氮添加对高寒草甸植物花期物候和群落结构的影响

测定了2009-2011年3年氮素添加处理下，青藏高原东缘高寒草甸植物群落30个常见组分种的始花期、花期植株高度、群落高度(CWM H)和群落比叶面积(CWM SLA)，并用非度量多维尺度分析(NMDS)检验了氮素添加对群落水平的花期物候和群落结构的影响。结果表明，氮素添加后物种的花期植株高度显著增加(P<0.05)；莎草和禾草的始花期显著推迟(P<0.05)，豆科植物的始花期对氮素添加无明显响应，而其他双子叶类杂草的始花期的响应不一致：菊科的始花期推迟，毛茛科、龙胆科和玄参科的始花期均提前；高氮处理(HN)下的变化大于低氮处理(LN)。物种多样性随着氮素添加的增加而降低 (P<0.05)。氮素添加后群落高度和群落比叶面显著提高(P<0.05)。氮素添加显著降低了氮素处理和对照之间开花物候加权的群落结构相似性(Stress Value=0.08)。植物花期物候对氮素添加的响应差异可能会引起植物在繁殖及相互竞争共存上的新格局，最终改变群落组成。

Effects of nitrogen addition on flowering phenology, functional traits and community structure of alpine meadow in the Eastern Qinghai-Tibet Plateau

In this study, the effect of nitrogen addition on the flowering time plant height of 30 common species in an alpine meadow of the Qinghai Tibet plateau after 3 years was investigated. The effect of nitrogen addition on Community weighted means (CWMs) of two plant traits (CWM H) and (CWM SLA)was also studied. The community level phenology similarity and species composition similarity among nitrogen addition gradient were tested using a nonmetric multidimensional scaling (NMDS). The results showed that, Nitrogen addition significantly increased the height of species(P<0.05). The effect of nitrogen addition differed between gramineous and forbs species. The first flowering day was delayed in gramineous species (P<0.05). The first flowering day in forbs were either slightly advanced or delayed, but most of them have advanced the first flowering day (P<0.05). As might be expected the leguminous species flowering time was insensitivity to nitrogen addition. Nitrogen addition significantly increased (CWM H) and (CWM SLA) (P<0.05). Simpson's diversity Index decreased along with nitrogen addition level. Nonmetric multidimensional scaling (NMDS) ordination of phenologically weighed community similarity was among nitrogen addition gradient (Stress Value=0.08). The community level phenology similarity and species composition similarity were significantly decreased with nitrogen level, which implied that both community level phenology and community structure were responsive to nitrogen addition.