渤海泥质海岸典型防护林土壤微生物量季节动态变化

土壤微生物生物量碳、氮是研究土壤肥力、土壤养分转化、循环以及环境变化的重要指标。研究渤海泥质海岸白榆、刺槐、白蜡、群众杨、辽宁杨纯林和辽宁杨刺槐混交林及当地自然生灌草地土壤微生物生物量碳、氮的季节动态及与土壤养分含量变化的关系,以期为沿海防护林树种的选择及林地管理提供科学依据。结果表明:造林能显著增加土壤微生物生物量含量,其中白榆(25 a)土壤微生物生物量碳、氮最高,是对照的2.50倍和2.09倍。0—10 cm土壤层微生物生物量碳、氮大于10—30 cm土层,季节动态变化差异显著。在0—10 cm土层内,渤海泥质海岸典型防护林土壤微生物生物量碳、氮季节动态多表现为春秋两季较高,夏季较低的"V"字型变化;在10—30 cm土层内,防护林土壤微生物生物量碳季节变化规律与0—10 cm土层一致,表现为夏季较低春秋较高的"V"字型,微生物生物量氮主要表现有"V"字型、倒"V"字型与直线型3种变化形式。在0—30 cm土层内,白榆(25 a)、刺槐、白蜡、群众杨、辽宁杨刺槐混交林、白榆(10 a)、辽宁杨及灌草地微生物生物量碳对土壤有机碳的平均贡献率分别为1.59%、1.68%、1.42%、1.54%、2.29%、1.80%、2.02%和1.12%,土壤微生物生物量氮对土壤全氮的平均贡献率分别为1.85%、1.30%、1.08%、1.35%、2.49%、1.57%、2.08%和2.32%。不同类型防护林地土壤微生物量碳、氮之间显著正相关,它们与土壤全氮、有机碳显著正相关,与土壤电导率显著负相关,另外,土壤微生物量碳还与土壤速效磷含量显著正相关。从不同土层微生物量碳、氮季节动态来看,造林可以增加泥质海岸土壤微生物生物量,但是夏季地下水位升高,盐碱上扬,加之树木生长大量利用养分,土壤微生物生物量夏季较低。综合分析土壤微生物生物量和土壤营养库的贡献率,白榆纯林和辽宁杨刺槐混交林更有利于泥质海岸土壤微生物群落功能恢复和营养固定。

Seasonal dynamics of soil microbial biomass in typical shelterbelts on the Bohai muddy coast

Soil microbial biomass carbon and nitrogen are the important indicators to study soil fertility, soil nutrient transformation and circulation, and environmental changes. During this research, the seasonal dynamics of soil microbial biomass C and N contents and their relation with the changes of soil nutrients content in Ulmus pumila forest25 years old (UPM), 10 years old (UP)], Robinia pseudoacacia forest (RP), Fraxinus chinensis forest (FC), Populus popularis forest (PP), P.×liaoningensis forest (PL), mixed forest of P.×liaoningensis and R. pseudoacacia (PR) and CK (naturally occurring shrub-grassland) were investigated. The purpose of this study is to provide a scientific basis for selection of coastal shelterbelt tree species and forest management in this area. The results showed that soil microbial biomass increased significantly by afforestation. Among all the forest types, UPM has the highest soil microbial biomass C and N contents, which are 2.50 and 2.09 times than CK. The microbial biomass C and N contents in soil layer of 0-10 cm were larger than those in 10-30 cm soil layer, and the seasonal dynamic change of soil microbial biomass in two soil layers varied significant differently. In the 0-10 cm soil layer, the seasonal dynamics of soil microbial biomass C and N contents in the typical shelterbelts on Bohai muddy coast were higher in spring and autumn, and lower in summer, with a "V" shape trend. The change trend of soil microbial biomass C in the typical shelterbelt under 10-30 cm soil layer was consistent with that of 0-10 cm soil layer, which showed a lower in summer, and a higher in spring and autumn, also with a "V" shape trend. There are mainly three forms of microbial biomass N variation:"V", inverted "V", and straight line. In the 0-30 cm soil layer, the average contribution rates of soil microbial biomass C to soil organic carbon in UPM, RP, FC, PP, PR, UP, PL, and naturally occurring shrub-grassland were 1.59%, 1.68%, 1.42%, 1.54%, 2.29%, 1.80%, 2.02%, and 1.12%, respectively, and in the 0-30 cm soil layer, the contribution rates of soil microbial biomass N to soil total nitrogen were 1.85%, 1.30%, 1.08%, 1.35%, 2.49%, 1.57%, 2.08%, and 2.32%, respectively. The correlation of soil microbial biomass C and N in all forest types were significantly positive, and soil microbial biomass C and N had significantly positive correlation with soil total nitrogen and organic matter, and had significantly negative correlation with soil conductivity. In addition, soil microbial biomass C had significantly positive correlation with soil available P. From the results of seasonal dynamics of microbial biomass C and N in different soil layers, it could be drew the conclusion that microbial biomass increased by afforestation in muddy coastal soil, but ground water was rose in summer, accompanied by the increment of salt and alkali content, moreover, trees utilize large quantities of nutrients to maintain growth, thus, the soil microbial biomass was lower. Based on the comparison of soil microbial biomass C and N content and their contributions to soil N pools among all forest types, the conclusion can be made that UPM and PR are the most conducive tree species to the recovery of soil microbial function and nutrient fixation on the Bohai muddy coast.