森林生态系统DOM的来源、特性及流动

Origin, property and flux of dissolved organic matter in forest ecosystems

可溶性有机物质 (Dissolved Organic Matter)是森林生态系统主要的可移动碳库及重要的养分库。系统综述了森林生态系统 DOM的来源、组成、性质、季节动态 ;DOM释放与存留机制及影响因素 ;森林生态系统 DOM的流动及干扰对 DOM动态影响等。已有研究表明 DOM在森林生态系统 C、N、P循环、成土作用、污染物迁移等方面起着重要作用。今后森林生态系统 DOM的研究应集中于以下几方面 :(1 )确定森林生态系统中 DOM源和汇 ;(2 )评价森林水文条件对 DOM释放与存留的调节作用 ;(3)探讨全球气候变化对森林生态系统 DOM的影响 ;(4)可溶性有机氮 (Dissolved Organic Nitrogen)、可溶性有机磷 (DissolvedOrganic Phosphorus)动态与可溶性有机碳 (Dissolved Organic Carbon)动态的差别。

Dissolved organic matter (DOM) was the primary active carbon pool in forest ecos ystems and played an important role in the cycling of carbon, nitrogen, and phos phorus, in soil formation and in the transport of pollutants. The aim of this re view was to summarize the origin, property and flux of dissolved organic matter in forest ecosystems. Recent studies showed that litter and humus were the most important DOM sources in forest ecosystems. The soil microbe was also considered as a potential, i mportant source of DOM because it was highly labile. The rhizosphere was often a ssociated with a large carbon flux due to root turnover and exudatio n. Substantial amounts of DOM might well derive from this important belowground C s ource. However, the contribution of each of these sources to the DOM production in the forest floor and organic soil horizons was not fully understood. This que stion of the origin of DOM was important because it could help explain the mecha nism of DOM production and the major characteristics of leachate DOM in forests. Components of DOM were often classified according to some chemical and physical properties such as elements, functional groups, molecular weight, polarity and a cidity. Lots of information about components and chemical characters of DOM had been acquired based on classification. Spectrum analyses, such as IR and NMR, re vealed that hydrophilic and hydrophobic acids were the essential components of D OM. Numerous field studies showed seasonal variability in DOM concentrations and flu xes, which were related to precipitation, temperature, moisture, and litterfall input. In general, DOC concentrations in soil solution were higher in summer tha n in winter. Compared with DOC, there were fewer data available describing tempe rature effects on DON or DOP dynamics. Increased concentration of DOM following rewetting after dry periods and as a result of anaerobic conditions seemed to be the most important effect of soil moisture on the dynamics of DOM. The fluxes o f DOC and DON in forest floor leachates increased with increasing annual precipi tation and were also positively related to DOC and DON fluxes with throughfall. Concentration and flux of DOM in forests were the net result of processes that r eleased DOM—such as leaching from litter or desorption from the solid phase—an d processes that removed DOM, such as adsorption or decomposition. DOM concentra tions increased with passage of water from forest canopy to floor presumably due to leaf leaching, decreased due to abiotic sorption in the mineral soil, and re mained relatively low in the groundwater. These processes depended on external e nvironmental factors and the physical/chemical characteristics of the soil. In a ddition, laboratory control experiments on DOM dynamics had often contradicted t o field observations, primarily because hydrology had not been taken into accoun t. Land use changes, such as clear cutting of forest stands, afforestation, liming, fertilization and other management activities, influenced the dynamics of DOM b y (i) changing the input of organic matter, (ii) changing the substrate quality, and (iii) altering the rates, extent, and pathways of microbial degradation and synthesis of organic matter. Clear cutting and afforestation could influence DO M concentrations and fluxes diversely. But liming consistently resulted in enhan ced production of DOM due to stimulated mineralization Studies on dissolved organic nitrogen (DON) and dissolved organic phosphorus (DO P) dynamics in addition to dissolved organic carbon (DOC) were few. The rate of release and fates of DOC, DON and DOP in forest ecosystems might differ greatly. Controls on DOC might thus be not valid for DON and DOP. Despite intensive research in the last decade, uncertainties of DOM in forest ec osystems still remained for further studies: (1) Quantification of sources and s inks of DOM in forest ecosystems; (2) The assessment of hydrological processes c ontrols on the release and retention of DOM in forests; (3) The e