Litter Mass Research Articles

Steering the soil microbiome by repeated litter addition

AbstractMicrobial communities drive plant litter breakdown. Litters originating from different plant species are often associated with specialised microbiomes that accelerate the breakdown of that litter, known as home‐field advantage. Yet, how and how fast microbial communities specialise towards litter inputs is not known.Here we study effects of repeated litter additions on soil microbial community structure and functioning. We set up a 9‐month, full‐factorial, reciprocal litter transplant experiment with soils and litters from six plant species (three grasses and three trees). We measured fungal and bacterial community composition, litter mass loss and home‐field effects.We found that repeated litter additions resulted in convergence in fungal community composition driven by litter functional group (trees vs. grasses). Grasses enriched Sordariomycetes, while Tremellomycetes, Eurotiomycetes and Leotiomycetes were favoured by tree litter. Bacterial community composition, litter mass loss and home‐field effects were not affected by litter incubation, but there was a relationship between fungal community composition and mass loss.We conclude that repeated litter incubations can result in directional shifts in fungal community composition, while 9 months of litter addition did not change bacterial community composition and the functioning and specialisation of microbial communities.Testing further how repeated litter inputs affect microbial functioning is essential for steering decomposer communities for optimal soil carbon and nutrient cycling.

Soil burial has a greater effect on litter decomposition rate than nitrogen enrichment in alpine grasslands

AbstractAimsLitter is frequently buried in the soil in alpine grasslands due to grassland degradation, serious rodent infestation and frequent strong winds. However, the effects of various litter positions on litter decomposition rates and nutrient dynamics under nitrogen (N) enrichment in such areas remain unknown.MethodsA field experiment was performed in the alpine grasslands of northwest China to investigate the influence of litter position (surface, buried in the soil and standing) and N enrichment on litter decomposition, using data from two dominant grass species (Festuca ovina and Leymus tianschanicus) in control and N-enriched plots.Important FindingsLitter decomposition rates were much faster in buried litter and slower in standing litter than in surface litter. N enrichment significantly affected litter quality and then influenced decomposition. But no significant differences in litter mass remaining were observed between control and N-enriched soil burial. These results indicated that N enrichment significantly affected litter decomposition by changes in litter quality. In addition, all litter exhibited net carbon (C) and phosphorus (P) release regardless of treatments. Litter exhibited net N accumulation for litter from the control plots but showed N release for litter from N enrichment plots. These suggested that litter decomposition can be limited by N and N enrichment influenced N cycling of litter. Current study presented direct evidence that soil buried litter exhibited faster mass loss and C release, and that soil burial can be a candidate explanation why litter decomposes faster than expected in dryland.

Shrub encroachment balances soil organic carbon pool by increasing carbon recalcitrance in a temperate herbaceous wetland

In recent decades, temperate herbaceous wetlands have been widely experiencing shrub encroachment. By now, little has been known about whether such alteration in plant community would generate updated soil organic carbon (SOC) conservation strategies, and thus alter SOC dynamics. To assess the temporal dynamics of SOC stock and fractions after shrub encroachment into temperate herbaceous wetlands, we measured floor litter mass, fine root biomass, and SOC stock and fractions (i.e. labile C pool I, labile C pool II, and recalcitrant C pool) across the 0–50 cm soil profile in the open wetlands and shrub islands (Betula fruticose and Salix floderusii) with different basal diameter sizes (small, 10 ~ 15 cm; medium, 15 ~ 20 cm; and large, 20 ~ 30 cm) in the Sanjiang Plain of Northeast China. Regardless of shrub species, SOC stock initially decreased after shrub expansion, but gradually recovered to the initial level of herbaceous wetlands. Moreover, SOC stock correlated positively with fine root biomass, but showed no significant relationship with floor litter mass. The responses of SOC fractions to shrub expansion mainly occurred in the surface soils (0–15 cm), despite a slight change in recalcitrant C pool in 15–50 cm layer. In the surface soils, labile C pool decreased substantially, whereas recalcitrant C pool and recalcitrant index of SOC elevated with increasing shrub sizes. Shrub encroachment can recover SOC pool and enhance SOC recalcitrance in temperate herbaceous wetlands, and altered fine root biomass would account for shrub encroachment-induced SOC dynamics.

Changes in chemical element composition of Betula pendula litter during decomposition in a laboratory experiment simulating leaching and salinization

The aim of the study was to estimate changes in chemical composition of the white birch litter during decomposition in a laboratory experiment simulating leaching and salinization. Location and time of the study. Fresh litter of Betula pendula leaves were collected in the forest-steppe zone of Priobskoe plateau (40 km to the east of Novosibirsk, Russia) in October 2016. The incubation experiment was carried out in the laboratory of Agrochemistry of the Institute of Soil Science and Agrochemistry of the Siberian Branch of the Russian Academy of Sciences (Novosibirsk, Russia) during 105 days (24.05.2017–06.09.2017) at 24˚С). Methodology. Distilled water (50 ml) or the same volume of NaCl, Na2SO4, FeCl3, Fe2(SO4)3 solutions with concentrations of 0.3, 0.5, 0.7 and 1% were added to 2 g of air-dried birch litter (leaves). The litter was placed into 100 ml plastic cups. The salt concentration in solutions was chosen according to the soil salinity gradation, i.e. 0.3% as weak (0.2–0.4%), 0,5% as medium (0.4–0.6%), 0,7% as strong (0.6–0.8%), and 1% as solonchak (Classification…, 1977). After 24 hours surplus water or salt solutions were decanted and filtered, and the birch litter was air-dried. After that 5 ml soil-water suspension (soil:distilled water 1: 2.5 m/v) was added into half of the cups with litter, whereas another half of cups with litter received 5 ml of distilled water. The variant with litter and no water was also included, designated as “dry birch litter”. The cups with litter were closed up and incubated during 105 days in the thermostat (+24 °С) with periodic ventilation. After incubation the litter was air-dried and weighed. The litter mass loss after decomposition was calculated as a difference between a sample mass at the beginning and at the end of the experiment and expressed as percentage. Concentrations of Na, Fe, K, Ca, Mg, Zn, Cu, Ni were determined by atomic-absorption spectrophotometry (AAnalyst 400, Perkin Elmer Inc., USA) in water samples, 0,3–1% salt solutions and birch litter. The total number of cups with litter in the experiment was 150. The term «under leaching» refers to the decrease in chemical element concentration in the litter after incubation with water. The term «under salinization» refers to the increase of Na or Fe concentrations in the litter after incubation with salt solutions. The litter mass loss presented as air-dry mass, concentration of chemical elements in the litter and ash content are expressed on the oven- dry mass basis. Results. Under leaching the concentration of chemical elements was increased in water extracts (especially К, Са, Mg) and decreased in birch litter in the row: Na (3.6 times) –>К (2.4 times) –> Ni (1.9 times) –> Mg (1.4 times) –> Zn and Cu (1.3 times). In comparison with water, the interaction between litter and Na and Fe salt solutions (concentrations 0.3–1%) led to intensive leaching and, correspondingly, to the 1.3 times lower litter К content, as well as 1.2–1.5 times and 1.5-2.2 times lower Са and Mg content, respectively. The highest concentration of Са, Mg, Zn, Cu, Ni was detected in FeCl3 solutions at the start of the experiment. The maximal mass and ash content losses were detected in the dry birch litter. On average, leaching was found to decrease 1.4 times mass loss and ash content in the litter. The minimal mass and ash content losses under salinization were found after litter incubation with FeCl3 (0.3–1%) solutions. The difference in mass loss between variants litter-water and litter-soil water suspension was not detected, although litter ash content after addition of soil water suspension was 1.1–1.3 times higher. Conclusions. The interaction birch litter with water and Na and Fe salt solutions (0,3-1%) led to modification of elemental chemical composition of plant litter as a result of leaching of chemical elements (especially К, Са, Mg) from litter and increased concentrations of Na, Fe and some other elements (depending on the salt used). It led to the decrease in plant litter decomposition rate, which under the natural conditions in the south of West Siberia can take place as a result of temporary overwetting of the forest litter (for instance, in autumn or spring) as well as in areas occupied by saline soils.

Hydrological contraction patterns and duration of drying period shape microbial-mediated litter decomposition

The length and number of streams experiencing intermittency is expected to increase in response to human population growth, associated water use, and climate change. In these streams, habitat contraction may occur at distinct rates giving rise to drying periods of distinct duration. To date, the impact of drought installation rate and duration have been mostly overlooked. In this microcosm study, stream conditioned oak leaf litter was subjected to either a short (5 weeks) or a long (8 weeks) drying period, originating from a very slow, slow, or abrupt contraction. The effects of these treatments were compared at the end of the drying period in terms of microbial-mediated litter mass loss, fungal biomass, respiration, and sporulation rates. A very slow contraction pattern led to 1.3 times higher mass loss than both slow or abrupt contraction. Fungal biomass, respiration and sporulation rates were up to 2.3 times lower under slow than abrupt contraction. Both drying period durations inhibited leaf decomposition, suggesting an early, critical effect of drying on microbial-mediated processing, regardless of contraction pattern. This seems to be related to an impoverishment of leaf associated fungal communities and resultant lower functional efficacy – species richness decreased by up to 75% in response to a long (vs. short) drying period, despite the maintenance of mycelial biomass. Our results show the relevance of aquatic hyphomycetes to litter decomposition in dry streambeds, particularly following slower habitat contraction patterns. Faster wet-to-dry transitions and longer drying periods strongly impaired microbial functioning, with potential impacts on global processing rates and cascading effects through changes of detritus quality. If confirmed in field tests, such impacts on stream functioning may be mitigated by preserving riparian forests, which may protect against extreme drying events by buffering temperature changes.

Carbon Storage of Single Tree and Mixed Tree Dominant Species Stands in a Reserve Forest—Case Study of the Eastern Sub-Himalayan Region of India

In recent decades, carbon (C) management is an important point on the agenda to identify the best viable mitigation strategies for its reduction. The study was conducted at Jaldapara National Park located in the Eastern Himalayan region of India. The study quantified litter production, decomposition, periodic nutrient release, soil fertility status, and soil organic carbon (SOC) of five major forest stands i.e., Tectona grandis (TGDS), Shorea robusta (SRDS), Michelia champaca (MCDS), Lagerstroemia parviflora (LPDS) and miscellaneous stand (MS). A stratified random nested quadrate method was adopted for sample collection. Results reveal that the greatest amount of litter production and decomposition was under MCDS followed by MS, LPDS, SRDS, and the smallest under TGDS. The material annual turnover through litter decomposition in all the stands varies between 96.46% and 99.34%. The content and amount of the available nutrients in litter varied significantly among the stands. Moreover, release of these nutrients was nearly equal to the amount available in the initial litter mass. In general, the magnitude of the total nutrient return was in the same order as the total litter fall and the nutrient availability was more closely related to litter nutrient content and soil organic carbon. The range of pH (4.86–5.16), EC (0.34–0.50), soil moisture (27.01–31.03) and available primary nutrients (N: (0.21–0.26 Mg/ha), P: (0.09–0.12 Mg/ha), K: (0.13–0.14 Mg/ha)) also varied significantly among the stands. Significant positive correlations were observed between SOC, N and K. Both the fertility indices exhibited no definite pattern in the stands but a significant correlation between the two indicates the healthy soil fertility status of the stands. SOC varies significantly under different forest stands, but the greatest content was found under MS. The estimated SOC ranges between 75.9 and 107.7 Mg ha−1 up to 60 cm and is reported to be below the Indian average of 182.94 Mg ha−1. The present study strongly recommends that Tectona grandis, Shorea robusta, Michelia champaca, and Lagerstroemia parviflora should be the important commercial timbers of the Eastern Himalayan region because they may help further to increase the C sink in agricultural and degraded landscapes.

Leaf litter dynamics in Western Black Sea mountainous forest ecosystems

This study aimed to estimate leaf litter decomposition rates in eastern beech (Fagus orientalis Lipsky) and sweet chestnut (Castanea sativa Mill.) mixed stands in Akçakoca in the province of Düzce, located in the Western Black Sea region of Turkey. The sampling areas represent four different elevations and two aspects at each elevation. Amounts of annual beech and chestnut litterfall were estimated at 5.19 and 4.61 Mg·ha−1, respectively. Litter decomposition was examined over five time periods (0.25, 0.50, 1.25, 2.25, and 4.25 years) by using the litterbag method. The mass of remaining beech leaf litter was found to be 1.1, 1.2, 1.2, 1.4, and 1.3 times greater than the mass of chestnut leaf litter, respectively. However, estimated values for the decomposition rate constant (k) of chestnut for all time periods were found to be approximately 1.5 times greater than those of beech leaf litter. Litter in beech stands decomposed more rapidly at higher elevations during the first year but at lower elevations during the second year, likely due to increased temperature and precipitation for the corresponding years. Leaf litter in chestnut stands decomposed more rapidly at lower elevations in the second and fourth years, reflecting higher precipitation for those years.

Soil functional indicators in a mountain forest-rangeland mosaic of northern Iran

Soil plays an essential role in providing ecosystem services, especially in mountain ecosystems which are often considered as fragile and sensitive systems and commonly consist of a mosaic of forest and rangeland plant communities. The relationship between above-ground plant cover and the properties of soil organic and mineral layers in mountain areas are rarely studied. This research aimed to assess the effect of different land covers (i.e. forest, forest-rangeland ecotone, and rangeland) on soil functional indicators, i.e. fertility and biological activities, in the Hyrcanian region of northern Iran. We hypothesized that (i) the presence of tree cover enhances soil fertility and biological activities and creates hot spots (islands) of soil functional indicators especially in the topsoil, (ii) litter quality and organic matter fractions are the drivers for activities of soil organisms, nutrient cycles and transformation processes in mountain ecosystems. Litter (O-horizon including L, F and H layers) and mineral soil samples (in two separate depths of 0–10 cm and 10–20 cm) were taken using iron frames (30 × 30 cm). In total, 45 litter and 90 soil samples were transferred to the laboratory. Soil characteristic especially in the 0–10 cm depth, litter carbon (C), nitrogen (N) and C/N ratio were significantly affected by different land covers showing the maximum of soil organic C and microbial activity under forest. Our findings showed that the studied land covers, as well as litter and soil properties can be separated by PCA output. The first and second axes, accounted more than 50% of the explained variance in each of the studied soil depths. Soils with a better quality of litter (i.e. lower C/N ratio), higher values for organic matter fractions, soil fertility indicators and soil biological activities can be attributed to the forest. In contrast, positions of low soil fertility indicator values and biota abundance were imposed by forest-rangeland ecotone and rangeland. Although each land cover plays a prominent ecological role and takes its place in the evolutionary process, forests are essential because of their capacity to store and transform carbon and nutrients and to create hotspots identified by functional soil indicators. Based on our findings, soil functions decreased ranked in the order forest > forest-rangeland ecotone > rangeland, which can be assigned to the lower density of trees, and the amount of litter mass and litter quality. It can be concluded that tree covers have a prominent role in increasing soil functions, which should be given special consideration in the restoration of degraded mountain ecosystems.

Increased grazing intensities induce differentiation of the relationships between functional traits and aboveground plant biomass in shrub‐ and grass‐dominated community in desert steppe

AbstractGrazing disturbance plays a crucial role in regulating plant community structure and ecosystem function in drylands. However, few studies show that how grazing disturbance affects the relationships between functional traits and aboveground plant biomass (AGB). Here, we presented a comparative result from grazing experiment with three levels of grazing intensities (no grazing, moderate and heavy grazing) between shrub‐ and grass‐dominated community in desert steppe, Inner Mongolia. We measured vegetation characteristics and plant traits (plant height, LT: leaf thickness, SLA: specific leaf area, LDMC: leaf dry matter content, LCC: leaf carbon content and LNC: leaf nitrogen content) in the two communities across 2 years (2017–2018). We used the linear regression analysis and the structural equation modeling (SEM) to examine how grazing affect the associations of AGB with plant traits. We found that grazing decreased vegetation cover, AGB and litter mass in two communities, and caused the differences in AGB among two communities. Heavy grazing eliminated the associations of AGB with SLA and LCC in shrub community, while led to their positive or negative associations in grass community. The SEM showed that grazing indirectly decreased AGB through its effect on LT in shrub community, and its effect on plant height in grass community. These results suggest that changes in leaf traits induced by heavy grazing can explain AGB in grass‐ rather than shrub‐community, thereby possibly contributing to AGB differences between two communities. Indirect effects of increased grazing intensities on AGB in shrub or grass community are dependent on specific functional traits.

Meta-analysis shows non-uniform responses of above- and belowground productivity to drought

Terrestrial productivity underpins ecosystem carbon (C) cycling and multi-trophic diversity. Despite the negative impacts of drought on terrestrial C cycling, our understanding of the responses of above- and belowground productivity to drought remains incomplete. Here, we synthesized the responses of terrestrial productivity and soil factors (e.g., soil moisture, soil pH, soil C, soil nitrogen (N), soil C:N, fungi:bacteria ratio, and microbial biomass C) to drought via a global meta-analysis of 734 observations from 107 studies. Our results revealed that the productivity variables above- and belowground (i.e., net primary productivity, aboveground net primary productivity, belowground net primary productivity, total biomass, aboveground biomass, root biomass, gross ecosystem productivity, and net ecosystem productivity) were decreased across all ecosystems. However, drought did not significantly affect litter mass across all ecosystems, and the responses of above- and belowground productivity to drought were non-uniform. Furthermore, the responses of these productivity variables to drought were more pronounced with drought intensity and duration, and consistent across ecosystem types and background climates. Drought significantly decreased soil moisture, soil C concentrations, soil C:N ratios, and microbial biomass C, whereas it enhanced soil pH values and fungi:bacteria ratios. Moreover, the negative effects of drought on above- and belowground productivity variables were correlated mostly with the response of soil pH to drought among all soil factors. Our study indicated that litter biomass, which mostly represents productivity levels via traditional ecosystem models, was not able to predict the responses of terrestrial ecosystem productivity to drought. The strong relationship between the responses of soil pH and terrestrial productivity to drought suggests that the incorporation of soil pH into Earth system models might facilitate the prediction of terrestrial C cycling and its feedbacks to drought.

Site-specific responses of fungal and bacterial abundances to experimental warming in litter and soil across Arctic and alpine tundra

Vegetation change of the Arctic tundra due to global warming is a well-known process, but the implication for the belowground microbial communities, key in nutrient cycling and decomposition, is poorly understood. We characterized the fungal and bacterial abundances in litter and soil layers across 16 warming experimental sites at 12 circumpolar locations. We investigated the relationship between microbial abundances and nitrogen (N) and carbon (C) isotopic signatures, indicating shifts in microbial processes with warming. Microbial abundances were 2–3 orders of magnitude larger in litter than in soil. Local, site-dependent responses of microbial abundances were variable, and no general effect of warming was detected. The only generalizable trend across sites was a dependence between the warming response ratios and C:N ratio in controls, highlighting a legacy of the vegetation on the microbial response to warming. We detected a positive effect of warming on the litter mass and δ15N, which was linked to bacterial abundance under warmed conditions. This effect was stronger in experimental sites dominated by deciduous shrubs, suggesting an altered bacterial N-cycling with increased temperatures, mediated by the vegetation, and with possible consequences on ecosystem feedbacks to climate change.

Understory removal accelerates nucleic phosphorus release but retards residual phosphorus release in decomposing litter of Phyllostachys edulis in subtropical China

AbstractDespite the importance of understory vegetation for ecosystem processes and functions, its contribution to the dynamics of phosphorus (P) fractions in decomposing litter has rarely been studied in subtropical plantations. Herein, by conducting an understory removal (UR) experiment in a moso bamboo (Phyllostachys edulis) plantation of South China, we assessed the effect of understory species on leaf litter mass loss and P fractions (inorganic P, sugar P, nucleic P, and residual P) of moso bamboo over a 12‐month incubation period. We also examined the effect of UR on soil physicochemical properties, as well as fungal and bacterial phospholipid fatty acids (PLFAs). Our results showed that UR reduced litter decomposition rate (6.0–12.4%), but exhibited no effect on total P remaining in decomposing litter. Furthermore, UR produced variable effects on the amounts of P fractions in decomposing litter. Despite no changes were observed in the amount of inorganic and sugar P fractions, UR accelerated nucleic P release (3.0–6.6%), and residual P immobilization (9.2–27.9%) in decomposing litter. Moreover, UR increased fungal PLFAs (8.0–44.9%) but decreased bacterial PLFAs (18.7–36.8%) in the soil, leading to an increase in fungal to bacterial PLFAs ratio (34.5–80.9%). The correlation analysis showed that accelerated litter nucleic P release after UR was mainly attributed to the increases in soil fungal PLFAs, while decelerated litter residual P release was mainly resulted from the increased soil fungal PLFAs and decreased soil bacterial PLFAs. These results indicate that understory vegetation can mediate the dynamics of litter P fractions via its effect on soil microbial composition in subtropical plantations and suggest that understory vegetation is crucial to maintain soil P availability in moso bamboo plantations.

Metagenomic reconstruction of nitrogen and carbon cycling pathways in forest soil: Influence of different hardwood tree species

The soil microbiome plays an essential role in processing and storage of nitrogen (N) and carbon (C) and is influenced by vegetation above-ground through imparted differences in chemistry, structure, mass of plant litter, root physiology, and dominant mycorrhizal associations. We used shotgun metagenomic sequencing to quantify the abundance and distribution of gene families involved in soil microbial N and C cycling beneath three deciduous hardwood tree species: ectomycorrhizal (ECM)-associated Quercus rubra (red oak), ECM-associated Castanea dentata (American chestnut), and arbuscular mycorrhizal (AM)-associated Prunus serotina (black cherry). Chestnut exhibited the most distinct soil microbiome of the three species, both functionally and taxonomically, with a general suppression of functional genes in the nitrification, denitrification, and nitrate reduction pathways. These changes were related to low inorganic N availability in chestnut stands as soil was modified by poor, low-N litter quality relative to red oak and black cherry soils. Previous studies have used field biogeochemical process rates, isotopic tracing, and targeted gene abundance measurements to study the influence of tree species on ecosystem N and C dynamics. However, these approaches do not enable a comprehensive systems-level understanding of the relationship between microbial diversity and dynamics of N and C below-ground. We analyzed microbial metagenomes from soils beneath red oak, American chestnut, and black cherry stands and showed that tree species can mediate the abundance of key microbial genes involved in N and (to a lesser extent) C metabolism pathways in soil. We compare gene abundance values to measures of N and C flux from incubated soil. Our results highlight the genetic framework underlying tree species’ control over soil microbial communities, and below-ground C and N metabolism, and may enable land managers to select tree species to maximize C and N storage in soils.

Effect of Litter Size Manipulation on the Reproductive Performance of BALB/C Mice

Many of previous studies on lactating animals with natural litters did not support the negative link betweenlitter size and pup mass; however, artificial manipulation of litters could be an option to support that. Inthis study, we manipulated the litters of lactating BALB/C mice with having two groups. Enlarged litter SL(LS=8; N=5) and reduced litters SS (LS=2; N=6) were used in this experiment and also 7 virgin female micewere assigned for control group. Mother’s body mass and food intake were daily measured throughout theexperiment. Litter size, litter mass, pup mass, mortality rate of pups in the studied groups were also dailymeasured throughout lactation. The lactating mice in both groups significantly ate more food intake comparedto non –reproducing mice. Mice with enlarged litters had significantly greater food intake compared to themice with reduced litters. Litter masses at weaning of SL mice were significantly higher compared to theSS mice. However, pup mass at weaning was significantly lighter in SL mice compared to the pup mass inthe SS mice. Our present study concludes that the litter size of manipulated litters was negatively associatedwith pup mass at weaning

Signatures of an abiotic decomposition pathway in temperate forest leaf litter

Photodegradation helps explain why leaf litter mass loss rates are comparable between mesic environments and drylands, despite water availability limiting decomposer activity in drylands. With photodegradation, light energy directly mineralizes photoreactive organic molecules such as lignin, which contrasts with biotically-driven decomposition where lignin persists in decomposing leaf litter relative to other compounds. Photodegradation of leaf litter has largely been studied in dryland systems, but whether it occurs in mesic, deciduous forest systems is uncertain. As such, we examined potential photodegradation in maple and oak litter in the Southern Appalachian Mountains (USA) during the non-growing season, when newly fallen leaves are exposed to maximum solar radiation without deciduous canopies. The proportion of oxidized lignin in the leaf litter relative to other carbon compounds decreased with maximum solar radiation during the non-growing season. With a closed canopy, however, the proportion of total lignin relative to other compounds in the leaves increased. This pattern was particularly strong for the syringyl- S6 and guaiacyl-G6 lignin monomers. The relative proportion of S6 and G6 in the litters was reduced by 10–65% in the first 5 months. The largest reductions in lignin occurred on south-facing mountain slopes where solar radiation was highest (relative to north-facing slopes) in the Northern Hemisphere. Overall, however, the changes in lignin did not alter cumulative litter mass lost. Our results suggest that photodegradation promotes the transformation and relative loss of lignin in the early stages of litter decomposition in mesic deciduous forests.

Litter mass, deposition rate, and decomposition in nitrogen‐fertilized or grass–legume grazing systems

AbstractPlant litter deposition and decomposition play important roles in grassland nutrient cycling. The objective was to evaluate plant litter responses and estimate the N returns via plant litter in contrasting grazing systems, since legume inclusion is hypothesized to result in similar quantities of N return compared with N‐fertilized grass systems. Systems were (a) N‐fertilized bahiagrass (Paspalum notatum Flüggé) during summer with a mixture of N‐fertilized cereal rye (Secale cereale L.) and oat (Avena sativa L.) during winter (Grass+N); (b) bahiagrass (no N fertilizer) during summer and a rye–oat–clovers (Trifolium spp.) mixture + N in winter (Grass+Clover); and (c) bahiagrass (no N fertilizer in summer) with strip‐planted rhizoma peanut (Arachis glabrata Benth.) during summer with a rye–oat–clovers mixture + N during winter (Grass+CL+RP). Litter mass was greatest for Grass+N during October (4,430 kg organic matter [OM] ha−1) and least for Grass+CL+RP in June (490 kg OM ha−1). Litter N concentrations were greatest in Grass+N (16 g kg−1), with similar N concentration for Grass+Clover and Grass+CL+RP litter (14 g kg−1). Contribution of C3 species to litter mass increased from May to July but decreased thereafter. Overall, there was a net return of 47 kg N ha−1 yr−1 via litter across the three systems, and litter decomposition was similar in the three systems. Inclusion of forage legumes during cool and warm seasons in grazing systems has the potential to return similar amounts of N through plant litter deposition as grasses receiving moderate levels of N fertilizer.

Litter decomposition was retarded by understory removal but was unaffected by thinning in a Chinese fir [Cunninghamia lanceolata (Lamb.) Hook] plantation

Thinning and understory removal, which are commonly used in forest management, are expected to affect litter decomposition. However, little is known about how litter decomposition rates change in stands subject to both thinning and understory removal. This knowledge gap is urgent to be filled because the two practices are often applied simultaneously. In the present study, an experiment containing a complete factorial combination of thinning and understory removal was arranged in a Chinese fir (Cunninghamia lanceolata) plantation. Litter decomposition rate was determined by using litter bags, and litter bags with different mesh sizes (0.1 mm and 2 mm) were used to identify the effect of soil mesofauna on decomposition. The temperature, moisture, and microbial abundance of surface soil were also measured. Results showed that thinning did not change litter decomposition rate, partly because of the unresponsive soil temperature, moisture, and abundance of microbial groups following thinning. Understory removal markedly restricted litter mass loss by more than 20%. Despite an obvious decrease in soil microbial abundance following understory removal, this should not account for why understory removal lowered litter decomposition rate, because this negative effect on litter mass loss disappeared when soil mesofauna was excluded. In addition, no interaction between thinning and understory removal was detected on litter decomposition. We emphasized that (1) Understory removal retard litter decomposition by suppressing the activity of soil mesofauna rather than by reducing microbial abundance; (2) Understory removal caused an equal reduction in litter mass loss regardless of thinning treatment. We believe that these results provide an important guidance for evaluating the effect of thinning and understory removal on some ecological processes associated with litter decomposition (i.e. soil formation and CO2 emission from the soil to the atmosphere) in a fir plantation.

Decomposition of Herbivore-Damaged Leaves of Understory Species Growing in Oak and Pine Stands

Leaves are the largest component of forest litter. Their decomposition rate depends mainly on plant species, leaf chemical composition, microorganism biodiversity, and habitat conditions. It is known that herbivory by insects can modify the chemical composition of leaves, such as through induction. The aim of this study was to determine whether the rate of leaf decomposition is related to the susceptibility of the plant species to insect feeding and how leaf damage affects this rate. For our research, we chose six species differing in leaf resistance to insect damage: Cornus sanguinea, Frangula alnus, and Sambucus nigra (herbivore resistant), and Corylus avellana, P. padus, and Prunus serotina (herbivore susceptible). The decomposition of these plant leaves was examined in two monoculture forest stands, deciduous (Quercus robur) and coniferous (Pinus sylvestris). Litter decay rate k and change of litter mass, content of defensive metabolites (total phenols (TPh) and condensed tannins), and substances beneficial for organisms decomposing litter (nitrogen (N) and nonstructural carbohydrates (TNC)) were determined. Contrary to our expectations, leaf litter of herbivore-resistant species decomposed faster than that of herbivore-susceptible species, and damaged leaves decayed faster than undamaged leaves. We found that faster decaying leaf litter had a lower content of defensive compounds and a higher content of TNC and N, regardless of the plant species or leaf damage. Leaf litter decomposition caused a large and rapid decrease in the content of defensive compounds and TNC, and an increase in N. In all species, the tannin content was lower in damaged than in undamaged leaves. This pattern was also observed for TPh, except in S. nigra. We interpret this as the main reason for faster decay of damaged leaves. Moreover, the loss of leaf mass was greater under oak than pine stands, indicating that the microorganisms in deciduous stands are more effective at decomposing litter, regardless of leaf damage.

An integrated model to predict and prevent hypoxia in floodplain-river systems

Hypoxia can occur following rewetting of floodplains and cause severe impacts on aquatic biota and biogeochemical processes. The likelihood of such events is influenced by a number of factors including temperature, the mass of plant litter on the floodplain (which is influenced by the duration between inundation events), the volume of water available for dilution of oxygen-demanding dissolved organic matter, and the exchange of water to dilute and disperse that material. Using constructed infrastructure to generate managed inundations on floodplains increases the likelihood of hypoxic “blackwater” events relative to unregulated floods, as larger areas of floodplain are inundated at lower flow rates. A model (the “DODOC plugin”) was developed for the Source hydrological modelling software to inform risk mitigation strategies for these managed inundation events. This development enables the interaction between complex hydrology and floodplain inundation on the resulting release of dissolved organic carbon (DOC), and subsequent consumption of dissolved oxygen (DO), to be represented. Key functionality of the plugin includes the ability to represent (i) spatial variability in organic litter build up and degradation, (ii) DOC leaching from litter when inundated, (iii) DO consumption arising from microbial decomposition of the DOC, and (iv) reaeration processes from autotrophic productivity and turbulence as water passes over water level regulating structures. The model is configurable on both river channels (links) and floodplains (storages) to represent changes in DO from both natural and managed inundation events at the scale of an individual floodplain up to multiple floodplains and river reaches. The plugin was parameterised to successfully simulate DOC (R2 = 0.84–0.93) and DO (R2 = 0.74–0.92) along an approx. 100 km study reach of the River Murray in South Australia, once the different behaviour of the labile and refractory components of the DOC was represented in the model. A number of hypothetical operational scenarios were tested using the model to demonstrate parameter sensitivity and to inform planning of managed inundations. The development of the DODOC plugin demonstrates that complex water quality processes can be integrated into the Source (or other) hydrological software, to represent cumulative implications of floodplain inundation events and to minimise the risk of hypoxia.

Carbon and nitrogen transfer from litter to soil is higher in slow than rapid decomposing plant litter: A synthesis of stable isotope studies

Litter decomposability determines litter mass loss rate, but how it affects soil carbon (C) and nitrogen (N) storage remains elusive. We compiled data from 25 litter decomposition studies tracing the fate of C and N during decomposition using stable C and N isotopes. An average of 24% of C lost from decomposing litter was recovered in the soil independent of the decomposition stage and the experimental conditions. In contrast, a higher amount of N lost from decomposing litter was recovered in the soil in laboratory (80%) than in field (58%) experiments. The proportion of the total C and N lost that was transferred to the soil was higher for slowly than for rapidly decomposing litter types. Our results demonstrate substantial soil C and especially N input from decomposing litters and suggest that slowly decomposing litters favor soil C and N storage compared to more rapidly decomposing litters.