Environmental Responses Of Stoichiometry Traits Of Main Grassland Communities In The Qinghai-Tibet Plateau

Nitrogen(N)and phosphorus(P)are essential elements for plant growth,which cycling can limit most processes in ecosystems.N and P concentration and N:P ratios are important ecological stoichiometry traits in plant leaves,which can be considered as the result of a long-term adaptation of plants to the environment.However,on the biogeographic scale,the main drivers of leaf stoichiometry traits remain unclear.The Qinghai-Tibet Plateau has a unique type of terrestrial ecosystem,and the biochemical processes of its plant communities are more sensitive to climate change.Conduct largescale research of ecological stoichiometry in the Qinghai-Tibet Plateau is very valuable for understanding the various links between nutrient interactions and nutrient cycling.In this research,we used 65 grassland communities in Qinghai-Tibet Plateau as our research objects,which is across 8 latitudes and 12 longitudes.Initially,spatial distribution and correlation of community-level stoichiometry traits(including N and P concentration and N:P ratios)have been analyzed.Secondly,the linear relationship between environmental factors and community leaf stoichiometry was analyzed.Finally,a multi-factor generalized additive model was constructed to fit the correlation of environmental factors to stoichiometry traits,and these models can help us to explore the possible non-linear relationship between environmental factors and stoichiometry traits and the relative importance of environmental factors.The result indicates the following:(1)Community leaf N concentration usually is a stable trait,while P concentration is more susceptible to environmental changes.There is a significantly positive correlation between leaf N and P concentration in community level.And the variation of N:P ratios is mainly caused by the change of P concentration.(2)The grassland communities in the Qinghai-Tibet Plateau is mostly N-limited,while P-limited and co-limited communities are mainly distributed in high altitude areas with low temperature,strong sunshine and lack of soil nutrient.(3)There is no significant relationship between the total soil N and the leaf N concentration of the community,and the total soil P has a significant positive correlation to the leaf P concentration of the community.These indicate that the leaf N and P contents respond differently to the corresponding nutrient traits in the soil.(4)Community-level stoichiometry traits are significantly affected by climatic factors,and leaf P concentration is more responsive to environmental changes than N concentration.We speculated that temperature changes the leaf N and P concentration of communities by affecting the physical properties and microbial activity of soils in which communities are built.Precipitation may be an environmental factor limiting the concentration of N and P in the community level,while excessive sunlight is also a limitation factor in some sites.(5)The obtained optimal multi-factor generalized additive model shows that leaf N and P concentration in community level have different responses to environmental factors.Environment factors always have a non-linear influence on leaf N concentration,while they have a linear influence on leaf P concentration.We speculate that species in the main grassland communities of the Qinghai-Tibet Plateau have a consistent mechanism for acquisition and distribution strategies of P elements,so there is still a strong regularity of leaf P concentration to environmental factors in community level.However,these species here have large interspecies differences in the acquisition and distribution strategies of N elements,so the regularity presented at the community level is not obvious.