Seasonal grazing alters nutrient resorption and conservation, and affects spring growth of Stipa grandis

Nutrient resorption in autumn is a key mechanism of perennial plants for nutrient conservation and efficient use in grassland. Grazing effects on plant nutrient resorption may alter root nutrient conservation and affect plant growth in the subsequent spring. There are many studies on nutrient resorption and conservation of plants in grazing grassland, but few studies on its effect on plant growth in subsequent spring. Taking Stipa grandis, a dominant perennial grass in a semi-arid steppe as a model plant, we examined plant nitrogen (N) and phosphorous (P) resorption traits (resorption efficiency, proficiency and flux) and root nutrient conservation traits (root biomass and nutrient pool) in autumn, and plant growth traits (height, biomass and nutrient pool) in the subsequent spring, in an experimental grassland under four grazing-season treatments (i.e., grazing in spring, summer or autumn, or no grazing). We found that (1) 51-66% of N and 58-80% of P in S. grandis shoots were resorbed in autumn, and the resorption flux was the lowest under autumn grazing, and highest under spring grazing. (2) Root nutrient conservation traits were significantly reduced by summer grazing, slightly decreased by spring grazing, but not affected by autumn grazing. (3) Plant growth in next spring was the best under early spring grazing and the worst under autumn grazing, which was mainly affected by soil moisture rather than root nutrient storage. Our study provides insights into the process of plant nutrient cycling and a theoretical basis for establishing grazing system for grassland protection and rational utilization.