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• Litter decomposition determines carbon (C) backflow to the atmosphere and ecosystem nutrient cycling. Although sunlight provides the indispensable energy for terrestrial biogeochemical processes, the role of photodegradation in decomposition has been relatively neglected in productive mesic ecosystems. • To quantify the effects of this variation, we conducted a factorial experiment in the understorey of a temperate deciduous forest and an adjacent gap, using spectral-attenuation-filter treatments. • Exposure to the full spectrum of sunlight increased decay rates by nearly 120% and the effect of blue light contributed 75% of this increase. Scaled-up to the whole forest ecosystem, this translates to 13% loss of leaf-litter C through photodegradation over the year of our study for a scenario of 20% gap. Irrespective of the spectral composition, herbaceous and shrub litter lost mass faster than tree litter, with photodegradation contributing the most to surface litter decomposition in forest canopy gaps. Across species, the initial litter lignin and polyphenolic contents predicted photodegradation by blue light and ultraviolet B (UV-B) radiation, respectively. • We concluded that photodegradation, modulated by litter quality, is an important driver of decomposition, not just in arid areas, but also in mesic ecosystems such as temperate deciduous forests following gap opening.

Background and aimWherever sunlight reaches litter, there is potential for photodegradation to contribute to decomposition. Although recent studies have weighed the contribution of short wavelength visible and ultraviolet (UV) radiation as drivers of photodegradation, the relative importance of each spectral region across biomes and plant communities remains uncertain.MethodsWe performed a systematic meta-analysis of studies that assessed photodegradation through spectrally selective attenuation of solar radiation, by synthesizing 30 published studies using field incubations of leaf litter from 110 plant species under ambient sunlight.ResultsGlobally, the full spectrum of sunlight significantly increased litter mass loss by 15.3% ± 1% across all studies compared to darkness. Blue light alone was responsible for most of this increase in mass loss (13.8% ± 1%), whereas neither UV radiation nor its individual constituents UV-B and UV-A radiation had significant effects at the global scale, being only important in specific environments. These waveband-dependent effects were modulated by climate and ecosystem type. Among initial litter traits, carbon content, lignin content, lignin to nitrogen ratio and SLA positively correlated with the rate of photodegradation. Global coverage of biomes and spectral regions was uneven across the meta-analysis potentially biasing the results, but also indicating where research in lacking.ConclusionsAcross studies attenuating spectral regions of sunlight, our meta-analysis confirms that photodegradation is a significant driver of decomposition, but this effect is highly dependent on the spectral region considered. Blue light was the predominant driver of photodegradation across biomes rather than UV radiation.

Purpose In plant-soil systems, phosphorus partitioning during the annual cycle related to nitrogen partitioning remains largely unknown. The present study aims at assessing the soil-plant P allocation patterns of four tree species along four phenological stages and its relationship with tissues and soil N concentrations. Methods Cryptomeria japonica, Larix kaempferi, Fagus crenata and Robinia pseudoacacia trees were selected to sample coarse roots, sapwood, foliage, litter and soil during four phenological stages where total and Olsen extractable P and nitrogen content were measured respectively. Results Intra- and inter plant tissue nitrogen correlated well with phosphorus during the four phenological stages, especially root nitrogen. Fagus and Robinia were phosphorus limited, Larix was nitrogen limited and Cryptomeria co-limited. All species reabsorbed phosphorus and nitrogen from foliage prior to leaf abscission and stored nitrogen in roots and sapwood. Phosphorus storage was solely found in sapwood of Robinia . Soil dissolved ammonium correlated positively with nitrogen reabsorption efficiency during the green leaf stage, while single soil nutrient variables did not correlate with phosphorus reabsorption efficiency. Conclusions Plant tissues nitrogen partitioning correlated well with their respective phosphorus partitioning and the increase of soil NH 4 + correlated positively with nitrogen reabsorption efficiency, regardless of tree species during the green leaf stage. The results of this study show the intricate relationship that exists between nitrogen and phosphorus in the soil-plant continuum as well as the tree species specific internal cycling of these nutrients.

Leaf traits vary widely among plant species, correlating with leaf economics and growth-defense trade-offs. However, the relationship between trait variation and pathogen resistance remains unexplored. Here, we introduce a novel experimental approach to quantitatively assess pathogen resistance using the generalist fungus Sclerotinia sclerotiorum . In this system, leaf discs were infected either through the epidermis, evaluating physical and chemical defense, or a cut surface, solely evaluating chemical defense. We investigated pathogen resistance across 24 species ranging from annual herbs to evergreen tree species. Epidermal infection revealed higher pathogen resistance in evergreens compared with annual herb species, strongly correlated with the leaf economics spectrum. The cell wall content per leaf area explaind 61% of the interspecific variations in the pathogen resistance through epidermal infection. Pathogen resistance following cut-surface infection was associated with the accumulation of defensive chemicals, such as tannins and lignins. Our findings demonstrate how investments in physical and chemical defense enhance pathogen resistance, potentially driving evolutionarily shifts in leaf traits.

There is accumulating evidence that similar suites of plant traits may affect leaf palatability and leaf litter decomposability. However, the possible association between leaf herbivory and litter decomposition rates across species in species-diverse natural ecosystems such as tropical rain forests remains unexplored, despite its importance in estimating the herbivory effects on carbon and nutrient cycling of ecosystems. We found no strong association between leaf herbivory and litter decomposition rates across 40 tree species in a Malaysian tropical rain forest, even though the leaf and litter traits were tightly correlated. This is because the leaf and litter traits related to herbivory and decomposition rates in the field were inconsistent. Leaf toughness accounted for only a small part of the variation in the herbivory rate, whereas a number of litter traits (the leaf mass per area, lignin to nitrogen ratio, and condensed tannin concentration) accurately predicted the decomposition rate across species. These results suggest that herbivory rate across species may not be strongly related to single leaf traits, probably because plant—herbivore interactions in tropical rain forests are highly diverse; on the other hand, plant—decomposer interactions are less specific and can be governed by litter chemicals. We also investigated two factors, phylogeny and tree functional types, that could affect the relationship between herbivory and decomposition across species. Phylogenetic relatedness among the species did not affect the relationship between herbivory and decomposition. In contrast, when the plants were segregated according to their leaf emergence pattern, we found a significant positive relationship between herbivory and decomposition rates for continuous-leafing species. In these species, the condensed tannin to N ratios in leaves and litter were related to herbivory and decomposition rates, respectively. However, we did not observe a similar trend for synchronous-leafing species. These results suggest that the relationship between herbivory and decomposition may be more greatly affected by functional types than by phylogenetic relatedness among species. In conclusion, our results suggest that well-defended leaves are not necessarily less decomposable litter in a tropical rain forest community, implying that herbivory may not generate positive feedback for carbon and nutrient cycling in this type of ecosystem.

1. Habitat filtering and limiting similarity have been proposed as two opposing forces structuring community memberships. Community assembly theory proposes habitat filtering as a mechanism restricting community membership according to the ecological strategies of species in a given environment. Limiting similarity posits that some species exclude others that are ecologically similar. 2. We quantified nine ecophysiological and life‐history traits for 80 dipterocarp species in the 52‐ha Lambir Forest Dynamics Plot (FDP; Lambir Hills National Park, Sarawak, Malaysia). We studied forests on four soil types differing in fertility and moisture, focusing on soil resource availabilities as environmental determinants of habitat filtering processes. We used a null‐model approach to detect the strengths of habitat filtering and limiting similarity. We quantified the relative contributions of soil resources (nutrients and water) to habitat filtering by comparing the strength of habitat filtering processes (i.e. effect sizes) at the overall plot scale and at the individual soil‐type scale. We also compared the strengths of assembly processes among soil types. 3. Compared to a null model at microscale (20 × 20 m), trait range and variance were reduced for seven of nine functional traits, suggesting the importance of habitat filtering in the dipterocarp community. We also found a broader distribution of five traits, and more even spacing for seven traits (20 × 20 m), which is consistent with the concept of limiting similarity. Randomizations that swapped species occurrences within soil types (i.e. null models removing soil effects in assembly processes) were much closer to observed values, and there were no phylogenetic constraints on habitat association. Hence, soil resource availability acted as a habitat filtering mechanism in the FDP; relative contributions to habitat filtering ranged from 35% for seed mass to 77% for relative growth rate. Furthermore, soil types apparently affected the strengths of habitat filtering and limiting similarity. 4. Synthesis. We demonstrate that soil resource availability is a crucial determinant of habitat filtering in this species‐rich tropical rain forest; the strengths of assembly processes differed among soil types. Variation in soil resource availability can shape the distribution of traits through community assembly processes, promoting trait diversification and species coexistence.

1. Non-native invasive and nitrogen (N)-fixing plant species can cause large ecosystem-level impacts, particularly when they differ in functionally important plant traits from native and non N-fixing species. However, it remains unclear as to whether and how plant invasion status and Í fixation ability consistently influence key plant leaf and litter traits, and trait-driven processes like herbivory and decomposition. 2. We compared leaf and litter traits, leaf palatability and litter decomposability for 41 co-occurring woody species, including native N-fixers, native non N-fixers, invasive N-fixers and invasive non N-fixers, from a New Zealand floodplain. We tested the hypotheses that: (i) invasive and N-fixing species have higher foliar Í and specific leaf area, and lower concentrations of defensive phenolics and structural compounds than do native and non N-fixing species, and (ii) invasive and N-fixing species generally produce more decomposable litter and palatable foliage than do native and non N-fixing species. 3. Consistent with our hypotheses, invaders had higher foliar N and N : P ratio, and lower C : N ratio, than did native species. However, in contrast to our hypotheses, foliar phenolics were higher for the invaders while other leaf and litter traits were unaffected by invasion status. Further, N-fixers had higher Í and Í : Ñ ratios, and lower C : N ratios than did non N-fixers, but other leaf and litter traits were unaffected by Í fixation ability. 4. Leaf palatability was unaffected by invasion status but was higher for N-fixers than for non N-fixers. Litter decomposability was unaffected both by invasion status and N fixation ability. We found a significant positive relationship between leaf palatability and litter decomposability across all species, because similar traits, particularly the C : P ratio and total phenolic concentrations of plant tissues, were correlated with both processes. 5. Our results demonstrate that a small number of key traits, such as C : P ratio and total phenolic concentrations, drive both herbivory and decomposition irrespective of plant invasion status or N fixation ability. As such, they highlight that interspecific differences in particular plant traits, rather than plant functional group memberships based on invasion status and N fixation ability, are more effective in predicting palatability and decomposability.

Alpine and subalpine moorland communities have been altered by global warming and associated environmental changes. Vegetation changes in moorlands are of concern given the loss of biodiversity, especially among endemic biota, and the potential degradation of important ecosystem services, such as climate regulation and recreation. Although long-term analyses of vegetation data are urgently needed to assess potential vegetation shifts over the past century, when global warming has accelerated, such data are rarely available. In this study, we resurveyed historical moorland plots in 2020, which were surveyed once in 1933, in subalpine ecosystems in northern Japan that have been subjected to little direct human disturbance. We observed a landscape-wide increase in the occurrence of woody species and non-moorland species despite potential resampling errors. Such vegetation changes in moorlands are notable because they have occurred in parallel with the accelerating global warming. Warming can lead to an extended growing season and peat drying, which would explain the changes in vegetation that we observed. We thus provide valuable insights into the very long-term (over 90 years) changes in moorland plant communities. Our study fills a knowledge gap in the inferences of global change effects on mountainous moorlands and adds to the growing evidence that solutions are needed to mitigate the effects of climate change.

Accurate estimation of tree and forest biomass is key to evaluating forest ecosystem functions and the global carbon cycle. Allometric equations that estimate tree biomass from a set of predictors, such as stem diameter and tree height, are commonly used. Most allometric equations are site specific, usually developed from a small number of trees harvested in a small area, and are either species specific or ignore interspecific differences in allometry. Due to lack of site-specific allometries, local equations are often applied to sites for which they were not originally developed (foreign sites), sometimes leading to large errors in biomass estimates. In this study, we developed generic allometric equations for aboveground biomass and component (stem, branch, leaf, and root) biomass using large, compiled data sets of 1203 harvested trees belonging to 102 species (60 deciduous angiosperm, 32 evergreen angiosperm, and 10 evergreen gymnosperm species) from 70 boreal, temperate, and subtropical natural forests in Japan. The best generic equations provided better biomass estimates than did local equations that were applied to foreign sites. The best generic equations included explanatory variables that represent interspecific differences in allometry in addition to stem diameter, reducing error by 4-12% compared to the generic equations that did not include the interspecific difference. Different explanatory variables were selected for different components. For aboveground and stem biomass, the best generic equations had species-specific wood specific gravity as an explanatory variable. For branch, leaf, and root biomass, the best equations had functional types (deciduous angiosperm, evergreen angiosperm, and evergreen gymnosperm) instead of functional traits (wood specific gravity or leaf mass per area), suggesting importance of other traits in addition to these traits, such as canopy and root architecture. Inclusion of tree height in addition to stem diameter improved the performance of the generic equation only for stem biomass and had no apparent effect on aboveground, branch, leaf, and root biomass at the site level. The development of a generic allometric equation taking account of interspecific differences is an effective approach for accurately estimating aboveground and component biomass in boreal, temperate, and subtropical natural forests.

1. Land-use change can modify the functional composition of tree communities, which is an essential determinant of the ecosystem functions. The lack of consensus about the functional responses of tree communities to land-use change is a major uncertainty in the assessments of human impacts on terrestrial ecosystem functions. 2. In this study, we applied a machine-learning method to a large data set consisting of 2574 tree communities across Japan to examine changes in the functional composition of tree communities after land-use change while considering contexts including successional trajectories, forest types and the presence of gymnosperms. Specifically, we hypothesized that functional changes along successional gradients after land-use change can be different in different contexts. 3. Effects of two successional variables (stand age and basal area) on functional composition were highly significant throughout the study region. Changes in functional composition with changes in the two successional variables differed greatly, and the effects of basal area often outweighed those of stand age. 4. Tree communities with small basal area were generally characterized by functional traits related to the resource-acquisitive strategy, that is short adult stature, low leaf mass per unit area, small seeds, low wood density and large leaves, especially when gymnosperms were excluded from the analysis. Decreasing basal area but not decreasing stand age often led to a considerable loss in functional diversity. Despite these general trends, functional changes along successional gradients after land-use change were not necessarily parallel and the opposite patterns were sometimes observed among forest types, traits and taxonomic groups. 5. Synthesis. As a whole, our analyses demonstrate that the functional changes in tree communities after land-use change are highly evident in a given context but can be different under different contexts. These changes in functional composition can trigger variable changes in ecosystem functions such as carbon and nutrient cycling that depend on the context.