青藏高原高山草甸群落生物量及多样性对氮素添加的响应

为了探测大气氮沉降对高山草甸的影响,设置对照(N_0)、低氮14.3g·m~(-2)(N_5)、中氮28.6g·m~(-2)(N_(10))和高氮57.1g·m~(-2)(N_(20))4个氮素(NH_4NO_3)添加水平,连续3年对青藏高原东部的高山草甸群落进行施氮处理,测定各添加水平下群落生物量及物种多样性的变化。结果表明,随着氮素添加量的增加,地上生物量逐渐增加,在N_(20)达到最大,且地上生物量在空间格局上呈现向上转移的趋势;随氮素的增加,地下生物量先增大后减小,在N_(10)最大,且有向浅层表土(0-10cm深度)转移的趋势。各功能群中,禾草类植物的地上生物量从N_0到N_(20)逐渐增加,在N_(20)达到最大,其在地上总生物量中所占的比例也在N_(20)达到最大。另外,随着施氮量的增加,植物物种多样性呈现出逐渐降低的趋势。可以看出,氮素添加对高山草甸群落的结构有着明显的影响。

Response of biomass and species diversity to nitrogen addition in alpine meadows

In order to explore the effects of air nitrogen deposition on alpine meadows,four nitrogen levels (N0,0;N5,14.3 g · m-2;N10,28.6 g · m-2;N20,57.1 g · m-2) were established in alpine meadows in the eastern Tibetan Plateau,and the biomass and species diversity for each level were measured after three consecutive years of nitrogen addition.The aboveground biomass increased from N0 to N20,reaching the maximal value at N20.Regarding the spatial pattern,the aboveground biomass showed a trend of upward shift,that is,the plants grew taller.The belowground biomass increased initially but decreased afterwards as nitrogen addition increased,peaking at N10,and it showed a trend of shifting towards topsoil (0-10 cm depth).Among the three functional groups (grass,sedge and forbs),aboveground biomass of grass increased from N0 to N20,peaking at 20,and so did the ratio between the aboveground biomass and total aboveground biomass of grass.In addition,plant species diversity decreased gradually as nitrogen addition increased.In conclusion,nitrogen addition exerted an evident influence on the structure of alpine meadows.