Litter nitrogen concentration changes mediate effects of drought and plant species richness on litter decomposition.

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

Decomposition of plant litter is a key process for the flow of energy and nutrients in ecosystems that may be sensitive to the loss of biodiversity. Two hypothetical mechanisms by which changes in plant diversity could affect litter decomposition are (1) through changes in litter species composition, and (2) by altering the decomposition microenvironment. We tested these ideas in relation to the short‐term decomposition of herbaceous plant litter in experimental plant assemblages that differed in the numbers and types of plant species and functional groups that they contained to simulate loss of plant diversity. We used different litterbag experiments to separate the two potential pathways through which diversity could have an effect on decomposition. Our two litterbag trials showed that altering plant diversity affected litter breakdown differently through changes in decomposition microenvironment than through changes in litter composition. In the decomposition microenvironment experiment there was a significant but weak decline in decomposition rate in relation to decreasing plant diversity but no significant effect of plant composition. The litter composition experiment showed no effect of richness but significant effects of composition, including large differences between plant species and functional groups in litter chemistry and decomposition rate. However, for a nested subset of our litter mixtures decomposition was not accurately predicted from single‐species bags; there were positive, non‐additive effects of litter mixing which enhanced decomposition. We critically assess the strengths and limitations of our short‐term litterbag trials in predicting the longer‐term effects of changes in plant diversity on litter decomposition rates.

Aims Grazing intensity and grazing exclusion affect ecosystem carbon cycling by changing the plant community and soil micro-environment in grassland ecosystems. The aims of this study were: 1) to determine the effects of grazing intensity and grazing exclusion on litter decomposition in the temperate grasslands of Nei Mongol; 2) to compare the difference between above-ground and below-ground litter decomposition; 3) to identify the effects of precipitation on litter production and decomposition. Methods We measured litter production, quality, decomposition rates and soil nutrient contents during the growing season in 2011 and 2012 in four plots, i.e. light grazing, heavy grazing, light grazing exclusion and heavy grazing exclusion. Quadrate surveys and litter bags were used to measure litter production and decomposition rates. All data were analyzed with ANOVA and Pearson’s correlation procedures in SPSS. Important findings Litter production and decomposition rates differed greatly among four plots. During the two years of our study, above-ground litter production and decomposition in heavy-grazing plots were faster than those in light-grazing plots. In the dry year, below-ground litter production and decomposition in light-grazing plots were faster than those in heavy-grazing plots, which is opposite to the findings in the wet year. Short-term grazing exclusion could promote litter production, and the exclusion of light-grazing could increase litter decomposition and nutrient cycling. In contrast, heavy-grazing exclusion decreased litter decomposition. Thus, grazing exclusion is beneficial to the restoration of the light-grazing grasslands, and more human management measures 杨丽丽等: 内蒙古温带草原不同放牧强度和围栏封育对凋落物分解的影响 749 doi: 10.17521/cjpe.2016.0051 are needed during the restoration of heavy-grazing grasslands. Precipitation increased litter production and decomposition, and below-ground litter was more vulnerable to the inter-annual change of precipitation than above-ground litter. Compared to the light-grazing grasslands, heavy-grazing grasslands had higher sensitivity to precipitation. The above-ground litter decomposition was strongly positively correlated with the litter N content (R = 0.489, p < 0.01) and strongly negatively correlated with the soil total N content (R = 0.450, p < 0.01), but it was not significantly correlated with C:N and lignin:N. Below-ground litter decomposition was negatively correlated with the litter C (R = 0.263, p < 0.01), C:N (R = 0.349, p < 0.01) and cellulose content (R = 0.460, p < 0.01). Our results will provide a theoretical basis for ecosystem restoration and the research of carbon cycling.

Biodiversity loss in riparian forests has the potential to alter rates of leaf litter decomposition in stream ecosystems. However, studies have reported the full range of positive, negative and no effects of plant diversity loss on decomposition, and there is currently no explanation for such inconsistent results. Furthermore, it is uncertain whether plant diversity loss affects other ecological processes related to decomposition, such as fine particulate organic matter production or detritivore growth, which precludes a thorough understanding of how detrital stream food webs are impacted by plant diversity loss. We used a microcosm experiment to examine the effects of plant diversity loss on litter decomposition, fine particulate organic matter production, and growth of a dominant leaf-shredding detritivore, using litter mixtures varying in species composition. We hypothesized that plant diversity loss would decrease the rates of all studied processes, but such effects would depend on the leaf traits present in litter mixtures (both their average values and their variability). Our findings partly supported our hypotheses, showing that plant diversity loss had a consistently negative effect on litter decomposition and fine particulate organic matter production (but not on detritivore growth) across litter mixtures, which was mediated by detritivores. Importantly, the magnitude of the diversity effect and the relative importance of different mechanisms underlying this effect (i.e., complementarity vs. selection) varied depending on the species composition of litter mixtures, mainly because of differences in litter nutritional quality and trait variability. Complementarity was prevalent but varied in size, with positive selection effects also occurring in some mixtures. Our results support the notion that loss of riparian plant species is detrimental to key stream ecosystem processes that drive detrital food webs, but that the magnitude of such effects largely depends on the the order of species loss.

Nitrogen (N) deposition can reduce plant species richness and cause grassland degradation, thus affecting grassland ecosystem stability. Arbuscular mycorrhizal (AM) fungi play an important role in ecosystem stability. However, the influences of AM fungi on grassland ecosystem stability under N deposition remain unclear. We need more information on the impacts of N accumulation on the interactions between AM fungi and the plant community. To test the contribution of AM fungi to grassland stability under N deposition, a 5‐year field experiment was conducted in a temperate meadow with two manipulated factors, namely, N addition and AM fungi suppression. The plant species richness and diversity, biomass stability, litter decomposition, and greenhouse gas emissions were quantified. Under N addition, AM fungi did not affect the plant species diversity and richness but altered the coverages of different functional groups and increased the aboveground productivity and biomass stability. Litter decomposition increased under N addition and increased more in the treatment where AM fungi were not suppressed. The emissions of N2O and CH4 in the AM fungi suppression treatment were much higher than those in the nonsuppression treatment under N addition. Our results suggest that AM fungi can alter the plant community structure, increase plant productivity and community biomass stability, accelerate litter decomposition, and reduce the soil total N concentration and emissions of N2O and CH4 under N addition. Our results highlight that the conservation of AM fungi should be considered to alleviate grassland degradation and maintain grassland ecosystem multifunctionality in the future considering global change.

Soil fauna are important regulators of litter decomposition and nutrient transformation. Nitrogen deposition and rainfall changes driven by global changes could affect litter decomposition by changing environment and soil faunal community. Different mesh size (2 mm and 0.01 mm) litter bags were used to explore how soil meso- and micro-fauna contribute to decomposition of Stipa breviflora litter under nitrogen deposition and rainfall changes. The experiment followed split-plot design, with rainfall change (natural rainfall, CK; rainfall addition 30%, W; rainfall reduction 30%, R) as the main trement and nitrogen addition (0, N0; 30, N30; 50, N50; 100 kg·hm-2·a-1, N100) as the sub-treatment. The results showed that: 1) Rainfall change significantly affected litter decomposition rate, which was increased by rainfall addition. Moreover, litter decomposition rate was accelerated with increasing nitrogen addition rates. Litter residual rate decreased gradually with increasing N addition, and got to the highest in N100. Litter decomposition rate decreased first and then increased, and peaked in N50 in rain reduction and natural rainfall treatment. There was no significant interactions between rainfall change and nitrogen addition in affecting litter decomposition. 2) During the whole decomposition process, a total of 1577 soil meso- and micro-fauna were captured, belonged to 1 phyla, 3 classes, 13 orders (including suborders) and 49 families. The dominant groups were Acarina, Coleoptera larvae, and Collembola. Nitrogen addition significantly increased abundance and group numbers of soil meso- and micro-fauna. 3) The litter mass residue rate was significantly negatively correlated with abundance and group numbers of soil meso- and micro-fauna. The contribution rate of soil meso- and micro-fauna to litter decomposition increased with increasing rainfall. In summary, soil meso- and micro-fauna had a positive effect on decomposition of Stipa breviflora litter in desert steppe. Their contribution to litter was promoted by the enhancement of soil mesofauna abundance and group under rainfall and nitrogen addition. Excessive nitrogen would inhibit soil meso- and micro-fauna community and group density when water was insufficient, and would thus weaken the function of soil mesofauna to litter decomposition.

Changes in tree species composition have important effects on the overall rate of litter decomposition at a community level because litter decomposability varies among species and between leaf and wood litter. To understand how changes in tree species composition affect litter dynamics and carbon sequestration at the ecosystem level, it is important to clarify interspecific variations in leaf and wood litter decomposability, and the traits driving the variation. Using field data, field experiments, and laboratory experiments, we explored rates of leaf and wood litter decomposition and their relationships to traits of ten deciduous hardwood species in a temperate forest in Japan. Rates of leaf and wood litter decomposition at the community level were also estimated by considering species‐specific litter inputs and decomposition rates. Rates of leaf and wood litter decomposition were not correlated under either field or controlled laboratory conditions. This is probably because the traits that affect decomposition rate differ between leaf and wood litter. Interspecific variation in litter decomposability of leaves and wood was generally consistent between field conditions and laboratory experiments using a single fungus, suggesting that the decomposing fungi set the species‐specific decomposition rates. Moreover, the leaf and wood traits that affected decomposition by their specific fungi were different. The aboveground input of wood litter was less than half that of leaf litter, but its half‐life was &gt; 3 times longer, suggesting that wood and leaves make similar contributions to litter accumulation. Focusing on either leaf or wood litter alone may produce misleading estimates of how species composition changes affect litter dynamics at the community level. Our results provide insight into predicting the response of carbon dynamics to future climate change.

Global changes and declines in biodiversity at all taxonomic levels have intensified the scientific effort to understand the functional role of biodiversity as a regulator of ecosystem processes. Although evidence for a positive relationship between biodiversity and ecosystem functioning is accumulating from studies mainly performed in grasslands, little is known about the importance of this relationship in forest ecosystems, despite their huge ecological and socioeconomic importance. In this thesis I therefore assessed the effects of tree diversity on above- and belowground productivity and on litter decomposition along an experimentally manipulated diversity gradient in a temperate forest system, using different approaches including field and pot experiments. In chapter 1, I quantified the relative contributions of complementarity and selection to net effects of tree diversity on above- and belowground productivity, and assessed whether this relationship is influenced by planting density. I found that total productivity was increased in mixed compared with monospecific stands and that tree diversity effects on productivity occurred below rather than above ground and were density-dependent. Positive effects of tree diversity were related to complementarity rather than selection and were more pronounced at low planting density. This study demonstrates the potential role of niche separation in driving the biodiversity ecosystem functioning relationship in trees, and highlights the significance of belowground processes for driving this pattern. Chapter 2 looks deeper into the role of belowground competition in affecting root allocation of saplings. I tested whether trees increase root allocation in response to the presence of neighbours, and whether this response is more pronounced in the presence of con- compared with heterospecific competitors. Although belowground competition in tree pairs led to increased root production and root allocation, this effect was independent of the identity of the competitor, perhaps because neighbour recognition mechanisms are absent in trees. Increased root production more generally may have implications for carbon storage and nutrient retention within forest systems. In chapter 3, I examined the functional importance of after-life effects of tree species diversity and its interaction with soil fauna on a crucial ecosystem process, leaf litter decomposition. In particular I investigated the relative importance of different direct and indirect pathways through which litter species diversity can influence decomposition. Different litter species compositions varied greatly in decomposition rates, which interactively with soil fauna was more important than litter diversity per se for litter decomposition. However, decomposition in mixtures resulted in synergistic effects only in the absence of soil fauna, suggesting that small litter diversity effects may be masked by soil fauna activity. In chapter 4, I quantified intraspecific variation in litter quality and decomposition and the ecological consequences of intraspecific diversity on decomposition rates. Using European beech as a model species, I showed that there was considerable intraspecific variation in litter decomposition rates, although this was not related to litter quality. However, I also found synergistic effects on decomposition of mixing litter from different individuals, demonstrating the significance of intraspecific variation on this ecosystem process. Overall this study demonstrates the importance of biodiversity both among and within species for ecosystem functioning. However, diversity effects were relatively weak, and species composition was a consistently better predictor of variation in productivity and decomposition. This underscores the importance of specific species traits in driving ecosystem processes in tree communities.

Impact of vegetation community on litter decomposition: Evidence from a reciprocal transplant study with 13C labeled plant litter

Background and aims Litter decomposition is a key process controlling flows of energy and nutrients in ecosystems. Altered biodiversity and nutrient availability may affect litter decomposition. However, little is known about the response of litter decomposition to co-occurring changes in species evenness and soil nutrient availability. Methods We used a microcosm experiment to evaluate the simultaneous effects of species evenness (two levels), identity of the dominant species (three species) and soil N availability (control and N addition) on litter decomposition in a Mongolian pine (Pinus sylvestris var. mongolica) plantation in Northeast China. Mongolian pine needles and senesced aboveground materials of two dominant understory species (Setaria viridis and Artemisia scoparia) were used for incubation. Results Litter evenness, dominant species identity and N addition significantly affected species interaction and litter decomposition. Higher level of species evenness increased the decomposition rate of litter mixtures and decreased the incidence of antagonistic effects. A. scoparia-dominated litter mixtures decomposed faster than P. sylvestris var. mongolica-andS. viridis-dominated litter mixtures. Notably, N addition increased decomposition rate of both single-species litters and litter mixtures, and meanwhile altered the incidence and direction of nonadditive effects during decomposition of litter mixtures. The presence of understory species litters stimulated the decomposition rate of pine litters irrespective of N addition, whereas the presence of pine litters suppressed the mass loss of A. scoparia litters. Moreover, N addition weakened the promoting effects of understory species litters on decomposition of pine litters. Conclusions Pine litter retarded the decomposition of understory species litters whereas its own decomposition was accelerated in mixtures. Nitrogen addition and understory species evenness altered species interaction through species-specific responses in litter mixtures and thus affected litter decomposition in Mongolian pine forests, which could produce a potential influence on ecosystem C budget and nutrient cycling.

Global changes such as increasing CO2, rising temperature, and land-use change are likely to drive shifts in litter inputs to forest floors, but the effects of such changes on litter decomposition remain largely unknown. We initiated a litter manipulation experiment to test the response of litter decomposition to litter removal/addition in three successional forests in southern China, namely masson pine forest (MPF), mixed coniferous and broadleaved forest (MF) and monsoon evergreen broadleaved forest (MEBF). Results showed that litter removal decreased litter decomposition rates by 27%, 10% and 8% and litter addition increased litter decomposition rates by 55%, 36% and 14% in MEBF, MF and MPF, respectively. The magnitudes of changes in litter decomposition were more significant in MEBF forest and less significant in MF, but not significant in MPF. Our results suggest that change in litter quantity can affect litter decomposition, and this impact may become stronger with forest succession in tropical forest ecosystem.

Nitrogen (N) deposition not only alters the physiological processes of individual plant, but also leads to world‐wide biodiversity loss. However, little is known about how the hierarchical responses from individual physiological processes to plant community structure would have cascading effects on soil carbon (C) cycling. Here, we assessed whether changes in plant chemical composition and community composition under increasing N input would affect the turnover rate of litter layer and soil C loss via heterotrophic respiration (Rh) in a temperate grassland. We showed that more than a decade’s N addition significantly decreased plant species richness, litter layer turnover rate and Rh. The 13C‐NMR results showed that, for individual species, N addition either increased the abundance of recalcitrant C groups such as alkyl and methoxyl, or decreased labile C groups such as carbohydrate, resulting in decreases in carbohydrate C‐to‐methoxyl C ratio (CC/MC) for most species. Our data also showed that with the increase in N deposition, the abundance of relatively high degradable dominant species, such as Agropyron cristatum and Artimesia frigida declined rapidly, and the relatively recalcitrant species such as Potentilla bifurca and Leymus chinensis become dominant. Changes in individual species’ chemical composition and plant community composition significantly decreased litter quality at community level, as indicated by the lower community‐level CC/MC at higher N addition rates. The result of step‐AIC model selection further showed that plant diversity loss and the decrease in community‐level CC/MC jointly explained the decrease in Rh after N addition best, and further relative importance partition result showed that these two factors respectively contributed 65.1% and 34.9% of the explained variation. Overall, we demonstrated that changes in plant chemical composition and diversity loss due to N addition reduced the quality of plant C input to soil, which further slowed down litter layer turnover rate and inhibited soil heterotrophic respiration. Our study complements the intermediate links of how shifts in plant community structure regulate soil C cycle under global changes. A plain language summary is available for this article.

Litter and root decomposition is an important source of soil organic matter and nutrients. To ascertain the contribution of litter and root to natural grassland nutrients in rocky desertification areas, from March 2017 to January 2018, the continuous soil column method, collector method, and litter decomposition method were used to study the soil nutrients, litter and root biomass, decomposition, and nutrient release of potential, moderate, and severe rocky desertification grasslands, as well as their responses to rocky desertification. The results showed that the litter and root decomposition rate showed a trend of being first fast and then slow, and the decomposition rate of litter and root was greater than 50% after 300 days. The annual litter decomposition rates of potential, moderate, and severe rocky desertification grasslands were 69.98%, 62.14%, and 49.79%, respectively, and the annual decomposition rates of root were 73.64%, 67.61%, and 64.09%, respectively. With a deepening degree of rocky desertification, the litter and root decomposition rate decreased. The decomposition coefficients, k, of litter in potential, moderate, and severe rocky desertification grasslands were 1.128, 0.896, and 0.668, respectively, and the decomposition coefficients, k, of root were 1.152, 1.018, and 0.987, respectively. The nutrient release processes of litter and root were different, and the release mode ultimately manifests as "release". In rocky desertification grasslands, the organic carbon (OC), total nitrogen (TN), total phosphorus (TP), and total potassium (TK) released by litter and root decomposition were 18.93-263.03 g·m-2·yr-1, 1.79-5.59 g·m-2·yr-1, 0.18-0.47 g·m-2·yr-1, and 0.66-3.70 g·m-2·yr-1, respectively. The contribution of root to soil nutrients was greater than that of litter. The degree of rocky desertification was negatively correlated with the biomass, decomposition rate, and nutrient return amount of litter and root. The results of this study provide direct field evidence and illustrate the contribution of litter and root decomposition in rocky desertification grasslands to soil nutrients.

C) and, based on that assumption, partitioned relationships among different pathways. In this original form, path analysis was not a simultaneous method (in the Smith et al. (1997) recently drew attention to some pit- sense that all parameters were estimated simultaneously) falls that can arise when trying to predict the responses nor did it include overall tests of model fit to data. In the of experimental manipulations from nonexperimental early 1970s, more general procedures were developed for

Evenness alters the positive effect of species richness on community drought resistance via changing complementarity