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Shallow soil with low water availability, poor nutrition, and limited living space is the key limiting factor of plant growth and reproduction in vulnerable karst regions. As pioneers adapted to these areas, little is known about the reproductive responses of annual herbs to these limited soil resources. In this study, we, therefore, investigated the reproductive strategies (“fight or flight”) of two annual Asteraceae herbs (Xanthium sibiricum and Bidens pilosa) growing in the harsh karst soil environment, by comprehensively considering biomass allocation, reproductive phenology, and seed production. X. sibiricum and B. pilosa were grown under three soil depths and three water availability levels in a full two-way randomized block design, then biomass allocation, initial flowering time, fruiting stage, life span and seed number and mass were examined. In X. sibiricum, reproductive allocation decreased with decreasing water availability, soil depth, and water availability + soil depth. Meanwhile, the initial flowering time, fruiting stage and life span were all delayed with moderate decreases in resources. However, in B. pilosa, reproductive allocation increased with decreasing soil resources, while initial flowering time, fruiting stage and life span remained unchanged under moderate resource decline. Under severe resource decline, both species showed a reduction in fruiting stage and life span. These results support the hypothesis that X. sibiricum tends to adopt a “fight” reproductive strategy in response to declining resources via changes in biomass allocation, reproductive phenology and seed production. In contrast, B. pilosa tends to adopt a “flight” strategy in terms of biomass allocation, while maintaining a relatively stable reproductive phenology and seed size to cope with the harsh living conditions. However, neither species coped well under severe declines in water availability, nutrition and living space. These findings help our understanding of how herbaceous plants can adjust their reproductive strategies to support their regeneration in harsh karst soil environments.

Aims The mechanism by which species diversity drives productivity in different ecosystems is controversial, possibly due to the confounding effects of key environmental variables. Karst ecosystems are fragile and are at great risk of species loss. In these ecosystems, soil depth is a key driver of community diversity and productivity. However, the influence of soil depth on the relationship between species diversity and productivity in karst ecosystems remains unclear.Methods We established artificial karst herbaceous communities with different soil depths and species richness levels and determined how two biodiversity effects—complementarity effect (effect of positive interactions among species) and selection effect (effect due to dominance of productive species)—contributed to productivity.Results Soil depth, species diversity, and different species combinations were significant predictors of productivity. Species diversity significantly positively affected productivity at all three soil depths, with the effect size of species diversity being the greatest in medium-depth soil. Net diversity effects were greater than 0 in all multi-species communities, indicating that complementarity and selection effects both positively influenced productivity. However, complementarity effect had a greater contribution to productivity than selection effect in all multi-species communities. Furthermore, the contribution of complementarity effect increased with increasing soil depth, while that of selection effect decreased.Conclusions Soil depth influences the relationship between species diversity and productivity in karst herbaceous communities. Furthermore, complementarity effect is the major mechanism by which diversity increases community productivity, particularly in shallow soil. Therefore, environmental variables should be seriously considered when studying the relationship between species diversity and function in other ecosystems.

Seedling emergence and establishment are fragile processes that determine the direction and structure of forest succession and regeneration. However, seedling emergence and establishment are easily affected by biotic and abiotic (environmental) factors. A dense and expanding understory of dwarf bamboo is one such important factor that can seriously hinder the seedling regeneration. We conducted a field experiment to investigate the emergence and establishment of canopy tree seedlings under artificially controlled densities of dwarf bamboo. We found that understory dwarf bamboo obstructed seedling emergence but reduced the death of seedlings. Although understory dwarf bamboo reduced the median retention time of seedlings, dense bamboo increased the mean survival time of seedlings. Our results suggest that understory dwarf bamboo has multiple selectivities for tree seedling emergence and establishment: high‐density dwarf bamboo was beneficial to evergreen species but lower‐density of bamboo was conducive to the survival of deciduous species, it means the dwarf bamboo potentially alters successional trajectories of forest communities. Path analysis revealed that the most important factors affecting tree seedling emergence and death were the abundance of seeds in the seed bank and the density of emerged seedlings, and that the soil temperature promoted seedling emergence but increased seedling death, the thickness of litter limited seedling emergence, and the leaf area index of the bamboo canopy limited seedling death. The present study suggests that dwarf bamboo can directly alter the microenvironment, significantly reducing light levels and soil temperature but increasing the thickness of litter and soil humus, thereby indirectly impacting the regeneration of tree seedlings. Our results indicate that various factors affected seedling emergence, and there were complex indirect relationships among these factors. In general, biological factors had a stronger influence on tree seedling regeneration than environmental factors., Understory dwarf bamboo is expanding rapidly and resulting in irregular bamboo shrub layer formation in forests. This was not only can alter the ground surface environment (such as light, thickness of litter, thickness of soil humus, soil temperature, and soil humidity), but also slowed down the speed and density of seedling emergence, and accelerated the rate of seedling death; it has inhibited the establishment of local woody species, acting as an “ecological filter” in forest regeneration. And the multivariate path analysis showed that seed bank and soil temperature were the most important decision factors affecting seedling emergence, and the density of emerged seedling was the decision factor for seedling mortality, exerting a density dependence effect, while the litter thickness, leaf area index with dwarf bamboo canopy and dwarf bamboo density were the key limitation factors for seedling mortality, and soil temperature is the important promoting factor for seedling death.

Resource availability and heterogeneity are recognized as two essential environmental aspects to determine species diversity and community abundance. However, how soil resource availability and heterogeneity determine species diversity and community abundance in highly heterogeneous and most fragile karst landscapes is largely unknown. We examined the effects of soil resource availability and heterogeneity on plant community composition and quantified their relative contribution by variation partitioning. Then, a structural equation model (SEM) was used to further disentangle the multiple direct and indirect effects of soil resource availability on plant community composition. Species diversity was significantly influenced by the soil resource availability in shrubland and woodland but not by the heterogeneity in woodland. Abundance was significantly affected by both soil resource availability and heterogeneity, whereas variation partitioning results showed that soil resource availability explained the majority of the variance in abundance, and the contribution of soil resource heterogeneity was marginal. These results indicated that soil resource availability plays a more important role in determining karst plant community composition than soil resource heterogeneity. Our SEMs further found that the multiple direct and indirect processes of soil resource availability in determining karst species diversity and abundance were different in different vegetation types. Soil resource availability and heterogeneity both played a certain role in determining karst plant community composition, while the importance of soil resource availability far exceeded soil resource heterogeneity. We propose that steering community restoration and reconstruction should be highly dependent on soil resource availability, and multiple direct and indirect pathways of soil resource availability for structuring karst plant communities need to be taken into account., Both limited resource availability and significant resource heterogeneity are key features of karst landscapes. Our study first considered simultaneously resource availability and heterogeneity in karst regions and then quantified and compared the effects of resource availability and heterogeneity on community abundance and species diversity from the relevance‐theoretic perspective. More importantly, our study has important guiding significance to the vegetation restoration.

Woody debris (WD) represents a globally significant carbon stock and its decomposition returns nutrients to the soil while providing habitat to microbes, plants and animals. Understanding what drives WD decomposition is therefore important. WD decomposition rates differ greatly among species. However, the role of bark in the process remains poorly known. We ask how, and how much, interspecific variation in bark functional traits related to growth and protection have afterlife effects on the decomposition of wood, partly mediated by animals. We examine the roles of bark cover and bark traits throughout the wood decomposition process. Synthesis. We find that: (1) bark effects on WD decomposition are species- and wood size-specific, (2) bark can enhance coarser WD decomposition but slows twig decomposition in some species, and (3) bark acts as an environmental filter to faunal assemblages in the early stage of wood decomposition. We highlight the need to account for bark effects on WD decomposition and offer an important complementary contribution to including woody species identity effects in biogeochemical and climate-change models via species bark traits.

Understory plant root proliferation into the litter layer occurs in many forest ecosystems and dramatically accelerates litter decomposition and nutrient release in the early stages. Mechanical fragmentation of leaf litter by fine roots could be one main reason, but its mechanism is poorly understood. To quantitatively assess the influence of fine roots on the mechanical fragmentation of leaf litter in the early decomposition process, we examined the effects of fine root mass of Lolium multiflorum on morphological and physical characteristics of decomposing litters of Symplocos setchuensis, a dominant species in a mid-subtropical evergreen broad-leaved forest of China, via a litter bag simulation experiment. The results showed that there were various fine root growth forms in/on decomposing litters, including the penetration and tearing of leaf epidermis, and the “walking or inserting” between the mesophyll tissue and the leaf veins. Fine root mass had a significant positive effect on the mass loss during litter decomposition (F = 8.543, P

Tree seed retention is thought to be an important factor in the process of forest community regeneration. Although dense understory dwarf bamboo has been considered to have serious negative effects on the regeneration of forest community species, little attention has been paid to the relationship between dwarf bamboo and seed retention. In a field experiment we manipulated the density of Fargesia decurvata, a common understory dwarf bamboo, to investigate the retention of seeds from five canopy tree species in an evergreen and deciduous broad-leaved mixed forest in Jinfoshan National Nature Reserve, SW China. We found that the median survival time and retention ratio of seeds increased with the increase in bamboo density. Fauna discriminately altered seed retention in bamboo groves of different densities. Arthropods reduced seed survival the most, and seeds removed decreased with increasing bamboo density. Birds removed or ate more seeds in groves of medium bamboo density and consumed fewer seeds in dense or sparse bamboo habitats. Rodents removed a greater number of large and highly profitable seeds in dense bamboo groves but more small and thin-husked seeds in sparse bamboo groves. Seed characteristics, including seed size, seed mass and seed profitability, were important factors affecting seed retention. The results suggested that dense understory dwarf bamboo not only increased seeds concealment and reduced the probability and speed of seed removal but also influenced the trade-off between predation and risk of animal predatory strategies, thereby impacting the quantity and composition of surviving seeds. Our results also indicated that dense understory dwarf bamboo and various seed characteristics can provide good opportunities for seed storage and seed germination and has a potential positive effect on canopy tree regeneration. (C) 2016 Elsevier Masson SAS. All rights reserved.

Karst rocky outcrops divert water into the surrounding soil patches in a phenomenon known as the “funnel” effect. Soil depth is a key limiting factor in vegetation restoration in karst landscapes, yet few studies have examined the influence of the karst rock funnel effect on soil-limited plant community assemblages and productivity. We established artificial herbaceous communities with seeds from a karst species pool to evaluate how the species composition and productivity of karst herbaceous communities respond to soil depth and the funnel effect. Three months after species establishment, we found that all artificial communities were dominated by two grasses, Miscanthus sinensis and Lolium multiflorum. Plant abundance increased significantly with increasing soil depth, mainly owing to an increase in the individual numbers of the dominant species. The community coverage, photosynthetically active radiation (PAR) canopy capture rate, and shoot, root and total biomass also increased significantly with increasing soil depth. Funnel size and the soil depth × funnel size interaction significantly affected root biomass and root/shoot ratio; however, there was no effect of funnel size or the soil depth × funnel size interaction on species abundance, species richness and diversity, coverage, PAR canopy capture rate, shoot biomass, or total biomass. Therefore, this microcosm experiment provides evidence that the species composition and productivity of karst herbaceous communities are shaped by soil depth. The supply of water via the funnelling effect from karst rocky outcrops did not significantly affect herbaceous community assemblages or productivity, except in terms of root biomass. We suggest that the conservation and development of soil resources in environments with karst rocky outcrops may be more effective for the restoration of karst herbaceous communities than ensuring an adequate water supply.

Karst rocky desertification (KRD) is a process of land degradation, which causes desert-like landscapes, deconstruction of endemic biomass, and declined soil quality. The relationship of KRD progression with above-ground communities (e.g. vegetation and animal) is well-studied. Interaction of soil desertification with underground communities, such as soil microbiome, however, is vastly unknown. This study characterizes change in soil bacterial community in response to KRD progression. Soil bacterial communities were surveyed by deep sequencing of 16S amplicons. Eight soil properties, pH, soil organic matter (SOM), total and available nitrogen (TN and AN), total and available phosphorus (TP and AP), and total and available potassium (TK and AK), were measured to assess soil quality. We find that the overall soil quality decreases along with KRD progressive gradient. Soil bacterial community compositions are distinguishingly different in KRD stages. The richness and diversity in bacterial community do not significantly change with KRD progression although a slight increase in diversity was observed. A slight decrease in richness was seen in SKRD areas. Soil pH primarily correlates with bacterial community composition. We identified a core microbiome for KRD soils consisting of; Acidobacteria, Alpha-Proteobacteria, Planctomycetes, Beta-Proteobacteria, Actinobacteria, Firmicutes, Delta-Proteobacteria, Chloroflexi, Bacteroidetes, Nitrospirae, and Gemmatimonadetes in this study. Phylum Cyanobacteria is significantly abundant in non-degraded soils, suggesting that Cyanobacterial activities might be correlated to soil quality. Our results suggest that Proteobacteria are sensitive to changes in soil properties caused by the KRD progression. Alpha- and beta-Proteobacteria significantly predominated in SKRD compared to NKRD, suggesting that Proteobacteria, along with many others in the core microbiome (Acidobacteria, Actinobacteria, Firmicutes, and Nitrospirae), were active in nutrient limiting degraded soils. This study demonstrates the relationship of soil properties with bacterial community in KRD areas. Our results fill the gap of knowledge on change in soil bacterial community during KRD progression.

Aim? The drivers of species assembly, by limiting the possible range of functional trait values, can lead to either convergent or divergent distributions of traits in realized assemblages. ...

Aims Many researches have shown that the interlaced roots of dwarf bamboo (Fargesia nitida) can influence the regeneration of trees and the growth of seedlings and saplings through competition for light, water and nutrients. We explore the effect of dwarf bamboo on the regeneration of Abies faxoniana on the forest edge and estimate the effect of dwarf bamboo on the dispersal and community development. We asked: 1) how will quantitative characteristics and population structure change under different densities of F. nitida, and 2) how will the density of F. nitida influence the growth and biomass allocation of A. faxoniana seedlingsMethods We sampled five belt transects and analyzed 30 plots within each transect in Wolong Giant Panda Nature Reserve (30°51′41″ N,102°58′21″ E) during August and September 2005. The transects were selected based on different densities of F. nitida (i.e., distance to the F. nitida cluster): 2 m outside the cluster (Zone 1), 1 m outside the cluster (Zone 2), 1 m inside the cluster (Zone 3), 2 m inside the cluster (Zone 4) and 3 m inside the cluster (Zone 5). We measured the height, basal diameter and crown of each A. faxoniana seedling. We used five BD classes: Ⅰ (0BD0.3 cm), Ⅱ (0.3 cm≤BD0.6 cm), Ⅲ (0.6 cm≤BD0.9 cm), Ⅳ (0.9 cm≤BD1.2 cm), Ⅴ (BD≥1.2 cm), and five size classes: Ⅰ (0H15 cm), Ⅱ (15 cm≤H30 cm), Ⅲ (30 cm≤H45 cm), Ⅳ (45 cm≤H60 cm), and Ⅴ (H≥60 cm). The seedlings were divided into two groups, large (H0.2 m) and small (H≤0.2 m), to explore the accumulation and allocation of biomass by A. faxoniana seedlings. We obtained data on biomass from regression equations based on a sample of 60 A. faxoniana seedlings.Important findings Regeneration and growth of A. faxoniana seedlings were restrained in the F. nitida-dominated zones, and dispersal of the A. faxoniana population and development of an A. faxoniana-dominated community were affected. Closer to F. nitida clusters, the number of old seedlings and the efficiency of transformation (seedling number ratio of the next BD class to the preceding BD class) were reduced (the older the A. faxoniana seedlings, the smaller the efficiency of transformation); the peak of number of seedlings moved from larger (Ⅲ) to the smallest size (Ⅰ); the total biomass and allocation of biomass aboveground of A. faxoniana seedlings decreased; and the presence of F. nitida restrained the height growth of small (Ⅰ) A. faxoniana seedlings (confirmed by regression of basal diameter and height). The expansion of crowns of bigger (Ⅲ) seedlings increased in moderate density (Zone 4) of F. nitida.

Forest structure and succession in Wolong Nature Reserve is influenced by the understory dwarf bamboo population. However, less is known about how the forest succession affects the dwarf bamboo population. To examine the bamboo ramet population growth of Fargesia nitida (Mitford) Keng f. et Yi and to determine how ramet population structure varies along the succession of coniferous forest, we sampled ramet populations of F. nitida from the following three successional stages: (i) a deciduous broad-leaved (BL) stand; (ii) a mixed broad-leaved coniferous (MI) stand; and (iii) a coniferous (CF) stand. We investigated the population structure, biomass allocation, and morphological characteristics of the bamboo ramet among the three stand types. Clonal ramets, constituting the bamboo population, tended to become short and small with succession. The ramet changed towards having a greater mass investment in leaves, branches and underground roots and rhizomes rather than in the culm. With respect to leaf traits, individual leaf mass and area in the BL stand were markedly bigger than those in both the MI and CF stands, except for no significant difference in specific leaf area. The age distribution showed that the bamboo population approached an older age with succession. The results demonstrate that the ramet population structure of F. nitida is unstable and its growth performance is inhibited by succession. (Managing editor: Ya-Qin Han)

According to the forest-growth-cycle theory, forest communities are dynamic, mosaic systems composed of patches in different developmental phases. Based on an investigation in a sample of tropical montane rain forest of Hainan Island in South China, four distinct growth phases or patch types were recognized and patterns of patch mosaics and changes in tree species diversity were studied. Diurnal changes in light and temperature regimes in different patch types of the forest growth cycle were measured and analysed. Our results were as follows: (1) The percentages of different patch types within the sampled forest community were for the gap phase 38.5%, building phase 28.5%, mature phase 27.0% and degenerate phase 6.0%; (2) The change of densities (number of individuals/ha) of trees in the forest growth cycle was mainly caused by the larger sized trees; (3) The changes of species diversity with the forest growth cycle showed a humpback pattern; (4) The average DBH, average height, average basal area at DBH, and average volume of each individual and stand volume all increased with the forest cycle process; (5) Tree species richness and tree density at each phase of the forest cycle were positively correlated; (6) The environmental factors changed significantly, both diurnally and with progress of the forest cycle. Light intensity and soil surface temperature changed more in the gap phase than the other three phases. A framework to explain the mechanism for maintaining biological diversity within the tropical montane forest of Hainan Island is described.

Conceptual frameworks relating plant traits to ecosystem processes such as organic matter dynamics are progressively moving from a leaf-centred to a whole-plant perspective. Through the use of meta-analysis and global literature data, we quantified the relative roles of litters from above- and below-ground plant organs in ecosystem labile organic matter dynamics. We found that decomposition rates of leaves, fine roots and fine stems were coordinated across species worldwide although less strongly within ecosystems. We also show that fine roots and stems had lower decomposition rates relative to leaves, with large differences between woody and herbaceous species. Further, we estimated that on average below-ground litter represents approximately 33 and 48% of annual litter inputs in grasslands and forests, respectively. These results suggest a major role for below-ground litter as a driver of ecosystem organic matter dynamics. We also suggest that, given that fine stem and fine root litters decompose approximately 1.5 and 2.8 times slower, respectively, than leaf litter derived from the same species, cycling of labile organic matter is likely to be much slower than predicted by data from leaf litter decomposition only. Synthesis. Our results provide evidence that within ecosystems, the relative inputs of above- versus below-ground litter strongly control the overall quality of the litter entering the decomposition system. This in turn determines soil labile organic matter dynamics and associated nutrient release in the ecosystem, which potentially feeds back to the mineral nutrition of plants and therefore plant trait values and plant community composition. © 2013 The Authors. Journal of Ecology © 2013 British Ecological Society.