Leaf Litter Decomposition Research Articles

Tree mycorrhizal type regulates leaf and needle microbial communities, affects microbial assembly and co-occurrence network patterns, and influences litter decomposition rates in temperate forest

BackgroundTree mycorrhizal types (arbuscular mycorrhizal fungi and ectomycorrhizal fungi) alter nutrient use traits and leaf physicochemical properties and, thus, affect leaf litter decomposition. However, little is known about how different tree mycorrhizal species affect the microbial diversity, community composition, function, and community assembly processes that govern leaf litter-dwelling microbes during leaf litter decomposition. MethodsIn this study, we investigated the microbial diversity, community dynamics, and community assembly processes of nine temperate tree species using high-resolution molecular technique (Illumina sequencing), including broadleaved arbuscular mycorrhizal, broadleaved ectomycorrhizal, and coniferous ectomycorrhizal tree types, during leaf litter decomposition.Results and discussionThe leaves and needles of different tree mycorrhizal types significantly affected the microbial richness and community composition during leaf litter decomposition. Leaf litter mass loss was related to higher sequence reads of a few bacterial functional groups, particularly N-fixing bacteria. Furthermore, a link between bacterial and fungal community composition and hydrolytic and/or oxidative enzyme activity was found. The microbial communities in the leaf litter of different tree mycorrhizal types were governed by different proportions of determinism and stochasticity, which changed throughout litter decomposition. Specifically, determinism (mainly variable selection) controlling bacterial community composition increased over time. In contrast, stochasticity (mainly ecological drift) increasingly governed fungal community composition. Finally, the co-occurrence network analysis showed greater competition between bacteria and fungi in the early stages of litter decomposition and revealed a contrasting pattern between mycorrhizal types.ConclusionOverall, we conclude that tree mycorrhizal types influence leaf litter quality, which affects microbial richness and community composition, and thus, leaf litter decomposition.

Effects of environmental factors on leaf litter decomposition of three species of Stipa

Plant litter decomposition plays an important role in carbon and nutrient cycling in terrestrial ecosystems. The influence of abiotic factors on the decomposition of plants in humid ecosystems is higher due to the favorable moisture conditions and the abundance of decomposer microorganisms. However, in arid and semi-arid ecosystems, plant litter decomposition is influenced by both abiotic and biotic factors, depending on sparse plant cover, high soil temperature, and low rainfall. The effects of environmental factors on leaf litter decomposition in arid and semi-arid Mongolian steppes are unclear. A field experiment was carried out in meadow steppe, typical steppe, and desert steppes of Mongolia to investigate the effect of environmental factors such as light-expose, shade, and climate conditions on three species of Stipa (Stipa baicalensis, Stipa grandis, Stipa gobica) representing different litter qualities over a two year of incubation (6, 12, 18 and 24 months). The results of the study revealed that the leaf litter decomposition rate differed among the three species, in which Stipa gobica had a relatively high leaf litter decomposition rate. Also, the rate of leaf decomposition of Stipa gobica was directly and indirectly correlated with leaf traits, while it was positively correlated to climatic conditions (r=0.55). However, for Stipa baicalensis, was negatively correlated to leaf traits (r=-0.56 – -0.63) and on the contrary, Stipa grandis was strongly positively correlated to leaf traits (r=0.68-0.89). Seasonality has an effect on the leaf litter decomposition, with the highest decomposition rate occurring from April to October, while the decomposition rate was very low from November to March. Гурван зүйл хялганын навчны задралд хүрээлэн буй орчны хүчин зүйлсийн үзүүлэх нөлөө Хураангуй. Ургамлын задрал нь хуурай газрын экосистем дэх нүүрстөрөгч болон шим тэжээлийн бодисын эргэлтэд чухал үүрэг гүйцэтгэдэг. Чийглэг экосистемийн ургамлын задралд абиотик хүчин зүйлийн нөлөө их байдаг нь чийгийн таатай нөхцөл, задлагч микрорганизм их байдагтай холбоотой. Харин хуурай болон хагас хуурай экосистемийн хувьд ургамлын бүрхэвч сийрэг, хөрсний температур өндөр, хур тунадасны хэмжээ бага байдгаас хамаарч ургамлын задралд абиоток, биотик хүчин зүйл нөлөөлдөг. Хуурай болон хагас хуурай Монгол орны нугажуу, хуурай болон цөлөрхөг хээрийн ургамлын навчны задралд хүрээлэн буй орчны хүчин зүйлс хэрхэн нөлөөлж байгаа нь тодорхойгүй хэвээр байна. Тиймээс энэхүү судалгааны ажлаар нугажуу хээр, хуурай хээр болон цөлөрхөг хээрийн зонхилогч үетэн ургамал болох гурван зүйл хялганын (Stipa baicalensis, Stipa grandis, Stipa gobica) навчны задралд хүрээлэн буй орчны хүчин зүйлс болон ургамлын шинж чанар хэрхэн нөлөөлж буй болон бүлгэмдэл хоорондын ялгааг илрүүлэх зорилготой ажиллалаа. Бид туршилтыг гэрэлтэй болон сүүдэрлэсэн хоёр хувилбартай 2 жилийн хугацаанд 4 удаагийн дээж хураалттай (6, 12, 18 болон 24 сар) хийж гүйцэтгэсэн. Судалгааны үр дүнд ургамлын навчны задрал нь хялганын гурван зүйл хооронд ялгаатай бөгөөд үүнээс Stipa gobica-ийн навчны задралын хурд харьцангуй өндөр болохыг тогтоов. Мөн Stipa gobica зүйлийн навчны задралын хурд нь навчны шинж чанараас эерэг болон сөрөг хамаарч байсан бол цаг уурын үзүүлэлтүүдтэй эерэг (r=0.55) хамааралтай байсан. Харин Stipa baicalensis зүйлийн хувьд навчны шинж чанараас сөрөг (r=-0.56 – -0.63) хамааралтай, Stipa grandis зүйлийн тухайд навчны шинж чанараас эерэг хүчтэй хамааралтай байна (r=0.68-0.89). Ургамлын навчны задралд улирлын байдал нөлөөтэй бөгөөд 4-р сараас 10-р сарын хооронд задралын хэмжээ хамгийн өндөр байсан бол 11-р сараас 3-р сар хүртэл задралын хурд маш бага байв. Үүнээс харахад нугажуу хээр болон хуурай хээрийн ургамлын задрал тухайн ургамлын шинж чанараас хамаардаг бол цөлөрхөг хээрийн ургамлын задралд хүрээлэн буй орчны хүчин зүйлс чухал нөлөөтэй байна. Түлхүүр үгс: Хялгана, навчны задрал, нарны гэрэл, сүүдэр, навчны шинж чанар, нугажуу хээр, хуурай хээр, цөлөрхөг хээр

Functional diversity of shredders, not species richness, drives the decomposition rate of leaf litter in ponds

Leaf litter decomposition is a critical ecosystem-level process in many freshwater habitats. Although ponds are likely to derive a large proportion of their energy from riparian vegetation, allochthonous organic matter decomposition in these water bodies has received little attention. We studied the breakdown rates of black alder (Alnus glutinosa (L.) Gaertn.) litter in ponds and provide the first evidence of the role of the taxonomic and functional diversity of pond-dwelling shredders in this ecosystem process. Despite a strong connection to riparian zones, the litter breakdown rates observed in ponds were generally lower than those reported in headwater streams. It seems that ponds provide less favorable conditions for shredder communities than headwaters. The rate of organic matter decomposition in ponds was significantly positively related to functional diversity, represented by the variability of shredder body size, while shredder species richness did not appear to be a reliable proxy for this ecosystem function. This finding is consistent with theoretical predictions that functional complementarity among species has a systematic effect on ecosystem processes. It also emphasizes that body size is a crucial functional trait mediating the effects of shredder diversity on litter decomposition in ponds.

Impacts of land use history on leaf litter input, chemical composition, decomposition and related nutrient cycling in young and old secondary tropical lowland rainforests (Sumatra, Indonesia)

BackgroundNutrient cycle in tropical forests is mainly driven by litter fall amounts and by litter decay due to litter physical and chemical properties. Apart from differences in site conditions, different successional stages of tropical rainforests may influence nutrient inputs to the soil via differences in litter fall and decay.MethodsWe studied leaf litter fall, decomposition and related nutrient input to the soil in two secondary tropical rainforest types differing in land-use intensity and history in the lowlands of Sumatra (Indonesia).ResultsMean annual litter fall was by 29.5% higher in the old than in the young secondary forests. In contrast, annual litter decomposition differed only marginally (54.9% vs. 52.1%) in young vs. old secondary forests. Litter chemical composition (C, N, P, K contents) did not differ between the forest types. Litter decomposition was also not different between the forest types (4.6% vs. 4.3% loss of initial weight per month). Consequently, annual nutrient input to the soil was primarily affected by differences in leaf litter production, thus, old secondary forests exceeded that of young secondary forests by 30% and 24% for C and N, but was not different regaring P and K among the two forest types.ConclusionsThe results indicate that litter nutrient inputs to the soil in the two types of secondary tropical lowland forests are most strongly influenced by aboveground litter production rather than litter chemical quality or litter decay. We conclude that the restoration status of secondary tropical lowland forests is crucial for the nutrient status of these forest ecosystems.

La descomposición de la hojarasca de Ochroma pyramidale (Malvaceae)

The tree Ochroma pyramidale is used to recover jungle areas that have been cultivated. This native species generates a thick layer of leaf litter that remains for several years. The objectives of this study were: 1) to know how much leaf litter is produced, 2) to estimate how long it persists in the soil, and 3) to identify the role of soil fauna in its decomposition. Leaf litter production was estimated at 11 Mg/ha/year, while over the course of 13 years the biomass and depth of the leaf litter layer measured in three sites previously planted with Ochroma showed a decrease of over 60%. In a leaf litter decomposition experiment, 37% of biomass was lost in 180 days. Soil mesofauna reduced the concentration of cellulose in leaf litter, while lignin decreased due to the time of permanence of the leaf litter in the soil. The high C:N proportion of the leaves, together with high lignin concentrations, could explain the low levels of loss and accumulation of biomass.

Dynamics of tannin variations in mangrove leaf litter decomposition and their effects on environmental nitrogen and microbial activity

Tannins play vital roles in regulating ecological processes in mangrove forests. However, how tannins affect nitrogen (N) cycling and microbial metabolism in mangrove ecosystems remains largely unexplored. In this study, we hypothesized the types and amounts of tannins released into seawater and sediments during leaf litter decomposition differed among mangrove plant species, thus their effects on N and microbial metabolism also varied. The alterations of tannins, and environmental N and microbial metabolism during leaf litter decomposition of Kandelia obovata, Avicennia marina, and Sonneratia apetala were evaluated by a microcosm-simulated tidal system. Results showed that total polyphenols (TPs) in seawater treated with K. obovata litter were significantly higher than those in A. marina and S. apetala treatments, although the trends of TP changes elicited an initial increase followed by a decrease during decomposition. The dynamic changes in TPs reduced the seawater N concentrations in K. obovata treatment but not in A. marina and S. apetala treatments. The results of microbial metabolism analysis revealed that leaf litter significantly increased microbial metabolic activities and diversities. The types of carbon sources utilized by sediment microorganisms differed among treatments, with the microbes in S. apetala and A. marina litter used more varieties of amino acids, lipids and sugars than those in K. obovata treatment, probably due to the rich amount of hydrolysable tannins (HTs) in the first two species while the last species only contained ondensed tannins (CTs). CTs released from K. obovata leaf litter not only bound nitrogen-containing macromolecular compounds such as amino acids and proteins but also carbohydrates like polysaccharides, which decreased the supply of C and N to sediment microbiota. These results reveal that the release of mangrove tannins during leaf litter decomposition is one of the key factors driving N cycling, and microbial activities and diversities in mangrove wetlands.

Leaf litter production and decomposition in a Riverine Mangrove forest in India

Leaf litter production and decomposition in a Riverine Mangrove forest in India

Physical traits are better drivers than secondary compounds for leaf litter decomposition in a tropical heath vegetation

Litter plays a crucial role in regulating nutrient and energy flows in tropical forests, and secondary compounds, specifically phenolic compounds and tannins, have been identified as the main drivers of litter decomposition in tropical rainforests. The effect of secondary compounds could be stronger in tropical forests with high solar incidence such as tropical heath vegetation (Restinga). To investigate if the importance of secondary compounds extends to Restinga, we evaluated the effect of 14 leaf litter traits, including phenolic compounds and tannins, on the litter decomposition of 26 species for two years. We found a large interspecific variation in both traits and decomposition rate among species. Specific leaf area (SLA) and water holding capacity (WHC) were the best individual predictors of litter decomposition. When combined with C, P, Ca, Mg, and Na, they were the best predictors of litter decomposition in Restinga. However, the low explanatory power (31 %) suggests that other biotic and abiotic factors may also play a crucial role in explaining litter decomposition in Restinga. Remarkably unlike previous studies in tropical rainforests, phenolic compounds and tannins had little or no significance as drivers of litter decomposition in Restinga. Our results suggest that the importance of phenolic compounds and tannins is context-dependent, and a comprehensive understanding of litter decomposition in Restinga requires inclusion of both abiotic and biotic factors.

Leaf litter decomposition and detrital communities following the removal of two large dams on the Elwha River (Washington, USA)

Large-scale dam removals provide opportunities to restore river function in the long-term and are massive disturbances to riverine ecosystems in the short-term. The removal of two dams on the Elwha River (WA, USA) between 2011 and 2014 was the largest dam removal project to be completed by that time and has since resulted in major changes to channel dynamics, river substrates, in-stream communities, and the size and shape of the river delta. To assess ecosystem function across the restored Elwha watershed, we compared leaf litter decomposition at twenty sites: 1) four tributary sites not influenced by restoration activities; 2) four river sites downstream of the upper dam (Glines Canyon Dam); 3) four river sites within the footprint of the former Aldwell Reservoir upstream of the lower dam (Elwha Dam); 4) four river sites downstream of the lower dam; and 5) four lentic sites in the newly developing Elwha delta. Three major findings emerged: 1) decomposition rates differed among sections of the Elwha watershed, with slowest decomposition rates at the delta sites and fastest decomposition rates just downstream of the upper dam; 2) aquatic macroinvertebrate communities establishing in leaf litterbags differed significantly among sections of the Elwha watershed; and 3) aquatic fungal communities growing on leaf litter differed significantly among sections. Aquatic macroinvertebrate and fungal diversity were sensitive to differences in canopy cover, water chemistry, and river bottom sediments across sites, with a stronger relationship to elevation for aquatic macroinvertebrates. As the Elwha River undergoes recovery following the massive sediment flows associated with dam removal, we expect to see changes in leaf litter processing dynamics and shifts in litter-dependent decomposer communities (both fungal and invertebrate) involved in this key ecosystem process.

Effects of soil fauna on leaf litter decomposition and nutrient release during a two-year field experiment in a poplar plantation

Effects of soil fauna on leaf litter decomposition and nutrient release during a two-year field experiment in a poplar plantation

Combined effects of salinization and temperature on microbial-mediated oak decomposition and invertebrate consumption

Water salinization is a recognized growing threat to freshwaters, whose consequences on streams’ function, per se or concomitantly with other stressors, are still far from clear. This microcosm study evaluated the combined effect of salinization (0 and 4 g/l NaCl) and temperature (5, 15, and 20 °C) on microbial-mediated oak leaf litter decomposition, with fungal biomass, sporulation, and microbial respiration as microbial descriptors. Invertebrate consumption was also assessed using the common shredder Sericostoma vittatum (Trichoptera, Sericostomatidae). Mass loss was affected by temperature and interaction between salinity and temperature. Under salt conditions, mass loss was higher at 15 °C and reduced (~ 10%) at 20 °C. Microbial activity was lower at 5 °C and higher at 15 and 20 °C, irrespective of salinity. Fungal biomass was affected by both temperature (5 < 20 < 15 °C) and salinity (4 < 0 g/l NaCl), although the interaction between both was not significant. The interaction of both variables affected the production of spores: salt addition strongly reduced sporulation rates at all temperatures despite a significant increase in conidial production with temperature. Invertebrate leaf consumption was significantly reduced only by salinization. Overall, our results seem to indicate that temperature may modulate the effect of salinization (at least at ≥ 4 g/l NaCl) on stream leaf decomposition. While stronger salinization effects may be observed at higher temperatures, a consistent strong inhibition of shredders’ feeding behavior promoted by salt, regardless of temperature, may anticipate important repercussions on streams’ secondary production throughout the year.

In situ effects of microplastics on the decomposition of aquatic macrophyte litter in eutrophic shallow lake sediments, China

The toxicity of microplastics (MPs) to aquatic organisms has been extensively studied recently. However, few studies have investigated the effects of MPs in sediments on aquatic ecosystem functioning. In the present study, we conducted an in situ experiment to explore the concentration-dependent effects (0.025%, 0.25%, 2.5%) and size-dependent effects (150–300 μm and 500–1000 μm) of polypropylene microplastics (PP MPs) on Vallisneria natans litter decomposition dynamics, in particular, the process associated with macroinvertebrates, microorganisms, as well as microalgae and/or cyanobacteria. The results showed that exposure to high concentrations and large sizes of PP MPs can accelerate leaf litter biomass loss and nutrition release. Moreover, microbial respiration, microalgal and/or cyanobacteria chlorophyll-a were also significantly affected by PP MPs. However, PP MPs have no effect on the abundance of associated macroinvertebrate during the experiment, despite the collection of five macroinvertebrate taxa from two functional feeding groups (i.e., collectors and scrapers). Therefore, our experiment demonstrated that PP MPs may enhance leaf litter decomposition through effected microbial metabolic activity, microalgal and/or cyanobacteria biomass in the sedimentary lake. Overall, our findings highlight that PP MPs have the potential to interfere with the basic ecological functions such as plant litter decomposition in aquatic environments.

Polystyrene size-dependent impacts on microbial decomposers and nutrient cycling in streams

The particle size of plastic is one of the most important factors influencing its ecotoxicity, but we are unclear about the effect of polystyrene (PS) particle size on microbial decomposers and consequent nutrient cycling in streams. Here, using microcosm experiments, we assessed how three PS sizes (50 nm, 1 μm, and 20 μm) influenced the process and consequences of leaf litter decomposition. Under acute exposure to 1 μm and 20 μm PS, fungal biomass significantly decreased, but microbial biomass significantly increased, indicating compensations may work between fungi and other microbial decomposers. After chronic exposure to 50 nm and 1 μm PS, the leaf decomposition rate decreased by 19.27 % and 15.22 %, respectively, due to the reduced microbial enzyme activity, fungal diversity, and dominance of Anguillospora. As a result, the regeneration of nutrients, especially phosphorus, was significantly depressed, which might influence the primary productivity of streams. Therefore, our results suggest that nanoscale PS has a greater impact on microbial activity, thus affecting their functioning in leaf litter decomposition and consequent nutrient cycling. The findings provide a data support for the risk assessment of plastic pollution in freshwater systems.

Leaf litter decomposition rates in freshwaters differ by ecosystem

Leaf litter decomposition rates in freshwaters differ by ecosystem

Nutrient cycling aspects as possible ecosystem functional indicators of successional stage in Semideciduous seasonal forest, Rio de Janeiro state, Brazil

Semideciduous Seasonal Forest is a phytophysiognomy of Atlantic Forest with high plant richness but low representativeness in few remnants areas in different successional stages. The assessment of the degree of conservation of those areas helps to indicate whether there is a need for taking strategies to favor forest succession. Thus, the aim of this study was to identify litterfall and its nutrient content, accumulated litter biomass on topsoil, leaf litter decomposition, and topsoil (0–10 cm) chemical attributes as possible indicators of successional stages in areas of Seasonally Semideciduous Forest. We collected available information in literature on CAPES Portal and Google Scholar (May/2021 to February/2022) for Pinheiral municipality, State of Rio de Janeiro, Brazil, which were evaluated by multivariate analysis. Accumulated litter biomass, nutrient content (N, P, K) in total litterfall, pH and P availability in topsoil, leaf litter decomposition constant, and half-life time of leaf litter were the most sensitive attributes to indicate the successional stage in the study area, according to Principal Component Analysis. This multivariate analysis indicated that areas in early successional stage were associated with higher values of leaves contribution, half-life of leaf litterfall, contents of Ca and K in total litterfall, whereas areas in middle successional stage were associated with higher values of pH, total organic carbon, exchangeable Ca2+, K+, and Mg+, sum of bases and cation exchange capacity, and lower values of extractable acidity and exchangeable Al3+ in the topsoil. Areas in advanced stages of succession were associated to higher values of total litterfall and its nutrient content (N, K, Mg), accumulated litter biomass, available P in topsoil, and leaf litter decomposition constant. The Cluster multivariate analysis revealed that the areas in advanced successional stage presented high dissimilarity in relation to the areas in early and middle successional stage.

Divergent Decomposition Patterns of Leaf Litter and Fine Roots from an Urban Forest in Mid-Subtropical China

Litter decomposition plays a pivotal role in carbon (C) and nutrient cycling in terrestrial ecosystems. However, little is known about the litter decomposition processes and nutrient dynamics in urban green space. In this study, the decomposition and nutrient dynamics of leaf litter and fine roots from Cinnamomum officinarum Nee ex Wall. and Elaeocarpus decipiens Hemsl. were studied in an urban forest in subtropical China. The results showed that the leaf litter mass loss, and nitrogen (N) and phosphorus (P) mineralization of E. decipiens were faster than that of C. officinarum in the first 180 days, but in the whole decomposition period, the leaf litter decomposition constant of C. officinarum was higher than that of E. decipiens. There was no difference in fine root decomposition constant and P mineralization, although the fine root N immobilization was higher relative to C. officinarum during the 90th to 270th days. Additionally, both the leaf litter mass loss, decomposition rate, and nutrient mineralization were faster than fine roots for these two tree species. The soil microbial biomass showed positive effects on leaf litter decomposition and negative effects on fine root decomposition. The correlation analysis indicated that initial litter quality, soil physicochemical properties, and microbial activity mainly affected early-stage litter decomposition and nutrient mineralization. Also, the leaf litter production and N and P storages of E. decipiens were higher than that of C. officinarum, suggesting faster decomposition rate and nutrient return for E. decipiens leaf litter. Consequently, we propose that tree species with fast nutrient return, such as E. decipiens, could be introduced to urban green space with pervious surfaces in respect of the nutrient balance. This work improves the understanding of litter decomposition and nutrient cycling and promotes the management for urban green space.

Agricultural impacts on lowland tropical streams detected through leaf litter decomposition

Stream ecosystems are highly vulnerable to changes in land use and vegetation in their catchments for two reasons: firstly, they receive inputs of nutrients, contaminants and sediments through runoff; and secondly, terrestrial leaf litter is the major basal resource supporting their food webs. Leaf litter decomposition by microorganisms and detritivores is thus a key stream ecosystem process, and a valuable functional indicator of impacts associated to agriculture and other alterations of human origin. Here, we investigated the joint effects of land use changes associated to agriculture (low, medium and high intervention areas: LI, MI and HI, respectively) in a tropical lowland catchment in Panama, through a decomposition experiment using three leaf litter types differing in nativeness (Ficus insipida, native to the study area; Alnus acuminata, native to Panama but not present in the study area; and Musa balbisiana, exotic to Panama). Lowland tropical areas are often poor in litter-consuming detritivores, and we accordingly observed a high contribution of microorganisms to total decomposition (>60% on average). However, only in the presence of detritivores, decomposition of Alnus discriminated among different degrees of agricultural intervention, being higher at the LI area. Leaf litter of the native Ficus showed higher microbial decomposition than the other types, possibly in relation to a home-field advantage effect. Despite the scarcity of detritivores in tropical lowland streams compared to tropical highland or temperate streams, our study indicates that their activity reflects impacts of land use change on these streams and they should therefore be included in assessments of anthropogenic impacts.

Agricultural land use weakens the relationship between biodiversity and ecosystem functioning

Leaf litter decomposition is a significant ecosystem process for streams' energy provisioning, while species‐specific decomposition rates often form a continuum from slow to fast decomposing species allowing for resources' availability to stream consumers over a longer time period after leaf fall. Leaf litter mixtures in streams typically comprise leaf species varying in their traits, allowing for litter diversity effects on decomposition. At the same time, agricultural land use, habitat characteristics, water quality and invertebrate composition modulate leaf litter decomposition. To identify leaf litter diversity effects and disentangle the roles of agricultural intensity, habitat characteristics, water quality and invertebrate composition for leaf litter processing in streams, we quantified leaf litter decomposition of three leaf species covering a gradient from slow to fast decomposing species, tested either individually or as a three‐species mixture. The study was conducted over 21 days across 18 streams with a gradient of agricultural intensity (percent agricultural land use) in their catchments. We found leaf litter diversity effects in terms of complementarity under low to intermediate agricultural intensity, given that slow decomposing leaf species decomposed almost twice as fast in the three‐species mixture compared to the observations on individual leaf species. This leaf litter diversity effect decreased with increasing agricultural intensity, suggesting that agriculture weakens the biodiversity–ecosystem functioning relationship. However, pathways by which agriculture affected decomposition differed between single‐species and mixed‐species scenarios. For the single‐species scenario, negative effects of agriculture appeared to be mediated through effects on the proportion of sensitive detritivore species and altered habitat characteristics. For the mixed‐species scenario, altered water quality negatively affected the proportion of sensitive detritivore species, in turn reducing the diversity effect on functioning. Our results suggest that the weakened biodiversity–ecosystem functioning relationship under increasing agricultural intensity might be a significant factor threatening carbon cycling and food web integrity in streams.

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

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

Mound‐building behaviour of a keystone bioturbator alters rates of leaf litter decomposition and movement in urban reserves

AbstractBioturbation, the disturbance of soil and litter by digging animals plays an important role for a variety of species and ecological processes in many ecosystems. The majority of studies globally on the ecosystem engineering effects of digging vertebrates have focussed on mammals, with birds, reptiles and amphibians remaining comparatively understudied. The loss of ecosystem engineers is a key conservation challenge, and the return of these species is increasingly seen as a priority for habitat restoration; yet this concept is highly novel when we consider urban ecosystems. The Australian brush‐turkey (Alectura lathami), historically a rainforest bird and now common in urban ecosystems, displaces significant quantities of soil and leaf litter through its foraging and nest‐building behaviour and has previously been described as an ecosystem engineer. Here, we tested the effect of brush‐turkey nest building on the decomposition rate of leaf litter, an important ecosystem process. We placed mesh bags of dried Angophora costata and Lantana camara leaves at increasing distances from brush‐turkey incubation mounds. We predicted that leaf litter closer to the nest would break down faster during the brush‐turkey breeding season due to increased turnover associated with nest mound maintenance. We found slower leaf litter decomposition in the breeding than the non‐breeding season, but a relatively greater rate of decomposition closer to the mound in the breeding season. Our results show a seasonal difference in the spatial pattern of leaf litter decomposition and movement; we interpret that brush‐turkey mound‐building behaviour was the key driver. The ecosystem services provided by brush‐turkeys are of particular interest for future research as this species is naturally recolonizing areas where it has been absent for decades, including urban areas. The effect of this species on ecosystem processes including nutrient cycling, seedbank stimulation and reduced fuel loads warrants further investigation.