Leaf Mass Loss Research Articles

Litter Decomposition of a Deciduous Tectona philippinensis and an Evergreen Parashorea malaanonan Across Contrasting Sites

Litter traits and site conditions alter nutrient inputs from deciduous and evergreen forests by influencing litter decomposition processes. Here, we investigated the leaf and stem mass loss rate (MLR) of a deciduous (Tectona philippinensis) and an evergreen (Parashorea malaanonan) tree species and the factors influencing it through an intersite experiment and litterbag method in secondary forests in Lobo, Batangas and Mount Makiling Forest Reserve (MMFR). Variations in initial litter quality (leaf area, specific leaf area (SLA), leaf thickness, vein density), and site factors (light intensity and temperature) were assessed. P. malaanonan has a lower SLA and vein density than T. philippinensis. The leaf and stem MLR were significantly higher in the mixed litter (44.09–57.83%) than that of a single-species litter of either T. philippinensis (28.16–41.83%) or P. malaanonan (33.60–47.66%). The leaf MLR of T. philippinensis was greater when placed in Lobo (where the litter originated) than at a different site (i.e., MMFR). Moreover, leaf litter decomposition was faster in T. philippinensis than in P. malaanonan, particularly during the rainy season. Overall, the study showed that litter decomposition in deciduous and evergreen differed across sites due to variations in litter quality and environmental variables. Keywords: decomposability traits, home-field advantage (HFA), intersite experiment, litter quality, mass loss rate

Large invertebrate decomposers contribute to faster leaf litter decomposition in Fraxinus excelsior-dominated habitats: Implications of ash dieback

Leaf litter decomposition is a major component of nutrient cycling which depends on the quality and quantity of the leaf material. Ash trees (Fraxinus excelsior, decay time ∼ 0.4 years) are declining throughout Europe due to a fungal pathogen (Hymenoscyphus fraxineus), which is likely to alter biochemical cycling across the continent. The ecological impact of losing species with fast decomposing leaves is not well quantified. In this study we examine how decomposition of three leaf species with varying decomposition rates including ash, sycamore (Acer pseudoplatanus, decay time ∼ 1.4 years), and beech (Fagus sylvatica, decay time ∼ 6.8 years) differ in habitats with and without ash as the dominant overstorey species. Ten plots (40 m × 40 m) were set up in five locations representing ash dominated and non-ash dominated habitats. In each plot mesh bags (30 cm × 30 cm, 0.5 mm aperture) with a single leaf species (5 g) were used to include (large holes added) and exclude macrofauna invertebrates (with a focus on decomposer organisms such as earthworms, millipedes, and woodlice). The mesh bags were installed in October 2020 and retrieved without replacement at exponential intervals after 6, 12, 24 and 48 weeks. Total leaf mass loss was highest in the ash dominated habitat (ash dominated: 88.5%, non-ash dominated: 66.5%) where macrofauna were the main contributor (macrofauna: 96%, microorganisms/mesofauna: 4%). The difference between macrofauna vs microorganisms and mesofauna was less pronounced in the non-ash dominated habitat (macrofauna: 68%, microorganisms/mesofauna: 31%). Our results suggest that if ash dominated habitats are replaced by species such as sycamore, beech, and oak, the role of macrofauna decomposers will be reduced and leaf litter decomposition rates will decrease by 25%. These results provide important insights for future ash dieback management decisions.

PRIORITIZATION OF TREE SPECIES BASED ON GREEN LEAF NUTRIENT LEACHING: AN APPROACH FOR SUSTAINABLE AGROFORESTRY PRACTICES

Nutrients leaching from litter (leaves, bark, needles and twigs) have a major contribution to the supply and cycling of nutrients to crops. Among the litter parts, leaves are the main and quick source of organic matter to the soil whereas, green leaves return more nutrients than other forms of leaves. The return potentiality of K, P and N through leaching from green leaves of the major agroforest tree species: Zizyphus jujuba, Melia azadirachta, Albizia saman, Dalbergia sissoo and Azadirachta indica are presented on this study. Green leaves of the studied tree species were collected and then leached in water (deionized). Nutrient release through a leaching experiment was conducted for 192 hours. Percentage (%) of green leaf mass loss and Total Dissolved Solid with Electrical Conductivity of the collected leaching water showed a curvilinear relationship with time significantly (p < 0.05). NH4, PO4 and K concentration of the collected leaching water of the individual cropland agroforest tree species was significantly (p < 0.05) increased for 72 hours in the initial stage but at the later stage remained constant. Individual tree species showed the same nutrient release (K > NH4 > PO4) pattern. The highest concentration of 5121 ppm NH4 and potassium (13357 ppm) was found for Melia azadirachta and the lowest concentration of 1424 ppm NH4 and potassium (4410 ppm) was observed for Albizia saman. Results from the study highlighted that M. azadirachta was the best among the studied tree species in terms of nutrient return followed by A. indica and D. sissoo.

A 60 GHz pulsed coherent radar for online monitoring of the withering condition of leaves

This paper introduces a novel sensor application for online monitoring of the withering condition of leaves. The proposed system is based on the millimeter-wave radar sensitivity and its signal variations that correlate with the water content in a leaf. To validate the experimental prototype, a 60 GHz pulsed coherent radar (PCR) coupled with a dielectric lens was configured. The data obtained by means of the radar sensor is correlated with the data of the conventional gravimetric using a modelling approach based on Beer-Lambert’s law. To the best of our knowledge this is the first proof-of-concept demonstrating the relation between the received signal amplitude from the millimeter-wave radar sensor and plant leaf mass loss.

Correction of leaf nutrient resorption efficiency on the mass basis

Abstract Nutrient resorption is a crucial mechanism for plant nutrient conservation, but most previous studies did not consider the leaf-mass loss during senescence due to lack of measured data. This would lead to an underestimation of nutrient resorption efficiency (NuRE), or calculating NuRE of various species based on the average mass loss at plant-functional-group level in the literature, thus affecting its accuracy. Here we measured the leaf-mass loss to correct NuRE with the species-specific mass loss correction factor (MLCF), so as to foster a more accurate calculation of the nutrient fluxes within and between plants and the soil. Green leaves and senesced leaves were collected from 35 dominant woody plants in northern China. Mass of green and senesced leaves were measured to calculate the MLCF at species level. The MLCF was reported for each of the 35 dominant woody plants in northern China. These species averagely lost 17% of the green-leaf mass during leaf senescence, but varied greatly from 1.3% to 36.8% mass loss across the 35 species, or 11.7% to 19.6% loss across the functional types. Accordingly, the MLCF varied from 0.632 to 0.987 across the 35 species with an average value 0.832. The NuRE corrected with MLCF was remarkably increased on the whole (e.g. both the average nitrogen and phosphorus NuRE became about 9% higher, or more accurate), compared with the uncorrected ones, especially in the case of low resorption efficiencies. Our field data provide reliable references for the MLCF of plants in related regions at both species and functional-type levels, and are expected to promote more accurate calculations of NuRE.

Pyrolysis and Combustion Characteristics of Leaf-like Fuel under Convection and Radiation Heating

ABSTRACT The heating of a fuel element representing a vertically oriented living manzanita leaf was computationally investigated. The computational conditions resembled a previous experimental setup where manzanita leaves were exposed to an upward stream of hot gases supplying the convective heating and a radiant panel providing the radiative heating. The simulations confirmed the experimental observations as to what the impact of the heating mode is on ignition. The convection-only and combined convection and radiation modes resulted in ignition and flaming whereas the radiation-only mode did not. The leaf mass loss versus time, the heating pattern of the leaf, the ignition time, and the flame spread pattern in simulations were in good agreement with the experimental findings. Furthermore, the simulations revealed the impact of the heating mode on thermochemical evolution of the leaves, formation of boundary layers on the leaf faces, ignition, and formation and propagation of the flame. An analysis based on the postprocessing of the numerical data showed that except for the first second, the fuel may be considered thermally thin. Ignition occurred near the lower corners of the leaf, which were exposed to the highest heat fluxes compared to the rest of the leaf. In the combined heating mode, the fuel pyrolyzed faster and ignition occurred earlier because the overall heat flux was larger. The computed heat release rates per unit volume showed that the flame is formed in the lower part of the leaf, and then moves and propagates upward. The computations revealed that the overall heat release by combustion of pyrolysis gas was not sensitive to the mode of heating.

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

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

Fungal richness does not buffer the effects of streams salinization on litter decomposition

Freshwater salinization is a world-wide phenomenon threatening stream communities and ecosystem functioning. In these systems, litter decomposition is a main ecosystem-level process where fungi (aquatic hyphomycetes) play a central role linking basal resource and higher levels of food-web. The current study evaluated the impact of aquatic hyphomycete richness on leaf litter decomposition when subjected to salinization. In a microcosm study, we analysed leaf mass loss, fungal biomass, respiration and sporulation rate by fungal assemblages at three levels of species richness (1, 4, 8 species) and three levels of salinity (0, 8, 16 g NaCl L‑1). Mass loss and sporulation rate were depressed at 8 and 16 g NaCl L‑1, while fungal biomass and respiration were only negatively affected at 16 g L‑1. A richness effect was only observed on sporulation rates, with the maximum values found in assemblages of 4 species. In all cases, the negative effects of high levels of salinization on the four tested variables superimposed the potential buffer capacity of fungal richness. The study suggests functional redundancy among the fungal species even at elevated salt stress conditions which may guarantee stream functioning at extreme levels of salinity. Nonetheless, it also points to the possible importance of salt induced changes on fungal diversity and identity in salinized streams able to induce bottom-up effects in the food webs.

Decomposição foliar da serapilheira de dois sistemas agroflorestais no Cerrado Sul-Mato-Grossense

Um dos indicadores importantes para um ecossistema é a serapilheira, pois ela fornece nutrientes e matéria orgânica que são essenciais para o funcionamento do ambiente. Assim sendo, o objetivo deste estudo foi avaliar a taxa de decomposição foliar da serapilheira e correlacioná-la com índices meteorológicos, em duas áreas com sistemas agroflorestais (SAF1) formado por diversas espécies de plantas e (SAF2) formado por Heveicultura e abacaxi, em uma região de Cerrado, no município de Pedro Gomes, MS. Para avaliação da decomposição da serapilheira folhas recém-caídas foram coletadas das áreas de estudo e transferidas à estufa por 96 horas. Em seguida, foram pesadas frações de 10 gramas e inseridas em litterbags. Foram alocados 20 litterbags em cada área de estudo e a remoção das amostras ocorreu aos 30, 60, 90 e 120 dias, retirando-se 5 amostras por área e época avaliada. Foi estimada a massa foliar remanescente dos litterbags, o tempo de meia vida (t ½) e a constante de decomposição (k). Posteriormente, a correlação de Pearson (r) entre as variáveis climáticas e k. A perda da massa foliar foi maior na área do SAF2, e em ambas as áreas a temperatura e precipitação tiveram influência na decomposição foliar da serapilheira.

Combined effects of freshwater salinization and leaf traits on litter decomposition

Freshwater salinization is a matter of major global concern due to its consequences on the aquatic biota and ecosystems functioning. Salt contamination negatively affects the leaf litter decomposition process, a key ecosystem-level process in forested streams that contributes to the recycling of nutrients and carbon storage. However, information on how additional factors may influence the magnitude of the response to salinization is scarce. In this microcosm study we assessed the importance of leaf (Castanea sativa; Quercus robur) traits, on aquatic hyphomycetes-mediated leaf litter decomposition and associated variables, in salt-contaminated (0, 1, 3 and 6 g/l NaCl) environments. The leaves were incubated individually, and in a mixture, for 28 days, under each tested salt concentration. Salinity depressed leaf mass loss, fungal biomass, respiration and sporulation rates, particularly at the highest salt concentration. Differences across leaf categories were observed in all parameters but fungal biomass, although the effects were not consistent across descriptors. All leaf categories responded with a similar intensity to salt contamination for all measured variables but sporulation rate. These results suggest that the deleterious influence of salt on litter decomposition occurs independently of the traits of the stream riparian subsidies.

Liming of acidified forests changes leaf litter traits but does not improve leaf litter decomposability in forest streams

Liming, the spreading of Ca/MgCO3 on terrestrial ecosystems, is often used as a way to promote the recovery of terrestrial and aquatic ecosystems affected by anthropogenic acidification. When liming is applied to a watershed, surface waters may be improved directly through water chemistry changes but also indirectly through possible changes in the quality of terrestrial organic matter inputs to the stream. The aim of this study was to evaluate the effect of liming on leaf litter chemical and structural traits and their consequences on another trait, leaf litter decomposability, giving the potential for a leaf litter to be decomposed.Beech (Fagus sylvatica, L.) leaf litter was collected in forested sites on acid bedrock (granite and sandstone), limed (9 or 21 years ago) or not (controls), as well as on two calcareous reference sites. Several leaf litter traits were determined for each collection site: carbon (C), nitrogen (N), phosphorous (P), calcium (Ca), magnesium (Mg), potassium (K), lignin and cellulose content, and leaf mass area and toughness. To compare leaf litter decomposability in aquatic ecosystem, leaf litters from all sites were placed in a reference forested headwater stream over a 128-day period, in fine and coarse mesh litter bags, and leaf mass loss dynamic as well as fungal biomass were evaluated.Liming significantly increased leaf litter Ca and Mg contents and decreased K content while other measured traits remained unchanged. Leaf litters collected in limed sites exhibited significantly lower decomposition rates in coarse mesh bags but similar decomposition rates in fine mesh bags. Liming had no significant effect on fungal biomass. In contrast, leaf litter collected on the calcareous, reference sites, showed significantly different trait profiles (e.g. higher Ca, Mg, K and P contents), leading to up to twice higher decomposition rates and fungal development.Our study shows that under our experimental conditions, increases in Ca and Mg leaf litter contents arising from acidic forests liming did not improve leaf litter microbial decomposition and even tended to reduce macroinvertebrate mediated decomposability. Concomitant changes in other leaf litter traits might be necessary to stimulate leaf litter decomposition. Liming with Ca/MgCO3 might thus not improve functional recovery of stream ecosystems in forests affected by acidification through an increase of litter quality.

Effects of microbial conditioning and temperature on the leaf-litter shredding activity of Phylloicus sp.

Few studies try to explain the effects in tropical lotic ecosystems of an increase in water temperature on the shredding activity of invertebrate shredders, particularly in association with the quality of the leaf litter and the degree of litter conditioning. Therefore, the aims of this study were as follows: i) to better understand how this key invertebrate shredder group affects the decomposition of different species of leaf litter under gradual increases in temperature and microbial conditioning; and ii) to verify the possible consequences on leaf mass loss (LML). Three species of leaf litter were used in two experiments. In experiment I, the litters of three species (Protium spruceanum, Richeria grandis and Inga laurina) at three conditioning levels (1, 7, 14 days) were tested under five different temperatures (20, 22, 24, 26 and 28°C). In experiment II, the leaf litters of three species were used, without conditioning, under four temperatures (20, 22, 26 and 27°C). The shredding performed by Phylloicus sp. was largely dependent on the lignin and cellulose concentrations in each leaf species, independent of conditioning. The presence or absence of conditioning may cause the shredders to use different energy compensation strategies in response to the temperature increases.

Nutrient resorption estimation compromised by leaf mass loss and area shrinkage: Variations and solutions

Leaf nutrient resorption helps plants minimize nutrient loss via litterfall. The commonly-used parameter to express the resorption, nutrient resorption efficiency (NuRE, the percentage of the leaf nutrient pool withdrawn before abscission), can be compromised by leaf mass loss (LML) and leaf area shrinkage (LAS) when they are not correctly accounted. However, the variations in LML and LAS and their consequences on real NuRE are still poorly understood. To explore the drivers of LML and LAS and their impact on NuRE, we conducted a comprehensive measurement on LML and LAS concomitant with NuRE for 46 deciduous woody species in a temperate forest. The LML and LAS ranged from –3.13% to 32.21% and 0.65% to 18.07%, respectively. On average, ignoring LML (LAS) underestimated the nitrogen and phosphorus resorption efficiencies by 6.93% and 7.39% (4.66% and 4.57%), respectively. The differences in LML and LAS among species and regions should be considered in NuRE studies. The LAS was significantly influenced by plant functional groups and leaf structural traits, while the LML was only weakly related to leaf-fall date. Green leaf area and thickness shrinkages could be used to model LAS. We finally provided suggestions for recovering the historical data and improving future measurements of NuRE.

Contribution of macroinvertebrate shredders and aquatic hyphomycetes to litter decomposition in remote insular streams

Shredders play a crucial role in litter decomposition in streams. However, in oceanic islands, many streams have low shredder density and richness, and microbes seem to be the main litter decomposers. Here, we evaluate the effects of shredders and aquatic hyphomycetes on litter decomposition in insular streams. Three leaf species differing in physical and chemical characteristics, Alnus glutinosa, Clethra arborea, and Cryptomeria japonica, were enclosed in bags of coarse and fine mesh to allow and avoid macroinvertebrate access to the litter, respectively, and incubated in six streams along a gradient of Limnephilus atlanticus (Trichoptera) density in Sao Miguel Island. In streams with higher L. atlanticus density, leaf mass loss was higher in coarse than fine mesh bags. However, no difference in litter mass loss was found between bag types in streams with no L. atlanticus, despite the presence of other shredder taxa. These results suggest that when L. atlanticus are present at relatively high densities, they significantly contribute to litter decomposition, while litter decomposition is mainly driven by microbes when L. atlanticus density is low, or they are absent. Moreover, litter decomposition depends on litter quality, with leaves with high nutrient concentration and low concentration of secondary compounds being preferred by shredders.

Salinisation effects on leaf litter decomposition in fresh waters: Does the ionic composition of salt matter?

Abstract Salinisation (i.e. increased ion concentrations) in fresh waters is a growing threat worldwide that impacts freshwater communities. However, less is known about how increased salt concentrations affect key ecosystem processes such as leaf decomposition. We designed a laboratory experiment to assess the effects of a concentration gradient (1, 3, and 6 g/L) of three different salts (NaCl, CaCl2 and CH3CO2K), on leaf litter decomposition mediated by microbial decomposers and the larvae of a cased caddis fly (Schizopelex festiva, Trichoptera). Leaf discs of Quercus robur inoculated with microbial decomposers (a mixture of 5 fungal species) were incubated in microcosms under every possible salt × concentration combination and without salt addition (control), with a single individual of the cased caddis fly. Half of the leaf disks were not available for consumption by the trichopteran and represent a microbial only treatment when leaf mass loss was measured. Leaf decomposition driven by microbial decomposers was not affected by salinity despite the fact that all salt treatments depressed fungal biomass and microbial respiration compared to the control. However, the caddis flies were strongly affected by the high salt concentrations and consumed less leaf material at 6 g/L salt concentrations compared to control microcosms. The feeding activity of the trichopteran further depended on the salt type: CaCl2 had the most deleterious effects. Salinisation of fresh waters depresses leaf litter decomposition, mainly through deleterious effects on detritivores, the magnitude of the response being dependent on the ionic composition. Our results reiterate the need to reduce terrestrial run‐off of salts into fresh waters because salinisation (especially increased levels of CaCl2) affects invertebrates and the key ecosystem processes they drive.

Metabolomic, functional, and ecologic responses of the common freshwater fungus Neonectria lugdunensis to mine drainage stress

Metal contamination of watersheds is a global problem. Here, we conducted litter decomposition studies with Neonectria lugdunensis, a cosmopolitan aquatic fungus. Fungal isolates from four reference (non-impacted) and six metal-contaminated streams (due to mine drainage) were exposed to mine drainage and reference stream waters in Central Portugal. Impact of mine drainage waters on N. lugdunensis hyphae was investigated by performing metabolomic profiling of 200 lipids and 25 amino acids (AA) with ultra-high performance liquid chromatography-mass spectrometry. In parallel, functional response of N. lugdunensis isolates was assessed through expression profiles of a functional gene, cellobiohydrolase I (CbhI). Ecological performance via leaf mass loss was also determined. Exposure to mine drainage waters altered the concentration of numerous AA and lipids. Most strikingly, a gradual increase in the concentration of the triacylglycerols (TAG) with shorter acyl chains and lesser unsaturation was observed after the exposure to mine drainage waters. In addition, the changes in the concentration of numerous TAG, lysophosphatidylcholines, and AA were more significant in the isolates from the metal-contaminated streams after exposure to mine drainage water. CbhI gene of the isolates from reference streams was down-regulated by metal stress, while those from metal-contaminated streams remained unaffected. Finally, leaf mass loss was influenced by both exposure to mine drainage waters and the origin of isolates. Overall, our study demonstrates unique functional signatures displayed by fungi under metal stress and the relevant role that fungal AA and lipids play to cope with metal toxicity.

Neotropical freshwater crabs (Decapoda: Pseudothelphusidae) shred leaves

Abstract Freshwater crabs are macroconsumers that are commonly found in Neotropical headwater streams that may play a key role in energy flow and nutrient cycling in detrital food webs. Although studies have examined the feeding habits of trichodactylid crabs, little is known of this behavior in pseudothelphusid species, and specifically whether they actually consume leaf material. We conducted three nine-day laboratory trials with pseudothelphusid crabs (Ptychophallus tumimanus (Rathbun, 1898)) and leaves (Koanophyllon pittieri) to investigate whether crabs shred leaves. We hypothesized that leaf mass loss would be faster with crabs present relative to control tanks with only leaves. Leaf mass loss was significantly higher (p < 0.001) in tanks with crabs (0.49 ± 0.07 g, mean ± 1 SD) compared to control tanks (0.31 ± 0.05 g). We observed crabs manipulating, shredding, and consuming leaves, with leaf fragments and egesta present in tanks with crabs but not in control tanks. Their consumption and egestion activity may affect nutrient availability and transformation by stimulating microbial activity during leaf breakdown and converting coarse particulate organic matter (CPOM) to fine particulate organic matter (FPOM). Therefore, freshwater crabs need to be considered when studying energy flow and nutrient cycling in detrital food webs of Neotropical headwater streams.

Significance of sunlight for organic matter degradation in aquatic systems

Degradation of organic matter (OM) is generally considered to be primarily governed by biotic factors in aquatic environments. However, a number of abiotic processes also play key roles in mediating OM-degradation. Sunlight can act as a principal abiotic driver of the degradation of terrestrial organic matter, but its importance for freshwater ecosystems and possible interactions with biotic drivers remains poorly understood. We carried out two microcosm experiments which focused on the role of sunlight on microbial and invertebrate-mediated OM degradation using two species of plant leaves and the aquatic invertebrate Asellus aquaticus. Results indicated that sunlight was the primary driver of leaf mass loss during the early stages of decomposition, whereas microbial communities had a negligible effect. Sunlight was observed to strongly affect invertebrate behavior as invertebrates avoided direct illumination. This alteration of behavior resulted in a reduction in the consumption of a leaf surrogate (DECOTAB) by A. aquaticus. Together, these results indicate that sunlight has the potential to strongly influence structural and functional attributes of shallow freshwater systems, and hence serve as an appraisal to consider sunlight as a significant direct and indirect physical driver governing OM degradation in shallow aquatic systems.

Intraspecific diversity affects stress response and the ecological performance of a cosmopolitan aquatic fungus

Abstract Fungi play an important role in organic matter turnover and ensure key ecosystem services in freshwaters. The relationships between intraspecific fungal diversity and key ecological processes remain largely unknown. We examined the effects of intraspecific diversity of Articulospora tetracladia, a cosmopolitan fungal decomposer thriving on plant detritus in streams. Alder leaves were inoculated with 1 or mixtures of 2–8 fungal strains for 35 d, and leaf litter decomposition and fungal reproduction were quantified in the presence and absence of 2 mg L−1 of cadmium (Cd), a common stressor in polluted streams. Intraspecific diversity and identity affected fungal reproduction, but not leaf decomposition. Under metal stress, leaf decomposition slightly increased with intraspecific diversity. Fungal reproduction increased with intraspecific diversity and was greater in mixed assemblages, either in the absence or presence of Cd. Effect size of intraspecific diversity was higher under Cd stress for fungal reproduction, but no differences were found for leaf mass loss, with or without metal. The impacts of intraspecific diversity loss may jeopardize fungal survival and fungal functions, namely microbial leaf decomposition and leaf litter condition for invertebrate shredders in streams, particularly under metal stress.

Towards a standardized protocol for measuring leaf area index in deciduous forests with litterfall collection

The leaf litter collection method is often used as a baseline for assessing leaf area index (LAI) measurements in forests by optical methods, but different protocols for measuring specific leaf area (SLA) may introduce biases in stand-level LAI estimates, which have not been quantified yet. To develop a standardized protocol for measuring SLA of leaf litter for estimating LAI via litterfall collection, we quantified the relative errors (RE) in the SLA measurements introduced by six protocols commonly-used in the literature with 46 deciduous woody species in a temperate forest, and assessed the stand-level LAI estimates derived from the SLA with eight permanent plots in the forest. The mean leaf area shrinkage from the litter collection across the species varied from 7.31 – 25.41% among the protocols, while the mean leaf mass loss varied from 2.07 – 24.68%. Compared with the reference, the mean RE of SLA introduced by the rest five protocols varied from −25.59 – 7.18%, and the subsequent RE of the stand-level LAI varied from −32.43 – 8.97%. We recommended a practical and reliable protocol for measuring SLA from leaf litter, i.e., weighing the dry mass first, then measuring the leaf area after rehydration with wet-filter-papers, and finally correcting for the leaf area shrinkage relative to the green leaf. We also provided general models for correcting for the SLA biases due to area shrinkage and mass loss of senesced leaves in temperate forests. Our findings will extend the direct measurements of LAI and improve the estimation of carbon and nutrient budgets in forest ecosystems.