关键词: N沉降, 细根分解, 养分释放, 根径

Abstract: This paper studied the nutrient content, accumulation, allocation, and cycling characteristics as well as their relationships with stand density in a 11-year-old Pinus elliottii plantation with five stand densities (1667, 2000, 2400, 3330, and 3900 trees·hm^-2) in northern Hunan of China, aimed to improve the nutrient use efficiency of Pinus elliottii plantation and maintain the long-term productivity of the forest land. In the stands, there existed great differences in the nutrient content among different organs, which was decreased in the order of leaf > branch  > trunk  > root > bark. The nutrient accumulation in individual tree decreased with the increase of stand density. The accumulated amounts of N, P, K, Ca, and Mg in the stands were 1542.3-2073.7 kg·hm^-2, among which, arbor layer accounted for 70.3%-77.4%. The nutrient uptake, retention, and return of the stands were 167.5-203.1, 110.3-155.0, and 48.1-58.8 kg·hm^-2·a^-1, respectively. The nutrient uptake and retention of the high density stands (3330 and 3900 trees·hm^-2) were significantly higher than those of the two lower density stands. The nutrient return was slightly decreased with the increase of stand density. Overall, with the increase of stand density, the nutrient turnover became longer, the nutrient cycling rate decreased, and the nutrient use efficiency increased. This study could provide theoretical and practical bases for developing the silvicultural measures, including stand density regulation, understory vegetation, and litter management, of Pinus elliottii plantations in northern Hunan of China.

Key words: nitrogen deposition, root diameter., nutrient release, fine root decomposition