Early stage litter decomposition rates for Swiss forests

The decomposition of belowground and aboveground tree litter was studied on five forest sites across Switzerland, ranging from 480 to 1500 m in altitude, and including calcareous and acidic soils. In addition to decomposition of local litter types (Picea abies, Fagus sylvatica, Castanea sativa), the decomposition of a standard beech litter was studied on all sites. After 2 years of decomposition, mass loss ranged from 18 to 71% across the different sites and litter types. The lowest decomposition rates were observed for beech roots, while mass loss was greatest for both spruce needles and spruce roots at the low-altitude site. Mass loss during the first winter correlated best with the content of water-soluble substances. After 1 year of incubation, mass loss of the standard litter varied less than did mass loss of local litter, but variance increased during the second year for aboveground litter. These observations indicate a smaller climatic influence on litter breakdown at the beginning of the decomposition process. Litter mass loss could be described using an exponential model with a decay constant depending on either lignin/N ratio or Mn content of the litter and annual soil temperature and throughfall precipitation as climatic variables. Modelling the observed mass loss indicated a strong influence of litter quality in the first 2 years of decomposition, confirming the field data from the standard litter experiment. The experiment will continue for some years and is expected to yield additional data on long-term decomposition.     

Fine root decomposition rates do not mirror those of leaf litter among temperate tree species

Elucidating the function of and patterns among plant traits above ground has been a major research focus, while the patterns and functioning of belowground traits remain less well understood. Even less well known is whether species differences in leaf traits and their associated biogeochemical effects are mirrored by differences in root traits and their effects. We studied fine root decomposition and N dynamics in a common garden study of 11 temperate European and North American tree species (Abies alba, Acer platanoides, Acer pseudoplatanus, Carpinus betulus, Fagus sylvatica, Larix decidua, Picea abies, Pseudotsuga menziesii, Quercus robur, Quercus rubra and Tilia cordata) to determine whether leaf litter and fine root decomposition rates are correlated across species as well as which species traits influence microbial decomposition above versus below ground. Decomposition and N immobilization rates of fine roots were unrelated to those of leaf litter across species. The lack of correspondence of above- and belowground processes arose partly because the tissue traits that influenced decomposition and detritus N dynamics different for roots versus leaves, and partly because influential traits were unrelated between roots and leaves across species. For example, while high hemicellulose concentrations and thinner roots were associated with more rapid decomposition below ground, low lignin and high Ca concentrations were associated with rapid aboveground leaf decomposition. Our study suggests that among these temperate trees, species effects on C and N dynamics in decomposing fine roots and leaf litter may not reinforce each other. Thus, species differences in rates of microbially mediated decomposition may not be as large as they would be if above- and belowground processes were working in similar directions (i.e., if faster decomposition above ground corresponded to faster decomposition below ground). Our results imply that studies that focus solely on aboveground traits may obscure some of the important mechanisms by which plant species influence ecosystem processes.     

Controls on long-term root and leaf litter decomposition in neotropical forests

Litter decomposition represents one of the largest annual fluxes of carbon (C) from terrestrial ecosystems, particularly for tropical forests, which are generally characterized by high net primary productivity and litter turnover. We used data from the Long-Term Intersite Decomposition Experiment (LIDET) to (1) determine the relative importance of climate and litter quality as predictors of decomposition rates, (2) compare patterns in root and leaf litter decomposition, (3) identify controls on net nitrogen (N) release during decay, and (4) compare LIDET rates with native species studies across five bioclimatically diverse neotropical forests. Leaf and root litter decomposed fastest in the lower montane rain and moist forests and slowest in the seasonally dry forest. The single best predictor of leaf litter decomposition was the climate decomposition index (CDI), explaining 51% of the variability across all sites. The strongest models for predicting leaf decomposition combined climate and litter chemistry, and included CDI and lignin ( R ²=0.69), or CDI, N and nonpolar extractives ( R ²=0.69). While we found no significant differences in decomposition rates between leaf and root litter, drivers of decomposition differed for the two tissue types. Initial stages of decomposition, determined as the time to 50% mass remaining, were driven primarily by precipitation for leaf litter ( R ²=0.93) and by temperature for root litter ( R ²=0.86). The rate of N release from leaf litter was positively correlated with initial N concentrations; net N immobilization increased with decreasing initial N concentrations. This study demonstrates that decomposition is sensitive to climate within and across tropical forests. Our results suggest that climate change and increasing N deposition in tropical forests are likely to result in significant changes to decomposition rates in this biome.     

中国森林和草地凋落物现存量的空间分布格局及其控制因素

凋落物是陆地生态系统的重要组成部分,它对生态系统的养分循环非常重要。凋落物现存量是凋落物输入量与分解量的净累积量,理论上影响凋落物输入过程和分解过程的因素都会对凋落物现存量产生重要影响。目前,我国科学家对部分区域典型陆地生态系统凋落物现存量及其影响因素进行了探讨,但迄今为止,全国尺度下的关于凋落物现存量评估的结果还未见报道。因此,如何准确地评估凋落物现存量对揭示生态系统应对全球变化具有重要意义。收集了2000—2014年公开发表文献中的森林和草地凋落物现存量数据(共1864个样点),并结合气候、土壤和地上生产力探讨了中国森林和草地凋落物现存量的空间格局及其主要控制因素,此外,还利用森林和草地凋落物的碳氮含量,结合凋落物现存量估算了不同区域和全国尺度的凋落物的碳氮贮量。分析结果表明:中国森林和草地的凋落物现存量存在较弱的经度和纬度格局,然而按照不同经度和纬度间隔整理数据后凋落物现存量表现出显著的空间分布格局。森林的凋落物现存量表现为随着经度和纬度的增加而逐渐增加,主要控制因素为温度。草地的凋落物现存量表现为随着经度的增加而逐渐升高,其主要影响因素为降水。森林和草地凋落物现存量在局部(或区域内)存在非常大的变异,这是造成其大尺度格局较弱的重要原因。结合1∶100万中国植被图的森林和草地面积数据,估算出中国森林的凋落物现存量约为1135.56 Tg,其碳氮贮量约为517.93 Tg C和15.33 Tg N;此外,中国草地的凋落物现存量约为119.63 Tg,其碳氮贮量分别为47.11 Tg C和1.59 Tg N。首次尝试对全国尺度森林和草地凋落物现存量及其碳氮贮量进行估算,其研究结论有助于揭示凋落物在碳氮循环中的重要作用,并可为准确评估中国陆地生态系统碳氮贮量提供重要参考。     

Soil depth- and root diameter-related variations affect root decomposition in temperate pine and oak forests

Aims Assessment of factors regulating root decomposition is needed to understand carbon and nutrient cycling in forest ecosystems. The objective of this study is to examine the effects of soil depth and root diameter on root decomposition and to analyze the relationship of root decomposition with factors such as soil environmental conditions and initial litter quality.     

Leaf litter decomposition rates in degraded and fragmented tropical rain forests of Borneo

Previously extensive tracts of primary rain forest have been degraded by human activities, and we examined how the effects of forest disturbance arising from habitat fragmentation and commercial selective logging affected ecosystem functioning in these habitats by studying leaf litter decomposition rates in litter bags placed on the forest floor. The rain forests of Borneo are dominated by trees from the family Dipterocarpaceae, and we compared leaf litter decomposition rates of three dipterocarp species at eight forest fragment sites (area 3–3529 ha) that had different histories of disturbance pre‐fragmentation: four fragments had been selectively logged prior to fragmentation and four had been formed from previously undisturbed forest. We compared these logged and unlogged forest fragments with sites in continuous forest that had been selectively logged (two sites) and fully protected and undisturbed (two sites). After 120 d, undisturbed continuous forest sites had the fastest rates of decomposition (52% mass loss). Forest fragments formed from unlogged forest (32% mass loss) had faster decomposition rates than logged forest fragments (28% mass loss), but slower rates than continuous logged forest (39% mass loss). Leaves of a light‐demanding species (Parashorea malaanonan) decomposed faster than those of a shade‐tolerant species (Hopea nervosa), but decomposition of all three dipterocarp species that we studied responded similarly to logging and fragmentation effects. Reduced decomposition rates in logged and fragmented forest sites may affect nutrient cycling and thus have detrimental consequences for forest regeneration. Conservation management to improve forest quality should be a priority, particularly in logged forest fragments.     

Correlation between leaf litter and fine root decomposition among subtropical tree species

Sampling disturbance has been shown to rapidly increase net nitrification rates in some forest soils. To gain insight on mechanisms, we investigated both gross and net rates of ammonification and nitrification in intact cores and mixed composite samples. Using the isotope pool dilution method, we studied samples from two northeastern USA watersheds, Brush Brook and Sleepers River in Vermont, where previous work had found high net nitrification rates. Gross ammonification was usually not significantly different between intact cores and mixed samples. However, gross and net nitrification rates in mixed samples were similar (mean ～24?µmol N?kg^?1?hr^?1 or ～8 mg N kg^?1 d^?1) and significantly higher than in intact cores (7.7 and 3.4?µmol N kg^?1?h^?1 for means of gross and net respectively). Nitrate consumption was decreased somewhat by disturbance but did not account for the large differences in net rates. Because there were similar gross ammonification rates in both treatments, increased nitrification in these disturbed soils must be a result of an increase in the utilization of ammonium by the ammonia oxidizers at the expense of other ammonium consumption pathways. Different mechanisms may operate in different soils; increased nitrification appears to be the primary pathway in these soils with high N cycling rates.     

No evidence of spatial root system segregation and elevated fine root biomass in multi-species temperate broad-leaved forests

Differences in spatial rooting patterns among coexisting species have been recognized as an important mechanism for generating biodiversity effects on ecosystem functioning. However, it is not yet clear whether complementarity in root space exploration is a universal characteristic of multi-species woody communities. In a temperate broad-leaved forest with a mosaic of species-poor and species-rich stands, we tested two hypotheses related to putative below-ground ‘overyielding’ in more diverse forests, (1) that species mixture results in a partial spatial segregation of the fine root systems of different species, and (2) that stand fine root biomass increases with tree species diversity. We investigated 12 stands either with one, three, or five dominant tree species (4 replicate stands each) under similar soil and climate conditions for stand fine root biomass and spatial root segregation in vertical and horizontal direction in the soil. Fine roots of different tree species were identified using a morphological key based on differences in colour, periderm surface structure, and branching patterns. In species-poor and species-rich stands, and in all tree species present, fine root density (biomass per soil volume) decreased exponentially with soil depth at very similar rates. Stand fine root biomass in the densely rooted upper soil (0–40 cm depth) was not significantly different between stands with 1, 3 or 5 dominant tree species. We conclude that ‘below-ground overyielding’ in terms of higher fine root biomasses in species-rich stands as compared to monospecific ones does not occur in these broad-leaved forests which most likely results from a missing complementarity in vertical rooting patterns of the present tree species.     

Plant presence reduces root and shoot litter decomposition rates of crops and wild relatives

Plant and Soil - Cerrado woody species are divided into a small group of aluminum (Al)-accumulating species and the rest of the woody species. Both groups grow well on acidic and Al-rich soils. We...     

Decomposition and nitrogen dynamics of 15N-labeled leaf, root, and twig litter in temperate coniferous forests

Litter nutrient dynamics contribute significantly to biogeochemical cycling in forest ecosystems. We examined how site environment and initial substrate quality influence decomposition and nitrogen (N) dynamics of multiple litter types. A 2.5-year decomposition study was installed in the Oregon Coast Range and West Cascades using ¹⁵N-labeled litter from Acer macrophyllum, Picea sitchensis, and Pseudotsuga menziesii. Mass loss for leaf litter was similar between the two sites, while root and twig litter exhibited greater mass loss in the Coast Range. Mass loss was greatest from leaves and roots, and species differences in mass loss were more prominent in the Coast Range. All litter types and species mineralized N early in the decomposition process; only A. macrophyllum leaves exhibited a net N immobilization phase. There were no site differences with respect to litter N dynamics despite differences in site N availability, and litter N mineralization patterns were species-specific. For multiple litter × species combinations, the difference between gross and net N mineralization was significant, and gross mineralization was 7–20 % greater than net mineralization. The mineralization results suggest that initial litter chemistry may be an important driver of litter N dynamics. Our study demonstrates that greater amounts of N are cycling through these systems than may be quantified by only measuring net mineralization and challenges current leaf-based biogeochemical theory regarding patterns of N immobilization and mineralization.     

Litter decomposition rates in Canadian forests

The effect of litter quality and climate on the rate of decomposition of plant tissues was examined by the measurement of mass remaining after 3 years’ exposure of 11 litter types placed at 18 forest sites across Canada. Amongst sites, mass remaining was strongly related to mean annual temperature and precipitation and amongst litter types the ratio of Klason lignin to nitrogen in the initial tissue was the most important litter quality variable. When combined into a multiple regression, mean annual temperature, mean annual precipitation and Klason lignin:nitrogen ratio explained 73% of the variance in mass remaining for all sites and tissues. Using three doubled CO₂ GCM climate change scenarios for four Canadian regions, these relationships were used to predict increases in decomposition rate of 4–7% of contemporary rates (based on mass remaining after 3 years), because of increased temperature and precipitation. This increase may be partially offset by evidence that plants growing under elevated atmospheric CO₂ concentrations produce litter with high lignin:nitrogen ratios which slows the rate of decomposition, but this change will be small compared to the increased rate of decomposition derived from climatic changes.     

Dynamics of fine roots in five Chinese temperate forests

We used a minirhizotron method to investigate spatial and temporal dynamics of fine roots (diameter ≤2 mm) in five Chinese temperate forests: Mongolian oak forest, aspen-birch forest, hardwood forest, Korean pine plantation and Dahurian larch plantation. Fine root dynamics were significantly influenced by forest type, soil layer, and sampling time. The grand mean values varied from 1.99 to 3.21 mm cm⁻² (root length per minirhizotron viewing area) for the fine root standing crop; from 6.7 to 11.6 μm cm⁻² day⁻¹ for the production; and from 3.2 to 6.1 μm cm⁻² day⁻¹ for the mortality. All forests had a similar seasonal “sinusoidal” pattern of standing crop, and a “unimodal” pattern of production. However, the seasonal dynamics of the mortality were largely unsynchronized with those of the production. The minimum values of standing crop, production and mortality occurred in March for all forests, whereas the maximum values and occurrence time differed among forest types. The standing crop, production and mortality tended to decrease with soil depth. The different spatiotemporal patterns of fine roots among the forests highlight the need for forest-specific measurements and modeling of fine root dynamics and forest carbon allocation.     

Leaf litter stoichiometry affects decomposition rates and nutrient dynamics in tropical forests under restoration in Costa Rica

Active restoration strategies increase the production of leaf litter in tropical forests, but little is known about their effect on litter decomposition and subsequent nutrient release. We quantified changes in leaf litter stoichiometry during decomposition in former pasture sites under contrasting restoration strategies (natural regeneration, applied nucleation/islands tree planting and plantation), as well as in nearby primary forest. Litterbags were employed to evaluate decomposition. We used a leaf mixture of either the four planted tree species in the plantation and island treatments or the nearby primary forest and compared them under a factorial design. Decomposition rates were similar between restoration treatments (p > 0.5), but leaves decomposed faster in the forest mixture than in the plantation mixture (p < 0.01). The content of Ca, Mg, K, P, and the C:N ratio were higher in the forest mixture at the beginning and during decomposition (p < 0.05); the N content in the plantation mixture was higher at the beginning but lower during decomposition (p < 0.05), which meant greater mobilization of nitrogen per unit of carbon lost. K and P had a strong initial release, while Mg was released more gradually. N and Ca had an irregular pattern of initial fast release, immobilization, and re‐release in the later stages. We conclude that the differences in rates of decomposition and nutrient release in these systems under restoration were at least partly determined by the floristic heterogeneity and chemical quality of the leaf litter that reaches the soil.     

6种温带森林凋落量年际及年内动态

森林凋落物量及其组分因生态系统结构特征和环境变化而表现出明显的时间动态,从而影响森林生态系统物质循环和生态服务功能。连续6年观测帽儿山地区6种温带森林凋落物量及组份的时间动态、温度和降雨量等气象因子,旨在深入了解该地区森林生态系统的物质循环过程及调控因子。结果表明:6种森林的年落凋落量差异显著,平均值依次为:蒙古栎林(4.60 t/hm~2)﹥杂木林(4.21 t/hm~2)﹥硬阔叶林(4.03 t/hm~2)﹥红松林(3.95 t/hm~2)﹥杨桦林(3.89 t/hm~2)﹥落叶松林(3.85 t/hm~2)。各森林年凋落量的年际变化表现为"升高-降低"交替波动模式,但总体上呈上升趋势。凋落物各组份的年际变化不同,枝凋落量变化较为稳定;叶凋落量与凋落总量一致,升高-降低波动明显;繁殖器官及其他凋落量随林龄增加而增加。各森林凋落物量的年内变化呈单峰曲线波动,最大值出现时间因林型而异。枝凋落量在年内表现为双峰曲线模式波动;叶凋落量年内呈单峰曲线模式波动,并与凋落总量年内动态一致;繁殖器官与其他凋落量年内动态波动平缓,无明显凋落峰值。降雨量显著影响年凋落物量(P0.05),分别解释了凋落总量、叶凋落量90%、87%变化。平均温度、积温和总降雨量显著影响凋落量年内动态,总降雨量的影响作用最为突出。因此,除林分自身的生物学特性外,降雨是影响该温带森林凋落量年内、年际动态的重要因素。     

Effect of woody plant expansion on decomposition of fine root mixtures in a grass-dominated temperate wetland

Wetlands Ecology and Management - Little is known about the effect of woody plant expansion on decomposition of root mixtures in grass-dominant temperate wetlands. Here, we collected fine roots...     

Ant colonization and coarse woody debris decomposition in temperate forests

Ants are ubiquitous, abundant and have widespread impacts on ecological communities and ecosystem processes. However, ant effects on coarse woody debris decomposition are unexplored. Several ant species colonize coarse woody debris for nesting, and this puts them in contact with fauna and microbes that utilize coarse woody debris as habitat and food, potentially influencing nutrient cycling and, ultimately, forest productivity. We report results from a field experiment employing 138 artificial ant nests (routed pine blocks) across five locations in southeastern US deciduous forests. We examine the correspondence between ant, termite and wood-eating fungi colonization and variation in coarse woody debris decomposition. After 1 year, nests colonized by ants had 5% more mass than those not colonized. Ant colonization corresponded with significantly less termite- and fungal-mediated decomposition of the nests. Without ants, termites removed 11.5% and fungi removed 4% more wood biomass. Ants, termites and wood-eating fungi all colonized pine nests where temperatures were highest, and ants also preferred higher soil moisture whereas termites and fungi responded negatively to high soil moisture when temperatures were higher. Ants reduce termite colonies through predation, and may inhibit fungi through the secretion of antimicrobial compounds. Our results indicate that interactions between forest understory ants, termites and fungi may influence the rate of coarse woody debris decomposition—biotic interactions that potentially influence forest structure and function.     

不同营林措施对马尾松细根分解与养分释放的影响

细根(直径≤2 mm)是森林生态系统重要的碳库之一,其寿命短、代谢活性高,对外界环境变化十分敏感.了解不同营林措施对细根分解和养分释放的影响,对于合理开展森林经营管理具有重要意义.以三峡库区马尾松(Pinus massoniana)飞播林为对象,设置未择伐(NC)、除灌(SC)、伐除非马尾松(NPMC)和伐除优势马尾松(DPMC)等营林措施,在处理3年后,利用分解袋法研究不同营林措施对相同初始基质质量的马尾松细根分解和养分释放的影响.经过1年的分解,不同营林措施明显改变了土壤温湿度、土壤养分以及土壤微生物量碳氮,而对马尾松细根分解速率的影响不显著(P>0.05),细根分解速率与各环境因子间均无显著相关性.在分解过程中,各营林措施的细根C残留率逐渐降低,表现为DPMC>SC>NC>NPMC.N呈现先逐渐累积后释放的状态,P呈现释放-累积-释放的状态,且抚育择伐显著降低了P释放速率.短期来看,不同营林措施造成的林内环境因素变化不足以成为影响马尾松细根分解的主导因素,细根初始基质质量仍是影响细根分解的决定性因素.抚育择伐提高了细根C释放速率,降低了N和P元素的释放速率.     

Impact of fine litter chemistry on lignocellulolytic enzyme efficiency during decomposition of maize leaf and root in soil

Residue recalcitrance controls decomposition and soil organic matter turnover. We hypothesized that the complexity of the cell wall network regulates enzyme production, activity and access to polysaccharides. Enzyme efficiency, defined as the relationship between cumulative litter decomposition and enzyme activities over time, was used to relate these concepts. The impact of two contrasting types of cell walls on xylanase, cellulase and laccase efficiencies was assessed in relation to the corresponding changes in residue chemical composition (xylan, glucan, lignin) during a 43-day incubation period. The selected residues were maize roots, which are rich in secondary cell walls that contain lignin and covalent bridges between heteroxylans and lignin, and maize leaves having mostly non-lignified primary cell walls thus making the cellulose and hemicelluloses less resistant to enzymes. Relationships between C mineralization and change in residue quality through decomposition indicated that the level of substitution of arabinoxylans (arabinan to xylan ratio) provides a good explanation of the decomposition process. In leaves enriched in primary cell walls, arabinose substitution of xylan controlled C mineralization rate but hampered polysaccharide decomposition, but to a lesser extent than in roots in which arabinoxylans were mostly cross-linked with lignin. Enzyme activity was higher in leaf than root amended soils while enzyme efficiency was systematically higher in the presence of roots. This apparent paradox suggests that residue quality could preselect the microbial community. Indeed, we found that microorganisms exhibited an initial rapid growth in the presence of a high quality litter and produced enzymes that are not efficient in degrading recalcitrant cell walls while, in the presence of the more recalcitrant maize roots, microbial biomass grew more slowly but produced enzymes of higher efficiency. This high enzyme efficiency could be explained by the synergistic action of hydrolytic and oxidative enzymes even in the early stage of decomposition.     

根系在凋落物层生长对凋落叶分解及酶活性的影响

根系向凋落物层生长是森林生态系统存在的普遍现象,研究根系存在对凋落物分解的影响对理解森林生态系统的养分物质循环具有重要意义.在福建三明市楠木和格氏栲林进行1年的凋落叶分解试验,设置有根处理和无根处理(对照),研究根系生长对凋落叶分解速率、养分释放和酶活性的影响.结果表明:在分解360 d后,有根处理楠木和格氏栲凋落叶干...