根系输入对森林土壤碳库及碳循环的影响研究进展

植物根系输入是森林土壤碳库的重要来源。全球气候变化可能引起森林地下部分碳通量改变,进而影响森林土壤碳库及碳循环。笔者综述了根系输入对土壤碳累积、土壤活性碳库(包括土壤微生物生物量碳和可溶性有机碳)和土壤碳库稳定性的影响,综合分析了森林土壤呼吸、土壤微生物和土壤酶活性对根系输入变化的响应。分析发现:①根系输入减少可能减弱根际的激发效应,使土壤有机碳(SOC)短期增加,但从长期来看根系输入的缺失会导致SOC的减少;②根系分泌的一些物质促进土壤初始团聚体的形成,但其对矿物-有机质结合物稳定性的影响还不完全清楚;③根系输入减少会降低土壤呼吸作用;④微生物群落结构对根系输入变化的响应主要取决于微生物对底物质量和数量的适应,而这些响应在不同森林生态系统间可能也有差异;另外,酶合成主要取决于与微生物生长相关的资源分配到酶生产中的成本效率。目前,关于根系输入对碳循环,特别是土壤呼吸的研究比较多,但根系输入物组成复杂,微生物与酶对不同根系输入物的响应机制尚不清楚,这些响应在不同森林生态系统中也有差异;此外,根系输入对土壤碳库稳定性的作用常被忽视,根系与微生物的相互作用对碳循环和土壤碳库稳定性的影响还有很大不确定性。建议加强植物根系、土壤和微生物的相互关系研究,以深入理解气候变化背景下森林生态系统碳循环。

Advances in effects of root input on forest soil carbon pool and carbon cycle

Plant root inputs are an essential source of forest soil carbon pools.Climate change may cause variations in the carbon flux below ground,affecting forest soil carbon pools and carbon cycles.In this article,we have reviewed the effects of root input on soil carbon accumulation,soil active carbon pools(including soil microbial biomass carbon and soluble organic carbon),and the stability of soil carbon pools.Furthermore,we have discussed the impacts of forest soil respiration,soil microorganisms,and soil enzyme activities on root inputs.We found that:(1)Decreased root input may reduce the priming effect of the rhizosphere and subsequently increase soil organic carbon in the short term but decrease it in the long term;(2)Root exudates may promote the initial formation of aggregates,but its effect on the stability of the metal-organic complex is unclear;(3)Decreased root input reduces soil respiration;(4)The response of the microbial community structure to root input mainly depends on the adaptation of microorganisms to substrate quality and quantity,which vary among forest ecosystems.In addition,whether enzyme synthesis is upregulated depends mainly on the cost efficiency of allocating resources for microbial growth to enzyme production.Many studies have investigated the carbon cycle of root input,especially soil respiration;however,the composition of root input is complex,and the response mechanisms of microorganisms and enzymes to different root inputs are unclear.These responses also differed among forest ecosystems.In addition,the effect of root input on the stability of the soil carbon pool is often neglected;the influence of the interaction between the root system and microorganisms on the carbon cycle and the stability of the soil carbon pool remains uncertain.We suggest strengthening the research on the links among plant roots,soil,and microorganisms,which would contribute to a deeper understanding of the carbon cycle of forest ecosystems in the context of climate change.