Litter Lignin Research Articles

Effects of graphene oxide composite additive on the species abundance and diversity of microorganisms in saline-alkali soil

Saline-alkali soil is common in north China, especially in the Datong district in north Shanxi province. Improving the soil will benefit the environment and society. Graphene oxide (GO) has been shown to benefit agricultural and forest soils. Herein we explore three different experimental conditions of CK (CK means irrigated with tap water), CJ (CJ means 0.2 g of bacteria addition and irrigated with tap water) and CJ25 (CJ25 means 0.2 g of composited bacteria plus 25.0 mg/L of graphene oxide added and irrigated with tap water) for saline-alkali soil by the addition of optimized amounts of graphene oxide and external bacteria. Our results show that the addition of 25.0 mg/L graphene oxide and microbial agents increases the number of bacteria and fungi in the soil and improves the species abundance of bacteria and fungi in the saline-alkali soil, while having little effect on species richness. The graphene oxide and bacterial treatment increased the abundance of Proteobacteria, Actinobacteriota, Chloroflexi, Pseudomonas, Ascomycota, Mortierella and Fusarium. These bacteria have been shown to produce proteolytic enzymes and cellulases that decompose lignin and cellulose in litter, and thus play important roles in carbon and nutrient cycling. The addition of graphene oxide and microorganisms provide a viable way to improve saline-alkali soils.

Isotopic analysis (δ13C and δ2H) of lignin methoxy groups in forest soils to identify and quantify lignin sources

The relative apportion of above and below ground carbon sources is known to be an important factor in soil organic matter formation. Although lignin is the most abundant aromatic plant material in the terrestrial biosphere, our understanding of lignin source contributions to soil organic matter (SOM) is limited due to the complex molecular structure and analysis of lignin. In this study, we novelly apply the dual isotopic analysis (δ13C and δ2H values) of lignin methoxy groups (LMeO) with the Bayesian mixing model, MixSIAR, to apportion lignin sources in two contrasting soil types, a podzol and a stagnosol. Results of the isotopic analysis of LMeO demonstrate the ability of δ2H LMeO values to discriminate between above and below ground lignin sources, while δ13C LMeO values discriminated between photosynthesising and non-photosynthesising tissues. In the stagnosol subsurface horizons, a decreasing proportion of the leaf litter lignin was observed with increasing organic matter degradation, cumulating in the Ah horizon being dominated by lignin from roots. The podzol sites indicated a similar reduction in leaf litter lignin with an increase in organic matter degradation and depth. However, the Ah horizon was shown to accumulate lignin from the above ground woody material. Furthermore, given the significant abundance of LMeO groups in the terrestrial biosphere and the extremely depleted δ13C LMeO values in leaf litter, we employed a mass balance approach to determine the extent in which the 13C bulk enrichment generally associated with isotopic fractionation during organic matter decomposition can be attributed to the shift in lignin sources. Analysis reveals that 14 % and 11 % of bulk 13C enrichment can be attributed to the transition in LMeO sources from leaf litter to roots in the stagnosol and podzol, respectively. Thus, models relying on 13C enrichment with depth as an indicator of carbon turnover may be partially overestimating rates.

Dual Effect of Microplastics and Cadmium on Stream Litter Decomposition and Invertebrate Feeding Behavior

This study investigates the combined effect of microplastics and cadmium on the decomposition of litter, the structure of fungal communities, and the feeding behavior of invertebrates in an aquatic ecosystem. Through a series of microcosm experiments, we demonstrate that exposure to MPs and Cd significantly reduced the decomposition of leaf litter. Notably, the cumulative impact of combined MP and Cd exposure was found to be greater than their individual effects. During this process, the carbon–nitrogen ratio of the litter increased, while dehydrogenase activity and fungal biomass were inhibited. Additionally, the relative abundance of Ascomycota and Basidiomycota fungi decreased, weakening their role in the decomposition of leaf litter. Conversely, MPs and Cd reduced the relative content of leaf litter lignin, improving its quality as food, thereby leading to an increase in the feeding rate of invertebrates. This dual effect indicates that micropollutants suppress the decomposition of litter by regulating microbial metabolic activity and fungal community structure but promote invertebrate feeding. Our findings provide crucial insights into the adverse effects of MPs and Cd on the structure and diversity of aquatic fungal communities, which could have long-term impacts on the food webs and nutrient cycling progress of aquatic ecosystems.

Potential effects of soil petroleum contamination on decomposition of Artemisia annua plant litter.

The accumulation of petroleum contaminants in phytoremediating plants can significantly impact the decomposition of their litter. However, the mechanisms underlying these effects and the potential influence of the contaminant concentration remain unclear. In this study, litter from Artemisia annua plants grown in soil with varying concentrations of petroleum (0, 15, 30, and 45 g kg-1) was collected. The litter samples were then inoculated with soil microorganisms and subjected to an indoor simulation of decomposition under controlled temperature and humidity conditions. Changes in the chemical properties, activities of decomposition-related enzymes in the litter, and decomposition rates were measured. Additionally, structural equation modeling was employed to analyze the mechanism through which soil petroleum contamination affects litter decomposition. The findings revealed several key points: (1) increasing soil petroleum contamination tended to reduce the concentration of carbon and nitrogen in litter while increasing those of lignin and total petroleum hydrocarbons (TPH). (2) Soil petroleum contamination tended to increase the activities of both total lignocellulases and total nutrient cycling-related enzymes in litter. (3) Soil petroleum contamination might indirectly inhibit the activity of lignocellulases by increasing the concentration of lignin and TPH in litter. However, it might also directly accelerate the activity of these enzymes, resulting in contradictory effects on litter decomposition. (4) Finally, A. annua litter produced in soil contaminated with 15 and 30 g kg-1 of petroleum exhibited significantly lower decomposition rates than that from uncontaminated soil.

Short-term nitrogen deposition changes chemical composition of litter and soil organic matter in a Moso bamboo forest

To investigate the effects of short-term nitrogen (N) deposition on organic matter composition of litter and soil in Moso bamboo (Phyllostachys edulis) forests, we established a N-addition treatments (50 kg N·hm-2·a-1) to simulate the ambient and N deposition in a subtropical Moso bamboo forest from July 2020 to January 2022. We analyzed the organic matter composition of Moso bamboo leaf/root litter and soil by using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) technique. The results showed that short-term N deposition significantly increased the relative content of soil phenols by 50.9%, while significantly decreased fatty acids by 26.3%. The rela-tive content of alkanes & alkenes and lignin in leaf litter was significantly increased by 51.9% and 33.5%, respectively, while that of phenols and polysaccharides significantly decreased by 52.2% and 56.3%. In root litter, eleva-ted N significantly decreased the relative content of polycyclic aromatic hydrocarbons by 16.6%. Moreover, the relative content of fatty acids in soil organic matter was significantly positively correlated with the relative content of poly-saccharides in leaf litter. The relative content of phenols in soil organic matter was significantly positively correlated with the relative content of lignin, and negatively correlated with the relative content of polysaccharides in leaf litter. Our results demonstrated that short-term N deposition did not change the concentration of total organic carbon, total nitrogen, and C/N of the soil, leaf litter, and root litter, but significantly altered the chemical composition of organic matter. In addition, the changes in chemical composition of organic matter in soil under short-term N deposition were affected by the composition of organic matter in leaf litter.

Does Spartina invasion affect the carbohydrate assimilation of polychaetes in mangroves? A case study in the Zhangjiang Estuary Mangrove National Nature Reserve

Carbohydrates, which form a large pool of carbon in plant litter, are a major driver of litter dynamics and benthic food webs in Spartina-invaded mangrove ecosystems. However, there are large gaps in knowledge regarding the effects of exotic leaf litter carbohydrates on benthic carbon assimilation. In this study, the dynamics of carbohydrates, including cellulose, lignin and monosaccharides (glucose, mannose, galactose, xylose and arabinose), during the leaf litter decomposition of the exotic Spartina alterniflora (SA) and the native mangrove plant Kandelia obovata (KO) were analyzed and compared. Meanwhile, the differences in the δ13C values of cellulose and lignin were used to analyze the utilization of leaf litter carbohydrates by polychaetes after Spartina invasion. Our results showed that the decomposition rate of exotic SA leaf litter was lower than that of KO leaf litter. The contents of cellulose, glucose and galactose in SA leaf litter were higher than those in KO leaf litter (P < 0.05). The decomposition rates of cellulose and monosaccharides (arabinose, xylose, mannose and galactose) in KO leaf litter were faster than those in SA leaf litter (P < 0.05). However, there was no significant difference in the decomposition rates of lignin in the leaf litter between exotic SA leaf litter and native KO leaf litter (P > 0.05). In the native KO plot, the carbohydrates of KO leaf litter contributed to >55% (cellulose, 26.91–28.02%; lignin, 28.05–28.64%) of the organic carbon sources of polychaetes. However, in the exotic SA plot, the carbohydrates of exotic SA leaf litter contributed to >65% (cellulose, 36.83–38.30%; lignin, 28.47–30.52%) of the organic carbon sources of polychaetes. The obtained results suggested that Spartina invasion increased the assimilation of cellulose by polychaetes. The high content and low decomposition rate of cellulose in the carbohydrates of exotic SA leaf litter might be important mechanisms for the carbon assimilation changes in the benthos of Spartina-invaded mangrove ecosystems. Given that Spartina has colonized in the Zhangjiang Estuary Mangrove Reserve, this study provides a theoretical basis for the recovery of benthos after ecological restoration. Furthermore, the mechanisms of carbohydrate assimilation by different benthos of different ecosystems should be comprehensively considered in the future.

Dynamics of litter decomposition rate and soil organic carbon sequestration following vegetation succession on the Loess Plateau, China

Litter quality determines the decomposability of litter and the proportion of recalcitrant residues, which in turn can affect the accumulation of soil organic carbon (SOC). However, the impact of litter decomposition on SOC turnover following vegetation succession has not been systematically studied. To clarify the dynamics and mechanisms of litter decomposition and SOC sequestration following vegetation succession, this study conducted a decomposition experiment across four successional stages: grassland (∼30 years), shrubland (∼60 years), pioneer forest (∼110 years), and climax forest (∼160 years). This study also analyzed the litter quality and the SOC turnover rate. The results showed that litter decomposition rates gradually decreased with vegetation succession. Litter lignin content (LC), and nitrogen content (LN) were the major factors controlling the change of litter decomposition rate. Litter with a high LC: LN ratio and lignin: LN ratio exhibited a lower decomposition rate, whereas the opposite was found for litter with a higher LN content. The increase in the SOC content mainly occurred in the early successional stage (<110 years), with a higher litter decomposition rate and SOC turnover rate. At the later stage (≥110 years), the SOC was close to saturation, together with low rates of litter decomposition and SOC turnover. The variation trend of the mineral-associated organic carbon (MAOC) content was the same as that of the SOC content, resulting from continuous litter inputs. Based on the above results, litter inputs can significantly increase the SOC content in the early successional stage, and soil carbon sequestrations gradually reach saturation in the late successional stage. The findings of this study strengthen our understanding of the changes in litter decomposition and its contribution to SOC sequestration following vegetation succession.

Temperature dependency of litter decomposition is not demonstrated under reciprocal transplantation of tussock leaves along an altitudinal gradient

Abstract Decomposition rates are an important component of carbon sequestration rates in soils, potentially mitigating future climate change. Here we aim to better understand decomposition's relationship with temperature in natural conditions. In snow‐tussock grassland dominated by Chionochloa rubra on Mount Tongariro, Tongariro National Park, New Zealand, we measured decomposition of Chionochloa leaf litter along an ≈ 700 m altitudinal gradient, as a space‐for‐temperature experiment, representing 4.2°C of warming. We examined decomposition rates in a full reciprocal translocation of litter bags between eight plots as both the origin of eight litter types and the eight destinations of plating out of litter bags, over 4 years using six replicates, and modelled their relationships to environmental variates. Litter decomposed progressively over time, but at the same rate along the altitudinal gradient. There was no home‐field advantage. In terms of litter quality, decomposition rates were related only to litter lignin, or fibre or litter N. Only decomposition at Year 4, and that only when organised by litter destination, showed a relationship to mean annual temperature jointly with soil C, and this was only weak and implausible. When studied across the full reciprocal transplant, there were no significant interactions between Origin and Destination data with or without Years. Therefore litter from each plot decomposed at the same rate as other plots' litter at all altitudes, allowing for small, often irregular differences in litter quality and micro‐environment. Despite the few modelled differences, decomposition rates show no plausible trends in our altitude‐for‐temperature substitution. We suggest this may be a universal finding, except perhaps under different moisture regimes. Thus, under projected climate warming scenarios, changes in temperature will not directly affect decomposition rates, and cannot influence C sequestration in nature. Read the free Plain Language Summary for this article on the Journal blog.

Amazonian deforestation and its influence on soil biotic factors and abiotic properties

Deforestation in the Amazonian rainforest is the main cause of biodiversity loss, soil erosion, and climate change. Land covers influence the soil properties, soil biota community composition, and litter properties by providing habitat and nutrients. Our aim here was to present a quantitative analysis of the soil biochemical properties, soil biota assemblage, and litter properties associated with four land covers (primary Amazon rainforest, pasture, Hevea brasiliensis, and deforested sites) from the Brazil’s Legal Amazon, Rio Branco, Acre. The non-metric multidimensional scaling (NMDS) grouped the land covers in four groups considering the dissimilarities on soil biota abundance between each other. The SEM models showed that deforestation increased the soil pH, and decreased SOC, TN, P, microbial N biomass, microbial C biomass, litter lignin content, litter N, C and P contents, and biodiversity indices (Margalef index, and α diversity). The results of our study highlighted the importance of considering land covers in Brazil’s Legal Amazon, based on a sustainable way to improve soil quality and soil biodiversity, since even the studied monocropping system (pasture) showed decreases in habitat provision (litter deposition) and nutrient availability. Thus, the use of forest systems (H. brasiliensis) or the preservation of primary Amazon rainforest may positively influence the soil chemical properties, soil biota, and litter properties.

Plant litter chemistry controls coarse‐textured soil carbon dynamics

Abstract As soils store more carbon (C) than the Earth's atmosphere and terrestrial biomass together, the balance between soil C uptake in the form of soil organic matter (SOC) and release as CO2 upon its decomposition is a critical determinant in the global C cycle regulating our planet's climate. Although plant litter is the predominant source of C fuelling both soil C build‐up and losses, the issue of how litter chemistry influences this balance remains unresolved. As a contribution to solving that issue, we traced the fate of C during near‐complete decomposition of 13C‐labelled leaf and root litters from 12 plant species in a coarse‐textured soil. We separated the soil organic carbon into mineral‐associated organic matter (MAOM) and particulate organic matter (POM) pools, and investigated how 14 litter chemical traits affected novel SOC formation and native SOC mineralization (i.e. the priming effect) in these soil fractions. We observed an overall net increase in SOC due to the addition of litter, which was stronger for root than for leaf litters. The presumed stable MAOM‐C pool underwent both substantial stabilization and mineralization, whereas the presumably less stable POM‐C pool showed substantial stabilization and reduced mineralization. Overall, the initial increase in soil C mineralization was fully counterbalanced by a later decrease in native soil C mineralization. POM‐C formation as well as MAOM‐C formation and mineralization were positively related to the initial litter lignin concentration and negatively to that of the nitrogen leachates, whereas the opposite was observed for POM‐C mineralization. Synthesis. Our results highlight the importance of litter chemical traits for SOC formation, and stabilization, destabilization and mineralization. In our coarse‐textured soil, the amount of MAOM‐C did not change despite large C fluxes through this pool. The litter chemical traits that drove these processes differed from those frequently reported for fine‐textured soils far from mineral‐associated C saturation. To account for these discrepancies, we propose an integrative perspective in which litter quality and soil texture interactively control soil C fluxes by modulating several SOC stabilization and destabilization mechanisms. Irrespective, our results open new critical perspectives for managing soil C pools globally.

Changes in Soil Organic C Fractions and C Pool Stability Are Mediated by C-Degrading Enzymes in Litter Decomposition of Robinia pseudoacacia Plantations.

Litter decomposition is the main source of soil organic carbon (SOC) pool, regarding as an important part of terrestrial ecosystem C dynamics. The turnover of SOC is mainly regulated by extracellular enzymes secreted by microorganisms. However, the response mechanism of soil C-degrading enzymes and SOC in litter decomposition remains unclear. To clarify how SOC fraction dynamics respond to C-degrading enzymes in litter decomposition, we used field experiments to collect leaf litter and SOC fractions from the underlying layer in Robinia pseudoacacia plantations on the Loess Plateau. Our results showed that SOC, easily oxidizable organic C, dissolved organic C, and microbial biomass C increased significantly during the decomposition process. Litter decomposition significantly decreased soil hydrolase activity, but slightly increased oxidase activity. Correlation analysis results showed that SOC fractions were significantly positively correlated with the litter mass, lignin, soil moisture, and oxidase activity, but significantly negatively correlated with cellulose content and soil pH. Partial least squares path models revealed that soil C-degrading enzymes can directly or indirectly affect the changes of soil C fractions. The most direct factors affecting the SOC fractions of topsoil during litter decomposition were litter lignin and cellulose degradation, soil pH, and C-degrading enzymes. Furthermore, regression analysis showed that the decrease of SOC stability in litter decomposition was closely related to the decrease of soil hydrolase to oxidase ratio. These results highlighted that litter degradation-induced changes in C-degrading enzyme activity significantly affected SOC fractions. Furthermore, the distribution of soil hydrolases and oxidases affected the stability of SOC during litter decomposition. These findings provided a theoretical framework for a more comprehensive understanding of C turnover and stabilization mechanisms between plant and soil.

Forest gaps slow lignin and cellulose degradation of fir (Abies faxoniana) twig litter in an alpine forest

Forest gaps are an essential driver of litter decomposition in alpine forest ecosystems, but how gap size influences lignin and cellulose degradation in twig litter remains poorly understood. Here, we conducted an 8-year decomposition experiment to assess twig litter decomposition (i.e., mass loss, cellulose and lignin degradation) in four gap size classes in an alpine forest of Southwest China, including (1) large gaps (15–20 m in diameter), (2) medium gaps (10–15 m in diameter), (3) small gaps (<10 m in diameter) and (4) closed canopies. After 8 years of decomposition, the remaining mass, lignin and cellulose of twig litter was 32.71–36.85%, 39.82–49.84% and 15.77–21.34% across the gap size classes, respectively. Compared to the closed canopy, forest gaps decelerated the decomposition processes of twig litter, with significantly higher remaining of mass, lignin and cellulose of twig litter observed in the small gaps. However, changes in the gap size from small gaps to large gaps did not affect the decomposition rate or lignin and cellulose degradation of twig litter during the study. Furthermore, gap-induced changes in litter chemistry (i.e., N and P contents, C/N and lignin/N ratios) and microclimate (i.e., soil temperature and freeze–thaw events) had significant effects on the lignin and cellulose degradation of twig litter. These results indicate that the formation of gaps might slow the lignin and cellulose degradation of twig litter and that gap effects vary with changes in litter chemical properties among different litter substrates (i.e., leaves and twigs) in alpine forests.

Dose-responses for solar radiation exposure reveal high sensitivity of microbial decomposition to changes in plant litter quality that occur during photodegradation.

Plant litter decomposition is a key process for carbon (C) turnover in terrestrial ecosystems. Sunlight has been shown to cause and accelerate C release in semiarid ecosystems, yet the dose-response relationships for these effects have not been evaluated. We conducted a two-phase experiment where plant litter of three species was subjected to a broad range of cumulative solar radiation (CSR) exposures under field conditions. We then evaluated the relationships between CSR exposure and abiotic mass loss, litter quality and the subsequent biotic decomposition and microbial activity in litter. Dose-response relationships demonstrated that CSR exposure was modestly correlated with abiotic mass loss but highly significantly correlated with lignin degradation, saccharification, microbial activity and biotic decay of plant litter across all species. Moreover, a comparison of these dose-response relationships suggested that small reductions in litter lignin due to exposure to sunlight may have large consequences for biotic decay. These results provide strong support for a model that postulates a critical role for lignin photodegradation in the mechanism of photofacilitation and demonstrate that, under natural field conditions, biotic degradation of plant litter is linearly related with the dose of solar radiation received by the material before coming into contact with decomposer microorganisms.

Warming and grazing enhance litter decomposition and nutrient release independent of litter quality in an alpine meadow

Abstract Warming and grazing, and litter quality jointly determine litter decomposition and nutrient releases in grazing ecosystems. However, their effects have previously been studied in isolation. We conducted a two factorial experiment with asymmetric warming using infrared heaters and moderate grazing in an alpine meadow. Litter samples were collected from all plots in each treatment, among which some subsamples were placed in their original plots and other samples were translocated to other treatment plots to test the relative effects of each treatment on litter decomposition and nutrient releases. We found that warming rather than grazing alone significantly increased total losses of litter mass, total organic carbon, total nitrogen (TN) and total phosphorus (TP) per unit area due to increases in both mass loss rates and litter biomass. However, grazing with warming did not affect their total mass losses because increased mass loss was offset by decreased litter biomass compared with the control. Seasonal mean soil temperature better predicted litter decomposition than litter lignin content or carbon to nitrogen ratio. There were interactions between warming and grazing, but there were no interactions between them and litter quality on litter decomposition. The temperature sensitivity of TN loss was higher than that of TP loss per unit area. Our results suggest that increased temperature has a greater effect on litter decomposition and nutrient release than change in litter quality, and that more N release from litter could result in greater P deficiency in the alpine meadow.

Stronger effect of litter quality than micro‐organisms on leaf and root litter C and N loss at different decomposition stages following a subtropical land use change

Abstract Litter decomposition contributes largely to global carbon (C) and nitrogen (N) cycling, and it is strongly determined by litter quality and microbial community composition in ways that are poorly understood. Here, we conducted a 2‐year field litter decomposition experiment by collecting leaf and root litter of crops (from cropland), shrubs (from shrubland) and wood (from woodland) and placing samples for decomposition in woodland soil in central China to investigate the effects of litter quality and microbial community composition on C and N losses of leaf and root litter of three species under different decomposition stages. Our results showed that the leaf litter C and N losses of shrubs were significantly higher than those of crops and wood, whereas the root litter C and N losses of crops were significantly higher than those of shrubs and wood. Generally, the leaf litter C and N losses of the three species were higher on average than those of fine root litter during the whole decomposition period. For the C loss of the three species, litter lignin and phosphorus as well as initial litter quality were predominant drivers of root litter decomposition, while litter lignin, cellulose and hemicellulose concentrations were dominant for leaf litter decomposition. For N loss, litter stoichiometry and litter quality directly governed leaf and root litter N loss, and the initial litter quality largely regulated N loss at the late decomposition stage. Unexpectedly, the effect of microbial community composition on litter C and N losses was relatively weak and only exhibited an effect on litter C and N losses during the early stage of decomposition. Thus, our results revealed the huge disparity in C and N loss of plant species and litter types at different decomposition stages, which should be considered jointly when evaluating their roles in plant–soil feedbacks under global land use change. A free Plain Language Summary can be found within the Supporting Information of this article.

Mycorrhizal associations of tree species influence soil nitrogen dynamics via effects on soil acid–base chemistry

AbstractAimPlants and their associated microbes influence nutrient cycling in terrestrial ecosystems, yet we have a limited understanding of how soil acidity mediates the process. Here, we investigate whether reported differences in nitrogen (N) cycling between forests dominated by arbuscular mycorrhizal (AM) trees and ectomycorrhizal (ECM) trees are related to changes in soil acid–base chemistry induced by mycorrhizal associations.LocationGlobal.Time period1969–2018.Major taxa studiedTrees.MethodsWe measured and synthesized variables of leaf litter quality, soil acid–base chemistry and N cycling from: (1) a landscape‐scale study of 230 subplots varying widely in AM tree dominance in a 25 ha forest plot; (2) a regional‐scale study of 40 AM‐ and 56 ECM‐dominated plots in 10 temperate forests across the eastern USA; (3) a continental‐scale study of &gt; 3,000 forest plots from 10 ecoregions across the contiguous USA; and (4) a global meta‐analysis of 105 study sites with co‐occurring AM and ECM forest stands.ResultsAcross all spatial scales, ECM‐dominated forests were associated with greater soil acidity. In particular, ECM‐dominated soils exhibited lower soil pH and base cations, although the magnitude of mycorrhizal‐associated differences in soil acid–base chemistry depended on the biomes, with differences being more pronounced in temperate than in sub/tropical forests. Higher lignin and lower base cations in ECM tree leaf litter were related to greater soil acidity in ECM‐dominated forests. Moreover, the lower inorganic N concentrations and slower N transformation rates in ECM‐dominated forests were associated with their greater soil acidity.Main conclusionsOur results indicate that the scale‐invariant feedbacks between plant nutrient‐use strategies and soil properties have the potential to impact forest community assembly and ecosystem processes, particularly in the context of global change.

Litter mass and nitrogen disappearance in year‐round nitrogen‐fertilized grass and legume–grass forage systems

AbstractPlant litter is an important nutrient pool in grasslands. Most estimates of N return from litter are based on incubation of attached plant material (live or senescent) instead of dead, detached material on the soil surface. Our objective was to quantify mass, chemical composition, and N disappearance from soil‐surface litter for year‐round forage systems based on N‐fertilized grasses (GN) (290 kg N ha–1 yr–1) or legume–grass mixtures (LG) (30 kg N ha–1 yr–1) when grazed or harvested for hay. Litter mass and composition were measured in winter and summer over 2 yr, and litter was incubated for 180 d to quantify N disappearance. Summer litter mass was greater for GN than LG under grazing (2,840 vs. 1,730 kg ha–1) and hay management (2,780 vs. 1,240 kg ha–1). Cool‐season litter mass for GN was also greater than LG (1,990 vs. 1,200 kg ha–1). Initial litter N concentrations for GN and LG were 26 vs. 23 and 21 vs. 20 g N kg–1 organic matter in summer and winter, respectively. Litter lignin concentration and C/N and lignin/N ratios remained relatively constant. At the end of incubation, remaining litter biomass ranged from 63 to 85%. Nitrogen disappearance was greater for GN than LG, averaging 43 vs. 19 kg ha–1 yr–1, respectively, due to greater herbage accumulation and litter mass for GN. We conclude that year‐round forage systems including legumes contribute important quantities of N via aboveground litter decomposition, but amounts are likely less than for grass systems receiving relatively large N fertilizer inputs.

Impacts of litter decay on organic leachate composition and reactivity

Litter decomposition produces labile and recalcitrant forms of dissolved organic matter (DOM) that significantly affect soil carbon (C) sequestration. Chemical analysis of this DOM can provide important knowledge for understanding soil DOM dynamics, but detailed molecular analyses on litter derived DOM are scarce. Here we use ultrahigh resolution mass spectrometry (FT-ICR MS) to characterize the molecular composition of DOM from fresh and progressively decomposed litter samples. We compared high reactive (HR) and low reactive (LR) litter sources with regard to changes in the chemistry and bioavailability of leachates throughout the early phase of litter decay. We show that litter reactivity is a driver of chemical changes in the leached DOM of litter species. Birch, alder and Vaccinium (i.e. HR) litter initially produced more DOM with a higher lability than that of spruce, pine and wood (i.e. LR) litter. Labile oxidized phenolic compounds were abundant in leachates produced during the initial HR litter decay stages, indicating litter lignin degradation. However, the similarity in chemistry between HR and LR leachates increased during the litter decay process as highly leachable structures in HR litter were depleted. In contrast, chemistry of leachates from LR litter changed little during the litter decay process. The oxygenated phenolic compounds from HR litter were driving the lability of HR leachates and the changes in relative abundance of molecules during DOM incubation. This appeared to result in the creation of stable aliphatic secondary microbial compounds. In LR leachates, lability was driven by labile aliphatic compounds, while more resistant phenolic compounds were associated with recalcitrance. These results show how DOM dynamics follow different paths depending on litter reactivity, which has important implications for soil biogeochemistry and C sequestration.

半干旱草地不同植物枯落物分解对放牧和封育的响应

为探究放牧和封育对半干旱草地植物枯落物分解的影响，选取赖草、牛枝子及其混合物为研究对象，调查了不同网孔分解袋中宁夏半干旱草地植物枯落物分解特征及对放牧和封育的响应规律。结果表明：（1）放牧样地250目网孔中，枯落物质量残留率表现为牛枝子显著高于赖草和混合物（P<0.05），而在放牧样地30目网孔、封育样地2种网孔中，枯落物质量残留率均表现为3种枯落物间无显著差异。（2）250目网孔中，放牧和封育样地枯落物分解衰减常数均表现为混合物显著高于牛枝子，而赖草居中；并且，牛枝子枯落物分解衰减常数表现为封育样地显著高于放牧样地。30目网孔中，放牧和封育样地枯落物分解衰减常数均表现为赖草、混合物显著高于牛枝子（P<0.05）；并且，牛枝子枯落物分解衰减常数表现为封育样地显著高于放牧样地（P<0.05）。（3）在放牧样地，仅牛枝子枯落物R_m表现为30目显著低于250目网孔（P<0.05），k表现为30目显著高于250目网孔（P<0.05）；土壤动物对枯落物分解的贡献率表现为混合物显著低于牛枝子，赖草居中（P<0.05）。而在封育样地，仅牛枝子枯落物k表现为30目显著高于250目网孔（P<0.05）；土壤动物对枯落物分解的贡献率表现为混合物和牛枝子均显著高于赖草，且混合枯落物的土壤动物贡献率表现为封育样地显著高于放牧样地（P<0.05）。（4）枯落物残留率与其初始N、P、木质素/N、C/P呈显著相关性（P<0.05）；枯落物分解衰减常数与其初始N、P、木质素、N/P、C/P和木质素/P间均呈显著相关性（P<0.05）。研究表明，植物种类组成显著影响枯落物的残留率和分解衰减常数。放牧与封育管理通过影响网孔中土壤动物分布来调控半干旱区草地植物枯落物的分解，而且封育管理更有利于促进土壤动物对低质量枯落物（牛枝子）的分解。;This present study was to explored litter decomposition of different plant species under grazing and enclosure management in semi-arid grassland ecosystems. The remaining mass and decay constant (k) of Leymus secalinus, Lespedeza potaninii litter, and their mixture were investigated within 30-and 250-mesh litterbags in semiarid grasslands under grazing and enclosure management in Ningxia. In addition, the contribution of litter arthropods to decomposition was analyzed in order to discuss the effects of grazing management on decomposition process. The results showed that:(1) there was a significant higher final litter mass remaining rate (R_m) in L. potaninii than in L. secalinus and mixture from 250-mesh litterbags in grazing grasslands, whereas there were no significant differences in R_m of plant litter either from 30-mesh litterbags in grazing grasslands, or from both size-mesh treatments in enclosure grasslands. (2) In 250-mesh litterbags, the k was significantly higher in the mixture than in L. potaninii in both grasslands under grazing and enclosure managements, with the intermediate values in L. secalinus litter (P<0.05). But the k of L. potaninii was significantly higher in enclosure than in grazing grasslands (P<0.05). In 30-mesh litterbags, the litter decay constant (k) was significantly higher in L. secalinus and mixture than in L. potaninii in both grasslands under grazing and enclosure managements; the k of L. potaninii litter was significantly higher in enclosure than in grazing grasslands (P<0.05). (3) In grazing grassland, the R_m of L. potaninii was significantly higher in 250-mesh than 30-mesh (P<0.05), while k was significantly higher in 30-mesh than in 250-mesh. There were significantly lower values in the mixture than in L. potaninii, with the intermediate values in L. secalinus (P<0.05). In enclosure grassland, the k of L. potaninii was significantly higher in 30-mesh than 250-mesh (P<0.05), while the contribution rate of litter arthropods to litter decomposition was significant higher in the mixture and L. potaninii than in L. secalinus. The contribution rate of litter arthropods to mixture litter decomposition was significantly higher in enclosure than in grazing grasslands (P<0.05). (4) The R_m indicated a positive correlation with litter lignin/N and litter C/P, but it indicated a negatively correlation with litter initial N and P content. And the k indicated a positive correlation with litter initial N and P, while it indicated a negatively correlation with litter lignin, N/P, C/P and lignin/P. It was suggested that plant species composition presented a significant effect on the litter final mass remaining and decay constant. The effect of grazing management on litter arthropod distribution between different mesh-size litterbags induced the decomposition differences between various species of plant litter. In conclusion, the enclosure management was conducive to promoting the contribution of litter arthropods to low-quality litter (i.e., L. potaninii) decomposition in semi-arid grasslands.

Leaf litter lignin degradation in response to understory vegetation removal in a Masson pine plantation

AbstractUnderstory vegetation changes, caused by forestry management, can alter the litter species composition and microclimate in situ, which while profoundly influence litter lignin degradation processes, is seldom investigated. To reveal the effects of these changes, understory vegetation in plots was treated as follows: no understory vegetation removal; only shrub removal; only herb removal; and, both shrub and herb removal. Single‐ and mixed‐species litterbags (1.0 mm mesh with uncut leaf litter) matching the treated vegetation characteristics (complied with a 7:2:1 air‐dried mass ratio for the litter form trees, shrubs, and herbs) were placed on the floor. After 2 years, 5.9% (single‐tree litter in the plots with shrub removal) to 41.4% (mixture in the plots with no understory vegetation removal) of the initial lignin content was degraded among litterbag types and plot treatments. Incidence of nonadditive effects was reduced, and the nonadditive lignin degradation rate varied but remained low among plot treatments when understory vegetation was removed. In all plot treatments, lignin degradation rate was higher in single‐shrub or single‐herb litter than in single‐tree litter (at least 9.7% ± 1.2% for the deviation). Mixtures in the plots, with no understory vegetation removal, exhibited a greater lignin degradation rate than that of the litter mixtures in the other plots. Path analysis indicated that microbial biomass nitrogen, average temperature, and lignin concentration were positively correlated with lignin degradation rate. Therefore, in addition to the litter species composition, alterations in microclimate as a result of understory vegetation changes can be a key factor that influence lignin degradation rate.