The Effects Of Nitrogen And Silicon Fertilization On Plant Community Structure And Stoichiometric Characteristics Of Alpine Meadow

Alpine meadow is important in constitute of the grassland ecosystem,whose productivity was mainly restricted by nitrogen element.Exogenous nitrogen fertilization could increase aboveground productivity but also reduce species diversity.Silica could promote plant growth by alleviating the negative effects of biotic or abiotic stress.However,the effects of nitrogen fertilization incorporation with silicon on plant community structure and the content of carbon,nitrogen,phosphorus and silicon in plants and soil are rarely involved.To explore the effects of fertilization on the characteristics of the alpine meadow community,the C,N,P,Si element content and stoichiometric characteristics of the soil and each functional group plant,we carried out an experiment including nitrogen fertilization(NH₄NO₃,the nitrogen application rates were 10.5 g·m^-2,21 g·m^-2and 31.5 g·m^-2),silicon fertilization(H₂Si O₃,the amount of silicon applied was 2.87 g·m^-2)and nitrogen fertilization incorporation with silicon in alpine meadow on Qinghai-Tibet Plateau.The main research results are as follows:（1）Nitrogen fertilization,silicon fertilization,and nitrogen fertilization incorporation with silicon all increased the community weighted mean height and increased the aboveground biomass the of grasses,cyperaceae,weed and the whole community.Nitrogen fertilization reduced species richness and the Shannon-wiener index,while silicon fertilization increased the Shannon-wiener index.The nitrogen fertilization incorporation with silicon had a significant interaction effect on the Shannon-wiener index and the aboveground biomass of the whole community and grasses.At the fertilization combination of nitrogen 21 g·m^-2 and silicon 2.87 g·m^-2,the aboveground biomass of gramineae,cyperaceae and weed reached a relatively high magnitude,and the total aboveground biomass reached maximum.At the same time,the Shannon-wiener index under silicon application is much higher than the without silicon treatment.（2）The species composition of the community were altered by the nitrogen fertilization but not the silicon fertilization.Nitrogen fertilization incorporation with silicon had a significant interaction effect on the species composition.The Poa pratensis,Potentilla berry,Euphorbia japonica,and Euphorbia euphorbia accounted for the variation of species composition between fertilization treatments.（3）Nitrogen fertilization,silicon fertilization,and nitrogen fertilization incorporation with silicon had no significant effect on the carbon（C）content of grasses,cyperaceae and weeds,but significantly increased the content of total nitrogen（TN）and total silicon（Si）of grasses and cyperaceae.Both the silicon fertilization and nitrogen fertilization incorporation with silicon significantly increased the total phosphorus（TP）content of all the three functional groups.At the fertilization combination of nitrogen added was 21 g·m^-2 and silicon 2.87 g·m^-2,the TN,TP and total Si contents of all the three functional groups of plants reached a relatively high magnitude.（4）Nitrogen fertilization,silicon fertilization,and nitrogen fertilization incorporation with silicon all had no significant effect on soil TN content,but decreased soil p H and soil organic carbon（SOC）,TP and available phosphorus（AP）.Meanwhile,at the same nitrogen fertilization,the content of soil SOC and TP and AP in silicon fertilization treatment were significantly higher than without silicon fertilization treatment.Nitrogen fertilization,silicon fertilization,and nitrogen fertilization incorporation with silicon all increased soil available nitrogen content and soil effective Si content.The content of nitrate nitrogen and ammonium nitrogen in the soil reached the maximum at the fertilization combination of nitrogen 21 g·m^-2 and silicon 2.87 g·m^-2.（5）Regardless of whether silicon or not,soil carbon/nitrogen（C:N）and carbon/phosphorus（C:P）gradually decreased,but soil nitrogen/phosphorus（N:P）gradually increased with nitrogen fertilization.Regardless of whether silicon or not,the C:N and N:P of gramineous and cyperaceae gradually decreased and increased with the nitrogen fertilization,respectively.Nitrogen fertilization has no effect on the C:P of grasses and cyperaceae,while silicon fertilization and combined fertilization of nitrogen and silicon significantly reduced the C:P of grasses and cyperaceae.（6）Shannon-Wiener index and aboveground biomass of weeds were positively correlated with soil available silicon content,and community weighted mean height was positively correlated with soil available nitrogen content.The total nitrogen content of gramineae and cyperaceae plants were positively correlated with the soil available nitrogen content.The total phosphorus content of grasses,cyperaceae and weeds were positively correlated with the soil available silicon content,and the total silicon content of grasses and cyperaceae plants were negatively correlated with the soil available silicon content.In summary,nitrogen fertilization,silicon fertilization,and nitrogen fertilization incorporation with silicon all promoted the absorption of N and Si elements in grasses,cyperaceae and weeds.The silicon fertilization and nitrogen fertilization incorporation with silicon promoted the absorption of P by all the three functional groups.Nitrogen fertilization incorporation with silicon mitigated the limitation of N and P nutrient elements on plant growth,and finally ultimately increased the aboveground biomass of plants.The fertilization of nitrogen caused the decreasing of species diversity and altered the species composition of the community,however,the silicon fertilization or nitrogen fertilization incorporation with silicon not only directly increased growth of plants,but also alleviated the decline in species diversity caused by nitrogen fertilization.The results showed that the biomass and species diversity of the alpine meadow plant community reached a relatively high magnitude and P and Si elements can complete the needs of plant growth at the fertilization combination of nitrogen 21g·m^-2 and silicon 2.87 g·m^-2.This study enriched our understanding on the effects of nitrogen fertilization and silicon fertilization on alpine meadows.Moreover,it also provided a theoretical basis of fertilization scheme of animal husbandry production for Alpine Meadow in Gannan.