作为森林生态系统的第二大碳通量,土壤呼吸在全球碳循环和气候变化中发挥着重要作用。通过探究土壤呼吸对间伐和改变凋落物的响应规律以及响应之间的联系,能够为准确评价森林碳循环提供依据。针对不同强度(对照、轻度、中度、重度)间伐后的华北落叶松人工林,2016年5月至10月采用LI-8100土壤碳通量测量系统对其原状、凋落物去除、凋落物加倍的土壤呼吸进行观测。结果表明:土壤呼吸在生长季的8月份达到最高值,呈现出明显的季节动态。不同林分间伐处理下,中度间伐显著促进了土壤呼吸,使平均土壤呼吸速率升高了15.66%,轻度间伐和重度间伐对土壤呼吸的影响不显著;不同凋落物处理下,去除凋落物使平均土壤呼吸速率降低了40.16%,加倍凋落物使平均土壤呼吸速率升高了16.06%。中度间伐使土壤呼吸生长季通量增加了55.06 g C/m~2;去除凋落物使土壤呼吸生长季通量减少了153.48 g C/m~2,加倍凋落物使土壤呼吸生长季通量增加了79.87 g C/m~2。 土壤呼吸速率与土壤温度呈显著指数相关,而与土壤湿度无显著相关。不同林分间伐处理下,土壤呼吸的温度敏感性指数(Q_(10))为2.36-3.46,轻度间伐下Q_(10)值最高;凋落物去除和加倍均降低了土壤呼吸的温度敏感性。土壤温湿度对土壤呼吸存在着显著影响,能够解释土壤呼吸28.7%62.3%的季节变化。研究结果表明间伐和凋落物处理对华北落叶松人工林土壤CO_2释放的影响表现出一定的交互作用,中度间伐和加倍凋落物的交互作用对土壤呼吸的促进作用显著大于单一因子。可见,间伐作业通过改变土壤微环境和凋落物量,对土壤呼吸以及森林生态系统碳循环产生着重要影响。
英文摘要:
Soil respiration (R_s) , the second largest site of carbon flow in the forest ecosystem carbon budget,plays an important role in the global carbon (C) cycle and climate change. Understanding the effects of forest management practices (e.g. thinning) on R_s is crucial for the accurate estimation of forest carbon cycling. Simultaneously, aboveground litter management practices (removal, addition, and so on) can also influence R_s. However, little is known about the response of Ra to thinning and its relationship with the changes in litter production induced by thinning. We aimed to quantify the response of R_s rate to different thinning intensities and to explore the relationships between R_s and soil temperature and moisture as a result of different litter management practices. A thinning manipulation experiment was conducted in a Larix principis-rupprechtii plantation in Shanxi province, China, with the following treatments: heavy thinning, moderate thinning, low thinning and no thinning. In addition, three treatments--litterfall removal, litter addition and normal litterfall--were applied to analyze the relationship between differences in litter input and Rs. Rates of soil respiration were measured twice a month using the LI-8100 Automated Soil CO_2 Flux System from May to October 2016, while soil temperature and moisture at a depth of 5 cm were measured using temperature and moisture probes and data loggers. A significant difference was noted in R_s among the different thinning treatments (P<0.05). Clear monthly variations in were noted in the growing season, and R_s reached its peak value in August. Overall, moderate thinning increased R_s rate during the growing season by 15.7% from that of the no-thinning treatment. During the growing season, the R_s rate was lower by 40.16% with litterfall removal than that of normal litterfall; however, R_s rate was higher by 16.06% with litter addition than that of normal litterfall. Moderate thinning increased accumulative R_s by 55.06 g C/m~2 during the growing season. Under litter removal conditions, accumulative R_s decreased by 153.48 g C/m~2 during the growing season, while accumulative Rs increased with litter addition by 79.87 g C/m~2. During the growing season, R_s exhibited significant exponential relationships with soil temperature, while there were no significant differences in soil moisture among the various treatments. Temperature sensitivity (Q_(10)) values of R_s ranged from 2.36 to 3.46 in the various thinning intensities, with the highest Q_(10) value in the low thinning stand. The Q_(10) value were lower with the litter removal and litter addition treatments than those of normal litterfall. The interaction of soil temperature and moisture had a significant effect on R_s. The best fitting model with temperature and moisture explained 28%-62% of the variation in R_s. The results indicated that the interaction between thinning treatments and litter changes has a significant effect on the R_s in L. principis-rupprechtii plantations. The compound effect of moderate thinning and litter addition on R_s is significantly greater than that of any single factor. In conclusion, thinning played a considerable role in altering R_s and carbon cycle in forest ecosystems by influencing the soil micro-environment and litter production rates.