黄土高原不同树种枯落叶混合分解效应

混交林中不同树种枯落物混合分解是否产生促进或抑制作用是评价种间关系和混交适宜性的重要依据之一。以黄土高原主要树种为对象,通过室内枯落叶混合分解模拟试验,结果表明:(1)沙棘、白榆、柠条和小叶杨枯落叶分解最快(周转期1 a左右),其次为旱柳、侧柏和白桦枯落叶(周转期略大于1 a),紫穗槐、辽东栎和刺槐枯落叶分解稍慢(周转期1.5 a左右),而樟子松、落叶松和油松枯落叶分解最慢(周转期略大于2 a)。(2)对于针叶树,与油松枯落叶混合,存在明显促进分解作用的是侧柏、落叶松,其次是白桦、沙棘和刺槐;与樟子松枯落叶混合,存在明显促进分解作用的是落叶松、侧柏、沙棘、白榆,其次是柠条、紫穗槐和小叶杨,而存在明显抑制分解作用的是刺槐,其次是白桦和辽东栎;与落叶松枯落叶混合,存在较明显促进分解作用的是白榆、白桦和辽东栎,存在较明显抑制作用的是刺槐;紫穗槐与侧柏枯落叶混合存在较明显的抑制分解作用。(3)对于阔叶树,与小叶杨枯落叶混合,存在较明显促进分解作用的是紫穗槐,其次是辽东栎和刺槐;与刺槐枯落叶混合,存在较明显促进分解作用的是白榆和沙棘,存在明显抑制分解作用的是柠条,其次是辽东栎和白桦;与白桦枯落叶混合,存在较明显促进分解作用的是辽东栎和紫穗槐,存在较明显抑制分解作用的是柠条;白榆与辽东栎、旱柳枯落叶混合均存在较明显的促进分解作用,而白榆与柠条枯落叶混合存在较明显的抑制分解作用;紫穗槐与旱柳、沙棘枯落叶混合均存在较明显的促进分解作用,而紫穗槐与柠条枯落叶混合有较明显的抑制作用。     

UV-B辐射对马尾松凋落叶分解和养分释放的影响

由大气臭氧层减薄导致的UV-B辐射变化将直接影响到凋落物的分解。目前,有关UV-B辐射影响木本植物凋落物分解的研究还很少,在国内还没有开展。采用分解袋法开展了马尾松凋落叶在自然环境和UV-B辐射滤减两种辐射环境下的分解试验。结果表明：在UV-B辐射滤减环境下的马尾松凋落叶年分解速率比对照环境减慢了47.74%。UV-B辐射极显著(p<0.01)地加快了马尾松凋落叶的分解速率,促进了凋落叶中碳、磷、钾的释放和木质素的降解,对氮的释放无明显影响。研究结果意味着UV-B辐射将加快马尾松林的营养循环速度,降低马尾松林凋落物层的碳储量。     

减雨对南亚热带马尾松人工林凋落物分解的影响

为探究气候变化背景下降雨格局改变对马尾松人工林凋落物分解及养分释放过程的影响,以南亚热带马尾松(Pinus massoniana)人工林为研究对象,设置穿透雨减少50%和不减雨(对照)处理,开展连续观测野外降水控制实验。采用凋落物分解袋法,研究了减雨处理对南亚热带马尾松人工林凋落叶分解速率及养分释放的影响,以及凋落叶分解速率的影响因素。结果表明:凋落叶分解2年后,减雨处理和对照林凋落叶残留率分别为38.09%和38.06%;凋落叶分解过程中碳元素表现为淋溶-富集-释放,而氮元素表现为富集,减雨50%在一定程度上促进了氮的富集,但未达到显著水平。相关分析表明,凋落叶的残留率与氮浓度和月积温呈显著负相关,与碳/氮呈显著正相关。本研究发现,减雨50%并未改变马尾松凋落叶分解速率和养分释放模式,凋落叶的残留率与氮浓度、碳/氮及月积温密切相关。     

Response of litter decomposition and related soil enzyme activities to different forms of nitrogen fertilization in a subtropical forest

With the continuing increase in the impact of human activities on ecosystems, ecologists are increasingly becoming interested in understanding the effects of nitrogen deposition on litter decomposition. At present, numerous studies have investigated the effects of single form of nitrogen fertilization on litter decomposition in forest ecosystems. However, forms of N deposition vary, and changes in the relative importance of different forms of N deposition are expected in the future. Thus, identifying the effects of different forms of N deposition on litter decomposition in forest ecosystems is a pressing task. In this study, two dominant litter types were chosen from Zijin Mountain in China: Quercus acutissima leaves from a late succession broad-leaved forest and Pinus massoniana needles from an early succession coniferous forest. The litter samples were incubated in microcosms with original forest soil and treated with four different forms of nitrogen fertilization [NH₄ ⁺, NO₃ ⁻, CO(NH₂)₂, and a mix of all three]. During a 5-month incubation period, litter mass losses, soil pH values, and soil enzyme activities were determined. Results show that all four forms of nitrogen fertilization significantly accelerate litter decomposition rates in the broadleaf forest, while only two forms of nitrogen fertilization [i.e., mixed nitrogen and CO(NH₂)₂] significantly accelerate litter decomposition rates in the coniferous forest. Litter decomposition rates with the mixed nitrogen fertilization were higher than those in any single form of nitrogen fertilization. All forms of nitrogen fertilization enhanced soil enzyme activities (i.e., catalase, cellulase, invertase, polyphenol oxidase, nitrate reductase, urease, and acid phosphatase) during the litter decomposition process for the two forest types. Soil enzyme activities under the mixed nitrogen fertilization were higher than those under any single form of nitrogen fertilization. These results suggest that the type and activity of the major degradative enzymes involved in litter decomposition vary in different forest types under different forms of nitrogen fertilization. They also indicate that a long-term consequence of N deposition-induced acceleration of litter decomposition rates in subtropical forests may be the release of carbon stored belowground to the atmosphere.     

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.     

Insight into the temperature sensitivity of forest litter decomposition and soil enzymes in subtropical forest in China

Aims With the continuing increase in the impact of human activities on ecosystems, ecologists are increasingly interested in understanding the effects of high temperature on litter decomposition since litter decomposition and the accompanying release of nutrients and carbon dioxide are key processes in ecosystem nutrient cycling and carbon flux. This study was conducted to evaluate the temperature sensitivity of forest litter decomposition and soil enzymes during litter decomposition in subtropical forest in China.Methods Two dominant litter types were chosen from Zijin Mountain in China: Quercus acutissima leaves from a broadleaf forest (BF) and Pinus massoniana needles from a coniferous forest (CF). The litter samples were incubated in soil microcosms at ambient control temperature (20°C) and 10°C warmer. During a 5-month incubation, chemical composition of litter samples, litter mass losses, and related soil enzyme activities were determined.Important findings Three main results were found: (i) high temperature accelerated decomposition rates of both litter types, and the temperature sensitivities of litter decomposition for BF leaves and that for CF needles are equivalent basically, (ii) high temperature enhanced soil enzyme activities in the two forest types, and the temperature sensitivities of polyphenol oxidase were significantly higher than those of the other soil enzymes and (iii) the temperature sensitivities of nitrate reductase were significantly higher in the CF soil than in the BF soil, while there was no significant difference in the temperature sensitivities of the other soil enzymes between BF and CF. As a long-term consequence, the high-temperature-induced acceleration of litter decomposition rates in these subtropical forests may cause carbon stored belowground to be transferred in the atmosphere, which may alter the balance between carbon uptake and release, and then alter the global carbon cycle in the coming decades.     

黄土高原樟子松和落叶松与其他树种枯落叶混合分解对土壤的影响

通过采集树木枯落叶与土壤进行室内混合分解培养试验,研究了黄土高原常见的樟子松和落叶松与其他树种枯落叶混合分解对土壤性质的影响及存在的相互作用,从而为不同树木种间关系的探索和该地区人工纯林的混交改造提供科学指导。结果表明:12种枯落叶单一分解均明显提高了土壤脲酶(54%—110%)、脱氢酶(85%—288%)和磷酸酶(81%—301%)活性以及有机质(29%—55%)和碱解N(12%—49%)含量,但对土壤速效P含量和CEC的影响存在较大差异。综合而言,樟子松分别与白桦、刺槐、白榆、柠条和落叶松枯落叶混合分解在对土壤性质的影响中存在相互促进作用,而分别与小叶杨、沙棘、紫穗槐、侧柏和辽东栎枯落叶混合分解在对土壤性质的影响中存在相互抑制作用;落叶松分别与刺槐、白桦、小叶杨和紫穗槐枯落叶混合分解在对土壤性质的影响中存在相互促进作用,而分别与柠条、侧柏、辽东栎、沙棘、油松和白榆枯落叶混合分解在对土壤性质的影响中存在相互抑制作用。     

Effects of litter types, microsite and root diameters on litter decomposition in Pinus sylvestris plantations of northern China

Background and aims

Litter decomposition is a major process in the carbon (C) flow and nutrient cycling of terrestrial ecosystems, but the effects of litter type, microsite, and root diameter on decomposition are poorly understood.

Methods

Litterbags were used to examine the decomposition rate of leaf litter and roots at three soil depths (5, 10 and 20 cm) over a 470-day period in Pinus sylvestris plantations in northern China.

Results

Leaves and the finest roots decomposed more quickly at 5 cm depth and coarser roots (>1-mm) decomposed more quickly at 10 and 20 cm depth. Roots generally decomposed more quickly than leaf litter, except at 5 cm deep; leaves decomposed more quickly than the coarsest roots (>5-mm). Root decomposition was strongly influenced by root diameter. Leaves experienced net nitrogen (N) immobilization and coarse roots (>2-mm) experienced more N release than fine roots. Significant heterogeneity was seen in N release for fine-roots (<2-mm) with N immobilization occurring in smaller (0.5–2-mm) roots and N release in the finest roots (<0.5-mm).

Conclusions

Soil depth of litter placement significantly influenced the relative contribution of the decomposition of leaves and roots of different diameters to carbon and nutrient cycling.     

早期分解中油松与阔叶树种凋落叶混合分解效应及其相互影响

以油松（Pinus tabuliformis Carrière）和5种阔叶树的凋落叶为对象,使用分解袋法在室内进行为期6个月的针阔混合分解实验,研究产生的混合分解效应、针阔凋落叶对彼此分解速率的影响及其可能产生机理。结果显示：（1）油松分别与红桦（Betula albo-sinensis Burk.）、灰楸（Catalpa fargesii Bur.）、太白杨（Populus purdomii Rehd.）凋落叶混合对分解速率均产生加性效应,但其中油松凋落叶分解受到显著促进,而阔叶凋落叶分解受到显著抑制。油松与杜仲（Eucommia ulmoides Oliver）凋落叶混合时两者分解速率均显著降低,油松与槭树（Acer tsinglingense Fang et Hsieh）凋落叶混合时两者分解速率均显著提高;（2）总体而言,在蔗糖酶、羧甲基纤维素酶和多酚氧化酶参与凋落叶分解的主要时期,红桦、灰楸、太白杨分别与油松凋落叶混合分解使土壤中这3种酶的活性较油松单独分解时显著提高,而较阔叶凋落叶单独分解时显著降低;油松与杜仲混合分解使这3种酶活性较两者单独分解时显著降低,而油松与槭树混合分解则产生相反效果。本研究结果表明,从凋落叶混合分解对物质循环影响的角度考虑,红桦、灰楸、太白杨和槭树可以用于油松纯林的混交改造,但应注意混交对阔叶树种分解的抑制;杜仲与油松凋落叶混合分解将会妨碍彼此养分循环,不宜混交改造。     

三峡库区森林凋落叶化学计量学性状变化及与分解速率的关系

凋落物分解是森林生态系统生物元素循环和能量流动的重要环节,其过程是植物与土壤获得养分的主要途径。为了量化凋落叶化学计量学性状变化过程对分解的影响及对凋落物-土壤生物化学连续体的深层理解,用凋落物分解袋法研究了不同林型各自凋落叶化学计量学性状变化及与分解速率关系,结果表明:林下各自凋落叶分解速率是马尾松林栓皮栎林马尾松-栓皮栎混交林,马尾松林、栓皮栎林、马尾松-栓皮栎混交林凋落叶分解50%和95%的时间分别是2.11 a和9.15 a,1.93 a和8.45 a,1.76 a和7.77 a;凋落叶分解过程中,化学计量学性状变化明显,分解450 d后马尾松-栓皮栎混交林碳释放最快,栓皮栎林最慢;3种凋落叶起始N含量是栓皮栎林最高,马尾松林最低,分解450 d后马尾松林、栓皮栎林和马尾松-栓皮栎混交林N含量分别增加了66.67%、44.91%和44.52%,而P含量分别释放了30.80%、38.89%和42.29%。凋落物不同化学计量学性状与分解速率关系不同,3种林型凋落叶分解速率均与N含量呈正相关(P0.01),与C含量(P0.01)、C/N比(P0.01)呈负相关,与N/P比呈负二次函数关系(P0.01),而P含量与3种林型关系不同,与栓皮栎林(P0.01)和马尾松林(P0.05)呈负线性关系,与马尾松-栓皮栎混交林呈负二次函数关系(P0.05)。研究表明,不同林型凋落叶分解中的养分动态趋向利于分解变化,N、P养分动态是生态系统碳平衡和凋落物分解速率的主要因素,混交林中混合凋落物的养分迁移是分解相对较快的原因。     

Silicon controls microbial decay and nutrient release of grass litter during aquatic decomposition

The decomposition rate of plant litter is important for the carbon cycle. Element stoichiometry and hardly degradable carbon compounds are main factors controlling the decomposition rate of plant litter. Recent research has linked these factors to silicon availability during plant growth, but no research focused on the effect of silicon on litter decomposition. We therefore conducted a batch experiment to assess the effect of silicon availability to plants on litter degradation, nutrient release and multi elemental stoichiometry. Experiments were conducted in the presence or absence of invertebrate shredders (Gammarus pulex). We show that nutrient content (affected by silicon availability during plant growth) has a strong impact on nutrient turnover, while DOC, N, and Mn were mainly controlled by invertebrate feeding. The carbon turnover during microbial litter decay was strongly influenced by the silicon availability during plant growth, with quicker potential C turnover of litter with higher silicon content. In both Si-rich and Si-poor litter, feeding by invertebrate shredders positively impacted turnover rates, but effects were less pronounced in Si-rich litter. It can be concluded that silicon availability in wetlands dominated by reed plays an important role in carbon sequestration, nutrient cycling, and remobilization during aquatic litter decay.     

Drought conditions alter litter decomposition and nutrient release of litter types in an agroforestry system of China

Evaluating how decomposition rates and litter nutrient release of different litter types respond to changes in water conditions is crucial for understanding global carbon and nutrient cycling. However, it is unclear how decreasing water affects litter mixture interactions for the maize–poplar system in arid regions. Here, the responses of the litter decomposition process and litter mixture interactions in the agroforestry system to changes in water conditions (control, light drought, and moderate drought) were tested. Moderate drought significantly decreased the decomposition rate for poplar leaf and mixed litters, and decomposition rate was significantly reduced for maize straw litter in light and moderate drought stress. The mass loss rates of maize straw and mixed litters were significantly higher than that of the poplar leaf litter under drought conditions, but there was no significant difference among the three litter types in the control. There was no interaction between mass loss of the mixed litter in the control and light drought conditions, and the litter mixture interaction showed nonadditive synergistic interactions under moderate drought. In terms of nutrient release, there was also no interaction between litter mixture with nitrogen and carbon, but there was antagonistic interaction with potassium release under the light drought condition. Our results demonstrate that drought conditions can lead to decreasing decomposition rate and strong changes in the litter mixture interactions from additive effects to nonadditive synergistic effects in moderate drought. Moreover, light drought changed the mixture interaction from an additive effect to an antagonistic interaction for potassium release.     

Limit values for plant litter decomposing in two contrasting soils—influence of litter elemental composition

The decomposition dynamics of four types of needle litter and three types of leaf litter were followed for 3 years at two very contrasting coniferous forest systems, a nutrient-rich silver fir (Abies alba Mill.) forest in south Italy (Monte Taburno) and a nutrient-poor Scots pine (Pinus sylvestris L.) forest in central Sweden (Jädraås). Decomposition of the same litter type at the two sites did not differ in the early stages but proceeded further at the nutrient-rich forest site than at the nutrient-poor one. Limit values for decomposition were calculated and the differences for the same litter type between the two contrasting coniferous systems were investigated. At both sites six of the seven litter types gave significant (asymptotic) limit values for decomposition, which varied with litter type. For four litter types out of six the limit values differed significantly between the two sites and were always higher at the nutrient-rich site (Monte Taburno). Using all available data for litters incubated at the two sites revealed that at the nutrient-poor site (Jädraås) there was a significant negative relationship between litter N levels and limit values and there was also a significant negative relationship between initial concentrations of heavy metals (e.g. Zn, Cd, Cu) and limit values. In contrast, at the site Monte Taburno, rich in nutrients and in heavy metals, there was no such relationship.     

Response of degradative enzymes to N fertilization during litter decomposition in a subtropical forest through a microcosm experiment

With the continuing increase in human activities causing accelerating rates of anthropogenic nitrogen deposition inputs into forests, there is considerable interest in understanding the effects of nitrogen deposition on litter decomposition. Two dominant litters were chosen from Zijin Mountain in China: Quercus acutissima from a broad-leaved forest and Pinus massoniana from a coniferous forest. The litters were incubated in microcosms and treated with a gradient of nitrogen fertilization. During a 6-month incubation, changes in chemical composition (i.e., lignin, total carbohydrate, and nitrogen), litter mass losses, soil pH values, and the activities of degradative enzymes were determined. Results showed that medium-nitrogen and high-nitrogen fertilization significantly accelerated litter decomposition rates of leaves, while only the high-nitrogen fertilization significantly accelerated litter decomposition rates of needles. The results also showed that cellulase and nitrate reductase were primarily responsible for litter decomposition in the broad-leaved forest, while catalase, cellulase, and acid phosphatase were primarily responsible for litter decomposition in the coniferous forest under conditions of no N fertilization; catalase, cellulase, and acid phosphatase were primarily responsible for litter decomposition in the broad-leaved forest, while catalase, cellulase, invertase, and nitrate reductase were primarily responsible for litter decomposition in the coniferous forest under conditions of N fertilization. Nitrogen fertilization-stimulated litter decomposition was due to the fact that the activities of enzymes, particularly cellulase, were accelerated.     

Decomposition and nutrient dynamics in mixed litter of Mediterranean species

In the last decade a great research effort addressed the effects of litter diversity on ecosystem functions, reporting both synergistic and antagonistic effects for decomposition dynamics. Four coexisting Mediterranean species, representing a range of litter quality, were used to arrange litter mixtures at three diversity levels for a litterbag decomposition experiment. Species identity appeared as the major determinant for litter mass loss (Coronilla emerus～Hedera helix>Festuca drymeia>Quercus ilex) and nutrient release, with rates for all leaf litter types following the sequence K>N>Mg≥Ca>>Fe. Additive diversity effects were prevalent pooling together all data but also for nutrients separately. Antagonistic interactions were more common than synergistic in the cases of mass loss, N and Ca contents, but not for K, Mg and Fe dynamics. The number of species in the litterbag significantly affected the outcome of non-additive interactions, which were mostly antagonistic for two-species mixtures, and synergistic for the combined 4 species. Litter quality appears to be the most important factor affecting mass loss and nutrient dynamics, while litter diversity, influencing the rates of these processes, plays an important role in reducing their variability, thus suggesting a greater stability of ecosystems properties in presence of mixed litter.     

Fate of organic carbon during decomposition of different litter types in Japan

Carbon dynamics during litter decomposition have been described in a variety of forest ecosystems and provided insights into carbon flow in soils. To quantitatively assess how decomposition processes vary between litter types, solid-state ¹³C cross-polarization and magic-angle spinning nuclear magnetic resonance (CPMAS NMR) technique was applied to analyze conifer (cedar, cypress) and hardwood (chinquapin, beech, oak, birch) litter which had degraded during a 3 year litterbag experiment throughout Japan. The results were used to identify compositional changes and estimate decomposition constants (k values) in exponential equations. Total litter and carbon type mass losses during decomposition varied significantly between litter types, being affected by the initial physicochemical litter quality. Concomitant increases and decreases in carbonyl and O/N-alkyl C compositions, respectively, were observed for all litter types, but aromatic and aliphatic C dynamics were less consistent. In hardwoods, [aromatic/aliphatic C ratio] was generally stable during decomposition, suggesting that, in hardwoods, the decomposabilities of aromatic and aliphatic C were similar. In the conifers, an increasing [aromatic/aliphatic C ratio] during decomposition suggested that aromatic C was more recalcitrant than aliphatic C. These results suggest that different decomposition processes between litter types might be related to different aromatic and aliphatic C behaviors, as affected by lignin stability and lipid leachability and biosynthesis. Variations in the k values for total litter and carbon types were not obvious between litter types, although the mass loss patterns differed significantly. The k values estimated in this study may contribute to predictions of soil carbon dynamics and the validation of carbon compartment models in forest ecosystems.     

Boreal peat properties link to plant functional traits of ecosystem engineers

Aims

Warming has the potential to alter plant litter mass loss and nutrient release during decomposition. However, a great deal of uncertainty remains concerning how other factors such as litter species or substrate quality might modify the effects of increased temperature on decomposition. Meanwhile, the temperature sensitivity of plant litter decay in tropical and subtropical forest ecosystems remains poorly resolved.

Methods

This study was designed to assess the effects of experimental warming on litter decomposition and nutrient release of two contrasting tree species (Schima superba and Machilus breviflora) by translocating model forest ecosystems from the high-elevation sites to the lower-elevation sites in subtropical China. Translocating model mountain evergreen broad-leaved forest (MEBF) to the altitude of 300 m and 30 m increased the average monthly soil temperature at 5 cm depth by 0.88 and 1.84 °C, respectively during the experimental period. Translocating model coniferous and broad-leaved mixed forest (CBMF) to the altitude of 30 m increased the average monthly soil temperature at 5 cm depth by 0.85 °C.

Results

We found that experimental warming accelerated litter decomposition in both model forest types, and the promoting efficiency was greater when the temperature increased. The litter with high quality (Schima superba) had stronger response to warming than low quality litter (Machilus breviflora). Warming accelerated Na, K, Mg, P, N and Ca release from Schima superba litter, but only simulated Ca release from Machilus breviflora litter. Overall, litter decomposition was controlled by the order: soil temperature > litter quality > soil moisture > litter incubation forest type under experimental warming in the subtropical China.

Conclusion

We conclude that leaf litter decomposition was facilitated by experimental warming in subtropical China. Litter species might modify the effects of increased temperature on litter decomposition; however, forest type has no effect on litter decomposition.

     

Effects of microclimate,litter type,and mesh size on leaf litter decomposition along an elevation gradient in the Wuyi Mountains,China

Litter decomposition is an important ecosystem process regulated by both biotic factors (e.g., decomposers and litter types) and abiotic factors (e.g., temperature and moisture). This study examined the regulatory effects of soil fauna and microclimate on decomposition of two substrates (Castanopsis carlesii and Pinus taiwanensis) along an elevation gradient in four ecosystems of zonal vegetation types in southeastern China: evergreen broadleaf forest (EVB), coniferous forest (COF), dwarf forest (DWF), and alpine meadow (ALM). Our objective was to identify the mechanisms by which microclimate, substrate, and fauna control litter decomposition, especially where variations in ecosystem structure and environment are markedly shown across an elevation gradient. The hypotheses were as follows: (1) litter decomposition within the same litter type would decrease across the elevation gradient, (2) litter decomposition would be lower in poorer nutrient quality substrate across the four sites, and (3) litter dynamics, influenced by strong interactions among ecosystem type, litter type, and decomposers, would vary by elevation gradient due to microclimate effects (i.e., temperature and moisture). The decomposition rates of C. carlesii were significantly higher than those of P. taiwanensis at EVB, COF, and DWF sites; however, they were not significantly different at the ALM site. Low elevation forests possessed a microclimate (warm and humid) that favors decomposer activities and also appeared to possess a decomposer community adapted to consuming large amounts of leaf litter, as indicated by the rapid leaf litter loss. Litter decomposition in micro-mesh bags proceeded more slowly compared to litter in meso-mesh and macro-mesh litterbags across the elevation gradient, indicating that restricting some detritivore access to litter reduced litter mass loss. We suggest that microclimate and faunal contributions to plant litter decomposition differ markedly across the ecosystems in the Wuyi Mountains.     

Endogenous versus exogenous nutrient affects C, N, and P dynamics in decomposing litters in mid-subtropical forests of China

The effect of nutrient availability on litter decomposition has been a major focus of global change ecology. The relative impacts of endogenous (litter) and exogenous (soil) nutrient availability remain unclear. We studied the nutrient dynamics of decomposition in litter from two species with contrasting litter nutrient contents and stoichiometry: Pinus massoniana and Castanopsis sclerophylla. During a 540-day field incubation, we manipulated exogenous nutrient levels by adding microbially available C (+C), N (+N), P (+P), and all three (+CNP) at 90-day intervals. Relative to the no-nutrient control (CK), nutrient additions decreased organic C retention in C. sclerophylla, with the greatest effect observed in +CNP. Nitrogen content in P. massoniana litter similarly increased with nutrient addition, particularly +P and +CNP. The P addition treatments also increased P content in the litter of both species. Nitrogen content in C. sclerophylla and organic C content in P. massoniana were unaffected by nutrient additions. The C/N and C/P ratios in decomposing C. sclerophylla litter were significantly lower in the CK treatment, while those of P. massoniana litter were influenced by the interaction of nutrient addition and decomposition time. Increased availability of C, N, and P individually and collectively alters nutrient release dynamics in decomposing foliar litter. Litter quality, as determined by source species, is a key determinant of the impact of exogenous nutrient inputs. A stronger effect of P addition than N addition indicates a relatively N-rich and P-poor ecosystem.