relationship between uptake amount and age. At the age of 30 years gross uptake of N and P was

107.73 and 20.20 kg-1

ha-1

yr-1

, respectively. This report is well within the range of uptake (87-

256 kg-1

ha-1

yr-1

for N and 4-134 kg-1

ha-1

yr-1

for P) in different forest types and plantations.

However, quantum of uptake for both N and P towards the lower range shows comparatively less

nutrient demanding nature of the species.

The nitrogen use efficiencies were 181, 211 and 191 g of tree aboveground dry matter

produced per g of N supplied by uptake and retranslocation in the sapling, pole stage and mature

stands, respectively. Field vegetation was more efficient in nitrogen use than trees. Stand

belowground/aboveground and fine root/coarse root biomass ratios decreased with tree age. With

only slightly higher fine root biomass, almost three times more nitrogen had to be taken-up from

soil for biomass production in the mature stand than in the sapling stand. Retranslocation

supplied 17–42% of the annual N, P and K requirements for tree aboveground biomass

production. Precipitation and throughfall were important in transferring K and Mg, and also N in

the sapling stand. Litter fall was an important pathway for N, Ca, Mg and micro nutrients,

especially in the oldest stands (Heljä-Sisko Helmisaari, 1995).

2.9. Role of Leaf Potassium in Water Use Efficiency

Adequate amounts of K can enhance the total dry mass accumulation of crop plants under

drought stress in comparison to lower K concentrations (Egilla et al., 2001). This finding might

be attributable to stomatal regulation by K+ and corresponding higher rates of photosynthesis

(Marschner, 2012). Furthermore, K is also essential for the translocation of photoassimilates in

root growth. Root growth promotion by increased appropriate K supply under K-deficient soil

was found to increase the root surface that was exposed to soil as a result of increased root water

uptake (Romheld and Lindhauer, 2010). Lindhauer (1985) reported that fine K nutrition not only

increased plant total dry mass and leaf area, but also improved the water retention in plant tissues

under drought stress.

Potassium plays a crucial role in turgor regulation within the guard cells during stomatal

movement. As stomatal closure is preceded by a rapid release of K+ from the guard cells into the

leaf apoplast, it is reasonable to think that stomata would be difficult to remain open under K-

deficient conditions. Some studies also stated that K deficiency may induce stomatal closure and

inhibit photosynthetic rates in several crop plants (Jin et al., 2011; Tomemori et al., 2002).

Conversely, many studies suggest that K had no effect on stomatal conductance and

photosynthetic rates under well-watered conditions, but K starvation could favor stomatal

opening and promote transpiration, compared with K sufficiency in several plants under drought

stress. Furthermore, photosynthetic rate was decreased under drought stress in K-deficient plants.

During drought stress, the stomata cannot function properly in K+-deficient plants,

resulting in greater water loss. Drought stress did not decrease water use efficiency (WUE),

whereas it did increase WUE by rapid stomata closing during water deficit. Adequate levels of K

nutrition enhanced plant drought resistance, water relations, WUE and plant growth under

drought conditions (Egilla et al., 2005).

Hsiao and Lauchli (1986) observed substantial variation in stomatal responses to

variation in K+ availability in different species and concluded that although stomatal conductance

was lower under low K+ levels this may occur only at an advanced stage of K deficiency.

2.10. Specific Leaf Weight

Specific Leaf Weight (dry matter per unit leaf area-SLW) showed that all genotypes were

decreased under drought stress conditions, as pointed out by Vanaja et al., (2011). Specific leaf

weight was shown to be a valuable index for comparing photosynthesis by various parts of a tree

canopy over a season or throughout an entire year. Mean annual photosynthetic rate in five

separate portions of a spruce canopy was directly proportional to observed differences in specific

leaf weight (r2 = 0.99). Annual carbon uptake was a function of total foliage biomass (r

2 = 0.96).

When foliage biomass at each crown segment was adjusted for differences in specific leaf

weight, reflecting differences in photosynthetic rates, the predictive equation further improved C

(r2 = 0.99). Specific leaf weight is recommended as an index for comparing the relative effects of

various silvicultural treatments on photosynthesis (Oren Ram, 1984).

Specific leaf weight was shown to be positively correlated to transpiration efficiency in

peanuts and in other species. The reason for this relationship is not clear, but could be due to the

association of thicker leaves with higher photosynthetic capacity (Brown and Byrd, 1996).