Abstract
Plant–plant interactions play a key role in the function and structure of communities. The combined effect of drought stress and grazing disturbance on shaping plant–plant interactions is still poorly understood, while this combination is common in semiarid ecosystems. Four species including Stipa grandis, which is dominant in the typical steppe, and Stipa krylovii, Artemisia frigida, and Cleistogenes squarrosa, which are dominant species in the S. grandis degraded communities, were selected as study targets. We conducted a competition experiment (uniformly dense monoculture or mixture, respectively) under controlled conditions, including both drought stress and mowing disturbance, and calculated the relative interaction index (RII) of tiller number and RII of biomass for each species under each condition. (a) Under the same condition, the RII of tiller number and that of biomass for the same species usually showed reverse trends. (b) Mowing disturbance rather than drought stress played a negative role in influencing S. grandis’ or S. krylovii’s RII of tiller number and played a positive role in influencing A. frigida's RII of biomass. (c) Drought stress rather than mowing disturbance played a positive role in influencing C. squarrosa’s RII of tiller number. (d) Neighbor species significantly influenced S. grandis’ RII of tiller number, S. krylovii’s RII of tiller number, A. frigida's RII of tiller number and biomass, and C. squarrosa’s RII of biomass. These results could provide an explanation for why S. krylovii, A. frigida, and C. squarrosa can replace S. grandis and become the dominant species when S. grandis communities undergo a process of degradation due to overgrazing or climatic drought in natural communities. The present study provided powerful evidences for species replacement in the typical steppe of Inner Mongolia and elucidated the driving mechanisms of S. grandis communities’ retrogressive succession.
Highlights
Understanding the process of retrogressive succession of plant community is very important in the restoration and protection ecology as well as in applied ecology (He & Bertness, 2014)
Our study showed that the mowing disturbance but not drought stress was the main driver of reducing competitive capacity of S. grandis, which would cause the retrogressive succession of S. grandis communities
Under drought treatment (D−)M+ treatment, S. grandis’ relative interaction index (RII) of tiller number was negative when S. grandis was grown with A. frigida and neutral when S. grandis was grown with the other two species (Figure 2b), while S. krylovii’s RII of tiller number was negative when S. krylovii was grown with S. grandis, neutral when S. krylovii was grown with A. frigida, and positive when S. krylovii was grown with C. squarrosa (Figure 3b)
Summary
Understanding the process of retrogressive succession of plant community is very important in the restoration and protection ecology as well as in applied ecology (He & Bertness, 2014). Even though the relationships between the characteristics (or stress types) of the target species and the result of the plant–plant interaction are complicated and may be species specific, it goes to the core of retrogressive succession. Fully understanding such relationships of the main species in a particular community is very important for ecologist. Understanding how the combination of grazing disturbance and drought stress influences plant–plant interactions of the main species in Inner Mongolia Steppe of China is of critical importance for explaining the community retrogressive succession in this region, and guiding sustainable management practices of semiarid grassland ecosystems of China.
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