Root Decomposition Research Articles

Rhizosheaths stimulate short-term root decomposition in a semiarid grassland

Rhizosheaths are frequently found in arid and semiarid ecosystems, but their impacts on root decomposition rates and associated carbon (C) and nutrient fluxes remain unclear. We investigated mass, C and nitrogen (N) loss for the roots of Stipa krylovii and Carex korshinskii; the roots were exposed to rhizosheaths, bulk soil, or no soil in litterbags during a 102-d short-term decomposition experiment. Compared with no soil addition, rhizosheath addition increased the mass loss by 39% for S. krylovii, a sheath-forming grass, and by 11% for C. korshinskii, a non-sheath-forming grass. Rhizosheath addition also increased root C loss by 39% and N loss by 41% for S. krylovii but did not significantly alter root C or N loss for C. korshinskii, which may be due to a “home-field advantage” effect. In contrast, bulk soil addition did not alter mass, C, or N loss for either plant species, possibly because bulk soils contained fewer nutrients (C, N, and phosphorus) than rhizosheaths. We demonstrate for the first time that conventional root decomposition studies that do not account for rhizosheaths will underestimate the root mass, C and N loss by >20% in semiarid grasslands. Future studies should emphasize the crucial yet unappreciated role of rhizosheaths in driving soil organic matter cycling.

Predicting longleaf pine coarse root decomposition in the southeastern US

Storage of belowground carbon (C) is an important component of total forest C. However, belowground C changes temporally due to forest growth and tree mortality (natural and via harvesting) and these fluctuations are critical for modeling C in forests under varying management regimes. To date, little progress has been made in quantifying the rate of decay of southern pines in general, and specifically in longleaf pine (Pinus palustris Mill.) coarse root systems. Decomposition rates of lateral roots and tap roots of longleaf pine were quantified in situ under field conditions across the species’ range to create a model for necromass loss. The roots of 37 longleaf pine stumps were excavated from Florida, Georgia, Louisiana, and North Carolina. The age of the trees when cut ranged from 14 to 260 years, and the time since cut ranged from 5 to 70 years. Remaining lateral roots to a 1 m depth plus the entire tap root were removed, dried, weighed and analyzed for C and nitrogen (N) content. Total dry necromass of harvested roots ranged from 8 to 195 kg tree−1. Soil C and N content at 15 cm depth were significantly higher near the stump compared to half-way between and adjacent to the nearest living longleaf pine. A regression model was developed to predict necromass loss. The final model included years since cut, stump diameter, and average minimum monthly air temperature as predictors (R2 = 0.83). For example, a 100-year-old tree would have a predicted root decomposition rate (k) of −0.120 for lateral roots and −0.038 per year for tap roots. Results suggest that longleaf pine coarse roots persist in the environment longer than the tap roots of loblolly pine.

A belowground perspective of temperate old-growth forests: Fine root system structure in beech primeval and production forests

Old-growth forests differ from managed forests by a generally higher biodiversity, larger carbon stores, and greater heterogeneity of aboveground structures. It is not known whether the aboveground structural diversity of old-growth forests is mirrored in root system structure, e.g. by greater root biomass, the occurrence of root gaps, and a different fine root morphology. We studied the fine root system of beech (roots <2 mm in diameter) in three development stages (initial, optimum, terminal) of a primeval beech (Fagus sylvatica) forest in the Slovakian Carpathians and compared it to a nearby beech production forest close to harvest. We conducted root coring to 30 cm depth in 16 plots (84 sampling locations) with subsequent detailed analysis of fine root bio- and necromass, and fine root morphology. Despite lower aboveground wood mass, the production forest had on average about 15% larger beech fine root biomass and necromass totals than the primeval forest, though the differences were not significant. Contrary to expectation, the spatial variation of fine root biomass in the 0–30 cm layer in the structurally diverse primeval forest was not higher than in the more homogeneous production forest. Also, fine root morphology did not differ between primeval and production forest.Across the three primeval forest stages, fine root biomass tended to peak in the optimum stage, but the difference was not significant, and no alteration in fine root morphology across the stages was detected. Fine root necromass increased significantly from the initial to the terminal stage, pointing at higher fine root mortality and/or reduced root decomposition in forest patches with many senescent trees and canopy gaps. Yet, soil fertility did not decrease toward the terminal stage of forest development. From the fine root biomass data, no root gaps could be detected in the terminal stage, perhaps due to rapid gap colonization by beech saplings. We conclude that the structural differences between the fine root systems of beech primeval and production forest were relatively small. Canopy heterogeneity seems to be a less important factor determining root distribution in the primeval forest than soil heterogeneity, which can be high in production forests as well.

Modelling the management of forest ecosystems: Importance of wood decomposition

AbstractScarce and uncertain data on woody debris decomposition rates are available for calibrating forest ecosystem models, owing to the difficulty of their empirical estimations. Using field data from three experimental sites which are part of the North American Long‐Term Soil Productivity (LTSP) Study in south‐eastern British Columbia (Canada), we developed probability distributions of standard wood stake mass loss of Populus tremuloides and Pinus contorta. Using a Monte Carlo approach, 50 synthetic decomposition rate values per debris type were used to calibrate the ecosystem‐level forest model FORECAST. Significant effects of uncertainty of pine stake mass loss rates on estimated tree growth were found, especially in moderately managed forests, as estimations of available nitrogen were affected. Consequently, our work has shown that projections of tree growth under management conditions depend on accurate estimations of woody debris decomposition rates, and special effort should be done in create reliable databases of decomposition rates for their use in tree growth and yield modelling.Recommendations for Resource Managers Maintaining woody debris on site, particularly large roots, should be favored. Significant influences of wood decomposition rates on tree growth were found, especially in moderately managed forests, because belowground woody debris became an important reservoir of nutrients needed to maintain tree growth rates. Forest floor and stump removal are therefore discouraged. When using ecological models for estimating tree growth, uncertainty associated with calibrating woody debris decomposition processes should be taken into consideration if moderate management is planned. Special efforts should be made to gather site‐ and species‐specific woody debris decomposition rates, particularly for medium and coarse roots (diameter above 2.5 cm). Creating a database of standardized branch and root decomposition rates would greatly reduce the uncertainty of model estimations of tree growth.

Dynamics of nutrient concentration and microbial community composition during fine root decomposition in subtropical Mytilaria laosensis and Cunninghamia lanceolata plantations.

We conducted a 12-month fine root decomposition experiment under 19-year-old Mytilaria laosensis and Cunninghamia lanceolate plantations to explore the dynamics of nutrient concentration and microbial community composition. The aim of this study was to provide insights into nutrient cycling under plantations with different tree species. Our results showed that the initial concentrations of phosphorus (P) and potassium (K) were significantly higher in the fine root of M. laosensis than those in C. lanceolata, which significantly decreased with decomposition. Nitrogen (N) concentration in fine roots of both species increased with decay time. The variation of N concentration in fine root of C. lanceolata lagged behind that in M. laosensis. During the decomposition, magnesium (Mg) concentration in fine root of C. lanceolata showed no significant changes, but that of M. laosensis decreased at the initial decay stage and increased thereafter and was significantly lower than that of C. lanceolata at the 8th month. The ratio of fungi to bacteria (F/B) of both species decreased at the initial stage and then increased, with significantly higher F/B in fine root of M. laosensis than that of C. lanceolate after one-year decay. Redundancy analysis (RDA) showed that changes in N and K concentrations and C/N ratio explained 37.2%, 14.5% and 14.8% of the variations in microbial community composition of C. lanceolata fine root respectively. However, during the decay of M. laosensis fine root, concentrations of Mg and K were key factors, accounting for 35.9% and 17.6% of the variations in microbial community composition, respectively. We concluded that other nutrients beyond N, such as Mg, might also be an important factor affecting root decomposition in different tree species.

Negative effects of litter richness on root decomposition in the presence of detritivores

Abstract Decomposition is a vital process underlying many ecosystem functions. Although a growing number of studies have tested how litter richness affects the decomposition of above‐ground plant organs, knowledge remains limited about the decomposition of root mixtures. Here, we used a field experiment in a subtropical forest to investigate how species richness in root litter mixtures (air‐dried fresh fine roots) affects the decomposition of root litter material. On the basis of the concept of resource complementarity, we hypothesized that root litter would decompose faster as the richness of the root litter mixture increased. In addition, we expected the presence of detritivores would modify the effect of root richness on mass loss, because detritivores might experience bottom‐up effects from specific plant species and might affect microbial decomposer communities. We found that the richness level of root litter mixtures did not affect mass loss in the absence of detritivores. In the presence of detritivores, all root litter types decomposed faster. Notably, the positive effect of detritivores was stronger at low root litter richness than at high root litter richness, particularly during the early stages of decomposition (the first two sampling points) when litter mass loss was roughly double at low root litter richness compared to that at high root litter richness. The composition of the root fungal community measured at the last sampling point did not differ significantly across root richness levels, and was not affected by the presence of detritivores. Synthesis. Our findings demonstrate that detritivores modify the relationship between root litter diversity and root litter decomposition in subtropical forest ecosystems. This highlights an importance of cascade effects between different trophic organisms on ecosystem functioning. A plain language summary is available for this article.

Stable isotopic constraints on global soil organic carbon turnover

Abstract. Carbon dioxide release during soil organic carbon (SOC) turnover is a pivotal component of atmospheric CO2 concentrations and global climate change. However, reliably measuring SOC turnover rates on large spatial and temporal scales remains challenging. Here we use a natural carbon isotope approach, defined as beta (β), which was quantified from the δ13C of vegetation and soil reported in the literature (176 separate soil profiles), to examine large-scale controls of climate, soil physical properties and nutrients over patterns of SOC turnover across terrestrial biomes worldwide. We report a significant relationship between β and calculated soil C turnover rates (k), which were estimated by dividing soil heterotrophic respiration rates by SOC pools. ln( − β) exhibits a significant linear relationship with mean annual temperature, but a more complex polynomial relationship with mean annual precipitation, implying strong-feedbacks of SOC turnover to climate changes. Soil nitrogen (N) and clay content correlate strongly and positively with ln( − β), revealing the additional influence of nutrients and physical soil properties on SOC decomposition rates. Furthermore, a strong (R2 = 0.76; p &lt; 0.001) linear relationship between ln( − β) and estimates of litter and root decomposition rates suggests similar controls over rates of organic matter decay among the generalized soil C stocks. Overall, these findings demonstrate the utility of soil δ13C for independently benchmarking global models of soil C turnover and thereby improving predictions of multiple global change influences over terrestrial C-climate feedback.

Field 13C Pulse Labeling of Pea, Wheat, and Vetch Plants for Subsequent Root and Shoot Decomposition Studies

ABSTRACT: Isotopic labeling of plants is useful in tracking the fate of carbon (C) from different plant parts in a soil-plant system when these parts decompose simultaneously. Pulse labeling is a relatively simple technique and is amenable for use in the field. Therefore, we evaluated a 13CO2 pulse-labeling method to label crop plants under subtropical field conditions for simultaneous root and shoot decomposition studies. Wheat (Triticum aestivum L.), pea (Pisum sativum L.), and vetch (Vicia sativa L.) plants were grown inside polyvinyl chloride (PVC) cylinders and pulse labeled once a week for a total of 11 times. After harvest, ‘’paired’’ treatments were designed by combining 13C-labeled shoots with unlabeled roots and unlabeled shoots with 13C-labeled roots, resulting in six treatments (2 combinations × 3 species), plus an unamended control treatment. The 13C enrichment of plant parts, chemical fractions, 13C recovery, and distribution in roots, shoots, and soil were determined. Soil CO2 emissions were measured continuously by the alkaline trap method for 180 days. Plant dry matter production and chemical composition were not modified by 13C labeling. The maximum level of 13C enrichment (δ13C) in plants was +495 ‰ in wheat, +426 ‰ in pea, and +378 ‰ in vetch plants. All three crops showed similar patterns of 13C distribution in the following order: shoots > roots > soil. On average, 81 to 89 % of the recovered 13C was in the shoots, 7 to 14 % was in the roots, and 2.7 to 4.3 % was in the soil. The rate of C mineralization and cumulative C mineralization were not different between ‘’paired’’ treatments of the three crops, showing that the paired treatments were equally degradable. The pulse-labeling technique used under field conditions allowed for production of sufficiently labeled wheat, pea, and vetch plants. Therefore, it is a practical approach with respect to resource demand (tracer and labor costs), and it is suitable for in situ labeling.

Effects of elevated CO2, increased nitrogen deposition, and plant diversity on aboveground litter and root decomposition

AbstractGlobal change‐induced litter decomposition strongly affects the carbon (C) and nitrogen (N) dynamics in grassland ecosystems. However, few studies show the interactive effects of global change factors on litter and root decomposition. We conducted a four‐year grassland field experiment to examine the quality and decomposition of litter and root in a three‐factorial experiment with elevated CO2, increased N deposition, and plant species richness. We found that elevated CO2 decreased the litter N content and root lignin content. N addition increased the root N content and decreased the litter lignin content. Increasing plant richness decreased the N and lignin contents in litter and root. In contrast to the quality changes, elevated CO2 had no effect on decomposition of litter and root. N addition increased the C loss of the litter by 4.8%, but did not affect C and N loss in root. Increasing plant richness affected the C and N loss in litter and root. ANCOVAs showed that tissue quality and root biomass affected the C and N loss in litter and root, and soil C and N affected the N loss of litter and root. However, changes in tissue quality, biomass, and soil as covariates did not significantly change the effects of CO2, N, and plant richness on decomposition. The structural equation model showed that elevated CO2 indirectly decreased litter N loss and increased root N loss, while N addition indirectly increased the C and N loss in litter and root, via their effects on tissue quality. Increasing plant richness increased litter C and N loss, but indirectly decreased root C and N loss. N deposition can accelerate litter and root decomposition, thus modifying the limitation of elevated CO2 on soil N availability. Biodiversity loss greatly alters litter and root decomposition, potentially driving any changes in C and N cycling. Our study clearly demonstrates a relative certainty of a predicted increase in the C loss and N release in litter and root decomposition with increased N deposition, whereas the effects of elevated CO2 and plant diversity changes on decomposition strongly differ between litter and root in grassland ecosystems.

Clearcutting alters decomposition processes and initiates complex restructuring of fungal communities in soil and tree roots.

Forest management practices often severely affect forest ecosystem functioning. Tree removal by clearcutting is one such practice, producing severe impacts due to the total reduction of primary productivity. Here, we assessed changes to fungal community structure and decomposition activity in the soil, roots and rhizosphere of a Picea abies stand for a 2-year period following clearcutting compared to data from before tree harvest. We found that the termination of photosynthate flow through tree roots into soil is associated with profound changes in soil, both in decomposition processes and fungal community composition. The rhizosphere, representing an active compartment of high enzyme activity and high fungal biomass in the living stand, ceases to exist and starts to resemble bulk soil. Decomposing roots appear to separate from bulk soil and develop into hotspots of decomposition and important fungal biomass pools. We found no support for the involvement of ectomycorrhizal fungi in the decomposition of roots, but we found some evidence that root endophytic fungi may have an important role in the early stages of this process. In soil, activity of extracellular enzymes also decreased in the long term following the end of rhizodeposition by tree roots.

中国温带和亚热带8个树种叶和吸收根协同分解

PDF HTML阅读 XML下载 导出引用 引用提醒 中国温带和亚热带8个树种叶和吸收根协同分解 DOI: 10.5846/stxb201704110634 作者: 作者单位: 山东省科学院海洋仪器仪表研究所,山东省科学院海洋仪器仪表研究所,山东省科学院海洋仪器仪表研究所,山东省科学院海洋仪器仪表研究所,山东省科学院海洋仪器仪表研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（31300414，41406104） A coordinated decomposition between leaf litter and absorptive roots across eight temperate and subtropical tree species in China Author: Affiliation: Institute of Oceanographic Instrumentation,Shandong Academy of Sciences,Institute of Oceanographic Instrumentation,Shandong Academy of Sciences,Institute of Oceanographic Instrumentation,Shandong Academy of Sciences,Institute of Oceanographic Instrumentation,Shandong Academy of Sciences,Institute of Oceanographic Instrumentation,Shandong Academy of Sciences Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:叶和细根（ < 2mm）是森林生态系统的分解主体，二者是否协同分解，将极大影响所属植物在生态系统碳（C）循环中的物种效应。已有研究显示，叶和细根的分解关系具有极大的不确定性，认为很大程度上归因于细根内部具有高度的异质性，导致叶和细根在功能上不相似。为此，使用末梢1级根和细根根枝作为研究对象，它们在功能上同叶类似，称为吸收根。通过分解包法，分别在黑龙江帽儿山和广东鹤山，研究了2个阔叶树种和2个针叶树种（共8个树种）的叶和吸收根持续2a多的分解。结果发现，分解速率k（a-1，负指数模型）在8个树种整体分析时具有正相关关系（P < 0.05），在相同气候带或植物生活型水平上是否相关，受叶的分解环境及吸收根类型的影响；N剩余量整体上并不相关，亚热带树种的叶和细根根枝的N剩余量在分解1a后高度显著正相关，温带树种的叶和1级根的N剩余量在分解2a后显著高度正相关。本研究中，根-叶分解过程是否受控于相同或相关的凋落物性质是决定根-叶分解是否相关的重要原因，其中分解速率与酸溶组分正相关、与酸不溶组分负相关。比较已有研究，总结发现，根-叶分解关系受物种影响较大，暗示气候变化导致物种组成的改变将极大影响地上-地下关系，也因此影响生态系统C循环。 Abstract:Leaves and fine roots ( < 2mm) account for the majority of annual litter production in forests. Whether their decomposition is coordinated would largely influence species effects on terrestrial ecosystem C cycling. Currently, the relationship between leaf and root decomposition is still highly uncertain, which may be caused by the ambiguous and arbitrary definition of fine roots. Within fine roots, only the distal root tips (R1) or root branches (R1-3) are functionally comparable to leaves as resource acquisition organs (absorptive roots). Here, we investigated decomposition of leaf litter and absorptive roots using litter bags for two years across eight temperate and subtropical tree species in China. Results showed that decay rates k (a-1, negative exponential model) were positively correlated between leaf litter and absorptive roots when all eight temperate and subtropical trees were examined in combination, but when tree species were separated by climate zones or growth forms, the correlation was influenced by the soil depth at which leaf litter decomposition occurred, and the type of absorptive roots. N remaining in the leaf and root was not correlated when all eight trees were examined in combination. However, N remaining in the leaf and root was highly and positively correlated between leaf and R1-3 among subtropical trees after one year of decomposition, and between leaf and R1 among temperate trees after two years of decomposition. Here, the correlation between the decomposition of leaf and root was mainly influenced by whether both leaf and root decomposition were controlled by the same or related litter chemistry. In this study, all litter decay rates were positively related to acid soluble C fractions, but negatively related to acid insoluble C fractions. Summarizing results from our study and other studies, we found that the relationship between leaf and root decomposition was largely affected by species. Therefore, species composition dynamics due to climate change would largely affect above-and below-ground relationships and thus ecosystem C cycling. 参考文献 相似文献 引证文献

Leaf and root production, decomposition and carbon and nitrogen fluxes during stand development in tropical moist forests, north-east India

In the present study we investigated the production and decomposition of leaves, branches and roots in two moist regenerating tropical forests (5 and 15 years old; RF-5 and RF-15 respectively) and a natural forest (NF) in north-east India. Total litter input increased during vegetation succession (759, 1089 and 1284 g m–2 year–1 in RF-5, RF-15 and NF respectively), whereas the contribution of soft litter decreased sharply. Decomposition over 450 days indicated significant seasonal (P &lt; 0.001) patterns in mass loss of litter components, with greater rates during the wet period. Soil CO2 efflux was strongly seasonal. C stock loss followed patterns similar to those of mass loss, whereas N increased initially, followed by its gradual release. Rainfall explained 74–90% of the variability in mass loss rates. Concentrations of cellulose and N were significantly positively correlated with mass loss at an early stage of decomposition (r = 0.54–0.65, P &lt; 0.05), whereas lignin : N and C : N ratios were negatively correlated with mass loss at later stages. Regenerating forests adapted ecosystem-level strategies that induced early leaf fall to reduce soil water loss, increase organic matter return to the soil and conserve N through immobilisation during the process of decomposition to speed up vegetation succession in the regenerating forest.

Aboveground and Root Decomposition of Cereal Rye and Hairy Vetch Cover Crops

Core IdeasHairy vetch decomposed faster than cereal rye.Hairy vetch released N within two weeks of termination.Biomass belowground decomposed more quickly than aboveground.Cover crop N release occurred earlier than maximum crop uptake due to late planting.Synchronizing cover crop decomposition and nutrient release with cash crop uptake can provide benefits to agroecosystems but can be difficult to implement. The objectives of this study were to quantify the aboveground and belowground decomposition and nutrient release of two cover crops, hairy vetch (Vicia villosaRoth) and cereal rye (Secale cerealeL.), after termination with herbicides through a 16‐wk period during the cash crop growing season using litterbags and intact root cores. Plant Root Simulator probes monitored mineral N in the soil. Hairy vetch aboveground (k= 0.4505) and root (k= 0.6821) biomass decomposed at a faster rate than aboveground (k= 0.1368) and root (k= 0.1866) biomass of cereal rye. Hairy vetch had higher initial N content in aboveground (41.9 g kg–1) and root (16.5 g kg–1) biomass than cereal rye (11.5 and 8.3 g kg–1, respectively). Hairy vetch had a lower C to N ratio than cereal rye in both aboveground (9.52 vs. 34.72) and root biomass (17.31 vs. 40.31) contributing to decomposition differences. Hairy vetch rapidly decomposed after cover crop termination in the spring, therefore growers should consider delaying termination of this cover crop until close to cash crop planting to decrease the risk of N loss. Cereal rye residues decompose much slower and may also immobilize N because of its high C to N ratio. A better understanding of how aboveground and belowground cover crop characteristics influence decomposition will help to optimize cover crop nutrient release with cash crop uptake.

Effects of fine root decomposition on bacterial community structure of four dominated tree species in Mount Taishan, China

Effects of fine root decomposition on bacterial community structure of four dominated tree species in Mount Taishan, China

Potential contributions of root decomposition to the nitrogen cycle in arctic forest and tundra.

Plant contributions to the nitrogen (N) cycle from decomposition are likely to be altered by vegetation shifts associated with climate change. Roots account for the majority of soil organic matter input from vegetation, but little is known about differences between vegetation types in their root contributions to nutrient cycling. Here, we examine the potential contribution of fine roots to the N cycle in forest and tundra to gain insight into belowground consequences of the widely observed increase in woody vegetation that accompanies climate change in the Arctic. We combined measurements of root production from minirhizotron images with tissue analysis of roots from differing root diameter and color classes to obtain potential N input following decomposition. In addition, we tested for changes in N concentration of roots during early stages of decomposition, and investigated whether vegetation type (forest or tundra) affected changes in tissue N concentration during decomposition. For completeness, we also present respective measurements of leaves. The potential N input from roots was twofold greater in forest than in tundra, mainly due to greater root production in forest. Potential N input varied with root diameter and color, but this variation tended to be similar in forest and tundra. As for roots, the potential N input from leaves was significantly greater in forest than in tundra. Vegetation type had no effect on changes in root or leaf N concentration after 1 year of decomposition. Our results suggest that shifts in vegetation that accompany climate change in the Arctic will likely increase plant‐associated potential N input both belowground and aboveground. In contrast, shifts in vegetation might not alter changes in tissue N concentration during early stages of decomposition. Overall, differences between forest and tundra in potential contribution of decomposing roots to the N cycle reinforce differences between habitats that occur for leaves.

Degradation changes in plant root cell wall structural molecules during extended decomposition of important agricultural crop and forage species

Little is known regarding changes in cell wall structural molecules (lignin, cellulose and hemicellulose) as plant roots decompose, despite their importance for soil organic matter (OM) formation. The objectives of this study were to quantify changes in root composition during 270 d incubations of ten important grain and forage crops utilizing forage fiber analysis and to characterize the changes in cell wall composition and structure using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Large, species-dependent variation was observed in the extent of root tissue decomposition over time, ranging from 82.5% of initial mass for alfalfa to 21.5% for switchgrass. Fiber analysis revealed that initial rapid decomposition increased lignin concentration and cellulose concentration while hemicellulose declined, whereas all three moieties degraded proportionally thereafter. Similar trends were found in the ratios between the DRIFTS diagnostic peaks for lignin, cellulose and the carbonyls of hemicellulose and wax components. Spectra illustrated changes during decomposition, particularly in more extensively decomposed roots. Features potentially indicative of suberin preservation were found in the region between 2800 cm−1 and 3000 cm−1. Examination of the region between 1000 cm−1 and 1300 cm−1 revealed possible change in hemicellulose structure. The results illustrate the effect of differences in cell wall composition and structure during root decomposition and expand understanding of the role of roots in soil OM dynamics. Variability in root degradation and change in cell wall composition among species demonstrate that characterization of a broad range of individual species is necessary to predict root contributions to soil C.

Dynamics of multiple elements in fast decomposing vegetable residues

Litter decomposition regulates the cycling of nutrients and toxicants but is poorly studied in farmlands. To understand the unavoidable in-situ decomposition process, we quantified the dynamics of C, H, N, As, Ca, Cd, Cr, Cu, Fe, Hg, K, Mg, Mn, Na, Ni, Pb, and Zn during a 180-d decomposition study in leafy lettuce (Lactuca sativa var. longifoliaf) and rape (Brassica chinensis) residues in a wastewater-irrigated farmland in northwestern China. Different from most studied natural ecosystems, the managed vegetable farmland had a much faster litter decomposition rate (half-life of 18–60d), and interestingly, faster decomposition of roots relative to leaves for both the vegetables. Faster root decomposition can be explained by the initial biochemical composition (more O-alkyl C and less alkyl and aromatic C) but not the C/N stoichiometry. Multi-element dynamics varied greatly, with C, H, N, K, and Na being highly released (remaining proportion<20%), Ca, Cd, Cr, Mg, Ni, and Zn released, and As, Cu, Fe, Hg, Mn, and Pb possibly accumulated. Although vegetable residues serve as temporary sinks of some metal(loid)s, their fast decomposition, particularly for the O-alkyl-C-rich leafy-lettuce roots, suggest that toxic metal(loid)s can be released from residues, which therefore become secondary pollution sources.

Decomposition of Leaves and Fine Roots in Three Subtropical Plantations in China Affected by Litter Substrate Quality and Soil Microbial Community

Leaf and root litter decomposition has been a major research focus. However, the possible effects of belowground microbial community structure and diversity on this process are poorly understood. Understanding the biochemical mechanisms controlling aboveground decomposition processes is important to predict the changes of soil carbon and nutrient cycling in response to changes of forest management regimes. Here, we explore the biochemical controls of leaf and fine root decomposition in three subtropical plantations (Ford Erythrophleum (Erythrophleum fordii Oliver), Masson Pine (Pinus massoniana Lamb.)), and a mixed plantation containing both species) using the litterbag method, and soil microbial communities were determined using phospholipid fatty acid profiles. Overall, leaves decomposed more rapidly than fine roots, potentially due to the faster degradation of their cellulose component, but not lignin. In addition, leaf and fine root decomposition rates varied among plantations, being higher in E. fordii and lower in P. massoniana. Substrate quality such as N, Ca, lignin concentration, and C/N ratio were responsible for the decomposition rate changes among plantation types. Moreover, we used redundancy analysis to examine the relationships between litter decomposition and soil microbial community composition and diversity. Results revealed that actinobacteria and arbuscular mycorrhizal fungi community were the key determinants affecting leaf and fine root litter decomposition, respectively. Our work demonstrates that litter decomposition was linked to substrate quality and to the structure of soil microbial communities, and evidences the probable role of E. fordii in increasing soil nutrient availability, especially N, P and Ca. Additional data on phospholipid fatty acid (PLFA) or DNA marker groups within the litterbags over time may provide insights into litter decomposition dynamics, which represents potential objectives for future long-term decomposition studies.

Phosphorous fractions in soils of rubber-based agroforestry systems: Influence of season, management and stand age

Rubber-based agroforestry system is a vital management practice and its productivity is often controlled by soil phosphorus (P) nutrient, but little information is available on P fractions dynamics in such system. The aim of this study was to examine the seasonal, management and stand age effects on P fractions, acid phosphatase activity, microbial biomass P, other physical-chemical properties and litter and roots in four systems: 10-year-old rubber mono- (YM) and intercropping (YI) with N-fixing species (NFS), 22-year-old mono- (MM) and intercropping (MI) in Xishuangbanna, Southwestern China. Most P fractions varied seasonally at different depths, with highest values in the fog-cool season (i.e. labile P at 5–60cm, non-labile P and total P at 30–60cm). By contrast, moderately labile P varied little over time, except in MI that had lower values in the rainy season. Compared with their monoculture counterparts, YI doubled resin-Pi concentration but decreased NaHCO3-extractable P, HCl-Pi and residual-Po at the 0–30cm depth, whereas MI had hardly any changes in P species at the 60-cm depth. Surprisingly, residual-Po was enriched down to the deepest soil (30–60cm) in both YI and MI in the fog-cool season. All P fractions, except NaOH0.1-Pi, were greatly reduced with increasing stand age. In addition to plants uptake, these changes can be explained by seasonality in soil environments (e.g. moisture, temperature, pH and microbial activity) and decomposition of litter and roots. Moreover, YI decreased labile Po stock, but MI increased moderately labile Pi at the 60-cm depth across seasons. The results imply that a large amount of residual-Po exists in acidic Oxisol from China and that they can be reasonably exploited to reduce the application of P fertilizers, highlighting the importance of Po pool. Taken together, intercropping mature rubber plantation with NFS appears to be an effective way to enhance productivity while maintaining adequate soil P concentration over the long run.

Fire-derived charcoal might promote fine root decomposition in boreal forests

Boreal forest soils are a huge carbon sink, but the forests are regularly subjected to fire disturbance. The fine roots in these forests substantially contribute to soil carbon accumulation. Charcoal is a fire by-product that influences ecosystem processes including soil organic matter decomposition. However, the extent to which charcoal affects fine root decomposition is unclear. We performed field litterbag experiments over 515 days involving the incubation of fine larch roots with varying concentrations of charcoal in soil. At the end of experiment the loss of root mass in samples incubated with higher concentrations of charcoal was greater (42% and 40%) than that in the control (30%) and a treatment containing the average measured soil charcoal content (27%). The degree of mass loss generally increased with increasing charcoal content. Our result provides the first field evidence that fire-derived charcoal may enhance the decomposition of fine larch roots, and consequently CO2 release from boreal forests.