油松叶凋落物分解速率、养分归还及组分对间伐强度的响应

研究密度对叶凋落物基质物质及分解速率的影响具有重要意义。2002年在北京市延庆县营盘村附近中山，对造林密度为3 130株/hm2的18年生油松人工林设置0、35.7%、49.2%、64.2% 4个间伐强度的处理，3年后，应用分解网袋法比较叶凋落物分解速率、养分归还及初始物质的变化。结果表明:①样地Ⅰ～Ⅳ油松叶凋落物年分解速率分别为25.81%、26.25%、27.68%和25.96%，周转期为10.04、9.84、9.24和9.97年，用分解速率来评价间伐效果可行。②在分解的前2个月，N、P、K、Mg等迅速释放；在观测的14个月内，叶片N、Mg归还呈释放 固定交替规律，P、K呈释放-固定-稳定趋势，4个样地油松Ca的归还规律均不相同。③样地Ⅰ～Ⅳ油松叶凋落物归还的养分分别为10.806、31.016、31.798和39.365 g/kg。样地Ⅰ的叶凋落物质量较差，N、Ca在分解的14个月内分别固定了2.567和0.767 g/kg。④间伐能降低叶凋落物木质素/N、C/N，加速凋落物的分解速率。⑤间伐增加叶凋落物中粗灰分含量，从而有效克服了因分解速率加快而伴生的向土壤中返还大量单宁、树脂等酸性物质的矛盾。⑥叶片中木质素/N、C/N和粗灰分是评价间伐效果的较好指标。 

Responses of decomposition rate,nutrient return and composition of leaf litter to thinning intensities in Pinus tabulaeformis plantation

It is vital to study the effects of density on the substrate quality and decomposition rate of the leaf litter. In 2002, the experiment of thinning intensities with four different treatments of 0(Ⅰ), 35.7%(Ⅱ), 49.2%(Ⅲ) and 64.2%(Ⅳ) on the undergrowth were carried out in the 18-year-old Pinus tabulaeformis-stands with initial density of 3 130 trees/hm² in middle hilly lands of Yingpan of Yanqing Country, Bejing. Three years later, the decomposition rate, amount of nutrient return and characteristics of leaf litter were compared by litter bag method. The results show that the annual dry matter loss of leaf litter in the plots of Ⅰ, Ⅱ, Ⅲ and Ⅳ was 25.81%, 26.25%, 27.68% and 25.96%, respectively. The turnover via leaf litter fall was 10.04, 9.84, 9. 24 and 9.97 years, respectively. Therefore, it is feasible and convenient to evaluate the thinning effect on decomposition rate. In the first two months, the nutrient of N, P, K and Mg was released sharply. In the whole observation of 14 months, the return of both nutrient N and Mg in the four plots exhibited a cycle with release accumulation. The return of P and K indicated the trend of release accumulation relative balance. However, the return of Ca was different from each other in the four plots. The total nutrient return of the four elements (N, P, K, Mg) in the plots was 10.806, 31.016, 31.798 and 39.365 g/kg, respectively. Specifically, the quality of leaf litter in the plot Ⅰ was the worst that the N and Ca were accumulated only 2.567 and 0.767 g/kg, respectively. Thinning could decrease the ratios of lignin to N and C to N and accelerate the decomposition rate of leaf litter. The content of the crude ash in the leaf litter was enhanced by thinning. It prevents the acidic material such as tannin and resin from returning to the soil. The effect of thinning intensity is evaluated by the ratio of lignin to N, the ratio of C to N and the ash content in the leaf litter.