间伐对杉木人工林土壤理化性质的季节影响

以南京市溧水林场实施了4种间伐强度（CK:0%、LIT:30%、MIT:50%、HIT:70%）的25 a生杉木人工林为研究对象，探讨了间伐7 a后0—20 cm土层的土壤温度、含水率、土壤全C、全N、全P，C/N和N/P的季节变化。结果表明，间伐对土壤理化性质的影响存在明显的季节差异性。春季，间伐对土壤温度、含水率和全C均无显著影响，MIT显著降低了土壤全N和全P的22%和26%，HIT显著降低了土壤全N的11%。夏季，间伐对土壤温度、全N、全P和N/P无显著影响，但3种间伐强度均显著提高了土壤含水率，平均为22%，MIT和HIT均显著降低了土壤全C和C/N。秋季，间伐对土壤理化性质的各个指标均有不同程度的显著影响。其中，3种间伐强度均显著提高了土壤温度、含水率、N/P，但显著降低了全P。冬季，间伐对土壤理化性质影响较小，除MIT显著降低了土壤温度而提高了土壤C/N及HIT显著提高了土壤全P外，间伐对其余指标均无显著影响。这些结果表明，在评价间伐对土壤理化性质影响时应考虑季节差异。间伐7 a后林内土壤全N和全P在一定程度上有所降低，尤其是土壤全P，建议在春季对LIT施适量的氮肥，对MIT施适量的氮肥和磷肥，在秋季对3种间伐处理施适量的磷肥，以提高土壤肥力促进林木生长。从土壤N和P年平均值来看，HIT最有利于保持林地的氮磷养分，LIT次之，MIT最差。

Seasonal Dynamics of Soil Physical and Chemical Properties after Thinning for 7 Years in Chinese Fir Plantation

Seasonal dynamics of soil temperature, soil water content, soil total C, soil total N, soil total P, C/N and N/P at 0—20 cm soil depth among four thinning intensities (CK:0%, LIT:30%, MIT: 50%, HIT: 70%) of Chinese fir (25 years) plantation in Nanjing Lishui Forest Farm were examined. Results showed that the effect of thinning on soil physical and chemical properties varied among seasons. In spring, thinning had no significantly effect on soil temperature, soil water content and soil total C. Compared with control treatment, MIT and HIT significantly decreased soil total N by 22% and 11%, respectively, and MIT also significantly decreased soil total P by 26%. In summer, no any significant difference was observed for soil temperature, soil total N,soil total P and soil N/P between thinned and control treatments, while all thinned intensities significantly increased soil water content, with an average of 22%, and both MIT and HIT significantly decreased soil total C and soil C/N. In autumn, all studied indexes of soil significantly changed under thinning. Soil temperature, soil water content, soil N/P in all thinned plots were significantly higher than those of control plot, but the changes of soil total P was opposite. In winter, the effect of thinning on soil was not so obvious, except that MIT significantly decreased soil temperature, and MIT and HIT significantly increased soil C/N and soil total P, respectively, no other significantly differences were observed between thinned and control plots. These results showed that it was important to take seasonal differences into consideration in evaluating the effect of thinning on soil physical and chemical properties. After seven years of thinning, soil total N and total P in thinned plots were lower than those of control plot in some degree. Therefore, in order to increase soil nutrient resources in thinned plots, we suggested that nitrogen fertilizer should be applied in LIT plot in the spring, phosphorus fertilizer was highly needed in all thinned plots in the autumn, and both nitrogen and phosphorus fertilizers should be applied in MIT in the spring. From the perspective of annual soil total N and total P, HIT was the best thinning intensity to maintain the soil N and P among three treatments, and then it was followed by LIT.