Leaf Litter Diversity Research Articles

Utilizing the diversity of arbuscular mycorrhizal fungi and sweet potato leaf litter for the growth and production of andrographolide compounds in Andrographis paniculata

Utilizing the diversity of arbuscular mycorrhizal fungi and sweet potato leaf litter for the growth and production of andrographolide compounds in Andrographis paniculata

Abundance and Diversity of Leaf Litter and Subsoil Arthropods in Four Different Sites of Three Agroecological Zones of Northwest Part of Bangladesh

Leaf litter and subsoil arthropods are biotic factors of an ecosystem that play a significant role in nutrient cycling between soil and vegetation. The present study aimed to explore the abundance and diversity of leaf litter and subsoil arthropods in four different sites of three agroecological zones of the Northwest part of Bangladesh. A total of 1920 individuals belonging to 17 orders, 28 families and 34 species were found in the present study where 1099 individuals (14 orders, 23 families, 28 species) from Rajshahi University Campus (Site A), 259 individuals (6 orders, 7 families, 8 species) from Rajshahi Fruit Research Center (Site B), 354 individuals (7orders, 13 families, 13 species) from Kakon Hat Municipality (Site C) and 208 individuals (5 orders, 10 families, 10 species) from Chalan Beel (Site D) were collected during the period from November 2021 to October 2022. In this study, within the three agroecological zones, the highest number of individuals was recorded in Site A (n=1099, 57.24%) and the lowest number in Site D (n=208, 10.83%). Among 17 orders Coleoptera (624, 32.50%) was the first dominant order, Hymenoptera (414, 21.56%) was the second largest order, followed by Araneae (202, 10.52%) and the least dominant order was Metastigmata (8, 0.42%). Formicidae was the most dominant family among collected 28 families, sharing 376 individuals of the total captured individuals and Staphylinidae, sharing 198 individuals, was the second largest family, whereas Tenebrionidae (n=8), Psychodidae (n=8), and Laelapidae (n=8) were the minor dominant families in this study. Among the total of 34 species, Lasioderma sp. was the most dominant species, sharing 189 individuals with 9.84% of the total collected individuals whereas Alphitobius sp., Psychoda sp., and Hypoaspis sp. were least dominant species, and each species of these three comprised of only 8 members. In this study, 15 species were very common, 5 were common, 7 were fairly common, and 7 were rare. The values of Shannon diversity index (H'), Simpson’s diversity index (I-D), Margalef diversity index (DMg), Menhinick Richness index (DMn), Berger Parker dominance index (d) and Pielou’s evenness index (J') were 3.22, 0.95, 4.37, 0.78, 0.10, respectively. The study was the first attempt to examine the abundance and diversity of leaf litter and subsoil arthropods in four different sites of three agroecological zones in the northwest part of Bangladesh. Further study may be necessary for molecular identification of these species.

Sexual morph of Allophoma tropica and Didymella coffeae-arabicae (Didymellaceae, Pleosporales, Dothidiomycetes), including novel host records from leaf litter in Thailand

ABSTRACT Studying the taxonomy, diversity and host preference of leaf litter inhabiting microfungi contributes towards elucidating hidden taxa, their host affinities and recovering novel life modes dwelling inside forest ecosystems. Leaf litter-inhabiting microfungi also play a crucial role in forest ecosystems through decomposition and nutrient recycling. This study resulted in the introduction of saprobic Didymellaceae microfungi from Doi Tung Forest Reserve, Chiang Rai, northern Thailand. Fungal isolates were characterised based on morphology and molecular phylogeny of the nuclear ribosomal DNA (ITS, LSU) and protein-coding genes (tub2, rpb2). Allophoma tropica and Remotididymella ageratinae are recorded from dead leaves of Nayariophyton zizyphifolium (Malvaceae), and Didymella coffeae-arabicae from Dalbergia cultrata and Afzelia xylocarpa (Fabaceae). This study also reports the sexual morph of Allophoma tropica and Didymella coffeae-arabicae and provides molecular evidence for the first reports of sexual morphs from Thailand.

Contrasting Effects of Leaf Litter Quality and Diversity on Oviposition of Mosquitoes.

The quality and diversity of leaf litter are important variables in determining the availability of energy in detritus-based food webs. These factors can be represented by the stoichiometric proportion between carbon and multiple nutrients, and the mixture of litter from different taxonomic and/or functional origins. In aquatic ecosystems, factors that accelerate litter decomposition can influence the secondary productivity of planktonic microbiota, which act as a link between litter and higher trophic levels. This study aimed to analyze the influence of litter quality and diversity on the oviposition behavior of medically important mosquitoes. We hypothesized that both factors would have a positive effect on the attraction of female mosquitoes and would stimulate a greater amount of oviposition. To test this hypothesis, microcosms containing isolated leaf litter leachates from four plant species were used to manipulate gradients of litter quality, and microcosms with all leachates combined were used to test the effects of litter diversity. The results showed a positive effect of litter quality (p < 0.05) on mosquito oviposition rate, with lower C:P ratio litter species (high-quality litter) presenting higher oviposition rates than litter species with high C:P ratios (low-quality litter). However, contrary to our expectations, litter diversity had a negative effect (p = 0.002) on the magnitude of egg-laying by mosquitoes. Our results highlight the importance of litter quality and diversity for insect reproductive behavior. Our data shows that litter quality can serve as a crucial indicator of a suitable environment utilized by female mosquitoes for oviposition. This finding can enhance our ability to understand and develop effective methods for mitigating the reproduction of medically significant mosquitoes, whether by allowing us to predict, based on the composition of vegetation species, areas more prone to mosquito infestation, or by using high-quality litter in oviposition traps. Furthermore, maintaining vegetation diversity can help control mosquito reproduction.

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.

Litter and soil biodiversity jointly drive ecosystem functions.

The decomposition of litter and the supply of nutrients into and from the soil are two fundamental processes through which the above- and belowground world interact. Microbial biodiversity, and especially that of decomposers, plays a key role in these processes by helping litter decomposition. Yet the relative contribution of litter diversity and soil biodiversity in supporting multiple ecosystem services remains virtually unknown. Here we conducted a mesocosm experiment where leaf litter and soil biodiversity were manipulated to investigate their influence on plant productivity, litter decomposition, soil respiration, and enzymatic activity in the littersphere. We showed that both leaf litter diversity and soil microbial diversity (richness and community composition) independently contributed to explain multiple ecosystem functions. Fungal saprobes community composition was especially important for supporting ecosystem multifunctionality (EMF), plant production, litter decomposition, and activity of soil phosphatase when compared with bacteria or other fungal functional groups and litter species richness. Moreover, leaf litter diversity and soil microbial diversity exerted previously undescribed and significantly interactive effects on EMF and multiple individual ecosystem functions, such as litter decomposition and plant production. Together, our work provides experimental evidence supporting the independent and interactive roles of litter and belowground soil biodiversity to maintain ecosystem functions and multiple services.

Intraspecific variation in leaf litter alters fitness metrics and the gut microbiome of consumers.

Biodiversity can have cascading effects throughout ecosystems. While these effects are better understood at coarser taxonomic scales of biodiversity, there has been a resurgence in investigating how biodiversity within species may have cascading effects on communities and ecosystems. We investigate the broader trophic implications of intraspecific variation in the riparian tree, Alnus rubra, where immediately local or 'home' litter decomposes faster than 'away' litter in aquatic and terrestrial systems. With climate change shifting the distributions of plants across the globe, it is essential to understand how shifts in the intraspecific traits of leaf litter may have reverberating effects throughout ecosystems. Here, we find that intraspecific variation in leaf litter has fitness implications for invertebrate consumers, including the algivorous Dicosmoecus and detrivorous Psychoglypha caddisflies, which exhibited increased body size and muscle nitrogen content when incubated within in-situ river mesocosms supplied with local A. rubra litter. Litter source altered caddisfly gut microbiomes by increasing relative abundance of methanogens and methanotrophs among the non-local treatment group. Additionally, Dicosmoecus supplied with non-local litter may have shifted their diet towards a higher proportion of algae, as inferred from shifts in gut microbiome composition and isotopic ratios of muscle tissue. Overall, our study demonstrates that shifting distributions of plant genotypes across the globe may cause plant-microbe mismatches that will disrupt patterns of decomposition and may have consequences on the fitness and foraging behavior of consumers.

Leaf litter carbon, nitrogen and phosphorus stoichiometry of Chinese fir (Cunninghamia lanceolata) across China

The stoichiometric characteristics of plant tissue (living or dead) can influence carbon (C) and nutrient dynamics in forest ecosystems. Numerous investigations have focused on green leaves in site or regional areas, but few on leaf litter, especially for tree species with a wide distribution. Here, we collected 57 leaf litter samples of Chinese fir from 19 sites across subtropical China and determined the C, N and P concentrations and stoichiometric ratios, and related these leaf litter variables with geographical and climatic variables, as well as with soil chemistry, which were assessed through soil sampling at the 19 sites. The results showed that the mean leaf litter C, N and P concentrations (namely nutrient resorption proficiency, NuRP) were 458.3 ± 4.0 mg g−1, 8.9 ± 0.3 mg g−1, and 0.46 ± 0.02 mg g−1, respectively. The mean C:N, C:P, and N:P ratios were 52.9 ± 1.9, 1049.8 ± 43.8, and 19.8 ± 0.6, respectively. Concentrations of leaf litter N and P were strongly positively correlated with each other (p < 0.001), while no significant correlation was found between the C and N, or C and P concentrations (p>0.05). The leaf litter stoichiometry showed linear or nonlinear relationships with the geographical, climatic and soil chemical variables. Hierarchical partitioning (HP) analysis showed that the geographical and climatic variables explained most of the variation in leaf litter C and N concentrations and in the N:P ratio. Variation in the leaf litter P concentration was mainly regulated by soil chemical variables. Overall, our findings indicated that the resorption proficiency of the leaf litter was at intermediate level for both N and P. The leaf litter stoichiometry of Chinese fir was driven by the geographical location, mean temperature and precipitation conditions and soil nutrient status at a regional scale. Our results provided new insights into the ability of Chinese fir to adapt to future climate conditions, and also increased our understandings of drivers of the elemental biogeochemical cycle.

Leaf litter identity rather than diversity shapes microbial functions and microarthropod abundance in tropical montane rainforests.

In tropical forest ecosystems leaf litter from a large variety of species enters the decomposer system, however, the impact of leaf litter diversity on the abundance and activity of soil organisms during decomposition is little known. We investigated the effect of leaf litter diversity and identity on microbial functions and the abundance of microarthropods in Ecuadorian tropical montane rainforests. We used litterbags filled with leaves of six native tree species (Cecropia andina, Dictyocaryum lamarckianum, Myrcia pubescens, Cavendishia zamorensis, Graffenrieda emarginata, and Clusia spp.) and incubated monocultures and all possible two‐ and four‐species combinations in the field for 6 and 12 months. Mass loss, microbial biomass, basal respiration, metabolic quotient, and the slope of microbial growth after glucose addition, as well as the abundance of microarthropods (Acari and Collembola), were measured at both sampling dates. Leaf litter diversity significantly increased mass loss after 6 months of exposure, but reduced microbial biomass after 12 months of exposure. Leaf litter species identity significantly changed both microbial activity and microarthropod abundance with species of high quality (low C‐to‐N ratio), such as C. andina, improving resource quality as indicated by lower metabolic quotient and higher abundance of microarthropods. Nonetheless, species of low quality, such as Clusia spp., also increased the abundance of Oribatida suggesting that leaf litter chemical composition alone is insufficient to explain variation in the abundances of soil microarthropods. Overall, the results provide evidence that decomposition and microbial biomass in litter respond to leaf litter diversity as well as litter identity (chemical and physical characteristics), while microarthropods respond only to litter identity but not litter diversity.

Effects of heavy metal-mediated intraspecific variation in leaf litter on the feeding preferences of stream detritivores

Plant litter inputs from terrestrial ecosystems are indispensable resources for stream ecosystems. Heavy metal pollution in the environment may indirectly affect the food webs of streams by changing the traits of leaf litter. In the present study, willow leaf litter was collected in polluted and non-polluted sites (natural willow), and leaf litter was produced in the lab by exposing willow saplings to different concentrations of heavy metals in water (cultivated willow). The collected willow leaf litter was used for feeding preference experiments with stream detritivores (shrimps and snails). Metal pollution significantly decreased the lignin concentration and toughness of litter and increased Zn and Cd concentrations. Both detritivores preferred to consume metal-enriched litter, with their consumption rates of this litter being significantly higher than those of non-enriched litter. The toughness of the willow litter was the key factor determining the feeding preferences of shrimps and snails. The detritivores that consumed metal-enriched leaf litter contained more Zn and Cd in their bodies than those that consumed non-enriched litter. The Zn and Cd concentrations in shrimp faeces were higher for shrimps that consumed metal-enriched litter than for those that consumed non-enriched litter. The heavy metal concentrations and chemical oxygen demand (COD) of the water following litter consumption were significantly higher for the metal-enriched litter than for the non-enriched litter, resulting in decreased water quality in the former context. The specific resource allocation patterns that result from heavy metal pollution in the environment will have ecological consequences.

Intraspecific niche partitioning in macrodetritivores enhances mixed leaf litter decomposition

Abstract In biodiversity and ecosystem functioning research, the consideration of intraspecific trait variation and multiple trophic levels – both largely overlooked so far – has been proposed as a promising step towards a consensus about causal relationships and mechanisms. Soil invertebrates contribute crucially to leaf litter decomposition and thus to the functioning of one of the most diverse ecosystem components on Earth. On the one hand, a positive effect of leaf litter diversity on decomposition was shown by several studies. On the other hand, at the interspecific level, differences in body size and feeding traits of consumers influence this process by interacting with leaf litter traits that define decomposability, such as nutrient content and physical properties. It is also known that the feeding niche of consumers can vary during their ontogeny as it depends on individual body size, metabolism and physiology. However, whether and how intraspecific trait variation of macrodetritivores contributes through niche partitioning to the positive effect of litter combinations on decomposition was never investigated. Here, we tested experimentally the effect of intraspecific body size differences in the common terrestrial isopod species Oniscus asellus on the decomposition of the two co‐occurring litter species Acer platanoides and Betula pendula. We hypothesized complementary resource use by two distinct isopod body size classes, leading to decreased competition and higher overall litter decomposition. In a full factorial design with all possible combinations of litter species and isopod body size classes, litter mixtures enhanced decomposition beyond the additive effect of each single species, especially in isopod mixed‐body size treatments. Our results suggest an interaction between litter and consumer diversity driving intraspecific feeding niche partitioning. Although the focus on a single detritivore species does not allow for generalizations, our results should stimulate the investigation of the mechanisms of biotic interactions among individual organisms. A free Plain Language Summary can be found within the Supporting Information of this article.

Soil macrofauna and leaf functional traits drive the decomposition of secondary metabolites in leaf litter

Leaf litter decomposition is closely linked to soil nutrient cycling. Both vary with environmental conditions, leaf litter diversity, faunal decomposer community and leaf litter chemistry. Polyphenols, i.e. phenolics and tannins, are important secondary metabolites in leaf litter and are considered a major impediment to whole-leaf decomposition. While the function of polyphenols is well studied, the mechanisms and drivers of their decomposition are largely unknown. We reasoned that polyphenol decomposition is driven by the same factors as whole-leaf decomposition. We hypothesized that polyphenol decomposition rates increase with leaf litter richness, decrease with macrofauna exclusion and are related to traits characterizing leaf litter quality.We measured decomposition rates of polyphenols in leaf litter of seven subtropical Chinese tree species, sampled at five dates and in a fully factorial design that manipulated litter richness and macrofauna access. We further estimated leaf carbon and nitrogen contents and leaf toughness using near-infrared spectroscopy.We showed that 1) phenolics and tannin decomposition rates did not depend on leaf litter species richness, 2) the decomposition rates of phenolics and tannins were up to one magnitude higher than whole-leaf decomposition rates, 3) the exclusion of macrofauna increased phenolics and tannin decomposition rates, 4) the leaf nitrogen content positively affected the phenolics decomposition rates and 5) the tannin-to-nitrogen ratio was the best predictor of whole-leaf decomposition.We conclude that the fast decomposition of phenolics and tannins in the early stages of whole-leaf litter decomposition is an essential ecological process. Low molecular weight phenolics that enter the soil can accelerate microbial growth, while potentially toxic tannins leave the leaf tissue, and thus, enable the consecutive whole-leaf decomposition. Our study is the first to show that macrofauna occurrence negatively affects the decomposition of ecological relevant secondary plant metabolites. This points to the importance of considering biotic interactions between different trophic levels to fully understand the mechanisms of leaf litter decomposition.

Changes in climate and vegetation with altitude on Mount Batilamu, Viti Levu, Fiji

Abstract:To investigate changes in vegetation and climate with altitude, we established forest plots and recorded climatic data at 100-m intervals between 550–1100 m asl on the western slopes of Mount Batilamu, Mount Koroyanitu range, Viti Levu, Fiji. Trees with a dbh ≥10 cm were identified and measured in 21 10 × 10-m plots, starting at 750 m altitude. Temperature and relative humidity sensors were deployed in two habitats, leaf litter and 50 cm above the ground, and two vegetation types, grasslands and forest, at six altitudes over a 48-h period. Two significantly distinct forest types, lowland and montane, were present. Montane forest was found at higher elevations (&gt;950 m asl) and had significantly higher stem density. Mean temperature decreased significantly with altitude and was strongly moderated by vegetation type (lower average and less variation in forest). While average relative humidity significantly increased with altitude, it was strongly moderated by both habitat and vegetation type (higher average and less variation in leaf litter and forest). The lapse rate varied with time of day (higher during the day) and vegetation type (higher in grasslands). Therefore, vegetation and microhabitats create unique microclimates, and this should be considered when investigating current or future climatic patterns along altitudinal gradients on forested mountains.

Landscape configuration alters spatial arrangement of terrestrial-aquatic subsidies in headwater streams

Freshwater ecosystems depend on surrounding terrestrial landscape for resources. Most important are terrestrial leaf litter subsidies, which differ depending on land use. We lack a good understanding of the variation of these inputs across spatial scales. We sought to determine: (1) the relative importance of local versus catchment-level forestation for benthic leaf litter biomass in streams, (2) how landscape configuration alters these relationships, and (3) how land use affects the quality and diversity of leaf litter subsidies. We measured biomass and identity of benthic leaf litter in 121 reaches in 10 independent catchments seasonally over the course of a year. We assessed direct and indirect effects of forestation, reach position, and seasonality on leaf litter biomass using structural equation models, and assessed how leaf litter diversity varied with land use. In catchments with forested headwaters, the degree of forestation and reach position in the catchment influenced benthic leaf litter biomass indirectly through local reach-scale forestation. In catchments where forest was only located downstream, or with minimal forest, none of these factors influenced reach-level benthic leaf litter. Leaf litter diversity peaked in fall in all land use types, but was generally lowest in forested reaches. Not only habitat amount, but its location relative to other habitats is important for ecosystem function in the context of cross-ecosystem material flows. Here, lack of upstream forest altered spatial patterns of leaf litter storage. Studies with high spatiotemporal resolution may further reveal effects of landscape configuration on other ecosystems.

Diverse effects of degree of urbanisation and forest size on species richness and functional diversity of plants, and ground surface-active ants and spiders.

Urbanisation is increasing worldwide and is regarded a major driver of environmental change altering local species assemblages in urban green areas. Forests are one of the most frequent habitat types in urban landscapes harbouring many native species and providing important ecosystem services. By using a multi-taxa approach covering a range of trophic ranks, we examined the influence of degree of urbanisation and forest size on the species richness and functional diversity of plants, and ground surface-active ants and spiders. We conducted field surveys in twenty-six forests in the urban region of Basel, Switzerland. We found that a species’ response to urbanisation varied depending on trophic rank, habitat specificity and the diversity indices used. In plants, species richness decreased with degree of urbanisation, whereas that of both arthropod groups was not affected. However, ants and spiders at higher trophic rank showed greater shifts in species composition with increasing degree of urbanisation, and the percentage of forest specialists in both arthropod groups increased with forest size. Local abiotic site characteristics were also crucial for plant species diversity and species composition, while the structural diversity of both leaf litter and vegetation was important for the diversity of ants and spiders. Our results highlight that even small urban forests can harbour a considerable biodiversity including habitat specialists. Nonetheless, urbanisation directly and indirectly caused major shifts in species composition. Therefore, special consideration needs to be given to vulnerable species, including those with special habitat requirements. Locally adapted management practices could be a step forward to enhance habitat quality in a way to maximize diversity of forest species and thus ensure forest ecosystem functioning; albeit large-scale factors also remain important.

Leaf litter diversity and structure of microbial decomposer communities modulate litter decomposition in aquatic systems

AbstractLeaf litter decomposition is a major ecosystem process that can link aquatic to terrestrial ecosystems by flows of nutrients. Biodiversity and ecosystem functioning research hypothesizes that the global loss of species leads to impaired decomposition rates and thus to slower recycling of nutrients. Especially in aquatic systems, an understanding of diversity effects on litter decomposition is still incomplete.Here we conducted an experiment to test two main factors associated with global species loss that might influence leaf litter decomposition. First, we tested whether mixing different leaf species alters litter decomposition rates compared to decomposition of these species in monoculture. Second, we tested the effect of the size structure of a lotic decomposer community on decomposition rates.Overall, leaf litter identity strongly affected decomposition rates, and the observed decomposition rates matched measures of metabolic activity and microbial abundances. While we found some evidence of a positive leaf litter diversity effect on decomposition, this effect was not coherent across all litter combinations and the effect was generally additive and not synergistic.Microbial communities, with a reduced functional and trophic complexity, showed a small but significant overall reduction in decomposition rates compared to communities with the naturally complete functional and trophic complexity, highlighting the importance of a complete microbial community on ecosystem functioning.Our results suggest that top‐down diversity effects of the decomposer community on litter decomposition in aquatic systems are of comparable importance as bottom‐up diversity effects of primary producers.Aplain language summaryis available for this article.

Leaf litter diversity positively affects the decomposition of plant polyphenols

Leaf litter decomposition is closely linked to nutrient cycling and driven by environmental conditions, species-specific leaf chemistry, and here in particular by polyphenols composition. However, not much attention has been paid on the decomposition of polyphenols themselves. We hypothesized that phenolics and tannin decomposition rates are species-specific and positively affected by litter species richness. Leaf litter of three Chinese tree species was exposed to field decomposition conditions, aggregated in mixtures of different species richness (1-, 2-, 3-species mixtures). We sampled litter five times over the course of 171 days, calculated species-specific total phenolics and total protein precipitable tannin decomposition rates, assessed changes in polyphenol composition using HPLC, and tentatively identified compounds by LC-ESI-MS/MS. Leaf litter richness effects on phenolics and tannin decomposition rates were positive, except for Sapindus-specific tannins, and differed between leaf litter species. Decomposition duration changed polyphenol compositions, and significantly interacted with leaf litter species richness with increasing effects of litter richness with time. Litter diversity effects on polyphenol decomposition are crucial for whole leaf litter decomposition. The contrasting dependencies of phenolics and tannin decomposition rates on leaf litter richness may provide explanations for equivocal results in leaf litter mixture experiments.

Experimental nitrogen and phosphorus additions increase rates of stream ecosystem respiration and carbon loss

AbstractNitrogen (N) and phosphorus (P) enrichment reduces organic carbon (C) storage in detritus‐based stream ecosystems, but the relative effects of N and P concentrations and ratios on stream metabolic rates have not previously been tested. We tracked changes in whole‐stream ecosystem respiration (ER) and gross primary productivity (GPP), particulate organic matter (POM) standing stocks, fungal biomass, and POM‐specific respiration rates before and during 2 yr of experimental N and P enrichment in five forest streams. Nutrient additions (∼ 96 μg N L−1 to ∼ 472 μg N L−1 and ∼ 10 μg P L−1 to ∼ 85 μg P L−1) targeted dissolved N : P molar ratios of 2, 8, 16, 32, and 128. Whole‐stream ER was positively related to standing stock of wood, a seasonably stable POM compartment that varied by up to 2× among streams. Nutrient enrichment generally increased ER but had no effect on low‐level GPP. Prior to nutrient enrichment, ER was higher at lower N : P, but during enrichment ER increased with increasing N : P. Respiration rates on leaf litter and wood increased with enrichment but decreased with increasing P, and the quantity of leaf litter generally declined with increasing N. Respiration rates on fine benthic organic matter (FBOM) were higher with increasing N : P, and FBOM standing stocks decreased with increasing N. Fungal biomass did not change with nutrient enrichment. Compared to pre‐enrichment conditions, nutrients increased seasonal variation in leaf litter standing stocks and whole‐stream respiration rates. Our results demonstrate how nutrient‐stimulated loss of C from detritus‐based ecosystems occurs through the maintenance of enhanced respiration rates on detrital resources that are particularly sensitive to N inputs.

Latitudinal Patterns and Climatic Drivers of Leaf Litter Multiple Nutrients in Chinese Broad-Leaved Tree Species: Does Leaf Habit Matter?

Leaf litter nutrients play a key role in nutrient cycling in forest ecosystems, yet our current knowledge of the ways in which climate controls leaf litter nutrients remains uncertain, especially for broad-leaved tree species in China. We performed a meta-analysis of geographic patterns of leaf litter nutrients of Chinese broad-leaved tree species in relation to climatic variables and leaf habit (as a discrete classification of tree species). We found that mean leaf litter carbon (C), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) were 458.36, 10.11, 0.72, 6.37, 14.22 and 2.59 mg−1 g, respectively. Leaf litter nutrients did not diverge between leaf habits where they coexisted. These leaf litter nutrients displayed significant latitudinal trends, partly driven by climatic factors and a shift in leaf habit. Mean annual precipitation explained the largest amount of total variation in leaf litter C, N, P and K, and mean annual temperature was the most important predictor for leaf litter Mg, whereas leaf habit was the largest contributor to total variation in leaf litter Ca. We further found that the relationships between climate and leaf litter nutrients were distinguishable for evergreen and deciduous broad-leaved tree species. Collectively, our study differed from previous studies that evaluated leaf litter nutrients and only focused on N and P, and substantiated that leaf litter nutrients in forest ecosystems were affected by climate and leaf habit, but the strengths of the influences of these factors were strongly contingent on leaf litter nutrient identity. Therefore, alteration of climate would directly and indirectly (via a shift in species composition) affect latitudinal patterns of leaf litter nutrients and thus the associated nutrient flux and ecosystem functioning. Our study also underlined the need to include multiple nutrients to explore the influence of climate on leaf litter nutrient stoichiometry.

Linking spatial patterns of leaf litterfall and soil nutrients in a tropical forest: a neighborhood approach.

Leaf litter represents an important link between tree community composition, forest productivity and biomass, and ecosystem processes. In forests, the spatial distribution of trees and species-specific differences in leaf litter production and quality are likely to cause spatial heterogeneity in nutrient returns to the forest floor and, therefore, in the redistribution of soil nutrients. Using mapped trees and leaf litter data for 12 tree species in a subtropical forest with a well-documented history of land use, we: (1) parameterized spatially explicit models of leaf litter biomass and nutrient deposition; (2) assessed variation in leaf litter inputs across forest areas with different land use legacies; and (3) determined the degree to which the quantity and quality of leaf litter inputs and soil physical characteristics are associated with spatial heterogeneity in soil nutrient ratios (C:N and N:P). The models captured the effects of tree size and location on spatial variation in leaf litterfall (R² = 0.31-0.79). For all 12 focal species, most of the leaf litter fell less than 5 m away from the source trees, generating fine- scale spatial heterogeneity in leaf litter inputs. Secondary forest species, which dominate areas in earlier successional stages, had lower leaf litter C:N ratios and produced less litter biomass than old-growth specialists. In contrast, P content and N:P ratios did not vary consistently among successional groups. Interspecific variation in leaf litter quality translated into differences in the quantity and quality (C:N) of total leaf litter biomass inputs and among areas with different land use histories. Spatial variation in leaf litter C:N inputs was the major factor associated with heterogeneity in soil C:N ratios relative to soil physical characteristics. In contrast, spatial variation soil N:P was more strongly associated with spatial variation in topography than heterogeneity in leaf litter inputs. The modeling approach presented here can be used to generate prediction surfaces for leaf litter deposition and quality onto the forest floor, a useful tool for understanding soil-vegetation feedbacks. A better understanding of the role of leaf litter inputs from secondary vegetation in restoring soil nutrient stocks will also assist in managing expanding secondary forests in tropical regions.