(Table 1) Bioclimatic subzones and soil characteristics along the Yamal Arctic Transect, northwestern Siberia

Sustainability of tundra vegetation under changing climate on the Yamal Peninsula, northwestern Siberia, home to the world's largest area of reindeer husbandry, is of crucial importance to the local native community. An integrated investigation is needed for better understanding of the effects of soils, climate change and grazing on tundra vegetation in the Yamal region. In this study we applied a nutrient-based plant community model - ArcVeg - to evaluate how two factors (soil organic nitrogen (SON) levels and grazing) interact to affect tundra responses to climate warming across a latitudinal climatic gradient on the Yamal Peninsula. Model simulations were driven by field-collected soil data and expected grazing patterns along the Yamal Arctic Transect (YAT), within bioclimate subzones C (high arctic), D (northern low arctic) and E (southern low arctic). Plant biomass and NPP (net primary productivity) were significantly increased with warmer bioclimate subzones, greater soil nutrient levels and temporal climate warming, while they declined with higher grazing frequency. Temporal climate warming of 2 °C caused an increase of 665 g/m**2 in total biomass at the high SON site in subzone E, but only 298 g/m**2 at the low SON site. When grazing frequency was also increased, total biomass increased by only 369 g/m**2 at the high SON site in contrast to 184 g/m**2 at the low SON site in subzone E. Our results suggest that high SON can support greater plant biomass and plant responses to climate warming, while low SON and grazing may limit plant response to climate change. In addition to the first order factors (SON, bioclimate subzones, grazing and temporal climate warming), interactions among these significantly affect plant biomass and productivity in the arctic tundra and should not be ignored in regional scale studies.位于西伯利亚西北部的亚马尔半岛（Yamal Peninsula）拥有全球规模最大的驯鹿牧场，该区域内冻原植被在气候变化下的可持续性，对当地原住民社群而言至关重要。为深入解析亚马尔区域内土壤、气候变化与放牧对冻原植被的影响，需开展综合性调查研究。本研究采用基于养分机制的植物群落模型——ArcVeg，以评估在亚马尔半岛的纬度气候梯度下，土壤有机氮（soil organic nitrogen, SON）水平与放牧这两个因子如何交互作用，进而影响冻原植被对气候变暖的响应。本研究的模型模拟以野外采集的土壤数据，以及亚马尔北极样带（Yamal Arctic Transect, YAT）沿线的预设放牧模式为驱动参数，模拟范围覆盖生物气候亚区（bioclimate subzones）C（高北极区）、D（北低北极区）与E（南低北极区）。植物生物量与净初级生产力（net primary productivity, NPP）随生物气候亚区温度梯度升高、土壤养分水平提升以及时序性气候变暖而显著增加，反之则随放牧频率升高而降低。在E亚区的高SON位点，升温2℃的时序性气候变暖可使总生物量增加665 g/m²，而在低SON位点仅增加298 g/m²。当同时提升放牧频率时，E亚区高SON位点的总生物量仅增加369 g/m²，而低SON位点仅增加184 g/m²。本研究结果表明，高水平土壤有机氮可维持更高的植物生物量，并增强植物对气候变暖的响应；而低水平土壤有机氮与放牧则可能抑制植物对气候变化的响应。除上述一级影响因子（SON、生物气候亚区、放牧及时序性气候变暖）外，这些因子间的交互作用也会显著影响北极冻原的植物生物量与生产力，在区域尺度研究中不容忽视。