The effects of defoliation on plant community, root biomass and nutrient allocation and soil chemical properties on semi-arid steppes in northern China

Semi-arid steppes in northern China have severely deteriorated over the past 50 years, mostly due to improper grazing management. A defoliation experiment was conducted on a Leymus chinensis-dominated semi-arid steppe to provide guidelines of grazing management and favor long-term restoration of degraded grasslands. There were five defoliation treatments: non-defoliation (no cutting during growing season) as control; light defoliation (cut 15 cm above ground level); medium defoliation (10 cm); hard defoliation (5 cm) and severe defoliation (2 cm). Results showed that hard and severe defoliation significantly reduced the concentrations of soluble carbohydrates in rhizomes and fibrous roots and decreased the belowground biomass and the ratio of below/aboveground biomass. Defoliation increased plant species diversity, but decreased biomass of L. chinensis significantly. The biomass of L. chinensis under light defoliation was lower than that in control, indicating L. chinensis was highly sensitive to defoliation. Defoliation intensity in general had no significant effect on soil chemical properties during the experimental period, suggesting that soil chemical properties might have a greater tolerance to short-term heavy defoliation compared to plant community. However, prolonged intensive defoliation would result in severe ecological consequences. Further studies are required to investigate the response of soil chemical properties to long-term defoliation.

► Defoliation reduced biomass and soluble carbohydrates in roots and rhizome. ► L. chinensis showed high sensitivity to defoliation. ► Soil chemical properties were relatively stable after three years' defoliation. ► A light defoliation might be feasible if grazing was necessary in semi-arid steppe.