基于N：P化学计量特征的高寒草甸植物养分状况研究

Plant N Status in the Alpine Grassland of the Qinghai-Tibet Plateau: Base on the N∶ P Stoichiometry

土壤养分条件影响不同功能群植物的养分状况与生长,这在施肥实验中已得到充分验证.然而,自然养分梯度下植物-土壤养分耦合关系的研究仍然缺乏.基于植物N∶P化学计量学特征,本研究探讨青藏高原亚高寒草甸自然养分梯度下不同功能群植物氮状况及生物量变化.2008年、2009年N∶P比值分别为9.83和11.57,其低群落N∶P比验证了该地区自然植被主要受到N素的限制.偏冗余分析(partial RDA)结果显示,随着土壤氮素可利用性的增加杂草生物量比例上升,而豆科、禾草生物量比例下降.豆科的固氮作用以及禾草的高养分利用效率分别提高其在氮限制植被中的竞争力;这些结果表明,全球氮沉降的增加将提高杂草的优势度.豆科生物量比例与群落、非豆科植物的N∶P显著正相关,表明豆科植物能够改善群落的氮状况,包括降低非豆科植物的氮限制水平.

Plants from different functional groups show distinct response to nitrogen （N） addition, however, the patterns and underlying mechanisms across the natural N availability gradient remain unexplored. In present studies, effects of soil N fertility on aboveground N pools and production were examined, and the N： P stoiehiometry was compared among forbs, graminoids, and legumes on an alpine grassland located in northeast of Qinghai-Tibet Plateau. Mean N： P ratios of the whole community in 2008 and 2009 were 9.83 and 11.57, respectively, indicating that the sub-alpine grassland was mainly N-limited. The partial redundancy analysis （ partial RDA） showed that the biomass percentage of forbs increased, while those of legumes and graminoids decreased with the soil N availability. It suggested that legumes and graminoids were more competitive than forbs in the natural N-limited grassland, which may be due to the N2-fixation ability and high nutrient use efficiency, respectively. Under the projected increasing N deposition, the vegetation tended to shift from graminoids and legumes to forbs. Significant relationships were found between the percentage of legumes biomass and N： P （phosphorus） ratio for the whole community and non-legumes, indicating that legumes could improve the community N status as well as non-legumes N status on the alpine grassland.