Affect Litter Decomposition Research Articles

Ultraviolet radiation accelerates photodegradation under controlled conditions but slows the decomposition of senescent leaves from forest stands in southern Finland

Depending on the environment, sunlight can positively or negatively affect litter decomposition, through the ensemble of direct and indirect processes constituting photodegradation. Which of these processes predominate depends on the ecosystem studied and on the spectral composition of sunlight received. To examine the relevance of photodegradation for litter decomposition in forest understoreys, we filtered ultraviolet radiation (UV) and blue light from leaves of Fagus sylvatica and Betula pendula at two different stages of senescence in both a controlled-environment experiment and outdoors in four different forest stands (Picea abies, Fagus sylvatica, Acer platanoides, Betula pendula). Controlling for leaf orientation and initial differences in leaf chlorophyll and flavonol concentrations; we measured mass loss at the end of each experiment and characterised the phenolic profile of the leaf litter following photodegradation. In most forest stands, less mass was lost from decomposing leaves that received solar UV radiation compared with those under UV-attenuating filters, while in the controlled environment UV-A radiation either slightly accelerated or had no significant effect on photodegradation, according to species identity. Only a few individual phenolic compounds were affected by our different filter treatments, but photodegradation did affect the phenolic profile. We can conclude that photodegradation has a small stand- and species-specific effect on the decomposition of surface leaf litter in forest understoreys during the winter following leaf fall in southern Finland. Photodegradation was wavelength-dependent and modulated by the canopy species filtering sunlight and likely creating different combinations of spectral composition, moisture, temperature and snowpack characteristics.

Changes in seasonal precipitation distribution but not annual amount affect litter decomposition in a secondary tropical forest.

In the tropics of South China, climate change induced more rainfall events in the wet season in the last decades. Moreover, there will be more frequently spring drought in the future. However, knowledge on how litter decomposition rate would respond to these seasonal precipitation changes is still limited. In the present study, we conducted a precipitation manipulation experiment in a tropical forest. First, we applied a 60% rainfall exclusion in April and May to defer the onset of wet season and added the same amount of water in October and November to mimic a deferred wet season (DW); second, we increased as much as 25% mean annual precipitation into plots in July and August to simulate a wetter wet season (WW). Five single‐species litters, with their carbon to nitrogen ratio ranged from 27 to 49, and a mixed litter were used to explore how the precipitation change treatments would affect litter decomposition rate. The interaction between precipitation changes and litter species was not significant. The DW treatment marginally accelerated litter decomposition across six litter types. Detailed analysis showed that DW increased litter decomposition rate in the periods of January to March and October to December, when soil moisture was increased by the water addition in the dry season. In contrast, WW did not significantly affect litter decomposition rate, which was consistent with the unchanged soil moisture pattern. In conclusion, the study indicated that regardless of litter types or litter quality, the projected deferred wet season would increase litter decomposition rate, whereas the wetter wet season would not affect litter decomposition rate in the tropical forests. This study improves our knowledge of how tropical forest carbon cycling in response to precipitation change.

Direct and understorey-mediated indirect effects of human-induced environmental changes on litter decomposition in temperate forest

Human-induced environmental changes in temperature, light availability due to forest canopy management, nitrogen deposition, and land-use legacies can alter ecosystem processes such as litter decomposition. These influences can be both direct and indirect via altering the performance of understorey vegetation. To identify the direct and indirect effects of environmental changes on litter decomposition, we performed an experiment with standardised green and rooibos teas. The experiment was conducted in a temperate mixed deciduous forest, and treatments (temperature, light, and nitrogen) were applied to mesocosms filled with ancient and post-agricultural forest soil. Both green tea and rooibos teas were more rapidly decomposed in oligotrophic soil than in eutrophic soil. The direct effects of the treatments on litter decomposition varied among the two litter types, incubation times, and soil fertility groups. Warming and agricultural legacy had a negative direct effect on the decomposition of the green tea in the high soil fertility treatment during the early decomposition stage. In contrast, agricultural legacy had a positive direct effect on the decomposition of rooibos tea. Soil enriched with nitrogen had a negative direct effect on the decomposition of green tea in mesotrophic soil in the early decomposition stage and on rooibos tea in later stage. The indirect effects of the treatments were consistently negative, as treatments (especially the temperature and light treatments in the early decomposition stage) had a positive effect on plant cover, which negatively affected litter decomposition. Our results indicate that warming, increased nitrogen deposition, and land use legacy can directly stimulate the decomposition of labile litter on more fertile soils. Furthermore, warming and increased light had stronger positive direct effects on understorey herbaceous cover, which leads to slower decomposition rates, especially in more fertile soils. Therefore, the indirect effects of environmental changes related to the understorey layer on litter decomposition can be more important than their direct effects, thus should not be overlooked.

Short- and Long-Term Effects of Snow-Depth on Korean Pine and Mongolian Oak Litter Decomposition in Northeastern China

Changes in snow-depth induced by climate change can affect litter decomposition, but it remains unclear whether the effects of snow-depth on litter decomposition vary among seasons. Our aim was to assess the possible short- and long-term effects of snow-depth on foliar litter decomposition for Korean pine (Pinus koraiensis) and Mongolian oak (Quercus mongolica). A snow-depth manipulation experiment that included snow-removal, control and snow-addition treatments was conducted in northeastern China. All the snowfall was intercepted by transparent plexiglass in the snow-removal treatment and then transferred to the snow-addition treatment. Three replicate litterbags per species were buried in each treatment and sampled in the freezing onset, deep freezing and thawing stages and in the early, middle and late snow-free seasons from November 2014 to October 2015. Our results showed that the oak litter decomposed faster than the pine litter, but the magnitude of the effect of snow-depth was greater for the latter because of differences in litter chemical traits. Litter mass loss decreased with decreasing snow-depth in the snow-covered season but increased in the following snow-free season. The short-term effect resulting from the changes in soil environments affected litter decomposition during the snow-covered season, while the long-term effect due to litter chemical traits and the microbial biomass carbon concentration controlled the decomposition in the snow-free season. These results indicated that snow-depth significantly influences the foliar litter decomposition of the two tree species with contrasting initial qualities, but the effects differed between the snow-covered and snow-free seasons. These results deepen our understanding of biogeochemical cycling in cold regions.

Plant phylogenetic history explains in‐stream decomposition at a global scale

Abstract Evolutionary history and adaptation to climate shape plant traits. Some include leaf traits that influence litter quality. Thus, evolutionary history should affect litter decomposition, a crucial ecosystem process. In addition, litter decomposition is directly influenced by climate. We consequently expect plant phylogeny, adaptation and climate to jointly influence litter decomposition. These effects and their interactions have yet to be untangled at a global scale. Here we present an analysis of variation in litter decomposition rates in rivers and streams across 285 published studies for 239 species (from ferns to angiosperms) distributed at 494 locations world‐wide. We estimated the relative contributions of climatic conditions and phylogenetic heritage on litter decomposition rates, partitioning phylogenetic from climatic effects at the site and species levels using phylogenetic eigenvector analysis and phylogenetic linear mixed models. In addition, we modelled transitions in decomposition rates under a suite of multiple adaptive‐regime Ornstein–Uhlenbeck models to test the hypothesis that natural selection has shaped clade‐level litter decomposition rates. Leaf litter decomposition rate exhibited a significant phylogenetic signal. Modelling decomposition rate as a function of location, climatic niche and phylogeny consistently recovered phylogeny alone as one of the top models in species‐level analyses. Since many previous studies have focused on the same species across many locations, we also conducted analyses at the species × site level. Both phylogenetic and climatic factors were favoured in models of this analysis, but the single most important predictor for angiosperms and for all taxa analysed together was phylogeny alone. Synthesis. For plant species distributed globally at nearly 500 locations we found that plant phylogenetic history is a critically important predictor of litter decomposition rate in rivers and streams, explaining more of the variance in decomposition than site or climatic regime. Thus, our study demonstrates the influence of evolutionary history on suites of plant traits that shape a key ecosystem process.

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.

Resource-ratio theory predicts mycorrhizal control of litter decomposition.

Ecosystems with ectomycorrhizal plants have high soil carbon:nitrogen ratios, but it is not clear why. The Gadgil effect, where competition between ectomycorrhizal and saprotrophic fungi for nitrogen slows litter decomposition, may increase soil carbon. However, experimental evidence for the Gadgil effect is equivocal. Here, we apply resource-ratio theory to assess whether interguild fungal competition for different forms of organic nitrogen can affect litter decomposition. We focus on variation in resource input ratios and fungal resource use traits, and evaluate our model's predictions by synthesizing prior experimental literature examining ectomycorrhizal effects on litter decomposition. In our model, resource input ratios determined whether ectomycorrhizal fungi suppressed saprotrophic fungi. Recalcitrant litter inputs favored the former over the latter, allowing the Gadgil effect only when such inputs predominated. Although ectomycorrhizal fungi did not always hamper litter decomposition, ectomycorrhizal nitrogen uptake always increased carbon : nitrogen ratios in litter. Our meta-analysis of empirical studies supports our theoretical results: ectomycorrhizal fungi appear to slow decomposition of leaf litter only in forests where litter inputs are highly recalcitrant. We thus find that the specific contribution of the Gadgil effect to high soil carbon : nitrogen ratios in ectomycorrhizal ecosystems may be smaller than predicted previously.

Diverse recalcitrant substrates slow down decomposition of leaf litter from trees in a serpentine ecosystem

Litter decomposition in serpentine ecosystems has been studied solely addressing heavy metals like Ni. We aimed to show how leaf nutrients, cell-wall components and lamina mass per area and microbial communities affect litter decomposition in a cool-temperate serpentine ecosystem. Reciprocal transplant leaf-litter decomposition was observed in three tree species (Clethra barbinervis, Magnolia obovata, and Quercus serrata) common to serpentine and non-serpentine ecosystems. Thirteen litter quality variables of the initial litter and microbial respirations from decomposed litter were assessed. Litter from the serpentine ecosystem decomposed slower than that from the non-serpentine ecosystem. Compared with all species, C. barbinervis showed high heavy metal concentration, cellulose content, and lamina dry mass per area; M. obovata showed low Ca concentration; and Q. serrata exhibited high lignin/N ratio in litter from the serpentine ecosystem. Litter placed in the serpentine site decomposed faster than that placed in the non-serpentine site, but basal microbial respiration rates from litter did not differ between decomposition sites. Litter from serpentine ecosystems adversely influenced decomposition rate owing to its diverse recalcitrant litter quality. Our study suggested the feasibility of litter quality evaluation based on multiple litter traits for better-understanding of litter decomposition in serpentine ecosystems.

The effects of simulated deposited nitrogen on nutrient dynamics in decomposing litters across a wide quality spectrum using a 15N tracing technique

Nitrogen (N) deposition affects litter decomposition. However, how nutrients, especially deposited N are immobilized and released in decomposing litters with different qualities (C/N and C/P) remains unclear. We conducted a laboratory microcosm experiment with four litter types and a combination of a coniferous and deciduous litter treated with N addition (6 mg 99.99% 15N g−1 litter) and control by measuring N-deposition effect on mass (NDEM), N (NDEN), and P remaining percentages (NDEP), deposited 15N immobilized abundance, and microbial composition and enzyme activities in decomposing litters during two years of incubation. The values of NDEM, NDEN, and NDEP were generally greater for the litters with intermediate C/N and C/P than those with the highest and lowest ratios after 360 days, although these parameters varied among different quality litters before 180 days. Immobilized exogenous 15N abundance by microbes showed an increasing trend with increasing litter C/N and C/P across the whole 720-day period. Both C/N and C/P were generally correlated with decomposition rate, 15N immobilization abundance, the microbial richness, and main enzyme activities in decomposing litters. N-deposition effects on N and P dynamics in decomposing litters varied with their C/N and C/P, generally exerting an unimodal curve at later decomposition stages. Lower quality litter with higher C/N and C/P favoured N immobilization in response to N addition.

Presence of Mycorrhizal Fungal Hyphae Rather than Living Roots Retards Root Litter Decomposition

Although both living roots and mycorrhizal fungi are well known to interact with saprotrophic microbes to affect litter decomposition, their relative importance is largely unclear. Here, a two-year pot experiment was conducted with two ectomycorrhizal (Pinus elliottii and Pinus massoniana) and four arbuscular mycorrhizal (Cinnamomum camphora, Cunninghamia lanceolata, Michelia maudiae and Schima superba) subtropical tree species to evaluate the relative effects of living roots and mycorrhizal fungal hyphae on their own root litter decomposition and to test whether these effects differed between ectomycorrhizal and arbuscular mycorrhizal trees. To achieve these objectives, litterbags with 50-µm and 1-mm mesh sizes filled with root litter of a given tree species were simultaneously installed in pots planted with the same species and unplanted pots filled with composite soil for all species. Effects of living roots alone were calculated as differences in root litter decomposition between 50-µm and 1-mm mesh litterbags installed in planted pots. Mycorrhizal hyphal effects were calculated as differences in root litter decomposition between 50-µm litterbags installed in planted and unplanted pots. The presence of mycorrhizal fungal hyphae significantly reduced root litter mass loss and inhibited the activities of β-glucosidase and phenol oxidase, while effects of living roots alone were non-significant when all tree species were pooled and inconsistent at the tree species level. Mycorrhizal fungal hyphae induced decreases in root litter mass loss that were markedly related to their inhibitory effects on β-glucosidase and phenol oxidase activities. When tree species were grouped by their mycorrhizal types, non-significant differences were observed between ectomycorrhizal and arbuscular mycorrhizal trees in their living root or mycorrhizal fungal effects on root litter decomposition. These findings highlight the important roles of mycorrhizal fungi in mediating litter decomposition via interacting with saprotrophic microbes and suggest that changes in tree carbon allocation to mycorrhizal fungi owing to global change may affect soil carbon storage.

Decomposition time, chemical traits and climatic factors determine litter-mixing effects on decomposition in an alpine steppe ecosystem in Northern Tibet

In the context of rapid species diversity loss, whether and how species diversity affects litter decomposition in alpine ecosystems remain unclear. Here, we aimed to assess the impact of litter mixing on decomposition and the influencing factors of such litter-mixing effects (LMEs). We incubated the litter of four alpine steppe species in monocultures and all possible litter combinations and analysed the mass remaining over three years. Litter mixing showed more frequent antagonistic effects than synergistic effects in the early stage of the experiment; however, the LME might change from antagonistic to synergistic at the latter stage of incubation. The magnitude of the LMEs increased as decomposition progressed. The four-species mixture resulted in more antagonistic effects, while the magnitude of the non-additive effects showed no relationship with species richness. Litter chemical traits and climatic factors affected the direction and magnitude of the non-additive effects, but these influences were time-dependent. Additionally, the fast-decomposing and slow-decomposing litter species had negative and positive responses to the litter mixture, respectively. Our results demonstrate that the LME was determined by decomposition time, chemical traits and climatic factors and suggest that assessing the relative individual performances of the litter components in a mixture is an important way to examine the mechanisms underlying LMEs.

Priming effect of litter mineralization: the role of root exudate depends on its interactions with litter quality and soil condition

Root exudation can prime microbial synthesis of additional exoenzymes and consequently accelerate organic carbon (C) and nitrogen (N) mineralization. Such exudate induced priming effect (EPE) has been hypothesized to depend on exudate rate and stoichiometry. Little is known about how EPE would affect litter decomposition. We employed a microcosm experiment to evaluate the influence of root exudate on litter nutrient release and microbial enzyme functions. Leaf litters of Pinus massoniana, Quercus variabilis and Robinia pseudoacacia were incubated under two soil conditions (fertile versus barren). Solutions of chemicals often found in root exudates with contrasting C:N ratios were inoculated frequently into the microcosms to simulate exudation. By comparing with a water control, exudate effect was determined. In barren soils, exudates with C:N ratio of 10 significantly decelerated C loss of R. pseudoacacia, all N-containing exudates significantly enhanced the N-cycling related enzymes in decomposing Q. variabilis, while C-only exudate accelerated N loss of P. massoniana. In fertile soils, C-only exudate promoted the N-cycling related enzymes in decomposing R. pseudoacacia. A stoichiometric C:N constraint on microbial utilization of exudates arose in decomposing recalcitrant litters in barren soil. EPE and its stoichiometric constraint depend on interactions with litter quality and soil condition. The findings arouse the consequences of exudate rate and stoichiometry changes in determining soil nutrient balance.

Altered leaf litter quality exacerbates the negative impact of climate change on decomposition

Abstract Leaf litter decomposition is a key component of global biogeochemical cycles that influence soil carbon storage, nutrient availability and plant productivity. Ongoing climate change will lead to warmer and drier conditions in many dryland regions, potentially affecting litter decomposition and nutrient dynamics. Climate change effects can be direct and/or indirect, for example, through changes in litter quality, yet their relative importance on litter decomposition remains unclear. We conducted a manipulative study in a semi‐arid shrubland to assess the effects of leaf litter quality, forecasted climate change, that is, +2.5°C warming (W), 30% rainfall reduction (RR) as well as their interaction (W + RR) to elucidate their relative effects on litter decomposition. Climatic effects alone reduced decomposition of a homogeneous Control leaf litter collected from Helianthemum squamatum shrubs growing in unmanipulated plots by 23.4%, 18.1% and 29.8% in the W, RR and W + RR treatments respectively. Leaf litter quality was lower in shrubs that had been growing in warmed plots (W and W + RR), as they had lower nutrient concentrations (P, Fe) and higher C:N and C:P ratios than leaf litter produced under ambient (Control) conditions. Lignin concentration was significantly lower in litter from W + RR plots, yet when both climate and litter quality were considered simultaneously, decomposition rates were 32.0%, 26.3% and 39.9% lower in W, RR and W + RR plots compared to Controls. In addition, we found greater microbial N immobilization in leaf litter incubated within warmed (W and W + RR) than within non‐warmed plots (Control and RR). Structural equation modelling showed that higher litter moisture and microbial biomass contents stimulated decomposition. Simulated climate change (W, RR and W + RR) reduced decomposition indirectly by negatively affecting litter moisture contents and litter microbial biomass. Microbial nitrogen immobilization was stimulated by the lower quality (i.e. high C:N ratios) of the leaf litter collected in shrubs from warmed plots (W and W + RR). Synthesis. Our findings indicate that forecasted climate change conditions slow down C and N cycling in a dryland ecosystem, an effect that is further exacerbated by climate change‐induced reductions in litter quality and related reductions in bacterial and fungal biomass in litter.

Long-term N and S addition and changed litter chemistry do not affect trembling aspen leaf litter decomposition, elemental composition and enzyme activity in a boreal forest

The effect of long-term nitrogen (N) and sulfur (S) deposition on litter mass loss and changes in carbon (C), N, and S composition and enzyme activities during litter decomposition was investigated in a boreal forest. This study included four N × S treatments: control (CK), N application (30 kg N ha−1 yr−1), S application (30 kg S ha−1 yr−1), and N plus S application (both at 30 kg ha−1 yr−1). Two experiments were conducted for 22 months: 1) a common litter decomposition experiment with litter bags containing a common litter (same litter chemistry) and 2) an in-situ litter decomposition experiment with litter from each treatment plot (and thus having different litter chemistry). Litterbags were placed onto the four treatment plots to investigate the direct effect of N and S addition and the combined effect of N and/or S addition and litter chemistry on litter decomposition, respectively. Regardless of the source of litter, N and/or S addition affected C, N and S composition at a certain period of the experiment but did not affect litter mass loss and enzyme activity throughout the experiment, indicating that the N and S addition rates were below the critical level required to affect C and N cycling in the studied ecosystem. However, the greater change in N composition per unit of litter mass loss in the N addition treatment than in the other treatments in the common litter but not in the in-situ litter experiment, suggests that the effect of N addition on N loss and retention depends on the initial litter chemistry. We conclude that the studied N and S addition rates did not affect litter decomposition and elemental cycling in the studied forest ecosystem even though the N and S addition rates were much greater than their ambient deposition rates.

Does nanosized plastic affect aquatic fungal litter decomposition?

Abstract Nanosized plastics are an emerging concern in freshwater ecosystems, raising the question whether they put freshwater ecological processes at risk. Litter decomposition is a major ecological function in forested streams which is mainly driven by aquatic hyphomycetes. Here we investigated whether increasing concentrations (up to 102.4 mg/L) of nanosized polystyrene plastics (NPPs; 100nm) affect litter decomposition by five widely distributed species of aquatic hyphomycetes. Results showed that average litter decomposition decreased by 8% relative to the control when exposed to 102.4 mg/L NPPs. Aquatic hyphomycete species differed in their sensitivity to NPPs. The greatest inhibition of litter decomposition was found with Tetracladium marchalianum, where it dropped from 37 (control) to 16% (102.4 mg/L of NPP). Overall our study highlights the emerging risks and potential dangers of NPPs to freshwater ecosystem functioning. It also indicates that the impact of NPPs may be species specific.

Roots, mycorrhizal fungi and altitude as determinants of litter decomposition and soil animal communities in tropical montane rainforests

This study assesses the importance of root- and mycorrhiza-derived resources for decomposition processes and as food resources for microarthropod communities along an altitudinal gradient of tropical montane rainforests in southern Ecuador. At 1000, 2000 and 3000 m microcosms with openings of different mesh sizes (4 mm, 45 μm) or closed were exposed in the field, manipulating accessibility by roots and mycorrhizal fungi. The microcosms contained undisturbed soil with a mixture of leaf litter from three abundant plant species from the site at which the microcosms were exposed. After 12 months water content, microbial biomass, remaining litter mass, C-to-N ratio and the soil microarthropod community structure were analysed. Water content and C-to-N ratio were lower and microbial biomass was highest at the lowest altitude, while litter decomposition and microarthropod abundance were at a maximum at the intermediate altitude. Exclusion of roots and mycorrhizal fungi did not affect litter decomposition, but decreased the abundance and diversity of Oribatida, while the abundance of Collembola increased in closed microcosms. The effect of root and mycorrhizal exclusion on all investigated parameters did not differ between the three altitudes. The results indicate that in nutrient limited tropical montane rainforests mycorrhizal fungi suppress the activity of other microorganisms, potentially competing for litter-derived resources, at each of the investigated altitudes. Collembola benefitted from this reduced competition while Oribatida strongly depended on root-derived resources.

Nitrogen deposition effect on forest litter decomposition is interactively regulated by endogenous litter quality and exogenous resource supply

Atmospheric nitrogen (N) deposition affects litter decomposition. However, how endogenous litter quality and exogenous resource supply alter the N deposition effect on litter decomposition and deposited N immobilized by microbes remains unclear. We conducted a laboratory experiment to examine how the N deposition effect on litter decomposition varies with endogenous litter quality (needle litter with higher C/nutrients, low quality litter versus leaf litter with low C/nutrients, high quality litter) and exogenous resource supply (five treatments: N addition alone; N plus non-N nutrient and/or carbon addition; control) using a 15N tracing method. Nitrogen deposition increased the % mass and % N remaining across the decomposition process. Adding non-N nutrients increased the N deposition effect on % mass and % N remaining in the decomposing high quality litter but not in the low quality litter. Moreover, the % P remaining was increased in the low quality litter but was decreased in the high quality litter under N deposition. However, adding N and non-N nutrients together increased the % P remaining in both decomposing litters. The immobilized exogenous 15N abundance (IEN) was much higher in the decomposing low quality litter than high quality litter. For low quality litter, resource addition treatments affected IEN, but their effects depended on decomposition stages. For high quality litter, carbon addition alone generally increased IEN across the 720 days. Nitrogen deposition effect on litter decomposition could be altered by exogenous resource supply, but the pattern ultimately depended on endogenous litter quality. Nitrogen deposition generally suppressed the litter decomposition and non-N nutrients addition enhanced the inhibition effects of N deposition on litter decomposition, especially of high quality litter, while lower quality litter tended to immobilize more exogenous deposited N. Thus, the magnitude of both non-N nutrient availability and litter quality needs to be taken into consideration when assessing the effects of N deposition on litter decomposition.

Effects of elevated atmospheric CO2 concentration and temperature on litter decomposition in streams: A meta‐analysis

AbstractThe metabolism of forest streams depends on the decomposition of plant litter of terrestrial origin. In turn, the rate at which litter decomposes depends on litter characteristics, decomposer activity, environmental characteristics, and their interactions. Atmospheric changes, such as increases in atmospheric carbon dioxide concentration ([CO2]) and in temperature, may affect all these variables. Here, we report the results of a meta‐analysis of 41 studies conducted worldwide between 1993 and 2017 on the effects of elevated atmospheric [CO 2], elevated temperature, or both (temperature + [CO 2]) on litter decomposition in streams. Elevated temperature significantly increased litter decomposition rates, whereas elevated [CO 2] and temperature + [CO 2] did not significantly affect litter decomposition rates. The effect of elevated temperature did not depend on the type of study (i.e., laboratory or field study, correlative field or manipulative field study) but in correlative field studies, the temperature effect was stronger over latitudinal than altitudinal gradients. Effects of elevated temperature also did not depend on the type of decomposer community (microbial or microbial and macroinvertebrates) but effects were always significant for total litter decomposition (both microbes and macroinvertebrates involved), whereas microbial‐driven litter decomposition was significantly affected only in manipulative studies. Effects of elevated temperature did not depend on the litter identity, although significant effects were found for some litter genera but not others. In terrestrial ecosystems, the elevated temperature was found to increase litter decomposition rates, whereas elevated [CO 2] decreased litter decomposition rates. Study type (laboratory or field) and litter identity were important moderators of the response of litter decomposition to elevated temperature and [CO 2] in terrestrial ecosystems. These differences between soil and stream ecosystems may be partially due to intrinsic differences (such as moisture that is not limiting in streams) between these ecosystems. In addition, our meta‐analysis is geographically biased with most studies being conducted in Europe. More studies in other parts of the world could allow for a better understanding of the effects of climate warming and [CO 2] increases on litter decomposition, the global carbon cycle, and biochemistry in streams.

Litter species diversity is more important than genotypic diversity of dominant grass species Stipa grandis in influencing litter decomposition in a bare field

Studies have indicated that plant litter diversity can affect litter decomposition at both species diversity and genotypic diversity level within a species. However, the essence and relative importance of these two diversity levels on litter decomposition remain unknown. Here, two independent one-factor experiments, litter species diversity and litter genotypic diversity of the dominant species—Stipa grandis, were carried out to explore the effects of initial litter quality, litter composition and diversity on decomposition of mass, nitrogen (N), carbon (C) and phosphorus (P) simultaneously. The results showed that: (1) there were significant relationships between the initial litter N, C/N, lignin/N and the decomposition rate of N, between the initial litter P, N/P and the decomposition rate of P, and the litter composition significantly influenced litter mass, N, C and P remaining in both litter species and genotypic diversity experiments; and (2) litter species diversity significantly affected litter mass, N, C and P remaining, and non-additive relative mixture effects were mainly contributed by synergistic effects especially in 6-species mixtures; however, similar patterns were not found in litter genotypic diversity experiment. The present results emphasized that initial litter quality played the most important role in influencing litter decomposition of mass N, C and P, and suggested that litter species mixtures rather than litter genotypic mixtures of a dominant species could favor nutrient cycling in ecosystem of the semi-arid Inner Mongolia Steppe of China.

Multiple interactions between tree composition and diversity and microbial diversity underly litter decomposition

Litter decomposition determines carbon and nutrient cycling in terrestrial ecosystems. Prior research has addressed the importance of litter quality and microclimate on litter decomposition. However, the interacting relationships among litter chemical quality, the microenvironment, and micro-organisms - as well as their subsequent influence on litter decomposition - remain poorly understood. We sampled five forest types with varying overstory compositions in the subtropical forest of China and set up a reciprocal transplant litter decomposition experiment using a split-plot design. We used structural equation modeling (SEM) to examine the effects of litter species diversity and composition on litter decomposition rate through litter chemical properties. We also examined the effects of tree species diversity and composition on litter decomposition rate via litter moisture, microbial chemistry, and fungal diversity. Increased coniferous litter proportion restrained litter decomposition by decreasing litter N content. Litter species diversity and functional dispersion of litter C, N, and P contents had insignificant effects on litter decomposition. Overstory coniferous proportion and tree species diversity enhanced litter decomposition rates indirectly through their positive effects on litter moisture, fungal properties (a composite variable of fungal richness and squared fungal guild diversity), and microbial chemistry (a composite variable of microbial carbon and phosphorus). Our results highlighted that coniferous litter proportion and overstory coniferous proportion had opposite effects on litter decomposition via litter nitrogen content and the microenvironment, respectively. Furthermore, fungal community plays a key role in how overstory species composition and microclimate affect litter decomposition.