Fine Root Decomposition Rates Research Articles

Dynamics of Fine Root Decomposition in Different Vegetation Types: Investigating the Impact of Soil Fungal Communities and Enzyme Activities

Fine root decomposition plays a vital role in driving the carbon cycle in terrestrial ecosystems, as it constitutes a substantial part of annual net primary production and, as transient tissues, returns to the soil within relatively short timescales. Soil fungal communities and enzyme activities strongly influence this process. In this study, we used an in situ soil core decomposition method to compare the fine root decomposition rates of Liriodendron chinense (Hemsl.) Sargent, Cunninghamia lanceolata (Lamb.) Hook, and Phyllostachys edulis (Carrière) J.Houz forests over a 1-year period (March 2021–March 2022). We quantified the chemical attributes of fine roots and soil enzymatic activities across different forests, detected fungal communities via ITS rRNA gene sequencing, and forecasted fungal functional groups using the FUNGuild database. The results showed that fine root decomposition was fastest in the Liriodendron chinense (Hemsl.) Sargent forest (77.2%) and the slowest for Cunninghamia lanceolata (Lamb.) Hook (59.2%). Structural equation modeling (SEM) results indicated that the carbon content of fine roots and the functional groups of soil fungi are crucial to fine root decomposition. They not only directly influence fine root decomposition but also promote it through soil enzymatic activities, clearly suggesting that changes in soil enzymatic activities can be employed to explain the ecological effects of the root decomposition process. This study illuminates significant differences in the chemical characteristics of fine roots, soil enzymatic activities, and soil fungal communities among different forest types, all of which significantly affect fine root decomposition.

Manganese indicates root decomposition rates across soil layer, root order, and tree species: Evidence from a subtropical forest

Different spatial locations provide different external conditions for root decomposition, while species and root order cause obvious differences in root substrate quality. Both differences in internal and external conditions may determine root decomposition rate. We explored the effects of decomposition position, root order, and species differences on root decomposition, and determined the role of manganese (Mn) in root decomposition. We conducted a fine root decomposition experiment using roots from Schima superba, Cleyera japonica, and Eurya loquaiana (separated into orders 1−3, 4−5, and 6) in the litter layer, and at 0−10 cm, 20−30 cm, and 40−50 cm soil depth in a subtropical forest. Root mass and concentration of C, N, P, Mn, condensed tannins and total phenolics were measured during two years of decomposition. Root decomposition rates decreased with increasing soil depth for all root samples. Compared to decomposition at 0−10 cm soil depth, remaining mass (% of initial) declined by 7%–34% in the litter layer and increased by 17%–37% at 40−50 cm soil depth. Lower-order roots had a higher decomposition rate than higher-order roots in the litter layer, but at 40−50 cm soil depth, we observed the opposite. Root litter Mn concentration and remaining mass were negatively correlated during the whole decomposition period including the early, middle, and late stages. Initial root Mn content was negatively correlated with remaining mass after two years of decomposition in the litter layer, and at 20−30 cm, 40−50 cm soil depth. However, no significant relationship between mass remaining and initial root N, P, condensed tannins and total phenolics were observed in the subsoil. Variance partitioning showed that the soil layer contributes significantly to the variance in remaining root mass, C, and Mn, whereas root order group contributed more than the soil layer to remaining root N and P. Our results indicate that soil depth is more important than root order for fine root decomposition rate at a site scale. Relative root decomposition rate between lower- and higher-order roots depends on the decomposition environment. Overall, this study strongly suggests that root Mn concentration (whether in initial or other decomposition stages) was much more consistently correlated with mass remaining than traditional predictors of N, P, condensed tannins, or total phenolics. Root Mn concentration greatly indicates root decomposition rates across soil layers, root orders, and species. Initial root Mn concentration and Mn supply capacity of the decomposition environment jointly control root decomposition rates throughout the decomposition process.

A less complex but more specialized microbial network resulted in faster fine-root decomposition in young stands of Robinia pseudoacacia

Microorganisms play an important role in litter decomposition. Bacteria and fungi colonize litter during the decomposition process; therefore, understanding the interactions of bacterial and fungal communities can yield insight into litter decomposition dynamics. Most studies have focused on leaf litter decomposition, but thus far, there has been little information on the dynamic changes in soil microbial composition at the different stages of fine-root decomposition. Therefore, we conducted a 210-day incubation experiment on the fine roots of Robinia pseudoacacia to explore how the temporal dynamics of soil enzyme activities and microbial communities are related to the decomposition of R. pseudoacacia at four different stand ages (15, 25, 35 and 45 years) during vegetation restoration. The results showed that the fine-root decomposition rate was higher for young stands of R. pseudoacacia. We found that the oxidase activity was significantly higher in the young stands (15 and 25 years) than in the old stands (35 and 45 years), while the hydrolase activity showed the opposite trend. The main reason for the higher decomposition rate in young stands of R. pseudoacacia was the high oxidase enzyme activities and less complex but more specialized microbial network of younger stands. The occurrence network was used to identify the keystone taxa by statistical analysis, and the key taxa changed from Acidobacteria to Proteobacteria during vegetation restoration. These findings demonstrate that vegetation restoration alters the soil microorganism community and network structure during fine-root decomposition of R. pseudoacacia. This finding is of great significance for understanding the role of microorganisms in regulating fine-root decomposition dynamics.

岩溶地区不同石漠化程度下草地细根对土壤养分的贡献

细根分解和周转是土壤有机质和养分的重要来源。为探明不同石漠化程度天然草地细根对土壤养分的贡献，于2017年3月至次年1月，采用土柱法和分解袋法，研究不同石漠化程度下天然草地的细根生物量、分解和养分释放动态及对石漠化的响应。结果表明：3种不同石漠化程度下草地的细根生物量随季节均呈现先增加后降低的趋势，随石漠化程度的加剧均呈现逐渐降低的趋势，潜在、中度和强度石漠化草地的细根生物量分别为3355.65、2944.02 g/m²和1806.80 g/m²。细根分解速率呈现先快后慢的趋势，分解300天后的残留率均低于50%。细根有机碳、全氮、全磷和全钾的释放过程具有显著不同，释放模式最终均表现为"释放"，潜在、中度和强度石漠化草地细根的有机碳、全氮、全磷、全钾的年归还量分别为32.46-161.08、0.24-3.88、0.08-0.32、0.15-2.78 g/m²。随石漠化程度的加剧，细根生物量和分解率呈现逐渐降低趋势，土壤有机碳、全氮归还量呈现逐渐增加趋势。;The degradation land of rocky desertification is one of the most serious problems on economic development, ecosystem restoration and reconstruction in Southwest China. Grassland is one of the main vegetation types in karst area, and its fine root is sensitive to the response of environmental conditions, which determines the growth and development of plants and soil nutrition status. Fine root also has an indicator effect on the environmental changes, and can reflect the health status of grassland ecosystem. As the intermediary connecting the aboveground and underground parts of vegetation, fine root plays an important role in the matter exchange and energy transfer between plants and soil, helps plants sequestrate carbon and provide for nutrient and water uptake into plants. Fine root decomposition and turnover contribute significantly to element cycling in grassland ecosystems. In karst area, fine root dynamics are controlled by the complex interaction of environmental and biotic factors. In order to explore the contribution of fine root to soil nutrients in three grasslands with different degrees of rocky desertification, the sequential soil coring and root bag methods were used to study the fine root biomass, dynamic of decomposition and release of nutrient and their responses to rocky desertification in the potential, medium and severe rocky desertification grasslands from March 2017 to January 2018. The results showed that the fine root biomass increased first and then decreased with the seasons in the three types of grasslands with different degrees of rocky desertification, while decreased with the intensification of rocky desertification. The fine root biomass was 3355.65 g/m², 2944.02 g/m² and 1806.80 g/m² in the potential, medium and severe rocky desertification grasslands. The decomposition rate of fine root showed the fast-slow trend, and the residual rate of dry matter was all less than 50% after 300 days. The releasing process of fine root organic carbon, nitrogen, phosphorus and potassium was significantly different, and the pattern of releasing was release finally. The annual return amount of fine root organic carbon, total nitrogen, total phosphorus and total potassium was 32.46-161.08 g/m², 0.24-3.88 g/m², 0.08-0.32 g/m² and 0.15-2.78 g/m², respectively. With the intensification of rocky desertification, fine root biomass and fine root decomposition rate showed a gradually decreasing trend, while the releasing of soil organic carbon and total nitrogen showed a gradually increasing trend. Therefore, knowledge of fine root dynamics and nutrient release across a broad karst area with the ability to examine the feedbacks occurring between fine root and rocky desertification is critical to our understanding of the nutrient cycle and for protecting degraded grassland and restoring vegetation.

Measurements of fine root decomposition rate: Method matters

Fine root decomposition plays a major role in biogeochemical cycle in forests. Litterbags and intact cores are predominant methods for measuring fine root decomposition rate. However, their efficacies have not been critically reviewed. In this study, we identify six sources of error for both methods including use of unrepresentative substrates, changes in decomposer community composition, altered effects of living roots and mycorrhizal fungi, differences in experimental duration length and sampling regime, confounding of spatiotemporal resolution, and limited temporal resolution. We present an indirect method to quantify fine root decomposition rate by integrating soil core and minirhizotron measurements into a new equation. The indirect method requires measuring more fine root parameters but can generally overcome the weaknesses associated with litterbag and intact core methods. Directly measuring the decomposition rate inevitably disturbs interactions between roots, soil fauna and rhizosphere microbes, which could significantly undermine the credibility of the estimates. Indirect measurement based on fine root growth and death rates, biomass and necromass that can be assessed reliably should be the future choice.

Degradation-driven changes in fine root carbon stocks, productivity, mortality, and decomposition rates in a palm swamp peat forest of the Peruvian Amazon

BackgroundAmazon palm swamp peatlands are major carbon (C) sinks and reservoirs. In Peru, this ecosystem is widely threatened owing to the recurrent practice of cutting Mauritia flexuosa palms for fruit harvesting. Such degradation could significantly damage peat deposits by altering C fluxes through fine root productivity, mortality, and decomposition rates which contribute to and regulate peat accumulation. Along a same peat formation, we studied an undegraded site (Intact), a moderately degraded site (mDeg) and a heavily degraded site (hDeg) over 11 months. Fine root C stocks and fluxes were monthly sampled by sequential coring. Concomitantly, fine root decomposition was investigated using litter bags. In the experimental design, fine root stocks and dynamics were assessed separately according to vegetation type (M. flexuosa palm and other tree species) and M. flexuosa age class. Furthermore, results obtained from individual palms and trees were site-scaled by using forest composition and structure.ResultsAt the scale of individuals, fine root C biomass in M. flexuosa adults was higher at the mDeg site than at the Intact and hDeg sites, while in trees it was lowest at the hDeg site. Site-scale fine root biomass (Mg C ha−1) was higher at the mDeg site (0.58 ± 0.05) than at the Intact (0.48 ± 0.05) and hDeg sites (0.32 ± 0.03). Site-scale annual fine root mortality rate was not significantly different between sites (3.4 ± 1.3, 2.0 ± 0.8, 1.5 ± 0.7 Mg C ha−1 yr−1 at the Intact, mDeg, and hDeg sites) while productivity (same unit) was lower at the hDeg site (1.5 ± 0.8) than at the Intact site (3.7 ± 1.2), the mDeg site being intermediate (2.3 ± 0.9). Decomposition was slow with 63.5−74.4% of mass remaining after 300 days and it was similar among sites and vegetation types.ConclusionsThe significant lower fine root C stock and annual productivity rate at the hDeg site than at the Intact site suggests a potential for strong degradation to disrupt peat accretion. These results stress the need for a sustainable management of these forests to maintain their C sink function.

Effects of sulfuric, nitric, and mixed acid rain on the decomposition of fine root litter in Southern China

BackgroundChina has been increasingly subject to significant acid rain, which has negative impacts on forest ecosystems. Recently, the concentrations of NO3− in acid rain have increased in conjunction with the rapid rise of nitrogen deposition, which makes it difficult to precisely quantify the impacts of acid rain on forest ecosystems.MethodsFor this study, mesocosm experiments employed a random block design, comprised of ten treatments involving 120 discrete plots (0.6 m × 2.0 m). The decomposition of fine roots and dynamics of nutrient loss were evaluated under the stress of three acid rain analogues (e.g., sulfuric (SO42−/NO3− 5:1), nitric (1:5), and mixed (1:1)). Furthermore, the influences of soil properties (e.g., soil pH, soil total carbon, nitrogen, C/N ratio, available phosphorus, available potassium, and enzyme activity) on the decomposition of fine roots were analyzed.ResultsThe soil pH and decomposition rate of fine root litter decreased when exposed to simulated acid rain with lower pH levels and higher NO3− concentrations. The activities of soil enzymes were significantly reduced when subjected to acid rain with higher acidity. The activities of soil urease were more sensitive to the effects of the SO42−/NO3− (S/N) ratio of acid rain than other soil enzyme activities over four decomposition time periods. Furthermore, the acid rain pH significantly influenced the total carbon (TC) of fine roots during decomposition. However, the S/N ratio of acid rain had significant impacts on the total nitrogen (TN). In addition, the pH and S/N ratio of the acid rain had greater impacts on the metal elements (K, Ca, and Al) of fine roots than did TC, TN, and total phosphorus. Structural equation modeling results revealed that the acid rain pH had a stronger indirect impact (0.757) on the decomposition rate of fine roots (via altered soil pH and enzyme activities) than direct effects. However, the indirect effects of the acid rain S/N ratio (0.265) on the fine root decomposition rate through changes in soil urease activities and the content of litter elements were lower than the pH of acid rain.ConclusionsOur results suggested that the acid rain S/N ratio exacerbates the inhibitory effects of acid rain pH on the decomposition of fine root litter.

The coordination between leaf and fine root litter decomposition and the difference in their controlling factors

AbstractAimAs the two largest components of plant detritus input, leaf and root litter together determine ecosystem vegetation turnover and nutrient cycling rates. However, the similarities and differences between the factors controlling their decomposition remain unknown. We evaluated the relationship between leaf and fine root litter decomposition across biomes and analysed how litter traits, climate, soil conditions and decomposers shape their relationship.LocationGlobal.Time period1984–2020.Major taxa studiedVascular plants.MethodsWe collected 352 paired leaf and fine root decomposition rates (k values) and ancillary traits, climate, soil condition and decomposer abundance data from 88 sites spanning the major global biomes. Boosted regression trees (BRTs) were applied to partition the factors that control root and leaf decomposition rates.ResultsAveraged across all biomes, leaf litter decomposes significantly faster (kleaf = .72) than fine root litter (kroot = .42). The BRTs indicated that plant traits best explained the variance in both leaf and root litter decomposition. The key chemical traits of leaf litter and fine root litter, including C:N, [P], N:P, [lignin], [cellulose], [non‐structural carbohydrates] and [tannins], were positively correlated. Therefore, leaf and fine root k values were positively correlated within and across biomes, even after removing the influence of climate, soil conditions and decomposers. However, climate and decomposers had different impacts on leaf and fine root decomposition. Climate induced a greater impact on fine root litter decomposition, whereas decomposers had a greater influence on leaf litter decomposition.Main conclusionsOur finding indicates that plants evolve a coordinated nutrient supply‐and‐demand strategy. The plants with high nutrient demand produce labile leaf and fine root litter, which decomposes fast to meet their high nutrient requirements. However, leaf and fine root decomposition are also mediated by different combinations of trait, climate, soil condition and decomposer factors, which weakens the coordination between leaf and fine root decomposition.

The role of mangrove fine root production and decomposition on soil organic carbon component ratios

Mangrove fine roots are an important contributor to soil organic matter (SOC), yet how their production and decomposition affect SOC accumulation across the sea-land gradient is still elusive. This study aimed to investigate the influencing path of biotic and abiotic factors of fine root production and decomposition dynamics on SOC component ratios involving particulate organic carbon (POC)/SOC, dissolved organic carbon (DOC)/SOC, and microbial biomass carbon(MBC)/SOC. Based upon sequential root coring and the litter bag method, the production, and decomposition of mangrove fine roots were investigated. The production and turnover rate of mangrove fine roots increased from 90.9 g·m−2 to 510.9 g·m−2 and 0.44 yr−1 to 1.49 yr−1 across the sea-land gradient respectively. After one year of decomposition, 69.5–80.8% and 58.3–69.2% of low-order and high-order fine roots remained, respectively. Decomposition rates of both low-order and high-order fine roots were significantly slower in the landward zone than in the seaward zones. Redundancy analysis (RDA) illustrated that vegetation biomass and soil salinity were respectively the main biotic and abiotic factors affecting the production and decomposition of mangrove fine roots and they explained 91.2% of mangrove fine root production and decomposition. Stepwise regression analysis indicated that the production of fine roots was mainly influenced by mangrove vegetation biomass while their decomposition was negatively affected by soil salinity. POC and SOC increased significantly from 20.13 t·ha−1 to 58.71 t·ha−1 and 78.42 t·ha−1 to 139.01 t·ha−1 respectively while DOC/SOC and MBC/SOC reduced from 0.33 to 0.24 and from 0.55 to 0.44 across the sea-land gradient. RDA results indicated that low-order fine root production was the major control of the ratio of SOC components among the production and decomposition of low-order and high-order fine roots, explaining 90.9% of SOC component ratio changes. Based upon structural equation modeling, the path coefficient of biotic and abiotic factors POC/SOC was 0.914 (P < 0.001), indicating that mangrove fine root production affecting by vegetation biomass and soil salinity was the main drive of SOC accumulation. Nevertheless, mangrove fine root decomposition played a minor role in SOC component change. The information gained in this study will facilitate policy decisions concerning the restoration of mangrove forests in China.

Changes in fine root decomposition of primary Pinus koraiensis forest after clear cutting and restoration succession into secondary broad-leaved forest

Fine root decomposition is one of the primary mechanisms by which nutrient uptake and C exchange occur in terrestrial ecosystems, which will be likely affected by forest succession. Herein, we compared the fine root decomposition rates of primary Korean pine forest (PK) and secondary broad-leaved forest (SF) using the litter bag method; then conducted an in-depth analysis of differences in the PK and SF fine root decomposition process. Our results demonstrated that the fine root decomposition in PK was significantly faster than that in SF. In general, the percent (%) mass of the main nutrient elements remaining in SF fine roots was significantly higher than that in PK, indicating that PK can more efficiently return soil nutrients through fine root decomposition. We also found that the succession of PF to SF induced significant alternation of the microbial community composition and decreased activities of soil enzymes. Structural equation modeling further demonstrated that fine root K and lignin were the key substrate-level factors affecting fine root decomposition, while actinomycetes and fungi PLFA biomass change played the most important role among all the functional groups. Finally, we determined that fine root degradation was driven by polyphenol oxidase and acid phosphatase enzymatic activities. This study elucidates the complex interactions between fine root substrate and soil physiochemical properties and demonstrates how they affect fine root decomposition via soil microorganisms. Given that these changes continue over long time scales, the secondary forest will experience increased difficulty return to the original primary Korean pine broad-leaved forest vegetation.

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

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 (< 1 mm) of Deyeuxia angustifolia (grass) and Betula fruticosa (shrub) from a freshwater wetland in the Sanjiang Plain, Northeast China, and decomposition rates of their monocultures and mixtures (with 2:1 and 1:2 mass ratios) were determined by measuring carbon (C) mineralization and mass loss with a 365 days incubation experiment. Meanwhile, litter mixing effects were assessed by the differences in observed decomposition rates of root mixtures and predicted values based on the performance of component species decomposing alone. Betula fruticosa fine roots had higher N, total polyphenol, and condensed tannin concentrations than D. angustifolia fine roots. By the end of incubation, B. fruticosa fine roots generally had greater C mineralization rate and mass loss than the other three root treatments. Notably, both C mineralization rate and mass loss were lower than the expected values in the B. fruticosa-dominant mixture, whereas there were no significant differences between observed and expected values in the D. angustifolia-dominant mixture. Our findings imply that the increase in woody plant abundance will exert influences on fine root decomposition rates through altered substrate quality and litter mixing effects in grass-dominated temperate wetlands.

Phosphorus addition accelerates fine root decomposition by stimulating extracellular enzyme activity in a subtropical natural evergreen broad-leaved forest

Nitrogen (N) plays a vital role in litter decomposition by interacting with microbial activity in temperate and boreal ecosystems. However, in tropical and subtropical forests, where low soil phosphorus (P) availability is widespread, how P affects litter decomposition remains unclear. In the present study, litter-bag method was used to conduct fine root decomposition by P addition experiment in a subtropical natural evergreen broad-leaved forest. Fine roots were collected from two tree species: Cunninghamia lanceolata and Castanopsis carlesii, and their mixture in equal proportion as well. At the end of 2-year experiment, we found an enhancement of soil total P, available P, pH and microbial biomass carbon content, and increased abundance of all the examined microbial groups and total PLFA biomass after P addition. Annual decomposition constants of fine roots of both tree species and the mixture (0.615–1.049) were all elevated, but to different extents by P addition, with fine roots of lower initial P concentration corresponding to higher increase in decomposition rate. Average acid phosphatase activities during decomposition were significantly decreased, but there was a general increase for β-glucosidase (βG), cellobiohydrolase (CBH), phenol oxidase, peroxidase (PerOx) and N-acetyl glucosaminidase (NAG) activities. The response ratios of enzyme activities, which differed for the three experimental fine roots, corresponded to the individual increase in decomposition rates. Correlation analysis demonstrated that fine root decomposition rates were significantly related to initial P concentration, extractives and acid-insoluble fractions of fine roots, and activities of βG, CBH, NAG and PerOx as well. Taken together, our results demonstrate that fine root decomposition can be constrained by P availability through affecting microbial activity in this subtropical natural forest.

Exogenous and endogenous nitrogen differentially affect the decomposition of fine roots of different diameter classes of Mongolian pine in semi-arid northeast China

Nitrogen (N) addition could affect litter decomposition through its direct effects on soil N availability and indirect effects on initial litter chemistry. The aim of this study was to evaluate the relative contribution of these direct and indirect effects to the decomposition of fine roots with different diameter classes. A two-year reciprocal replant–transplant field experiment was conducted in a Mongolian pine (Pinus sylvestris var. mongolica) plantation to examine the relative effect of exogenous and endogenous N enrichment induced by N addition (10 g N m−2 yr.−1) on the decomposition of fine roots with different diameter classes: < 0.5 mm (small fine root, SFR) and 0.5–2 mm (large fine root, LFR). The LFR had significantly higher decomposition rates (k: 0.315–0.397 yr.−1) than the SFR (0.245–0.274 yr.−1) after 2 years of incubation. Exogenous N (i.e., increased soil N availability due to N addition) had no significant effect on the decomposition rates of fine roots, whereas endogenous N (i.e. increased N concentration in litter due to N addition) inhibited and accelerated the decomposition of SFR and LFR, respectively. Endogenous N decreased the net release of N but both endogenous and exogenous N increased the net release of phosphorus (P) from SFR. By contrast, exogenous and endogenous N decreased the net release of N and P from LFR. Our results suggest that N addition affected fine root decomposition indirectly by changing the chemical traits of fine roots rather than directly through changing soil N availability. Elevated input and decreased net N release of fine roots might be a potential mechanism explaining the increases of total organic carbon and total N in the semi-arid forest soil under N addition. Our study also suggests that SFR may be a more important source of stable soil organic matter relative to LFR.

Retention trees slow post-harvest fine-root decomposition in a coastal temperate rainforest

Fine roots are a dominant, but often overlooked source of carbon (C) in forest soils, and decomposition of this material may have important consequences for C storage and turnover in forest ecosystems. Forest harvesting modifies soil physicochemical properties and microbial communities, which may lead to faster decomposition rates, but the effect of harvesting on fine-root decomposition is rarely investigated. Variable-retention harvesting, where some trees are left on site after harvest, often results in lower soil moisture and temperature, and increased ectomycorrhizal diversity relative to clearcut harvesting. As such, this harvesting practice may influence fine-root decomposition rates. In Douglas-fir forests in coastal British Columbia, we measured fine-root (<2 mm diameter) decomposition rates in variable-retention (aggregate and dispersed arrangements), clearcut, and uncut treatments, and determined if any effects persisted as stands aged. Within the variable-retention treatments, we also examined if fine-root decomposition rates varied with distance from retention trees or retention patches. Further, we determined which soil physicochemical variables best explained variation in fine-root carbon loss after two years of decomposition. Increased tree coverage slowed fine-root decomposition; fine roots decomposed as slowly under variable-retention treatments as in uncut stands, and 15–19% more carbon was retained in these treatments relative to the clearcut treatment. Fine roots also decomposed faster with increasing distance from retention patches or retention trees as decomposition was twofold slower in the aggregate centre relative to open areas, with similar patterns observed in the dispersed retention treatment. However, fine roots decomposed at similar rates in forests and stands with more advanced regeneration, suggesting the effects of harvesting on decomposition rates was not persistent. Across all sampling locations, 37% of the variation in fine-root carbon loss was explained by fine-root biomass, and nitrate, potassium and sulphate availability. Nitrate availability was also positively correlated with the proportional mass of carbon lost during the decomposition experiment, suggesting that fine-root decomposition is sensitive to harvesting-induced changes in soil physicochemistry, and that variable-retention harvesting moderates the effects of harvesting on decomposition rates. These findings indicate that shortly after harvest, retention of even single trees can prevent the increase in fine-root decomposition rates associated with clearcut harvesting in these coastal Douglas-fir forests. Accordingly, management practices such as variable-retention harvesting that retain some trees in a cutblock may reduce soil C losses following forest harvesting.

Limited Effects of Variable-Retention Harvesting on Fungal Communities Decomposing Fine Roots in Coastal Temperate Rainforests.

Fine root litter is the principal source of carbon stored in forest soils and a dominant source of carbon for fungal decomposers. Differences in decomposer capacity between fungal species may be important determinants of fine-root decomposition rates. Variable-retention harvesting (VRH) provides refuge for ectomycorrhizal fungi, but its influence on fine-root decomposers is unknown, as are the effects of functional shifts in these fungal communities on carbon cycling. We compared fungal communities decomposing fine roots (in litter bags) under VRH, clear-cut, and uncut stands at two sites (6 and 13 years postharvest) and two decay stages (43 days and 1 year after burial) in Douglas fir forests in coastal British Columbia, Canada. Fungal species and guilds were identified from decomposed fine roots using high-throughput sequencing. Variable retention had short-term effects on β-diversity; harvest treatment modified the fungal community composition at the 6-year-postharvest site, but not at the 13-year-postharvest site. Ericoid and ectomycorrhizal guilds were not more abundant under VRH, but stand age significantly structured species composition. Guild composition varied by decay stage, with ruderal species later replaced by saprotrophs and ectomycorrhizae. Ectomycorrhizal abundance on decomposing fine roots may partially explain why fine roots typically decompose more slowly than surface litter. Our results indicate that stand age structures fine-root decomposers but that decay stage is more important in structuring the fungal community than shifts caused by harvesting. The rapid postharvest recovery of fungal communities decomposing fine roots suggests resiliency within this community, at least in these young regenerating stands in coastal British Columbia.IMPORTANCE Globally, fine roots are a dominant source of carbon in forest soils, yet the fungi that decompose this material and that drive the sequestration or respiration of this carbon remain largely uncharacterized. Fungi vary in their capacity to decompose plant litter, suggesting that fungal community composition is an important determinant of decomposition rates. Variable-retention harvesting is a forestry practice that modifies fungal communities by providing refuge for ectomycorrhizal fungi. We evaluated the effects of variable retention and clear-cut harvesting on fungal communities decomposing fine roots at two sites (6 and 13 years postharvest), at two decay stages (43 days and 1 year), and in uncut stands in temperate rainforests. Harvesting impacts on fungal community composition were detected only after 6 years after harvest. We suggest that fungal community composition may be an important factor that reduces fine-root decomposition rates relative to those of above-ground plant litter, which has important consequences for forest carbon cycling.

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.

Dynamics of fine root decomposition and its affecting factors of Pinus massoniana in the Three Gorges Reservoir Area, China.

A decomposition experiment for a year was conducted at Jiulingtou Forest Farm, Zigui County, Hubei Province, China to examine the decomposition dynamics of fine roots with different diameters (<0.5, 0.5-1 and 1-2 mm) and its main affecting factors for Pinus massoniana. The results showed that the decomposition rate decreased with the increasing root diameter. The annual decomposition rates for fine roots with diameters <0.5, 0.5-1 and 1-2 mm were 34.0%, 28.0% and 25.7%, respectively. The decomposition rate of <1 mm fine root decreased along time, and 1-2 mm fine root increased first and then decreased. In the fine root decomposition process, N, P and Ca concentrations increased along time, and K concentration decreased firstly, then increased, and then decreased along time. Fine root decomposition rate was significantly related to initial chemical composition (N, P, K, Ca, C/N and C/P) of fine roots. Ca concentration in fine root and soil temperature were the major factors affecting fine root decomposition.

Decomposition rates of fine roots from three herbaceous perennial species: combined effect of root mixture composition and living plant community

Aims In most ecosystems, plant roots from different species decompose in mixtures and in the presence of living roots; however much root decomposition research has focused on how roots of individual species or artificial mixtures decompose in the absence of living plants. We thus examined two poorly studied components of root litter decomposition: 1) whether decomposition of root mixtures can be predicted from the sum of the decomposition rates of each component species and 2) how living plants influence rates of root decomposition.

Condensed tannin effects on decomposition of very fine roots among temperate tree species

Below-ground litter is the dominant soil carbon and nutrient input in many ecosystems, yet the general functional traits underlying below-ground decomposition remain elusive. As defensive compounds, condensed tannin (CT) might be expected to be abundant in very fine roots (<0.5 mm) and are associated with decomposition dynamics. Here, we quantified the interspecific variation in fine root CT concentrations and examined the functional significance of CT for fine root decomposition over four years among 15 Chinese temperate tree species. Concentrations of CT varied between 5.82% and 16.02% among species. After four years of decomposition, initial litter nutrients explained no interspecific variation in fine root decomposition rates in this relatively nutrient-rich temperate forest. In contrast, substrate carbon compounds strongly control the process of fine root decomposition and CT was important for predicating fine root decomposition rates. Our results imply that the strong negative effects of CT on fine root decomposition can have great impacts on soil biological processes.

Effects of experimental throughfall reduction and soil warming on fine root biomass and its decomposition in a warm temperate oak forest

Fine root dynamics play a critical role in regulating carbon (C) cycling in terrestrial ecosystems. Examining responses of fine root biomass and its decomposition to altered precipitation pattern and climate warming is crucial to understand terrestrial C dynamics and its feedback to climate change. Fine root biomass and its decomposition rate were investigated in a warm temperate oak forest through a field manipulation experiment with throughfall reduction and soil warming conducted. Throughfall reduction significantly interacted with soil warming in affecting fine root biomass and its decomposition. Throughfall reduction substantially increased fine root biomass and its decomposition in unheated plots, but negative effects occurred in warmed plots. Soil warming significantly enhanced fine root biomass and its decomposition under ambient precipitation, but the opposite effects exhibited under throughfall reduction. Different responses in fine root biomass among different treatments could be largely attributed to soil total nitrogen (N), while fine root decomposition rate was more depended on microbial biomass C and N. Our observations indicate that decreased precipitation may offset the positive effect of soil warming on fine root biomass and decomposition.