关键词: 木荷, 林龄, 氮重吸收效率, 磷重吸收效率, 磷限制

Abstract: Nitrogen (N) and phosphorus (P) resorption is a key nutrient use strategy for trees to cope with nutrient limitation and improve nutrient use efficiency. The variation and mechanism of N and P resorption of trees with stand development are still unclear. In this study, we measured N and P concentrations of fresh and senescent leaves of Schima superba across different stand ages (6, 18, 26 and 34 years old) in Nanping, Fujian Province, and calculated nutrient resorption efficiency. Combining with the concentrations of soil total N (STN), total P (STP), ammonium N, nitrate N and available P (AP), we further explored the regulation mechanism of nutrient resorption in S. superba leaves across different stand ages. The results showed that STN and STP concentrations changed signi-ficantly with increasing stand age. The STP concentration of 6-year-old plantation was significantly higher than that of 26- and 34-year-old plantations. The STN concentration of 26-year-old plantation was significantly higher than that of 6-, 18- and 34-year-old plantations. With increasing stand age, TN concentration of fresh leaves in 34-year-old S. superba was significantly higher than that of 6-, 18- and 26-year-old S. superba. There was no significant difference in TP concentration of fresh leaves, TN and TP concentrations of senescent leaves in different stand ages (P>0.05). Leaf N resorption efficiency (R_N) increased with increasing stand age, ranging from 35.48% to 44.52%, with an average of 38.25%. Leaf P resorption efficiency (R_P) decreased with increasing stand age, ranging from 30.99% to 53.50%, with an average of 40.42%. The relative resorption efficiency of N and P (R_N∶R_P) of 6- and 18-year-old S. superba was less than 1, and that of 26- and 34-year-old S. superba was greater than 1. Foliar P and N concentrations of the four stands were less than 1 and 20 g·kg^-1, respectively. The N/P in fresh leaves increased significantly with increasing stand age, ranging from 17.62-24.40 and greater than 16, indicating that the growth of S. superba was limited by P. Leaf R_N was positively correlated with soil ammonium N, nitrate N and STN/STP ratio. Leaf R_P was positively correlated with soil available P concentration and negatively correlated with ammonium N (P<0.05). R_N∶R_P was significantly positively correlated with STN/STP ratio (P<0.05), indicating a positive feedback mechanism between soil nutrient concentration and nutrient resorption. Our results showed that leaf R_N increased to meet the N demand with the development of S. superba plantation. However, leaf R_P decreased, resulting in increased P limitation. It is indicated that P resorption may not be the dominant mechanism underlying its adaptation to P limitation. Other ways of S. superba to cope with P limitation, as well as the interaction mechanism of P resorption with changes in soil ammonium N concentration should be further studied.

Key words: Schima superba, stand age, nitrogen resorption efficiency, phosphorus resorption efficiency, phosphorus limitation