effects of plant cover on properties of rhizosphere and inter-plant soil in semiarid valley, sw...

7/25/2019 Effects of Plant Cover on Properties of Rhizosphere and Inter-Plant Soil in Semiarid Valley, SW China

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Effects of plant cover on properties of rhizosphere and inter-plant soilin a semiarid valley, SW China

Laiye Qu a, 1, Yuanyuan Huang a,b, 1, Keming Ma a , *, Yuxin Zhang a, Arjen Biere c

a State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Science, Chinese Academy of Sciences, Beijing 100085, Chinab Soil and Water Science Department, University of Florida, P.O. Box 110510 Gainesville, FL 32611, USAc Department of Terrestrial Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Droevendaalsesteeg 10, 6708 PB Wageningen, The Netherlands

a r t i c l e i n f o

Article history:

Received 29 July 2015Received in revised form6 November 2015Accepted 7 November 2015Available online 27 November 2015

Keywords:

Artemisia gmelinii

Plant coverPlant-soil interactionSoil microbesSoil aggregates

a b s t r a c t

Plant establishment is widely recognized as an effective way to prevent soil erosion in arid and semiaridecosystems.Artemisia gmelinii, a pioneering species in many degraded ecosystems in China, is effective inimproving soil properties and controlling runoff and soil loss, but mechanisms underlying soilimprovement are not well understood. We therefore investigated how the presence and cover of

A. gmelinii affect soil physico-chemical properties and soil microbial communities in differently sized soilaggregates in the rhizosphere and inter-plant soil in the Upper Minjiang River arid valley of China. Wefound that A. gmelinii presence signicantly improved soil quality in terms of soil structure, watercontent, aggregate-associated carbon and nutrients, and soil microbial biomass and activities. Interest-ingly, also inter-plant soils were strongly inuenced by adjacent-plant-cover, showing enhanced soilorganic carbon, total carbon, nitrogen and phosphorus, and reduced soil bulk density and pH withincreasingA. gmeliniicover in plots. In turn, theA. gmelinii-induced changes in inter-plant soil propertiescould explain a large part of the observed variation in microbial biomass, carbon and nitrogen. Impor-tantly, effects of the presence and cover of A. gmelinii on soil properties were mostly specic forparticular aggregate size classes. Specically, A. gmelinii signicantly increased P accumulation only in

small macroaggregates (250e2000 mm) illustrating the importance of this aggregate class in terms ofplant-mediated phosphorus accumulation, critical for P uptake in this P limited area. Our results thusindicate that A. gmelinii not only improves soil physical and microbial conditions in its rhizosphere butalso in inter-plant soil, and that increasingA. gmeliniicover has the potential to reduce runoff and soilloss and to promote revegetation.

2015 Elsevier Ltd. All rights reserved.

1. Introduction

Soil erosion is one of the most formidable threats to the conser-vation of soil resources in arid and semiarid areas and is one of the

main contributing factors to desertication (Rillig et al., 2003).Vegetation plays an important role in improving soil quality andreducing runoff and soil loss (Xu et al., 2009). Presence and type ofplant cover can affect resource availability, soil structure, nutrientcycles and microbial community dynamics (Rutigliano et al., 2004;

Zuazo and Pleguezuelo, 2008; Rutigliano et al., 2009) in semiaridregions.

The patchy distribution of vegetation in dryland results in thewell-documented islands of fertility and a discontinuous dis-

tribution of soil resources, such as water and nutrients(Schlesinger et al., 1996; Aguiar and Sala, 1999). Under shrubs, ahigher vegetation cover generally results in increased inputs ofcarbon and nutrients (Vinton and Burke, 1995), improved soilstability due to the protection from erosion by wind and water,and higher concentrations and activity of microbial populations invegetated patches than in bare soil (Gallardo and Schlesinger,1992; Whitford and Sobhy, 1999; Belnap and Phillips, 2001;Lopez et al., 2003). Thus, the mere presence of a living shrub isthe dominant driving factor both for soil physical-chemicalcharacteristics and for the activities of microbial communities(Ben-David et al., 2011). Increasing plant cover, moreover,

* Corresponding author. 18 Shuangqing Road, Haidian District, Research Centerfor Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085,China. Tel./fax: 86 10 6284 9104.

E-mail address:[email protected](K. Ma).1 Laiye Qu and Yuanyuan Huang contributed equally to the manuscript.

Contents lists available atScienceDirect

Soil Biology & Biochemistry

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m/ l o c a t e / s o i l b i o

http://dx.doi.org/10.1016/j.soilbio.2015.11.004

0038-0717/

2015 Elsevier Ltd. All rights reserved.

Soil Biology & Biochemistry 94 (2016) 1e9
mailto:[email protected]://www.sciencedirect.com/science/journal/00380717http://www.elsevier.com/locate/soilbiohttp://dx.doi.org/10.1016/j.soilbio.2015.11.004http://dx.doi.org/10.1016/j.soilbio.2015.11.004http://dx.doi.org/10.1016/j.soilbio.2015.11.004http://dx.doi.org/10.1016/j.soilbio.2015.11.004http://dx.doi.org/10.1016/j.soilbio.2015.11.004http://dx.doi.org/10.1016/j.soilbio.2015.11.004http://www.elsevier.com/locate/soilbiohttp://www.sciencedirect.com/science/journal/00380717http://crossmark.crossref.org/dialog/?doi=10.1016/j.soilbio.2015.11.004&domain=pdfmailto:[email protected]


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intensies plantesoil interactions that vary with plant type due todifferences in qualitative and quantitative input of litter and rootexudates (Ludwig et al., 2005). While many studies have docu-mented effects of plants on physico-chemical and microbialproperties of rhizosphere soil, effects of increasing plant cover onproperties of bare inter-plant soil are less well understood. Insightinto such effects is important as the improvement of bare soil,especially its soil fertility and soil stability, is the basis for suc-cessful revegetation of seedlings in semi-arid areas (Song et al.,2010). In this study, we therefore investigate not only how thepresence of a semi-arid shrub affects the physico-chemical andmicrobial properties of its rhizosphere soil, but also how plantcover affects the physico-chemical and microbial properties ofinter-plant soil.

Restoration ecologists have long recognized the integral role ofsoil, especially its physical and chemical properties, in the suc-cessful revegetation of degraded sites (Heneghan et al., 2008). Soilmicrobial communities are essential for a wide range of ecosystem-level processes, such as decomposition, nutrient cycling, soil carbonstorage and maintenance of soil structure (Suding et al., 2004;Kardol and Wardle, 2010). It is generally believed that microor-ganisms increase the stability of aggregates in several ways

(Vaisanen et al., 2005). For example, fungi alone inuence soil ag-gregation in ecosystems in a variety of ways (Rillig, 2004): theirmycelium causes the mechanical enmeshment of soil particles, andfungal compounds can act as binding agents (Rillig, 2004; Vaisanenet al., 2005). Soil microbes might therefore serve as key contribu-tors to degraded dryland restoration and their effects may beintertwined with changes in soil aggregate properties. The inte-gration of soil microbial community studies with soil aggregatesand physico-chemical studies can thus be regarded as essential indeveloping in-depth knowledge on belowground dynamics. Hence,in this study we rst investigate how vegetation cover affects thesize distribution of soil aggregates in inter-plant soils and thephysico-chemical properties of each of four differently sized soilaggregate fractions, and then assess how differences in the physico-

chemical properties of these aggregates are associated with soilmicrobial properties.

Artemisia gmelinii is a short semiarid shrub with a relativelysmall leaf area and dense canopy that is effective in improving soilproperties and controlling runoff and soil loss (Xu et al., 2009). It isan important pioneering species in degraded regions of the upperMinjiang River valley in China (Liet al., 2008; Xu etal., 2009).In oneof these regions, a long-term area of natural restoration was initi-ated in 1998. The objectives of this studywere: (1) totestthe effectsofA. gmelinii on soil physico-chemical and microbial characteristicsof both rhizosphere and inter-plant soils, (2) to determine whetheran increase in the cover ofA. gmelinii can improve the quality ofadjacent bare inter-plant soil, (3) to better understand howA. gmeliniicontributes to the soil improvement of inter-plant soil

through effects on physico-chemical and microbial properties ofdifferent classes of soil aggregates.

2. Materials and methods

2.1. Study sites

The study site was located at Maoxian county(313702000e314405300N, 1035400400e1035605200E), which is partof the dry-warm valley of the upper Minjiang River, one of the fourprincipal tributaries of the Yangtze River (Xuet al., 2009; Song et al.,2010). Local topographical features of this area are characterized bymountain peaks 1500e3500 m above the deep river valley. Themean annual temperature is 11.2 C, mean annual precipitation is

494 mm and mean annual evaporation is 1332 mm. The aridity

index (the ratio of potential maximum evaporation to rainfall) forthis area is within a range from 1.5 to 3.5, which is typical ofsemiarid environments (Xu et al., 2009). The predominant soil typeis classied as Calcic cambisols (FAO-UNESCO, 1988). The area hasbeen largely devegetated in the past and is now undergoingrevegetation. Regional vegetation mainly consists of drought-tolerant arid shrubs and sparse grasses (Ma et al., 2004; Xu et al.,2009). A. gmeliniiis a predominant semi-shrub in this area and isan important pioneering species associated with arid and semiaridecosystem restoration in China. It is a relatively short shrub thatforms a dense, umbrella-shaped canopy, with branches and leavesthat often reach the ground.

2.2. Experimental design

Within soils of similar age, topography, parent material, andclimate regime, we selected a typical area (ca. 50 m 50 m) pre-dominantly occupied byA. gmelinii. Other species in the study areawererare. Thirty 1 m 1 m plots were randomly selected. The plotsspanned a wide range of values for the projected area (plant cover)ofA. gmelinii.

2.3. Soil sampling

All of the plots were sampled in July 2010. From each of thethirty plots, ten soil samples were collected. Five samples weretaken as close to the centre of the plants as possible and com-bined into one composite rhizosphere (undereplant) sample.Five other soil samples per plot were taken from the centre ofinterspaces between the plants and combined into one compositeinter-plantsample. This resulted in a total of 60 soil samples foranalysis. Soil cores were taken to a depth of 5 cm with a 5-cmdiameter soil corer, excluding the litter layer. Each sample wassubsequently divided into three parts. The rst part was preparedfor determining aggregate fractions, associated total soil carbon

(TC), nitrogen (TN) and phosphorus (TP) and water stable ag-gregates in the 1e2 mm size class (WSA1e2 mm). To avoid physicaldisturbance of the soils, samples of the rst part were sealed inaluminum boxes immediately. The second part was sieved to2 mm to remove litter and roots. This part was used to measuresoil microbial biomass carbon and nitrogen (MBC, MBN), basalrespiration (BR), and phospholipid fatty acids (PLFAs). Prior totransport, all soil samples were kept at approximately 4 C. In thelaboratory, all samples were kept at 4 C except for the sub-samples for PLFA analysis, which were frozen (80 C) untilfurther analysis. The third part was also sieved to 2 mm toremove litter and roots, then was dried at 70 C for 48 h for soilphysico-chemical analysis.

2.4. Percent cover estimation

Before sampling, a visual percent-plant-cover estimation wasmade for each of the 1 m1 m plots. This estimate was rened byanalyzing photographs from each plot that were taken simulta-neously using a Canon EOS 40D (Canon Inc., Japan). The actual plantcover in each photo was determined using Adobe Photoshop CS4Extended 11.0 (Adobe Systems Inc., USA). We opened the MagicWant Tool, and clicked a pixel representing the dominant color ofplants or soil, respectively, determining the base color. Using thedefault tolerance setting of 32, the resulting selections corre-sponded very well with the distinction between plant and soil areamade by eye. We then separately calculated the number of pixelsrepresenting plant and soil area, respectively. Plant cover was

estimated as follows:

L. Qu et al. / Soil Biology & Biochemistry 94 (2016) 1e92


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Plant cover % 100*Number of plant pixels=

Number of plant soil pixels (1)

2.5. Soil chemical and physical characteristics

Gravimetric water content (GWC) was measured by oven-dryingthe third category samples at 105 C until the weight becameconstant. Soil pH and electrical conductivity (EC) were determinedin a 1:2.5 (w/v) soil-water suspension. Bulk density (BD) was esti-mated using the oven-dried soil sample mass and volume. Un-drained shear strength was measured in-situ using the inspectionvane tester (stand 14.05, Eijkelkamp, Netherlands).

Glomalin, a glycoprotein produced by arbuscular mycorrhizalfungi that plays an important role in soil aggregation, was quanti-ed in soils as glomalin-related soil protein (GRSP). Two GRSPpools, dened as Bradford-reactive soil proteins (BRSPs), weredistinguished by their extraction conditions and chosen quanti-cation method (Wright and Upadhyaya, 1998; Rillig, 2004; Janoset al., 2008). The easily extractable BRSPs (EE-BRSPs, EEG) were

obtained by autoclaving samples for 30 min at a pH of 7.0 in 20 mmcitric acid. For total BRSPs (T-BRSPs, TG), the same samples weresubjected to sequential 60 min cycles of autoclaving in 50 mm citricacid at a pH of 8.0, and were then centrifuged at 10,000gfor 5 minto remove soil particles. After three cycles of extraction andcentrifugation, the supernatant was clear/light yellow, as describedbyWright and Upadhyaya (1998). The GRSP concentration in theextracts was determined by Bradford assay, using bovine serumalbumin as a standard.

For WSA1e2 mmestimation, 4 g samples of soil aggregates weremoistened by capillary action for 10 min. The water stability ofaggregates was then measured with a wet-sieving method usingthe apparatus (Eijkelkamp, Netherlands) and procedure describedinKemper and Rosenau (1986). Percentage of water-stable aggre-gates was calculated using the mass of aggregated soil remainingafter wet sieving and the total mass of aggregates at the beginning(Rillig et al., 2002).

Aggregate size classes were isolated by wet sieving as describedby Elliott (1986) and Cambardella and Elliott (1993). The soilsamples were gently broken down by hand along natural planes ofweakness between aggregates. A series of sieves were used toseparate soil into four fractions, large macroaggregates(>2000 mm), small macroaggregates (250e2000 mm), micro-aggregates (53e250 mm) and non-aggregated silt and clay particles(


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Macdonald et al., 2009). When necessary, data was log trans-formed. The signicance of the canonical axis was tested using theMonte Carlo permutation test. All multivariate techniques wereperformed with CANOCO 4.5 (Biometris, Wageningen, theNetherlands).

3. Results

3.1. Effects of the presence of A. gmelinii on belowground properties

The paired-sample t-test (Table 1) shows that the presence ofA. gmelinii signicantly increased gravimetric water content (GWC),water stable aggregates in the 1e2 mm size class (WSA1e2 mm),easily-extractable glomalin (EEG), total glomalin (TG) and soilorganic carbon, whereas it lowered shear strength (SS) and bulkdensity (BD). The pH and electrical conductivity (EC) were notsignicantly affected. Effects ofA. gmeliniion total soil carbon (TC)and phosphorus (TP) varied among soil aggregate size classes. TCwas signicantly higher in under-plant soils than in inter-plantsoils in large macroaggregates (>2000 mm), small macroaggre-gates (250e2000 mm), and microaggregates (53e250 mm), while itremained unchanged in non-aggregated silt and clay particles(


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soil quality. Soil water deciency was ameliorated and soil organiccarbon was signicantly increased by plant establishment. TC andTN accumulated most strongly under plants. These resultsdemonstrate the important role ofA. gmeliniiin improving the soilquality in this semi-arid area. The magnitude of the carbon andnutrient accumulation under plants differed among differentlysized soil aggregates. The aggregate hierarchy model predicts that Cconcentration will increase with increasing aggregate size classbecause larger aggregate size classes are composed of smalleraggregate size classes plus organic binding agents (Tisdall andOades, 1982; Six et al., 2000). In our study, the concentrations ofTC and TN were highest in small macroaggregates (250e2000 mm),in which the accumulation of carbon and nitrogen under plants wasmost evident. In cultivated soils, also total P is expected to increasewith increasing soil aggregate size. Wright (2009)found that ag-gregation increased P sequestration in humic-fulvic acid and re-sidual fractions and that P storage in organic pools increased withincreasing aggregate size. In our study, the magnitude of changes inP concentrations with aggregate size were relatively small. But the

presence ofA. gmelinii still signicantly increased P accumulation insmall macroaggregates (250e2000 mm). Therefore, among soil sizeclasses, the small macroaggregates may be important in terms ofphosphorus accumulations, which may be closely related to Puptake in this semiarid area. This indicates the potential impor-tance of macroaggregates for rehabilitation, since low P concen-trations and water content are the most limiting factors for plantgrowth in this semiarid valley of the Upper Mingjiang River (Xuet al., 2009; Song et al., 2010).

Increases in organic carbon content generally enhance the soil'smacroaggregate content and macroporosity, and thereby reduce itsbulk density (Dunkerley and Brown, 1995). Aggregate stabilitycould determine the capacity of aggregates to resist the effects ofwater and rainfall. Increases in water stable aggregates in the1e2 mm size class (WSA1e2 mm) are generally associated with morerecalcitrance to runoff and less soil loss. In our study, A. gmeliniipresence decreased bulk density values in the surface soils,increased WSA1e2 mmvalues, and increased macroaggregate (largemacroaggregates and small macroaggregates) contents of carbon

Table 2

Soil microbial characteristics (means) of rhizosphere (under-plant) and inter-plant soil.The paired-sample t-test indicates signicanceof differences betweenunder-plant andinter-plant soils. Abbreviations are as follows: R averaged value of under-plant to inter-plant ratios, MBC microbial biomass carbon, MBN microbial biomass nitrogen,BR basalrespiration, G Gram negative bacterial PLFAs, G Gram negative bacterial PLFAs, B bacterial PLFAs, AM arbuscularmycorrhizal fungalPLFAs, Fungi fungalPLFA.

MBC mg/kg MBN mg/kg BR mgCO2-C/g/h G nmol/g G nmol/g B nmol/g AM nmol/g F nmol/g

Under-plant 587.87 39.97 0.520 54.27 30.78 85.05 12.46 8.25Inter-plant 340.57 8.76 0.265 36.06 18.21 54.26 6.94 4.88

R 1.943 4.594 2.301 3.112 2.774 2.868 2.508 2.230t 10.176 11.603 9.009 3.748 4.614 4.099 4.913 4.946df 29 29 29 28 28 28 26 28P


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and nitrogen. Therefore, our results indicate that A. gmeliniigenerally improved soil physical conditions and the potential inreducing runoff and soil loss. The only exception to this was theeffect ofA. gmeliniion sheer strength, an indicator of resistance to

soil erosion, which was actually lower for under-plant than forinter-plant soil. However, this effect may have been be due to thehigher soil water content under plants, that often results indecreased sheer strength (Fan and Su, 2008), and does not neces-sarily indicate a negative impact on reducing runoff and soil loss.Interestingly, we found that the small macroaggregates containedthe highest concentrations of total carbon and nitrogen of all soilaggregate size classes in all three cover classes studied. This in-dicates this size aggregates maybe important in terms of carbonand nitrogen related dynamics in our study site.

In addition to soil carbon and nutrients under plants, soilmicrobial biomass was also strongly accumulated underA. gmeliniiplants, and the extent of their accumulation was larger than that oftotal soil carbon and nitrogen (Tables 1 and 2), indicating the high

sensitivity of microbial parameters to A. gmelinii presence andgrowth, consistent with other studies (Panikov, 1999). Throughintensied microbial activities, A. gmelinii could promote soil car-bon, nitrogen and phosphorous dynamics, which is expected tocreate a positive feedback to the plant, and to further increasemacroaggregate levels and to enhance soil stability.

4.2. Inuence of A. gmelinii cover on inter-plant soils

Our results clearly show that not only soil directly under plants,but also inter-plant soils were inuenced by the presence ofA. gmeliniiand that effects on inter-plant soils generally increasedwith plant cover. With increasing plant cover, the proportion ofmacroaggregates increases at the expense of microaggregates on

inter-plant soil. The proportion of macroaggregates is a good

indicator to represent the ability of soil to resist soil erosion(Barthes and Roose 2002). Our results indicate the improvement ofsoil structure due to the effects of adjacent increasing plant coveron increasing the proportion of macroaggregates in inter-plant

soil. Total soil carbon and nitrogen in inter-plant soils increasedwith increasing plant cover and the magnitude of the changediffered among soil size classes (Fig. 2), even though the values ofthese parameters were still lower compared to those in under-plant soils.

Bulk density is an important characteristic that affects keysoil functions such as water-holding capacity, inltrability, aeration,plant germination and root growth (Moraa and Lazarob, 2014).Higher plant cover signicantly reduced soil bulk density of inter-plant soil, which strongly indicates an improvement in soilphysical properties (Fig. 1). The shear strength and water stableaggregates in the 1e2 mm size class (WSA1e2 mm) did not signi-cantly differ among cover classes, although the percent content ofWSA1e2 mm in large macroaggregates and small macroaggregates

increased from low to high cover classes (data not shown). In ourstudy, both easily extractable glomalin (EEG) and total glomalin(TG) signicantly correlated with soil organic carbon, while nosignicant correlation could be found between water stableaggregates in the 1e2 mm size class and soil organic carbon.However,A. gmeliniicover reduced soil pH, which means the alkalistress in soils in this area may be ameliorated.

Microbial biomass and activity in inter-plant soils increasedwith increasing plant cover (Fig. 3). This is expected to alter carbonand nutrient dynamics among soil size classes and further accel-erate soil aggregation. Younger and more labile organic matter ispostulated to be more prevalent in macroaggregates than inmicroaggregates (Tisdall and Oades, 1982). In general, microbialcommunities associated with larger aggregate size classes (largeand small macroaggregates) were found to have a signicantly

Fig. 2. Soil physico-chemical properties for inter-plant soils with low (60% cover) (n 10) plant cover. Error bars

represent SEs of the means. Letters in lowercase indicate signicant differences (Tukey's HSD test, P < 0.05) among different plant cover classes within each soil aggregate size class.

Abbreviations are the same asTable 1.



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faster respiratory response than the communities associated withmicroaggregates (Vaisanen et al., 2005). Unfortunately, we could

not separate the microbial biomass of soil size classes in this study.Our study clearly demonstrates that the physico-chemicalproperties that drive soil microbial groups and activities stronglydepend on the microbial parameters that are considered. Basalrespiration was primarily associated with easily extractable andtotal glomalin (related to soil organic matter), and total soil carbonand nitrogen in large macroaggregates and small macroaggregates.By contrast, microbial biomass carbon and nitrogen were closelyrelated to total soil carbon and nitrogen in non-aggregated silt andclay particles, and to soil organic matter. Therefore, total carbon andnitrogen in large macroaggregates and small macroaggregates areimportant for microbial activity, whereas total carbon and nitrogenin non-aggregated silt and clayparticles areimportant for microbialbiomass accumulation in our system. Biomass of arbuscular

mycorrhizal fungi and Gram-positive and Gram-negative bacteria

in inter-plant soils were most strongly associated with TP in smallmacroaggregates (250e2000 mm) and TN in microaggregates

(53e250 mm). By contrast, fungal biomass was mainly constrainedby TC in microaggregates (53e250 mm) and was strongly associatedwith water stable aggregates in the 1e2 mm size class.

In conclusion, we found that A. gmelinii establishment signi-cantly increased aggregate-associated carbon and nutrients, accu-mulated soil microbial biomass and intensied microbial activities,and improved soil physical quality, which would further increasethe potential of A. gmelinii in reducing runoff and soil loss. Theinter-plant soils were strongly inuenced by adjacent A. gmeliniicover, resulting in gradually increasing soil quality with increasingcover.

Land degradation is a serious issue in arid and semi-arid regionsof China.A. gmelinii is a promising species to use as the target nativeplant to naturally rehabilitate the degraded region not only in the

upper Minjiang River valley but also in other semi-arid regions in

Fig. 3. Soil microbial properties for inter-plant soils with low (60% cover) (n 10) plant cover. Error bars

represent SEs of the means. Letters in lowercase indicate signicant differences (Tukey's HSD test, P < 0.05) among different plant cover classes. Abbreviations are the same as

Table 2.

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China. In a broader perspective, our results indicate that carefullyselected native plant species may play an important role in reha-bilitation of degraded soil systems in semi-arid regions, providing avaluable alternative for the current tendency to plant introduced

tree species for that purpose.

Acknowledgments

This research was supported by National Natural ScienceFoundation of China (No. 31170581) and China Scholarship Council(No. 201404910206) to Dr. Laiye Qu.

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Shear

pH

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SWC BD

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SOC

TC1

TC2

TC3

TC4

TN1TN2

TN3

TN4

TP1

TP2

TP3

TP4

Axis 1 (83.1%)

Axis2(7.8

%)

Fig. 4. Biplot of redundancy analysis (RDA), with soil physico-chemical properties, of soil microbial characteristics obtained from all inter-plant soils (Monte Carlo permutation tests

P 0.004). The solid arrows represent soil physico-chemical properties and the dotted arrows represent different microbial parameters.

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