Degradation Gradient Research Articles

Benthic Community Metrics Track Hydrologically Stressed Mangrove Systems

Mangrove restoration efforts have increased in order to help combat their decline globally. While restoration efforts often focus on planting seedlings, underlying chronic issues, including disrupted hydrological regimes, can hinder restoration success. While improving hydrology may be more cost-effective and have higher success rates than planting seedlings alone, hydrological restoration success in this form is poorly understood. Restoration assessments can employ a functional equivalency approach, comparing restoration areas over time with natural, reference forests in order to quantify the relative effectiveness of different restoration approaches. Here, we employ the use of baseline community ecology metrics along with stable isotopes to track changes in the community and trophic structure and enable time estimates for establishing mangrove functional equivalency. We examined a mangrove system impacted by road construction and recently targeted for hydrological restoration within the Rookery Bay National Estuarine Research Reserve, Florida, USA. Samples were collected along a gradient of degradation, from a heavily degraded zone, with mostly dead trees, to a transition zone, with a high number of saplings, to a full canopy zone, with mature trees, and into a reference zone with dense, mature mangrove trees. The transition, full canopy, and reference zones were dominated by annelids, gastropods, isopods, and fiddler crabs. Diversity was lower in the dead zone; these taxa were enriched in 13C relative to those found in all the other zones, indicating a shift in the dominant carbon source from mangrove detritus (reference zone) to algae (dead zone). Community-wide isotope niche metrics also distinguished zones, likely reflecting dominant primary food resources (baseline organic matter) present. Our results suggest that stable isotope niche metrics provide a useful tool for tracking mangrove degradation gradients. These baseline data provide critical information on the ecosystem functioning in mangrove habitats following hydrological restoration.

Changes of bacterial versus fungal community composition along a forest degradation gradient of logged-over tropical rain forests, and their consequences on soil enzyme activities in Malaysian Borneo

Changes of bacterial versus fungal community composition along a forest degradation gradient of logged-over tropical rain forests, and their consequences on soil enzyme activities in Malaysian Borneo

Bio-monitoring of coral reef health based on benthic foraminifera in Makadi Lagoon, Hurghada, Red Sea Coast, Egypt: Application of the standard FoRAM index

The Red Sea Coast near Hurghada City is under continuous development in the tourism sector because of its natural heritage of corals reefs. This region is one of the favorite destinations of leisure tourism throughout the world. These activities lead to high environmental stress that affects the water quality and growth of coral reefs. The Foraminifera in Reef Assessment and Monitoring index (FoRAM Index) is one of the cost effective and fast results methods of bio-monitoring. The FoRAM Index is applied in the Makadi and Ras Disha Bays near to Hurghada. Topographic analysis shows that the tourist facilities are concentrated at the outlet of the low gradient valleys especially at Makadi bay. The FoRAM Index is supported with a statistical analysis of the foraminiferal association that resulted in the identification of three microtypes. These microtypes are stress tolerant rich Microtype 1, heterotrophic foraminifera rich Microtype 2 and symbionts-bearing foraminifera Microtype 3. The foraminiferal population pattern in these microtypes is similar to the groupings of the FoRAM Index. The values of the FoRAM Index range between 3.8 and 6.8 and these values reflect healthy water that supports the growth of coral reefs. However, a degradation gradient occurs in Makadi Bay indicating the impact of concentrated tourism activity on the water quality. The values observed in Ras Disha Bay can be considered as background for spatial and future studies. The FoRAM Index is a highly recommended application for economic and rapid bio-monitoring. The results are valuable for stakeholders planning for sustainable development and management of ecotourism.

Global changes in the odonate family ratios in response to the tropical forest degradation

Odonates (dragonflies and damselflies) can indicate the ecological health of aquatic biota within the rich but vulnerable biodiversity of tropical forests. The reaction of odonates to deforestation can be measured by changes in coarse taxonomic ratios. Suborder Zygoptera are thermal conformers susceptible to overheating, having the affinity with shaded, intact sites. Anisoptera have exothermic regulation and better dispersal capacities, suggesting their association with more altered, open environments. Similarly, with an increasing degradation, the proportion of Anisoptera species in assemblages should increase. However, based on the data from different continents, the Zygoptera/Anisoptera ratio may be too simple, strongly biased, and not applicable at the global scale. The main reason is that the most diverse, abundant, and cosmopolitan families, Coenagrionidae (Zygoptera) and Libellulidae (Anisoptera), comprise a great proportion of habitat generalists with high migratory capacity and affinity with open habitats. In this study, we sampled odonates from three bioregions (Indomalaya, Afrotropics, and Neotropics) over the gradient of tropical forest degradation with a comparable sampling effort to assess the suitability of species richness and suborder-based (Zygoptera/Anisoptera) and family-based (Libellulidae/other Anisoptera and Coenagrionidae/other Zygoptera) ratios and their abundance-weighted versions for monitoring tropical forest degradation. Our results show that simple Odonata as well as Zygoptera and Anisoptera richness are poor indicators of the forest biota alteration. Family-level indices weighted by relative abundance, especially those involving Coenagrionidae, were more sensitive to changes in forest conditions compared to suborder-level indices. Collectively, our results suggest that for biomonitoring, where financial resources and time are commonly critical, family-level ratio metrics may be effective tools to indicate even slight alterations of aquatic biota resulting from forest degradation. Although these indices have the potential for broader application, their effectiveness across tropical bioregions warrants further validation.

Land Degradation Affects Soil Microbial Properties, Organic Matter Composition, and Maize Yield

Land degradation severely affects soil functions, thereby weakening crop productivity. However, the quantitative effects of the soil organic matter (SOM) composition and soil microbial properties on maize yield remain unclear under different levels of land degradation. Here, a gradient of land degradation was selected for sampling in the Horqin Sandy Land in northeast China. The results show that the relative abundances of aliphatic and aromatic groups decreased by 21.51% and 86.01% with increasing land degradation, respectively, and the considerable increase in polysaccharide groups led to a decrease in stability and resistance to SOM decomposition. Microbial properties, such as microbial biomass carbon, basic respiration, qCO2, and enzyme activities, decreased as a result of land degradation. The phospholipid fatty acid content and the ratio between bacteria and fungi markedly decreased with an increasing level of land degradation, and the ratio of G+ to G− markedly increased. Correlation analysis confirmed that the microbial properties were significantly related to the SOM composition, and the random forest model indicated that fungi were key factors affecting maize yield (7.15%, p < 0.05). Moreover, the results of the structure equation modelling revealed that land degradation reduced the soil physiochemical properties, resulting in a decrease in microorganisms, causing variations in the SOM composition and directly leading to a decrease in crop yield. The effect of microorganisms (β = 0.84 ***) on maize yield was greater than that of the SOM composition (β = 0.53 **). Our investigation can provide a theoretical basis for the conservation of the cropland in Horqin Sandy Land.

Plant species diversity and functional diversity relations in the degradation process of desert steppe in an arid area of northwest China

Species and functional diversity play a major role in the stability and sustainability of grassland ecosystems. However, changes in species and functional diversity during grassland degradation in arid areas as well as the underlying mechanisms remain unclear. In this study, we surveyed the vegetation and soil properties of arid regions across a degradation gradient to explore the shifts in species and functional diversity in plant communities, their relationships and key determinants during desert steppe degradation. Our results found significant variability in species diversity and functional diversity across degradation stages. Species diversity (Shannon-Wiener index (H), and Pielou index) and functional diversity (functional evenness (FEve) index, and Rao's quadratic entropy (RaoQ) index) tended to increase initially and then decrease with increasing grassland degradation. The Patrick index, Simpson index, functional richness (FRic) index, functional divergence (FDiv) index, and functional dispersion (FDis) index declined as grassland degradation increased. The relationships between species diversity and functional diversity indices at different stages of degradation in the desert steppe were inconsistent. From no to heavy degradation grasslands, the correlation between species diversity and functional diversity gradually weakened. Specifically, there was a significant correlation between Patrick (R) and FRic indices (R2 > 0.7) on both non-degraded and light degraded grasslands, but there was no significant correlation between R and FRic indices in moderately and heavily degraded grasslands (R2 < 0.7), and R2 gradually decreased. Redundancy analysis and partial least squares path modeling showed that grassland degradation has a significant direct effect on the species diversity and functional diversity. In addition grassland degradation has direct and indirect effects on the species diversity through soil available nitrogen, organic matter and total nitrogen. Functional diversity is directly or indirectly affected by species diversity, soil available nitrogen, organic matter and total nitrogen, soil moisture content, soil bulk density, and pH value. In summary, the relationship between species and functional diversity indices gradually weakened from areas with no degradation to heavy degradation in arid desert grasslands. Our study reveals the patterns and relationships between species diversity and functional diversity throughout the process of grassland degradation, demonstrating a gradual decrease in ecosystem stability and sustainability as degradation advances. Our results have significant implications for the restoration of grassland degradation and the management of ecosystem services in arid steppe regions.

Alpine meadow degradation decreases soil P availability by altering phoD-harbouring bacterial diversity

Context Soil degradation is usually accompanied by significant changes in phosphorus (P) availability, which complicates soil management. However, the effect of ecosystem degradation on soil P availability remains poorly understood, especially in the alpine ecosystem, which is one of the most understudied and vulnerable terrestrial habitats of the planet. Aims Assess the effect of meadow degradation on soil P availability in the alpine ecosystem. Methods Changes in soil P-related properties, phoD-harbouring bacterial communities, and alkaline phosphatase levels were investigated in four alpine meadows along a degradation gradient (non-degraded, lightly degraded, moderately degraded, and severely degraded) on the Tibetan Plateau. Key results We found meadow degradation reduced alkaline phosphatase activity by 6.3–11.22% and soil P availability by 27.1–42.4% compared to the respective values in the non-degraded meadows, but this negative impact was only observed in moderately and severely degraded meadows. Meadow degradation caused a P limitation on the phoD-harbouring community and a decline in the abundance of phoD genes and diversity of phoD-harbouring bacterial communities, with an increase in oligotrophic groups (e.g. Actinobacteria) and a reduction in copiotrophic groups (e.g. Proteobacteria). The degradation-induced reduction in soil C supply and plant biomass decreased soil P availability by lowering the activity of alkaline phosphatases, which are closely associated with phoD-harbouring bacterial structure and diversity. Alloactinosynnema and Actinomadura were identified as the key taxa contributing to alkaline phosphatases activity. Conclusions Alpine meadow degradation decreases soil P availability by altering phoD-harbouring bacterial diversity. Implications Our results revealed the mechanisms of decreased P availability during alpine meadow degradation, which can guide the restoration of degraded meadow ecosystems.

The impact of desertification on soil health stability in Semi-Arid alpine Regions: A case study of the Qilian Mountains in the northeastern Tibetan Plateau, China

Desertification poses a serious threat to ecosystem health, and with global changes, the variability and uncertainty of ecological functions in semi-arid alpine regions are increasing. A pressing issue is quantifying how desertification affects the soil system functions in these areas. However, empirical evidence is still lacking in exploring the interaction between desertification degradation gradients and soil functions under natural conditions by coupling soil physicochemical properties, soil microbiota, and vegetation. For this purpose, we conducted a survey sampling of soil and vegetation at five sites with no, light, moderate, severe and extremely severe desertification in Qinghai Area of Qilian Mountains National Park, China. We introduced a new concept soil health stability (SHS) to represent the actual health status of soil systems in semi-arid alpine regions and assessed the impact of desertification on this stability. We observed that the intensification of desertification has led to a significant decrease in soil organic matter, relative abundance of soil microorganisms, and plant factors. The contributions of plant factors and soil microbiota to SHS showed a negative correlation with the degradation gradient. SHS varied across different degradation gradients, rather than following a single linear relationship, with a relatively rapid decline in the transition from non-desertification to moderate desertification. Our work emphasizes that the coupled contributions of soil physicochemical properties, soil microbiota, and vegetation to SHS. It calls for intensified prevention and treatment of mild and moderate desertification, while providing new methods and deeper scientific understanding for accurately evaluating soil system functions in semi-arid alpine regions.

Multiple stressors alter greenhouse gas concentrations in streams through local and distal processes.

Streams are significant contributors of greenhouse gases (GHG) to the atmosphere, and the increasing number of stressors degrading freshwaters may exacerbate this process, posing a threat to climatic stability. However, it is unclear whether the influence of multiple stressors on GHG concentrations in streams results from increases of in-situ metabolism (i.e., local processes) or from changes in upstream and terrestrial GHG production (i.e., distal processes). Here, we hypothesize that the mechanisms controlling multiple stressor effects vary between carbon dioxide (CO2) and methane (CH4), with the latter being more influenced by changes in local stream metabolism, and the former mainly responding to distal processes. To test this hypothesis, we measured stream metabolism and the concentrations of CO2 (pCO2) and CH4 (pCH4) in 50 stream sites that encompass gradients of nutrient enrichment, oxygen depletion, thermal stress, riparian degradation and discharge. Our results indicate that these stressors had additive effects on stream metabolism and GHG concentrations, with stressor interactions explaining limited variance. Nutrient enrichment was associated with higher stream heterotrophy and pCO2, whereas pCH4 increased with oxygen depletion and water temperature. Discharge was positively linked to primary production, respiration and heterotrophy but correlated negatively with pCO2. Our models indicate that CO2-equivalent concentrations can more than double in streams that experience high nutrient enrichment and oxygen depletion, compared to those with oligotrophic and oxic conditions. Structural equation models revealed that the effects of nutrient enrichment and discharge on pCO2 were related to distal processes rather than local metabolism. In contrast, pCH4 responses to nutrient enrichment, discharge and temperature were related to both local metabolism and distal processes. Collectively, our study illustrates potential climatic feedbacks resulting from freshwater degradation and provides insight into the processes mediating stressor impacts on the production of GHG in streams.

Impact of grassland degradation on soil multifunctionality: Linking to protozoan network complexity and stability

Soil protozoa, as predators of microbial communities, profoundly influence multifunctionality of soils. Understanding the relationship between soil protozoa and soil multifunctionality (SMF) is crucial to unraveling the driving mechanisms of SMF. However, this relationship remains unclear, particularly in grassland ecosystems that are experiencing degradation. By employing 18S rRNA gene sequencing and network analysis, we examined the diversity, composition, and network patterns of the soil protozoan community along a well-characterized gradient of grassland degradation at four alpine sites, including two alpine meadows (Cuona and Jiuzhi) and two alpine steppes (Shuanghu and Gonghe) on the Qinghai-Tibetan Plateau. Our findings showed that grassland degradation decreased SMF for 1–2 times in all four sites but increased soil protozoan diversity (Shannon index) for 13.82–298.01 % in alpine steppes. Grassland degradation-induced changes in soil protozoan composition, particularly to the Intramacronucleata with a large body size, were consistently observed across all four sites. The enhancing network complexity (average degree), stability (robustness), and cooperative relationships (positive correlation) are the responses of protozoa to grassland degradation. Further analyses revealed that the increased network complexity and stability led to a decrease in SMF by affecting microbial biomass. Overall, protozoa increase their diversity and strengthen their cooperative relationships to resist grassland degradation, and emphasize the critical role of protozoan network complexity and stability in regulating SMF. Therefore, not only protozoan diversity and composition but also their interactions should be considered in evaluating SMF responses to grassland degradation, which has important implications for predicting changes in soil function under future scenarios of anthropogenic change.

Ecosystem function associated with soil organic carbon declines with tropical dry forest degradation

AbstractForest degradation is increasingly recognized as a major threat to global biodiversity and the multiple ecosystem services forests provide. This study examined the impacts of forest degradation on soil quality and function in a seasonally dry tropical forest (SDTF) of Ecuador. Previous studies of SDTFs have focused on the impacts of land‐use conversion on soils, while this study assessed the less visible but pervasive effects of degradation. We compared soil physical–chemical properties, enzymatic activity, particulate organic carbon (POC) and mineral‐associated organic carbon (MAOC) along a gradient of SDTF degradation in both the dry and rainy season. Our findings showed a consistent and steady reduction in soil quality (total C and N) and function (dehydrogenase and β‐glucosidase activity) that paralleled the loss of vegetative structure and diversity along the degradation gradient. Soil physical–chemical properties were less variable and enzymatic activity was generally higher in the dry season compared to the rainy season. We also showed for the first time a significant and uniform decrease in POC and MAOC with degradation in SDTF. The relative proportion of these two components was constant along the gradient except in the most degraded state (arid land), where POC was higher in proportion to MAOC, suggesting that extreme forest degradation may cause this ecosystem to cross a functional tipping point. These findings address an important knowledge gap for SDTFs by showing a consistent loss of soil quality and functionality with degradation, and suggest that extreme degradation can result in an alternate state with compromised resilience.

Biogeomorphological floodplain dynamics along a degradation gradient of an Alpine river

AbstractChannel migration, furcation, and vegetation succession are characteristic processes of braided gravel rivers in Alpine regions. These are associated with a frequent turnover of large parts of the active floodplain. However, more than one century of river regulation has reduced or destroyed most of these ecosystem dynamics. More recently, there have been attempts to restore at least some sections of degraded rivers, while there is little monitoring of the biogeomorphological dynamics of such rivers. Thus, we did a four‐year analysis of four representative sections of the upper River Isar in Southern Germany differing in their degree of naturalness. Dynamics of channels, gravel bars, and vegetation were recorded by drone images, and braiding and gravel indices were calculated. When comparing the near‐natural, semi‐natural, degraded or restored sections, there was a gradient of decreasing channel migration, gravel bank expansion, and bank erosion due to a reduced turnover frequency. Biogeomorphological variation among years correlated with log peak discharge within the four sections. In addition, the cover and height growth of vegetation increased with river degradation, and channel migration was positively related to the braiding index. The total turnover of the active river corridor and of the vegetation were positively correlated with log peak discharge within the four sections. The floodplain dynamics of the restored section were improved compared to the degraded section but did not reach a near‐natural state. Thus, Alpine river sections with contrasting degrees of naturalness differ in terms of habitat turnover and vegetation succession, and these characteristics can only partially be restored by local measures.

Drivers of functional diversity in small-bodied mammals across a deforestation frontier in the Southern Brazilian Amazon

Deforestation remains the most pervasive driver of biodiversity erosion across tropical forests. Understanding how species can cope with such habitat changes is particularly important along the rapidly expanding agricultural frontiers. To do so, we used a functional perspective examining small mammal responses to habitat loss, fragmentation, and degradation across the ‘Arc of Deforestation’ in the Southern Brazilian Amazon. Small mammals were surveyed using a combination of conventional and pitfall traps across 20 forest fragments—ranging from 42 to 4743 ha—in addition to two relatively continuous forest sites (> 7000 ha). These fragments lie isolated by a cattle pasture matrix of varying grazing intensity. We then analysed taxonomic and functional diversity patterns—represented by Simpson Diversity and Rao Quadratic entropy indices—in Generalised Linear Models containing local- to landscape-scale predictors of variation. Further, we used a functional trait composition approach based on community-weighted mean trait values to depict and predict small mammal functional variations across this degradation gradient. From a total of 847 individuals recorded belonging to 24 taxa, functional responses tended to follow the taxonomic diversity, both increasing with fragment area. The functional dimension further was promoted by low fire-related disturbance. Functional trait composition was mainly driven by habitat quality, represented by tree density, arthropod biomass, and fire-related disturbance. Our results reinforce that small forest fragments sustain depauperate small mammal assemblages both taxonomically and functionally. Accounting for habitat quality further allows for boosting the persistence across functional groups. Our findings can be used to improve the efficiency of management practices thereby maximising the multiple dimensions of small mammal diversity and their associated ecosystem services across tropical deforestation frontiers.

Microbial Community Response to Alpine Meadow Degradation and Its Impact on Soil Nutrient Cycling

The degradation of alpine meadows on the Qinghai–Tibet Plateau is a major issue affecting both the ecology and the economy. Microorganisms play an important role in soil nutrient cycling and the regulation of ecosystem function. This study aimed to investigate the species composition and diversity of microbial communities and understand the response of microbial communities to changes in physicochemical properties resulting from meadow degradation. In this study, the soil bacterial and fungal communities’ composition and diversity of alpine meadows of degradation gradient were sequenced by high-throughput sequencing. During the process of grassland degradation, there were 59 bacterial taxa and 29 fungal taxa showing significant differences. The relative abundance of meadow pathogenic fungi significantly increased (p &lt; 0.05). PICRUSt2 analysis showed a decrease in synthesis-related functional gene abundance and an increase in metabolism-related functional gene abundance. FUNGuild analysis showed that symbiotic and saprophytic nutrient fungi decreased significantly (p &lt; 0.05). The soil nutrient cycling was mainly influenced by the beta diversity of microbial communities. Grassland degradation affects soil structure, thereby affecting the diversity of soil microbial composition and functional soil nutrient content. This work reveals the response of microbial communities to the degradation of alpine meadows and their impact on nutrient cycling, providing theoretical support for the protection and sustainable development of alpine meadows.

Towards interpretable learned representations for ecoacoustics using variational auto-encoding

Ecoacoustics is an emerging science that seeks to understand the role of sound in ecological processes. Passive acoustic monitoring is being used to collect vast quantities of soundscape audio recordings to study variations in acoustic community and monitor biodiversity. However, extracting relevant information from soundscape recordings is non-trivial. Recent approaches to machine-learned acoustic features appear promising but are limited by at least three issues: inductive biases, lack of interpretability and crude temporal integration. In this paper we introduce a novel self-supervised representation learning algorithm for ecoacoustics - a convolutional Variational Auto-encoder (VAE) - and directly address these shortcomings. Firstly, we train the network on soundscape recordings from temperate and tropical field sites along a gradient of ecological degradation to provide a more relevant inductive bias than prior approaches. Secondly, we present a new method that allows interpretation of the latent space for the first time, giving insight into the basis of classification. Thirdly, we advance existing methods for temporal aggregation of learned embeddings by encoding latent features as a distribution over time. Under our approach to increase interpretability, we provide insight into how learned features drive habitat classification for the first time: inspection of latent space confirms that varying combinations of biophony, geophony and anthrophony are used to infer sites along a degradation gradient. Our novel temporal encoding method increases sensitivity to periodic signals and improves on previous research that uses time-averaged representations for site classification. This approach also reveals the contribution of hardware-specific frequency response that create a potential bias; we demonstrate how a simple linear transformation can be used to mitigate the effect of hardware variance on the learned representation under our approach. Our novel approach paves the way for development of a new class of deep neural networks that afford more interpretable learned ecoacoustic representations to advance both fundamental and applied science and support global conservation efforts.

Coastal degradation regulates the availability and diffusion kinetics of phosphorus at the sediment-water interface: Mechanisms and environmental implications

Coastal wetlands have experienced considerable loss and degradation globally. However, how coastal degradation regulates sediment phosphorus (P) transformation and its underlying mechanisms remain largely unknown in subtropical coastal ecosystems. This study conducted seasonal field measurements using high-resolution diffusive gradient in thin films (DGT) and dialysis (Peeper) techniques, as well as a DGT-induced fluxes in sediments (DIFS) model, to evaluate the mobilization and diffusion of P along a degradation gradient ranging from pristine wetlands to moderately and severely degraded sites. We observed that sediment P is diminished by coastal degradation, and severely degraded sites exhibit a decline in the concentration of available P, despite the presence of distinct seasonal patterns. High-resolution data based on DGT/Peeper analysis revealed that labile P and soluble reactive P (SRP) concentrations varied from 0.0006 mg L−1 to 0.084 mg L−1 (mean 0.0147 mg L−1) and from 0.0128 mg L−1 to 0.1677 mg L−1 (mean 0.0536 mg L−1), respectively. Coastal degradation had a substantial impact on increasing SRP and labile P concentrations, particularly at severely degraded sites. Although severely degraded wetlands appeared to be P sinks (negative P flux at these sites), we did also observe positive diffusive flux in October, indicating that coastal degradation may accelerate the diffusion and remobilization of sediment P into overlying water. The simulations of the DIFS model provided compelling proof of the high resupply capacity of sediment P at severely degraded sites, as supported by the increased R and k-1 values but decreased Tc values. Taken together, these results suggest coastal degradation reduces the sediment P pool, primarily attributed to the strong remobilization of P from the sediment to porewater and overlying water by enhancing the resupply capability and diffusion kinetics. This acceleration induces nutrient loss which adversely impacts the water quality of the surrounding ecosystem. To reduce the adverse effects of coastal degradation, it is essential to adopt a combination of conservation, restoration, and management efforts designed to mitigate the risk of internal P loading and release, and ultimately maintain a regional nutrient balance.

Resilience of tropical invertebrate community assembly processes to a gradient of land use intensity

Understanding how community assembly processes drive biodiversity patterns is a central goal of community ecology. While it is generally accepted that ecological communities are assembled by both stochastic and deterministic processes, quantifying their relative importance remains challenging. Few studies have investigated how the relative importance of stochastic and deterministic community assembly processes vary among taxa and along gradients of habitat degradation. Using data on 1645 arthropod species across seven taxonomic groups in Malaysian Borneo, we quantified the importance of ecological stochasticity and of a suite of community assembly processes across a gradient of logging intensity. The relationship between logging and community assembly varied depending on the specific combination of taxa and stochasticity metric used, but, in general, the processes that govern invertebrate community assembly were remarkably robust to changes in land use intensity.

Effects of alpine meadows with different degradation gradients on the stability of the soil micro-foodweb in the Tibetan Plateau

Resource-transfer connections among bacteria, fungi, and microbivorous nematodes play an integral role in the decomposition pathways of soil micro-foodweb. Exploring the response of soil bacteria, fungi, and nematodes to grassland degradation is crucial for predicting the direction and trajectory of degradation. However, the knowledge about soil bacteria-fungi-nematode interactions in ecosystem function and nutrient cycling must be highlighted properly, especially in the Qinghai-Tibet Plateau. Therefore, this study focuses on four alpine meadows at different degenerate gradients (non-degraded grassland, slightly degraded grassland, moderately degraded grassland, and severely degraded grassland) on the Qinghai-Tibet Plateau. The investigation of soil bacteria-fungi-nematode interactions uses high-throughput sequencing and correlation network analysis. The results demonstrate significant variations in the composition of soil nematode genera, and bacterial and fungal phyla, across different degradation stages. Moreover, the diversity of nematodes, bacteria and fungi declined as grassland degradation worsened. Principal component analysis (PCA) revealed that alpine meadows with varying degradation gradients significantly influenced the community structure of bacteria, fungi, and nematodes. Mantel analysis indicated that soil water content (P < 0.05), total phosphorus (P < 0.05), and total nitrogen (P < 0.05) were the primary soil properties affecting the soil bacterial community. Similarly, available soil potassium (P < 0.05), microbial biomass carbon (P < 0.05), and microbial biomass nitrogen (P < 0.05) were the main soil factors influencing the soil fungal community. In contrast, the correlation between individual soil characteristics and soil nematodes did not reach a significant level, suggesting that a blend of physical and chemical properties regulates the soil nematode community. As grassland degradation intensified, the number of links in the interaction network of bacteria, fungi, and nematodes increased. Particularly, the networks between fungi and nematodes expanded, and the key species within each network varied with the different stages of grassland degradation. Concurrently, soil micro-foodweb decomposition pathways shifted. In the ND treatment, bacteria and fungi jointly dominated the degradation channels of the soil micro-food web, while the LD and MD treatments mainly dominated the degradation channels of fungi. On the other hand, SD treatment was dominated by bacterial degradation channels. This research adds to our theoretical understanding of meadow soil micro-foodwebs and the sustainable use of alpine grasslands in the Qinghai-Tibet Plateau.

Destructive selective logging in tropical forests causes soil carbon loss through forest degradation and soil redox change

Soil organic C (SOC) stock in tropical forests can be reduced significantly after logging, not only due to lowered above ground biomass (AGB) and consequentially reduced organic matter (OM) input, but also consumption on sequestrated soil C protected by OM-mineral association. In this study, we studied the loss of mineral-associated OM after logging in the main rooting zone (e.g., 0–30 cm), and examined a hypothetical twofold underlying mechanism of SOC reduction: first, decrease in AGB limiting OM input; second, decrease in soil redox potential (Eh) leading to the reductive dissolution of short-range-ordered iron (SRO Fe) minerals that destabilize some mineral-associated OM. Thirty-five plots at different degradation levels were investigated for both above- and belowground properties. AGB and tree community composition were employed as indicators of forest degradation gradient; multiple physicochemical properties in top-30 cm soils were measured every 10 cm depth. We analysed the relationship between AGB and soil C with the mediator SRO Fe, and investigated the role of soil Eh in linking the changes in AGB and SRO Fe. Our results revealed simultaneous decreases in AGB, SRO Fe and soil C in top-30 cm soils, and SRO Fe mediated 43 % of the hypothetical causal effect of AGB on soil C in deeper (20–30 cm) soil. Soil Eh decreased with decreasing AGB in a logistic pattern, dropping to a reductive regime (Eh7 ≤ 0.05 V) when more than half of the AGB was removed from the pristine level. Mean SRO Fe stock in the reductive soils was significantly lower than that in the oxic soils (Eh7 > 0.05 V), and the loss of SRO Fe correspond to the decomposition of OM in 10–30 cm soils. We suggest that the reductive shift in soil is caused by the weakened evapotranspiration as destructive selective logging inflicts canopy openness and succession failure. This study presents the possibility that forest degradation may reduce the size of protected soil C pool resulting from the loss of soil SRO Fe minerals.

Bacterial diversity of herbal rhizospheric soils in Ordos desert steppes under different degradation gradients

Objectives This study explored the effects of different degradation gradients on bacterial diversity in the rhizospheric soils of herb plants. Methods The alpha diversity, species composition and correlations of bacterial communities in the rhizospheric soils of herb plants were studied using metagenomics 16SrDNA gene high-throughput sequencing. Results The diversity of bacterial communities in the rhizospheric soils of herb plants differed during the degradation of desert steppes. An analysis of bacterial community alpha diversity indices showed the bacterial diversity and species evenness of rhizospheric soils were best in moderately degraded desert steppes. Among all samples, a total of 43 phyla, 133 classes, 261 orders, 421 families, 802 genera and 1,129 species were detected. At the phylum level, the predominant bacterial phyla were: Actinobacteria, Proteobacteria, Acidobacteria, Gemmatimonadetes, Chloroflexi, Planctomycetes and Bacteroidetes. At the genus level, the predominant bacterial genera were: RB41, Sphingomonas, WD2101_soil_group_unclassified, Pseudomonas and Actinomyces. The relative abundance of unknown genera was very large, which deserves further research. At the phylum and genus levels, the species abundance levels under slight and moderate degradation were significantly higher than those under extreme degradation. Correlation network diagrams showed there were many nodes in both slightly deteriorated and moderately deteriorated soils, and the node proportions were large and mostly positively correlated. These results indicate the bacterial communities in rhizospheric soils under slight or moderate deterioration are relatively stable. The rhizospheric soil microbes of desert steppes can form a stable network structure, allowing them to adequately respond to environmental conditions. Conclusions The bacterial communities in the rhizospheric soils of herb plants differ between different degradation gradients. The species number, abundance and diversity of bacterial communities in rhizospheric soils are not directly correlated with degree of degradation. The abundance, species diversity and species abundance of bacterial communities in the rhizospheric soils of moderately degraded desert steppes are the highest and most stable. The soil bacterial diversity is lowest in severely degraded desert steppes.