Saori Fujii

Biotic homogenization and differentiation of soil faunal communities in the production forest landscape: taxonomic and functional perspectives

Biotic homogenization has been reported worldwide. Although simplification of communities across space is often significant at larger scales, it could also occur at the local scale by changing biotic interactions. This study aimed to elucidate local community processes driving biotic homogenization of soil faunal communities, and the possibility of biotic re-differentiation. We recorded species of oribatid mites in litter and soil layers along a gradient of forest conversion from monoculture larch plantation to primary forests in central Japan. We collected data for functional traits of the recorded species to quantify functional diversity. Then we quantified their taxonomic/functional turnover. Litter diversity was reduced in the larch-dominated stands, leading to habitat homogenization. Consequently, litter communities were biologically homogenized and differentiated in the plantations and in the natural forest, respectively. Turnover of functional traits for litter communities was lower and higher than expected by chance in the plantations and in the natural stand, respectively. This result suggests that the dominant assembly process shifts from limiting similarity to habitat filtering along the forest restoration gradient. However, support for such niche-based explanations was not observed for communities in the soil layer. In the monocultures, functional diversity expected from a given regional species pool significantly decreased for litter communities but not for those in the soil layer. Such discrepancy between communities in different layers suggests that communities more exposed to anthropogenic stresses are more vulnerable to the loss of their functional roles. Our study explains possible community processes behind the observed patterns of biological organization, which can be potentially useful in guiding approaches for restoring biodiversity.

Low multifunctional redundancy of soil fungal diversity at multiple scales

Theory suggests that biodiversity might help sustain multiple ecosystem functions. To evaluate possible biodiversity-multifunctionality relationships in a natural setting, we considered different spatial scales of diversity metrics for soil fungi in the northern forests of Japan. We found that multifunctionality increased with increasing local species richness, suggesting a limited degree of multifunctional redundancy. This diversity-multifunctionality relationship was independent of the compositional uniqueness of each community. However, we still found the importance of community composition, because there was a positive correlation between community dissimilarity and multifunctional dissimilarity across the landscape. This result suggests that functional redundancy can further decrease when spatial variations in identities of both species and functions are simultaneously considered at larger spatial scales. We speculate that different scales of diversity could provide multiple levels of insurance against the loss of functioning if high-levels of local species diversity and compositional variation across locations are both maintained. Alternatively, making species assemblages depauperate may result in the loss of multifunctionality.

Null model approaches to evaluating the relative role of different assembly processes in shaping ecological communities

Various local processes simultaneously shape ecological assemblages. β-diversity is a useful metric for inferring the underlying mechanisms of community assembly. However, β-diversity is not independent of γ-diversity, which may mask the local mechanisms that govern community processes across regions. Recent approaches that rely on an abundance-based null model could solve this sampling issue. However, if abundance varies widely across a region, the relative roles of deterministic and stochastic processes may be substantially misestimated. Furthermore, there is additional uncertainty as to whether null models used to correct γ-dependence in β-diversity should be independent of the observed patterns of species abundance distributions or whether the models should reflect these patterns. Here, we aim to test what null models with various constraints imply about the underlying processes shaping β-diversity. First, we found that an abundance-driven sampling effect could substantially influence the calculation of γ-corrected β-diversity. Second, we found that the null models that preserve the species abundance patterns could better reflect empirical patterns of spatial organization of individuals. The different implications generated from different applications of the null model approach therefore suggest that there are still frontiers regarding how local processes that shape species assemblages should be quantified. Carefully exploring each facet within different assembly processes is important.

A stronger coordination of litter decomposability between leaves and fine roots for woody species in a warmer region

Key messageThere is a positive correlation between leaf and root decomposition across species, both in a warm-temperate forest in Japan, as well as globally.AbstractEvaluating the effects of plant species traits on litter decomposition would increase our understanding of plant–soil feedbacks in forest ecosystems. Currently, an assessment of a possible coordination between leaf and root decomposition across different species is required. However, previous studies have generated conflicting results. We hypothesized that such inconsistencies may be attributed to differences in local climatic effects on the decomposition process. We focused on the linkages between leaf and fine-root decomposition of woody species in a warm-temperate forest, which have not been addressed in previous studies. We found a significant positive correlation between leaf and root decomposition, and this linkage may be attributed to a wider range of decomposition rates across the species in our study forest. Additionally, we combined our data with those of previous studies of woody species to infer a global linkage in the decomposition process between leaves and roots. We found a positive correlation in decomposition rates between leaves and roots at the global scale, as well as a relatively strong correlation in warmer regions. These results support the importance of litter quality on biogeochemical processes and suggest that synergetic interactions between climate and plant communities could be amplified in a warmer future.

A quantitative protocol for DNA metabarcoding of springtails (Collembola).

We developed a novel protocol with superior quantitative analysis results for DNA metabarcoding of Collembola, a major soil microarthropod order. Degenerate PCR primers were designed for conserved regions in the mitochondrial cytochrome c oxidase subunit I (mtCOI) and 16S ribosomal RNA (mt16S) genes based on published collembolan mitogenomes. The best primer pair was selected based on its ability to amplify each gene, irrespective of the species. DNA was extracted from 10 natural communities sampled in a temperate forest (with typically 25-30 collembolan species per 10 soil samples) and 10 mock communities (with seven cultured collembolan species). The two gene regions were then amplified using the selected primers, ligated with adapters for 454 technology, and sequenced. Examination of the natural community samples showed that 32 and 36 operational taxonomic units (defined at a 90% sequence similarity threshold) were recovered from the mtCOI and mt16S data, respectively, which were comparable to the results of the microscopic identification of 25 morphospecies. Further, sequence abundances for each collembolan species from the mtCOI and mt16S data of the mock communities, after normalization by using a species as the internal control, showed good correlation with the number of individuals in the samples (R = 0.91-0.99), although relative species abundances within a mock community sample estimated from sequences were skewed from community composition in terms of the number of individuals or biomass of the species. Thus, this protocol enables the comparison of collembolan communities in a quantitative manner by metabarcoding.

Seasonal ozone uptake by a warm-temperate mixed deciduous and evergreen broadleaf forest in western Japan estimated by the Penman-Monteith approach combined with a photosynthesis-dependent stomatal model.

Canopy-level stomatal conductance over a warm-temperate mixed deciduous and evergreen broadleaf forest in Japan was estimated by the Penman-Monteith approach, as compensated by a semi-empirical photosynthesis-dependent stomatal model, where photosynthesis, relative humidity, and CO2 concentration were assumed to regulate stomatal conductance. This approach, using eddy covariance data and routine meteorological observations at a flux tower site, permits the continuous estimation of canopy-level O3 uptake, even when the Penman-Monteith approach is unavailable (i.e. in case of direct evaporation from soil or wet leaves). Distortion was observed between the AOT40 exposure index and O3 uptake through stomata, as AOT40 peaked in April, but with O3 uptake occurring in July. Thus, leaf pre-maturation in the predominant deciduous broadleaf tree species (Quercus serrata) might suppress O3 uptake in springtime, even when the highest O3 concentrations were observed.

Ecological consequences through responses of plant and soil communities to changing winter climate

Community processes are now undergoing substantial reconfiguration because of climate change. Although the effects of climate change on ecosystems are currently a major concern, the issues tightly associated with winter climate change have been underrepresented. Given the importance of winter climate variables and events for determining the spatial distribution of communities and their phenological and physiological responses, and the functional roles of each species, all of which are expected to substantially influence community dis/re-assemble in the future, this review focuses on the ecological responses and consequences of terrestrial communities to changing winter climate. In particular, the effects on processes supported by biological interactions are largely undetermined. In this context, focusing on plant–soil feedback as a major interactive multi-system is worthwhile; these interactions can be disentangled through careful evaluation of the functional roles of organisms involved in the feedback (i.e., plants and soil organisms). The underlying mechanisms are indeed complex because direct (i.e., changes in physical conditions) and indirect pathways (i.e., plant-mediated influences on soil-organisms and vice versa) from winter climate change influence the functionality of future ecosystems. To face these issues, the framework of response–effect-traits deserves research priority since this can define community re-organization as the accumulated responses of individual species, which determines the stability and performance of ecosystem functioning. Thus, research that quantifies functional responses and roles of organisms under a changing climate will continue to be essential for the issues of winter climate change, which may become more serious and significant in the near future.

Concordance and discordance between taxonomic and functional homogenization: responses of soil mite assemblages to forest conversion.

The compositional characteristics of ecological assemblages are often simplified; this process is termed “biotic homogenization.” This process of biological reorganization occurs not only taxonomically but also functionally. Testing both aspects of homogenization is essential if ecosystem functioning supported by a diverse mosaic of functional traits in the landscape is concerned. Here, we aimed to infer the underlying processes of taxonomic/functional homogenization at the local scale, which is a scale that is meaningful for this research question. We recorded species of litter-dwelling oribatid mites along a gradient of forest conversion from a natural forest to a monoculture larch plantation in Japan (in total 11 stands), and collected data on the functional traits of the recorded species to quantify functional diversity. We calculated the taxonomic and functional β-diversity, an index of biotic homogenization. We found that both the taxonomic and functional β-diversity decreased with larch dominance (stand homogenization). After further deconstructing β-diversity into the components of turnover and nestedness, which reflect different processes of community organization, a significant decrease in the response to larch dominance was observed only for the functional turnover. As a result, there was a steeper decline in the functional β-diversity than the taxonomic β-diversity. This discordance between the taxonomic and functional response suggests that species replacement occurs between species that are functionally redundant under environmental homogenization, ultimately leading to the stronger homogenization of functional diversity. The insights gained from community organization of oribatid mites suggest that the functional characteristics of local assemblages, which support the functionality of ecosystems, are of more concern in human-dominated forest landscapes.

Ungulates decelerate litter decomposition by altering litter quality above and below ground

Ungulates can greatly affect forest ecosystems’ functional characteristics. However, limited information is available about their influence on litter decomposition, a major ecosystem process, despite disturbance of ungulates on vegetation through selective browsing and trampling. This study focused on effects of the presence/absence of deer herbivory on decomposition of leaves and roots of three major tree species in a Hokkaido, Japan forest. Our litterbag experiment showed that litter decomposition was significantly faster for both leaves and roots in a deer exclosure than in a control site with deer herbivory. Possible factors for this slowed decomposition because of deer presence include their physical disturbance on soil through trampling. In both sites, the remaining mass of litter was positively correlated with the C:N ratio and lignin content. When analyzed for leaf litter, species with lower C:N ratio and lignin content showed lower litter mass remaining in both sites. Deer generally prefer species with a low leaf C:N ratio and lignin content; the results suggest that leaves of palatable species were less resistant to decomposition. A similar interspecific difference in decomposition was not observed for roots, most likely resulting from the small difference in root litter quality among species. In this forest, tree species with unpalatable leaves, which are becoming predominant, likely decreases leaf litter decomposition, as leaves of palatable plants decompose more rapidly. Roots, however, are not exposed to browsing, regardless of aboveground palatability, and remain within soil as a recalcitrant slowly decomposing litter substrate. These synergetic influences could allow deer herbivory to reduce overall plant decomposition rates aboveground and belowground via changes in plant species composition.

A rapid method of non-destructive DNA extraction from individual springtails (Collembola)

In this study, we describe an easy and rapid method for non-destructive DNA extraction from a single Collembola individual, without dissection, lysis of the specimen, or purification of extracted DNA. We demonstrate that, after a single specimen has been heat-treated in Tris-EDTA (TE) buffer using a standard thermocycler, the solution can be used for PCR amplification of the mitochondrial cytochrome c oxidase subunit 1 (COI) gene region, typically used for DNA barcoding. With this method, the morphological features of Collembola commonly used for species identification are well preserved. This DNA extraction method is preferable for DNA barcoding where the sequencing and preservation of a large number of small and fragile specimens are required.