Abstract
Nitrogen deposition is recognized as one of the major threats to the ecosystem function of alpine grasslands on the Qinghai-Tibetan Plateau (QTP). However, few studies have documented the gradient responses of plant species, functional groups, and communities in alpine grassland ecosystems to various levels of N deposition on the QTP. We applied eight linear mixed-effect models combing acidification, eutrophication, and phosphorus availability to explore if the responses of functional traits (particularly plant height and specific leaf area) of plants from dominant species to functional groups and whole communities in different types of grassland to nitrogen deposition were consistent with the same or different models. We found that the specific leaf area of Stipa capillata, non-forb, and community-weighted mean value in the alpine steppe were synchronous and related to acidification with nitrogen addition; the height of Stipa capillata, non-forb, and community-weighted mean value in the alpine steppe was synchronous and related to acidification, eutrophication, and phosphorus availability with nitrogen addition; the height and specific leaf area of Elymus breviaristatus to functional groups and community-weighted mean value in cultivated grasslands (CGs) were synchronous and related to acidification, eutrophication, and phosphorus availability with nitrogen addition. Most of the responses of functional traits of plants to acidification, eutrophication, and phosphorus availability associated with nitrogen deposition in the alpine steppe and the CG were synchronous, while only the response of the specific leaf area of forb functional groups to eutrophication associated with N deposition in the alpine steppe was asynchronous.
Highlights
Nitrogen (N) deposition is recognized as one of the major threats to global biodiversity (Phoenix et al, 2010; Payne et al, 2017), which has increased sixfold since the 1860s (Field et al, 2014) and is expected to continue to increase in the future on a global scale (Bobbink et al, 2010)
We found that the specific leaf area of Stipa capillata, non-forb, and community-weighted mean value in the alpine steppe were synchronous and related to acidification with nitrogen addition; the height of Stipa capillata, non-forb, and community-weighted mean value in the alpine steppe was synchronous and related to acidification, eutrophication, and phosphorus availability with nitrogen addition; the height and specific leaf area of Elymus breviaristatus to functional groups and community-weighted mean value in cultivated grasslands (CGs) were synchronous and related to acidification, eutrophication, and phosphorus availability with nitrogen addition
We conducted the manipulated experiments with N addition at different gradients in both alpine steppe (AS) and CG on the Qinghai-Tibetan Plateau (QTP) to test three hypotheses, namely, (1) eutrophication, acidification, and P availability associated with N deposition impact the functional traits of plants of alpine grasslands; (2) there are cascading effects of N deposition on the functional traits of plants from dominant species to functional groups and whole communities of the alpine grasslands; and (3) the responses of alpine plant functional traits to N deposition vary with grassland types
Summary
Nitrogen (N) deposition is recognized as one of the major threats to global biodiversity (Phoenix et al, 2010; Payne et al, 2017), which has increased sixfold since the 1860s (Field et al, 2014) and is expected to continue to increase in the future on a global scale (Bobbink et al, 2010). Few studies have documented the gradient responses of plant species, functional groups, and communities in alpine grassland ecosystems to various levels of N deposition on the QTP. The limited studies from temperate and tropical forests have shown inconsistent results about the responses of the functional traits of plants to N deposition, i.e., some scholars stated that functional traits were the conductors of the N deposition on communities (Wang et al, 2018), whereas some other scholars reported that plant traits were not related to N deposition (Moreau et al, 2015) It is even less clear about the responses of functional traits of plants from dominant species to functional groups, and whole communities in different types of grassland to N deposition were consistent with the same or different. We conducted the manipulated experiments with N addition at different gradients in both AS and CG on the QTP to test three hypotheses, namely, (1) eutrophication, acidification, and P availability associated with N deposition impact the functional traits of plants of alpine grasslands; (2) there are cascading effects of N deposition on the functional traits of plants from dominant species to functional groups and whole communities of the alpine grasslands; and (3) the responses of alpine plant functional traits to N deposition vary with grassland types
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