title: Legumes mitigate ecological consequences of a topographic gradient in a northern Mongolian steppe.
abstract: Topography should create spatial variation in water and nutrients and play an especially important role in the ecology of water-limited systems. We use stable isotopes to discern how plants respond both to ecological gradients associated with elevation and to neighboring legumes on a south-facing slope in the semi-arid, historically grazed steppe of northern Mongolia. Out of three target species, Potentilla acaulis, Potentilla sericea, and Festuca lenensis, when >30 cm from a legume, all showed a decrease in leaf δ(15)N with increasing elevation. This, together with measures of soil δ(15)N, suggests greater N processing at the moister, more productive, lower elevation, and more N fixation at the upper elevation, where cover of legumes and lichens and plant-available nitrate were greater. Total soil N was greater at the lower elevation, but not lichen biomass or root colonization by AMF. Leaf δ(13)C values for P. acaulis and F. lenensis are consistent with increasing water stress with elevation; δ(13)C values indicated the greatest intrinsic water use efficiency for P. sericea, which is more abundant at the upper elevation. Nearby legumes (<10 cm) moderate the effect of elevation on leaf δ(15)N, confirming legumes' meaningful input of N, and affect leaf δ(13)C for two species, suggesting an influence on the efficiency of carbon fixation. Variation in leaf %N and %C as a function of elevation and proximity to a legume differs among species. Apparently, most N input is at upper elevations, pointing to the possible importance of grazers, in addition to hydrological processes, as transporters of N throughout this landscape.
authors: Department of Biology, University of Pennsylvania, Philadelphia, PA 19104-6018, USA. bcasper@sas.upenn.edu
authors: Brenda B
authors: BB
authors: Casper
authors: Robert
authors: R
authors: Goldman
authors: Ariuntsetseg
authors: A
authors: Lkhagva
authors: Brent R
authors: BR
authors: Helliker
authors: Alain F
authors: AF
authors: Plante
authors: Laura A
authors: LA
authors: Spence
authors: Pierre
authors: P
authors: Liancourt
authors: Bazartseren
authors: B
authors: Boldgiv
authors: Peter S
authors: PS
authors: Petraitis
mesh_terms: D002244:Carbon / Q000378:metabolism; D002247:Carbon Isotopes; D007887:Fabaceae / Q000378:metabolism / Q000502:physiology*; D005843:Geography; D008986:Mongolia; D009584:Nitrogen / Q000378:metabolism; D009586:Nitrogen Fixation; D009587:Nitrogen Isotopes; D018515:Plant Leaves / Q000378:metabolism; D012987:Soil / Q000737:chemistry
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D012987:Soil; D002244:Carbon; D009584:Nitrogen