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.     

Effects of sediment-borne nutrient and litter quality on macrophyte decomposition and nutrient release

Macrophyte decomposition is a critical process that affects carbon and nutrient cycling, and energy flow, although the majority of the details involved in the process remain unclear. For the present study, a litter bag experiment was conducted to investigate the effects of sediment-borne nutrient and litter quality on the decomposition rates and nutrient release of four macrophyte life forms (emergent macrophyte: Phragmites australis, free-floating macrophyte: Hydrocharis dubia, floating-leaved macrophyte: Nymphoides peltata, submerged macrophyte: Ceratophyllum demersum), and a species mixture. Our results indicated that litter quality significantly influenced macrophyte decomposition and nutrient release. High-quality litter species (high initial nitrogen and phosphorus contents, as well as low C:N, C:P, and N:P ratios) decomposed more rapidly than low-quality litter species, and the initial C:N and C:P ratios, rather than the initial N and P contents, were effective indicators of the decomposition rate of macrophytes. Sediment-borne nutrients had little effect on the decomposition rate, yet a strong effect on the release of N and P, although the interactions between litter quality and sediment-borne nutrients significantly affected the decomposition rate. Three-way ANOVA analysis revealed that the litter quality imparted a more potent effect on the macrophyte decomposition rate and release of N and P than sediment-borne nutrients. These results implied that litter quality interacts with sediment-borne nutrients and may control macrophyte decomposition in shallow lakes.     

A literature synthesis resolves litter intrinsic constraints on fungal dynamics and decomposition across standing dead macrophytes

The standing dead phase is an important stage in the decomposition of emergent vegetation in marsh wetlands, yet few studies have examined how intrinsic litter traits constrain rates of standing litter decomposition or fungal colonization across plant tissue types or species. To address broad constraints on the decomposition of standing dead litter, we conducted a systematic survey of emergent standing dead decomposition studies that measured decay rates and/or fungal biomass, and litter % lignin, carbon:nitrogen (C:N) and/or carbon:phosphorus (C:P). Across 52 datasets, litter of low C:N and C:P ratios exhibited increased decomposition rates (r = −0.737 and −0.645, respectively), whereas % lignin was not significantly correlated with decomposition rates (r = 0.149). Mixed-effects models for litter decomposition rates indicated significant effects of litter molar C:N and C:N + lignin as an additive model, with the former providing marginally better support. Litter % lignin, however, was strongly negatively correlated with fungal biomass (r = −0.669), indicating greater fungal colonization of low-lignin litter, and not correlated with C:N (r = −0.337) and C:P (r = −0.456) ratios. The best-supported model predicting fungal biomass was litter molar C:N, with the C:N + lignin additive model also showing significant effects. Fungal carbon-use efficiency (CUE) also had a strong negative correlation with % lignin (r = −0.604), molar C:N (r = −0.323) and C:P (r = −0.632) across datasets. Our study demonstrates the constraining effects that litter stoichiometry and % lignin elicit on decomposition of standing dead litter and fungal colonization, respectively. These findings improve our understanding of biogeochemical cycling and prediction of the fates of C and nutrients in wetlands.     

Hydrologic control of litter decomposition in seasonally flooded prairie marshes

The effect of seasonal inundation on the decomposition of emergent macrophyte litter (Scolochloa festucacea) was examined under experimental flooding regimes in a northern prairie marsh. Stem and leaf litter was subjected to six aboveground inundation treatments (ranging from never flooded to flooded April through October) and two belowground treatments (nonflooded and flooded April to August). Flooding increased the rate of mass loss from litter aboveground but retarded decay belowground. Aboveground, N concentration decreased and subsequently increased earlier in the longer flooded treatments, indicating that flooding decreased the time that litter remained in the leaching and immobilization phases of decay. Belowground, both flooded and nonflooded litter showed an initial rapid loss of N, but concentration and percent of original N remaining were greater in the nonflooded marsh throughout the first year. This suggested that more N was immobilized on litter under the nonflooded, more oxidizing soil conditions. Both N concentration and percent N remaining of belowground litter were greater in the flooded than the nonflooded marsh the second year, suggesting that N immobilization was enhanced after water-level drawdown. These results suggest different mechanisms by which flooding affects decomposition in different wetland environments. On the soil surface where oxygen is readily available, flooding accelerates decomposition by increasing moisture. Belowground, flooding creates anoxic conditions that slow decay. The typical hydrologic pattern in seasonally flooded prairie marshes of spring flooding followed by water-level drawdown in summer may maximize system decomposition rates by allowing rapid decomposition aboveground in standing water and by annually alleviating soil anoxia.     

Decomposition patterns of leaf litter of seven common canopy species in a subtropical forest: N and P dynamics

Litter decomposition, governing nutrient and C cycling, is strongly influenced by the chemical litter quality. In order to determine the interspecific variation in leaf decomposition rates and to understand the chemical basis for such variation, decomposition dynamics of seven common canopy species was investigated over 2year using the litterbag technique in a subtropical evergreen broad-leaved forest on Okinawa Island, Japan. The species studied are representatives of the vegetation in the study area and differed significantly in their chemical litter quality. Dry mass loss at the end of study varied in the order: Distylium racemosum< Quercus miyagii< Rapanea neriifolia< Symplocos confusa< Castanopsis sieboldii< Schima wallichii< Daphniphyllum glaucescens. All species showed a pattern characterized by a rapid initial decomposition followed by lower rates except for D. glaucescenswhich decomposition rate appeared to be rather constant. In the late phase, decomposition rates were correlated positively to initial N and ash contents and negatively to lignin content, lignin:N, C:N, and C:P ratios. The effects of N and lignin content or lignin:N ratio were stronger than other quality parameters. There was a wide range in patterns of N and P concentrations, from a net accumulation to a rapid loss in decomposition. The correlation between N and P release suggests that N and P dynamics may have influenced each other during litter decomposition. Analysis of initial quality for species showed that the C:P ratios were extremely high (range 1639–3811) but the N:P ratios were from 28 to 56, indicating a likely P-limitation for this forest. Our results suggest that P is an important control of litter decomposition and N and P dynamics.     

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)。     

冬小麦生境中土壤养分对凋落物碳氮释放的影响

土壤养分影响植物生长, 进而影响凋落物质量和产量; 凋落物质量和产量影响凋落物分解过程。基于一个生长实验和一个相同环境分解实验, 研究了冬小麦(Triticum aestivum)生境中养分可利用性对凋落物碳(C)和氮(N)释放的影响。结果显示: (1)冬小麦凋落物产量、叶/根C:N比、C释放量和N释放量随土壤养分梯度呈单调变化; (2)土壤养分影响叶凋落物丢失率而不影响根凋落物丢失率; (3)初始叶/根C:N比与其C、N释放量之间存在负相关关系; (4)分解过程降低叶C:N比和根C:N比。结果表明: 生境中土壤养分的提高可加速凋落物C、N归还, 这反过来可能促进冬小麦生长, 因此这种效应是正反馈; 初始C:N比可预测凋落物C、N释放量。     

Forest plantation diversification with Leguminosae tree species: Consequences on litter decomposition and nutrient recycling

Mixed tree plantations provide greater ecosystem services than monocultures. Leguminosae tree species can be appropriate complements to achieve a sustainable soil management target. A key aspect of species trait complementarity is the litter mixture effects in the litter decomposition process. We evaluated how the mixture of poplar litter (Populus deltoides Marsh.) with Leguminosae tree species modulated the litter decomposition process and C, N and P recycling, through changes driven by the Leguminosae litter chemical traits. Under field conditions, we compared poplar litter alone (monoculture) with its 50:50 mixture with Enterolobuim contortisiliquum (Vell.) Morong., or Peltophorum dubium (Spreng.). Compared to poplar litter, its mixture with E. contortisiliquum had a 25% lower C:N ratio and a similar N:P ratio, whereas mixture with P. dubium had a 9% lower C:N and a 29% lower N:P ratios. The mixture with E. contortisiliquum showed a 64% faster decomposition rate, and 55% and 203% faster C and N release rates, respectively, compared to poplar. In contrast, in the mixture with P. dubium, there was no difference in the litter, C and N decay rates with poplar litter alone. The mixture with P. dubium had a 37% lower P retention compared to poplar, whereas P was released rather than retained in the mixture with E. contortisiliquum. The mixture with E. contortisiliquum showed a net antagonistic effect in the litter decomposition rate. However, in the mixture, poplar litter decomposed 33% faster and the E. contotrtisiliquum litter decomposed 35% slower than species alone. The C:N and N:P ratios in the litter mixture were relevant traits shaping the magnitude and direction of litter decomposition and nutrient recycling processes. The incorporation of both Leguminosae to monospecific poplar plantations could contribute to counteract P limitation in this system and to improve soil fertility and functioning.     

Changes of several characteristics of native litter during its exposure in periodically flooded biotopes

The litter-bag method was used to expose the native litter in five stands of three wetland communities (four of them were in a sedge-and-grass marsh and one was a willow carr) with increasing soil water content (a hydrosere) for 15 months in 1978 and 1979. The litter-mass changes, rates of litter decomposition, ash, N, P, K, Na and Ca contents were determined and expressed in terms of concentration and % remaining of initial amount of the respective element. Two main factors were distinguished that controlled the above characteristics: the overlying biomass effect that was most obvious at the end of August 1978, and the strong flood effect of spring 1979. The data on the living and dead plant biomass from all marsh sites and some data on climatic and hydrological conditions are also included.     

漓江流域岩溶区檵木群落不同恢复阶段凋落物分解初期动态

为探究漓江流域岩溶区檵木群落不同恢复阶段凋落物的分解情况,运用凋落物袋法研究其凋落物分解初期动态。结果表明:经过1a的分解,檵木群落凋落物失重大小顺序为:灌木阶段乔灌阶段乔林阶段。檵木群落灌木阶段、乔灌阶段和乔林阶段凋落物分解50%所需的时间分别为1.28a、1.38a、1.41a,分解95%所需的时间分别为5.54a、5.97a和6.09a。经过1a的分解,凋落物养分动态变化为:灌木阶段和乔灌阶段C含量总体上升,乔林阶段C含量总体下降;3个恢复阶段N和纤维素含量总体上升;灌木阶段和乔林阶段P含量总体下降,乔灌阶段P含量总体上升;灌木阶段木质素含量总体上升,而乔灌阶段和乔林阶段木质素含量总体下降。相关分析表明,灌木阶段凋落物分解速率分别与C,N,P,C/P,N/P之间呈显著或极显著相关性,乔灌阶段凋落物分解速率与N和木质素/N之间呈显著或极显著相关性,乔林阶段凋落物分解速率分别与N,纤维素、C/N和木质素/N之间呈显著或极显著相关性。     

模拟N沉降下不同林龄马尾松林凋落叶分解-土壤C、N化学计量特征

模拟N沉降对森林生态系统的影响是当今全球变化生态学研究的一个热点问题,土壤碳库对N沉降比较敏感,N沉降增加了凋落叶分解过程中外源N含量,间接影响凋落叶分解的化学过程并改变凋落叶分解速率,因此,研究模拟N沉降下凋落叶分解-土壤C-N关系对预测森林C吸存有重要意义。利用原位分解袋法研究了模拟N沉降下三峡库区不同林龄马尾松林(Pinus massoniana)凋落叶分解过程中凋落叶-土壤C、N化学计量响应及其关系;N沉降水平分对照(CK,0 g m~(-2)a~(-1))、低氮(LN,5 g m~(-2)a~(-1))、中氮(MN,10 g m~(-2)a~(-1))和高氮(HN,15 g m~(-2)a~(-1))。结果表明:分解540 d后,N沉降促进20年生和30年生马尾松林凋落叶分解,46年生马尾松林中仅低氮处理促进凋落叶分解,4种处理均是30年生分解最快,说明同一树种起始N含量低的凋落叶对N沉降呈正响应,N沉降处理促进起始N含量低的凋落叶分解,起始N含量高的凋落叶分解过程中易达到"N饱和"。N沉降抑制20年生和46年生凋落叶C释放(低于对照0.62%—6.69%),促进30年生C释放(高于对照0.28%—5.55%);30年生和46年生林分N固持量均高于对照(高于对照0.15%—21.34%),20年生则低于对照(5.70%—13.87%),说明模拟N沉降处理促进起始C含量低的凋落叶C释放和起始N含量低的凋落叶N固持。N沉降处理下仅30年生马尾松林土壤有机碳较对照增加,且土壤有机质与凋落叶C、N和分解速率呈正相关,与凋落叶C/N比呈显著负相关;土壤总氮与凋落叶分解速率、凋落叶N含量呈正相关,土壤有机碳/总氮比与凋落叶C、N含量呈正相关;对照处理中凋落叶分解指标对土壤养分影响顺序是分解速率凋落物C含量凋落物C/N比凋落物N含量,低、中、高氮处理中则是凋落物C含量分解速率凋落物N含量凋落物C/N比。研究表明低土壤养分含量马尾松林对N沉降呈正响应,N沉降促进低土壤养分马尾松林凋落叶分解并提高土壤肥力;凋落叶质量和土壤养分含量低的生态系统土壤C对N沉降响应更显著。     

Decomposition of roots of three plant communities in a Dutch salt marsh

Results of the first published study on root decomposition in a West European salt marsh are presented. In situ decomposition of roots of Spartinetum, Puccinellietum and Halimionetum communities were investigated using litter bags. Both the temporal pattern of decomposition and decomposition rate of belowground tissues of the three communities differed during 30 weeks in the marsh; Puccinellietum root litter lost 30–45% ash-free dry weight, Halimionetum root litter 17–26% and Spartinetum root litter 7–17%. Compared to aboveground decomposition in salt marshes these rates are low, however they are in the range of results reported for American and Australian salt marshes. Decomposition rates of root material buried at depths of 10 and 20 cm differed and there was a community × depth interaction. Initial content of structural components was highest in Halimionetum root litter and lowest in Puccinellietum root litter. Integrated soil temperature was highest in the Puccinellietum habitat, while flooding frequency was lowest in the Halimionetum habitat. Results indicate that environmental conditions can cause irregular fluctuations in belowground decomposition rates.     

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。     

Decomposition of Spartina anglica,Elytrigia pungens and Halimione portulacoides in a Dutch salt marsh in association with faunal and habitat influences

Decomposition of Spartina anglica, Elytrigia pungens and Halimione portulacoides was studied for 20.5 months in situ in two habitats on a salt marsh in The SW Netherlands. Litter bags of three different mesh sizes were used to exclude meio- and/or macrofauna. The middle-marsh habitat was flooded more frequently than the plant-debris habitat in the highest marsh zone. Decomposition of the three species followed an exponential pattern of decay: instantaneous decay rates varied from 0.0026 to 0.0054 per day. Decay rates were significantly influenced by habitat factors and fauna, while there was a significant interaction between plant species and habitat. In case of a significant meio- and/or macrofauna effect, this became noticeable 12–16 weeks after the start of decomposition and resulted in a difference of 5–10% ash-free dry weight remaining after 20.5 months. Nematodes were the dominant microfaunal group in the plant litter. Densities were influenced by habitat conditions but not by resource quality, season and meio- and/or macrofauna. Only initial C/N and C/P ratios were correlated with differences in decomposition rates between the plant species. During the later stages of decomposition N and P concentrations of the plant litter were higher in the plant-debris habitat than in the middle-marsh habitat, probably as a result of fluctuating detritivores densities. The course of the decomposition process differed per plant species and per habitat. The results of this study underline the importance of knowledge of long-term decomposition rates.     

Decomposition of emergent macrophytes in a Wisconsin marsh

Loss of both dry weight and nutrients during decomposition was measured using litter bags, both in a natural marsh and in controlled experiments. At 348 days dry weight remains of Typha latifolia, Sparganium eurycarpum, Scirpus fluviatilis shoot litter in the marsh were 47.5, 26.9, 51.4% respectively, and for the rootrhizome litter were 59.1, 42.1, 27.8% (Scirpus > Sparganium > Typha). Under controlled conditions both temperature and type of water produced significant effect on dry weight loss of Typha leaves. Sterilization and antibiotics effectively inhibited the growth and activities of decomposers. Initial weight, N, P, Ca, and Mg losses resulted chiefly from leaching. These elements accumulated in spring and summer; N exhibited the highest accumulation. In the laboratory, N accumulation occurred within 15 days, as a result of microorganisms inhabiting the litter. Increase in P, Ca, Mg in later stages of decomposition were attributed to microorganisms, epiphytes, and precipitation from solution. High C : N ratios and relatively low P, Ca, Mg in original standing crop may be the cause of low herbivore consumption, whereas the relative increases in N, P, Ca, Mg in decomposed litter provide a more nutrient-rich substrate for detritivores. Much of the nutrient uptake in the annual cycle is via microbial and detritivore growth rather than by macrophyte producers.     

氮、磷养分有效性对森林凋落物分解的影响研究进展

通过对相关研究文献的综述结果表明,氮(N)和磷(P)是构成蛋白质和遗传物质的两种重要组成元素,限制森林生产力和其他生态系统过程,对凋落物分解产生深刻影响。大量的凋落物分解试验发现在土壤N有效性较低的温带和北方森林,凋落物分解速率常与底物初始N浓度、木质素/N比等有很好的相关关系,也受外源N输入的影响;而在土壤高度风化的热带亚热带森林生态系统中,P可能是比N更为重要的分解限制因子。然而控制试验表明,N、P添加对凋落物分解速率的影响并不一致,既有促进效应也有抑制效应。为了深入揭示N、P养分有效性对凋落物分解的调控机制,"底物的C、N化学计量学"假说、"微生物的N开采"假说以及养分平衡的理论都常被用于解释凋落物分解速率的变化。由于微生物分解者具有较为稳定的C、N、P等养分需求比例,在不同的养分供应的周围环境中会体现出不同的活性,某种最缺乏的养分可能就是分解的最重要限制因子。未来的凋落物分解研究,应延长实验时间、加强室内和野外不同条件下的N、P等养分添加控制试验,探讨驱动分解进程的微生物群落结构和酶活性的变化。     

森林凋落物分解重要影响因子及其研究进展

当前 ,森林凋落物分解被放在陆地生态系统碳平衡背景下进行研究 ,认识凋落物分解过程的影响因素和影响机理对理解地表碳平衡具有重要意义。凋落物在分解过程中 ,伴随有养分含量的变化 ,低品质凋落物在分解前期 (可达 2～ 3年 )会从环境中固定养分 ,特别是氮磷养分 ,而在后期则会释放出养分。凋落物本身的养分含量是影响分解速率的重要因素 ,高养分含量的凋落物分解快些 ,阔叶凋落物比针叶凋落物分解快些。有资料显示 ,在总分解率为2 9 4 %的构成中 ,理化因素、微生物因素与土壤动物因素对凋落物分解的贡献率分别为 7 2 %、8 0 %和 14 2 %。不同类型凋落物在分解过程中的土壤动物类群也不同 ,它也是造成凋落物分解速率不同的关键因素 ,通常阔叶树种凋落物分解过程中 ,会有更多的微节肢动物出现。CO2浓度升高将造成植物有机质含碳量与其它养分的比值升高 ,形成低品质的凋落物 ,从而间接影响凋落物分解速率 ,一般认为 ,全球CO2 浓度升高会加强土壤作为碳汇的功能。     

Leaf litter decomposition and nutrient dynamics in a subtropical forest after typhoon disturbance

Decomposition of typhoon-generated and normal leaf litter and their release patterns for eight nutrient elements were investigated over 3 yr using the litterbag technique in a subtropical evergreen broad-leaved forest on Okinawa Island, Japan. Two common tree species, Castanopsis sieboldii and Schima wallichii, representative of the vegetation and differing in their foliar traits, were selected. The elements analyzed were N, P, K, Ca, Mg, Na, Al, Fe and Mn. Dry mass loss at the end of study varied in the order: typhoon green leaves > typhoon yellow leaves > normal leaves falling for both species. For the same litter type, Schima decomposed faster than Castanopsis. Dry mass remaining after 2 yr of decomposition was positively correlated with initial C:N and C:P ratios. There was a wide range in patterns of nutrient concentration, from a net accumulation to a rapid loss in decomposition. Leaf litter generated by typhoons decomposed more rapidly than did the normal litter, with rapid losses for N and P. Analysis of initial quality for the different litter types showed that the C:P ratios were extremely high (range 896 – 2467) but the P:N ratios were < 0.05 (range 0.02 – 0.04), indicating a likely P-limitation for this forest. On average 32% less N and 60% less P was retranslocated from the typhoon-generated green leaves than from the normal litter for the two species, Castanopsis and Schima. An estimated 2.13 g m^–2 yr^–1 more N and 0.07 g m^–2 yr^–1 more P was transferred to the soil as result of typhoon disturbances, which were as high as 52% of N and 74% of P inputted from leaf litter annually in a normal year. Typhoon-driven maintenance of rapid P cycling appears to be an important mechanism by which growth of this Okinawan subtropical forest is maintained.     

西藏东南部色季拉山主要类型森林叶片和枯落物养分含量特征

为阐明不同生长年限森林叶片和不同分解程度枯落物养分含量特征,为植物-土壤养分循环研究提供科学依据。以藏东南色季拉山几种典型森林植被(雪山杜鹃(Rhododendron aganniphum)、海拔4000 m和3900 m区域急尖长苞冷杉(Abies georgei var. smithii)、川滇高山栎(Quercus aquifolioides))为研究对象,分析了1年生和2年生植物叶片及不同分解程度枯落物有机碳(OC)、全氮(TN)、全磷(TP)和全钾(TK)含量。结果表明:色季拉山森林叶片和枯落物OC含量表现为2年生叶片1年生叶片未分解枯落物(ND)半分解枯落物(SD)完全分解枯落物(CD),即老叶片以C积累为主,而枯落物OC含量随分解程度的增加而下降,叶片OC平均含量(68.5%)显著高于中国平均水平(45.5%);叶片N、P、K含量表现为1年生2年生,即新叶以N、P、K等营养物质的吸收积累为主。枯落物TN含量低于中国森林的平均水平(12.03 g/kg),而TP含量显著高于中国森林平均水平(0.74 g/kg),枯落物TN和TP以SD最高,即分解初期表现为净固定,而后期则呈净释放,TK含量随分解程度的增加而增加,表现为K的净固定;叶片C∶N,C∶P和C∶K表现为2年生1年生,枯落物C∶N,C∶P和C∶K随着分解程度的增加而显著降低;叶片N∶P处于较低水平(6.08),显著低于全球平均水平(16.0),表现出明显的N限制营养型;研究结果为科学阐明藏东南森林生态系统植被-土壤养分循环研究提供了数据支撑。