Litter Mass Loss Research Articles

Intrapopulation genotypic variation in leaf litter chemistry does not control microbial abundance and litter mass loss in silver birch, Betula pendula

Differences among plant genotypes can influence ecosystem functioning such as the rate of litter decomposition. Little is known, however, of the strength of genotypic links between litter quality, microbial abundance and litter decomposition within plant populations, or the likelihood that these processes are driven by natural selection. We used 19 Betula pendula genotypes randomly selected from a local population in south-eastern Finland to establish a long-term, 35-month litter decomposition trial on forest ground. We analysed the effect of litter quality (N, phenolics and triterpenoids) of senescent leaves and decomposed litter on microbial abundance and litter mass loss. We found that while litter quality and mass loss both had significant genotypic variation, the genotypic variation among silver birch trees in the quantity of bacterial and fungal DNA was marginal. In addition, although the quantity of bacterial DNA at individual tree level was negatively associated with most secondary metabolites of litter and positively with litter N, litter chemistry was not genotypically linked to litter mass loss. Contrary to our expectations, these results suggest that natural selection may have limited influence on overall microbial DNA and litter decomposition rate in B. pendula populations by reworking the genetically controlled foliage chemistry of these populations.

Aquatic invertebrates increase litter breakdown in Neotropical shallow semi-arid lakes

The feeding behavior of shredders and scrapers (invertebrates) is important for litter processing in aquatic ecosystems. We assessed the importance of invertebrate activity for organic matter breakdown in shallow lakes (macrophyte covered or macrophyte free), testing whether the abundance of scrapers was greater than that of shredders, and if macrophytes increased scraper density and consequently, the rate of leaf litter breakdown. We used litter bags with senescent leaves to assess the density, richness and biomass of invertebrates and assessed the mass loss of litter after oven drying. The mean decomposition coefficient (k = -0.0037day−1) was lower than reported rates for other semi-arid lakes. We observed greater leaf breakdown in litter bags with coarse mesh, indicating the importance of scrapers, but potentially also microbes. However, leaf-associated invertebrates (averaged across both types of lakes) had low densities (4.7 ind.g−1), biomass (8.3 mg g−1) and richness (12 taxa), which may explain similar breakdown rates between lakes. Semi-aquatic Coleoptera and Mollusca were the most diverse taxa because they are capable of tolerating high hydrological stress associated with shallow lakes in semiarid areas. Planorbidae, which are intermediate hosts for the human parasitic trematode Schistosomamansoni, were almost absent in the macrophytic lake, suggesting that macrophytes may reduce the Planorbidae density and play an important role in human health.

Micro-decomposer communities and decomposition processes in tropical lowlands as affected by land use and litter type.

We investigated how the land-use change from rainforest into jungle rubber, intensive rubber and oil palm plantations affects decomposers and litter decomposition in Sumatra, Indonesia. Litterbags containing three litter types were placed into four land-use systems and harvested after 6 and 12months. Litter mass loss and litter element concentrations were measured, and different microbial groups including bacteria, fungi and testate amoebae were studied. After 12months 81, 65, 63 and 53% of litter exposed in rainforest, jungle rubber in oil palm and rubber plantations was decomposed. In addition to land use, litter decomposition varied strongly with litter type and short-term effects differed markedly from long-term effects. After 6months, oil palm and rubber litter decomposed faster than rainforest litter, but after 12months, decomposition of rainforest litter exceeded that of oil palm and rubber litter, reflecting adaptation of bacteria and fungi to decompose structural compounds in rainforest litter but not (or less) in rubber and oil palm litter. Bacterial and fungal community composition and testate amoeba species number and density varied strongly with litter type, but little with land use. However, community composition of testate amoebae was mainly affected by land use. Generally, changes in bacteria, fungi and testate amoebae were linked to changes in litter element concentrations, suggesting that element ratios of litter material as basal resource for the decomposer food web shape the structure of decomposer communities and decomposition processes via bottom-up forces. Overall, changing rainforest to monoculture plantations shifts the decomposer community structure and negatively affects litter decomposition.

Negative effects of litter richness on root decomposition in the presence of detritivores

Abstract Decomposition is a vital process underlying many ecosystem functions. Although a growing number of studies have tested how litter richness affects the decomposition of above‐ground plant organs, knowledge remains limited about the decomposition of root mixtures. Here, we used a field experiment in a subtropical forest to investigate how species richness in root litter mixtures (air‐dried fresh fine roots) affects the decomposition of root litter material. On the basis of the concept of resource complementarity, we hypothesized that root litter would decompose faster as the richness of the root litter mixture increased. In addition, we expected the presence of detritivores would modify the effect of root richness on mass loss, because detritivores might experience bottom‐up effects from specific plant species and might affect microbial decomposer communities. We found that the richness level of root litter mixtures did not affect mass loss in the absence of detritivores. In the presence of detritivores, all root litter types decomposed faster. Notably, the positive effect of detritivores was stronger at low root litter richness than at high root litter richness, particularly during the early stages of decomposition (the first two sampling points) when litter mass loss was roughly double at low root litter richness compared to that at high root litter richness. The composition of the root fungal community measured at the last sampling point did not differ significantly across root richness levels, and was not affected by the presence of detritivores. Synthesis. Our findings demonstrate that detritivores modify the relationship between root litter diversity and root litter decomposition in subtropical forest ecosystems. This highlights an importance of cascade effects between different trophic organisms on ecosystem functioning. A plain language summary is available for this article.

Early stage litter decomposition across biomes

Through litter decomposition enormous amounts of carbon is emitted to the atmosphere. Numerous large-scale decomposition experiments have been conducted focusing on this fundamental soil process in order to understand the controls on the terrestrial carbon transfer to the atmosphere. However, previous studies were mostly based on site-specific litter and methodologies, adding major uncertainty to syntheses, comparisons and meta-analyses across different experiments and sites. In the TeaComposition initiative, the potential litter decomposition is investigated by using standardized substrates (Rooibos and Green tea) for comparison of litter mass loss at 336 sites (ranging from −9 to +26 °C MAT and from 60 to 3113 mm MAP) across different ecosystems. In this study we tested the effect of climate (temperature and moisture), litter type and land-use on early stage decomposition (3 months) across nine biomes. We show that litter quality was the predominant controlling factor in early stage litter decomposition, which explained about 65% of the variability in litter decomposition at a global scale. The effect of climate, on the other hand, was not litter specific and explained <0.5% of the variation for Green tea and 5% for Rooibos tea, and was of significance only under unfavorable decomposition conditions (i.e. xeric versus mesic environments). When the data were aggregated at the biome scale, climate played a significant role on decomposition of both litter types (explaining 64% of the variation for Green tea and 72% for Rooibos tea). No significant effect of land-use on early stage litter decomposition was noted within the temperate biome. Our results indicate that multiple drivers are affecting early stage litter mass loss with litter quality being dominant. In order to be able to quantify the relative importance of the different drivers over time, long-term studies combined with experimental trials are needed.

Interactions among decaying leaf litter, root litter and soil organic matter vary with mycorrhizal type

Abstract Root‐derived inputs are increasingly viewed as primary controls of soil organic matter (SOM) formation; however, we have a limited understanding of how root decay rates depend on soil factors, and how decaying roots influence the breakdown of leaf litter and SOM. We incubated root and leaf litter (alone and in combination) from arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) trees in soils collected from forest plots dominated by AM and ECM trees in a factorial design. In each microcosm, we quantified litter decay rates and the effects of decaying litters on soil C balance. We hypothesized that (1) AM root litters would decompose faster than ECM root litters, (2) root litter decay would be greatest when decomposed in “home” soils (e.g. AM litters in AM soils and ECM litters in ECM soils) and (3) root and leaf litters would decompose faster when decaying in the same microcosms than when decaying in separate microcosms, resulting in the largest CO2 losses. Overall, AM root litter decomposed faster than ECM root litter, and the magnitude of this effect depended on soil origin. AM litters decayed fastest in AM soils, but ECM and mixed AM–ECM litters were unaffected by soil origin. Decaying roots increased leaf litter mass loss, but only in microcosms containing soils of the same origin (e.g. AM litters in AM soils; mixed litters in mixed soils). Carbon losses were dominated by microbial respiration, and the magnitude of this flux depended on litter type and soil origin. When leaves and roots decayed together, respiratory losses exceeded those from microcosms containing leaves and roots alone, with the largest losses occurring in each litters' “home” soil. In AM soils, elevated losses were driven by roots accelerating leaf decay, while in ECM soils, elevated losses resulted from roots and leaves accelerating the decay of SOM; in mixed soils, root‐induced increases in leaf and SOM decay contributed to elevated C losses. Synthesis. Our results suggest that root, leaf and SOM decay are intertwined, and that measurements of these processes in isolation may lead to incorrect estimates of the magnitude and source of C losses from soils.

Dynamics of Litter Carbon and Nitrogen in Forest Fallows following Shifting Cultivation in Mizoram, Northeast India

In this study, a field trial was carried out on organic matter, carbon (C) and nitrogen (N) dynamics of different litter components (i.e. leaf, branch, roots less than 2 mm and 2-5 mm) in forest fallows (3 years: FL-3, 5 years: FL-5 and 10 years: FL-10) at Muallungthu, Mizoram using litter bag techniques. The rate of organic matter loss and release of C and N was faster in leaf and fine root (less than 2 mm) compared to branch and coarse roots (2-5 mm). Further, litter mass loss rate was higher in longer fallow (FL-10) compared to shorter fallow (FL-3 and FL-5). Results showed that mass loss and release of C and N was largely depending on the initial litter quality, abiotic variables and litter microorganisms. Release of C followed the patter similar to that of mass loss, whereas, N release showed an initial release followed by a slow release or marginal increase that indicate the tendency of N immobilization. Results indicate that the addition of litter from the adjoining forest adds organic matter, C and N in shifting cultivation that may help in sustaining soil fertility and crop productivity of shifting agriculture sites in northeastern hill regions of Mizoram.

Nutrient limitation or home field advantage: Does microbial community adaptation overcome nutrient limitation of litter decomposition in a tropical peatland?

Abstract Litter decomposition is an important control on carbon accumulation in tropical peatlands. Stoichiometric theory suggests that decomposition is regulated by elemental ratios in litter while the home field advantage (HFA) hypothesis predicts that decomposer communities are adapted to local conditions. To date, the relative importance of these contrasting theories for litter decomposition and therefore the carbon balance of tropical peatlands remain poorly understood. We conducted two in situ litter decomposition experiments in a lowland tropical peatland. The first experiment tested the importance of the stoichiometric theory using a factorial nutrient addition experiment at two sites with contrasting vegetation (Raphia taedigera and Campnosperma panamensis) to assess how nutrient addition affected microbial enzyme activity and litter mass loss at the peat surface and at 50 cm depth. The second experiment tested the importance of HFA by reciprocal translocation of leaf litter from R. taedigera and C. panamensis forests, which differed in both litter chemistry and soil nutrient availability, to separate the influence of litter chemistry and soil/site properties on litter mass loss. The activities of hydrolytic enzymes involved in the decomposition of large plant polymers were stimulated by nitrogen addition only where nitrogen availability was low relative to phosphorus, and were stimulated by phosphorus addition where phosphorus availability was low. The addition of nitrogen, but not phosphorus, increased leaf litter decomposition under waterlogged conditions at 50 cm depth, but not at the peat surface. Decomposition was greatest for autochthonous litter irrespective of site nutrient status, indicating that adaptation of the microbial community to low nutrients can partly overcome nutrient limitation, and suggesting that HFA can influence litter decomposition rates. Synthesis. Our study shows that leaf litter decomposition and the activity of microbial enzymes in tropical peatlands are constrained in part by nutrient availability. However, such nutrient limitation of litter decomposition can be overcome by adaptation of the microbial community.

Precipitation and Nitrogen Deposition Alter Litter Decomposition Dynamics in Semiarid Temperate Steppe in Inner Mongolia, China

Plant litter decomposition is one of the most important links connecting plants to the soil through the carbon (C) and nitrogen (N) cycles. Climate change scenarios predict changes in precipitation and N deposition, and previous studies have demonstrated that increases in the availability of water and N affect the litter decomposition rate and nutrient release. We studied the effects of increased N deposition and precipitation on changes in the remaining mass and the C and N contents of shoot litter after decomposition in a typical steppe in Inner Mongolia, China. The treatments included the addition of NH4NO3 at rates equivalent to 0, 25, 50, and 100 kg∙N∙ha−2yr−1 with and without added water. The addition of water proved to be a more effective practice than amendment with NH4NO3 for improving the litter decomposition rate; the addition of water significantly increased the rate of litter decomposition (P < 0.001), whereas the addition of N alone had no apparent effect on litter mass loss. However, a repeated measures analysis of variance (ANOVA) showed that the interaction of water and N significantly affected both mass loss and litter N content (P < 0.05), and a linear relationship was identified between litter mass loss and litter decomposition time (P < 0.001). No correlation was found between litter mass loss and organic C content, but a significant positive correlation was found between residual litter mass and N content (P < 0.01). Although the study was conducted over a relatively short period, our results indicate that increased precipitation could potentially promote litter decomposition, whereas increased N input has little effect. The effects of time on litter mass loss and residual C and N concentrations indicate the need for long-term trials that measure the complete process of litter decomposition and the peaks of C and N release.

Contrasting above- and belowground organic matter decomposition and carbon and nitrogen dynamics in response to warming in High Arctic tundra.

Tundra regions are projected to warm rapidly during the coming decades. The tundra biome holds the largest terrestrial carbon pool, largely contained in frozen permafrost soils. With warming, these permafrost soils may thaw and become available for microbial decomposition, potentially providing a positive feedback to global warming. Warming may directly stimulate microbial metabolism but may also indirectly stimulate organic matter turnover through increased plant productivity by soil priming from root exudates and accelerated litter turnover rates. Here, we assess the impacts of experimental warming on turnover rates of leaf litter, active layer soil and thawed permafrost sediment in two high-arctic tundra heath sites in NE-Greenland, either dominated by evergreen or deciduous shrubs. We incubated shrub leaf litter on the surface of control and warmed plots for 1 and 2years. Active layer soil was collected from the plots to assess the effects of 8years of field warming on soil carbon stocks. Finally, we incubated open cores filled with newly thawed permafrost soil for 2years in the active layer of the same plots. After field incubation, we measured basal respiration rates of recovered thawed permafrost cores in the lab. Warming significantly reduced litter mass loss by 26% after 1year incubation, but differences in litter mass loss among treatments disappeared after 2years incubation. Warming also reduced litter nitrogen mineralization and decreased the litter carbon to nitrogen ratio. Active layer soil carbon stocks were reduced 15% by warming, while soil dissolved nitrogen was reduced by half in warmed plots. Warming had a positive legacy effect on carbon turnover rates in thawed permafrost cores, with 10% higher respiration rates measured in cores from warmed plots. These results demonstrate that warming may have contrasting effects on above- and belowground tundra carbon turnover, possibly governed by microbial resource availability.

不同土壤厚度、水分和种植方式对喀斯特两种草本凋落物分解质量损失和化学计量特征的影响

不同土壤厚度、水分和种植方式对喀斯特两种草本凋落物分解质量损失和化学计量特征的影响

Biotic and abiotic modifications of leaf litter during dry periods affect litter mass loss and nitrogen loss during wet periods

Abstract Decomposition of organic matter in semi‐arid ecosystems is a key component of the terrestrial carbon (C) cycle. The well‐known inaccuracies in predicting litter decay in water‐limited regions were lessened by considering solar radiation as an abiotic decay driver of photodegradation. Moreover, exposure to high solar irradiance in dry periods often led to massive facilitation of litter decay in subsequent wet periods (“photoacceleration”), though in many studies this effect was absent. Recently, water vapour and dew were identified as modulators enabling substantial microbial degradation during rainless periods. Here, we investigated, (1) whether the activity of micro‐organisms modifies litter traits, such as litter quality and microbial community in dry periods, consequently altering the loss of litter mass and nitrogen (N) in wet periods, and (2) whether it can co‐occur with photoacceleration. By successively introducing litter to the field at the beginning and the end of the dry season, we found that microbial activity during the dry season affected litter mass and N loss during the wet season. Low microbial activity in the dry season led to inhibition of mass loss in the wet season, while high microbial activity led to facilitation of mass loss. Microbial activity during the dry season also caused strong inhibition of N loss from litter during the wet season, likely by enhancing the dry‐season N loss. A microclimate manipulation experiment using radiation filters showed that microbial activity and exposure to solar radiation jointly modified the litter during the dry season and affected subsequent decay in the wet season. Knowledge of biotic and abiotic modifications of litter during dry periods and their implication for wet periods enhances our understanding of litter decay in semi‐arid regions. Furthermore, it can improve biogeochemical model predictions of C and N cycling in drylands and in the many regions that are projected to experience a drier climate during the coming decades. A plain language summary is available for this article.

Microbial decomposition is highly sensitive to leaf litter emersion in a permanent temperate stream

Drought frequency and intensity in some temperate regions are forecasted to increase under the ongoing global change, which might expose permanent streams to intermittence and have severe repercussions on stream communities and ecosystem processes. In this study, we investigated the effect of drought duration on microbial decomposition of Populus nigra leaf litter in a temperate permanent stream (Oliveira, NW Portugal). Specifically, we measured the response of the structural (assemblage composition, bacterial and fungal biomass) and functional (leaf litter decomposition, extracellular enzyme activities (EEA), and fungal sporulation) parameters of fungal and bacterial communities on leaf litter exposed to emersion during different time periods (7, 14 and 21d). Emersion time affected microbial assemblages and litter decomposition, but the response differed among variables. Leaf decomposition rates and the activity of β-glucosidase, cellobiohydrolase and phosphatase were gradually reduced with increasing emersion time, while β-xylosidase reduction was similar when emersion last for 7 or more days, and the phenol oxidase reduction was similar at 14 and 21days of leaf emersion. Microbial biomass and fungal sporulation were reduced after 21days of emersion. The structure of microbial assemblages was affected by the duration of the emersion period. The shifts in fungal assemblages were correlated with a decreased microbial capacity to degrade lignin and hemicellulose in leaf litter exposed to emersion. Additionally, some resilience was observed in leaf litter mass loss, bacterial biomass, some enzyme activities and structure of fungal assemblages. Our study shows that drought can strongly alter structural and functional aspects of microbial decomposers. Therefore, the exposure of leaf litter to increasing emersion periods in temperate streams is expected to affect decomposer communities and overall decomposition of plant material by decelerating carbon cycling in streams.

Fungal communities influence decomposition rates of plant litter from two dominant tree species

The home-field advantage hypothesis (HFA) predicts that plant litter decomposes faster than expected underneath the plant from which it originates. We tested this hypothesis in a decomposition experiment where litters were incubated reciprocally in neighbouring European beech and Norway spruce forests. We analysed fungal communities in the litter through DNA metabarcoding and evaluated the effect of mesofauna (mites and springtails) on litter mass loss by using different litter-bag mesh sizes. Accounting for general differences in decomposition between litter and forest types, we found a significant home field advantage of 24%. Litter decomposed faster in the beech forest but spruce litter decomposed faster than beech litter. Fungal communities showed a clear dependency on both forest and litter type. Mesofauna did not affect litter mass loss rates or microbial species composition.

Effects of Plant Growth Form and Water Substrates on the Decomposition of Submerged Litter: Evidence of Constructed Wetland Plants in a Greenhouse Experiment

Wetland plants are important components in constructed wetlands (CWs), and one of their most important functions in CWs is to purify the water. However, wetland plant litter can also increase eutrophication of water via decomposition and nutrient release, and few studies have focused on the interspecific variation in the decomposition rate and nutrient release of multiple plant species in CWs. Here a greenhouse litter-bag experiment was conducted to quantify the decomposition rates and nutrient release of 7 dominant macrophytes (2 floating plants and 5 emergent plants) in three types of water substrate. The results showed that plant litter species and growth forms significantly affected the litter mass losses. The nutrient release was significantly different among plant litter species, but not between floating and emergent plants. Litter traits, such as litter lignin, total nitrogen (TN) and total phosphorus (TP) can well predict the decomposition rates of submerged litter. These results indicated that submerging litter in water did not change the relationships between litter traits and litter decomposition rates, and leaching might play a more important role in the decomposition of submerged litter in CWs than that in other terrestrial ecosystems. These findings can provide suggestions for managers about the maintenance of constructed wetlands.

Land use not litter quality is a stronger driver of decomposition in hyperdiverse tropical forest.

In hyperdiverse tropical forests, the key drivers of litter decomposition are poorly understood despite its crucial role in facilitating nutrient availability for plants and microbes. Selective logging is a pressing land use with potential for considerable impacts on plant–soil interactions, litter decomposition, and nutrient cycling. Here, in Borneo's tropical rainforests, we test the hypothesis that decomposition is driven by litter quality and that there is a significant “home‐field advantage,” that is positive interaction between local litter quality and land use. We determined mass loss of leaf litter, collected from selectively logged and old‐growth forest, in a fully factorial experimental design, using meshes that either allowed or precluded access by mesofauna. We measured leaf litter chemical composition before and after the experiment. Key soil chemical and biological properties and microclimatic conditions were measured as land‐use descriptors. We found that despite substantial differences in litter quality, the main driver of decomposition was land‐use type. Whilst inclusion of mesofauna accelerated decomposition, their effect was independent of land use and litter quality. Decomposition of all litters was slower in selectively logged forest than in old‐growth forest. However, there was significantly greater loss of nutrients from litter, especially phosphorus, in selectively logged forest. The analyses of several covariates detected minor microclimatic differences between land‐use types but no alterations in soil chemical properties or free‐living microbial composition. These results demonstrate that selective logging can significantly reduce litter decomposition in tropical rainforest with no evidence of a home‐field advantage. We show that loss of key limiting nutrients from litter (P & N) is greater in selectively logged forest. Overall, the findings hint at subtle differences in microclimate overriding litter quality that result in reduced decomposition rates in selectively logged forests and potentially affect biogeochemical nutrient cycling in the long term.

Legacy effects of altered flooding regimes on decomposition in a boreal floodplain

Background and aimsSince long-term experiments are scarce, we have poor understanding of how changed flooding regimes affect processes such as litter decomposition.MethodsWe simulated short- and long-term changed flooding regimes by transplanting turfs between low (frequently flooded) and high (in-frequently flooded) elevations on the river bank in 2000 (old turfs) and 2014 (young turfs). We tested how incubation elevation, turf origin and turf age affected decomposition of standard litter (tea) and four types of local litter.ResultsFor tea, we found that the initial decomposition rate (k) and stabilization (S) of labile material during the second decomposition phase were highest at high incubation elevation. We found intermediate values for k and S in young transplanted turfs, but turf origin was not important in old turfs. Local litter mass loss was generally highest at high incubation elevations, and effects of turf origin and turf age were litter-specific.ConclusionWe conclude that incubation elevation, i.e., the current flooding regime, was the most important factor driving decomposition. Soil origin (flooding history) affected decomposition of tea only in young turfs. Therefore, we expect that changes in flooding regimes predominantly affect decomposition directly, while indirect legacy effects are weaker and litter- or site-specific.

Tree regeneration retards decomposition in a temperate mountain soil after forest gap disturbance

Disturbances significantly affect the carbon (C) cycle of forest ecosystems. Surviving trees from an understory layer are recognized to play an important role in post-disturbance C dynamics. However, their influence on decomposition of soil organic matter (SOM), an important ecosystem C pool, has yet to be rigorously investigated. Over four consecutive years, we investigated the effects of advance spruce regeneration on decomposition processes in a mountain soil after forest gap disturbance. Gap disturbance was accomplished by clear cut harvest and decomposition was assessed by combining measurements of soil CO2 efflux, heterotrophic respiration, soil enzymes activity, and mass loss from standardized litter bags. Soil CO2 efflux showed no response to gap formation, independent of whether regeneration was present or absent, indicating that reduced autotrophic respiration was offset by accelerated heterotrophic respiration from decomposing microbes. Incubation studies revealed no effects of gap disturbance on heterotrophic respiration and its temperature sensitivity under controlled lab conditions. Since potential enzyme activities, at a given temperature, did not respond to gap formation either, it appears that neither C nor other nutrient limitations of the decomposing microbes changed in this SOM-rich mountain forest soil after disturbance. Mass loss of standardized litter was ∼5% higher after gap formation in plots without regeneration, while under the regeneration it remained at control stand levels. Our findings indicate that canopy removal by gap disturbance lead to an increase in decomposition, primarily due to warmer soil conditions. However, an established regeneration retards decomposition due to its modulating effect on soil temperature. Our study therefore shows that facilitating regeneration pre-disturbance can reduce post-disturbance soil C losses from decomposition.

Links between plant and fungal diversity in habitat fragments of coastal shrubland.

Habitat fragmentation is widespread across ecosystems, detrimentally affecting biodiversity. Although most habitat fragmentation studies have been conducted on macroscopic organisms, microbial communities and fungal processes may also be threatened by fragmentation. This study investigated whether fragmentation, and the effects of fragmentation on plants, altered fungal diversity and function within a fragmented shrubland in southern California. Using fluorimetric techniques, we assayed enzymes from plant litter collected from fragments of varying sizes to investigate enzymatic responses to fragmentation. To isolate the effects of plant richness from those of fragment size on fungi, we deployed litter bags containing different levels of plant litter diversity into the largest fragment and incubated in the field for one year. Following field incubation, we determined litter mass loss and conducted molecular analyses of fungal communities. We found that leaf-litter enzyme activity declined in smaller habitat fragments with less diverse vegetation. Moreover, we detected greater litter mass loss in litter bags containing more diverse plant litter. Additionally, bags with greater plant litter diversity harbored greater numbers of fungal taxa. These findings suggest that both plant litter resources and fungal function may be affected by habitat fragmentation’s constraints on plants, possibly because plant species differ chemically, and may thus decompose at different rates. Diverse plant assemblages may produce a greater variety of litter resources and provide more ecological niche space, which may support greater numbers of fungal taxa. Thus, reduced plant diversity may constrain both fungal taxa richness and decomposition in fragmented coastal shrublands. Altogether, our findings provide evidence that even fungi may be affected by human-driven habitat fragmentation via direct effects of fragmentation on plants. Our findings underscore the importance of restoring diverse vegetation communities within larger coastal sage scrub fragments and suggest that this may be an effective way to improve the functional capacity of degraded sites.

Relationships among leaf functional traits, litter traits, and mass loss during early phases of leaf litter decomposition in 12 woody plant species.

Litter 'quality' or decomposability has historically been estimated through measuring chemical attributes, such as concentrations of nitrogen or 'lignin'. More recently, foliar functional traits, which may incorporate indications of the physical structures of tissues, have been found to correlate with litter mass loss rates. However, these traits may not be adequate to predict early rates of mass loss, in which two factors are crucial: the amount of material quickly lost through leaching, and the ease of access of decomposer organisms to the more labile tissues in the interior of the litter. We investigated relationships among physical and chemical traits in foliage and litter of 12 species native to British Columbia and then observed how these traits related to mass loss during the first 3months (Phase I) and between 3 and 12months (Phase II). Novel traits measured in this study include cuticle thickness, litter leaching loss, and litter water uptake. Foliar and litter traits both co-varied along spectra, but several chemical traits, such as nitrogen concentration, changed from foliage to litter, i.e., during senescence. Phase I mass loss was best predicted by leaching loss and traits relating to leaching, such as cuticle thickness and specific leaf area. Phase II mass loss was predicted by traits that may relate to decomposer access and activity, such as leaf dry matter content and foliar nitrogen. Physical traits predicted mass loss as well or better than chemical traits, suggesting that physical characteristics of litter are important in determining early rates of decomposition.