The impact of grazing on biodiversity and forest succession in the Brazilian dry forest region is constrained by non-equilibrium dynamics.

The impacts of grazing on rangelands have historically been studied within the framework of the equilibrium model, which predicts significant impacts of grazing on ecosystems. However, in recent decades, studies have observed a non-equilibrium pattern, suggesting that abiotic factors play a primary role compared to grazing. These studies are primarily focused on rangelands, despite animal husbandry occurring in other biomes, such as seasonally dry tropical forests. Our study examines the influence of goat grazing on biodiversity and forest succession in the Brazilian dry forest (Caatinga). Considering its high interannual precipitation variability, we hypothesize a response that aligns with the non-equilibrium paradigm. We established a gradient of grazing intensity and history in areas at different stages of vegetation succession. A survey of tree - shrub and herbaceous species was conducted at each site and the biomass of both strata was quantified. Linear mixed models and Permanova were employed to assess differences in richness, composition, structure, and biomass among the areas. Our results suggest that grazing (history and intensity) and forest fallow age did not affect species richness, but only species composition. Low and high grazing intensity drive ecosystems toward similar compositions, which align with the non-equilibrium model predictions. Biomass in the herbaceous layer remained unaffected by grazing history, intensity, or forest fallow age, whereas woody biomass was influenced by grazing intensity in older forest fallows. Although trees in low-intensity grazing sites were significantly taller compared to those in other levels, overall, grazing did not disrupt the natural succession process. Older forest fallows exhibited greater diversity and higher basal area compared to new forest fallows, irrespective of grazing intensity. Our findings suggest that: a) grazing has minimal effects on biodiversity and biomass due to non-equilibrium dynamics, and b) with appropriate management, grazing can coexist with the conservation of the Caatinga.

Initial microbiome and tree root status structured the soil microbial community discrepancy of the subtropical pine-oak forest in a large urban forest park.

Plant-microbe-soil interactions control over the forest biogeochemical cycling. Adaptive plant-soil interactions can shape specific microbial taxa in determining the ecosystem functioning. Different trees produce heterogeneous soil properties and can alter the composition of soil microbial community, which is relevant to the forest internal succession containing contrasting stand types such as the pine-oak forests. Considering representative microbial community characteristics are recorded in the original soil where they had adapted and resided, we constructed a soil transplant incubation experiment in a series of in situ root-ingrowth cores in a subtropical pine-oak forest, to simulate the vegetational pine-oak replacement under environmental succession. The responsive bacterial and fungal community discrepancies were studied to determine whether and how they would be changed. The pine and oak forest stands had greater heterogeneity in fungi composition than bacteria. Original soil and specific tree root status were the main factors that determined microbial community structure. Internal association network characters and intergroup variations of fungi among soil samples were more affected by original soil, while bacteria were more affected by receiving forest. Specifically, dominant tree roots had strong influence in accelerating the fungi community succession to adapt with the surrounding forest. We concluded that soil microbial responses to forest stand alternation differed between microbiome groups, with fungi from their original forest possessing higher resistance to encounter a new vegetation stand, while the bacteria community have faster resilience. The data would advance our insight into local soil microbial community dynamics during ecosystem succession and be helpful to enlighten forest management.

Light competition drives species replacement during secondary tropical forest succession.

Light competition is thought to drive successional shifts in species dominance in closed vegetations, but few studies have assessed this for species-rich and vertically structured tropical forests. We analyzed how light competition drives species replacement during succession, and how cross-species variation in light competition strategies is determined by underlying species traits. To do so, we used chronosequence approach in which we compared 14 Mexican tropical secondary rainforest stands that differ in age (8-32 year-old). For each tree, height and stem diameter were monitored for 2 years to calculate relative biomass growth rate (RGR, the aboveground biomass gain per unit aboveground tree biomass per year). For each stand, 3D light profiles were measured to estimate individuals' light interception to calculate light interception efficiency (LIE, intercepted light per unit biomass per year) and light use efficiency (LUE, biomass growth per intercepted light). Throughout succession, species with higher RGR attained higher changes in species dominance and thus increased their dominance over time. Both light competition strategies (LIE and LUE) increased RGR. In early succession, a high LIE and its associated traits (large crown leaf mass and low wood density) are more important for RGR. During succession, forest structure builds up, leading to lower understory light levels. In later succession, a high LUE and its associated traits (high wood density and leaf mass per area) become more important for RGR. Therefore, successional changes in relative importance of light competition strategies drive shifts in species dominance during tropical rainforest succession.

The biological controls of soil carbon accumulation following wildfire and harvest in boreal forests: A review.

Boreal forests are frequently subjected to disturbances, including wildfire and clear-cutting. While these disturbances can cause soil carbon (C) losses, the long-term accumulation dynamics of soil C stocks during subsequent stand development is controlled by biological processes related to the balance of net primary production (NPP) and outputs via heterotrophic respiration and leaching, many of which remain poorly understood. We review the biological processes suggested to influence soil C accumulation in boreal forests. Our review indicates that median C accumulation rates following wildfire and clear-cutting are similar (0.15 and 0.20 Mg ha-1 year-1, respectively), however, variation between studies is extremely high. Further, while many individual studies show linear increases in soil C stocks through time after disturbance, there are indications that C stock recovery is fastest early to mid-succession (e.g. 15-80 years) and then slows as forests mature (e.g. >100 years). We indicate that the rapid build-up of soil C in younger stands appears not only driven by higher plant production, but also by a high rate of mycorrhizal hyphal production, and mycorrhizal suppression of saprotrophs. As stands mature, the balance between reductions in plant and mycorrhizal production, increasing plant litter recalcitrance, and ectomycorrhizal decomposers and saprotrophs have been highlighted as key controls on soil C accumulation rates. While some of these controls appear well understood (e.g. temporal patterns in NPP, changes in aboveground litter quality), many others remain research frontiers. Notably, very little data exists describing and comparing successional patterns of root production, mycorrhizal functional traits, mycorrhizal-saprotroph interactions, or C outputs via heterotrophic respiration and dissolved organic C following different disturbances. We argue that these less frequently described controls require attention, as they will be key not only for understanding ecosystem C balances, but also for representing these dynamics more accurately in soil organic C and Earth system models.

Long-term shift towards shady and nutrient-rich habitats in Central European temperate forests.

Biodiversity world-wide has been under increasing anthropogenic pressure in the past century. The long-term response of biotic communities has been tackled primarily by focusing on species richness, community composition and functionality. Equally important are shifts between entire communities and habitat types, which remain an unexplored level of biodiversity change. We have resurveyed > 2000 vegetation plots in temperate forests in central Europe to capture changes over an average of five decades. The plots were assigned to eight broad forest habitat types using an algorithmic classification system. We analysed transitions between the habitat types and interpreted the trend in terms of changes in environmental conditions. We identified a directional shift along the combined gradients of canopy openness and soil nutrients. Nutrient-poor open-canopy forest habitats have declined strongly in favour of fertile closed-canopy habitats. However, the shift was not uniform across the whole gradients. We conclude that the shifts in habitat types represent a century-long successional trend with significant consequences for forest biodiversity. Open forest habitats should be urgently targeted for plant diversity restoration through the implementation of active management. The approach presented here can be applied to other habitat types and at different spatio-temporal scales.

Fungal community structure shifts in litter degradation along forest succession induced by pine wilt disease.

Fungi play a crucial role in decomposing litter and facilitating the energy flow between aboveground plants and underground soil in forest ecosystems. However, our understanding how the fungal community involved in litter decomposition responds during forest succession, particularly in disease-driven succession, is still limited. This study investigated the activity of degrading enzyme, fungal community, and predicted function in litter after one year of decomposition in different types of forests during a forest succession gradient from coniferous to deciduous forest, induced by pine wilt disease. The results showed that the weight loss of needles/leaves and twigs did not change along the succession process, but twigs degraded faster than needles/leaves in both pure pine forest and mixed forest. In pure pine forest, peak activities of enzymes involved in carbon degradation (ß-cellobiosidase, ß-glucosidase, ß-D-glucuronidase, ß-xylosidase), nitrogen degradation (N-acetyl-glucosamidase), and organic phosphorus degradation (phosphatase) were observed in needles, which subsequently declined. The fungal diversity and evenness (Shannon's diversity and Shannon's evenness) dropped in twig from coniferous forest to mixed forest during the succession. The dominant phyla in needle/leaf and twig litters were Ascomycota (46.9%) and Basidiomycota (38.9%), with Lambertella pruni and Chalara hughesii identified as the most abundant indicator species. Gymnopus and Desmazierella showed positively correlations with most measured enzyme activities. Functionally, saprotrophs constituted the main trophic mode (47.65%), followed by Pathotroph-Saprotroph-Symbiotroph (30.95%) and Saprotroph-Symbiotroph (10.57%). The fungal community and predicted functional structures in both litter types shifted among different forest types along the succession. These findings indicate that the fungal community in litter decomposition responds differently to disease-induced succession, leading to significant shifts in both the fungal community structure and function.

Global dominance of lianas over trees is driven by forest disturbance, climate and topography.

Growing evidence suggests that liana competition with trees is threatening the global carbon sink by slowing the recovery of forests following disturbance. A recent theory based on local and regional evidence further proposes that the competitive success of lianas over trees is driven by interactions between forest disturbance and climate. We present the first global assessment of liana-tree relative performance in response to forest disturbance and climate drivers. Using an unprecedented dataset, we analysed 651 vegetation samples representing 26,538 lianas and 82,802 trees from 556 unique locations worldwide, derived from 83 publications. Results show that lianas perform better relative to trees (increasing liana-to-tree ratio) when forests are disturbed, under warmer temperatures and lower precipitation and towards the tropical lowlands. We also found that lianas can be a critical factor hindering forest recovery in disturbed forests experiencing liana-favourable climates, as chronosequence data show that high competitive success of lianas over trees can persist for decades following disturbances, especially when the annual mean temperature exceeds 27.8°C, precipitation is less than 1614 mm and climatic water deficit is more than 829 mm. These findings reveal that degraded tropical forests with environmental conditions favouring lianas are disproportionately more vulnerable to liana dominance and thus can potentially stall succession, with important implications for the global carbon sink, and hence should be the highest priority to consider for restoration management.

Des preuves de plus en plus nombreuses suggèrent que la competition entre lianes et les arbres menace le puits de carbone mondial en ralentissant la récupération des forêts après une perturbation. Une théorie récente, fondée sur des observations locales et régionales, propose en outre que le succès compétitif des lianes sur les arbres est dû aux interactions entre la perturbation forestière et le climat. Nous présentons la première évaluation mondiale de la performance relative des lianes par rapport aux arbres en réponse aux perturbations forestières et aux facteurs climatiques. En utilisant un ensemble de données sans précédent, nous avons analysé 651 échantillons de végétation représentant 26,538 lianes et 82,802 arbres, issus de 556 emplacements uniques dans le monde entier, tirés de 83 publications. Les résultats montrent que les lianes ont de meilleure performances par rapport aux arbres (augmentation du ratio liane-arbre) lorsque les forêts sont perturbées, sous des zones chaudes aves précipitations faibles, et vers les basses altitudes tropicales. Nous avons également constaté que les lianes peuvent être un facteur critique entravant la récupération des forêts dans les forêts perturbées connaissant des climats favorables aux lianes, car les données de chronoséquence montrent que le succès compétitif élevé des lianes sur les arbres peut persister pendant des décennies après les perturbations, surtout lorsque la température annuelle moyenne dépasse 27.8°C, que les précipitations sont inférieures à 1614 mm et que le déficit hydrique climatique est supérieur à 829 mm. Ces découvertes révèlent que les forêts tropicales dégradées avec des conditions environnementales favorables aux lianes sont disproportionnellement plus vulnérables à la dominance des lianes, et peuvent ainsi potentiellement entraver la succession, avec d'importantes implications pour le puits de carbone mondial et devraient donc être la plus haute priorité à considérer pour la gestion de la restauration.

Simulation and prediction of changes in tree species composition in subtropical forests of China using a nonlinear difference equation system model.

Changes in tree species composition are one of the key aspects of forest succession. In recent decades, significant changes have occurred in the tree species composition of subtropical forests in China, with a decrease in coniferous trees and an increase in broad-leaved trees. This study focuses on Zhejiang Province, located in the subtropical region of China, and utilizes seven inventories from the National Continuous Forest Inventory (NCFI) System spanning 30 years (1989-2019) for modeling and analysis. We categorized tree species into three groups: pine, fir, and broadleaf. We used the proportion of biomass in a sample plot as a measure of the relative abundance of each tree species group. A novel nonlinear difference equation system (NDES) model was proposed. A NDES model was established based on two consecutive survey datasets. A total of six models were established in this study. The results indicated that during the first two re-examination periods (1989-1994, 1994-1999), there was significant fluctuation in the trend of tree species abundance, with no consistent pattern of change. During the latter four re-examination periods (1999-2004, 2004-2009, 2009-2014, 2014-2019), a consistent trend was observed, whereby the abundance of the pine group and the fir group decreased while the abundance of the broad-leaved group increased. Moreover, over time, this pattern became increasingly stable. Although the abundances of the pine group and the fir group have been steadily declining, neither group is expected to become extinct. The NDES model not only facilitates short-term, medium-term, and even long-term predictions but also employs limit analysis to reveal currently obscure changing trends in tree species composition.

Adaptive Relationships in Hemi-Boreal Forests: Tree Species Responses to Competition, Stress, and Disturbance.

European Union forest policy calls for closer-to-nature forest management, but natural disturbances and forest succession are ecological phenomena that are difficult to characterize and integrate into sustainable forest management practices. Therefore, the aim of this study is to explore the adaptive properties of Lithuania's hemi-boreal forest ecosystems. To accomplish this, we first reviewed (i) the potential natural forest communities, (ii) the successional dynamics, and (iii) adaptive strategies of forest trees, and second, we synthesised the adaptive relationships using these three reviews. The results firstly identified that Lithuania's potential natural forests are broadly divided into two climatically based zonal formations: (i) mesophytic and hygromesophytic coniferous and broadleaved forests and (ii) mesophytic deciduous broadleaved and coniferous-broadleaved forests. Secondly, the review of successional dynamics showed that each tree species can be categorised into various end communities and plant functional groups. Using the differences in tree establishment and phenological development modes we identified four forest dynamic types of tree adaptive strategies: stress-resistant ruderals, competitive stress-sensitive ruderals, ruderal stress-sensitive competitors, and stress-resistant competitors. Such functional redundancy leads to a variety of tree responses to competition, stress, and disturbance, which reduces the risk of loss of forest ecosystem functioning. Finally, the synthesised review on the adaptive relationships of each forest tree community shows both the niche position of each hemi-boreal forest tree species and how they should be managed in the organization of plant communities. We believe that this research can serve as a guide for future relevant research and the development of appropriate methods for sustainable forest management.

Partitioning and integrating of plant traits and phylogeny in assessing diversity along secondary forest succession in Loess Plateau of China.

Assessing plant diversity during community succession based on plant trait and phylogenetic features within a community (alpha scale) and among communities (beta scale) could improve our understanding of community succession mechanism. However, whether changes of community functional diversity at alpha and beta scale are structured by different traits and whether integrating plant traits and phylogeny can enhance the ability in detecting diversity pattern have not been studied in detail. Thirty plots representing different successional stages were established on the Loess Plateau of China and 15 functional traits were measured for all coexisting species. We first analyzed the functional alpha and beta diversity along succession by decomposing species trait into alpha and beta components and then integrated key traits with phylogenetic information to explore their roles in shaping species turnover during community succession. We found that functional alpha diversity increased along successional stages and was structured by morphological traits, while beta diversity decreased during succession and was more structured by stoichiometry traits. Phylogenetic alpha diversity showed congruent pattern with functional alpha diversity because of phylogenetic conservation of trait alpha components (variation within community), while beta diversity showed incongruent pattern due to phylogenetic randomness of trait beta components (variation among communities). Furthermore, only integrating relatively conserved traits (plant height and seed mass) and phylogenetic information can raise the detecting ability in assessing diversity change. Overall, our results reveal the increasing niche differentiation within community and functional convergence among communities with succession process, indicating the importance of matching traits with scale in studying community functional diversity and the asymmetry of traits and phylogeny in reflecting species ecological differences under long-term selection pressures.

The contrasting responses of abundant and rare microbial community structures and co-occurrence networks to secondary forest succession in the subalpine region.

Knowledge of variations in abundant and rare soil microbial communities and interactions during secondary forest succession is lacking. Soil samples were gathered from different secondary successional stages (grassland, shrubland, and secondary forest) to study the responses of abundant and rare bacterial and fungal communities, interactions and driving factors to secondary forest succession by Illumina sequencing of the 16S and ITS rRNA genes. The results showed that the α-diversities (Shannon index) of abundant bacteria and fungi revealed no significant changes during secondary forest succession, but increased significantly for rare bacteria. The abundant and rare bacterial and fungal ß-diversities changed significantly during secondary forest succession. Network analysis showed no obvious changes in the topological properties (nodes, links, and average degree) of abundant microbial networks during secondary forest succession. In contrast, these properties of the rare microbial networks in the secondary forest were higher than those in the grassland and shrubland, indicating that rare microbial networks are more responsive to secondary forest succession than abundant microorganisms. Additionally, rare microbial networks revealed more microbial interactions and greater network complexity than abundant microbial networks due to their higher numbers of nodes and links. The keystone species differed between the abundant and rare microbial networks and consisted of 1 and 48 keystone taxa in the abundant and rare microbial networks, respectively. Soil TP was the most important influencing factor of abundant and rare bacterial communities. Successional stages and plant richness had the most important influences on abundant and rare fungal communities, respectively. C:P, SM and N:P were mainly related to abundant and rare microbial network topological properties. Our study indicates that abundant and rare microbial communities, interactions and driving factors respond differently to secondary forest succession.

[Response Characteristics of Soil Organic Carbon Pool and Its Chemical Composition During Secondary Forest Succession in the Loess Plateau].

In order to explore the characteristics of the soil organic carbon(SOC)pool and its chemical composition during the succession of secondary forests in the Loess Plateau, samples of the primary stage (Populus davidiana forest), transition stage (Populus davidiana and Quercus wutaishansea mixed forest), and top stage (Quercus wutaishansea forest) of secondary forest succession in the Huanglong Mountain forest area of the Loess Plateau in Northern Shaanxi were selected as the research object. The variation characteristics of SOC content, storage, and its chemical composition at different soil depths (0-10, 10-20, 20-30, 30-50, and 50-100 cm) were analyzed. The results showed that:① the contents and storage of SOC increased significantly with the secondary forest succession process (P<0.05). The content of SOC decreased significantly with the increase in soil depth, and the storage of SOC increased from 64.8 Mg·hm-2 in the primary stage to 129.2 Mg·hm-2 in the top stage, with an increase of 99%. ② During the succession of secondary forests, in the surface (0-30 cm) soil organic carbon, the relative content of aliphatic carbon components that have a simple structure and can be decomposed more easily decreased, and the relative content of aromatic carbon components that have a complex structure and cannot be decomposed easily increased, indicating that the chemical composition of organic carbon stability of surface-layer soil increased significantly with the process of secondary forest succession. However, the stability of the chemical composition of SOC in the deep layer (30-100 cm) first increased and then decreased, that is, the transition stage>the top stage>the primary stage. ③In the process of secondary forest succession, the stability of SOC chemical composition in the primary stage and transition stage increased significantly with the increase in soil depth. The top stage tended to be stable, and the deep soil carbon stability decreased slightly. ④ Pearson correlation analysis showed that during the secondary forest succession process, SOC storage and chemical composition stability were significantly negatively correlated with soil total phosphorus content. In general, the content and storage of SOC in the 0-100 cm soil increased significantly during the secondary forest succession, playing the role of a "carbon sink." The stability of the chemical composition of SOC in the surface layer (0-30 cm) increased significantly, but in the deep layer (30-100 cm), it increased first and then decreased.

Carbon stress causes earlier budbreak in shade-tolerant species and delays it in shade-intolerant species.

PREMISE: Climate change may lead to C stress (negative C balance) in trees. Because nonstructural carbohydrates (NSC) are required during metabolic reactivation in the spring, C stress might delay budbreak timing. This effect is expected to be greater in shade-intolerant than in shade-tolerant species, owing to the faster C economy in the shade-intolerant. METHODS: We experimentally induced C stress in saplings of six temperate tree species that differed in their light requirements by exposing them to either full light or shade from summer to spring, then recorded the date of first budbreak for the individuals. Because the levels of C reserves that represent effective C stress may differ among species, we estimated the degree of C stress by recording survival during the experiment and measuring whole-sapling NSC concentrations after budbreak. RESULTS: Shade reduced NSC concentrations and increased the sugar fraction in the NSC in all species. In the shade, shade-intolerant species had higher mortality and generally lower NSC concentrations than the shade-tolerant species, indicating a trend for more severe C stress in species with faster C economy. In shade-intolerant species, budbreak started earlier and proceeded faster in full light than in shade, but in shade-tolerant species budbreak was delayed in full light. The effects of the light environments on budbreak were not greater in shade-intolerant than in shade-tolerant species. CONCLUSIONS: Our study reveals a correspondence between budbreak responses to light and the light requirements of the species. This finding confirms that C metabolism has a significant role in triggering budbreak and demonstrates that whether C stress accelerates or delays budbreak depends on the species' light requirements.

Functional shifts in soil fungal communities regulate differential tree species establishment during subalpine forest succession.

Soil fungi can differentially affect plant performance and community dynamics. While fungi play key roles in driving the plant-soil feedbacks (PSFs) that promote grassland succession, it remains unclear how the fungi-mediated PSFs affect tree species establishment during forest succession. We inoculated pioneer broadleaf (Betula platyphylla and Betula albosinensis) and nonpioneer coniferous tree seedlings (Picea asperata and Abies faxoniana) with fungal-dominated rooting zone soils collected from dominant plant species of early-, mid- and late-successional stages in a subalpine forest, and compared their biomass and fungal communities. All tree species accumulated abundant pathogenic fungi in early-successional inoculated soil, which generated negative biotic feedbacks and lowered seedling biomass. High levels of soil ectomycorrhizal fungi from mid- and late-successional stages resulted in positive biotic PSFs and strongly facilitated slow-growing coniferous seedling performance to favour successional development. B. albosinensis also grew better in mid- and late-successional soils with fewer pathogenic fungi than in early-successional soil, indicating its large susceptibility to pathogen attack. In contrast, the growth of another pioneer tree, B. platyphylla, was significantly suppressed in late-successional soil and was mostly driven by saprotrophic fungi, despite the unchanged pathogenic fungal community traits between the two fast-growing species. This unexpected result suggested a host specificity-dependent mechanism involved in the different impacts of fungal pathogens on host trees. Our findings reveal a critical role of functional shifts in soil fungal communities in mediating differential PSFs of tree species across successional stages, which should be considered to improve the prediction and management of community development following forest disturbances.

Invasive alien acacias rapidly stock carbon, but threaten biodiversity recovery in young second-growth forests.

Under the UN-Decade of Ecosystem Restoration and Bonn Challenge, second-growth forest is promoted as a global solution to climate change, degradation and associated losses of biodiversity and ecosystem services. Second growth is often invaded by alien tree species and understanding how this impacts carbon stock and biodiversity recovery is key for restoration planning. We assessed carbon stock and tree diversity recovery in second growth invaded by two Acacia species and non-invaded second growth, with associated edge effects, in the Brazilian Atlantic Forest. Carbon stock recovery in non-invaded forests was threefold lower than in invaded forests. Increasingly isolated, fragmented and deforested areas had low carbon stocks when non-invaded, whereas the opposite was true when invaded. Non-invaded forests recovered threefold to sixfold higher taxonomic, phylogenetic and functional diversity than invaded forest. Higher species turnover and lower nestedness in non-invaded than invaded forests underpinned higher abundance of threatened and endemic species in non-invaded forest. Non-invaded forests presented positive relationships between carbon and biodiversity, whereas in the invaded forests we did not detect any relationship, indicating that more carbon does not equal more biodiversity in landscapes with high vulnerability to invasive acacias. To deliver on combined climate change and biodiversity goals, restoration planning and management must consider biological invasion risk. This article is part of the theme issue 'Understanding forest landscape restoration: reinforcing scientific foundations for the UN Decade on Ecosystem Restoration'.

Dynamics of soil microbial communities involved in carbon cycling along three successional forests in southern China.

Dynamics of plant communities during forest succession have been received great attention in the past decades, yet information about soil microbial communities that are involved in carbon cycling remains limited. Here we investigated soil microbial community composition and carbohydrate degradation potential using metagenomic analysis and examined their influencing factors in three successional subtropical forests in southern China. Results showed that the abundances of soil bacteria and fungi increased (p ≤ 0.05 for both) with forest succession in relation to both soil and litter characteristics, whereas the bacterial diversity did not change (p > 0.05) and the fungal diversity of Shannon-Wiener index even decreased (p ≤ 0.05). The abundances of microbial carbohydrate degradation functional genes of cellulase, hemicellulase, and pectinase also increased with forest succession (p ≤ 0.05 for all). However, the chitinase gene abundance did not change with forest succession (p > 0.05) and the amylase gene abundance decreased firstly in middle-succession forest and then increased in late-succession forest. Further analysis indicated that changes of functional gene abundance in cellulase, hemicellulase, and pectinase were primarily affected by soil organic carbon, soil total nitrogen, and soil moisture, whereas the variation of amylase gene abundance was well explained by soil phosphorus and litterfall. Overall, we created a metagenome profile of soil microbes in subtropical forest succession and fostered our understanding of microbially-mediated soil carbon cycling.

Forest succession improves the complexity of soil microbial interaction and ecological stochasticity of community assembly: Evidence from Phoebe bournei-dominated forests in subtropical regions.

Forest succession is a central ecological topic, due to the importance of the associated dynamic processes for terrestrial ecosystems. However, very little is currently known about the community assembly and interaction of soil microbial communities along forest successional trajectories, particularly regarding the microbial community dynamics in contrasting seasons. To bridge these knowledge gaps, we studied soil bacterial and fungal community compositions, assemblages, and co-occurrence networks in a well-established successional gradient of Phoebe bournei-dominated forest, spanning about 65 years of forest development in a subtropical region. Illumina MiSeq sequencing of 16S and ITS genes was employed for the assessment of soil bacterial and fungal community composition and diversity, respectively. The relative abundance and α-diversity of soil bacteria and fungi showed a differential trend over forest succession. The dominant fungal phyla (Basidiomycota and Ascomycota) changed more frequently than the dominant bacterial phyla (Proteobacteria, Acidobacteriota, and Actinobacteriota), indicating that soil fungi have a more sensitive relationship with forest succession compared with bacteria. The soil microbial community variation induced by forest succession was significantly affected by soil total phosphorus, dissolved organic carbon content and pH. Compared to deterministic processes, stochastic processes mainly dominated the community assembly of soil microbial communities. Meanwhile, the relative importance of stochasticity in soil fungal communities increased in the later stages. In Particular, dispersal limitation and drift accounted for a large proportion of bacterial and fungal community assembly, respectively. In addition, the co-occurrence networks of soil microbial communities became more complex as succession proceeds. Soil bacteria and fungi exhibited more competition and cooperation along the forest successional gradient. Collectively, our findings suggest that forest succession improves the complexity of soil microbial interactions and the ecological stochasticity of community assembly in Phoebe bournei-dominated forests, providing key insights into the relationship between microbial communities and forest succession.

Soil Fungal Community Structure and Function Shift during a Disease-Driven Forest Succession.

Forest succession is important for sustainable forest management in terrestrial ecosystems. However, knowledge about the response of soil microbes to forest disease-driven succession is limited. In this study, we investigated the soil fungal biomass, soil enzyme activity, and fungal community structure and function in forests suffering succession processes produced by pine wilt disease from conifer to broadleaved forests using Illumina Miseq sequencing coupled with FUNGuild analysis. The results showed that the broadleaved forest had the highest fungal biomass and soil enzyme activities in C, N, and S cycles, whereas the conifer forest had the highest enzyme activity in the P cycle. Along the succession, the fungal diversity and richness significantly increased (P < 0.05). The fungal communities were dominated by Ascomycota (42.0%), Basidiomycota (38.0%), and Mortierellomycota (9.5%), among which the abundance of Ascomycota significantly increased (P < 0.05), whereas that of Basidiomycota and Mortierellomycota decreased (P < 0.05). The abundance of species Mortierella humilis, Lactarius salmonicolor, and Russula sanguinea decreased, whereas that of Mortierella minutissima increased (P < 0.05). The forests in different succession stages formed distinct fungal communities and functional structures (P < 0.05). Functionally, the saprotrophs, symbiotrophs, and pathotrophs were the dominant groups in the conifer, mixed, and broadleaved forests, respectively. Soil pH and soil organic carbon were the key factors influencing the fungal community and functional structures during the succession. These findings provide useful information for better understanding the plant-microbe interaction during forest succession caused by forest disease. IMPORTANCE The studies on soil fungal communities in disease-driven forest succession are rare. This study showed that during the disease-driven forest succession, the soil enzyme activity, soil fungal diversity, and biomass increased along succession. The disease-driven forest succession changed the soil fungal community structure and function, in which the symbiotrophs were the most dominant group along the succession. These findings provide useful information for better understanding the plant-microbe interaction during forest succession caused by forest disease.

A healthier water use strategy in primitive forests contributes to stronger water conservation capabilities compared with secondary forests.

Water conservation is an important ecological function of forest ecosystems, plant water use strategy is a key factor in regulating forest ecosystem water balance. However, there are still insufficient studies on the water conservation capacity and water use strategies of different forest types, especially in climate-sensitive areas. In this study, we determined the stable isotope values (δD, δ18O and d-excess) of plant water, soil water and precipitation from two typical stand types (primary forest and secondary forest) on Changbai Mountain to reveal plant water use and evaluated the water conservation capacity. The results indicated that rainwater infiltrated into the soil combined with piston flow and preferential flow in the primary forest, and preferential flow was the only form of flow in the secondary forest. The main tree species in the primary forest formed a relatively stable water use niche. Among them, the water use pattern of Quercus mongolica Fisch. ex Ledeb (Qm.) was transformed between shallow and deep soil layers with strong ecological plasticity. The dominant species in secondary forest derived water from similar soil layers with intense interspecific competition. By comparing the water use patterns, the secondary forest conformed to the hypothesis of "two water worlds", while the primary forest conformed to the hypothesis of one reservoir. The primary forest ecosystem had stronger water conservation capacity than secondary forest ecosystem due to the regulable water use strategies of plants and the stable water conservation capacity of the soil. These results will provide theoretical support and a reference for plan future forest management strategies in the climate-sensitive areas.

Hurricanes increase tropical forest vulnerability to drought.

Rapid changes in climate and disturbance regimes, including droughts and hurricanes, are likely to influence tropical forests, but our understanding of the compound effects of disturbances on forest ecosystems is extremely limited. Filling this knowledge gap is necessary to elucidate the future of these ecosystems under a changing climate. We examined the relationship between hurricane response (damage, mortality, and resilience) and four hydraulic traits of 13 dominant woody species in a wet tropical forest subject to periodic hurricanes. Species with high resistance to embolisms (low P50 values) and higher safety margins ( SMP50 ) were more resistant to immediate hurricane mortality and breakage, whereas species with higher hurricane resilience (rapid post-hurricane growth) had high capacitance and P50 values and low SMP50 . During 26 yr of post-hurricane recovery, we found a decrease in community-weighted mean values for traits associated with greater drought resistance (leaf turgor loss point, P50 , SMP50 ) and an increase in capacitance, which has been linked with lower drought resistance. Hurricane damage favors slow-growing, drought-tolerant species, whereas post-hurricane high resource conditions favor acquisitive, fast-growing but drought-vulnerable species, increasing forest productivity at the expense of drought tolerance and leading to higher overall forest vulnerability to drought.