The Mechanism Of Warming And Dasiphora Fruticosa Effects On Soil Phosphorus Cycling In Alpine Meadows

Phosphorus is an important element of living organisms,it is crucial for the growth of plants and microorganisms,and plays a central role in ecosystem functions and processes.The transformation among the various phosphorus fractions determines the availability of soil phosphorus,and the most important and fastest source of available phosphorus in the soil comes from phosphorus mineralization led by phosphatase.Recent researches mainly focus on the conversion between the various fractions of soil phosphorus,but few studies have combined soil phosphorus fraction,phosphatase gene and phosphatase activity to systematically explore the dynamics of soil phosphorus cycle and mechanisms of change.The phosphorus cycle is affected by many factors.Temperature is the main abiotic factor that determines the rate of phosphorus cycling,and the understory plant community is the main biotic factor that regulates the transformation of soil organic and inorganic phosphorus.Global warming has led to the rise of temperature of global surface,and changing the function of ecosystems on a global scale.Warming significantly change the vegetation composition of the Qinghai-Tibet Plateau,and the problem of shrub encroachment in alpine meadow has become increasingly prominent.In the Qinghai-Tibet Plateau,shrub meadow is the most abundant meadow type of plant species,and the spatial mosaic of shrub usually shows obvious heterogeneity of soil organic carbon,nitrogen and phosphorus availability.Therefore,exploring the effects of warming and typical shrub D.fruticosa on soil phosphorus cycling at alpine meadow in Qinghai-Tibet Plateau can help us forecast the future changes of alpine meadow ecosystem function in Qinghai-Tibet Plateau under climate warming condition.The experiment was conducted at the Gannan Grassland Ecosystem Wild Scientific Observatory and Research Station in Maqu County,Gannan Tibetan Autonomous Prefecture,Gansu Province,and combined treatments of warming by open-top air chamber and removal of dominant shrub Dasiphora fruticosa.The content of soil organic and inorganic phosphorus,acid and alkaline phosphatase activities and abundance of enzyme encoding genes were selected to assess the dynamic of phosphorus cycling in soil.We also measured indicators such as the understory vegetation community,soil physicochemical properties,and soil bacterial and fungal communities.We used two-way analysis of variance to explore the effect of warming,D.fruticosa and their interaction on soil phosphorus cycling,and used regression analysis to explore the relationship among phosphatase activity,genes and soil organic and inorganic phosphorus content.What's more,correlation analysis and redundancy analysis as well as structural equation model were used to explore the direct and indirect effect of warming,D.fruticosa and their interaction on the phosphorus cycling.We get the following results:1.Warming,D.fruticosa and their interaction significantly impacted soil phosphorus fractions and phosphatase-encoding genes.Warming reduced soil inorganic phosphorus content,but did not affect the content of total phosphorus and organic phosphorus.D.fruticosa significantly increased the content of soil total phosphorus and organic phosphorus,but reduced inorganic phosphorus.The interaction of D.fruticosa and warming had a significant impact on inorganic phosphorus.In addition,D.fruticosa significantly increased the abundance of soil phoD gene,while warming had no significant effect on genes,but their interaction had a significant positive effect on both phoC and phoD genes.In addition,the phosphatase activities were not significantly affected by treatments.2.There were significant correlations between soil phosphorus fractions and phosphatase encoding genes,but phosphatase activities were not correlated with phosphorus fractions or phosphatase encoding genes.The abundance of phoD gene was negatively correlated with inorganic phosphorus content,but positively correlated with organic phosphorus content.Both phoC gene abundance and phosphatase activity were not affected by soil inorganic and organic phosphorus content,and there was neither significant correlation between acid and alkaline phosphatase activities and the corresponding phoC and phoD gene abundance.3.The direct and indirect pathways of warming and D.fruticosa and their interaction on soil phosphorus fractions,phosphatase-encoding genes and phosphatase activities,while fungi played crucial roles in mostly indirect pathways.Warming directly reduced soil inorganic phosphorus content,but D.fruticosa had both direct and indirect ways to influence inorganic phosphorus and organic phosphorus.The interaction of warming and D.fruticosa indirectly inhibited the inorganic phosphorus content through modifying fungal abundance.The interaction between warming and D.fruticosa had a significantly positive effect on gene abundance directly.Warming indirectly inhibited the abundance of phoC,but it had no significant effect on the phoD.D.fruticosa can not only directly increase the abundance of phoD,but also indirectly inhibited phoC through bacterial or fungal diversity.In addition,phosphatase activities were not affected by warming or D.fruticosa neither the interactions of them in direct pathway,but warming and D.fruticosa indirectly impacted phosphatase activities.Our research showed that both warming and D.fruticosa affected the soil phosphorus cycling,and we found that D.fruticosa can alleviate the negative effect of warming on the soil phosphorus cycle of alpine meadows on the Qinghai-Tibet Plateau.We also found the weak correlation between soil phosphorus fractions,phosphatase genes and enzyme activities in this experiment,with only correlation between alkaline phosphatase gene phoD and soil phosphorus fractions.The pathways of warming,D.fruticosa and interactions on soil phosphorus fractions,phosphatase genes and enzyme activities were quite different,while fungi participated in most indirect pathways in modifying soil phosphorus cycling.Our research demonstrated the dominant shrub effects to mitigate the negative impact of global warming on the ecosystem phosphorus cycle in alpine meadow of the Qinghai-Tibet Plateau,and reveled the changes of the soil phosphorus cycle in the Qinghai-Tibet Plateau under global climate change,and it also provides a theoretical basis for predicting the changes in the primary productivity and ecosystem functions of the Qinghai-Tibet Plateau in the future.