凋落物的树种多样性与杉木人工林土壤生态功能

通过模拟试验和野外调查对凋落物的树种多样性与杉木人工林土壤生态功能之间关系进行了研究。林分取样调查的结果表明 ,有两个树种凋落物覆盖的几个杉阔混交林土壤脲酶和蔗糖酶活性均明显高于只有杉木凋落物覆盖的杉木纯林土壤 ,酸性磷酸酶活性也呈现相同的变化趋势 ,这 3种土壤酶活性均以具有凋落物种类最多的次生常绿阔叶林土壤最高。除了土壤酶活性升高之外 ,杉阔混交林的土壤有机质和全氮含量也明显高于仅有一种杉木凋落物覆盖的杉木纯林土壤。采用杉木叶凋落物与不同阔叶树种凋落物处理土壤的模拟试验结果表明 ,在凋落物投放量和 (1 5NH4 ) 2 SO4 施用量相同的控制条件下 ,随着投放的凋落物树种组成的增加 ,土壤中 1 5N的残留量也随之增加 ,而其损失量却随之减少 ;土壤中杉木幼树对于 1 5N的吸收量以及杉木幼树的单株鲜重也随着处理凋落物组成树种的增加而增加 ,具有不同树种数量的凋落物处理之间差异显著 (p<0 .0 5 )。可见随着凋落物树种多样性的增加 ,不仅土壤有机质和全氮含量这两个基本的质量指标得到明显改善 ,而且土壤酶活性、土壤养分保蓄功能以及保证幼树良好生长等的生态功能明显改善

Effects of species diversity of litter on the ecological functions of Cunninghamia lanceolata (Lamb.) Hook. plantation soil

Based on a field study and pot trial, the effects of species diversity of litter on the ecological functions of Cunninghamia lanceolata plantation forest soil were examined. In the field study, four plantation forest stands with similar site quality, one C. lanceolata pure stand and three of its mixed stands with Alnus cremastogyne, Kalopanax septemlobus, and Michelia macclurei, respectively, were investigated. Soil samples taken from each stand were analyzed for enzyme activity, total N, SOM, and total phenolics. A stand of nearby secondary evergreen broadleaved forest was also investigated and sampled as a control. A additional 7-mo pot trial was set up by incorporating the litter of several broadleaved tree species as well as C. lanceolata needle litter into potted soil planted with C. lanceolata saplings to compare the effects of litter species diversity on soil qualities. There were four different treatments with litter from four different species, given combinations of C. lanceolata litter with that of M. macclurei, Castanopsis carlesii, K. septemlobus. The soil of each pot was also treated with 200mg of (()~(15)NH 4) 2SO 4-N (with ()~(15)N abundance of 20.97%) to track the fate of labeled ()~(15)N under the effects of the mixed litter treatment. The results of the field study showed that the activity of urease and invertase in soil covered by C. lanceolata litter mixed with a broadleaved species within mixed plantations was significantly higher than the activities in soil covered by only C. lanceolata litter under its monoculture. The activity of acidic phosphatase in soil also changed in the same pattern among sampled forest stands. The activities of the three soil enzymes were greatest in the adjacent secondary evergreen broadleaved forest. In addition, the concentration of soil organic matter and total nitrogen increased in the mixed-species C. lanceolata plantation compared with the C. lanceolata monoculture. The results of the pot trial showed that although the concentration of (()~(15)NH 4) 2SO 4 in soil at the end of experiment increased, the loss of (()~(15)NH 4) 2SO 4 from the soil decreased as the number of species of litter in the mixture increased. The fresh weight and uptake of ()~(15)N by C. lanceolata saplings increased with the increase in the number of species of litter in the mixture (p<0.05).It is suggested that as the mixed-species litter was incorporated into the soil, there were significant improvements not only in the basic indices of soil quality such as soil organic matter and total nitrogen, but also in other soil quality indices such as the activity of soil enzyme, capacity of preserving soil nutrients and ensuring the growth of saplings in soil.