Grazing‐induced shifts in community functional composition and soil nutrient availability in Tibetan alpine meadows

Abstract

1. The functional structure of plant communities can be altered by grazing through two main mechanisms: species turnover (i.e. changes in species occurrence and relative abundance), and by intraspecific trait variability (ITV), which is driven by phenotypic responses of individual plants and shifts in the relative abundance of genotypic variants within species.Studies of grassland ecosystem function under grazing often focus on community changes induced by species turnover, which ignores the effects of ITV on biomass productivity, soil carbon, or nutrient availability. By quantifying the relative contribution of both effects on shifts in community-wide traits, we highlight the role of ITV in community functional response to grazing and its implications for ecosystem function in Tibetan alpine meadows.2. We measured three chemical traits (LC, LN, LP: leaf carbon, leaf nitrogen, and leaf phosphorus concentrations) and two morphological traits (SLA: specific leaf area, LDMC: leaf dry matter content) that are critical components of plant production and forage quality in grazed and ungrazed plots. Using variance decomposition of community weighted means (CWM) for these foliar traits, we distinguished the relative importance of ITV versus change in species occurrence and abundance in response to grazing and the associated changes in soil carbon and nutrient availability. Accepted ArticleThis article is protected by copyright. All rights reserved.3. The CWM for foliar nutrients and SLA CWM increased in response to grazing together with decreases in soil carbon and nutrient stores, especially LP CWM enrichment and loss of available soil P. The LP CWM was strongly negatively correlated with LDMC CWM , which was significantly higher in ungrazed plots. These community-wide trait responses to grazing were generally best captured by ITV and not changes in species occurrence and abundance, although ITV was consistently correlated with species turnover for all traits. Synthesis and applications.In response to continuous grazing, plants in Tibetan alpine meadows increase specific leaf area and foliar nutrients but tend to have lower leaf dry matter content, a response consistent with faster growth and regrowth under grazing. This intraspecific trait variability response drives a shift in community function from conservative, slow-growing resource use in ungrazed meadows to exploitative resource use under grazing.This community-wide functional response enhances forage quality, in turn favouring the secondary productivity of small herbivorous mammal communities, but also contributes to accelerated depletion of soil available phosphorus. We discuss the implications of these results for biodiversity conservation, ecosystem function and rangeland sustainability in the Qinghai-Tibetan Plateau, especially with regard to managing grazing rotation to strike a balance between favouring secondary productivity of domesticated stock versus small herbivorous mammals.

Environmental controls override grazing effects on plant functional traits in Tibetan rangelands

“…This points to fast growth, rapid nutrient recycling and non‐conservative nutrient use strategy under more intense grassland management. Similar results were also found in desert grasslands in China (An, ), and alpine meadows in Tibet (Niu, He, & Lechowicz, ). However, lower SLA and leaf nutrient contents under grazing have been reported from typical grass steppes in Inner Mongolia (Bai et al, ) as well as from alpine humid meadows in the eastern part of the Qinghai‐Tibetan Plateau (Elumeeva, Onipchenko, & Wu, ).…”

“…Similar results were also found in desert grasslands in China (An, 2012), and alpine meadows in Tibet (Niu, He, & Lechowicz, 2016).…”

Trait‐abundance relation in response to nutrient addition in a Tibetan alpine meadow: The importance of species trade‐off in resource conservation and acquisition

“…Similarly, when N fertilizer was added in plant communities, competition for soil available P and/or light resource become more important to community assembly, leading to significant correlations between SRA and SLA (and LPC). These correlations also supported hypothesis of grazing‐induced P‐limitation in this meadows (Niu et al., ), which further explain why we find significant LPC‐abundance relation in these Tibetan alpine meadows: Abundance species in grazing rangeland are these with high leaf P content and fast growth rate (Niu, He, & Lechowicz, ).…”

“…Based on the experimental design from previous studies (Niu, He, & Lechowicz, 2016a;Niu et al, 2015), we chose ten common species in all plots to measure the key functional traits. These species accounted for 43%~76% of the above-ground biomass in these communities.…”

Grazing management options for restoration of alpine grasslands on the Qinghai‐Tibet Plateau

“…The Qinghai-Tibet Plateau is called the "Roof of the World" (Qiu 2008, Wang et al 2008. Besides livestock production, this high plateau also provides a variety of other ecosystem services, including fiber production, carbon sequestration, maintenance of the biodiversity (conservation), and recreation (Niu et al 2016). Alpine grasslands in the Qinghai Tibet Plateau have however been regionally degrading.…”