不同坡位对琉球松人工林凋落物及其养分归还量的影响

对日本冲绳岛北部不同坡位的琉球松人工林凋落物量及其养分归还量进行了为期3年的观测研究，结果表明，琉球松成林年凋落物量为6．54～8．05Mg·hm^-2·年^-1，其凋落高峰出现在6、7月份．台风干扰对年凋落物量及其季节动态影响显著．凋落物不同组分的养分含量差异明显．年均养分归还总量为113．4～154．6kg·hm^-2·年^-1，其中氮素归还量最大，占42．2％；各养分归还量的大小依次为N>Ca>K>Mg>Na>P．两调查林分由于立地条件的显著差异，年均凋落物量及其相应的养分归还量亦存在明显差异．在立地条件较好的下坡，林分P1的年均凋落物量达8．05Mg·hm^-2·年^-1，高于立地条件相对较差的上坡的林分P2的23．1％；其相应的年养分归还量为：N66、04，P1.63，K17．42，Ca48.31，Mg14.65和N。6、57kg·hm^-2·年^-1，分别高于林分P2的39.7％、48.8％、39．4％、32.9％、24.8％和49.3％．两林分凋落物的养分利用效率分别是N为122和138，P为4934和5945，K为462和523，林分P1明显低于林分P2，这与林分P2的立地条件较差相关．可见，所调查的琉球松林是一种高效的养分利用系统。

Effects of site condition on litterfall and related nutrient return in Pinus luchuensis plantations

Over three years study on the dynamics of litterfall and related nutrient return in Pinus luchuensis plantations at different sites of northern Okinawa Island, Japan showed that the annual litterfall biomass ranged from 6.54 to 8.05 Mg x hm(-2) x yr(-1), with a peak from June to July. Typhoons had a strong influence on the timing and mass of litterfall. There were significant differences in nutrient concentrations among the different components of litterfall. The annual total nutrient input from litterfall ranged from 113.4 to 154.6 kg x hm(-2) x yr(-1), of which, N input was the greatest and contributed 42.2% of the total. The nutrient input was in order of N > Ca > K > Mg > Na > P. Due to the significantly different site conditions, there were significant differences in annual litterfall mass and related nutrient inputs between the two sampling stands. The annual mean litterfall mass of the sampling stand P1 on the lower slope reached 8.05 Mg x hm(-2) x yr(-1), which was 23.1% greater than that of P2 on the upper slope. The annual mean nutrient inputs were N 66.04, P 1.63, K 17.42, Ca 48.31, Mg 14.65 and Na 6.57 kg x hm(-2) x yr(-1), and were 39.7%, 48.8%, 39.4%, 32.9%, 24.8% and 49.3% higher in P1 than in P2, respectively. The nutrient use efficiency in litter production was higher in P2 (e.g., N 138, P 5945 and K 523) than in P1 (e.g., N 122, P 4934 and K 462), which should be attributed to the relatively lower fertility of soil in P2. The results from the study suggested that Pinus luchuensis plantation in Okinawa was a high efficiency system.