Decomposition of litter from three major plant species of jarrah (Eucalyptus marginata Donn ex Sm.) forest in relation to site fire history and soil type

Rates of weight loss and release of N, P, K, S, Ca, Mg, Na, and Cl from litter of several species in jarrah (E. marginata Donn ex Sm.) forest were measured in relation to site fire history and soil type. Weight loss from leaf litter decreased in the order jarrah > marri (E. calophylla R. Br. ex Lindl.) > Banksia grandis Willd. After 18 months on the forest floor senesced leaves of jarrah, marri and Banksia had lost 45%, 42% and 19%, respectively, of their original weight. Although greatest rates of decomposition occurred on a site burnt 3 y previously by an intense autumn fire and slowest rates on a site which had not been burnt for 8 y, the differences between burn sites were small in comparison with the total weight loss from decomposing litter. The order of release of nutrients from decomposing eucalypt litter was P<N<Ca<S<Mg<Cl<K<Na. There appears to be only slow release of N and P from the litter layer of these forests in the period between successive control burns. Fresh jarrah leaves, which are similar in chemical composition to leaf litter falling after crowns have been scorched by intense fire, decompose rapidly in comparison with senescent leaf tissue. Release of nutrients, particularly N and P, is also more rapid from fresh leaves than from leaf litter. Rates of decomposition of green leaves differed between soil types in the order reddish gravels > dark sandy duplex soil > yellow gravels. These differences may be related to the higher nutrient status of the reddish gravel soils.     

Litter decomposition and nitrogen mineralization of soils in subtropical plantation forests of southern China,with special attention to comparisons between legumes and non-legumes

Litter decomposition and nitrogen mineralization were investigated in subtropical plantation forests in southern China. The CO₂ –C release from incubated litter and the forest floor of Acacia mangium, Acacia auriculaeformis, Eucalyptus citriodora, Pinus elliotii and Schima superba stands were used to estimate relative rates of litter decomposition. Decomposition was not positively correlated with litter nitrogen. E. citridora litter decomposed most rapidly and A. mangium litter most slowly, both with and without the addition of exotic nitrogen. Aerobic incubation and intact soil core incubation at 30 °C over a period of 30 days were used to assess nitrogen mineralization of six forest soils. Although there were differences in results obtained using the two methods, patterns between legume and non-legume species were the same regardless of method. All soils had pH values below 4.5, but this did not prevent nitrification. The dominant form of mineral nitrogen was nitrate for legume species and ammonium for non-legume species. The nitrogen mineralization potential was highest for soils in which legumes were growing.     

Foliage litter turnover and earthworm populations in three beech forests of contrasting soil and vegetation types

Summary Leaf litter decomposition, levels of accumulated litter as well as the abundance and biomass of earthworms were measured in three mature beech forests in southern Sweden: one mor site, one poor mull site, and one rich mull site. The disappearance rate of beech litter, measured with litter bags, increased with increasing soil fertility. On the rich mull site, the disappearance rate was much higher than in the two other forests, due to the combined effects of higher earthworm activity, more favouable soil moisture conditions, and higher litter quality. Incubating the litter in finely meshed bags (1-mm mesh) to exclude macrofauna had a great effect on litter mass loss in the rich mull site, but it had only a minor effect in the other sites. Simultaneous incubations of local and transplanted leaf litter on the three study sites showed that the substrate quality of the litter increased in the order: mor site — poor mull site — rich mull site. Lignin, N, and P concentrations of the leaf litter failed to explain the observed differences in decomposition rates, and acid/base properties are suggested to be more important. Earthworm numbers per m² were 2.5 (1 species) in the mor, 40 (6 species) in the poor mull and 220 (9 species) in the rich mull forest. Soil chemical conditions, notably pH, were suggested as the main factors determining the inter-site differences in abundance and species composition of earthworms. The role of litter decomposition and earthworm activity in the accumulation of organic matter in the forest floor in different types of beech woodlands are discussed.     

Effects of elevated CO2 and nitrogen fertilization pretreatments on decomposition on tallgrass prairie leaf litter

Standing dead and green foliage litter was collected in early November 1990 from Andropogon gerardii (C₄), Sorghastrum nutans (C₄), and Poa pratensis (C₃) plants that were grown in large open-top chambers under ambient or twice ambient CO₂ and with or without nitrogen fertilization (45 kg N ha⁻¹). The litter was placed in mesh bags on the soil surface of pristine prairie adjacent to the growth treatment plots and allowed to decay under natural conditions. Litter bags were retrieved at fixed intervals and litter was analyzed for mass loss, carbon chemistry, and total Kjeldahl nitrogen and phosphorus. The results indicate that growth treatments had a relatively minor effect on the initial chemical composition of the litter and its subsequent rate of decay or chemical composition. This suggests that a large indirect effect of CO₂ on surface litter decomposition in the tallgrass prairie would not occur by way of changes in chemistry of leaf litter. However, there was a large difference in characteristics of leaf litter decomposition among the species. Poa leaf litter had a different initial chemistry and decayed more rapidly than C₄ grasses. We conclude that an indirect effect of CO₂ on decomposition and nutrient cycling could occur if CO₂ induces changes in the relative aboveground biomass of the prairie species.     

Fine root growth and nutrient release in decomposing leaf litter in three contrasting vegetation types in central Amazonia

We tested the hypothesis that the growth of fine roots upward into the leaf litter, forming a ‘surface root mat’, found widely in Amazonian forests, is of adaptive value for plants of poor soils because it makes possible more rapid uptake of limiting nutrients. We assessed the effect of invasion by fine roots on the rates of loss of dry mass and nutrient content of leaf litter over 1 year in three plots in each of three contrasting forest types in central Amazonia: the stunted facies of heath forest known as campina (SHF), the taller facies of heath forest known as campinarana (THF), both on spodosols, and the surrounding lowland evergreen rain forest (LERF) on ultisol. Pairs of bags filled with freshly fallen leaves from the trees of Clitoria fairchildiana (Fabaceae) were placed on the litter layer; in order to prevent roots entering the control bag in each pair that bag was lifted from the forest floor and turned over each week, while the treatment bag was left undisturbed. From each plot, four pairs of litter bags were retrieved after 30, 60, 120, 180, 270 and 360 d, and all roots that had grown into the litterbags were carefully removed. The leaves and roots from each bag were oven-dried for nutrient analysis. In no forest type was there a significant difference in the rate of loss of dry matter from the litter between the bags with and without roots. The amounts of roots invading the litter bags increased significantly in the sequence SHF < THF < LERF. In no forest did the presence of roots have a significant effect on the rate of disappearance of N or P from the leaf material, or on the rate of accumulation of Fe and Al. In the SHF there was no significant effect of invasion by roots on the rates of disappearance of Ca, Mg, Mn or Zn, but in the THF, the rates of disappearance of these four elements between 270 and 360 d were significantly greater in the presence of roots. In the LERF the results were similar, but the effects of roots started earlier—the rates of disappearance of Ca and Mg were significantly enhanced between 120 and 360 d. The results from the SHF may be interpreted to suggest that the growth of fine roots (and their fungal associates) upward into leaf litter is unlikely to be explained wholly by their role in the efficient recovery of mineral nutrients.     

The influence of a neotropical herbivore (<Emphasis Type="Italic">Lamponius portoricensis</Emphasis>) on nutrient cycling and soil processes

The role of phytophagous insects in ecosystem nutrient cycling remains poorly understood. By altering the flow of litterfall nutrients from the canopy to the forest floor, herbivores may influence key ecosystem processes. We manipulated levels of herbivory in a lower montane tropical rainforest of Puerto Rico using the common herbivore, Lamponius portoricensis (Phasmatidea), on a prevalent understory plant, Piper glabrescens (Piperaceae), and measured the effects on nutrient input to the forest floor and on rates of litter decomposition. Four treatment levels of herbivory generated a full range of leaf area removal, from plants experiencing no herbivory to plants that were completely defoliated (>4,000 cm² leaf area removed during the 76-day study duration). A significant (P<0.05) positive regression was found between all measures of herbivory (total leaf area removed, greenfall production, and frass-related inputs) and the concentration of NO ₃ ⁻ in ion exchange resin bags located in the litter layer. No significant relationship was found between any of the herbivory components and resin bag concentrations of NH ₄ ⁺ or PO ₄ ⁻ . Rates of litter decay were significantly affected by frass-related herbivore inputs. A marginally significant negative relationship was also found between the litter mass remaining at 47 days and total leaf area removed. This study demonstrated a modest, but direct relationship between herbivory and both litter decomposition and NO ₃ ⁻ transfer to the forest floor. These results suggest that insect herbivores can influence forest floor nutrient dynamics and thus merit further consideration in discussions on ecosystem nutrient dynamics.     

Evaluation of the faster initial decomposition of tropical floating leaves ofNymphaea elegans Hook

Contributions of abiotic and biotic processes to the decomposition of floating leaves ofNymphaea elegans were separately evaluated by comparing the rate obtained from anin situ experiment of submerging dry leaf material in a lake, and that from a laboratory experiment of submerging dry leaf material in lake water with a bio-fixing reagent. It took 8 days to decompose 79.4% of the initial dry weight of the floating leaf ofN. elegans in a tropical lake. Of the dry weight loss, 32.9% and 67.1% were atributed to abiotic and biotic decomposition, respectively. The relationship between decomposition rate and the mesh size of the leaf litter bags was examined by the application of a mathematical model. A reasonable value of decomposition loss at an early stage could be obtained using a bag with a mesh opening of 9.9 mm². The decomposition rate of floating leaves is faster than that of other aquatic plants. Rapid decomposition ofN. elegans leaves may be attributed to the fact that the plant has a low carbon to nitrogen ratio.     

Influence of leaf litter type on the chemical evolution of a soil parent material (sandstone)

The influence of leaves of Quercus suber L. and Eucalyptus globulus Labill. and needles of Pinus pinaster Ait. on a sandstone substrate was assessed through lysimetric studies during a ten-year period at a site in Central Portugal. The decomposition rate of Q. suber leaf litter was similar to that of E. globulus and higher than that of P. pinaster needle litter. The proportion of nitrogen released from the Q. suber leaf litter was higher than that lost from the other organic species. Such a release was proportional to the initial nitrogen content in the substrates. The concentrations of both NH₄-N and NO₃-N were much higher in leachates collected under Q. suber leaf litter than in those collected under the other organic substrates. A similar trend was found in the leachates collected under the mineral substrate influenced by the studied organic substrates. The leachate concentrations of mineral N (especially NO₃-N) were higher from the mineral substrate under Q. suber leaf litter than from this organic substrate itself. The mineral substrate under leaf litter of E. globulus or needle litter of P. pinaster showed an increase in exchangeable base cations and pH values, and a decrease in extractable Al. Conversely, in the substrate with Q. suber leaf litter there was only a slight increase in exchangeable base cations and pH values, and a decrease in extractable Al. These results combined with those obtained in soils under E. globulus plantations indicate that changes found in these soils are due to soil and forest management practices rather than to the decomposition process of the respective of leaf litter.     

Decomposition of eucalypt litter on rehabilitated bauxite mines

The initiation of nutrient cycling is important in developing a self-sustaining ecosystem, where inputs of fertilizer are not required, on rehabilitated open-cut mines. The loss of dry weight, surface area and nutrients from senescent jarrah (Eucalyptus marginata) leaves enclosed in litterbags for 18 months were measured on 27 rehabilitated bauxite mines and in two jarrah forests on the Darling Plateau in Western Australia. Respiration and acetylene reduction by the litter were also determined. Linear trends were found between litter decomposition on rehabilitated mines and understorey cover density, litter cover and a measure of the effect of the revegetation on soil moisture. During decomposition, N was retained relative to litter dry weight and, in most cases, amounts of N increased. Losses of Ca and S were correlated with dry weight losses. Sodium, Cl, Mg and K were lost from the litter by leaching. Rehabilitation techniques, including sowing a legume understorey and replacement of the topsoil, should favour the development of nutrient cycling on mined areas.     

Disappearance of overstorey and understorey litter in an open eucalypt forest

Litter accumulation dynamics and first year rates of disappearance were investigated for leaves of overstorey and understorey species in the mixed eucalypt forest in the Griffith University study area, Queensland, Australia. The average biomass of the litter layer, was 10.2 t/ha. The wood and overstorey leaf litter formed 62.7% of the accumulated litter biomass, and were spread continuously across the ground. The distribution of shrub litter was discontinuous, being concentrated in localized patches beneath individual plants. The litter bag and tethered leaf techniques were used to measure the rate of disappearance of overstorey and shrub leaves. The ‘pairedquadrat’ technique was used to measure the weight loss of the grasses. The small leaves of the dominant shrub, Pultenaea villosa Willd. disappeared most rapidly, followed by the overstorey leaves, grasses and Acacia leaves. Fragmentation by physical factors and litter fauna appeared to be the major factors responsible for the disappearance of the overstorey leaves during the first year of exposure. The data suggest that removal of leaf constituents by leaching and microbial decomposition were more important for the shrub litter than the overstorey leaves. Fractional disappearance rates (loss constants) obtained from the short term weight loss measurements, and calculated using the steady-state model of litter accumulation (k=L/X), overestimated the rate of litter disappearance and litter decomposition. For the overstorey leaves in particular, the loss constants also overestimated the rate of loss of material from the litter layer since the fragmented and consumed tissues accumulated in the fraction of comminuted fragments before moving into the humus/soil subsystem. A compartment model of the components of the litter layer in the mixed eucalypt forest is presented. It incorporates overstorey and understorey litter accession, accumulation and disappearance data. The adoption of a two dimensional decomposition/accumulation matrix is suggested as an appropriate framework within which to simulate the dynamics of the litter subsystem in mixed eucalypt forest ecosystems.     

Litter and forest-floor dynamics in aPinus resinosa plantation in Wisconsin

Summary Breakdown of dry matter and release of nutrients from decomposing leaf litter and forest-floor material were measured in a 34-year-old red pine (Pinus resinosa Ait.) plantation in central Wisconsin using (1) leaf-litter bags (2) litterfall and forest-floor nutrient data and an exponential decay function, and (3) nutrient flux data and a mass balance equation. After one year of decomposition, 77% of the original dry matter in leaf-litter bags remained. The release of macronutrients in decomposing leaf litter was K>Mg>P, S>N>Ca, and the release of micronutrients and aluminum was Mn, B>Al>Cu>Zn. Nitrogen in decomposing leaf litter showed the leaching, accumulation, and final release phases delineated by Berg and Staff⁴. Half-lives of dry matter and nutrients in the forest floor ranged from 0.5 (K) to 39 (Al) yr. Forest-floor turnover rates of the various elements followed the same trends as in leaf-litter bags except that Ca turned over more readily than P, S, and N and Zn turned over more readily than the other micronutrients. A forest-floor nutrient balance sheet confirmed that the macronutrients N and Ca are accumulating most readily in the forest floor. The overall implications of these trends for tree nutrition are discussed.     

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。     

滇中亚高山地带性植被凋落物分解对模拟氮沉降的响应

模拟氮（N）沉降对凋落物分解特征的影响对研究森林生态系统物质循环响应大气N沉降的内在机理和应对N沉降全球化具有重要意义。从2018年2月至2019年1月，对滇中亚高山常绿阔叶林（Evergreen broad-leaf forest）和高山栎林（Quercus semecarpifolia forest）两种地带性植被进行模拟N沉降试验，利用尼龙网袋法对两种林型凋落叶和凋落枝进行原位分解试验，N沉降处理水平分别为对照CK（Control check，0 g N m^-2 a^-1）、低氮LN（Low nitrogen，5 g N m^-2 a^-1）、中氮MN（Medium nitrogen，15 g N m^-2 a^-1）和高氮HN（High nitrogen，30 g N m^-2 a^-1）。结果表明：常绿阔叶林凋落叶和凋落枝分解率分别为44.84%和21.96%，均高于高山栎林的35.97%（凋落叶）和17.51%（凋落枝）；N沉降处理使得常绿阔叶林和高山栎林的凋落叶和凋落枝质量损失95%的时间在对照（CK）的基础上均有一定程度的增加，其中以HN处理下最为显著；经过1年的分解，两种林型凋落叶、枝纤维素和木质素降解均受到N沉降的抑制作用；两种林型中凋落物质量残留率、纤维素和木质素残留率三者间呈极显著正相关。针对滇中亚高山区域范围内的两种地带性植被，凋落物分解对N沉降的响应方向主要取决于凋落物基质质量，其中尤以纤维素和木质素为重要影响因素。     

Litterfall,leaf decomposition and litter colonization of Tessaria integrifolia (compositae) in the Parana river floodplain

Litterfall and leaf decomposition rates were measured in Choui Island, 45 km downstream from the confluence of the Paraná and Paraguay rivers. The material was collected biweekly from April 1985 through September 1986. Decomposition was measured in situ by the litter bag technique.Annual litterfall of Tessaria integrifolia gallery forest measured in the period April 1985 to March 1986 was 8.15 t ha^-1. Leaf litterfall was seasonal, i.e. significantly less leaf litter was shed during the high water phase than during the low water phase. The half life of the T. integrifolia litter over 38 days of decomposition was 20 days. At the beginning of the experiment, 15 and 38 days subsamples of remaining detritus were analyzed in order to determine changes in the nutrient content. After 38 days of incubation, the order of nutrient disappearance was Ca > K > N > Mg > Na > P.The number of invertebrates per g remaining litter of Tessaria integrifolia increased between incubations days 7 and 31. Collector-gatherers were more abundant after 38 days incubation; there were no shredders colonizing the leaf litter bags.     

Decomposition process in Negev ecosystems

Summary The effects of supplemental water and natural rainfall on decomposition were studied in the Negev Highland desert, Israel. There was a mass loss of approximately 40% in Hammada scoparia leaves and Salsola inermis litter placed on the soil surface and buried in fine mesh bags. There was an annual mass loss of 80% in S. inermis litter buried in large fiberglass mesh bags. Supplemental water provided during the wet season (January to March) did not result in more rapid decomposition of litter of the annual grass Stipa capensis but irrigation during the dry season (August to September) produced a marked increase in the decomposition rate of S. capensis. These data suggest that rain events, not water quantity, are the most important regulators of decomposition in the Negev. Annual rates of decomposition were higher than predicted by models utilizing actual evapotranspiration and lignin content as regulating variables. Rates of decomposition were equal to those reported for tropical wet forests.     

Impacts of Falcataria moluccana Invasion on Decomposition in Hawaiian Lowland Wet Forests: The Importance of Stand-level Controls

Invasive species have the capacity to substantially alter soil processes, including rates of litter decomposition. Currently, the few remaining native-dominated lowland wet forests in Hawai’i are being invaded by Falcataria moluccana, a large, fast-growing, N₂-fixing tree. In this study, we sought to determine the extent to which Falcataria invasion alters decomposition in these lowland wet forests, and whether changes resulted from differences in litter substrate type, lava flow age and type, forest stand type and associated soil biota, or some combination of these factors. We measured decomposition rates and nitrogen (N) and phosphorus (P) dynamics of Metrosideros polymorpha and Falcataria leaf litter in native-dominated and Falcataria-invaded stands on 48- and 300-year-old a’a lava flows and a 213-year-old pāhoehoe flow in the Puna district of eastern Hawai’i. Despite significant differences in the initial quality of Metrosideros and Falcataria litter, in nearly all cases mass remaining of the two litter types did not differ within a given forest stand, whether native-dominated or invaded. Instead, stand type accounted for large differences in the decomposition of both litter types, and litter decomposed two to 10 times faster in Falcataria-invaded stands than it did in their native-dominated counterparts on each lava flow. Dynamics of N (that is, immobilization or release) during decomposition were affected by stand, litter, and lava flow type; P dynamics were affected by stand and flow type, but not litter type. Although not definitive proof of causality, the decay rates of both species were positively correlated to previously measured inputs of N mass and P mass via litterfall as well as availability of soil N and P, characteristics that all increased substantially with Falcataria invasion. Given the degree of change to a host of ecosystem processes, including decomposition, after invasion by Falcataria, these transformed forest ecosystems may best be viewed as fundamentally new and different, in both structure and function, from the native ecosystems they have replaced.     

西双版纳热带季节雨林凋落叶分解与土壤动物群落：两种网孔分解袋的分解实验比较

 以西双版纳热带湿性季节沟谷雨林混合凋落叶作为分解基质,在不同位置季节雨林样地,采用不同网孔（ 2和0.15 mm）分解袋,开展大中型土壤动物对雨林凋落叶分解影响的实验,测定了不同网孔分解袋土壤动 物多样性、凋落叶分解速率和主要养分元素释放状况。结果显示：2 mm网孔分解袋土壤动物类群相对密度 年均值为2.67～2.83目•g－1凋落物干重,个体相对密度年均值为22.3～21.77个•g－1凋落物干重,显著 高于0.15 mm网孔分解袋的类群相对密度0.27～0.28目•g－1凋落物干重和个体相对密度2.88～2.77个•g－ 1凋落物干重（p<0.01）,并且0.15 mm网孔分解袋中极少量的动物个体主要为小型类群弹尾目和蜱螨目（ 原生动物、湿生土壤动物线虫不计）,由此我们视2 mm网孔分解袋凋落叶分解由绝大多数土壤动物和其它 土壤生物共同作用,而0.15 mm网孔分解袋基本排除了大中型土壤动物对袋内凋落叶分解的影响。2 mm网 孔分解袋凋落叶物质失重率（71%左右）、分解率指数（1.88～2.44）和主要养分元素释放率明显高于 0.15 mm分解袋（34%～35%,0.48～0.58）。通过比较两种不同网孔分解袋凋落叶失重率和元素释放率的 差异,显示出季节雨林大中型土壤动物群落对凋落叶物质损失的贡献率为年均值46%左右,并使凋落叶C/N 和C/P明显降低,而对不同元素释放率的影响不同,其中对N、S和Ca元素释放率的影响较大,而对K素释放 的影响作用最小。相关分析显示,2 mm网孔分解袋内土壤动物群落类群和个体的相对密度与凋落叶物质残 留率有较好的负相关关系,而群落香农多样性指数与凋落叶分解率指数表现出一定的正相关关系。     

Browsing-induced Effects on Leaf Litter Quality and Decomposition in a Southern African Savanna

We investigated the linkages between leaf litter quality and decomposability in a savanna plant community dominated by palatable-spinescent tree species. We measured: (1) leaf litter decomposability across five woody species that differ in leaf chemistry; (2) mass decomposition, nitrogen (N); and carbon (C) dynamics in leaf litter of a staple browse species (Acacia nigrescens) as well as (3) variation in litter composition across six sites that experienced very different histories of attack from large herbivores. All decomposition trials included litter bags filled with chopped straw to control for variation in site effects. We found a positive relationship between litter quality and decomposability, but we also found that Acacia and straw litter mass remaining did not significantly vary between heavily and lightly browsed sites. This is despite the fact that both the quality and composition of litter returned to the soil were significantly different across sites. We observed greater N resorption from senescing Acacia leaves at heavily browsed sites, which in turn contributed to increase the C:N ratio of leaf litter and caused greater litter N immobilization over time. This, together with the significantly lower tree- and herb-leaf litter mass beneath heavily browsed trees, should negatively affect decomposition rates. However, estimated dung and urine N deposition from both browsers and grazers was significantly greater at high- than at low-herbivory sites. We hypothesize that N inputs from dung and urine boost litter N mineralization and decomposition (especially following seasonal rainfall events), and thereby offset the effects of poor leaf litter quality at chronically browsed sites. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Decomposition of litter in sub-alpine forests of Eucalyptus delegatensis,E. pauciflora and E. dives

The rate of decomposition of summer leaf-fall (abscised leaves), winter leaf-fall (containing some green leaves) and mature green (picked) leaves was assessed in sub-alpine forests of E. delegatensis (R. T. Baker), E. pauciflora (Sieb. ex Spreng) and E. dives (Schau.) in the Brindabella Range, Australian Capital Territory, using litter bag and tethered leaf techniques. The relative contribution of leaching, microbial respiration and grazing by invertebrate macrofauna to loss of leaf weight was determined. The effect of leaching and microbial respiration was assessed in terms of weight loss per unit area of leaf (specific leaf weight), while losses due to macro-faunal grazing were assessed by measuring reductions in leaf area. Litter decomposition constants for litter components (leaf, bark, wood) and total litter were determined from long-term records of litterfall and accumulated litter. Weight losses of abscised leaves during the initial 12 months ranged from 25% for E. pauciflora to 39% for E. delegatensis and were almost entirely due to reduction in specific leaf weight. Losses in the weight of leaves falling in winter ranged from 38 to 49%, while green leaves lost 45 - 59%. Approximately 50% of the total weight loss of green leaves was due to a loss in leaf area caused by skeletonization by litter macrofauna. Thus abscised leaves rather than green leaves must be used for measuring litter decomposition rates since abscised leaves constitute most of the litterfall in eucalypt forests. Leaves placed in the field in autumn decomposed slowly during the first summer, while the rate increased during the second winter and summer. Low litter moisture content appears to limit decomposition in the initial summer period in all communities, after which litterfall provides a mulch which reduces the rate of desiccation of lower litter layers. A simple linear regression model relating decomposition rate to the number of days (D) when litter moisture content exceeded 60% ODW accounted for 63-83% of the variation in decomposition of leaves in the field. Inclusion of mean monthly air temperature (T) and the product of D and T (day degrees when litter was wet) in a multiple linear regression increased the variation in decomposition accounted for to 80 – 90%. The rate of weight loss showed a positive linear relationship with the initial concentration of nitrogen (N) or phosphorus (P) in the leaf. These concentrations are an index of the decomposability of leaf substrates (e.g. degree of sclerophylly or lignification). The rate of loss of specific weight was similar for tethered leaves and for leaves enclosed in mesh bags. Measured loss in specific leaf weight after 70 – 90 weeks was less than that predicted using decomposition constants (k).     

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.