林下植被去除对水曲柳人工林土壤呼吸、微生物和根系动态的短期影响

Short-term effect of understory removal on the dynamics of soil respiration,microbial biomass,and root growth in a Fraxinus mandschurica Rupr. plantation

以水曲柳(Fraxinus mandschurica Rupr.)人工林为研究对象,探索林下植被去除处理对2015年生长季土壤呼吸、土壤5 cm温度和含水量,土壤微生物生物量碳(MBC)和氮(MBN)动态以及细根生产量的影响。结果表明:植被去除导致土壤呼吸速率高于对照(平均11.87%),并在8月末和9月初达到显著差异;土壤温度和含水量也在处理后增加,土壤呼吸速率对温度的敏感程度(Q10值)比对照提高15.26%。重复测量方差分析显示,林下植被去除对土壤呼吸及其他指标影响不显著,但取样时间的影响均显著,而且二者对土壤呼吸速率、温度和含水量的影响存在显著交互作用。植被处理后,水曲柳细根年生产量比对照略增加,而其他树种(主要为灌木)明显降低;土壤表层(0~10 cm)和亚表层(10~20 cm)MBC分别比对照降低12.68%和21.16%,MBN降低16.76%和25.48%,但是MBC和MBN差异均未达到显著水平。两种处理中土壤呼吸速率仅与土壤温度呈显著指数相关。林分土壤温度的升高,以及细根总生物量和组成的变化,可能是导致林下植被去除后土壤呼吸出现季节性增加的重要原因。本研究结果对理解温带地区林下植被去除对森林土壤呼吸的影响与机制提供了理论参考。

Understory removal was implemented in a Fraxinus mandschurica Rupr. plantation in order to investigate its effect on soil respiration, soil temperature and water content at 5 cm depth, fine root production, and soil microbial biomass carbon （MBC） and nitrogen （MBN） during the growing season in 2015. The results showed that average soil respiration rate increased by 11.87% after understory removal, particularly from the late August to the early September. The soil temperature and water content also increased. The temperature sensitivity of soil respiration （i.e., Q10 value） showed an increment of 15.26% in understory removal treatment. Repeated measures ANOVA indicated that the effects of understory removal on soil variables were not significant, whereas sampling date did. Additionally, there were interaction effects between understory removal and sampling date on the soil respiration rate, temperature and water content. Fine root production of F. mandschurica increased （P〉0.05）, whereas that of other species （mainly shrubs） was markedly decreased after understory removal. Understory removal decreased MBC by 12.68% and 21.16%, and MBN 16.76% and 25.48% at the depth of 0-10 cm and 10-20 cm respectively, despite all of which were not statistically significant. In both the control and treatment plots, soil respiration rates was only exponentially correlated with soil temperature （P〈0.01）. Overall, the higher soil temperature and greater fine root production, as well as the alternation of fine root population may contribute to the seasonal increase in soil respiration rate following understory removal. Our findings yield some insights into the interrelationship between understory removal application and soil respiration in temperate forests.