Acid-unhydrolyzable Residue Research Articles

Carbon (δ13C) and Nitrogen (δ15N) Isotope Dynamics during Decomposition of Norway Spruce and Scots Pine Litter

We studied the dynamics of stable carbon (δ13C) and nitrogen (δ15N) isotopes in litter from Norway spruce (NSL) (Picea abies) and Scots pine (SPL) (Pinus silvestris) during in situ decomposition over a period of more than 4 years. Relative to initial values, δ13CNSL showed a weak enrichment (0.33‰), whereas δ13CSPL was depleted (−0.74‰) at the end of decomposition. Both litter types experienced a depletion in δ15N during decomposition; δ15NNSL decreased by −1.74‰ and δ15NSPL decreased by −1.99‰. The effect of the selective preservation of acid-unhydrolyzable residue (AUR) in lowering δ13C of the residual litter was evident only in SPL. In the NSL, only in the initial stage did C/N have a large effect on the δ13C values. In the later stages, there was a non-linear decrease in δ13CNSL with a simultaneous increase in AUR concentrations, but the effect size was large, suggesting the role of lignin in driving δ13C of residues in later stages. Depletion in 15N in the residual litters concomitant with the increase in N concentration suggests bacterial transformation of the litter over fungal components. A consistent decline in δ15N values further implies that bacterial dominance prompted this by immobilizing nitrate depleted in 15N in the residual litter.

Molecular diversity and the fate of biochemical fractions of eucalypt tissues in soil

The molecular diversity of the source substrate has been regarded as a significant controller of the proportion of plant material that is either mineralized or incorporated into soil organic matter (SOM). However, quantitative parameters to express substrate molecular diversity remain elusive. In this research, we fractionated leaves, twigs, bark, and root tissues of 13C-enriched eucalypt seedlings into hot water extractables (HWE), total solvent (acetone) extractables (TSE), a cellulosic fraction (CF), and the acid unhydrolyzable residue (AUR). We used 13C NMR spectroscopy to obtain a molecular diversity index (MDI) based on the relative abundance of carbohydrate, protein, lignin, lipid, and carbonyl functional groups within the biochemical fractions. Subsequently, we obtained artificial plant organs containing fixed proportions (25%) of their respective biochemical fractions to be incubated with soil material obtained from a Haplic Ferralsol for 200-days, under controlled temperature (25 ± 1 °C) and moisture adjusted to 70–80% of the soil water holding capacity. Our experimental design was a randomized complete block design, arranged according to a factorial scheme including 4 plant organs, 4 biochemical fractions, and 3 blocks as replicates. During the incubation, we assessed the evolution of CO2 from the microcosms after 1, 2, 3, 4, 7, 10, 13, 21, 28, 38, 45, 70, 80, 92, 112, 148, 178 and 200 days from the start of the incubation. After the incubation, soil subsamples were submitted to a density fractionation to separate the light fraction of SOM (LFOM) i.e., with density <1.8 g cm−3. The heavy fraction remaining was submitted to wet-sieving yielding the sand-sized SOM (SSOM) and the mineral-associated SOM (MAOM), with particle-size greater and smaller than 53 µm, respectively. We found that HWE and AUR exhibited comparatively higher MDIs than the TSE and CF. During the incubation, HWE and CF were the primary sources of 13C-CO2 from all plant organs and after 92 days, the respiration of the TSE of bark and roots increased. Otherwise, the AUR contributed the least for the release of 13C-CO2. There were no significant relationships between the MDI and the amount of 13C transferred into the LFOM or SSOM. Otherwise, the transfer of 13C into the MAOM increased as a linear-quadratic function of MDI, which in turn was negatively correlated with the total 13C-CO2 loss. Overall, the MDI exerted a stronger control on the 13C-labeled MAOM than on 13C-CO2 emissions, highlighting the need to improve our ability to distinguish and quantify direct plant inputs from those of microbial origin entering soil C pools.

Changes in acid-hydrolyzable carbohydrates and acid-unhydrolyzable residue during foliar litter decomposition of Castanopsis carlesii and Chinese fir in a subtropical forest headwater stream

Changes in acid-hydrolyzable carbohydrates and acid-unhydrolyzable residue during foliar litter decomposition of Castanopsis carlesii and Chinese fir in a subtropical forest headwater stream

Initial Carbon Quality of Newly Shed Foliar Litter in an Alpine Forest from Proximate Analysis and 13C NMR Spectroscopy Perspectives

The initial carbon (C) quality of plant litter is one of the major factors controlling the litter decomposition rate and regulating C sequestration, but a comprehensive understanding is still lacking. Here, we used proximate analysis and 13C nuclear magnetic resonance (NMR) with spectral editing techniques to quantify the variations in the initial C quality for four dominant species (fir: Abies faxoniana Rehd. et Wils.; spruce: Picea asperata Mast; willow: Salix paraplesia Schneid; and rosa: Rosa omeiensis Rolfe.), including the organic compositions and C-based chemical structures of newly shed foliar litter over eight months in an alpine forest on the eastern Tibetan Plateau. The results indicated that the fractions of acid-soluble extractives (ASE) and acid-unhydrolyzable residues (AUR) were the main fractions of organic components, and aliphatic C and O-alkyl C were the main functional C groups for all plant species. Under the effects of the plant species, higher levels of ASE (37.62%) and aliphatic C (35.44%) were detected in newly shed rosa foliar litter, while higher levels of AUR (fir: 37.05%; spruce: 41.45%; and willow: 40.04%) and O-alkyl C (fir: 32.03%; spruce: 35.02%; and willow: 32.34%) were detected in newly shed fir, spruce and willow foliar litter. Moreover, the A/O-A and HB/HI ratios in rosa litter were 0.88 and 1.15, respectively, which were higher than those in fir, spruce and willow litter. The C quality of newly shed foliar litter varied seasonally due to the litter quality and environmental conditions, especially nitrogen (N), dissolved organic carbon (DOC), manganese (Mn) and monthly air temperature. We also found that C loss during 4-year litter decomposition was highly related to the aromatic C and phenolic C contents in newly shed foliar litter, suggesting that litter decomposition was strongly controlled by the initial recalcitrant C fractions. We conclude that the C quality of newly shed foliar litter in rosa might be structurally stable and more resistant to degradation than that of fir, spruce and willow, which contain abundant labile C fractions, and the initial recalcitrant C fractions are closely related to C loss during litter decomposition, which might contribute to soil C sequestration in alpine forests.

Fungal Community Composition as Affected by Litter Chemistry and Weather during Four Years of Litter Decomposition in Rainshadow Coastal Douglas-Fir Forests.

Climate and litter chemistry are major factors influencing litter decay, a process mediated by microbes, such as fungi, nitrogen-fixing bacteria and ammonia-oxidizing bacteria. Increasing atmospheric CO2 concentrations can decrease nitrogen (N) and increase condensed tannin (CT) content in foliar litter, reducing litter quality and slowing decomposition. We hypothesized that reduced litter quality inhibits microbes and is the mechanism causing decomposition to slow. Litterbags of Douglas-fir needles and poplar leaves with a range of N (0.61–1.57%) and CT (2.1–29.1%) treatment and natural acid unhydrolyzable residue (35.3–41.5%) concentrations were placed along climatic gradients in mature Douglas-fir stands of coastal British Columbia rainshadow forests. The structure (diversity, richness and evenness) and composition of microbial communities were analyzed using DGGE profiles of 18S, NifH-universal and AmoA PCR amplicons in foliar litter after 7, 12, 24 and 43 months of decay. High CT and low N concentrations in leaf litter were associated with changes in microbial community composition, especially fungi. Contrary to our hypothesis, high CT and low N treatments did not inhibit microbial colonization or diversity. The joint effects of air temperature and soil moisture on microbial community composition at our sites were more important than the effects of initial litter chemistry.

Long-Term Effects of Climate and Litter Chemistry on Rates and Stable Fractions of Decomposing Scots Pine and Norway Spruce Needle Litter—A Synthesis

We have reviewed information on early-, late- and limit-value decomposition stages for litter of Norway spruce (Picea abies) and Scots pine (Pinus silvestris). This synthesis covers c 16 studies/papers made along a climatic gradient; range in mean annual temperature (MAT) from −1 to +7 °C and mean annual precipitation (MAP) from 425 to 1070 mm. Scots pine has an early stage dominated by carbohydrate decomposition and a late stage dominated by decomposition of lignin; Norway spruce has just one stage dominated by lignin decomposition. We used data for annual mass loss to identify rate-regulating factors in both stages; climate data, namely, MAT and MAP, as well as substrate properties, namely, nitrogen (N), acid unhydrolyzable residue (AUR), manganese (Mn). Early-stage decomposition for Scots pine litter was dominated positively by MAT; the late stage was dominated negatively by MAT, N, and AUR, changing with decomposition stage; there was no effect of Mn. Norway spruce litter had no early stage; decomposition in the lignin-dominated stage was mainly negative to MAP, a negative relationship to AUR and non-significant relationships to N and MAT. Mn had a positive relationship. Limit values for decomposition, namely, the accumulated mass loss at which decomposition is calculated to be zero, were related positively to Mn and AUR for Scots pine litter and negatively to AUR for Norway spruce litter. With different sets of rate-regulating factors as well as different compounds/elements related to the limit values, the decomposition patterns or pathways are different.

Temporal dynamics of mixed litter humification in an alpine treeline ecotone

Loss of plant diversity affects mountain ecosystem properties and processes, yet few studies have focused on the impact of plant function type deficiency on mixed litter humification. To fill this knowledge gap, we conducted a 1279-day litterbag decomposition experiment with six plant functional types of foliar litter to determine the temporal dynamic characteristics of mixed litter humification in a coniferous forest (CF) and an alpine shrubland (AS). The results indicated that the humus concentrations, the net accumulations and their relative mixed effects (RME) of most types were higher in CF than those in AS at 146 days, and humus net accumulations fell to approximately -80% of the initial level within 1279 days. The RME of the total humus and humic acid concentrations exhibited a general change from synergistic to antagonistic effects over time, but the mixing of single plant functional type impeded the formation of fulvic acid due to consistently exhibited antagonistic effects. Ultimately, correlation analysis indicated that environmental factors (temperature, snow depth and freeze-thaw cycles) significantly hindered litter humification in the early stage, while some initial quality factors drove this process at a longer scale. Among these aspects, the concentrations of zinc, copper and iron, as well as acid-unhydrolyzable residue (AUR):nitrogen and AUR:phosphorous, stimulated humus accumulation, while water-soluble extractables, potassium, magnesium and aluminium hampered it. Deficiencies in a single plant functional type and vegetation type variations affected litter humification at the alpine treeline, which will further affect soil carbon sequestration, which is of great significance for understanding the material circulation of alpine ecosystems.

Variability of decomposing ability among fungi associated with the bleaching of subtropical leaf litter

ABSTRACT A diverse array of fungi take part in decomposition, but the variability of their decomposing ability is not fully understood. A total of 49 isolates of Ascomycota and Basidiomycota were obtained from bleached areas of leaf litter in a subtropical forest in southern Japan, and their ability to decompose leaves and recalcitrant compounds was quantified in pure culture. Mass loss of leaves of Castanopsis sieboldii (Fagaceae) and Schima wallichii (Theaceae) was evaluated at 20 C for 12 wk in vitro. Fungi caused a loss of −0.4% to 34.3% of the original leaf mass. The greatest mass loss was caused by four isolates of Mycena (Tricholomataceae). Isolates of Lachnocladiaceae caused greater mass loss of recalcitrant compounds, registered as acid-unhydrolyzable residue (AUR), which includes lignin, relative to Xylariaceae. Isolates of Rhytismataceae, Lachnocladiaceae, Marasmiaceae, and Omphalotaceae exhibited selective decomposition of AUR, Mycena exhibited simultaneous decomposition of AUR and components other than AUR, and Xylariaceae exhibited selective decomposition of components other than AUR. Mass losses of leaves and AUR caused by each fungal isolate were similar for C. sieboldii and S. wallichii. The Mycena isolates obtained from C. sieboldii caused greater mass losses of leaves and AUR than those obtained from the other tree species, suggesting a “home-field advantage” of decomposing potentialities, with implications for natural interactions beyond the in vitro system evaluated here.

Seasonal dynamics of organic components in fresh foliar litters at different gap positions in an alpine forest on the eastern Tibetan Plateau

The organic components in fresh litters are important chemical traits for evaluating the initial quality that controls decomposition of plant litter. This study aimed to assess the seasonal dynamics and drivers of organic components in four dominant fresh litters and their variations at different gap positions in an alpine forest on the eastern Tibetan Plateau. We measured the water- (WSE), organic- (OSE), acid-soluble extractables (ASE) and acid-unhydrolyzable residues (AUR) in fresh litters of fir (Abies faxoniana), cypress (Sabina saltuaria), azalea (Rhododendron lapponicum), and cherry (Cerasus duclouxii) at the gap center, gap edge, and under the closed canopy over 1 year in an alpine forest. The contents of organic components significantly varied among litter species and collecting time, and the ASE content also showed significant variations among gap positions. Manganese (Mn) was negatively related to the OSE content, and dissolved organic carbon (DOC) was the most significant factor affecting WSE and AUR contents. Magnesium (Mg) was the factor of great magnitude that significantly influenced the ASE content, and the correlation coefficient between Mg and ASE in the gap center was higher than that in other gap positions. The contents of organic components were markedly controlled by litter species over time, and ASE content varied significantly after gap formation. The seasonal dynamics of these organic components were strongly mediated by litter nutrients, such as Mg, Mn, calcium (Ca), and nitrogen (N), while DOC was a significant factor controlling WSE and AUR contents in fresh litters in this alpine forest.

Decomposition of Organic Chemical Components in Wood by Tropical Xylaria Species.

The ability of Xylaria species obtained from tropical wood and leaf litter to cause a mass loss of lignin and carbohydrates in wood was examined in vitro with pure culture decomposition tests. The mass loss of wood of four tree species caused by nine Xylaria isolates ranged from 4.5% to 28.4% of the original wood mass. These Xylaria isolates have a potential ability to decompose lignin and other recalcitrant compounds, collectively registered as acid unhydrolyzable residues or Klason lignin in wood. The origin of isolates (i.e., isolates from wood versus leaf litter) did not affect the mass loss of acid unhydrolyzable residue in wood. The Xylaria isolates tested generally caused a selective decomposition of polymer carbohydrates in wood in preference to acid unhydrolyzable residue. The mass loss of acid unhydrolyzable residue caused by Xylaria isolates varied with the tree species of the wood and was negatively related to the initial content of acid unhydrolyzable residue in wood, implying the limiting effect of lignin and recalcitrant compounds on wood decomposition by Xylaria isolates.

Litter chemical traits strongly drove the carbon fractions loss during decomposition across an alpine treeline ecotone

The decomposition of litter carbon (C) fraction is a major determinant of soil organic matter pool and nutrient cycling. However, knowledge of litter chemical traits regulate C fractions release is still relatively limited. A litterbag experiment was conducted using six plant functional litter types at two vegetation type (coniferous forest and alpine shrubland) in a treeline ecotone. We evaluated the relative importance of litter chemistry (i.e. Nutrient, C quality, and stoichiometry) on the loss of litter mass, non-polar extractables (NPE), water-soluble extractables (WSE), acid-hydrolyzable carbohydrates (ACID), and acid-unhydrolyzable residue (AUR) during decomposition. Litter nutrients contain nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), sodium (Na), magnesium (Mg), aluminium (Al), manganese (Mn), zinc (Zn), iron (Fe) and copper (Cu), litter C quality contains C, WSE, NPE, ACID, and AUR, and stoichiometry was defined by C:N, C:P; N:P, ACID:N, and AUR:N. The results showed single exponential model fitted decomposition rates of litter mass and C fractions better than double exponential or asymptotic decomposition, and the decomposition rates of C fractions were strongly correlated with initial litter nutrients, especially K, Na, Ca. Furthermore, the temporal dynamics of litter nutrients (Ca, Mg, Na, K, Zn, and Fe) strongly regulated C fractions loss during the decomposition process. Changes in litter C quality had an evident effect on the degradation of ACID and AUR, supporting the concept of “priming effect” of soluble carbon fraction. The significant differences were found in the release of NPE, WSE, and ACID rather than AUR among coniferous forest and alpine shrubland, and the vegetation type effects largely depend on the changes in litter stoichiometry, which is an important implication for the change in plant community abundance regulate decay. Collectively, elucidating the hierarchical drivers of litter chemistry on decomposition is critical to soil C sequestration in alpine ecosystems.

Heterogeneity in Decomposition Rates and Nutrient Release in Fine-Root Architecture of Pinus massoniana in the Three Gorges Reservoir Area

Fine-root decomposition contributes a substantial amount of nitrogen that sustains both plant productivity and soil metabolism, given the high turnover rates and short root life spans of fine roots. Fine-root decomposition and soil carbon and nitrogen cycling were investigated in a 1-year field litterbag study on lower-order roots (1–2 and 3–4) of Pinus massoniana to understand the mechanisms of heterogeneity in decomposition rates and further provide a scientific basis for short-time research on fine-root decomposition and nutrient cycling. Lower-order roots had slower decay rates compared with higher-order roots (5–6). A significantly negative correlation was observed between the decay constant mass remaining and initial N concentrations as well as acid unhydrolyzable residues. Results also showed that in lower-order roots (orders 1–2 and 3–4) with a lower C:N ratio, root residual N was released and then immobilized, whereas in higher-order roots (order 5–6) with a higher C:N ratio, root residual N was immobilized and then released in the initial stage. In the later stage, N immobilization occurred in lower-order roots and N release in higher-order roots, with the C:N ratio gradually decreasing to about 40 in three branching-order classes and then increasing. Our results suggest that lower-order roots decompose more slowly than higher-order roots, which may result from the combined effects of high initial N concentration and poor C quality in lower-order roots. During the decomposition of P. massoniana, N release or N immobilization occurred at the critical C:N ratio.

Decomposition of leaf mixtures and absorptive-root mixtures synchronously changes with deposition of nitrogen and phosphorus

Leaves and absorptive roots, the plant tissues that acquire resources, decompose quite differently due to their distinct morphology, chemistry, and decomposition microenvironments. Root litters of different species often decompose in mixtures in natural forests or mixed plantations, similar to leaf litters. However, the mechanisms behind leaf mixture decomposition and root mixture decomposition and their responses to nutrient deposition remain poorly understood. We used a nutrient-addition manipulative experiment to investigate the individual and interactive effects of nitrogen (N) and phosphorus (P) on leaf mixture decomposition and absorptive-root mixture decomposition of Pinus massoniana and Schima superba forests in subtropical China. Four treatments were employed: control (CTRL), +N (120 kg N ha−1y−1), +P (40 kg P ha−1y−1), and +NP (120 kg N and 40 kg P ha−1y−1). Both the leaves and roots of P. massoniana and S. superba decomposed faster when in mixtures (observed) than in isolation (expected) under all treatments. The synergistic effects were decreased with +N and +NP relative to the CTRL for the leaf mixtures, but only with +NP for the root mixtures. The differences (observed - expected) of the extracellular enzymatic activities (EEAs) of microorganisms were decreased with +N in the leaf mixtures relative to the CTRL, and the differences (observed - expected) of acid unhydrolyzable residue (AUR) loss were decreased with +NP in the root mixtures. The differences (observed - expected) of mass loss were positively correlated with microbial EEAs differences for the leaf mixtures and with AUR loss difference for the root mixtures. Our results indicate that the decomposition of both the leaf mixtures and the root mixtures had synergistic effects. The decreased synergistic interactions under nutrient addition were associated with microbial EEAs for the leaf mixtures and with AUR loss for the root mixtures. These findings highlight the contrasting mechanisms underlying the decomposition of above-ground mixtures and below-ground mixtures, and imply a slow cycling of carbon and nutrients under atmospheric nutrient deposition.

Alterations of early-stage decomposition of leaves and absorptive roots by deposition of nitrogen and phosphorus have contrasting mechanisms

Nitrogen (N) deposition may inhibit decomposition by decreasing microbial growth and activity (microbial mechanism) and/or increasing the binding of inorganic N ions to the acid-unhydrolyzable residue (AUR) in decomposing litter (chemical mechanism). How increased phosphorus (P) deposition affects decomposition and mediates the effect of N on this process, however, remains unclear. We used a nutrient-manipulative experiment to examine the individual and interactive effects of N and P on the decomposition of two fast-cycling organs (leaves vs. absorptive roots) in Pinus massoniana and Schima superba forests in subtropical China. The carbon fractions and microbial enzymatic activities in decomposing leaves and roots were also determined to identify the underlying mechanisms. Adding only N negatively affected the decomposition of absorptive roots but had no or a positive effect on foliar decomposition. Adding only P increased foliar decomposition but did not affect root decomposition. Adding both N and P had little effect on decomposition, except for a positive effect on P. massoniana leaves. The nutrient additions did not affect the amount of carbon remaining in the leaves, and adding only N increased the residual AUR content in the roots. Adding only P decreased the activity of acid phosphatase (AP) in the leaves. Foliar decomposition was correlated with microbial enzymatic activity but not AUR content. Root decomposition was correlated more strongly with AUR content than microbial enzymatic activity. The increased decomposition but decreased AP activity of the leaves with P addition suggests a stronger P limitation on the decomposition of leaves than roots in these subtropical forests. The stimulating effect of P on foliar decomposition may be due to a microbial mechanism, and a chemical mechanism may dominate the inhibitory effect of N on root decomposition. Our findings facilitate the mechanistic understanding of the effects of nutrient deposition on the decomposition of leaves and absorptive roots, and highlight the role of P deposition in mediating the effect of N on decomposition.

Effects of snow depth on acid-unhydrolyzable residue and acid-hydrolyzable carbohydrates degradation rates during foliar litter decomposition of Pinus koraiensis and Quercus mongolica

Differences in snow depth induced by climate change alter the microenvironments under snowpack, which affect litter decomposition. The degradation of acid-unhydrolyzable residue (AUR) and acid-hydrolyzable carbohydrates (ACID) is a key factor controlling soil organic matter formation. However, how snow depth affects the degradation is poorly understood. A snow depth manipulation experiment with snow-addition, snow-removal, and control treatments was conducted in Northeast China. Foliar litter of Pinus koraiensis and Quercus mongolica was placed on top of the ground in each treatment and sampled for six times from November 2014 to October 2015. AUR and ACID degradation rates decreased with the reduction of snow depth during the snow-covered season because of the insulating effect provided by snowpack; this relationship was reversed during the snow-free season due to more labile carbon remaining after the snowmelt. During the snow-covered season, AUR and ACID degradation rates were positively correlated to the sum of degree days above 0 °C. In contrast, AUR and ACID degradation rates were positively correlated with litter microbial biomass carbon during the snow-free season. Snow depth plays an important role in determining litter AUR and ACID degradation rates, but the effects on degradation rates differed between the snow-covered and snow-free seasons.

Nitrogen deposition increases root production and turnover but slows root decomposition in Pinus elliottii plantations.

Fine roots of woody plants comprise multiple root orders, which can be functionally partitioned into two pools: absorptive fine roots (AFRs, orders 1, 2) and transport fine roots (TFRs, orders 3-5). However, the function-based fine-root dynamics and especially their responses to increased nitrogen (N) availability remain unclear. We explored dynamic responses of both AFRs and TFRs of Pinus elliottii to N addition in subtropical China based on a 4-yr minirhizotron experiment and a two-stage - early (0.5yr) vs late (4yr) - decomposition experiment. N addition increased the production, mortality, and turnover of AFRs but not TFRs. High rates of N persistently inhibited AFR decomposition but affected TFR decomposition differentially at the early (no effect) and late (negative effect) stages. The increased production of AFRs was driven by N-induced decrease in foliar and soil phosphorus (P) concentrations. The decreased decomposition of AFRs might be due to the increased acid-unhydrolyzable residues in decomposing roots. AFRs are the resource-acquiring module, the increased carbon allocation to AFRs may represent a P-acquiring strategy when N no longer limits growth of P. elliottii. Our results suggest that AFRs and TFRs respond differently to N deposition, both in terms of production, mortality, and turnover and in terms of decomposition.

Evidence for the role and fate of water-insoluble condensed tannins in the short-term reduction of carbon loss during litter decay

Warmer temperatures associated with climate change have the potential to accelerate litter decay and subsequently release large amounts of carbon stored in soils. Condensed tannins are widespread secondary metabolites, which accumulate to high concentrations in many woody plants and play key roles in forest soil nutrient cycles. Future elevated atmospheric CO2 concentrations are predicted to reduce nitrogen content and increase tannin concentrations in plant tissues, thus reducing litter quality for microbial communities and slowing decomposition rates. How the distinct condensed tannin fractions (water-soluble, acetone:MeOH-soluble and solvent-insoluble) impact soil processes, has not been investigated. We tested the impact of condensed tannin and nitrogen concentrations on decay rates of poplar and Douglas-fir litter at sites spanning temperature and moisture gradients in coastal rainshadow forests in British Columbia, Canada. The three condensed tannin fractions were quantified using recent improvements on the butanol-HCl assay. Decay was assessed based on carbon remaining, while changes in litter chemistry were primarily observed using two methods for proximate chemical analyses. After 0.6 and 1 year of decay, more carbon remained in poplar litter with high, compared to low, condensed tannin concentrations. By contrast, more carbon remained in Douglas fir litter than poplar litter during this period, despite lower condensed tannin concentrations. Rapid early decay was especially attributed to loss of soluble compounds, including water-soluble condensed tannins. Water-insoluble condensed tannin fractions, which were transformed to acid-unhydrolyzable residues over time, were associated with reduced carbon loss in high condensed tannin litter.

Leaf litter decomposition of 12 tree species in a subtropical forest in Japan

AbstractThe leaf litter decomposition of 12 tree species was examined for three years in a subtropical forest in Japan to follow the pattern of changes in organic chemical constituents and nitrogen (N) and the relationship between these components. The remaining mass of the leaf litter reached 7–53% of the original mass at the end of the field incubation, and the decomposition constants (k) ranged from 0.37 to 2.39 year−1. The decomposition constant was significantly negatively correlated with the initial content of acid‐unhydrolyzable residue (AUR) for all 12 tree species. A net increase of AUR that lasted for the first 3 to 6 months was noted for leaf litter of four tree species. The absolute amount of total N increased initially and then decreased thereafter in leaf litter of five tree species, whereas total N mass decreased throughout the study period in leaf litter of the other species. Contents of AUR and total N in leaf litter generally increased linearly with the accumulated mass loss of litter during decomposition, resulting in positive slopes of linear regressions. Lignocellulose index and AUR to N ratio of the litter showed convergent trends for 12 tree species as the decomposition progressed. When compared with datasets for an Asian climatic gradient, the decomposition rates in the subtropical forest was intermediate between the rates in tropical and temperate forests, and AUR and N contents in decomposing litter were consistently lower than those in temperate forests, indicating faster loss of AUR and N.

Litter quality control of decomposition of leaves, twigs, and sapwood by the white-rot fungus Trametes versicolor

Litter quality plays predominant roles in plant litter decomposition by modifying the activity of decomposer fungi, but little is known about the response of the decomposing activity of individual fungal strains to variations in litter quality. In the present study, the variability in the decomposing ability of a single fungal strain (Trametes versicolor IFO30340) was quantified under pure culture conditions to elucidate litter quality measures that control the decomposition. We used a total of 72 litters from 51 plant species, including leaves, twigs, sapwood, bark, heartwood, and petioles of broad-leaved trees, coniferous trees, and grass. Mass loss of litter caused by the fungus ranged from 0.9 to 59.8% of the original litter mass, was significantly higher in leaves, twigs, and petioles than in heartwood, and was significantly higher in broad-leaved than in coniferous litter. Tissue type (leaf, sapwood, or twig) and the relative amount of acid-unhydrolyzable residues to total nitrogen were selected as predictor variables of the mass loss of litters. Fourier transform infrared (FT-IR) spectroscopy showed that guaiacyl units of lignin negatively affected the fungal decomposition.

Heterogeneity in decomposition rates and annual litter inputs within fine-root architecture of tree species: Implications for forest soil carbon accumulation

Fine roots (⩽2mm in diameter) of tree species, traditionally regarded as homogenous entities, are expected to be major contributors of forest soil organic carbon (C), but their contributions need to be reevaluated given the heterogeneity in many root characteristics within fine-root architecture. Here, literature data were synthesized to analyze whether there existed heterogeneity of decomposition rates within fine-root architecture of tree species and quantify the relative contributions of roots of each branching order to forest soil C storage by combining variations in annual litter inputs among fine-root branching hierarchies. Results showed the presence of heterogeneity in decomposition rates within fine-root architecture, and this pattern was influenced by classification methods (root order or diameter class). Specifically, the heterogeneity in decomposition rates was shown only when fine roots were classified by root order, but not when fine roots were classified by diameter class. The slower decomposition rates of lower-order roots (the first two orders) were related to their higher acid-unhydrolyzable residues. Furthermore, lower-order roots were found to account for 57–71% of annual root litter inputs of the first five orders. Given the slow decomposition rates and high annual litter inputs of lower-order roots of tree species, our findings suggest that lower-order roots should be important contributors to forest soil organic C.