Home-field advantage accelerates leaf litter decomposition in forests

Several leaf litter decay studies have indicated that decomposition occurs more rapidly when litter is placed beneath the plant species from which it had been derived than beneath a different plant species (i.e. home-field advantage, HFA), although support for this notion has not been universal. We provide the first quantification of HFA in relation to leaf litter decomposition using published litter mass loss data from forest ecosystems in North America, South America, and Europe. Our findings indicate that HFA is widespread in forest ecosystems; on average litter mass loss was 8% faster at home than away. We hypothesize that HFA results from specialization of the soil biotic community in decomposing litter derived from the plant above it. Climate and initial litter quality data can be used to explain about 70% of the variability in litter decomposition at a global scale, leaving about 30% unexplained. We suggest that HFA be recognized as a factor that explains some of this remaining variability.     

Relationships between soil–litter interface enzyme activities and decomposition in <Emphasis Type="Italic">Pinus massoniana</Emphasis> plantations in China

Purpose

Enzyme activities in decomposing litter are directly related to the rate of litter mass loss and have been widely accepted as indicators of changes in belowground processes. Studies of variation in enzyme activities of soil–litter interface and its effects on decomposition are lacking. Evaluating enzyme activities in this layer is important to better understand energy flow and nutrient cycling in forest ecosystems.

Materials and methods

Litter decomposition and the seasonal dynamics of soil–litter enzyme activities were investigated in situ in 20- (younger) and 46-year-old (older) Pinus massoniana stands for 540 days from August 2010 to March 2012 by litterbag method. We measured potential activities of invertase, cellulase, urease, polyphenol oxidase, and peroxidase in litter and the upper mineral soils, and evaluated their relationships with the main environment factors.

Results and discussion

Remaining litter mass was 57.6 % of the initial weights in the younger stands and 61.3 % in the older stands after 540-day decomposition. Levels of enzyme activity were higher in the litter layer than in the soil layer. Soil temperature, litter moisture, and litter nitrogen (N) concentration were the most important factors affecting the enzyme activities. The enzyme activity showed significantly seasonal dynamics in association with the seasonal variations in temperature, water, and decomposition stages. Remaining litter dry mass was found to be significantly linearly correlated with enzyme activities (except for litter peroxidase), which indicates an important role of enzyme activity in the litter decomposition process.

Conclusions

Our results indicated the important effects of biotic (litter N) and abiotic factors (soil temperature and litter moisture) on soil–litter interface enzyme activities. Overall significant linear relationship between remaining dry mass and enzyme activities highlighted the important role of enzyme activity in affecting litter decomposition processes, which will further influence nutrient cycling in forest ecosystems. Our results contributed to the better understanding of the mechanistic link between upper soil–litter extracellular enzyme production and litter decomposition in forest ecosystems.

     

Litter decomposition in primary forest and adjacent fire-disturbed forests in the Gran Sabana,southern Venezuela

Litter decomposition and nutrient dynamic were studied in tall primary forest (TF) and in adjacent slightly fire-affected (MF) and strongly fire-affected (LF) forests of the Gran Sabana, southern Venezuela. The aim of the study was to compare the mass and nutrient loss of litter in undisturbed forest and adjacent fire-disturbed forests growing under the same soil conditions. The results showed no significant differences in the dry-mass reduction among TF, MF, and LF after 1-year of decomposition. At the end of the decomposition period, the mass loss was 31% in TF, 24% in MF, and 25% in LF. With few exceptions, the initial nutrient content of the litter did not show significant differences among the studied forests. The initial litter was poor in nutrients, especially in P, with C/N ratio extremely high, particularly in LF. Both residual P content and C/N ratio were the most effective predictors of dry-mass loss. The general trend in the three studied forests was net N and to less extend P immobilization and release of K, Mg, and Ca. We concluded that during a 1-year period, the decomposition process was similar in undisturbed and adjacent fire-disturbed forests in the Gran Sabana and that the low litter decomposition seems to be mainly controlled by the low chemical quality of the decomposing litter.     

Litter decomposition and nutrient release in relation to atmospheric deposition of S and N in a dry tropical region

Temporal and spatial variations in litterfall, leaf litter decomposition and nutrient release were quantified along an air pollution gradient around an industrial area in a dry tropical region of India. Significant differences were found in litterfall between the sites. Litter decomposition rates also significantly varied among the study sites. Litter decomposition was faster at sites away from the industrial region with coal-fired power plants. The concentrations of N and P increased, whereas that of Ca and SO₄-S decreased in decomposing litter over time. The nutrient release pattern was also modified by atmospheric deposition. Concentrations of SO₂ and NO₂ were negatively correlated with relative mass loss. Turnover time of nutrients, except SO₄-S in decomposing litter was maximal at the site receiving highest atmospheric depositions. The study documents that industrial emissions significantly modified nutrient cycling in adjacent terrestrial ecosystems.     

Nitrogen addition enhances home-field advantage during litter decomposition in subtropical forest plantations

Nitrogen (N) exerts strong effects on litter decomposition through altering microbial abundance and community composition. However, the effect of N addition on plant–soil interactions such as home-field advantage (HFA: enhanced decomposition at a home environment compared to a guest environment) in relation to litter decomposition remains unclear. To fill this knowledge gap, we conducted a reciprocal litter transplant plus N addition experiment in Mytilaria laosensis and Cunninghamia lanceolata plantations for two years in subtropical China where anthropogenic N input is amongst the highest in the world. We found positive HFA effects (in which the calculation incorporates litter of both species) with litter mass loss 11.2% faster at home than in the guest environment in the N addition (50 kg N ha⁻¹ yr⁻¹) treatment, but no significant HFA effects were found in the control treatment. The magnitude of the HFA effect on carbon (C) release increased with N addition, while that on N release decreased. The HFA effects on phosphorus, potassium, calcium, sodium, and magnesium release were positive overall, but varied through time and the magnitude of the effects were different among elements. The greater HFA effects in the N addition treatment were associated with greater differences in microbial biomass and community composition between home and guest environments than in the control treatment. Our results indicate that anthropogenic N enrichment could lead to enhanced HFA effects, through modification of microbial communities, and thereby affect C sequestration and N cycling in subtropical forests.     

森林凋落物分解研究进展

 森林凋落物分解是森林生态系统养分生物循环的重要环节,而分解过程中所释放的CO2是全球碳素收支的重要组分,开展森林凋落物分解研究是充分认识森林生态系统结构和功能的基础。研究认为:凋落物分解的预测指标可分为3类,即环境指标(如实际蒸散量)、凋落物物理质量(如叶抗张强度)和化学质量指标(如C/N比、木质素/N比和C/P比等);凋落物分解过程中养分释放机制极其复杂,养分动态模式主要有淋溶—释放、淋溶—富集—释放和富集—释放3种,并因凋落物种类、分解阶段和元素本身性质的不同而异;凋落物混合分解并非单一树种分解的简单叠加,因树种组成和比例不同,基质的化学组成会发生变化,从而影响分解者的多样性、丰富度和生理活性,进而直接和间接地影响其分解速率;凋落物混合分解中可能存在无效应、促进效应和抑制效应;现有的研究结果显示,凋落物混合分解的适宜比例应与群落中不同树种的种群比例相一致;CO2浓度升高不仅影响凋落物的化学性质,而且与分解环境中土壤的生物活性密切相关,但CO2浓度升高并不改变凋落物质量与分解速率之间的关系;越来越多的研究显示,CO2浓度升高的环境下,植物群落的物种组成会产生变化,这种变化对养分循环速率的影响远大于单纯大气CO2浓度变化的影响。     

川西3种亚高山针叶林的养分和凋落物格局分析

Investigations were conducted to quantify litterfall, and litter and nutrient accumulation in forest floor, and to acquire information on litter decomposition and nitrogen and phosphorus release patterns in three different subalpine coniferous forests, a plantation （P1）, a secondary forest （SF）, and a primitive forest （PF）, in western Sichuan, China. The litter trap method was used to evaluate litterfall with the litterbag method being utilized for litter decomposition. Seasonal patterns of litterfall were similar in the three forests, with two peaks occurring in September-November and March-May. The plantation revealed an annual litterfall of 4.38 x 103 kg ha-1, which was similar to those of SF and PF, but P1 had a lower mass loss rate and a higher C/N ratio. The C/N ratio may be a sound predictor for the decomposition differences. N concentrations of leaf litter in both the secondary forest and primitive forest increased first and then decreased, and the percentages of their final/initial values were 108.9% and 99.9%, respectively. P concentration in the three forests increased by the end of the study. The results of litterfall and decomposition indicated that in the plantation the potential to provide nutrients for soil organic matter was similar to those of SF and PF; however, its slower decomposition rate could result in a somewhat transient accumulation of litter in the forest floor.     

不同氮源对三倍体毛白杨落叶分解的影响

为探索加快毛白杨落叶分解的途径, 采取室内培养的方法研究了添加铵态氮、硝态氮及混合氮对三倍体毛白杨落叶分解速度和主要营养元素释放的影响。结果表明, 添加氮源对三倍体毛白杨落叶分解有一定的促进作用, 不同氮源之间差异显著。140 d后, 施加铵态氮、混合氮和硝态氮的落叶分解率分别为46.0%、30.0%和28.8%, 而对照为27.4%, 处理间差异显著; Olson指数方程拟合结果表明,施加铵态氮、混合氮和硝态氮后落叶分解50%和95%所需时间分别为175 d、316 d、301 d和781 d、1 238 d、1 627 d,比对照分别缩短49.7%、9.2%、13.5%和52.0%、23.9%、14.1%。同时, 添加氮源后对落叶中N、P、K元素的释放影响有所不同, 其中对K元素的释放基本没有产生影响, 随着分解的进行, 不同处理落叶中K元素浓度逐渐降低。但添加氮源对N、P元素的释放产生了显著影响, 与对照相比, 添加氮源缩短了N、P释放的富集时间, 降低了富集的幅度;N、P的富集时间均从对照的21 d缩短到处理的7 d; N的富集幅度从对照为初始浓度的1.94倍降低到处理为初始浓度的1.32~1.56倍, P的富集幅度从对照为初始浓度的2.98倍降低到处理为初始浓度的1.70~2.26倍。因此添加氮源加快了落叶的分解速度,促进了落叶中N、P的释放, 有利于加快养分循环, 提高立地生产力。     

Decomposition and nutrient content of litter in a fertilized eucalypt forest

The decomposition and nutrient content of litter was studied for 2 years in regrowth Eucalyptus diversicolor forest to which N (0, 200 kg ha^-1 year^-1) and P (0, 30, 200 kg ha^-1) had been applied. The P addition increased, and the N addition decreased, the rate of dry weight loss of decomposing litter. Analysis of the coefficients of a double exponential decay model with components describing the release of labile and resistant fractions indicated that decomposition of the resistant component of litter was most affected by the fertilizer additions. Treatment with N reduced the rate of loss of this component and increased its half-life by approximately 30%, whereas P treatment increased its rate of decay and decreased its half-life by approximately 30%. P accumulated in litter during decomposition. P uptake and retention was greater in P-treated than untreated plots. The application of N reduced P accumulation in litter. An accumulation of N also occurred during decomposition, the amount of N imported into litter being greater on plots treated with N fertilizer. Treatment with N affected the amount of S in decomposing litter. Litter on N-treated plots either accumulated more S or released it more slowly than litter on plots not treated with N. The application of N as NH₄NO₃ decreased forest-floor litter pH, increased litter layer mass (by 15%), and increased the amount of N (by 34%) and S (by 32%) stored in the forest floor. Treatment with P reduced the amount of N (by 22%) stored in the litter layer. The application of 200 kg P ha^-1 in the absence of N increased the store of P in the litter layer by 80%, but when N and P were applied together the amount of P in the litter was not significantly different between P treatments.     

Dominant effects of litter substrate quality on the difference between leaf and root decomposition process above- and belowground

Initial decomposition rates, changes in organic chemical components (acid-insoluble fraction, holocellulose, polyphenols, soluble carbohydrates) and nutrient dynamics (K, Mg, Ca, P, N) were examined for fine roots and leaves of Japanese cypress (Chamaecyparis obtusa). Litterbag experiments designed to evaluate the relative effects of litter type and position of litter supply in the soil were carried out, considering that root and leaf litter typically occupy different locations and have different substrate qualities. Litterbags of roots and leaves were placed at two positions (on the soil surface and in the humus layer), and collected every 3 months over one year. The mass loss rate and N release were slower during root decomposition in the humus layer than during leaf decomposition on the soil surface. These differences between root and leaf decomposition were mainly caused by the litter type, and the effect of the position on decomposition was relatively small. Root litter was less influenced by position related effects, such as differences in humidity, than leaf litter, and this recalcitrant trait to environmental effects may be responsible for the slower mass loss rate and N release in root decomposition. The results of the present study suggest that fine roots are persistent in the soil and serve an important role in N retention in forest ecosystems because of their litter substrate quality.     

Moss and lichen decomposition in old-growth and harvested high-boreal forests estimated using the litterbag and minicontainer methods

Bryophytes and lichen are important components of many boreal forest ecosystems, making the quantification of moss and lichen decomposition rates critical to understanding the C cycle of these forests. Cryptogam decomposition has been predominantly studied in wetlands, while few studies exist for forest-habitat mosses and even fewer for foliose ground lichen. We used a) the litterbag and b) the minicontainer (MC) method to quantify the decomposition rates of i) feathermoss, ii) forest peatmoss, iii) foliose ground lichen, and iv) alder leaves (reference litter) in cool, wet high-boreal Labrador black spruce forests. A total of 1560 litter samples (360 litterbags, 1200 MCs) were incubated for two years in six forest stands of different disturbance origin: three old-growth stands of wildfire origin, and three recently clearcut stands. Litter samples were retrieved after 6.5, 13, 47, 57 and 109 weeks of field incubation, and analysed for mass loss, C, N, nutrient, and fibre content.While clearcut harvesting had no significant effect on litter decomposition at all, decomposition rates significantly differed between litter types, with residual mass increasing in the order alder ≤ lichen < feathermoss ≤ peatmoss. Compared to wetlands, forest moss litter was more labile in the studied forest types, with lichen producing especially fast-decomposing litter. Litter type was a better predictor of decomposition rates than individual chemical parameters, indicating that, even in extreme climates like in Labrador, substrate quality is more important in determining decomposition rates than environmental factors. For all litter types, decomposition models accounting for the seasonality of decay dynamics performed better than models assuming constant or continuously decreasing decay rates. Compared to the litter bag method, which yielded decomposition rates comparable to previous studies, the MC method overestimated decomposition rates for alder and lichen due to fragmentation artefacts. The small sample size of the MC method therefore outweighs its statistical advantages arising from ease of replication. In order to derive reliable estimates of litter decomposition, both the field incubation method and the applied decomposition model must therefore be selected to suit the studied litter types.     

茂兰喀斯特森林自然保护区凋落叶分解动态

[目的]研究喀斯特森林生态系统凋落叶分解特征,为喀斯特森林区石漠化防治及水土保持提供科学依据。[方法]采用1 mm网孔孔径分解袋,对茂兰喀斯特森林自然保护区不同树种凋落叶(落叶和常绿叶)在不同坡位的分解状况进行为期18个月的观测研究。研究茂兰喀斯特森林自然保护区凋落叶失重率和干重残留率动态变化、分解速率及养分释放特征。[结果]凋落叶分解过程呈现"快—慢—快"的周期变化,春夏季分解速度快于秋冬季,落叶树种凋落叶分解速度快于常绿树种凋落叶,不同坡位凋落叶的分解速度表现为:下坡中坡上坡。利用Olson模型对凋落叶分解50%和95%所需时间进行估测,发现落叶树种凋落叶分解50%和95%所需时间分别为0.95～1.66 a和4.13～7.19 a,常绿树种凋落叶分解50%和95%所需时间分别为1.14～1.69 a和4.92～7.30 a,二者无显著性差异。凋落叶分解速率低于中亚热带东部常绿阔叶林和常绿落叶阔叶混交林,但比同区域喀斯特次生林与人工林高。落叶树种凋落叶和常绿树种凋落叶的N元素释放模式为富集—释放模式,C含量随分解时间的波动差异显著,总体在不断减少,而C/N比呈逐步下降的趋势。[结论]由于不同树种凋落叶初始养分含量和叶片理化结构的差异,落叶比常绿叶具有更快的分解速率和养分释放速率,对促进喀斯特森林生态系统物质循环起着积极作用。     

Leaf litter fall and litter decomposition under Eucalyptus and coniferous plantations in Gambo District,southern Ethiopia

Abstract

Litter fall and its decomposition rate play an important role in nutrient recycling, carbon budgeting and in sustaining soil productivity. Litter production and the decomposition rate were studied on commonly planted broad-leaved Eucalyptus (Eucalyptus globulus, Eucalyptus camaldulensis, Eucalyptus saligna) and coniferous (Juniperus procera, Cupressus lusitanica, Pinus patula) plantation species and compared with the adjacent broad-leaved natural forest. The production of litter was recorded by litter traps and the decomposition rate was studied by nylon net bag technique. Litter production under broad-leaved plantation species and natural forest (that varied from 9.7 to 12.6 Mg ha^?1 y^?1) was significantly higher (p<0.05) than that under coniferous species (that varied from 4.9 to 6.6 Mg ha^?1 y^?1). The average concentration of C and N in fresh mature leaves was higher than in leaf-litter fall, implying that both C and N were either sorbed in the plant system or lost through decomposition, leaching or erosion during the leaf-litter fall period. The amount of N, which potentially returned to the soil through the leaf-litter fall, tended to be higher in natural forest than in Eucalyptus plantations. The residual litter mass in the litter bag declined with time for all species. The annual dry matter decay constant (k) varied from 0.07 m^?1 in Pinus patula to 0.12 m^?1 in Eucalyptus saligna. The half-time (t_0.5) decay varied from 6.0 for Eucalyptus saligna to 9.7 months for Pinus patula. The results suggest that the decomposition rate in Pinus patula was relatively lower than the other species and the litter production under broad-leaved Eucalyptus was comparatively higher than that in coniferous species. Overall the litter decomposition was fast for all species. The higher litter production and its relative faster rate of decomposition is a positive aspect to be considered during species selection for the restoration of degraded habitats given other judicious management practices such as prolonging the rotation period are adhered to.     

中国亚热带两种竹林凋落物输入量、凋落物分解和养分释放动态

Bamboos are one of the fast-growing and multiple use species in the world, and thus bamboo forests/plantations play an important role in C sequestration at regional and global levels. We studied aboveground litterfall, litter decomposition and nutrient dynamics for two years in two subtropical bamboo ecosystems in Southwest China so as to test the hypothesis that litter quality determine the rate and nutrient dynamics during decomposition of different litter fractions. Mean annual total aboveground litter production ranged from 494 to 434 g m-2 in two bamboo stands （P stand, dominated by Pleioblastus amarus and H stand, hybrid bamboo dominated by Bambusa pervariabilis x Dendrocalamopsis daii）. Bulk （-80%） of litter production was contributed by leaf litter in two stands followed by twigs and sheathes. Different litter fractions represented considerable variations in the rates of mass loss and nutrient release. Variation of the mass remaining after 2 years of decomposition was significantly explained by initial C/N ratio and initial P concentration. Initial concentrations of N, P, Ca, and Mg explained 57.9%, 95.0%, 99.8% and 98.1%, respectively, of the variations of these elements mass remaining after 2 years of decomposition. The patterns of nutrient dynamics and the final amount remaining were mainly determined by their initial litter substrate quality in tl~ese two subtropical bamboo plantations.     

Amounts and degradability of dissolved organic carbon from foliar litter at different decomposition stages

Litter is one of the main sources of dissolved organic carbon (DOC) in forest soils and litter decomposition is an important control of carbon storage and DOC dynamics. The aim of our study was to evaluate (i) effects of tree species on DOC production and (ii) relationships between litter decomposition and the amount and quality of DOC. Five different types of leaves and needles were exposed in litterbags at two neighboring forest sites. Within 12 months we sampled the litterbags five times and leached aliquots of field moist litter in the laboratory. In the collected litter percolates we measured DOC concentrations and recorded UV and fluorescence spectra in order to estimate the aromaticity and complexity of the organic molecules. Furthermore, we investigated the biodegradability of DOC from fresh and decomposed litter during 6 weeks incubations. Fresh sycamore maple litter released the largest amounts of DOC reaching about 6.2% of litter C after applying precipitation of 94 mm. We leached 3.9, 1.6, 1.0 and 3.3% carbon from fresh mountain ash, beech, spruce and pine litter, respectively. In the initial phase of litter decomposition significantly decreasing DOC amounts were released with increasing litter mass loss. However, after mass loss exceeds 20% DOC production from needle litter tended to increase. UV and fluorescence spectra of percolates from pine and spruce litter indicated an increasing degree of aromaticity and complexity with increasing mass loss as often described for decomposing litter. However, for deciduous litter the relationship was less obvious. We assume that during litter decomposition the source of produced DOC in coniferous litter tended toward a larger contribution from lignin-derived compounds. Biodegradability of DOC from fresh litter was very high, ranging from 30 to 95% mineralized C. DOC from degraded litter was on average 34% less mineralizable than DOC from fresh litter. Taking into account the large DOC production from decomposed needles we can assume there is an important role for DOC in the accumulation of organic matter in soils during litter decomposition particularly in coniferous forests.     

The effect of temperature on decomposition of leaf litter from two tropical forests by a microcosm experiment

A 120 days’ incubation experiment was conducted to analyze the effect of temperature on the decomposition of leaf litter (Altingia obovata) in two tropical primary montane rainforests with different precipitation conditions. The results showed no difference in mass loss of leaf litter between the two forests at 20 °C, in spite that Jianfengling forest had less precipitation than Diaoluoshan forest. But higher mass loss of leaf litter was found from Jianfengling forest site (30.1%) than that from Diaoluoshan forest site (25.9%) at 30 °C at the end of incubation. Lignin exhibited higher mass loss from Jianfengling forest (29.9%) than from Diaoluoshan forest (23.3%) at 20 °C, but no difference between two forest sites at 30 °C. Total carbohydrates were decomposed faster by the decomposers from Diaoluoshan forest site (42.7%) than that from Jianfengling forest site (36.3%) at 20 °C, but 46.6% and 38.5% for Jianfengling and Diaoluoshan montane rainforests, respectively, at 30 °C. Temperature increase did not significantly lead to the difference in mass loss of leaf litter for the two forest sites. Temperature increase did not affect lignin loss for Diaoluoshan forest, but reduced lignin loss for Jianfengling forest. Temperature increase accelerated the decomposition of carbohydrate for Jianfengling forest, but opposite for Diaoluoshan forest. The response of decomposition of leaf litter to forest type and temperature was positively related to the difference in microbial activities between both montane rainforests.     

Carbon and nitrogen turnover in response to warming and nitrogen addition during early stages of forest litter decomposition—an incubation experiment

Purpose

Little is known about the interactive effects of temperature, nitrogen (N) supply, litter quality, and decomposition time on the turnover of carbon (C) and N of forest litter. The objective of this study was to investigate the interactive effects of warming, N addition and tree species on the turnover of C and N during the early decomposition stage of litters in a temperate forest.

Materials and methods

A 12-week laboratory incubation experiment was carried out. The leaf litters including two types of broadleaf litters (Quercus mongolica and Tilia amurensis), a needle litter (Pinus koraiensis), and a mixed litter of them were collected from a broad-leaved Korean pine mixed forest ecosystem in northeastern China in September 2009. Nine treatments were conducted using three temperatures (15, 25, and 35 °C) combined with three doses of N addition (equal to 0, 75, and 150 kg?·?ha^?1?a^?1, respectively, as NH₄NO₃).

Results and discussion

After 12 weeks of incubation, the mass loss ranged between 12 and 35 %. The broadleaf litters had greater mass loss and cumulative CO₂–C emission than the needle litter. Temperature and N availability interacted to affect litter mass loss and decomposition rate. The dissolved organic carbon (DOC) and nitrogen (DON) concentrations in litter leachate varied widely with litter types. DOC increased significantly with increased temperature but decreased significantly with increased N availability. DON increased significantly with increased N availability but showed a higher level at the moderate decomposition temperature. The amounts of CO₂ and N₂O emission were significantly higher at 25 °C than those at 15 and 35 °C, and were significantly increased by the N addition.

Conclusions

The present study indicated relatively intricate temperature and N addition effects on C and N cycling during early stages of litter decomposition, implying that future increases in temperature and N deposition will directly affect C and N cycling in broad-leaved Korean pine mixed forest ecosystem, and may indirectly influence the ecosystem composition, productivity, and functioning in NE China. It is, therefore, important to understand the interactive effects of biotic and abiotic factors on litter decomposition in field conditions in order to assess and predict future ecosystem responses to environmental changes in NE China.     

Effects of High Nonexchangeable Aluminum on Decomposition and Nutrient Release from Chestnut Leaves

The effect of high nonexchangeable aluminum of a Cryptopodzolic soil derived from mica schist on decomposition and nutrient release from chestnut (Castanea sativa) leaf litter was studied in southern Switzerland using the litter bag technique. Variables studied were time (18 months), exposure (NW versus SE), and profile position of litter (L, O_f and A_h horizons). A site with a Haplumbrept (Al-poor) derived from cherty limestone provided a parent material contrast. Litter decay was chiefly controlled by microclimatic of sites rather than parent material. Litter decay differed between NW- and SE-exposed sites for L and O_f horizons. After 18 months, initial dry matter remaining in L, O_f and A_h positions was 58, 34 and 18%, respectively. All factors equal, the mobility series for nutrient release was K>Mg>Ca>P>N, but site and litter position affected element release. Only K and Mg were lost more rapidly than dry matter. Because dry matter and nutrient loss were similar for Al-rich and Al-poor sites, we conclude that Al content of soils had no influence on decomposition.     

Photoacceleration of plant litter decomposition in an arid environment

In arid ecosystems, abiotic processes facilitate the physical and chemical degradation of plant litter to the extent that decomposition models that use climatic and litter composition variables as surrogates for microbial activity are not predictive. The purpose of this study was to estimate the potential contribution of photodegradation to the decomposition of plant litters that varies in architecture and chemical composition. Litter of Pinus edulis, Juniperus monosperma and Populus deltoides were exposed to ambient and attenuated sunlight, with and without supplemental water additions, at a riparian forest site along the Middle Rio Grande (New Mexico, USA). Mass loss, elemental composition, and microbial extracellular enzyme activities (EEA) were measured over 639 days. The composition of the fungal communities associated with the decomposing litters was compared by analyses of fungal ITS nrDNA sequences. Litter exposed to ambient sunlight had greater mass loss rates than shaded litter, independent of the water treatment: Populus increased by 100%, Pinus by 86% and Juniperus by 46%. The increases were proportional to exposed litter surface area per g dry mass. EEA potentials, particularly oxidative activities, were low in comparison to those measured in mesic ecosystems. For Populus litter, the principal driver of photoacceleration appeared to be photodegradation of cellulose; for Pinus, it was photodegradation of polyphenols; for Juniperus accelerated mass loss was associated with photodegradation of both polysaccharides and polyphenols. Fungal community composition varied by litter type, but the dominant colonizers were yeasts and dark-septate hyphal taxa; a finding consistent with the low enzymatic oxidation potential. This study shows that photochemical oxidation can supplement enzymatic oxidation and increase decomposition rates. As a result, organic matter decomposition in arid ecosystems is not restricted to periods of high moisture availability as is plant production. This decoupling may partly account for the low soil organic matter content of these ecosystems.     

Non-additive effects vary with the number of component residues and their mixing proportions during residue mixture decomposition: A microcosm study

Poplar leaf litter and crop residues (leaves and stems) of two main crops (soybean and maize) collected from semiarid agroforestry systems of Northeast China were used in our microcosm study. The aims were to examine whether non-additive effects (synergistic or antagonistic) between poplar leaf litter and crop residues exist during decomposition and to identify the influence of residue mixing proportion on the incidence of non-additive effects of residue mixture for the same plant residues. We determined residue decomposition rate by measuring mass loss and N release. Synergistic effects between poplar leaf litter and crop residues were more common than additive effects in terms of mass loss and N release. Moreover, the interactive effects between tree leaf litter and crop residues on decomposition varied with the number of component residues and their mixing proportion. Three-residue mixtures produced synergistic effects on mass loss and N release, although two-residue mixtures showed an additive effect in some cases. In addition, as compared with equal proportion, mixing residues with unequal proportion increased the incidence of non-additive effects during decomposition of residue mixture. These findings highlight that residue decomposition dynamics in ecosystems should be assessed on the basis of plant residue mixtures and their mixing proportions, which may help us better understand nutrient dynamics and guide our decisions on nutrient management.