Coarsened soil reduces drought resistance of fibrous-rooted species on degraded steppe

Abstract

Grassland degradation is often accompanied by coarsened soil, which could change water and nutrient uptake by plant roots. Studying the effects of soil coarsening on species performance with different root systems under manipulated irrigation has important practical significance in grassland restoration under changing climate. We conducted a common garden experiment with three water treatments (control, drought stressed and water addition) and two soil texture (loamy soil which is fine and sandy soil which is coarse) under a rainout shelter to explore the effects of degradation on the growth and drought response of tap-rooted species and fibrous-rooted species. Three fibrous-rooted species (Setaira viridis, Cleistogenes squarrosa and Leymus chinensis) and three tap-rooted species (Medicago ruthenica, Artemisia frigida and Potentilla bifurca) were used in the study (P. bifurca failed to germinate). The results showed that three of the five selected species tended to have higher aboveground biomass, greater belowground biomass, larger height and longer root length in sandy soil than in loamy soil. For fibrous-rooted species, drought had negative influence on several plant traits in sandy soil, and had no influence on plant traits in loamy soil. For tap-rooted species, drought had negative influence on plant traits both in loamy soil and in sandy soil, and the influence was larger in loamy soil than in sandy soil. The results showed that loamy soil might provide a buffer against drought for fibrous-rooted species, but make tap-rooted species more sensitive to drought. Our results implied that degraded grasslands with coarsened soil might change community composition in the grassland, making tap-rooted species take the place of fibrous-rooted species. Thus, soil coarsening is an important factor in predicting drought resistance as well as composition of the community, and should be given more attention under future climate changes.