Degradation shifts plant communities from S- to R-strategy in an alpine meadow, Tibetan Plateau

The replacement of dominant sedges/grasses with secondary forbs is common in alpine rangelands, but the un-derlying plant ecological strategies and their relevance to leaf traits and their variabilities of different plant func-tional groups remain largely unknown. Here, we measured key leaf traits and analyzed the competitor, stress-tolerator and ruderal (CSR) strategies of major species with different functional groups (sedges, grasses and forbs) in an alpine meadow along a degradation gradient on the Tibetan Plateau. Our results indicated that S-selected species were dominant in both non-degraded (C:S:R = 1:95:4%) and severely degraded (C:S:R = 2:87:11%) meadows. However, there was a shift from S-to R-strategy in the communities after rangeland degra-dation. More specifically, sedges and grasses with a conservative strategy maintained stronger S-strategy to tol-erate degraded and stressful conditions. In contrast, forbs with an opportunistic strategy (increase 9.5% in R-score) tended to adapt to degraded stages. Moreover, 51.1% and 23.9% of the increased R-scores in forbs were accounted by leaf mass per area and specific leaf area, respectively. Generally, higher leaf water and nitrogen con-tents coupled with larger variations in leaf traits and flexible SR strategies in forbs enabled them to capitalize on lower soil water and nutrient availability. Our findings highlighted that the contrasting strategies of plant species in response to the decrease in available resources might lead to niche expansion of secondary forbs and loss of diversity in the degraded alpine meadow. The emerging alternative stable states in the degraded rangelands might bring about a predicament for rangeland restoration. (c) 2021 Published by Elsevier B.V.

Automated summary

This study revealed the contrasting ecological strategies of different plant functional groups (sedges, grasses, and forbs) in alpine meadows on the Tibetan Plateau along a degradation gradient, and their impact on leaf traits and competitive performance of secondary forbs during degradation. The results showed that the response of plant species to decreasing available resources could lead to niche expansion of secondary forbs and a decrease in diversity in degraded alpine meadows.