森林生态系统可溶性碳和颗粒碳通量

可溶性碳(Dissolved carbon,DC)和颗粒碳(particulate carbon,PC)通量作为森林生态系统碳收支的重要组分,在森林固碳功能的评价和模型预测中具有重要意义,但常因认识不足、测定困难等而在森林碳汇研究中被忽略。综述了森林生态系统DC和PC的组成、作用、相关生态过程及其影响因子,并展望了该领域应该优先考虑的研究问题。森林生态系统DC和PC主要包括可溶性有机碳、可溶性无机碳和颗粒有机碳,主要来源于生态系统的净初级生产量。DC和PC是森林土壤的活性碳库,主要以大气沉降、穿透雨和凋落物的形式输入森林土壤系统,并通过土壤呼吸、侧向运输及渗透流失的方式输出生态系统。从局域尺度看,DC和PC通量受根系分泌、细根分解、微生物周转等生物过程的影响较大;从区域尺度看,它们受土壤和植被特性、生态过程耦联关系、气候因子以及全球变化的综合影响。该领域应该优先考虑:(1)探索不同时空尺度下森林生态系统DC和PC通量的控制因子及其耦联关系,揭示其中的驱动机理;(2)探索DC和PC与其它森林生态系统碳组分的相互关系及转化,阐明DC和PC通量与其它养分之间潜在的生态化学计量关系;(3)探索全球变化,特别是人类活动(如森林经营)和极端干扰事件(如林火、旱涝、冰冻、冻融交替等)对森林生态系统DC和PC通量的影响。

Dissolved and particulate carbon fluxes in forest ecosystems

Forest provides the most significant ecosystem services among the terrestrial ecosystems, and plays an important role in sequestering carbon (C) and mitigating the ongoing global climate change. Dissolved carbon (DC) and particulate carbon (PC) fluxes are important components in forest C budgets. Quantifying fluxes of DC and PC in forest ecosystems is essential to better understanding the C cycling processes and improving the assessment and prediction of C sequestration capacity in the ecosystems. However, the budgets of DC and PC have often been ignored in forest C cycling studies largely due to knowledge shortage and difficulty in taking measurements. Here, we reviewed the recent progress in DC and PC studies in forest ecosystems. We discussed the composition and function of DC and PC, associated ecological processes and influencing factors, and finally pointed out future research priorities in this field.The DC and PC in a forest ecosystem mainly consist of dissolved organic C (DOC), dissolved inorganic C (DIC), particulate organic C (POC), black C and carbonate C, which fundamentally originate from net primary production of the ecosystem. DOC, an important active pool of C and nutrients, is mainly composed of carbohydrates, long-chain aliphatic compounds, aromatic compounds, proteins, and low molecular weight organic acids. The DOC content is correlated positively with concentrations of proteins and carbohydrates, but negatively with concentrations of carboxyl C. The DOC in soil solution is mainly derived from plant litter, soil humus, microbial debris, root exudates, and ectomycorrhizal mycelium. DIC consists of dissolved inorganic carbonate, dissolved bicarbonate, dissolved carbonate and dissolved carbon dioxide. It activates soil nutrient elements and thus enhances plant growth. POC is the major form of PC in forest soils that includes polymeric gel, organic fiber, cell fragments, microbial biomass (such as algae and bacteria), and polymerized DOC. Both DC and PC are labile C pools in the forest soil system, which enter the ecosystem from atmospheric deposition, throughfall and litterfall, and leave the ecosystem via soil respiration, lateral transport and seepage. At a small local scale, fluxes of DC and PC are mainly influenced by such biotic factors as root exudates, fine root decomposition and microbial turnover. At a large regional scale, they are jointly affected by soil and vegetation characteristics, coupling effects of ecological processes, climatic conditions and global changes. Future research priorities in this field should be: (1) to explore the factors controlling fluxes of DC and PC in forest ecosystems on various spatio-temporal scales, their potential coupling relationships and underlying mechanisms; (2) to understand interactions and transformation between DC/PC and other C fluxes in forest ecosystems, and explore potential stoichiometric relationships between DC/PC and other nutrients in the systems and (3) to explore effects of global changes on fluxes of DC and PC in forest ecosystems, particularly focusing on the effects of extreme disturbances, such as forest management, wildfire, drought, flooding, ice and frozen, and freeze-thaw cycles.