Early-stage litter decomposition and its influencing factors in the wetland of the Sanjiang Plain, China

Using the litter bag technique, the decomposition rates and their influencing factors were studied by investigating three wetland macrophytes, Calamagrostics angustifolia, Carex meyeriana and Carex lasiocapa, in Sanjiang Plain, Northeast China. It was revealed that C. lasiocapa lost 28.91% of its weight, C. angustifolia lost 31.98% and C. meyeriana lost 32.99% after 164 days. Another finding was that the amount of organic carbon in the litter of C. angustifolia and C. lasiocapa fluctuated, but continuously decreased in that of C. meyeriana. However, all the three types of litter released organic carbon. Nitrogen was released substantially from the litter of both C. angustifolia and C. meyeriana, but accumulated in the litter of C. lasiocapa. Phosphorus concentrations in all the three types of litter apparently decreased first and then slightly increased. Overall, P release was observed in all the three types of litter. The C/N and C/P ratios varied significantly in the decomposition process. The decomposition rates and nutrient content variations were simultaneously influenced by the quality of the litter as well as the environmental factors in the Sanjian Plain, but they were more strongly affected by the quality of the litter.     

三江平原典型湿地枯落物早期分解过程及影响因素

枯落物分解是湿地物质循环和能量流动的关键环节,是维持湿地功能的重要过程之一。采用分解袋法对三江平原3种典型湿地植物枯落物分解过程及影响因素进行了研究。研究表明,在164d实验过程中乌拉苔草分解速率始终最快;在分解前103d中毛果苔草分解速率大于小叶章,但在103~164d间小叶章分解速率大于毛果苔草;分解164d,小叶章、乌拉苔草和毛果苔草枯落物的失重率分别为初始重的31.98%、32.99%和28.91%。分解过程中小叶章和毛果苔草枯落物中有机碳浓度波动较大,而乌拉苔草枯落物中持续下降;3种枯落物有机碳绝对含量都表现为净释放。小叶章枯落物中N浓度波动较大,绝对含量发生净释放;毛果苔草枯落物N浓度持续增加,绝对含量净增加;乌拉苔草枯落物N浓度先增加后减少,绝对含量发生净释放。3种枯落物中P浓度都先迅速下降后缓慢上升,绝对含量都表现为净释放。3种枯落物中C/N和C/P也相应的发生变化。小叶章和乌拉苔草枯落物分解速率与枯落物C/P显著相关,而毛果苔草枯落物与枯落物N浓度显著相关;对应3种枯落物分解速率的主要环境因子分别为土壤含水量、土壤容重和土壤温度。3种枯落物分解速率和营养物质含量动态受到枯落物自身质量和温湿条件、周围环境营养状况等自然环境条件的共同影响,相比而言,受枯落物质量的影响更大。     

若尔盖高原湿地土壤-植物系统有机碳的分布与流动

 湿地碳素变化对全球气候变化的影响一直是国内外湿地研究的热点。国内对沼泽湿地碳循环的研究主要集中在三江平原,其它地区则鲜见报道。若尔盖高原位于全球气候变化最敏感的区域之一——青藏高原的东北部,冷湿的气候条件下沼泽十分发育,泥炭贮量丰富,沼泽面积和泥炭资源贮量均居中国首位。为了评估该区湿地在全球气候变化中的作用,作者以该区分布最为广泛的3种沼泽植物群落——木里苔草（Carex muliensis）群落、乌拉苔草（Carex meyeriana）群落和藏嵩草（Kobresia tibetica）群落以及最为典型的3种湿地土壤——泥炭土、泥炭沼泽土和草甸沼泽土为对象,采用田间腐解试验方法,系统研究了高原湿地植物——土壤系统中有机碳的分布与流动,其目的在于：1)探明该区湿地土壤有机碳的数量与分布状况;2)了解植物碳在向土壤流动过程中的消失与残留情况。结果表明,若尔盖高原湿地土壤的有机碳含量一般较高且随土层加深而降低;在植物由活体—立枯—残落物的不同阶段,植物不同化学组分中碳的消失率各异,其中易分解组分碳的消失率最大（3种群落分别为61.37%、69.59%和66.34%）,木质素碳的消失率（44.53%～52.98%）略大于纤维素碳的消失率（38.23%～43.86%）,3种群落植物碳的总消失率分别为53.8%、60.03%和55.18%;3种群落的植物残落物在土壤中分解一年和两年后的残留碳量分别为30 g·m﹣2和25.5 g·m﹣2,而植物残根的相应数值则分别高达179～223 g·m﹣2和161～208 g·m﹣2,说明若尔盖高原湿地生态系统中植物残根是形成土壤有机碳的主要来源。由于该区湿地的生物量较高,有机碳的流动量也相应较大。     

不同水分条件下毛果苔草枯落物分解及营养动态

于2009年5月至2010年5月采用分解袋法,研究了三江平原典型湿地植物毛果苔草枯落物分解对水分条件变化的响应,探讨了典型碟形洼地不同水位下枯落物分解1a时间内的分解速率与N、P等营养元素动态。分解1a内,无积水环境下枯落物失重率为34.99%,季节性积水环境下为27.28%,常年积水环境下随水位增加枯落物失重率分别为26.99%与30.67%,表明积水条件抑制了枯落物的分解。枯落物的分解随环境变化表现出阶段性特征,分解0—122 d内随水位增加枯落物失重率分别为16.09%、24.25%、23.53%与26.60%,即生长季内积水条件促进了枯落物有机质的分解及重量损失。而随实验进行,分解122—360 d内随水位增加毛果苔草枯落物的失重率分别为18.90%、3.02%、3.46%、4.03%,即在非生长季土壤冻融期积水条件抑制了枯落物分解(P<0.05)。水分条件对毛果苔草枯落物N元素的影响表现为积水条件促进生长季内枯落物的N固定,水位最高处毛果苔草N浓度显著高于无积水环境(P<0.05)。但进入冻融期后积水环境下枯落物N浓度与含量降低;其中季节性积水限制了枯落物的N积累能力,至分解360d时与初始值相比表现出明显的N释放(P=0.01)。毛果苔草枯落物分解61d时P出现富集,其中积水条件下P的富集作用增强,但与水位不相关。分解1a后毛果苔草枯落物表现为P的净释放,不同水分条件下枯落物P元素损失没有明显差异(P>0.05)。     

三江平原小叶樟、毛果苔草枯落物中氮素变化分析

以三江平原沼泽湿地主要优势植物小叶樟(Deyeuxiaangustifolia)和毛果苔草(Carexlasiocarpa)枯落物为例,探讨了N素在枯落物中的季节变化、含量特征以及对维持生态系统物质平衡的作用．结果表明,枯落物N含量随气温升高和地上生物量增大而减少;枯落物失重率随时间延长而增大;小叶樟年累积失重率为32．2％,毛果苔草为27．7％;小叶樟群落N素年累积输入量为1478mg     

鄱阳湖湿地优势植物枯落物的分解速率及碳、氮、磷释放动态特征

植物枯落物分解对生态系统碳通量和养分循环有至关重要的作用,这一过程主要由3个相互作用的因素决定,即化学（枯落物理化特性）、物理（气候和环境）以及生物（参与枯落物分解的微生物和无脊椎动物）因素。在气候和立地环境条件相同的情况下,枯落物质量是制约分解的内在因素。在鄱阳湖湿地开展了野外定位观测实验,采用分解袋技术研究了鄱阳湖湿地优势植物芦苇（Phragmite）、南荻（Triarrhena lutarioriparia）和薹草（Carex.cinerascens Kükenth）枯落物分解速率及碳（C）、氮（N）、磷（P）元素释放动态特的征差异性。结果表明,在0-150 d内三种植物枯落物的干物质分解速率和残留率以及碳相对归还指数（CRRI）、氮相对归还指数（NRRI）、磷相对归还指数（PRRI）差异性都极其显著。在0-150 d内分解速率都是芦苇的最大,薹草的次之,南荻最小。分解进行150 d后,芦苇、南荻和薹草枯落物干物质残留率依次约为56.57%、67.99%和60.88%,CRRI依次约为57.44%、34.58%和41.75%,NRRI依次约为50.71%、-22.66%、和23.18%,PRRI依次约为88.91%、79.27%和85.63%。用Olson负指数衰减模型拟合方程预测芦苇、南荻、薹草枯落物分解完成50%所需的时间大约依次为184 d、249 d和210 d,分解完成95%所需的时间依次为795 d、1078 d和908 d。芦苇和薹草枯落物碳、氮和磷在分解过程中都表现出净释放模式,而南荻枯落物的碳和磷也一直表现为净释放模式,但是氮一直表现为净积累模式。芦苇分解过程中的营养释放作用最强,而南荻群落对氮的吸收和富集效应最强。研究表明植物种类及基质物质量对枯落物分解及其养分释放有很强的调控作用。今后的研究应考虑不同物种枯落物混合时的分解过程以及分解过程中的微生物因素,以便能揭示植物群落物种多样性及微生物活动在湿地生物地球化学循环中的调控作用机制,以期为鄱阳湖湿地碳、氮和磷的生物地球化学循环提供更新的认识,为鄱阳湖湿地的科学管理、保护与恢复提供科学依据。     

放牧对青藏高原东部两种典型高寒草地类型凋落物分解的影响

为认识放牧对青藏高原东部中生性的高寒草甸草地和半湿生的沼泽草地凋落物分解的影响,在这两种草地上分别设置了围栏和放牧样地,研究了其各自的混合凋落物样品和4个优势物种(发草Deschampsiacaespitos、鹅绒委陵菜Potentilla anserine、木里苔草Carexmuliensis、藏嵩草Kobresiatibetica)凋落物的分解和养分释放动态,这4个优势物种也大致代表了当地沼泽草地生态系统在放牧和气候变暖驱动下逆行演替不同阶段的优势物种类群。结果表明,各优势物种凋落物的分解速率有显著差异;放牧在总体上促进了凋落物的分解,但不同物种的响应有所不同;放牧对凋落物C的释放影响不显著或有抑制作用,但对N、P的释放具有一定促进作用。对各优势物种凋落物分解和养分释放模式的分析表明,群落逆行演替过程中,凋落物分解和C释放加速,可能促进沼泽湿地退化的正反馈效应。草甸草地的退化标志物种鹅绒委陵菜具有较高的凋落物质量和分解速度,反映了中生条件下植物应对牲畜啃食采用"逃避"而非"抵抗"策略的趋向。     

凋落物输入对三江平原弃耕农田土壤基础呼吸和活性碳组分的影响

土壤有机碳的积累主要由土壤有机质的输入与输出间的净平衡决定的,植被的恢复和凋落物质的大量输入是土壤恢复的先决条件,凋落物的输入在土壤恢复过程中起着至关重要的作用.通过对不同类型凋落物输入到三江平原弃耕农田后土壤的基础呼吸、溶解有机碳(DOC)和土壤微生物量碳(MBC)的研究表明:相同种类凋落物输入后,输入到土壤总有机碳(TOC)背景值低的凋落物被微生物降解的速率大于TOC背景值高的土壤,TOC较低的土壤能够加快微生物对输入凋落物的分解,不利于有机质的积累;不同类型凋落物的输入使土壤基础呼吸、DOC和MBC等活性组分的生成和降解产生差异,改变了凋落物的降解速率,在三江平原研究的4种主要植被类型中,人工林凋落物最容易降解,小叶章、大豆的降解能力次之,玉米是最难降解的凋落物.     

Decomposition and nutrient dynamics of marsh litter in the Sanjiang Plain, Northeast China

The litterbag technique was used to study the decomposition and nutrient dynamics of marsh litter in the four communities, Carex pseudocuraica (C.pa), C. lasiocarpa (C.la), Deyeuxia angustifolia (D.aa), and D. angustifolia-Shrub (D.aa-Srb), in Sanjiang Plain, Northeast China. Decomposition was divided into two periods in the first year, with the mass loss ranging from 11.7% to 31.4% of the initial mass during summer and autumn, accounting for more than 75% of the annual loss. The decomposition rates ranged from 0.000 612 to 0.000 945 d^?1 depending on the depth of the flooding and its duration, and differed significantly in each community. The litter decomposed faster in communities with deeper and perennial flooding than in those with shallow and seasonal flooding. The initial ratios of C:N and C:P were also different among the four litter types, but these differences had no impact on the decomposition rates, suggesting that the main factor influencing the decomposition rates of marsh litter was the flooding status rather than the litter quality. The N concentrations in C.pa and C.la almost continuously increased over time, with their final values being 2.8 and 2.4 times higher than the initial ones, respectively. However, the nutrient dynamics in D.aa and D.aa-Srb offered another pattern, sharply falling in the first month and then gradually rising, with the values at the end of the experiment being close to those at the beginning. The litter accumulated substantial amounts of N in C.pa and C.la, while net N release from the litter was observed in both D.aa and D.aa-Srb. The difference may be caused by microorganisms' demand for nutrition, and then limited by the C:N ratios of litter and the availability of nitrogen from the soil and marsh water. In contrast with N dynamics, P concentrations of all the litter types apparently decreased during the first month, and then continued to decline in C.pa, remained constant in C.la and D.aa and increased slightly in D.aa-Srb. At the end of the experiment, the P concentrations decreased, respectively, by 56%, ?5%, 47% and 24% of the initial values of C.la, C. pa, D.aa and D.aa-Srb. The net P release was observed in all marsh litter over 480 days of decomposition and the intensity of the P release was different amongst communities, which may be regulated by ratios of initial C:P. The results suggested that in the marsh with the N limitation, litter tended to accumulate N and release P during decomposition and the intensity of accumulation or release was closely related to the initial C:N and C:P ratios.     

Decomposition of Carex and Sphagnum litter in two mesotrophic fens differing in dominant plant species

Peatlands can be classified into fens and bogs based on their hydrology. Development of fens to bogs is accompanied by the invasion of Sphagnum species. The purpose of this study was to determine how the decomposition process in fens is influenced by the transition from a vascular plant-dominated system to a Sphagnum -dominated system. We carried out a reciprocal litter bag experiment, using litter of Carex diandra , C. lasiocarpa , Sphagnum papillosum and S. squarrosum in a fen dominated by Sphagnum species and a fen without Sphagnum . Decomposition rate and nitrogen and phosphorus dynamics of the plant litter were measured in a field experiment for two years. Decomposition rate was highest for the Carex litter types and lowest for the Sphagnum litter types. Surprisingly, decomposition rates hardly differed between the two sites. Nutrient dynamics, however, showed a clear site-effect: In the Sphagnum site net mineralization was observed for all litter types whereas in the Carex site net immobilization was observed. These results show that carbon and nutrient cycles were coupled in a different way in a Sphagnum -dominated and a Carex -dominated site, respectively. Nutrient availability and adaptation of the microbial community to nutritional and other environmental conditions may be the main regulators of carbon and nutrient cycles in these peatlands.     

Root decomposition and soil nutrient and carbon cycling in two temperate fen ecosystems

Although root litter contributes to a large extent to soil organic matter accumulation in peatlands, decomposition of root litter is often neglected in studies on litter decomposition and carbon and nutrient cycling in these ecosystems. In this study, decomposition of root and rhizome litter of Carex diandra and Carex lasiocarpa was determined in two temperate fens, one dominated by Sphagnum species ( Sphagnum fen; soil pH=4.4) and one without a Sphagnum cover ( Carex fen; soil pH=5.7). One-year mass loss increased in the order: roots Carex diandra 相似文献   

三江平原典型湿地及其开垦后土壤中总硫变化的初步研究

以三江平原3种主要沼泽类型--小叶章(Calamagrostis angustifolia)沼泽、乌拉苔草(Carex meyeriana)沼泽、毛果苔草(Carex lasiocarpa)沼泽以及不同开垦年限的耕地为研究对象,对其土壤中总硫含量进行分析,3种沼泽中总硫量的顺序为小叶章沼泽(622．4mg·kg^-1)<乌拉苔草沼泽(820．5mg·kg^-1)、毛果苔草沼泽(1022．4mg·kg^-1),挠力河、鸭绿河、别拉洪河及浓江流域土壤中总硫量的顺序为挠力河(925．0mg·kg^-1)>鸭绿河(841．8mg·kg^-1)>浓江(636．5mg·kg^-1)>别拉洪河(520．8mg·kg^-1)沼泽湿地及耕地土壤总硫量在层次上具有明显的规律性,即由表土层向下,含量逐渐降低,1980～2000年开垦的耕地土壤中总硫含量平均值为180．5mg·kg^-1,而未开垦湿地中的总硫含量平均值为735．8mg·kg^-1。耕地中的总硫量显著低于湿地中的总硫量,并且开垦年限越长,土壤中的总硫量越低,表明湿地开垦导致土壤总硫明显流失。     

Decomposition and nutrient dynamics of marsh litter in the Sanjiang Plain, Northeast China

The litterbag technique was used to study the decomposition and nutrient dynamics of marsh litter in the four communities, Carex pseudocuraica (C.pa), C. lasiocarpa (C.la), Deyeuxia angustifolia (D.aa), and D. angustifolia-Shrub (D.aa-Srb), in Sanjiang Plain, Northeast China. Decomposition was divided into two periods in the first year, with the mass loss ranging from 11.7% to 31.4% of the initial mass during summer and autumn, accounting for more than 75% of the annual loss. The decomposition rates ranged from 0.000 612 to 0.000 945 d^-1 depending on the depth of the flooding and its duration, and differed significantly in each community. The litter decomposed faster in communities with deeper and perennial flooding than in those with shallow and seasonal flooding. The initial ratios of C:N and C:P were also different among the four litter types, but these differences had no impact on the decomposition rates, suggesting that the main factor influencing the decomposition rates of marsh litter was the flooding status rather than the litter quality. The N concentrations in C.pa and C.la almost continuously increased over time, with their final values being 2.8 and 2.4 times higher than the initial ones, respectively. However, the nutrient dynamics in D.aa and D.aa-Srb offered another pattern, sharply falling in the first month and then gradually rising, with the values at the end of the experiment being close to those at the beginning. The litter accumulated substantial amounts of N in C.pa and C.la, while net N release from the litter was observed in both D.aa and D.aa-Srb. The difference may be caused by microorganisms' demand for nutrition, and then limited by the C:N ratios of litter and the availability of nitrogen from the soil and marsh water. In contrast with N dynamics, P concentrations of all the litter types apparently decreased during the first month, and then continued to decline in C.pa, remained constant in C.la and D.aa and increased slightly in D.aa-Srb. At the end of the experiment, the P concentrations decreased, respectively, by 56%, -5%, 47% and 24% of the initial values of C.la, C. pa, D.aa and D.aa-Srb. The net P release was observed in all marsh litter over 480 days of decomposition and the intensity of the P release was different amongst communities, which may be regulated by ratios of initial C:P. The results suggested that in the marsh with the N limitation, litter tended to accumulate N and release P during decomposition and the intensity of accumulation or release was closely related to the initial C:N and C:P ratios.     

Effect of nitrogen addition on decomposition of Calamagrostis angustifolia litters from freshwater marshes of Northeast China

Wetland ecosystems store a large amount of organic carbon (C) in soils, due to the slow decomposition rates of plant litter and soil organic matter. Increased nitrogen (N) availability induced by human activities and global warming may accelerate litter decomposition and affect soil organic C dynamics in wetlands. In the present study, we investigated the effect of N addition on decomposition of Calamagrostis angustifolia litters from freshwater marshes in the Sanjiang Plain of Northeast China under field and laboratory conditions. First, we assessed the changes in initial litter chemical composition and subsequent decomposition following three years of N addition at the rate of 24 g N m⁻² year⁻¹ under field conditions. Our results showed that N addition increased litter N concentration and decreased C/N ratio, and thus stimulated litter decomposition. Secondly, we examined the effect of increased N availability (0, 25, 50 and 100 mg N g⁻¹ litter) on litter decomposition under laboratory conditions. Increased exterior N availability also enhanced microbial respiration and increased litter mass loss under both waterlogging and non-waterlogging conditions. In addition, waterlogging conditions inhibited microbial respiration and suppressed litter mass loss. These findings demonstrated that N addition increased litter decomposition rates through improved litter quality and enhanced microbial activity in freshwater marshes of Northeast China. This implies that increased N availability accelerates litter decomposition rates, and thus may cause substantial losses of soil C and diminish and even reverse the C sink function of wetlands in the Sanjiang Plain of Northeast China.     

Spatial patterns of litter decomposition in the littoral zone of boreal lakes

1. We studied the patterns of litter decomposition in lake littoral habitats and investigated whether decay rates, as an integrating proxy for environmental conditions in the sediment, would co‐vary with net carbon dioxide (CO₂) exchange and methane (CH₄) efflux. These gas fluxes are known to be sensitive to environmental conditions. Losses in the mass of cellulose, root, rhizome and moss litter were measured during 2 years in boreal littoral wetlands in Finland and compared with published data on concurrently measured gas fluxes. Four study sites covered a range of sediment types and hydrological conditions. 2. Decomposition was not linearly related to the duration of flooding but depended on sediment type. Readily decomposable litter fractions, such as cellulose and rhizome litter, lost mass at a faster rate in marshes with a longer period of flooding but wide water level fluctuations that hinder establishment of a Sphagnum cover, than in peat‐forming fens. In marshes, the mean first‐year mass losses were 83–99% and 19–62% for cellulose and rhizomes, respectively. In fens, the respective losses were 40–53% and 33%. In the first year, the loss in the mass of the more recalcitrant root litter did not differ between sites (mean 19–30%) and moss litter lost no mass. 3. The estimated first‐year carbon loss from belowground litter was about 0.1–0.3 times ecosystem respiration and roughly similar to net carbon gas (CO₂, CH₄) efflux, suggesting that vascular plants and recent plant residues contribute substantially to ecosystem release of carbon gases. On the other hand, at least 40% of the mass of the belowground litter remained on a littoral site after the first 2 years of decomposition. Slow decomposition may indicate the accumulation of organic‐rich sediments. The accumulated carbon could explain the excess CO₂ release found in most littoral sites. In continuously inundated sites decomposition rates were similar to those in periodically flooded sites, but ecosystem‐atmosphere CO₂ exchange fell to close to zero. This discrepancy implies that the released CO₂ is dissolved in water and may be exported into the pelagic zone of the lake.     

Microcosm tests of the effects of temperature and microbial species number on the decomposition of Carex aquatilis and Sphagnum fuscum litter from southern boreal peatlands

Increased decomposition rates in boreal peatlands with global warming might increase the release of atmospheric greenhouse gases, thereby producing a positive feedback to global warming. How temperature influences microbial decomposers is unclear. We measured in vitro rates of decomposition of senesced sedge leaves and rhizomes (Carex aquatilis), from a fen, and peat moss (Sphagnum fuscum), from a bog, at 14 and 20 degrees C by the three most frequently isolated fungi and bacteria from these materials. Decomposition rates of the bog litter decreased (5- to 17-fold) with elevated temperatures, and decomposition of the sedge litters was either enhanced (2- to 30-fold) or remained unaffected by elevated temperatures. The increased temperature regime always favoured fungal over bacterial decomposition rates (2- to 3-fold). Different physiological characteristics of these microbes suggest that fungi using polyphenolic polymers as a carbon source cause greater mass losses of these litters. Litter quality exerted a stronger influence on decomposition at elevated temperatures, as litter rich in nutrients decomposed more quickly than litter poorer in nutrients at higher temperatures (8.0%-25.7% for the sedge litters vs. 0.2% for the bryophyte litter). We conclude that not all peatlands may provide a positive feedback to global warming. Cautious extrapolation of our data to the ecosystem level suggests that decomposition rates in fens may increase and those in bogs may decrease under a global warming scenario.     

Simulation of the decomposition and nitrogen mineralization of aboveground plant material in two unfertilized grassland ecosystems

A simple model of the decomposition and nitrogen mineralization of plant material from two unfertilized grassland ecosystems has been developed, with only the proportion of leaves and stems in the original material, the initial nitrogen contents of these plant parts and temperature as input data. The model simulates carbon losses from stems and leaves, using a double exponential decay function, with the temperature sum as independent variable. Mineralization of nitrogen is not calculated via microbial growth rates, but simulated on the basis of the carbon utilization efficiency of the microorganisms and the critical C/N ratio, i.e. the C/N ratio of the litter at which the microbial demand for nitrogen is met exactly. The parameter values for leaching fractions of carbon and nitrogen, relative decay rates, microbial carbon utilization efficiencies and critical C/N ratios were derived from a litter bag experiment with 12 litter types (species) including both green and dead materials, carried out in two unfertilized grassland ecosystems differing in production level. The model was evaluated using a cross-validation method, in which one species was omitted from the parametrization procedure, and its decomposition and mineralization were predicted by the resulting model. In general there was good agreement between the observed and predicted amounts of carbon and nitrogen remaining for all green litter types/species, but carbon and nitrogen dynamics in the dead material of Festuca rubra were poorly predicted. This disparity has been attributed to the proportion of leaves in the material of Festuca rubra (95%) being far beyond the range of leaf proportions in the three litter types the calibration set consisted of (8–35%). When the data of all litter types were used to determine the model parameters, good agreement was obtained between measured and simulated values for the changes in nitrogen and carbon in all litter types of both the green and dead material series. Optimization yielded parameter values for microbial carbon utilization efficiencies of 0.30 for microorganisms associated with green litter and 0.35 for those associated with dead litter. The critical C/N ratios for green and dead material were found to be 29 and 36, respectively.     

季节性冻融期间土壤动物对高山草甸两种凋落叶失重的贡献

季节性冻融期间高山草甸凋落叶的分解可为生长季节植物生长提供必要的养分,对于维持生态系统物质循环和养分平衡具有重要作用。然而,土壤动物对凋落叶分解是否具有明显的贡献仍然缺乏一致认识。因此,以高山草甸代表性植物黄花亚菊(Ajania nubigena)和黑褐苔草(Carex atrofusca)凋落叶为研究对象,采用不同孔径凋落叶袋排除土壤动物的方法,研究冬季不同冻融时期(冻结前期、冻结期和融化期)土壤动物对凋落叶失重的贡献。整个季节性冻融期间土壤动物对黄花亚菊和黑褐苔草两种凋落叶失重率的作用分别为12.07%和4.03%,总贡献率分别为46.39%和24.14%。土壤动物对两种凋落叶失重率的作用均在融化期最大,而土壤动物对黄花亚菊凋落叶失重率的作用在冻结初期最小,土壤动物对黑褐苔草凋落叶失重率的作用在冻结期最小。整个季节性冻融期,土壤动物对凋落叶失重率的作用和贡献率与正积温和凋落叶初始C、N浓度和C/N比均呈显著的正相关关系。因此,季节性冻融期间土壤动物对高山草甸凋落叶分解具有明显的贡献,但这些过程受冻融格局和凋落叶初始质量的调控。     

Short-term response of CO<Subscript>2</Subscript> emissions to various leaf litters: a case study from freshwater marshes of Northeast China

Soil organic carbon (SOC) mineralization is an important process of carbon (C) cycling and budgeting associated with litter decomposition in terrestrial ecosystems. Research on altered plant-derived C input on soil C stability due to climate change is controversial and there remains considerable uncertainty in predicting soil C dynamics with the techniques currently available. In this study, we conducted a laboratory incubation experiment to test the effects of single- and mixed-Deyeuxia angustifolia (DA) and Carex lasiocarpa (CL) leaf litter addition on cumulative marshland soil CO₂ emission under waterlogged and non-waterlogged conditions in Sanjiang Plain, Northeast China. Results showed that the cumulative CO₂ emissions were significantly increased after leaf litter addition in both water conditions, and that the effect was more pronounced for DA amendment than CL regardless of water condition. The cumulative CO₂ efflux differed considerably between water conditions after DA addition, whereas no significant differences were found after CL addition. Remarkably impact of leaf litter types on cumulative CO₂ evolution was observed overall, water condition and interactions between leaf litter types and water conditions had no significant effect on CO₂ emissions, however. There were no non-additive effects of individual leaf litter type on total CO₂ efflux of the mixed-leaf litter addition treatments. The results of this study indicate that plant litter input to the C-rich marshy soil can induce rapid changes in SOC decomposition regardless of water conditions and that plant residue effects should be taken into consideration when assessing the dynamics of wetland soil system to the future climate scenarios.     

毛果苔草湿地枯落物及地下生物量动态

采用网袋法和土柱法分别对三江平原湿地毛果苔草（Carex lasiocarpa）种群枯落物及地下生物量的季节动态变化规律进行分析。结果表明,毛果苔草的立枯物总的变化趋势是其拟合曲线符合指数方程。以其凋落物的失重率表示分解速率,而日失重率是随着时间增长而不断减少,且日失重率的变化在0.7058％-0.2372％之间。毛果苔草全生长季（1999年5月2日-10月10日）枯落物总量为210.8876g·m^-2。毛果苔草地下生物量具有明显的垂直结构,呈倒金字塔形,数学模拟近于抛物线型。