高寒草甸植物始花期物候和生物量分配对氮添加的响应

Response of plant first flowering and biomass allocation to nitrogen addition in an alpine meadow

为探讨氮素添加对植物始花期和生物量分配关系的影响以及对群落的潜在影响,对青藏高原东缘高寒草甸植物群落中31个常见物种的始花期物候和繁殖分配对氮添加的响应以及始花期与生物量分配之间的关系进行研究,并基于各物种的始花期数据进行方差分析。结果表明:1)与自然对照相比,氮素添加处理下禾草类植物始花期显著推迟3~8 d(P<0.05),而双子叶杂草类植物对氮素添加的响应存在种间差异。进一步分析发现,两个菊科植物的始花期在高氮处理中显著推迟4 d(P<0.05);毛茛科、龙胆科和两个玄参科植物的始花期显著提前3~4 d(P<0.05);其余双子叶杂草的始花期变化不显著。总体上,高氮处理引起的始花期变化大于低氮处理。2)禾草类繁殖分配在氮添加后降低,并且在高氮处理中显著降低(P<0.05),大多数双子叶杂草植物的繁殖分配增加,在高氮处理引起的变化大于低氮处理。3)始花期与繁殖分配在对照中呈显著正相关(P<0.05),而在氮添加处理中呈不显著正相关(P>0.05);始花期与茎生物量分配极显著正相关(P<0.01),始花期与叶生物量分配显著负相关(P<0.05),相关程度随着氮添加梯度的增加而提高。群落中植物始花期物候和生物量分配对氮添加的不同响应可能会影响植物在资源分配和竞争共存上原有的平衡,进而引起未来群落的组成、结构和功能的变化。

In this study,we analyzed the response of flowering phenology and reproductive allocation to nitrogen addition in 31 common species in an alpine meadow community and its effect on the relationship between the first flowering day and biomass allocation.The results showed that nitrogen addition had a significant effect on both flowering phenology and reproductive allocation of the studied species.The first flowering day of graminoid species was significantly delayed by 3~8 days due to nitrogen addition(P<0.05).The response of first flowering day of forbs to nitrogen addition varied among species,with high-level nitrogen addition significantly delaying the first flowering day of two Compositae species by 4 days(Saussurea hieracioides and Saussurea nigrescens)(P<0.05);and advancing the first flowering day of Ranunculaceae,Gentianaceae and Scrophulariaceae species(Veronica eriogyne,Pedicularis kansuensis)by 3~4 days.The first flowering day of other forb species remained unchanged with nitrogen addition,while the effect of the high-level nitrogen addition on the first flowering day was greater in comparison to the effect of low-level nitrogen addition.All graminoid species tended to reduce reproductive allocation in response to nitrogen treatment,particularly with high-level nitrogen addition(P<0.05).For forb species,reproductive allocation increased in most species,with high-level nitrogen addition having a greater effect compared to low-level nitrogen addition.There was a significant positive correlation between the first flowering day and reproductive allocation in the control(P<0.05),however,this relationship was not observed in nitrogen addition treatments(P>0.05).The first flowering day showed a significant positive correlation with stem allocation(P<0.001)and a significant negative correlation with leaf allocation(P<0.05),with these trends increasing with the increasing amount of nitrogen addition.These results suggest that the different responses of flowering phenology and biomass allocation to nitrogen addition could alter the balance of plant resource allocation and competition coexistence in community,potentially leading to changes in community composition,structure and function.