[Responses of leaf nutrient resorption in marsh plants to shrub encroachment in Sanjiang Plain, China]

Based on the coverage of the shrub Spiraea salicifolia (0-100%) in the Sanjiang Plain, we examined the responses of nitrogen (N), phosphorus (P), and potassium (K) content, as well as nutrient resorption efficiency in the mature and senescent leaves of three dominant marsh plants (Deyeuxia purpurea, Carex schmidtii, and S. salicifolia) to four degrees of shrub encroachment: no shrub encroachment, light shrub encroachment (0-30%), moderate shrub encroachment (30%-70%), and heavy shrub encroachment (>70%). The results showed that shrub encroachment did not significantly affect N, P, and K contents in the mature leaves of the marsh plants. It significantly reduced K content in the senescent leaves of D. purpurea and S. salicifolia by 40.1% and 60.6%, respectively, and the N content in the senescent leaves of C. schmidtii by 25.3%. Nutrient resorption efficiency of marsh plants responded differently to shrub encroachment. After shrub encroachment, N, P, and K resorption efficiencies (NRE, PRE, KRE) of D. purpurea were significantly increased by 14.6%, 9.5%, and 3.2%, respectively. The NRE of C. schmidtii increased significantly by 12.6%, but KRE decreased significantly. For S. salicifolia, KRE increased significantly by 14.8%, while there were no significant changes in the NRE and PRE. C. schmidtii disappeared under the heavy shrub encroachment plots, whereas D. purpurea persisted. Redundancy analysis indicated that N, P, and K contents and N:P:K stoichiometric ratio of leaves were the main factors influencing nutrient resorption efficiency. Both D. purpurea and C. schmidtii adapted to shrub encroachment by adjusting leaf nutrient resorption. With the flexible nutrient allocation strategy, D. purpurea was better suited to nutrient-poor environment, forming a complementary nutrient utilization strategy with the encroachment of S. salicifolia.