Meadow Degradation Research Articles

Changes in survival and growth in response to different combinations of turbidity and duration in eelgrass Zostera marina plants

Increased water turbidity is considered a primary cause of the loss of seagrass meadows. This paper first quantified the interactive influence of different combinations of turbidity and duration on the responses of Zostera marina plants in terms of survivorship, morphology and growth. The recovery potential of Z. marina plants, as well as the degrees of potential correlations between key factors induced by the increased turbidity and the survival and growth variables, were assessed. The LT50 (lethal time that caused an increase in mortality to 50% of that of the control) and EC50 (effect concentration, i.e., turbidity level that caused a decrease in growth to 50% of that of the control) were calculated to reveal the quantitative relationship between turbidity and duration that resulted in limiting effects on the survival and growth of Z. marina plants. Z. marina plants were exposed to different combinations of water turbidity [4 (control), 50, 100, 200, 300 and 400 NTU] and duration (5, 10, 15 and 20 days), and then the plants were transferred to the control condition for over 30 days under laboratory conditions. The results showed that the recovery effort (the percentage of the survival of plants at the end of recovery to that of plants at the end of direct turbidity stress) of Z. marina exposed to different combinations of turbidity and duration was lower than 100%, indicating that short-term periods of increased water turbidity would lead to long-term effects on the survival of Z. marina plants. Water turbidity and duration displayed a significant interactive effect on the survival and growth of Z. marina plants. Regression analysis revealed that the relationship between water turbidity and duration that resulted in limiting effects on the survival and growth of Z. marina could be described as a strong inverse function. Spearman correlation analysis showed that the decrease in survival and growth of Z. marina plants was mostly caused by increased silt load in turbid waters, and subsequently by light reduction. This study will further develop our understanding of the degradation and disappearance of seagrass meadows induced by increased turbidity.

Sonar and in situ surveys of eelgrass distribution, reproductive effort, and sexual recruitment contribution in a eutrophic bay with intensive human activities: Implication for seagrass conservation

Seagrass beds are recognized as pivotal and among the most vulnerable coastal marine ecosystems globally. The eelgrass Zostera marina L. is the most widely distributed seagrass species and dominates the temperate northern hemisphere. However, an alarming decline in seagrass has been occurring worldwide due to multiple stressors. Seagrass meadow degradation is particularly serious in the Bohai Sea, in temperate China; however, large areas (> 500 ha) of seagrass meadows and population recruitment have rarely been reported in this area. In the present study, we report on a large eelgrass bed in a eutrophic bay of the Bohai Sea. Sonar and field survey methods were used to investigate the distribution of seagrass and its population recruitment. We also analyzed the major threats to this large seagrass bed. Results showed that a large Z. marina bed with an area of 694.36 ha occurred in this area of the Bohai Sea, with a peripheral area of ~25 km2. Seagrass canopy height and plant coverage had a significant correlation with water depth. Asexual reproduction principally occurred in autumn and played a dominant role in population recruitment in vegetated areas, where no seedlings successfully colonized. In contrast, a considerable number of seedlings survived in the seagrass meadow gaps, and thus played a critical role in the recruitment in these areas. The maximum reproductive shoot densities were about 100 and 70 shoots m−2 at sampling site (S)-1 and S-2 in 2018, respectively, which was about two times more than in 2019 (50 and 20 reproductive shoots m−2 at S-1 and S-2, respectively). The potential seed output per unit area in 2019 was about 1020 seeds m−2 at S-1 and 830 seeds m−2 at S-2, and the seed output in the study area was at a low level compared with global values. Overall, high spring and summer water temperature appeared to induce sexual reproduction of Z. marina in the study area, including reproductive effort, reproductive investment, and seedling development. Furthermore, eelgrass height, aboveground biomass, and density were significantly related to water temperature. Among the potential threatening factors to seagrass in this area, the activities of clam harvesting were intense with daily clam catches >2000 kg, leading to patchy seagrass meadows, especially in the fringe areas. The seagrass bed was also threatened by marine pollution (nutrient loading) and land reclamation. Therefore, the protection and restoration of this seagrass bed are strongly recommended. Our study will provide fundamental information for the conservation and management strategies of large eelgrass beds in the Bohai Sea.

Response of soil bacterial community characteristics to alpine meadow degradation

Response of soil bacterial community characteristics to alpine meadow degradation

Lateral flow between bald and vegetation patches induces the degradation of alpine meadow in Qinghai-Tibetan Plateau

Bald patches (BPs) are known to accelerate and simultaneously mitigate the process of desertification. However, the mechanisms of these two synchronous actions are little studied in high desert and cold systems; and the incidence of BPs on alpine meadows degradation in Qinghai-Tibetan Plateau (QTP) of China is still unavailable. This study first aims to investigate the soil properties and the erodibility of the system BPs-VPs at the Beiluhe basin in QTP. Then, we adopted dye tracer and HYDRUS-2/3D methods to interpret the water infiltration patterns from point scale to slope scale. The results show that the mattic epipedon layer on the top soil (0–20 cm) of VPs directly reduced the impact of raindrops on alpine meadow; and the adhesion of root system in VPs prevented the soil particles from stripping and washing away by runoff. The soil particles in BPs were easily eroded by rainfall, lowering the ground level of BPs relative to the ground level of VPs. The two patches therefore alternated to form an erosion interface where marginal meadow was likely detached by raindrops, and washed away through runoff. The saturated hydraulic conductivity (Ks) of surface soil (0–10 cm) was 124% higher in BPs than the VPs. Thereby, BPs caused a high spatial variation of infiltration and runoff in QTP. Moreover, this difference in Ks between the two patches conducted to a lateral flow from BPs to VPs, and to soil layers with different water contents. These findings highlight that the water flow features can potentially disturb the processes of freezing-thawing, frost heaves, and thaw slump; and accelerate the alpine meadow degradation. Therefore, land cover such as crop and vegetation should be applied over the bare soil surface to prevent the degradation of alpine meadow.

Soil water retention in alpine meadows under different degradation stages on the northeastern Qinghai-Tibet Plateau

Alpine meadow degradation has become serious in recent decades due to the combined effects of overgrazing, human activities and rodents, but very few studies focus on the possible impact of alpine meadow degradation on soil water retention on the Qinghai-Tibet Plateau. In this study, four degradation stages (non-degradation, ND; light degradation, LD; moderate degradation, MD; heavy degradation, HD) were selected. Results showed that (1) the aboveground biomass decreased with increasing degradation, while the belowground biomass first increased and then decreased with a maximum value in MD. (2) As the degree of degradation increased from ND to MD, the 0–10 cm soil bulk density (BD) and soil compaction (SC) decreased with the minimum values in MD (0.61 g cm−3 for BD and 1619.51 kPa for SC), while soil organic matter (SOM) increased with maximum value in MD (247.36 g kg−1), the 0–10 cm SOM in MD was the 1.5 times of that in ND. However, the 0–10 cm particle size distribution did not change significantly with increasing degradation, while the 20–40 cm clay content in HD was significantly higher than those of the other three degradation stages, (3) The MD stage displayed a strong water holding capacity in 0–10 cm soil layer due to its higher soil organic matter induced by the thick mattic epipedon. Meanwhile, the water holding capacity in the HD stage was higher than that of the other three degradation stages in the 20–40 cm soil layer owing to its higher capillary porosity. Furthermore, the soil water retention was greatly affected by the mattic epipdon through its effects on soil properties such as reducing BD and increasing SOM. Our results suggested that the mattic epipdon may play a crucial role in water retention in alpine ecosystems.

Multi-scale drivers of soil resistance predict vulnerability of seasonally wet meadows to trampling by pack stock animals in the Sierra Nevada, USA

BackgroundMeadow ecosystems have important ecological functions and support socioeconomic services, yet are subject to multiple stressors that can lead to rapid degradation. In the Sierra Nevada of the western USA, recreational pack stock (horses and mules) use in seasonally wet mountain meadows may lead to soil trampling and meadow degradation, especially when soil water content is high and vegetation is developing.MethodsIn order to improve the ability to predict meadow vulnerability to soil disturbance from pack stock use, we measured soil resistance (SR), which is an index of vulnerability to trampling disturbance, at two spatial scales using a stratified-random sampling design. We then compared SR to several soil and vegetation explanatory variables that were also measured at the two spatial scales: plant community type (local scale) and topographic gradient class (meadow scale).ResultsWe found that local-scale differences in drivers of SR were contingent on the meadow scale, which is important because multiple spatial scale evaluation of ecological metrics provides a broader understanding of the potential controls on ecological processes than assessments conducted at a single spatial scale. We also found two contrasting explanatory models for drivers of SR at the local scale: (1) soil gravimetric water content effects on soil disaggregation and (2) soil bulk density and root mass influence on soil cohesion. Soil resistance was insufficient to sustain pack stock use without incurring soil deformation in wet plant communities, even when plant cover was maximal during a major drought.ConclusionsOur study provides new information on seasonally wet meadow vulnerability to trampling by pack stock animals using multi-scale drivers of SR, including the contrasting roles of soil disaggregation, friction, and cohesion. Our work aims to inform meadow management efforts in the Sierra Nevada and herbaceous ecosystems in similar regions that are subject to seasonal soil saturation and livestock use.

Soil microbial community responses to soil chemistry modifications in alpine meadows following human trampling

Alpine meadow degradation induced by human trampling decreases plant biomass and species diversity, potentially altering soil chemistry and microbial community composition. We studied soil carbon (C), nitrogen (N) and phosphorus (P) plus soil bacterial and fungal community structure in alpine meadows, along a degradation gradient induced by human trampling at Wugong Mountain, China. As degradation increased (from 0 to 100% bare ground), pathotroph (both animal and plant hosts) and symbiotroph (especially ectomycorrhizae) fungal diversity increased but overall microbial diversity did not vary. Degradation altered fungal taxonomic composition with higher Cryptomycota and Mucoromycota diversity in more degraded sites. Path analyses indicated that fungal composition changes with degradation were mainly related to changes in soil C and P while bacterial changes were mainly related to changes in soil N and pH. Degradation modified bacterial taxonomic composition with higher Gemmatimonadetes but lower Acidobacteria, Cyanobacteria, and Planctomycetes diversity associated with lower pH, higher TN, lower NH4+, and higher NO3− in more degraded areas. The results indicate that trampling impacts both soil fungal and bacterial communities but these microbial groups respond to different soil chemistry modifications. These results highlighting soil microbial community changes suggest their importance in the restoration of degraded alpine meadows with human trampling and hence the rapid recovery of their function.

Long‐term seagrass degradation: Integrating landscape, demographic, and genetic responses

Abstract Seagrass meadows are crucial habitats on nearshore areas, which are exposed to human disturbances that frequently cause seagrass loss. Although demographic and mapping data have been widely used in long‐term monitoring programmes, the integration of multi‐locus genotype data through time remains rare. The present work links, for the first time, landscape, demographic, and genetic data for a seagrass, so as to explore long‐term responses to persistent human impacts. The temporal patterns in meadow area, shoot density, and clonal and genetic diversity of three Cymodocea nodosa meadows were compared: in one meadow directly affected by the construction of an industrial port and in two control areas. The hypothesis tested was that seagrass deterioration and subsequent habitat loss at the affected meadow would be associated with a reduction of seagrass clonal and genetic diversity. The results show significant reductions in both meadow area (from approx. 21 to 1.5 ha) and shoot density (from approx. 1,800 to 400 shoots per m2) at the impacted meadow, with concurrently reduced clonal and allelic richness (by approx. 22%), as well as heterozygosity (HLmean, approx. 21%; Hobs, approx. 12%). These descriptors, however, remained stable, or even increased, in the controls. Importantly for seagrass management, multi‐disciplinary analysis made it possible to link slower, large‐scale, landscape and genetic degradation processes with faster demographic deterioration on an intermediate meadow scale. Multi‐locus genotype data were also crucial for revealing long‐term degradation processes at the genetic level, which is undetectable by traditional monitoring techniques. In summary, this holistic approach provides a valuable framework for long‐term seagrass monitoring programmes to detect cumulative signals of seagrass meadow degradation across a range of scales.

Soil Bacterial Community Response and Nitrogen Cycling Variations Associated with Subalpine Meadow Degradation on the Loess Plateau, China.

Grassland degradation is an ecological problem worldwide. This study aimed to reveal the patterns of the variations in bacterial diversity and community structure and in nitrogen cycling functional genes along a subalpine meadow degradation gradient on the Loess Plateau, China. Meadow degradation had a significant effect on the beta diversity of soil bacterial communities (P < 0.05) but not on the alpha diversity (P > 0.05). Nonmetric multidimensional scaling (NMDS) and analysis of similarity (ANOSIM) indicated that the compositions of bacterial and plant communities changed remarkably with increasing meadow degradation (all P < 0.05). The beta diversities of the plant and soil bacterial communities were significantly correlated (P < 0.05), while their alpha diversities were weakly correlated (P > 0.05) along the meadow degradation gradient. Redundancy analysis (RDA) showed that the structure of the bacterial community was strongly correlated with total nitrogen (TN), nitrate nitrogen (NO3--N), plant Shannon diversity, plant coverage, and soil bulk density (all P < 0.05). Moreover, the abundances of N fixation and denitrification genes of the bacterial community decreased along the degradation gradient, but the abundance of nitrification genes increased along the gradient. The structure of the set of N cycling genes present at each site was more sensitive to subalpine meadow degradation than the structure of the total bacterial community. Our findings revealed compositional shifts in the plant and bacterial communities and in the abundances of key N cycling genes as well as the potential drivers of these shifts under different degrees of subalpine meadow degradation.IMPORTANCE Soil microbes play a crucial role in the biogeochemical cycles of grassland ecosystems, yet information on how their community structure and functional characteristics change with subalpine meadow degradation is scarce. In this study, we evaluated the changes in bacterial community structure and nitrogen functional genes in degraded meadow soils. Meadow degradation had a significant effect on bacterial community composition. Soil total nitrogen was the best predictor of bacterial community structure. The beta diversities of the plant and soil bacterial communities were significantly correlated, while their alpha diversities were only weakly correlated. Meadow degradation decreased the potential for nitrogen fixation and denitrification but increased the potential for nitrification. These results have implications for the restoration and reconstruction of subalpine meadow ecosystem on the Loess Plateau.

Too hot to handle: Unprecedented seagrass death driven by marine heatwave in a World Heritage Area.

The increased occurrence of extreme climate events, such as marine heatwaves (MHWs), has resulted in substantial ecological impacts worldwide. To date, metrics of thermal stress within marine systems have focussed on coral communities, and less is known about measuring stress relevant to other primary producers, such as seagrasses. An extreme MHW occurred across the Western Australian coastline in the austral summer of 2010-2011, exposing marine communities to summer seawater temperatures 2-5°C warmer than average. Using a combination of satellite imagery and in situ assessments, we provide detailed maps of seagrass coverage across the entire Shark Bay World Heritage Area (ca. 13,000km2 ) before (2002 and 2010) and after the MHW (2014 and 2016). Our temporal analysis of these maps documents the single largest loss in dense seagrass extent globally (1,310km2 ) following an acute disturbance. Total change in seagrass extent was spatially heterogeneous, with the most extensive declines occurring in the Western Gulf, Wooramel Bank and Faure Sill. Spatial variation in seagrass loss was best explained by a model that included an interaction between two heat stress metrics, the most substantial loss occurring when degree heating weeks (DHWm) was ≥10 and the number of days exposed to extreme sea surface temperature during the MHW (DaysOver) was ≥94. Ground truthing at 622 points indicated that change in seagrass cover was predominantly due to loss of Amphibolis antarctica rather than Posidonia australis, the other prominent seagrass at Shark Bay. As seawater temperatures continue to rise and the incidence of MHWs increase globally, this work will provide a basis for identifying areas of meadow degradation, or stability and recovery, and potential areas of resilience.

Characterization of the complete chloroplast genome of a poisonous weed on alpine meadow on the Qinghai-Tibet Plateau, Ligularia virgaurea (Asteraceae: Senecioneae)

Ligularia virgaurea (Asteraceae) is an indicator species of alpine meadow degradation. Here, the complete chloroplast genome of L. virgaurea was studied. The chloroplast genome of L. virgaurea is 151,185 bp in length. It has a typical quadripartite structure, containing a large single copy region of 83,369 bp, a small single copy region of 18,156 bp, and a pair of inverted repeated regions of 24,830 bp. A total of 132 functional genes were annotated, including eight rRNA genes, 37 tRNA genes, and 87 protein-coding genes. In the neighbour-joining phylogenetic tree based on chloroplast genome, the genus Ligularia clustered together, while L. virgaurea has a slightly more distant relationship with other Ligularia species.

Restoration efficiency of short-term grazing exclusion is the highest at the stage shifting from light to moderate degradation at Zoige, Tibetan Plateau

Grassland degradation has profound negative impacts on ecological functions, local economic development, and social stability. Although there are many studies on the alpine grassland degradation in the Tibetan Plateau, the variation in the response of alpine meadows to degradation and restoration processes, and the underlying mechanisms remain poorly understood. To explore these issues, we selected nine grassland degradation levels along an increasing gradient at Zoige in the Tibetan Plateau, and collected vegetation and soil samples in August 2017 and 2018 to assess the state of the grassland before and after grazing exclusion (GE), respectively. The results showed that above-ground biomass (AGB), below-ground biomass (BGB), Shannon–Wiener index, soil water content (SWC), soil organic carbon (SOC), total nitrogen (STN), and total phosphorus decreased gradually with severe degrees of degradation, whereas soil bulk density and pH increased. SWC in the topsoil presented the sharpest change in slope along the degradation gradient, indicating that SWC was a sensitive indicator of alpine meadow degradation in this area. One-year GE evidently increased SWC, SOC, STN, AGB, and BGB in lightly and moderately degraded grasslands. The restoration efficiency of GE first increased and then decreased along the degradation gradient, with the turning point appearing at the third or fourth degradation level. Based on these results, we can conclude that short-term GE is an effective method for grassland restoration in this humid area, and should be performed at the shift from light to moderate degradation stages when the efficiency of recovery is the highest. These findings could facilitate a better approach for the restoration of degraded alpine meadow ecosystems.

Influence of degradation on soil water availability in an alpine swamp meadow on the eastern edge of the Tibetan Plateau

Degraded ecosystems refer to systems that deviate from their natural state as a result of natural or anthropogenic disturbances. Alpine swamp meadows on the eastern edge of the Tibetan Plateau have dramatically degraded owing to climate change, overgrazing, and rodents. Understanding the influence of meadow degradation on soil water availability is essential for the development of hydrological models and alpine swamp meadows restoration, which has been poorly explored in the eastern Tibetan Plateau. In this study, we analyzed how degradation affects variation in soil water availability with a series of parameters derived from soil moisture content and soil water retention curves. Our results showed that (1) soil moisture content consistently decreased with degradation and increased with soil depth; (2) soil water retention curves decreased with increasing degradation due to coarser soils and organic matter loss. Field water capacity and the permanent wilting point decreased, whereas the air entry value increased with the severity of degradation; and (3) soil water availability, as represented by soil water potential, available soil water content and fraction was less responsive to degradation than individual soil moisture content or soil water retention curves, which showed similar decreasing trends. However, soil water potential, available soil water content and fraction under moderate and severe degradation were relatively lower than those under light degradation, especially in deep soil layers (>20 cm). Thus, swamp meadow degradation negatively influences soil water availability, which might impede water absorption by deeply rooted species, thereby inducing soil-water stress and possibly increasing drought vulnerability.

Restoration Practices Affect Alpine Meadow Ecosystem Coupling and Functions

Degradation of alpine meadows on the Qinghai-Tibetan Plateau is an important issue for ecological science, policy making, and the welfare of local herders. Destruction of alpine meadows results from degeneration of vegetation and soil systems and from the mechanical decoupling of the environment, grassland, livestock, and herders and, subsequently, discordance among these subsystems. In this study, systematic integration of restoration techniques based on the grassland agroecosystems coupling theory was developed for the management and restoration of degraded alpine meadows. To test the effectiveness of these integrated restoration techniques, we conducted restoration trials that included grazing management, enclosed, fertilization, overseeding, and sward ripping by evaluating the ecosystem coupling of soil, plant and livestock, and ecosystem functions. The results of this study suggest that comprehensive restoration practices include grazing and agronomy techniques (fertilizer, overseeding, and sward ripping) that result in the greatest level of ecosystem coupling, while the single restoration practice leads to poorly coupled ecosystems. Restoration practice changes in ecosystem functionality are positively related to changes in ecosystem coupling. Our results highlight the importance of diversified restoration practices for facilitating ecological coupling and functioning in the degraded alpine meadow. The restorative scheme also bridges the gap between restoration theory and practice by providing guidelines for herders and policy makers for the urgent task of restoring degraded alpine meadows.

Experimental study on the effects of multiple factors on spring meltwater erosion on an alpine meadow slope

Meadow degradation provides a major indication of increased soil erosion in alpine regions. Serious soil erosion is observed during the spring in particular because soil thawing coincides with the period of snowmelt and the meadow coverage is very low at this time. Studies relating to soil erosion caused by spring meltwater are, however, limited and controversial. Therefore, a field experimental study was conducted in a typical meadow in the Binggou watershed on the northern edge of the Tibetan Plateau to assess the impact of multiple factors on spring meltwater erosion on an alpine meadow slope. The multiple factors included three flow rates (1, 2, and 3 L/min), four slope gradients (10°, 15°, 20°, and 25°), and three underlying surface conditions (meadow, disturbed meadow, and alluvial soil). An equal volume of concentrated meltwater flow was used in all experiments. The results showed that rapid melting at a high flow rate could accelerate soil erosion; as the flow rate increased from 1 to 3 L/min, the total surface runoff increased by a factor of 0.7 and the total sediment yield increased by more than 6-fold. The influence of the slope gradient on the amount of runoff was positively linear and the influence was relatively low; when the slope increased from 10° to 25°, the total runoff only increased by 16%. However, the slope gradient had a strong impact on soil erosion. The total sediment yield doubled when the slope increased from 10° to 20° and then slightly decreased at 25°. The meadow could effectively reduce soil erosion, although when the meadow was disturbed, the total runoff increased by 60% and the sediment yield by a factor of 1.5. The total runoff from the alluvial soil doubled in comparison to the meadow, while the sediment yield increased nearly 7-fold. The findings of this study could be helpful to understand the characteristics and impact of multiple controlling factors of spring meltwater erosion. It also aims to provide a scientific basis for an improved management of alpine meadows as well as water and soil conservation activities in high-altitude cold regions.

Fragmentation and percolation thresholds in the degradation process of alpine meadow in the Three-River Headwaters region of Qinghai-Tibetan Plateau, China

Understanding the process and mechanisms of alpine meadow degradation is crucial for restoration and management in the Three-River Headwaters region, Qinghai-Tibetan Plateau, China. However, little is known about this complex and controversial problem because identification and quantification of the underlying causes is difficult. This research aimed to build a spatiotemporal dynamical model for alpine meadow degradation, capturing the natural process of erosion at the interface of barren patches and undamaged meadow. The model clarified the role of barren patches and meadow connectivity in degradation, and identified the ecological mechanisms and processes accounting for the spatial and temporal pattern of degradation. A fragmentation and percolation threshold exists in the process of meadow degradation, independent of spatial scale. An impulsive differential equation was used to investigate the consequence of periodic restoration of degraded meadow. Both the level of meadow degradation and the restoration period play crucial roles in determining whether the meadow can be successfully restored. This research has demonstrated theoretically that the effectiveness of meadow restoration by periodic effort depends on the degree of degradation.

高寒草甸退化对祁连山土壤微生物生物量和氮矿化速率的影响

高寒草甸退化对祁连山土壤微生物生物量和氮矿化速率的影响

青藏高原典型草地植被退化与土壤退化研究

PDF HTML阅读 XML下载 导出引用 引用提醒 青藏高原典型草地植被退化与土壤退化研究 DOI: 10.5846/stxb201809162019 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41771233） Different vegetation and soil degradation characteristics of a typical grassland in the Qinghai-Tibetan Plateau Author: Affiliation: Fund Project: The National Natural Science Foundation of China (General Program) 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:采用野外样方调查和室内分析法，探讨了青藏高原不同退化程度高寒草原和高寒草甸植被群落结构、植物多样性、地上-地下生物量、根系分配及土壤理化特性差异。研究表明：（1）随着退化程度加剧，高寒草原禾草优势地位未改变，高寒草甸优势种莎草逐渐被杂类草取代。（2）随着退化程度加剧，高寒草原地上生物量显著降低（P<0.05），高寒草甸地上生物量先保持稳定再下降。高寒草甸地下生物量较高寒草原地下生物量对退化响应更敏感。（3）高寒草原退化过程中，莎草地上物生量变化不明显（P>0.05），禾草地上生物量贡献率由88.12%减少至53.54%，杂类草地上生物量贡献率由0.08%增加至42.81%；高寒草甸退化过程中，禾草和杂类草地上生物量先增加后减小，莎草地上生物量占比由69.15%减少至0.04%，杂类草地上生物量占比由12.56%增加至92.61%。（4）随着退化程度加剧，高寒草原根系向浅层迁移，高寒草甸根系向深层迁移。（5）退化对高寒草甸土壤含水量（θ）、土壤有机碳（SOC）、总氮（TN）及土壤容重（BD）影响均比高寒草原更强烈。本研究对青藏高原退化草地恢复治理具有重要的参考价值。 Abstract:This study used a field sampling survey and laboratory analysis to investigate the different characteristics of community structure, above/belowground biomass, plant composition and diversity, root proportions in different soil layers, and soil physiochemical properties between alpine steppes and alpine meadows in the Qinghai-Tibetan Plateau. Five degradation stages were identified including non-degradation (ND), light degradation (LD), moderate degradation (MD), severe degradation (SD), and extreme degradation (ED). The results are as follows:(1) as degradation level increased, graminoid dominance in alpine steppes remained unchanged, but sedges in alpine meadows were gradually replaced by the subdominant forb species. (2) With increased alpine steppe degradation, there was a significant decrease in aboveground biomass (P<0.05). The grassland degradation did not affect significantly aboveground biomass with the exception of ED alpine meadows (P<0.05). The response of underground biomass to degradation in alpine meadows was more sensitive compared with alpine steppes. (3) The aboveground sedge biomass exhibited invisible trends with the increase of alpine steppe degradation. The proportion of aboveground graminoid biomass decreased from 88.12% (ND) to 53.54% (ED), while that of forbs increased from 0.08% (ND) to 42.81% (ED). In the process of the ecological succession of alpine meadow degradation, the aboveground graminoid and forb biomass significantly increased except a decrease in ED areas. The contribution of aboveground sedge biomass decreased from 69.15% (ND) to 0.04% (ED), while that of forbs increased from 12.56% (ND) to 92.61% (ED). (4) The alpine steppe root systems showed the increased shallowness as degradation levels increased. However, the alpine meadows showed an opposite trend. (5) The study determined that soil water content (θ), soil organic carbon (SOC), total nitrogen (TN), and bulk density (BD) of alpine meadows were more intensively influenced by degradation compared to those of alpine steppes. The results could provide a valuable reference for the restoration of the degraded grassland in the Qinghai-Tibetan Plateau. 参考文献 相似文献 引证文献

Formation of the productivity of grassland phytocenoses of non-cultivated slopes in the Precarpathian region depending on the modes of use and fertilization

The article is a study in soil science, with an analysis of the grassland phytocoenosis productivity in the Precarpathian region (Eastern Carpathian Foothills). The analysis of the level of land productivity according to the modes of use or fertilization type is carried out and it is established that grassland phytocoenoses of the Precarpathian region are the main source of forage for the livestock industry, and they hold the most important soil-forming position in the ecosystem of the territory. The main reason for the rapid loss of valuable species of grassland herbs from phytocoenoses and degradation of sown grass stands in the meadows of the Precarpathian region is the deterioration of nutrient status and water-air regime in the soil.&#x0D; The percentage ratio of agrobotanical groups in the grasslands is comprised by herbs, cereals, sedges. Three types of plants represent the herb group. Groundsel (Senecio congestus) is predominant species in this group. Less common herbs of grassland are starwort (Stellaria radians) and Jacob's-ladder (Polemonium acutiggorum Willd). Arctophila yellow (Arctophila fulva (Trin) Anders) dominates among the cereals.&#x0D; Application of mineral fertilizers on the grasslands under conditions of the Precarpathian region at the rate of N120P90K120 with split dressing in spring and after the first haymaking at the rate of N60 provides an increase in the yield of herbs compared with the control of 125.5 centners of herbage per ha.&#x0D; It is established that extensive use of grasslands on sod-podzolic soils of the Precarpathian region leads to the development of degradation processes in the soil, decreases the resistance of perennial grasses to adverse habitat conditions. The main signs of degradation of cultivated meadows are the decrease of nutrient content in soil, soil dehumification, reduction in the productivity of phytocoenoses, decrease of the phytocoenoses of grasses and an increase in the number of grasses in the botanical composition, reduction of the area of projective cover of soil by plants, degrowth of inflorescence of grasses, decrease of the number of rhizome species of grassland plants.&#x0D; Based on this, the article also proposes ways to preserve and improve the productivity of grassland phytocoenoses and the studied types of soils.

Influences of Plateau Zokor Burrowing on Soil Erosion and Nutrient Loss in Alpine Meadows in the Yellow River Source Zone of West China

Plateau zokors (Eospalax baileyi) are an agent actively involved in causing soil erosion and meadow degradation in the Yellow River Source Zone of West China. This study aims to quantify the amount of soil and nutrient loss from zokor mounds in relation to slope gradient and rainfall intensity, and to assess the amount of soil loss in zokor-infested areas compared with healthy meadows in Henan County, Qinghai Province. The results showed that zokor mounds were gradually lowered at a rate of 1.8–3.9 cm h−1. Soil loss occurred two min after the rain began, reaching the maximum level during the first 20 min. The rate of soil loss and nutrient loss increased with the rainfall intensity and slope gradient. When the rainfall intensity rose from 5 to 10 mm h−1, and from 10 to 15 mm h−1, the total soil loss on 10° slopes increased by 2.5 times and 3.9 times, respectively, and soil nutrient loss increased by 1.7 times and 2.7 times, respectively. As the slope gradient steepened to 20°, the corresponding figures were 2.8 times and 4.3 times for total soil loss, and 1.8 times and 2.9 times, respectively, for soil nutrient loss. When the slope rose to 30°, the soil loss increased by 3.0 and 4.5 times, and the soil nutrient loss increased by 1.8 times and 3.1 times, respectively. There was a power function between soil loss and surface runoff (S = 0.2371Q2.2307, R2 = 0.9529). The soil was eroded at a rate of 256.6 g m−2 h−1 from zokor mounds, 17.7 times higher than in intact meadows, and 1.8 times higher than in partially recovered meadows. Most of the eroded soils had a mean diameter of 0–1.2 mm. It is recommended that artificial control of plateau zokors should be implemented, together with other ecological restoration measures to restrain the soil erosion problem caused by zokor activities.