不同密度巨桉人工林凋落物分解过程中基质质量的变化

Changes in masses of substrates during litter decomposition in Eucalyptus grandis plantations with different densities

【目的】研究林分密度对巨桉(Eucalyptus grandis)人工林凋落物木质素和纤维素降解及基质质量组成的影响。【方法】收集巨桉人工林凋落物(叶和直径3~5mm的枝),部分凋落物在65℃烘干至恒质量并测定含水量、纤维素、木质素、C、N、P;部分自然风干后装入尼龙分解袋中,将分解袋置于稀疏(833株/hm2,株距×行距=1.5m×8m)、中密(1 333株/hm2,株距×行距=1.5m×5m)和高密(2 222株/hm2,株距×行距=1.5m×3m)巨桉林中自然分解,凋落叶于分解第60,120,180,210,240,300,360天取样,凋落枝于第90,180,270,360天取样,测定凋落物中养分、纤维素、木质素含量,计算碳/氮、木质素/氮、纤维素/氮、碳/磷、木质素/磷、纤维素/磷值,并采用Olson负指数衰减模型对木质素和纤维素残留率进行拟合。【结果】经过360d的分解,同一密度巨桉人工林凋落物中木质素的降解率小于纤维素的降解率。其中稀疏林凋落叶中木质素、纤维素的降解率分别为82.41%和93.77%,而凋落枝中木质素、纤维素的降解率分别为39.12%和65.65%。木质素、纤维素残留率拟合结果表明,分解系数k随着林分密度的增大而减小,稀疏林凋落物中木质素和纤维素质量损失50%和95%所需时间均短于高密林和中密林。随着巨桉林密度的减小,凋落物木质素和纤维素降解率增大,凋落物C/N减小,其中稀疏林的凋落叶、枝中C/N较初始值分别下降了12.73%和47.24%。凋落叶中木质素/N、C/P、木质素/P和凋落枝中纤维素/N、纤维素/P随着林分密度的减小而减小。【结论】四川华西雨屏区巨桉人工林凋落物分解过程中,不同林分密度对巨桉林凋落物基质质量有明显影响。

【Objective】The effects of stand density on degradation of lignin and cellulose,and composition of litter substrates during litter decomposition in Eucalyptus grandis plantations with different densities were studied.【Method】Litters were(leaves and twigs with diameter of 3-5mm)collected in Euca lyptus grandis plantations.Partial litters were dried by dryer at 65℃and contents of water,cellulose,lignin,C,N,and P were measured.Partial litters were air dried and put in nylon decomposition bags.The litter decomposition bags were placed in sparse forest(833trees/hm2,1.5 m×8 m),medium dense forest(1 333trees/hm2,1.5m×5m)and dense forest(2 222trees/hm2,1.5m×3m)for natural decomposition.Leaf samples were collected at days 60,120,180,210,240,300,and 360,while twig samples were collected at days 90,180,270,and 360.Then the contents of litter nutrients,cellulose,and lignin were measured,the values of C/N,lignin/N,cellulose/N,C/P,lignin/P,and cellulose/P were calculated,and the Olson negative exponential attenuation model was used to fit the residue rates of lignin and cellulose.【Result】After 360 days of decomposition,the degradation rate of lignin is less than that of cellulose in litter of Eucalyptus grandis plantations with same densities.The degradation rates of lignin and cellulose were82.41% and 93.77%in leaves of sparse forest,and 39.12% and 65.65%in twigs.The fit of residue rates of lignin and cellulose showed that the decomposition coefficient k decreased with the increase of density,and the times needed for 50% and 95% mass loss of lignin and cellulose were shorter than those for dense and medium dense forests.With decrease of density,the degradation rates of lignin and cellulose increased while C/N ratio decreased.Compared with initial values,the C/N ratios of leaf and twig in sparse forest were decreased by 12.73%and 47.24%,respectively.The lignin/N,C/P,and lignin/P in leaf and cellulose/N and cellulose/P in twig decreased as the decrease of stand density.【Conclusion】Stand density had significant effects on masses of substrates during litter decomposition in Eucalyptus grandis plantations in Rainy Area in Sichuan.