SPECIAL FEATURE Winter Climate Change

Vladimir G. Onipchenko • Alii M. KipkeevMikhail I. Makarov • Anna D. KozhevnikovaVictor B. Ivanov • Nadejda A. SoudzilovskaiaDzhamal K. Tekeev • Fatima S. SalpagarovaMarinus J. A. Werger • Johannes H. C. Cornelissen

Digging deep to open the white black box of snow root phenology

Received: 17 October 2013 / Accepted: 27 November 2013 / Published online: 11 December 2013� The Ecological Society of Japan 2013

Abstract Snow roots are specialized structures recentlydiscovered in the Caucasian alpine snow-bed plantCorydalis conorhiza. They form extensive networks thatgrow into snow packs against gravity, most probably togather nitrogen from snow. Here we test the hypothesisthat snow roots are true winter organs, i.e., they shouldalready start growth early in winter to lay down theinfrastructure for N capture from snow packs well be-fore their melt-out. This would require winter surfaceand soil temperatures continuously close to or abovefreezing. Excavations of snow roots from snow packs inJanuary and May, accompanied by temperaturerecordings and anatomical observations, supported ourhypothesis. These findings complete the annual cycle ofsnow root phenology. They also emphasize the evolu-

tionary and ecological significance of these specializedwinter organs. Moreover, their likely association with aparticular abiotic temperature and snow regime willfacilitate the search for snow roots in other species.

Keywords Alpine snow bed Æ Anatomy Æ Life history ÆNutrient uptake strategy Æ Snow roots Æ Winter ecology

Introduction

Snow roots are amazing specialized structures of alpineplants. They form extensive networks that grow into snowpacks against gravity, most probably to gather nutrientsfrom snow. They were discovered recently on Corydalisconorhiza Ledeb. (Papaveraceae) in melting snow in analpine snow bed community in the North-west Caucasus,southern Russia (Onipchenko et al. 2009; Fig. 1a, b).Nitrogen uptake from snow by C. conorhiza, and its sub-sequent translocation to the leaves,was demonstrated in anexperiment with 15N addition to snow packs (Onipchenkoet al. 2009). This ‘special’ plant N acquisition strategycomplements the list of other such strategies includingsymbioses with mycorrhizal fungi or N2-fixing bacteria,parasitism and carnivory (cf. Lambers et al. 2008). Weknow that the N acquisitive strategy of snow roots isassociated with their extremely high specific root lengthand their special anatomy, with small diameter and lack ofstructural deposits in the epidermis. However, this knowl-edge isbasedonlyonsnowroot samplingat the endof snowmelt in July (Onipchenko et al. 2009; Fig. 1a). To fullyappreciate the evolutionary advancement that snow rootsrepresent, we need to consider their whole annual cycleincluding their winter phenology. This will help us uncoverwhether (1) snow roots are merely an ephemeral springfeature, developing only duringmelt-out of the snow pack;or (2) they are a true winter organ, developing and per-sisting inside the snow pack throughout the alpine winter.As snow roots grow upward from the lower parts of thebelowground tubersofC.conorhiza, theywouldbeunlikely

V. G. OnipchenkoDepartment of Geobotany, Faculty of Biology, Moscow StateUniversity, Moscow 119991, Russia

V. G. Onipchenko Æ A. M. Kipkeev Æ F. S. SalpagarovaKarachaevo-Cherkessian University, Lenina ul. 29, Karachaevsk,Karachaevo-Cherkessian Republic 369200, Russia

V. G. Onipchenko Æ D. K. TekeevTeberda State Reserve, Badukskii 1, Teberda,Karachaevo-Cherkessian Republic 369210, Russia

M. I. MakarovDepartment of General Pedology, Faculty of Soil Science,Moscow State University, Moscow 119991, Russia

A. D. Kozhevnikova Æ V. B. IvanovTimiryazev Institute of Plant Physiology RAS, Botanicheskaya ul.35, Moscow 127276, Russia

N. A. Soudzilovskaia Æ J. H. C. Cornelissen (&)Systems Ecology Department of Ecological Science, Facultyof Earth and Life Sciences, VU University, De Boelelaan 1085,1081 HV Amsterdam, The NetherlandsE-mail: j.h.c.cornelissen@vu.nl

M. J. A. WergerDepartment of Plant Ecology and Biodiversity, Faculty of Science,Utrecht University, Utrecht, The Netherlands

Ecol Res (2014) 29: 529–534DOI 10.1007/s11284-013-1112-3

to start developing in early winter if the soil were deeplyfrozen then. However, in alpine areas of the temperatezone, temperatures in the lower part of the snow pack tendto be near 0 �C when the snow depth exceeds �0.5 m(Brooks et al. 1997; Pomeroy and Brun 2001). In alpineCaucasian snow beds, the snow depth does exceed 0.5 mand soil temperatures are close to zero throughout thewinter (see below). Accordingly, we hypothesized thatsnow roots can grow throughout the whole winter period.To test this hypothesis, we overcame the logistic challenges

of winter access to the Caucasian snow beds that host C.conorhiza and carried out a study to unveil the secrets ofwinter phenology and anatomy of snow roots.

Methods

The study was carried out in the alpine vegetation belton Mt. Malaya Khatipara in Teberda Nature Reserve,NW Caucasus, Russia (43�27¢ N, 41�42¢ E; altitude

Fig. 1 Annual cycle of Corydalis conorhiza snow roots in the field.a Snow roots just after snow melt, with new shoots pushingthrough in July. b Flowering shoots and remnants of the dead andpartially decayed snow roots on the soil surface, in August.

c Excavation of snow roots from snow pack in previously markedplot on 8 January 2013, when snow depth was 2.2 m. d Excavationof snow roots from adjacent spot in the same snow pack on 9 May2013, when snow depth was 3.5 m. Photos by V.G. Onipchenko

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2,800 m). Details about macroclimate, vegetation com-position and soil characteristics of the snow bed com-munity under investigation are given in Onipchenko(2004) and Onipchenko et al. (2009).

We monitored the temperatures at soil surface and at10 cm depth in the soil in two of the snow bed plots withC. conorhiza studied here for snow roots, using iButtonDS 1921Z sensors (Dallas Semiconductor, Dallas, TX;

Fig. 2 Morphology and anatomy of snow roots of Corydalisconorhiza. a Snow root collection using a sieve, January 2013. b–d Sections of the snow roots sampled in January 2013; e–i Sectionsof snow roots sampled in May 2013; b, f Cross-sections of themeristem zone (with aerenchymatous cortex in b); c, d, h Mature

snow root tissues; e Root tip; g Transition from meristem zone toelongation zone; i Root hairs protruding from a snow root section.AC Aerenchymatous cortex, C cortex, CC central cylinder,E endodermis, P pericycle, Ph phloem, R rhizodermis, RC rootcap, RH root hairs, X xylem. Photos by the authors

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precision ± 0.5 �C), year-round from the winter of2006/2007 through the winter of 2012/2013.

A site with high abundance of C. conorhiza wasmarked with a 4-m mast in the autumn of 2012. Weexcavated the snow pack in this spot on 8 January 2013,when the snow was 2.2 m deep (Fig. 1c). A snow sampleof the lowermost snow layer (snow lying directly on thesoil surface) with a surface area of 0.5 · 0.5 m and athickness of 50–70 mm was sealed into plastic bags. Thetotal amount of snow (13 L) in this sample was equiv-alent to 6.5 L water. The pit was subsequently filled inagain with the excavated snow. The sample was kept inthe laboratory (+20 �C) for 1 day to melt the snow. Thewater was subsequently filtered using a thin metal sieve(mesh size 0.25 · 0.25 mm). Roots were collected fromthe sieve (Fig. 2a) and fixed in 70 % ethanol for furtheranalysis.

A second snow excavation was carried out on 9 May2013 in the same area, several meters away from theJanuary pit in order to avoid any snow digging artefacts.At that moment snow depth there was 3.5 m and thesnow was much denser than in January (Fig. 1d). Welaid out three subplots in the vertical walls of the snowpit, i.e., �1 m apart. In each subplot, we took three

snow samples at 0–0.25, 0.25–0.50 and 0.50–0.75 mabove soil level, respectively. Each sample comprisedabout 2–3 L snow. We extracted and fixed the roots inthese snow samples in the same way as in January. Allsnow root samples were taken to the Timiryazev Insti-tute of Plant Physiology RAS, Moscow, for anatomicalobservations and photography as described in Oni-pchenko et al. (2009).

Results

Our monitoring of the soil surface temperatures duringthe entire period from winter 2006/2007 through winter2012/2013 showed that the winter of 2012/2013 waslargely representative of the longer-term annual tem-perature patterns (Fig. 3a, b). Also, the temperatureprofiles at 0.10 m soil depth were largely similar to thoseat the surface, without any subzero temperatures (datanot shown). These temperature data help to put theannual cycle of snow roots into their environmentalcontext. During the summer (early/mid July–August)high temperatures indicate the growing season. Aftercomplete melt-out, the new C. conorhiza shoots push

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Fig. 3 Soil surface temperature profiles in the snow bed areas from which snow roots were sampled. a Mean monthly temperatures overthe period 2006–2013. b Daily mean temperatures over the period October 2012–July 2013

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through their own snow roots, which then form a densewhite ‘blanket’ on the soil surface (Fig. 1a). In August,during flowering, these snow roots have already diedand partly decomposed (Fig. 1b). In autumn (Septem-ber to mid/late October) 2012, before the establishmentof the winter snow cover, the snow bed soil was notfrozen (Fig. 3b). At that time there was no visible evi-dence of previous year’s snow roots anymore (authors’observations). In 2012, the snow cover began to buildup on 1 November and the soil temperature becamestable on 8 November, when it ranged from +0.5to +1 (±1.0) �C. It then decreased very slowlyfrom November to snow melt-out in early July byabout 1 �C.

The January sample yielded a significant amount ofsnow roots (Fig. 2a; Table 1). These were the relativelythick, sturdy basal parts emerging from the lower partsof the tubers (Fig. 2a–d). Their total length was 3.32 m,their specific root length was about 350 m g�1. Meansnow root diameter was 0.349 ± 0.008 mm (mean ±SE, n = 56). Anatomical slides showed the followingmain features. The cortex was aerenchymatous (Fig. 2b–d) and the aerenchyma started to develop already in themeristem zone of the root (Fig. 2b). Cortical cells oftenformed thin ‘‘strips’’, while the cavities were very large.There were often five to eight cortical rows and thecentral cylinder was also wider than in May roots(Fig. 2b–d, cf. Fig. 2f–h). Root hairs were short andrare. Casparian strips in the endodermis were morepronounced in January snow roots (Fig. 2d) than inMay roots (cf. Fig. 2h). At ca. 250 mm per liter of snow,root density was not yet high in the snow layer up to50–70 mm from the soil surface.

In the May snow samples (Fig. 2e–i; Table 1), therewere practically no snow roots above 0.25 m above soillevel (

(January–May). Perhaps this could be tested by labelingsnow beds with 15N during winter; or by growing theplants in a climatized greenhouse with artificial snow ofdifferent N concentrations, and subsequently testing theplants’ growth performance. However, even if N uptakeduring spring snow melt (Onipchenko et al. 2009) weremore than that in winter itself (something still awaitingempirical testing), we have revealed that the snow rootinfrastructure to support this uptake is already fully inplace during peak snow cover in May, after a growingperiod that already started early in winter.

The biggest next challenge is now to check whetherthe Tree of Life features other plant species with snowroots, in closely related or distant taxa, in the Caucasusor in distant regions elsewhere in the world. Now thatwe have shown the likely association of snow rootphenology with temperatures around or (just) abovefreezing, this search can be narrowed down somewhat byfirst checking out snow bed areas with similar abioticregimes. Given the hidden nature of white snow rootsbelow a white cover, and their fast death and disap-pearance after snow melt-out, it is not unthinkable thatthey might even still be found in snow bed communitiesvisited by biologists or naturalists previously. It is alsolikely that the apparent dependence of C. conorhiza, andany yet undiscovered snow root species, on deep snowpacks with a particular soil temperature regime makessuch alpine specialists particularly vulnerable to winterwarming.

Acknowledgments This work was supported by RFBF No. 11-04-01215 to V.G.O. and M.I.M. and NWO grant 047.018.003 toJ.H.C.C. We also thank Dr. Makoto Kobayashi and the EcologicalSociety of Japan for organising the special symposium on Winterclimate change effects at the 2013 Annual Meeting in Shizuoka; andto Professor N. Kachi and Ecological Research for inviting andfunding J.H.C.C. to present snow root ecology there. We thankRichard van Logtestijn for text suggestions for the manuscript.

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Brooks PD, Schmidt SK, Williams MW (1997) Winter productionof CO2 and N2O from alpine tundra: environmental controlsand relationship to inter-system C and N fluxes. Oecologia110:403–413

Körner C (2003) Alpine plant life: functional plant ecology of highmountain ecosystems, 2nd edn. Springer, Berlin

Lambers H, Chapin FS, Pons TL (2008) Plant physiological ecol-ogy, 2nd edn. Springer, New York

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Onipchenko VG, Makarov MI, van Logtestijn RSP, Ivanov VB,Akhmetzhanova AA, Tekeev DK, Ermak AA, Salpagarova FS,Kozhevnikova AD, Cornelissen JHC (2009) New nitrogen up-take strategy: specialized snow roots. Ecol Lett 12:758–764

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Digging deep to open the white black box of snow root phenologyAbstractIntroductionMethodsResultsDiscussionAcknowledgmentsReferences