Abstract

Understanding the relationship between nitrogen addition and the diversity and productivity of alpine grassland plant communities is important for the sustainable development of grassland ecosystems. However, it is unclear how nitrogen addition, growth stage, and interactions between these factors affect plant biomass and diversity when regulating soil and plant nutrient factors. This study researched the temporal variations in plant community diversity and biomass after nitrogen addition in an alpine grassland from 2020 to 2021. Furthermore, this study used structural equation modeling to determine the direct and indirect pathways of plant and soil factors regulating plant biomass and diversity. Results showed that (1) nitrogen addition had significant effects on aboveground biomass, belowground biomass, and total biomass, while growth stage only had significant effects on aboveground biomass. Nitrogen addition, growth stage, and their interaction significantly affected the Shannon–Wiener diversity, the Margalef species richness, and the Pielou evenness. (2) Redundancy analysis indicated that total aboveground phosphorus, aboveground ammonium nitrogen, soil total nitrogen, and soil available nitrogen were the most significant explanatory variables for plant biomass variation, while soil available nitrogen, total soil nitrogen, and total belowground nitrogen were the key predicting factors for plant community composition variation. (3) Structural equation modeling revealed that plant biomass and diversity changed with nitrogen addition and growth stage. Nitrogen addition directly increased aboveground, belowground, and total biomass and indirectly affected plant biomass through the effectiveness of aboveground ammonium nitrogen, total aboveground phosphorus, and total soil nitrogen. Plant diversity was directly affected by the growth stage and indirectly by nitrogen addition through soil nitrogen and root nitrogen, which further affected plant diversity and evenness indices. The decrease in plant community diversity and species richness caused by nitrogen addition and different growth stages indirectly and negatively affected aboveground plant biomass. Overall, the results of this study indicate that plant biomass and diversity in alpine grasslands are affected by exogenous nitrogen addition and growth stage.

中文翻译：

---

高寒草甸植物多样性和生物量对氮添加和生长阶段的响应

摘要

了解氮添加与高寒草原植物群落多样性和生产力之间的关系对于草原生态系统的可持续发展具有重要意义。然而，尚不清楚氮添加、生长阶段以及这些因素之间的相互作用在调节土壤和植物营养因子时如何影响植物生物量和多样性。本研究研究了2020年至2021年高寒草地施氮后植物群落多样性和生物量的时间变化。此外，本研究利用结构方程模型确定了植物和土壤因子调节植物生物量和多样性的直接和间接途径。结果表明：（1）氮添加对地上生物量、地下生物量和总生物量有显着影响，而生育期仅对地上生物量有显着影响。氮添加、生长阶段及其相互作用显着影响香农-维纳多样性、Margalef 物种丰富度和 Pielou 均匀度。(2) 冗余分析表明，地上全磷、地上铵态氮、土壤全氮和土壤速效氮是植物生物量变化最显着的解释变量，而土壤速效氮、土壤全氮和地下全氮是关键植物群落组成变化的预测因素。(3)结构方程模型揭示植物生物量和多样性随着氮添加量和生长阶段的变化而变化。添加氮直接增加地上、地下和总生物量，并通过地上铵氮、地上总磷和土壤总氮的有效性间接影响植物生物量。植物多样性直接受生长阶段的影响，间接受氮添加（土壤氮和根系氮）的影响，进一步影响植物多样性和均匀度指数。氮添加和不同生长阶段引起的植物群落多样性和物种丰富度的下降间接地对地上植物生物量产生负面影响。总体而言，本研究结果表明高寒草原植物生物量和多样性受到外源氮添加和生长阶段的影响。