Short-term responses of nutrient resorption and stoichiometry to nitrogen addition in Castanopsis hystrix plantation

Nutrient resorption from senescing tissues is recognized as a strategy for plants to adapt to nutrient deficiency. However, how nutrient resorption regulates the balance of nutrient elements within plants remains unclear, particularly under conditions of increased soil nitrogen availability.

This study investigated the changes in nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) content in green and senescent leaves, as well as soil nutrient contents, in a subtropical Castanopsis hystrix plantation under different N addition treatments (Control, CK: 0 kg·hm^-2·a^-1; Low N, LN: 50 kg·hm^-2·a^-1; Medium N, MN: 100 kg·hm^-2·a^-1; High N, HN: 150 kg·hm^-2·a^-1). The overall patterns and main drivers of nutrient resorption efficiency and its stoichiometric ratios were also examined.

The results showed that the HN treatment significantly increased soil dissolved inorganic N (DIN) content, leading to a significant decrease in soil DOC∶DIN and a significant increase in soil DIN∶AP (P<0.05), indicating that long-term high N input exacerbates soil P limitation. Under N addition, the concentrations of N, P, Ca, and Mg in both green and senescent leaves showed an increasing trend. MN and HN significantly increased green leaf total N (TN) content; MN significantly increased green leaf total P (TP) content; LN and HN significantly increased green leaf Ca content. LN, MN, and HN significantly increased senescent leaf TN content; HN significantly increased senescent leaf Ca content. LN, MN, and HN significantly decreased nitrogen resorption efficiency (NRE); phosphorus resorption efficiency (PRE) was significantly reduced only under the LN treatment. N addition had no significant effect on potassium, calcium, or magnesium resorption efficiency (KRE, CaRE, MgRE). Furthermore, senescent leaf nutrient content was significantly negatively correlated with resorption efficiency, indicating that nutrient resorption in C. hystrix is primarily regulated by senescent leaf nutrient status.

Our findings provide a theoretical basis for nutrient management in subtropical C. hystrix plantations and for understanding ecological adaptation strategies under nitrogen deposition.