Effect of catchment characteristics on aquatic carbon export from a boreal catchment and its importance in regional carbon cycling

Inland waters transport and emit into the atmosphere large amounts of carbon (C), which originates from terrestrial ecosystems. The effect of land cover and land‐use practises on C export from terrestrial ecosystems to inland waters is not fully understood, especially in heterogeneous landscapes under human influence. We sampled for dissolved C species in five tributaries with well‐determined subcatchments (total size 174.5 km²), as well as in various points of two of the subcatchments draining to a boreal lake in southern Finland over a full year. Our aim was to find out how land cover and land‐use affect C export from the catchments, as well as CH₄ and CO₂ concentrations of the streams, and if the origin of C in stream water can be determined from proxies for quality of dissolved organic matter (DOM). We further estimated the gas evasion from stream surfaces and the role of aquatic fluxes in regional C cycling. The export rate of C from the terrestrial system through an aquatic conduit was 19.3 g C m^?2(catchment) yr^?1, which corresponds to 19% of the estimated terrestrial net ecosystem exchange of the catchment. Most of the C load to the recipient lake consisted of dissolved organic carbon (DOC, 6.1 ± 1.0 g C m^?2 yr^?1); the share of dissolved inorganic carbon (DIC) was much smaller (1.0 ± 0.2 g C m^?2 yr^?1). CO₂ and CH₄ emissions from stream and ditch surfaces were 7.0 ± 2.4 g C m^?2 yr^?1 and 0.1 ± 0.04 g C m^?2 yr^?1, respectively, C emissions being thus equal with C load to the lake. The proportion of peatland in the catchment and the drainage density of peatland increased DOC in streams, whereas the proportion of agricultural land in the catchment decreased it. The opposite was true for DIC. Drained peatlands were an important CH₄ source for streams.     

Extracellular dissolved organic carbon released from phytoplankton as a source of carbon for heterotrophic bacteria in lakes of different humic content

The quantitative importance of photosynthetically produced dissolved organic carbon (PDOC) released from phytoplankton as a source of carbon for pelagic, heterotrophic bacteria was investigated in four temperate Swedish lakes, of which two had low (≈20 mg Pt 1⁻¹), and two moderately high (60–80 mg Pt 1⁻¹) humic content. The bacterial assimilation of PDOC was estimated with the ¹⁴C method, and the total production of the heterotrophic bacteria was estimated with the [3H]thymidine incorporation method. The release of PDOC from natural communities of phytoplankton was not restricted to periods of photosynthesis, but often continued during periods of darkness. Heterotrophic bacteria often assimilated the labile components of the PDOC at high rates (up to 73% of the released PDOC was assimilated during the incubation in our experiments). The contribution of PDOC to bacterial production exhibited large within-lake seasonal variations, but PDOC was at certain times, both in humic and non-humic lakes, a quantitatively very important carbon source for the heterotrophic bacteria. Under periods of comparatively low primary production, heterotrophic bacteria in humic lakes appear to utilize allochthonous, humic substances as a substrate.     

Aquatic export of young dissolved and gaseous carbon from a pristine boreal fen: Implications for peat carbon stock stability

The stability of northern peatland's carbon (C) store under changing climate is of major concern for the global C cycle. The aquatic export of C from boreal peatlands is recognized as both a critical pathway for the remobilization of peat C stocks as well as a major component of the net ecosystem C balance (NECB). Here, we present a full year characterization of radiocarbon content (¹⁴C) of dissolved organic carbon (DOC), carbon dioxide (CO₂), and methane (CH₄) exported from a boreal peatland catchment coupled with ¹⁴C characterization of the catchment's peat profile of the same C species. The age of aquatic C in runoff varied little throughout the year and appeared to be sustained by recently fixed C from the atmosphere (<60 years), despite stream DOC, CO₂, and CH₄ primarily being sourced from deep peat horizons (2–4 m) near the mire's outlet. In fact, the ¹⁴C content of DOC, CO₂, and CH₄ across the entire peat profile was considerably enriched with postbomb C compared with the solid peat material. Overall, our results demonstrate little to no mobilization of ancient C stocks from this boreal peatland and a relatively large resilience of the source of aquatic C export to forecasted hydroclimatic changes.     

Increasing riverine export of dissolved organic carbon from China

River transport of dissolved organic carbon (DOC) to the ocean is a crucial but poorly quantified regional carbon cycle component. Large uncertainties remaining on the riverine DOC export from China, as well as its trend and drivers of change, have challenged the reconciliation between atmosphere-based and land-based estimates of China's land carbon sink. Here, we harmonized a large database of riverine in-situ measurements and applied a random forest model, to quantify riverine DOC fluxes (F_DOC) and DOC concentrations (C_DOC) in rivers across China. This study proposes the first DOC modeling effort capable of reproducing well the magnitude of riverine C_DOC and F_DOC, as well as its trends, on a monthly scale and with a much wider spatial distribution over China compared to previous studies that mainly focused on annual-scale estimates and large rivers. Results show that over the period 2001–2015, the average C_DOC was 2.25 ± 0.45 mg/L and average F_DOC was 4.04 ± 1.02 Tg/year. Simultaneously, we found a significant increase in F_DOC (+0.044 Tg/year², p = .01), but little change in C_DOC (−0.001 mg/L/year, p > .10). Although the trend in C_DOC is not significant at the country scale, it is significantly increasing in the Yangtze River Basin and Huaihe River Basin (0.005 and 0.013 mg/L/year, p < .05) while significantly decreasing in the Yellow River Basin and Southwest Rivers Basin (−0.043 and −0.014 mg/L/year, p = .01). Changes in hydrology, play a stronger role than direct impacts of anthropogenic activities in determining the spatio-temporal variability of F_DOC and C_DOC across China. However, and in contrast with other basins, the significant increase in C_DOC in the Yangtze River Basin and Huaihe River Basin is attributable to direct anthropogenic activities. Given the dominance of hydrology in driving F_DOC, the increase in F_DOC is likely to continue under the projected increase in river discharge over China resulting from a future wetter climate.     

Potential for long‐term transfer of dissolved organic carbon from riparian zones to streams in boreal catchments

Boreal regions store most of the global terrestrial carbon, which can be transferred as dissolved organic carbon (DOC) to inland waters with implications for both aquatic ecology and carbon budgets. Headwater riparian zones (RZ) are important sources of DOC, and often just a narrow ‘dominant source layer’ (DSL) within the riparian profile is responsible for most of the DOC export. Two important questions arise: how long boreal RZ could sustain lateral DOC fluxes as the sole source of exported carbon and how its hydromorphological variability influences this role. We estimate theoretical turnover times by comparing carbon pools and lateral exports in the DSL of 13 riparian profiles distributed over a 69 km² catchment in northern Sweden. The thickness of the DSL was 36 ± 18 (average ± SD) cm. Thus, only about one‐third of the 1‐m‐deep riparian profile contributed 90% of the lateral DOC flux. The 13 RZ exported 8.7 ± 6.5 g C m^?2 year^?1, covering the whole range of boreal stream DOC exports. The variation could be explained by local hydromorphological characteristics including RZ width (R² = 0.90). The estimated theoretical turnover times were hundreds to a few thousands of years, that is there is a potential long‐lasting supply of DOC. Estimates of net ecosystem production in the RZ suggest that lateral fluxes, including both organic and inorganic C, could be maintained without drawing down the riparian pools. This was supported by measurements of stream DO¹⁴C that indicated modern carbon as the predominant fraction exported, including streams disturbed by ditching. The transfer of DOC into boreal inland waters from new and old carbon sources has a major influence on surface water quality and global carbon balances. This study highlights the importance of local variations in RZ hydromorphology and DSL extent for future DOC fluxes under a changing climate.     

Soil frost enhances stream dissolved organic carbon concentrations during episodic spring snow melt from boreal mires

Changes in winter time conditions at high‐latitude ecosystems could severely affect the carbon exchange processes. Using a 15 year stream record combined with winter field measurements and laboratory experiment, we studied the regulation of dissolved organic carbon (DOC) concentration in stream water draining boreal mire during snow melt. The most unanticipated finding was that cold soils with deep soil frost resulted in increased snow melt DOC concentrations in the stream runoff. Wintertime field measurements of DOC concentrations below the mire soil frost showed that this phenomenon could be explained by freeze‐out of DOC giving higher levels of DOC in the soil water below the ice as the soil frost developed downwards in the mire. Experimental freezing of water with a certain DOC concentration in the laboratory further corroborated the freeze‐out of DOC. In this experiment, as much as 96% of the DOC was excluded from the ice, whereas the freeze‐out in the mire was less effective (60%). The difference between the proportion of DOC retained in pure water relative to the proportion retained in peat water during freezing is probably due to trapped DOC in the solid peat soil matrix. A simple mass‐balance model showed that to explain the higher stream DOC concentrations during a winter with deep soil frost, approximately 0.5% of the mire area needed to be hydrologically connected to the stream discharge. In the stream records, we also found that the DOC concentrations during snow melt episodic runoff were negatively related to increasing intensity of the snow melt episodes (dilution by low DOC snow melt water) and higher previous export of DOC.     

The significance of storms for the concentration and export of dissolved organic carbon from two Precambrian Shield catchments

Dissolved organic carbon (DOC) concentrations and DOC export arestudied during storms to examine the relationship between DOCconcentration and stream discharge and to assess the importance of stormson DOC export. Storms were monitored in seven subcatchments within twosmall watersheds (Harp 4--21 and Harp 3A) on the Precambrian Shield inCentral Ontario, Canada. Stream DOC concentrations increase during stormsby as much as 100% and 410% in Harp3A and Harp 4--21 respectively. The seasonal regression between DOC andstream discharge is significant in subcatchments without wetlands(r² > 0.7) but is not significant in thetwo subcatchments with small wetland areas (r² <0.06). On average, regressions based on weekly data yield accurate estimatesof DOC export but the variation in regressions among individual storms andthe small number of high DOC samples result in uncertainties of more than30% in DOC export. The period-weighted calculation ofDOC export from weekly data underestimates export by 14%and 22% in Harp 3A and Harp 4--21 respectively. Stormswere responsible for 57% to 68% of theDOC export in the autumn and 29% to 40%of the DOC export in the spring. A single large storm accounted for31% of the autumn DOC export in Harp 3A. The importanceof individual storms for DOC export and the variation in the relationshipbetween DOC and stream discharge among storms make it difficult to predictthe effects of climate change on DOC export and DOC concentrations.     

Accounting for littoral primary production by periphyton shifts a highly humic boreal lake towards net autotrophy

相似文献   

Export of dissolved organic carbon and nitrogen from Gleysol dominated catchments – the significance of water flow paths

In this study, we estimated whether changes in hydrological pathwaysduring storms could explain the large temporal variations of dissolvedorganic carbon (DOC) and nitrogen (DON) in the runoff of threecatchments: a forest and a grassland sub-catchment of 1600m² delineated by trenches, and a headwater catchment of 0.7km².The average annual DOC export from the sub-catchments was 185 kg DOCha^–1 y^–1 for the forest, 108 kg DOCha^–1 y^–1 for the grassland and 84 kgDOC ha^–1 y^–1 for the headwatercatchment. DON was the major form of the dissolved N in soil and streamwater. DON export from all catchments was approximately 6 kg Nha^–1 y^–1, which corresponded to 60% ofthe total N export and to 50% of the ambient wet N deposition. DOC andDON concentrations in weekly samples of stream water were positivelycorrelated with discharge. During individual storms, concentrations andproperties of DOC and DON changed drastically. In all catchments, DOCconcentrations increased by 6 to 7 mg DOC l^–1 comparedto base flow, with the largest relative increment in the headwatercatchment (+350%). Concentrations of DON, hydrolysable amino acids, andphenolics showed comparable increases, whereas the proportion ofcarbohydrates in DOC decreased at peak flow. Prediction of DOC and DONconcentrations by an end-member mixing analysis (EMMA) on the base ofinorganic water chemistry showed that changes in water flow pathslargely explained these temporal variability. According to the EMMA, thecontribution of throughfall to the runoff peaked in the initial phase ofthe storm, while water from the subsoil dominated during base flow only.EMMA indicated that the contribution of the DOC and DON-rich topsoil washighest in the later stages of the storm, which explained the highestDOC and DON concentrations as the hydrograph receded. Discrepanciesbetween observed and predicted concentrations were largest for thereactive DOC compounds such as carbohydrates and phenolics. Theyoccurred at base flow and in the initial phase of storms. This suggeststhat other mechanisms such as in-stream processes or a time-variantrelease of DOC also played an important role.     

Alternative explanations for rising dissolved organic carbon export from organic soils

Since 1988, there has been, on average, a 91% increase in dissolved organic carbon (DOC) concentrations of UK lakes and streams in the Acid Waters Monitoring Network (AWMN). Similar DOC increases have been observed in surface waters across much of Europe and North America. Much of the debate about the causes of rising DOC has, as in other studies relating to the carbon cycle, focused on factors related to climate change. Data from our peat‐core experiments support an influence of climate on DOC, notably an increase in production with temperature under aerobic, and to a lesser extent anaerobic, conditions. However, we argue that climatic factors may not be the dominant drivers of DOC change. DOC solubility is suppressed by high soil water acidity and ionic strength, both of which have decreased as a result of declining sulphur deposition since the 1980s, augmented during the 1990s in the United Kingdom by a cyclical decline in sea‐salt deposition. Our observational and experimental data demonstrate a clear, inverse and quantitatively important link between DOC and sulphate concentrations in soil solution. Statistical analysis of 11 AWMN lakes suggests that rising temperature, declining sulphur deposition and changing sea‐salt loading can account for the majority of the observed DOC trend. This combination of evidence points to the changing chemical composition of atmospheric deposition, particularly the substantial reduction in anthropogenic sulphur emissions during the last 20 years, as a key cause of rising DOC. The implications of rising DOC export for the carbon cycle will be very different if linked primarily to decreasing acid deposition, rather than to changes in climate, suggesting that these systems may be recovering rather than destabilising.     

Climate-induced changes in the dissolved organic carbon budgets of boreal lakes

During 20 years of climatic warming, drought and increased forest firesbetween 1970 and 1990, DOC concentrations declined by 15--25%in lakesof the Experimental Lakes Area, northwestern Ontario, allowing increasedpenetration of both UV and photosynthetically-active radiation (PAR), andcausing deeper euphotic zones and thermoclines. Decreased input to thelakes of DOC from terrestrial catchments and upstream lakes was theprimary reason for the decline, although in-lake removal also increasedslightly. Decreased streamflow caused by drought was more important thanforest fires in affecting DOC exports from catchments. Experimentalacidification of lakes caused even greater losses in DOC, by enhancing ratesof in-lake removal. DOC in Lake 302S, acidified to pH 4.5 during the1980s, declined to less than 10% of preacidificationvalues.     

富营养化湖泊溶解性有机碳生物可利用性研究进展

富营养化湖泊溶解性有机碳(DOC)包括内源和外源性碳源,不同来源碳源在物质化学结构组成和分子量级等方面具有显著差异,进而影响到对细菌的生物可利用性和碳素在食物网中的传递效率。根据国内外文献,综述了内外源DOC在碳稳定同位素值域上的显著差异,建议通过对DOC碳稳定同位素的分析来识别富营养化湖泊中DOC的主要来源;通过对比内外源DOC在碳水化合物、结合态中性糖和腐殖质含量上的差异,并结合细菌生长参数如细菌二级生产力、细菌呼吸作用及细菌生长效率来分析内外源DOC对细菌的生物可利用性。从富营养化湖泊DOC来源的角度探讨其生物可利用性和碳素传递效率,有助于了解富营养化湖泊食物网中碳素循环特征,加强对湖泊生态学的认识,为湖泊环境治理与保护提供科学依据。     

土地利用变化对挠力河流域可溶性有机碳输出的影响

采用野外采样、室内分析、GIS及统计分析相结合的方法,研究了挠力河流域河水可溶性有机碳（DOC）浓度的季节性动态,以及年均尺度上全流域、100 m河岸带土地利用变化对河水DOC输出的影响.结果表明： 基流状态下,河水DOC浓度在春季、夏季显著高于秋季;有湿地存在的子流域DOC浓度的季节性动态与无湿地存在的子流域存在显著差异,且有湿地存在的子流域中DOC浓度的季节性变异与整个流域的趋势一致;年均尺度上,DOC浓度与全流域湿地以及100 m河岸带范围内的水田面积百分比呈显著正相关,而与全流域尺度的林地百分比呈显著负相关（P<0.05）.表明湿地的存在是影响挠力河流域河水DOC季节性变异的重要因素;全流域的湿地以及100 m河岸带范围内的水田对其具有显著的促进作用,而林地对其有显著的减缓效应,流域过去几十年的土地利用变化改变了河水DOC的平衡状况.     

Untangling the complex issue of dissolved organic carbon uptake: a stable isotope approach

1. We estimated uptake of stream water dissolved organic carbon (DOC) through a whole-stream addition of a ¹³C-DOC tracer coupled with laboratory measurements of bioavailability of the tracer and stream water DOC.
2. The tracer, a leachate of ¹³C-labelled tree tissues, was added to the head waters of White Clay Creek, Pennsylvania, U.S.A., over a 2-h period and followed 1.27 km downstream to generate mass transfer coefficients for DOC lability classes within the tracer.
3. From the longitudinal ¹³C uptake curve, we resolved labile and semi-labile DOC classes within the ¹³C-DOC tracer comprising 82% and 18% of the tracer respectively.
4. Plug-flow laboratory bioreactors colonized and maintained with stream water were used to determine the concentration of stream water DOC fractions that had a similar lability to the labile and semi-labile classes within the tracer and we assumed that stream water DOC and tracer DOC with comparable lability fractions in the bioreactors behaved similarly in the stream, i.e. they had the same mass transfer coefficients.
5. A small fraction (8.6%) of the stream water DOC was labile, travelling 238 m downstream before being taken up. The remaining bioavailable stream water DOC was semi-labile and transported 4.5 km downstream before being taken up. These uptake lengths suggest that the labile DOC is an energy source within a stream reach, while the semi-labile DOC is exported out of the reach to larger rivers and the downstream estuary, where it may provide energy for marine microbial communities or simply be exported to the oceans.     

海洋异养细菌利用溶解有机碳的定量评估

【目的】惰性溶解有机碳(refractory dissolved organic carbon,RDOC)是海洋总有机碳的主体组分,RDOC在深海中可保存数千年,构成了巨大的碳储库,在调节气候变化中有重要作用。但RDOC的定量评估尚未有统一的标准方法。通过测定环境中能被异养细菌利用的溶解有机碳(biodegradable DOC,BDOC)可以反过来评估RDOC的量。本文对BDOC测定中一些关键步骤进行验证,为制定海洋RDOC评估标准奠定基础。【方法】本文评估了3种过滤方式及5种滤膜对DOC测定的影响,并评估了瓶子效应和稀释效应对细菌生长和DOC利用的影响。【结果】研究发现,(1) GF/F滤膜、GF-75滤膜、聚四氟乙烯(PTFE)滤膜(孔径0.2μm)、聚碳酸酯(PC)滤膜(孔径0.2μm)和聚四氟乙烯材质针孔过滤器(HA)(孔径0.2μm) 5种滤膜不会引入DOC污染;抽滤过滤和重力过滤方式过滤效果稳定、无污染,而在线过滤效果不稳定,易污染;(2)不同大小培养体系(30–480 mL;表面积/体积比为:1.64–0.67 cm–1)之间的细菌生长速率和DOC利用量没有显著性差异;(3)培养体系稀释度越高,细菌生长速率越高,对数生长期细菌丰度及DOC利用量越低。【结论】综合考虑,建议BDOC和RDOC测定实验中采用抽滤过滤的方式及不进行稀释的培养体系;常用的滤膜和培养体积对BDOC评估无显著影响。结合研究结果,我们提出了评估海洋RDOC的方法。     

Interactive climate factors restrict future increases in spring productivity of temperate and boreal trees

Climate warming is currently advancing spring leaf‐out of temperate and boreal trees, enhancing net primary productivity (NPP) of forests. However, it remains unclear whether this trend will continue, preventing for accurate projections of ecosystem functioning and climate feedbacks. Several ecophysiological mechanisms have been proposed to regulate the timing of leaf emergence in response to changing environmental cues, but the relative importance of those mechanisms remains unclear. Here, we use 727,401 direct phenological observations of common European forest trees to examine the dominant controls on leaf‐out. Using the emerging mechanisms, we forecast future trajectories of spring arrival and evaluate the consequences for forest carbon dynamics. By representing hypothesized relationships with autumn temperature, winter chilling, and the timing of spring onset, we accurately predicted reductions in the advance of leaf‐out. There was a strong consensus between our empirical model and existing process‐based models, revealing that the advance in leaf‐out will not exceed 2 weeks over the rest of the century. We further estimate that, under a ‘business‐as‐usual’ climate scenario, earlier spring arrival will enhance NPP of temperate and boreal forests by ~0.2 Gt per year at the end of the century. In contrast, previous estimates based on a simple degree‐day model range around 0.8 Gt. As such, the expected NPP is drastically reduced in our updated model relative to previous estimates—by a total of ~25 Gt over the rest of the century. These findings reveal important environmental constraints on the productivity of broad‐leaved deciduous trees and highlight that shifting spring phenology is unlikely to slow the rate of warming by offsetting anthropogenic carbon emissions.     

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。     

老爷岭多年冻土小流域春季冻融期径流溶解性有机碳变化特征

溶解性有机碳（DOC）的输移过程是流域碳循环中重要的组成部分,对全球碳循环产生重要影响。以大兴安岭多年冻土区的典型森林小流域-老爷岭流域为研究对象,获得2021年4月9日到6月30日冻融期降雨量、气温、土温等气象数据及逐日径流量、径流DOC浓度,计算了冻融循环期（4月9日-28日）和融化期（4月29日-6月30日）流域径流DOC的输出通量,揭示了径流DOC浓度及输出通量的影响因素。结果表明：（1）研究时段内,老爷岭流域径流DOC浓度变化范围为3.88-33.75 mg/L,流域上游的径流DOC浓度变化趋势与下游基本一致,DOC浓度随着温度的升高呈现下降趋势,4月份平均径流DOC浓度明显高于5、6月份。（2）研究时段内流域径流DOC总输出通量为3215.48 kg/km²,其中5月径流DOC输出通量高于4、6月份。径流量与径流DOC输出通量存在显著正相关关系（P<0.05）,是流域DOC输出通量的主导因素。（3）研究时段内流域DOC浓度与平均气温呈极显著负相关（R²=0.5048,P<0.001）;降水样品中的DOC浓度变化范围为1.06-9.42 mg/L,显著低于径流DOC浓度;土壤中DOC含量变化趋势与径流DOC变化趋势一致,0-10 cm、10-20 cm土壤平均DOC浓度范围为77.57-133.99 mg/L。（4）冻融循环期平均日径流DOC浓度（24.02 mg/L）显著（P<0.05）高于融化期（14.64 mg/L）,而融化期平均日DOC输出通量（48.02 kg/km²）是冻融循环期（9.52 kg/km²）的5倍。研究结果揭示了大兴安岭多年冻土小流域春季冻融期径流DOC的输移特征及其影响因素,对理解多年冻土区碳循环有重要意义。     

A comparison of phosphorus and DOC leachates from different types of leaf litter in an urban environment

1. The leaching rates of filterable reactive phosphorus (FRP) and dissolved organic carbon (DOC) from five leaf litter types commonly occurring in urban environments in Mediterranean regions of Southern Australia were compared. The relative composition, bioavailability and oxygen demand of this DOC were also assessed. Four tree species were assessed, including the native river red gum (Eucalyptus camaldulensis) and three introduced deciduous species, the English elm (Ulmus procera), London plane (Platanus acerifolia) and white poplar (Populus alba). Grass cuttings (mixed species) were selected as a common garden waste. 2. Except for English elm, the majority of FRP and DOC was released within the first 48 h. Grass cuttings released the highest amount of FRP with white poplar releasing the most DOC. Species that released relatively high amounts of DOC (white poplar, English elm, river red gum) released relatively low amounts of FRP. Conversely, species that released relatively low amounts of DOC (grass cuttings and London plane) tended to release relatively high amounts of FRP. 3. Analysis of DOC composition, combined with the differing oxygen demand and DOC depletion curves, demonstrated that there were substantial differences in the DOC leached from the leaf litter of the different species. Biochemical oxygen demand and the biodegradability of the DOC was positively correlated with the proportion of hydrophilic and hydrophobic acids present in the leachate. 4. These results demonstrate that simple measurements of nutrient release per gram of leaf litter would be insufficient to predict the ecological impact on receiving waters resulting from changes in dominant vegetation. Furthermore, the use of traps to prevent particulate leaf material from entering streams may have limited potential for reducing the load of dissolved nutrients. We conclude that any changes to vegetation type which substantially alter the timing of leaf fall or the composition of leaf leachates should be avoided.     

土壤溶解性有机碳在陆地生态系统碳循环中的作用

土壤溶解性有机碳(DOC)是有机碳库的活跃组分,在陆地生态系统碳循环中发挥重要作用.本文从碳循环重要性着手,综述了土壤DOC在土壤碳固持与温室气体排放中的作用;结合我国的现实情况(如土壤酸化、气候变暖等),探讨了土壤DOC的相关影响因素如土壤性质、环境因素、人为活动对土壤DOC的影响及作用机制,对进一步理解土壤DOC在陆地生态系统碳循环与温室气体减排中的作用具有重要意义.