Moderately Degraded Research Articles

Impact of Meadow Degradations on the Probabilistic Distribution Patterns of Physical and Mechanical Indices of Rooted Soil in the Upper Regions of the Yellow River, China

The shear strength (particularly soil cohesion) of rooted soil is an important parameter that reflects the true erodibility of meadows, particularly in meadows experiencing different degrees of degradation, ranging from undegraded (UD) through to lightly degraded (LD) and from moderately degraded (MD) to heavily degraded (HD). The cohesion of rooted soil is controlled not only by the soil moisture content and its natural density, but also by roots (including not only their density, spatial distribution, and diameters, but also their tensile strength). This study aimed to improve the current understanding of the erosion resistance of rooted soil and elucidate the impact of meadow degradation on the physical–mechanical indices of rooted soil. Based on this discussion, a one-way analysis of variance was performed at significance levels of 0.05 and 0.01 to test the impact of degradation on the physical–mechanical indices of rooted soil across degradation. Furthermore, the probabilistic distributions of the physical–mechanical indices were described using normal, gamma, Weibull, and generalized extreme values (GEV). The Kolmogorov–Smirnov (KS) test was used to identify the optimal distribution based on p-values and the Pearson correlation coefficient was used to quantify the correlation between the cohesion of rooted soil and other indices. The one-way ANOVA indicated that the soil’s natural density and soil moisture content decreased firstly, followed by an increase, the root amount and cohesion decreased, the root content experienced an initial increasing and then decreasing trend, and the internal friction angle exhibited a stepwise increasing trend. The four distributions sufficiently described the actual distribution of data on the physical–mechanical indices of rooted soil, except for the internal friction angle in UD and MD soils and the soil moisture content in MD soil. Additionally, the KS tests showed that the optimal distribution depended on both the physical–mechanical indices themselves and the degree of degradation. The Pearson correlation analysis showed that the correlation between cohesion and the other physical–mechanical indices varied considerably depending on the degree of degradation.

Soil microbial diversity and composition response to degradation of the alpine meadow in the southeastern Qinghai-Tibet Plateau.

With the interaction between global climate change and unreasonable human utilization, the alpine meadows on the Qinghai-Tibet Plateau have suffered various weathering degrees. Uncovering the degradation mechanism and restoration strategies can be facilitated by gaining insights into the diversity of soil microflora during meadow degradation. Therefore, we used Illumina sequencing technology to investigate the patterns of soil microbial diversity, microbial community composition, and the driving factors of microbial change in all non-degraded (ND), lightly degraded (LD), moderately degraded (MD), and severely degraded (SD) alpine meadows in the southeastern Qinghai-Tibet Plateau. Our results pointed out that with the intensification of degradation, vegetation characteristics were significantly reduced, and soil parameters significantly varied among all degraded meadows. The contents of soil organic carbon (SOC), total nitrogen (TN), available phosphorus (AN), and total phosphorous (AK) in soils decreased with the increase of degradation. The dominant bacterial phyla were the same regardless of the meadow degradation level with Actinobacteria (37.67%) and Proteobacteria (20.62%) having the highest relative abundance. Meanwhile, the dominant fungi were Ascomycota (49.9%). Based on the linear discriminant analysis (LDA) and effect size (LEfSe) method, 38 bacterial and 49 fungal species were found to be affected in the degraded alpine meadow, most of which belonged to Actinobacteria and Ascomycota, respectively. Mantel test analysis illustrated that the bacterial community was mainly significantly dependent on below-ground biomass, pH, soil organic carbon, and total nitrogen, while the fungal community was significantly dependent on soil organic carbon, total nitrogen, available nitrogen, and available potassium. These results suggest that the degeneration of alpine meadows contributes to the variability of the diversity and composition of microflora on the Tibetan plateau. Yet this effect is mainly dependent on soil factors.

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.

Influence of alpine meadow deterioration on soil microbial communities in the Yangtze River source region

Introduction: Although soil microbial populations are a good predictor of soil texture, little is known about how they react to alpine meadow deterioration.Methods: This study utilized Illumina HiSeq sequencing to investigate the effects of alpine meadow degradation on soil microbial communities in the Yangtze River source basin at five different degradation levels [i.e., non–degraded (ND), slightly degraded (LD), moderately degraded (MD), severely degraded (SD), and very severely degraded (VD)].Results: The results indicated that bacterial and fungal α-diversity were not substantially different (p > 0.05) across the damaged alpine meadows, while β-diversity significantly differed (p < 0.01), indicating a higher variation in the microbial community due to alpine meadow degradation. Proteobacteria reduced considerably (p < 0.05) by 8.75%, 22.99%, and 24.65%, while Acidobacteria increased significantly (p < 0.05) by 41.67%, 85.20%, and 108.67%, in MD, SD, and VD compared with ND, respectively. Ascomycota declined significantly (p < 0.05) in the MD, whereas unclassified phyla rose significantly (p > 0.05) in the VD compared to the ND. The heatmaps of bacterial and fungal communities revealed two clusters: a ND, LD, and MD group and a SD and VD group, suggesting significant changes in soil microorganisms of alpine meadow in the SD and VD. Redundancy analysis (RDA) revealed that soil moisture, soil bulk density, soil organic carbon, total nitrogen, and plant biomass could explain 73.8% and 39.4% of the variance in bacterial and fungal community structure, respectively.Discussion: These findings imply that degradation of the alpine meadow impacts both plant and soil qualities, ultimately leading to changes in soil microbial populations in the Yangtze River’s source region.

Impact of cattle night corralling on soil properties and vegetation in the semiarid degraded rangeland of Ethiopia

In Ethiopia, rangeland degradation is a severe environmental problem. To improve rangeland vegetation cover and support the rangeland-based livelihoods, it is imperative to repair degraded rangeland using different rehabilitative measures. This study was carried out to evaluate the effects of night cattle corralling impact on soil chemical parameters, herbaceous species compositions and biomass yield of degraded rangeland. To conduct the experiment, severely degraded (SD) and moderately degraded (MD) rangelands with an area size of 30m x10m (300m2) each was identified. Then, each of the selected rangeland types was separated into two paddocks with an area size of 10m x 15m (150 m2). The treatment paddocks of the severely and moderately degraded rangeland were treated by cattle impact tools corralling cattle every night in the paddock for one month (SDT1 and MDT1). While the second paddock in both rangeland types was used as a control without cattle impact tools (SDT2 and MDT2). A randomized complete block design was used and each treatment was replicated three times. The results showed that soil chemical parameters and herbaceous species compositions in both degraded rangeland paddocks treated with cattle impact tools (SDT1 and MDT1) changed significantly (p<0.05) than paddocks without cattle impact tools (SDT2 and MDT2). Likewise, there was an increased difference (p<0.05) in biomass yields of 2.98 ton/ha and 5.35ton/ha from severely and moderately degraded rangeland, respectively for paddocks treated with cattle impact tools (SDT1 and MDT2), compared to paddocks of biomass yield of 0.98 ton/ha and 2.78 ton/ha without cattle impact tools treatments for SDT2 and MDT2 respectively. Thus the result from this study emphasized the advantage of night cattle corralling impact tools for improved soil parameters and herbaceous species compositions of degraded rangeland. Hence, we concluded that employing cattle impact tools to restore degraded rangeland significantly improved soil physico-chemical properties, with ultimate effect on vegetation cover, vegetation compositions and herbaceous biomass yield, attributed from soil seed bank growth. Bangladesh Journal of Animal Science 51 (4): 152-162

Accelerated temporal turnover of the soil nematode community under alpine grassland degradation

AbstractSoil nematodes play pivotal roles in the soil food web. However, the trophic regulation on nematodes in the soil micro‐food web and its temporal dynamics are less explored. Here, we investigated the seasonal dynamics of soil nematode community in an alpine grassland on the Qinghai–Tibet Plateau at non‐degraded (ND), moderately degraded (MD) and severely degraded (SD) stages, either under open‐top chamber warming (W) or not (NW). Nematode richness was higher in SD than in MD and ND that did not differ, accompanied by a clear shift from the bottom‐up regulation via belowground productivity in ND to the top‐down regulation via omnivore and predator nematodes in SD. The intensified top‐down regulation in SD was explained by increased proportions of predator and omnivore nematodes, likely induced by the expanded soil pore size in SD. As a result, accelerated temporal turnover of nematode community was observed under grassland degradation, which were 0.006 (slope, p = 0.78), 0.045 (p = 0.07), and 0.077 (p = 0.001) in ND, MD, and SD, respectively. Moreover, grassland degradation strengthened the association between nematode density and ecosystem respiration, whose slope was higher in SD (0.0025, p < 0.05) than in MD (0.0008, p < 0.01) or ND (insignificant). In contrast, warming did not affect the temporal turnover of the nematode community, richness, nor its role in ecosystem respiration. Overall, we revealed the accelerated temporal turnover of nematode community and its strengthened role in determining ecosystem respiration under alpine grassland degradation, suggesting that trophic cascade changes under ecosystem degradation may alter the ecosystem functioning.

Increased availability of preferred food and decreased foraging costs from degraded grasslands lead to rodent pests in the Qinghai-Tibet Plateau

The increased population density of rodent species during ongoing grassland degradation further deteriorates its conditions. Understanding the effects of grassland degradation on rodent feeding habits is of great value for optimizing grassland management strategies. In this study, lightly degraded (LD), moderately degraded (MD), severely degraded (SD), and reseeded grassland (RG) were selected and their plant resources and soil physical properties were investigated. In addition, the study usedITS2barcode combined with the Illumina MiSeq sequencing method to analyze the food composition and proportion of plateau zokors in different grassland conditions. The results showed that, with grassland degradation, plant biomass decreased, but the relative proportion of forbs increased (LD: 32.05 ± 3.89%; MD: 28.97 ± 2.78%; SD: 49.16 ± 4.67% and RG: 10.93 ± 1.53%). Forbs were the main food of the plateau zokor, accounting for more than 90% of their diet, and the animal had a clear preference forPotentillaspecies; the soil compaction of feeding habits showed a decreasing trend in the 10–25 cm soil layer, suggesting a decreased foraging cost. Nutritional analysis showed that the stomach content of crude protein in zokors feeding on MD grassland was significantly higher than that of animals feeding on the other grassland types. Structural equation modeling showed that soil physical properties and the relative biomass of forbs had significant (P< 0.05) and extremely significant (P< 0.001) impacts on the population density of plateau zokors, with direct impact contribution rates of 0.20 and 0.63. As the severity of grassland degradation increased, although the aboveground and underground biomass of the plants decreased, the proportion of food preferred by the plateau zokor increased, and the corresponding changes in the feeding environment resulted in decreased foraging energy expenditure, thereby increasing the suitability of the degraded grassland for the plateau zokor. Compared with degraded grassland, the food diversity and evenness of zokors increased, the food niche width enlarged, and the proportion of weeds decreased in RG, which increased the difficulty of obtaining food. Reseeding in grassland management is therefore an effective way to control plateau zokors.

Degradation‐induced microbiome alterations may aggravate soil nutrient loss in subalpine meadows

AbstractGrassland degradation has become a serious environmental problem worldwide. However, the link between grassland degradation and soil functional microorganisms remains unclear. Here, we investigated the effects of subalpine meadow degradation on the taxonomic and functional communities of the soil microbiome on Mount Wutai on the eastern margin of the Loess Plateau, China, using shotgun metagenomic sequencing. The results showed that vegetation degradation decreased most soil nutrients (e.g., soil organic carbon [SOC, −48.9%], total nitrogen [TN, −15.2%] and carbon [TC, −38.3%]), leading to significant changes in the taxonomic (r = 0.892, p < 0.001) and functional compositions (r = 0.972, p < 0.001) of the microbial communities (explaining 66.6% and 64.5% of the variance, respectively). The structural equation model (SEM) showed that variations in the soil nutrient status and plant parameters caused by degradation resulted in changes in the microbial community structure and function. The variations in the plant and microbial communities during degradation altered carbon (C) and nitrogen (N) cycling separately or interactively. Among the C degradation‐related genes, the relative abundances of cellulose degradation, sugar utilization and chitin degradation genes in moderately degraded (MD) and heavily degraded (HD) meadows were significantly higher than those in nondegraded (ND) meadows (p < 0.05). The abundance of denitrification genes (nirK, nirS, norB and norC) and nitrification genes (pmoA/amoA, pmoB/amoB, pmoC/amoC and hao) was higher in all degraded meadows, which increased the risk of soil N loss. Our findings revealed the negative feedback of microbes due to subalpine meadow degradation, during which metabolically active microbes tended to accelerate soil nutrient loss.

Deep soil water deficit causes Populus simonii Carr degradation in the three north shelterbelt region of China

Large-scale afforestation exacerbates soil water scarcity in a semiarid region of northern China, causing the formation of a dried soil layer (DSL) and ecosystem degradation, and overmature Populus simonii Carr (>30 years) degradation in the Three North Shelterbelt Program (TNSP) area has recently been observed. Determining the relationship between degraded Populus simonii Carr and soil water deficit is essential for afforestation in semiarid regions. We monitored soil water content (SWC) to a 160 cm depth in an area with five degradation degrees (healthy, light degradation, moderate degradation, severe degradation, and dead) to investigate soil water dynamics and DSL characteristics from May 2018 to December 2021. The results showed that: compared with that of healthy Populus simonii Carr (94.7 ± 26.2 mm), the shallow layer (0–80 cm) soil water storage of severely degraded (114.1 ± 29.9 mm) and dead Populus simonii Carr (128.0 ± 35.7 mm) was restored by 19.4 mm and 33.3 mm, respectively. However, the deep-layer (80–160 cm) SWC was difficult to recover and a DSL gradually developed, the DSL − SWC was only 9.3–11.95 %. The deep-layer relative extractable soil water (REW) of healthy Populus simonii Carr was significantly higher than that of moderately degraded, severely degraded, and dead Populus simonii Carr (P < 0.05). The deep-layer SWC decreased with increasing degradation due to coarser soils and increased BD. A greater bulk density (BD) and higher sand proportion reduced the soil water holding capacity. Poor site conditions reduced the resistance of shelterbelts, causing the degradation and mortality of Populus simonii Carr during drought. Therefore, our results improve the understanding of the soil water dynamics and degradation mechanism of Populus simonii Carr, providing a theoretical basis for managing and maintaining the TNSP.

Changes in soil free-living diazotrophic community and co-occurrence patterns along desert wetland degradation gradient in the Mu Us Desert, northern China

Climate change and human activities have led to the degradation of desert wetlands. Free-living diazotrophs are vital to soil nitrogen input. However, a comprehensive understanding of how soil free-living diazotrophic community and co-occurrence patterns respond to desert wetland degradation is lacking. Here, quantitative polymerase chain reaction (qPCR) and amplicon sequencing targeted on nitrogenase ( nifH ) genes and network analysis were used to investigate soil free-living diazotrophic abundance, diversity and composition and co-occurrence patterns along the wetland degradation gradient [non-degraded (ND), lightly degraded (LD), moderately degraded (MD), and severely degraded (SD) wetlands] in the southeastern of Mu Us Desert, northern China. Results showed the abundance, Shannon, Simpson, Chao1 and Ace indexes decreased ( P < 0.05) by 14.6%, 20.7%, 2.1%, 46.5% and 45.0% at SD, respectively, whereas no significant difference ( P > 0.05) was observed between ND and LD. The relative abundance of Proteobacteria generally decreased across the degradation (53.5%–19.7%), while the variation was opposite for Cyanobacteria from ND to MD (6.2%–40.1%). Soil organic carbon had the strongest linkage with abundance, diversity and composition, followed by total nitrogen, moisture and pH. The lowest network nodes, edges and density were observed at MD and SD, indicating the complexity of free-living diazotrophic networks was reduced by continued degeneration. Overall, severe desert wetland degradation more negatively affects soil free-living diazotrophic abundance, diversity and network complexity than light degradation. The degradation promotes the growth of autotrophic diazotrophs, inhibiting heterotrophic diazotrophs. These changes are mostly related to the loss of soil organic carbon.

Responses of Soil Fungal Communities to Subalpine Meadow Degradation in Mount Wutai

Grassland degradation has become a worldwide ecological problem. Although soil microorganisms, as the main participants in the process of grassland degradation, play a key role in maintaining ecosystem function and improving soil productivity, little is known about the changes in microbial communities caused by grassland degradation and their relationship with soil properties and plant communities. In this study, we used Illumina MiSeq sequencing to analyze the soil fungal communities of subalpine meadow soil at four different degradation stages[i.e., non-degraded (ND), lightly degraded (LD), moderately degraded (MD), and heavily degraded (HD)] on Mount Wutai. The results showed that Ascomycota, Basidiomycota, and Zygomycota were the dominant phyla of soil fungi in the subalpine meadow, regardless of degradation stage. LEfSe showed that the subalpine meadows with different degradation degrees were enriched with different biomarkers. Compared with ND, MD and HD were enriched with more pathogenic fungi. Moreover, HD apparently decreased the richness and Shannon indexes of soil fungal communities compared with those of ND. Non-metric multidimensional scaling (NMDS) and similarity analysis (ANOSIM) indicated that the compositions and structures of fungal communities were significantly different among meadows with different degradation degrees (P<0.05). Redundancy analysis (RDA) showed that soil water content, total nitrogen, plant richness, and ammonium nitrogen were significantly correlated with the compositions and structures of fungal communities (P<0.05). There were significant correlations between α diversity and β diversity between plant and fungal communities (P<0.05), indicating strong coupling. The results of our study provide a theoretical basis for further research on the changes in soil fungal communities and their driving mechanism in different degradation stages of subalpine meadows.

Dynamics of Grassland Vegetation Composition across different Land-use Types on the Qinghai Tibet Plateau: Implications to Combat Grassland Degradation

The constant biotic and abiotic interventions on the Qinghai Tibet Plateau (QTP) are seriously degrading the grasslands and, at the same time, restricting the active ecosystem function and grassland vegetation distribution on the plateau. This research analyses the dynamics of grassland vegetation composition across three land uses and counties. The degree of grassland degradation was divided into four land-use types based, i.e., healthy grassland (HG), restored grassland (RG), moderately degraded (MD) grassland, and severely degraded (SD) grassland. About 32 plant species were recorded in Tiebujia county, 28 in Maqin county, and 18 in Maduo county. Results showed Poa crymophila, Polygonum sibiricum, Leontopodium nanum and Oxytropis falcatabunge as the most abundant grassland species in all land-uses and counties. The richness of species ranged from 8 to 12 species per land-use, suggesting low richness and diversity in restored and degraded grassland. A positive non-significantly mean change (p&lt;0.05) was detected for richness and evenness indices while a negative mean change (p&lt;0.05) was detected for Simpson and Shannon indices in the alpine meadow and steppe in both Maqin and Maduo county. The results imply that degradation affects grassland vegetation, health, and distribution across the QTP. Plant total cover for the healthy grassland covered far more areas than other land-uses. Urgent mitigation measures to halt grassland degradation and decline in plant vegetation composition on the plateau should be adopted.

Exchangeable Ca2+ content and soil aggregate stability control the soil organic carbon content in degraded Horqin grassland

Grasslands store 20–30% of global soil organic carbon (SOC) but a majority of grasslands are suffering degradation accompanied by SOC loss. SOC stock is determined by the balance between C input from plants and C output from microbial decomposition, but the relative importance of these factors in controlling SOC and the stabilization mechanisms of SOC are poorly understood. Here, we investigated the main factors influencing SOC loss along a grassland degradation gradient in the Horqin grassland, including non-degraded (ND), lightly degraded (LD), moderately degraded (MD), and severely degraded (SD) grasslands. The contents of SOC, TN and TP at the ND and LD sites were significantly higher than those at the MD and SD sites. Plant aboveground, belowground and litter biomass significantly decreased with the intensification of degradation. Compared to the ND site, the mean weight diameter of soil aggregates decreased by 8.70%, 17.39% and 26.1% at the LD, MD and SD sites, respectively. Exchangeable Ca2+ and Mg2+ contents also decreased along the degradation gradient. Moreover, the results of structural equation modeling indicated that grassland degradation reduced plant biomass, resulting in an increase in soil available phosphorus content, thus causing less energy losses for microbes through their deployment of extracellular enzymes, eventually leading to an increase in microbial carbon use efficiency. Correlation analysis also confirmed that microbial carbon use efficiency was positively correlated with the ratio of G+/G-. The results of boosted regression tree model suggested that exchangeable Ca2+ and mean weight diameter were the two most influential factors on SOC among the 13 studied variables. Stabilization mechanisms linked to chemical stabilization by polyvalent cations and soil aggregation were the most important controlling factors on SOC content during grassland degradation. In summary, although microorganisms mitigated soil carbon loss to some extent by decreasing their total biomass and increasing their carbon use efficiency, the weakened physical protection of SOC resulted in SOC loss during grassland degradation.

Variations of soil organic nitrogen fractions during degradation succession in the Gahai Wetland, Northwest China.

This study amined to explore the variation of soil organic nitrogen components across the degradation succession of Gahai Wetland. By combining field sampling and laboratory analysis, the content and distribution characteristics of soil organic nitrogen components, i.e., hydrolytic total nitrogen (HTN), unidentified acidolytic nitrogen (HUN), ammonium nitrogen (AMN), amino acid nitrogen (AAN) and acid amino sugar nitrogen (ASN) were investigated in undegraded (UD), lightly degraded (LD), moderately degraded (MD), and heavy degraded (HD) Gahai Wetland. The results showed that, in the 0-10 cm layer, the contents of total nitrogen (TN), HUN, AMN, and AAN in LD decreased by 17.3%, 19.4%, 8.6%, and -5.6%, 28.0%, 19.4%, 17.1% and 0 in MD, and 35.8%, 28.8%, 28.6% and 55.6% in HD, respectively. In the 10-20 cm layer, the four components decreased by 4.0%, 10.3%, 2.9% and 9.1% in LD, 21.0%, 18.3%, -2.9% and -9.1% in MD, and 9.9%, 38.9%, 21.2% and 51.4% in HD, respectively. The corresponding contents in the 20-40 cm soil layer did not change. The proportion of soil acid-hydrolyzed nitrogen components to TN under four degradation stages was HUN (25.9%-32.5%) &gt; AMN (6.7%-11.1%) &gt; AAN (4.8%-11.1%) &gt; ASN (1.2%-4.4%). Soil water content was the main driving factor for variations of soil organic nitrogen components as indicated by the results of redundancy analysis. Degradation of the Gahai Wetland significantly reduced the content of soil TN and the components of acid-hydrolyzed nitrogen in 0-10 cm soil layer, and weakened the nitrogen "sink" function of soils. The AAN and ASN were sensitive to wetland degradation.

Decreased precipitation frequency altered abundance, but not community structure, of soil nematodes in degraded grasslands

Rainfall patterns in arid and semi-arid regions are characterized by a reduction in rainfall frequency. However, under this novel climatic condition, potential changes in soil nematode community among different degraded grasslands remain unclear. We conducted a mesocosm experiment to test the effects of lower precipitation frequency (decreased by 50% from the long-term mean) on nematodes in the lightly degraded (LDG), moderately degraded (MDG) and severely degraded grasslands (SDG). The decreased precipitation frequency treatment significantly reduced the total abundance of nematodes by reducing soil moisture and enhancing moisture variability. Compared with other trophic groups of nematode, bacterivores were more sensitive to the altered precipitation and were significantly suppressed by higher soil moisture variation caused by lower precipitation frequency in the degraded grasslands. The decreased precipitation frequency treatment promoted plant belowground biomass through increasing soil moisture variation, which promoted plant parasites in LDG. However, in MDG and SDG, plant parasites were mainly suppressed by higher soil moisture variation under the altered precipitation frequency treatment, and were less impacted by the aforementioned stimulation in plant belowground biomass. The nematode community structure was not affected by the altered precipitation frequency treatment. This study provides experimental data for predicting responses of ecosystem functions to the projected changes in precipitation regimes. These findings are critical for making feasible decisions for the sustainable management of degraded grasslands.

The Impact of Neurocognitive Skills on Recognition of Spectrally Degraded Sentences.

Recent models theorize that neurocognitive resources are deployed differently during speech recognition depending on task demands, such as the severity of degradation of the signal or modality (auditory vs. audiovisual [AV]). This concept is particularly relevant to the adult cochlear implant (CI) population, considering the large amount of variability among CI users in their spectro-temporal processing abilities. However, disentangling the effects of individual differences in spectro-temporal processing and neurocognitive skills on speech recognition in clinical populations of adult CI users is challenging. Thus, this study investigated the relationship between neurocognitive functions and recognition of spectrally degraded speech in a group of young adult normal-hearing (NH) listeners. The aim of this study was to manipulate the degree of spectral degradation and modality of speech presented to young adult NH listeners to determine whether deployment of neurocognitive skills would be affected. Correlational study design. Twenty-one NH college students. Participants listened to sentences in three spectral-degradation conditions: no degradation (clear sentences); moderate degradation (8-channel noise-vocoded); and high degradation (4-channel noise-vocoded). Thirty sentences were presented in an auditory-only (A-only) modality and an AV fashion. Visual assessments from The National Institute of Health Toolbox Cognitive Battery were completed to evaluate working memory, inhibition-concentration, cognitive flexibility, and processing speed. Analyses of variance compared speech recognition performance among spectral degradation condition and modality. Bivariate correlation analyses were performed among speech recognition performance and the neurocognitive skills in the various test conditions. Main effects on sentence recognition were found for degree of degradation (p = < 0.001) and modality (p = < 0.001). Inhibition-concentration skills moderately correlated (r = 0.45, p = 0.02) with recognition scores for sentences that were moderately degraded in the A-only condition. No correlations were found among neurocognitive scores and AV speech recognition scores. Inhibition-concentration skills are deployed differentially during sentence recognition, depending on the level of signal degradation. Additional studies will be required to study these relations in actual clinical populations such as adult CI users.

Vertical and seasonal changes in soil carbon pools to vegetation degradation in a wet meadow on the Qinghai-Tibet Plateau

Wet meadows provide opportunities to decrease carbon dioxide (CO2) and methane (CH4) released into the atmosphere by increasing the soil organic carbon (SOC) stored in wetland systems. Although wet meadows serve as the most important and stable C sinks, there has been very few investigations on the seasonal distributions of SOC fractions in high-altitude wet meadows. Here, we studied the effects of four vegetation degradation levels, non-degraded (ND), lightly degraded (LD), moderately degraded (MD), and heavily degraded (HD), on the measured vertical and seasonal changes of SOC and its different fractions. Among these vegetation degradation levels, 0–10 and 10–20 cm soil depths in ND plots had significantly higher SOC contents than the other degradation levels had throughout the year. This is attributed to the relatively greater inputs of aboveground plant litter and richer fine-root biomass in ND plots. Particulate organic carbon (POC) and light fraction organic carbon (LFOC) showed similar vertical and seasonal variations in autumn, reaching a minimum. Moreover, microbial biomass (MBC) and easily oxidizable organic carbon (EOC) contents were highest in summer and the smallest in winter, while dissolved organic carbon (DOC) content was highest in spring and lowest in summer, and were mainly concentrated in the 0–20 cm layer. Pearson correlation analysis indicated that soil properties and aboveground biomass were significantly related to different SOC fractions. The results indicate that vegetation degradation reduces the accumulation of total SOC and its different fractions, which may reduce carbon sink capacity and soil quality of alpine wet meadows, and increase atmospheric environmental pressure. In addition, vegetation biomass and soil characteristics play a key role in the formation and transformation of soil carbon. These results strengthen our understanding of soil C dynamics, specifically related to the different C fractions as affected by vegetation degradation levels and soil depth, in wet meadow systems.

Divergent responses of the soil bacteria community to multi‐level nitrogen enrichment in temperate grasslands under different degrees of degradation

AbstractNitrogen (N) enrichment has been reported to affect the soil bacteria community in natural temperate grasslands. However, it remains unknown how the bacteria community responds to N enrichment in degraded grasslands. Here, we established multi‐level N enrichment experiments in temperate grasslands under non‐degraded (ND), moderately degraded (MD), severely degraded (SD), and extremely degraded (ED) sites in northern China. The bacteria community was investigated by high‐throughput sequencing and linked to major abiotic and biotic factors. We found bacterial diversity was lower in ED grassland than the other grasslands, and community composition highly varied across the four degrees of degradation. Change in bacterial diversity was due to the different variations in dominant phyla, and soil phosphorus content contributed to the variation in community composition across grasslands under increasing degradation. In ND, MD, and SD grasslands, bacterial diversity was not significantly altered by N enrichment below 30 g‐N m−2 yr−1 but declined when N enrichment was greater than 30 g‐N m−2 yr−1. The bacterial diversity loss was associated with the decreased soil pH under N enrichment. However, in ED grassland, bacterial diversity decreased when N enrichment was below 30 g‐N m−2 yr−1 and remained unchanged when N enrichment was greater than 30 g‐N m−2 yr−1. Change in bacterial diversity was modulated by soil N availability. Besides, N enrichment shifted bacterial community composition via changing soil N availability. Our study identified bacterial diversity loss in ED grassland and differently nonlinear responses of bacterial diversity to multi‐level N enrichment in grasslands under different degrees of degradation.

Vegetation degradation impacts soil nutrients and enzyme activities in wet meadow on the Qinghai-Tibet Plateau

Vegetation degradation, due to climate change and human activities, changes the biomass, vegetation species composition, and soil nutrient input sources and thus affects soil nutrient cycling and enzyme activities. However, few studies have focused on the responses of soil nutrients and enzymes to vegetation degradation in high-altitude wet meadows. In this study, we examined the effects of vegetation degradation on soil nutrients (soil organic carbon, SOC; total nitrogen, TN; total phosphorus, TP) and enzyme activities (i.e., urease, catalase, amylase) in an alpine meadow in the eastern margin of the Qinghai-Tibet Plateau. Four different levels of degradation were defined in terms of vegetation density and composition: primary wet meadow (CK), lightly degraded (LD), moderately degraded (MD), and heavily degraded (HD). Soil samples were collected at depth intervals of 0–10, 10–20, 20–40, 40–60, 60–80, and 80–100 cm to determine soil nutrient levels and enzyme activities. The results showed that SOC, TN, catalase and amylase significantly decreased with degradation level, while TP and urease increased with degradation level (P < 0.05). Soil nutrient and enzyme activity significantly decreased with soil depth (P < 0.05), and the soil nutrient and enzyme activity exhibited obvious "surface aggregation". The activities of soil urease and catalase were strongest in spring and weakest in winter. The content of TN in spring, summer, and autumn was significantly higher than observed in winter (P < 0.05). The soil TP content increased in winter. Soil amylase activity was significantly higher in summerm than in spring, autumn, and winter (P < 0.05). TP was the main limiting factor for plant growth in the Gahai wet meadow. Values of SOC and TN were positively and significantly correlated with amylase and catalase (P < 0.05), but negatively correlated with urease (P < 0.05). These results suggest the significant role that vegetation degradation and seasonal freeze–thaw cycle play in regulating enzyme activities and nutrient availability in wet meadow soil.

Response of soil labile organic carbon fractions and carbon-cycle enzyme activities to vegetation degradation in a wet meadow on the Qinghai–Tibet Plateau

Vegetation degradation resulting from climate change and human activities in wet meadows is an important issue worldwide. This phenomenon is known to influence soil labile organic carbon (LOC) and enzyme activities due to changes in environmental conditions. However, little is known about the response of LOC and enzyme activities to vegetation degradation in high-altitude wet meadows. In this study, we examined the response of LOC and carbon-cycle enzyme activities to different intensities of vegetation degradation (i.e., non-degraded (ND), slightly degraded (SD) moderately degraded (MD), and heavily degraded (HD)) in a Tibetan wet meadow. The contents of soil organic carbon (SOC), dissolved organic carbon (DOC), microbial biomass carbon (MBC) and light fraction organic carbon (LFOC) and the carbon-cycle enzyme activities (i.e., cellulase, amylase and β-glucosidase) were investigated in two growing seasons (2016 and 2017). We found that the content of soil SOC and LOC fractions declined with increasing soil depth in each degraded level except for HD. Vegetation degradation significantly decreased the amount of SOC at depths of 0–10 cm and 10–20 cm, and this decrease was attributed to the relative reduction of carbon source input and higher carbon decomposition. Vegetation degradation also significantly reduced the contents of SWC, DOC, MBC, LFOC, amylase and β-glucosidase in the topsoil layers (0–10 and 10–20 cm). However, the corresponding contents in deeper soil layers had no significant differences. In addition, the SWC, DOC, LFOC and the carbon-cycle enzyme activities were higher in 2016 than in 2017. Significant correlations were obtained between SWC, SOC, LOC fractions and enzyme activities. Soil moisture was found to be the main abiotic driver for variation of soil carbon and enzyme activities. Our results indicate that vegetation degradation in the Tibetan wet meadows decreased the quantity of topsoil labile carbon fractions and enzyme activities and heavily degraded vegetation may lead to a change of profile distribution in soil carbon pool.