Degraded Alpine Meadow Research Articles

Effects of Patchiness on Surface Soil Moisture of Alpine Meadow on the Northeastern Qinghai-Tibetan Plateau: Implications for Grassland Restoration

Surface soil moisture (SSM) is a key limiting factor for vegetation growth in alpine meadow on the Qinghai-Tibetan Plateau (QTP). Patches with various sizes and types may cause the redistribution of SSM by changing soil hydrological processes, and then trigger or accelerate alpine grassland degradation. Therefore, it is vital to understand the effects of patchiness on SSM at multi-scales to provide a reference for alpine grassland restoration. However, there is a lack of direct observational evidence concerning the role of the size and type of patches on SSM, and little is known about the effects of patches pattern on SSM at plot scale. Here, we first measured SSM of typical patches with different sizes and types at patch scale and investigated their patterns and SSM spatial distribution through unmanned aerial vehicle (UAV)-mounted multi-type cameras at plot scale. We then analyzed the role of the size and type of patchiness on SSM at both patch and plot scales. Results showed that: (1) in situ measured SSM of typical patches was significantly different (P < 0.01), original vegetation patch (OV) had the highest SSM, followed by isolate vegetation patch (IV), small bare patch (SP), medium bare patch (MP) and large bare patch (LP); (2) the proposed method based on UAV images was able to estimate SSM (0–40 cm) with a satisfactory accuracy (R2 = 0.89, P < 0.001); (3) all landscape indices of OV, with the exception of patch density, were positively correlated with SSM at plot scale, while most of the landscape indices of LP and IV showed negative correlations (P < 0.05). Our results indicated that patchiness intensified the spatial heterogeneity of SSM and potentially accelerated the alpine meadow degradation. Preventing the development of OV into IV and the expansion of LP is a critical task for alpine meadow management and restoration.

Grazing exclusion alters ecological stoichiometry of plant and soil in degraded alpine grassland

Grazing exclusion is one of the most effective practices to recover the degraded alpine grasslands in Tibetan Plateau. In addition, ecological stoichiometry serves as a key regulator of ecosystem function and is also closely related to nutrient process. However, knowledge about the plant-soil interactions of stoichiometry throughout the growing season is still poorly understood. In this study, we examined how grazing exclusion affected the change of C-N-P stoichiometry of plant-soil by carrying out monthly sampling in three sites. The sites were: 9 years grazing exclusion, GE9; 5 years grazing exclusion, GE5; and free grazing, FG in degraded alpine meadow. Plant and soil samples were collected five times during the growing season (May-September) to analyze plant biomass and ecological stoichiometry. Across plots, profound fencing changed plant biomass and ecological stoichiometry. Specifically, increases in green, litter and root biomass were observed under grazing exclusion. Fencing increased plant C content, C:N, C:P, N:P ratios but declined N and P contents. In contrast to the plant, there was an increasing concentrations of soil C, N and P. Our study highlighted, under grazing exclusion, grasslands advanced soil C not only by greater biomass input but also higher plant C content. Greater soil N was mainly fixed by plant production, while enhancement of soil P was mainly due to plant production recovery to stop water erosion. With a continuous improvement of nutrient pools under short-term (< 9 years) grazing exclusion, our results showed that a long-term fencing practice effect ought to be monitored to recovery degraded alpine grassland. These findings also indicated that ecological stoichiometry provides a new insight for better understanding of the mechanisms of grazing exclusion effects on nutrient process.

Bacterial richness is negatively related to potential soil multifunctionality in a degraded alpine meadow

Fungal richness and community composition are known to be positively associated with soil multifunctionality. However, the contributions of bacterial and fungal communities to the multiple soil functions of alpine meadow ecosystems have not been widely examined. Here, we surveyed the soil in Qinghai-Tibetan alpine meadows and classified the extent of degradation as undegraded, lightly degraded, moderately degraded, and severely degraded to clarify the associations between microbial diversity (including bacteria and fungi) and potential soil multifunctionality. Bacterial and fungal compositions were detected by sequencing of the 16S rDNA and internal transcribed spacer amplicons, respectively. Functions associated with nutrient cycling (dissolved organic nitrogen and carbon, available phosphorus, NO3–, NH4+, C, N, P-cycle enzymes) and climate regulation (CO2 and N2O emissions) were also examined. Bacterial, rather than fungal, richness was negatively associated with potential soil multifunctionality, which decreased along the degradation gradient. Structural equation modeling explained 79.6% of the variation in potential soil multifunctionality and confirmed that, in addition to bacterial community richness and composition, organic carbon and moisture were important drivers of potential soil multifunctionality. These results suggest that higher bacterial richness is associated with lower potential soil multifunctionality in alpine meadow ecosystems. Among the bacterial taxa, only ~ 12% of bacterial genera were identified as predictors of multifunctionality, suggesting functional redundancy of the bacterial community in the meadow ecosystem. Rhodanobacter, Mucilaginibacter, Rhodococcus, and Bosea, belonging to the Proteobacteria and the Actinobacteria phyla were identified as critical for maintaining potential soil multifunctionality. Our results suggest that bacterial richness is negatively related to potential soil multifunctionality in alpine meadow ecosystems and there is no correlation between potential multifunctionality and fungal richness.

Response of soil bacterial community characteristics to alpine meadow degradation

Response of soil bacterial community characteristics to alpine meadow degradation

Water addition promotes vegetation recovery of degraded alpine meadows by regulating soil enzyme activity and nutrients in the Qinghai–Tibetan Plateau

Effective grassland restoration practices can promote degraded meadows recovery. However, little has been documented regarding the effect of water addition on the restoration of degraded meadows in the Qinghai–Tibetan Plateau (QTP). A field experiment with five water addition levels was established to identify the interactions between soil bio-physicochemical properties and plant of the degraded alpine meadows in the Sanjiangyuan region, QTP. Soil enzyme activity (α-glucosidase, αG; β-1,4-glucosidase, βG; β-D-cellubiosidase, βDC; β-xylosidase, βX; β-1,4-N-acetylgucosaminidase, NAG; leucine aminopeptidase, LAP; phosphorus, P), microbial biomass C (MBC) and N (MBN), MBC: MBN, physicochemical properties (soil moisture content, SMC; bulk density, SBD; pH; total organic C, TOC; total N, TN; soil C: N; ammoniacal N, NH4+-N; nitrate N, NO3−-N; nitrite N, NO2−-N), and plant diversity and productivity were analyzed throughout the growing season. The results indicated that soil SMC, available N (NH4+-N and NO3−-N), TOC, the activities of αG, βDC, βX, NAG, MBC and MBN significantly increased with water addition levels, whereas the activity of LAP and P, and MBC: MBN decreased (p < 0.05). The redundancy analysis (RDA) and the subsequent path analysis found that soil biological (βG, βDC, βX, NAG, LAP, MBC, and MBN) and physicochemical properties, especially TOC, NH4+-N, and NO3−-N, were significantly related to plant diversity and productivity. The changes in soil enzyme activity (especially βDC, βG, LAP) under water addition might the key drivers affecting soil nutrients such as TOC, NO3−-N and NH4+-N, which subsequently increased plant coverage and productivity. Our findings suggested that the obviously increase in enzymes activity and nutrients might be beneficial for the vegetation recovery of degraded alpine meadow on the QTP under water addition.

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.

Shift in nurse effect from facilitation to competition with increasing size of Salix cupularis canopy in a desertified alpine meadow on the Tibetan Plateau

The Tibetan Plateau is among the most ecologically important and sensitive regions worldwide, which has undergone severe desertification in recent decades, particularly in the Zoige region. In an effort to stem the progression of desertification, shrubs such as Salix cupularis have been planted in some localities in this region. However, the mechanisms whereby the interspecific relationships between these shrubs and the undergrowth vegetation change in response to an increase in shrub canopy area remain unclear. In this study, we examined the traits of plant communities and analysed soil samples under S. cupularis in a degraded alpine meadow along a gradient of four different canopy areas (1.3–1.8, 3.8–5.5, 12.6–14.5, and 27.3–28.3 m2). Our results revealed that plant community characteristics shifted from facilitation to competition at a canopy area of 3.8–5.5 m2. However, changes in soil nutrients and the activities of sucrase and catalase were not detected until the canopy area of S. cupularis had reached 2.6–14.5 m2. Furthermore, we found that microbial communities, particularly bacteria, showed trends similar to those shown by soil properties. In line with expectations, we found that the soil fungal community showed trends opposite to those shown by the bacterial community. Our findings highlight that competition rather than facilitation tends to be the predominant interspecific relationship that develops in response to the continued growth of nurse plants. Consequently, these results provide evidence in support of the stress-gradient hypothesis, which states that interspecific competition is particularly prevalent in fertile environments, particularly when there are changes in facilitation during periods of increasing environmental stress. Importantly, with respect to the shift in interspecific relationships from facilitative to competitive, we demonstrate that the response of the belowground interactions was slower than that of interactions above ground. Collectively, our observations indicate that the nurse effect of S. cupularis on ecosystems could have significant implications for the restoration of desertified grasslands.

Vegetation and soil characteristics of degraded alpine meadows on the Qinghai-Tibet Pla-teau, China: A review

Alpine meadows account for 46.7% of grassland area on the Qinghai-Tibet Plateau, which is an important part of grasslands in China. Under the effects of climate change and human activities in recent years, alpine meadow has been degraded seriously. Vegetation and soil have shown different degradation trends. At large spatial scales, the degraded alpine meadows are characterized by decreases of vegetation coverage, increases of weed vegetation, soil degradation and even desertification. At the micro-scale, soil particle size, soil microorganisms, and soil enzymes in degraded alpine meadows changed. We analyzed the changes of vegetation and soil during the degradation of alpine meadow ecosystems by considering species diversity, plant community structure, plant biomass, soil physical properties, soil microorganisms, soil enzymes, and soil nutrients. We put forward some uncertainties in the current research and problems that needed further study. This review provided a scientific basis for a comprehensive understanding of the degradation mechanisms and patterns of alpine meadows, effective intervention in alpine meadow, and restoration of ecological function.

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.

Physicochemical properties and micromorphology of degraded alpine meadow soils in the Eastern Qinghai-Tibet Plateau

The Qinghai-Tibet Plateau is currently suffering from severe ecological problems. Soil degradation is a major environmental problem, and there is strong evidence that such processes present an immediate threat to both biomass and economic yields. The aim of the present study is to clarify the response mechanism of mattic epipedon during soil degradation process in alpine meadow, we investigated (1) morphological characteristics and physicochemical properties of soils, (2) soil micromorphology under different degradation stage. According to plant and land use coverage, three sites were chosen from the Hequ horse farm: lightly degraded meadow (HQ1-L); moderately degraded meadow (HQ2-M); and heavily degraded meadow (HQ3-H). A vegetation survey and soil profile morphology showed that Kobresia kansuensis was the dominant species in HQ1-L and HQ2-M, featuring in topsoil horizons rich in rhizogenic organic matter which creates turfs. There are strong relationships between the presence of the mattic epipedon (OA horizon) and soil physicochemical properties. Thus, exchangeable cations, cation exchangeable capacity (CEC), total nitrogen (TN), and organic carbon (OC) decrease during the degradation of grassland; however, the pH value shows an opposite trend. Exchangeable cations, CEC, TN, and OC provide an index of soil fertility to measure the degree of grassland degeneration. Soils were classified as Luvic Phaeozems, Haplic Phaeozems, and Calcaric Phaeozems. From the micromorphology of soils in thin section, considering soil degradation, the porosity and fractal dimension decrease, and the soil microstructure evolves to an intergrain micro-aggregate structure. Also, by counting the number of excrements in the soil thin sections, and combining this with the fractal dimension of the porosity, we found the HQ1-L is more conducive to soil fauna survival, by comparison to HQ2-M, and HQ3-H which follow HQ1-L in condicivity. These results suggest that the existence of the OA horizon (mattic epipedon) is directly related to soil degradation.

Reconsidering the efficiency of grazing exclusion using fences on the Tibetan Plateau

Grazing exclusion using fences is a key policy being applied by the Chinese government to rehabilitate degraded grasslands on the Tibetan Plateau (TP) and elsewhere. However, there is a limited understanding of the effects of grazing exclusion on alpine ecosystem functions and services and its impacts on herders’ livelihoods. Our meta-analyses and questionnaire-based surveys revealed that grazing exclusion with fences was effective in promoting aboveground vegetation growth for up to four years in degraded alpine meadows and for up to eight years in the alpine steppes of the TP. Longer-term fencing did not bring any ecological and economic benefits. We also found that fencing hindered wildlife movement, increased grazing pressure in unfenced areas, lowered the satisfaction of herders, and rendered substantial financial costs to both regional and national governments. We recommend that traditional free grazing should be encouraged if applicable, short-term fencing (for 4–8 years) should be adopted in severely degraded grasslands, and fencing should be avoided in key wildlife habitat areas, especially the protected large mammal species.

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.

Aeolian sediment fingerprinting in the Cuona Lake Section along the Qinghai-Tibetan Railway

Quantitative analyses of aeolian sediment provenance are necessary to elucidate aeolian sand pathways and define objective targets for control measures. In the present study, annual wind data and remote sensing information were utilized to ascertain the source of aeolian sediments along the Cuona Lake Section of the Qinghai-Tibetan Railway (QTR). Fingerprinting approach with different tracer selection strategies was used to assess contributions of each source types. The results indicated that (1) wind erosion behaviours that contribute to sand sediment occur mainly on the west side of sandy areas during October to April. The resultant drift potential of this period reached 1086.18 VU, indicating a high energy level. (2) The aeolian desertified land within the source area expanded by 8.05 km2 from 2001 to 2017. The degraded alpine meadow, bare hilly land and river courses were identified as potential sources of aeolian sediments. (3) The contributions from degraded alpine meadow, bare hilly land and river courses were estimated as 4%, 58% and 38%, respectively. Synthesising these results, appropriate control measures for the bare hilly land and river courses on the west side of Cuona Lake should be able to greatly restrict sand transport and alleviate the railway sand hazard. This study will provide a firm basis for sand hazard control in the Cuona Lake section and can be utilized as references for other regions encountering threats from aeolian sand.

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.

Spatiotemporal variation and simulation of vegetation coverage in a typical degraded alpine meadow on the Tibetan Plateau

The Qinghai-Tibetan Plateau is sensitive to global climate change and its vegetation is an important indicator of the change. Analyses of the mesoscale spatial variation of vegetation and its spatiotemporal influencing factors in alpine meadows are important for the management and model simulation of degraded meadows. We extracted data for vegetation coverage (VC) from digital photographs of a typically degraded alpine meadow for 22 occasions at 113 locations in a study plot. The spatial and temporal distribution, variability and influencing factors of VC were analyzed using classical statistics, geostatistics, temporal stability and correlation analysis. A first pedotransfer function was built for simulating temporal variation of VC. Average VC was 19.7 and 40.5% in the 2015 and 2016 growing seasons, respectively, and the classical and geostatistical parameters indicated moderate variability and a strong spatial dependence of the VC in the study plot. VC was correlated strongly negatively with soil bulk density and pH and strongly positively with soil organic-carbon density and total nitrogen and total potassium contents. VC was sinusoidally distributed in the 2015 growing season, which was mainly affected by rainfall-induced soil moisture condition, and was parabolically distributed in the 2016 growing season, which was mainly affected by temperature-dominated vegetation phenology. The mean coefficients of variation (CVs) of VC temporal variation in the 2015 and 2016 growing seasons were 39.8 and 36.5%, respectively, which were higher than the CVs (28.0 and 19.1%) for VC spatial variation, indicating that climate affected VC more than soil and topographical properties. The simulation of a pedotransfer function established by temporal variables i.e. 30 cm-depth soil-water content, air temperature and pressure was highly accurate and accounted for >60% of the temporal variability of VC. These results provide basic data and recommendations for the mesoscale simulation of vegetation in alpine meadows and a scientific basis for the management of degraded meadows.

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.

The forb, Ajania tenuifolia, uses soil nitrogen efficiently, allowing it to be dominant over sedges and Graminae in extremely degraded grasslands: Implications for grassland restoration and development on the Tibetan Plateau

AbstractPlant growth is mainly N‐limited in the alpine grasslands because of slow mineralization of soil organic matter due to low air temperature. Different plant species dominate in soils of different N concentrations. For example, more forbs occur in severely degraded alpine meadows than do sedges and Gramineae. We hypothesized that a more efficient uptake of low soil N by forbs than by sedges and Gramineae was the mechanism that allowed forbs to dominate. The amount and rate of soil N uptake and N allocation were determined in seven dominant alpine plant species using 15N isotope tracer. The plants, which included one forb, Ajania tenuifolia, three sedges, Kobresia humilis, Carex scabrirostris, and Carex enervis, and three Gramineae, Elymus nutans, Festuca sinensis, and Stipa purpurea, were maintained in pots with four different N concentrations (0, 50, 100, and 150 kg ha−1). The forb had the highest efficiency of N utilization (N uptake rate, 60.4%) in low N soil concentration, the Gramineae had intermediate efficiencies (27.9–47.9%), and the sedges had the lowest efficiencies (5.2–34.9%), and, consequently, our hypothesis was supported. N utilization of the seven species decreased with an increase in soil N concentration, from 32.1% at N50 to 18.0% at N150, which indicated that soil N uptake by plants was affected by soil N concentration. The mechanism used by forbs to be the dominant species in severely degraded alpine meadows was a more efficient utilization of soil N than Gramineae and sedges in conditions of low soil N. We concluded that plant species have different efficiencies in soil N uptake and utilization, which allow them to adapt and survive in habitats of different soil nutrition levels. These results implied that forbs should be reduced, and that Gramineae and sedges should be planted and N be added during the restoration and development of severely degraded grasslands on the Tibetan plateau when the soil N content is low.

One-year grazing exclusion remarkably restores degraded alpine meadow at Zoige, eastern Tibetan Plateau

Understanding the influences of grazing exclusion (GE) on soil properties and vegetation characteristics is essential for the assessment of grassland restoration. The objectives of this study are exploring the efficiency of short-term GE in restoring alpine meadow in the Zoige region, eastern Tibetan Plateau, with high rainfall amount. We conducted sampling surveys before and after one-year GE in alpine meadows with seven sequent degraded degrees. The results showed that one-year GE significantly increased soil organic carbon (SOC), soil total nitrogen (STN), soil water content (SWC), and plant biomass, while decreased soil bulk density (SBD) regardless of the degradation degree. These findings suggest that short-term GE may be an effective way to restore degraded alpine meadow. Aboveground and belowground biomass was significantly positively associated with SWC, SOC, STN, soil total phosphorus, and soil available nitrogen, but presented negative relationship with SBD. This shows the complicated interaction between vegetation and soil physiochemical properties that regulates the grassland recovery process. The degraded alpine meadow in this rainfall-rich region could rapidly recover once grazing disturbance was excluded. This study can provide technical support for restoration and sustainable management of alpine meadows on the Tibetan Plateau.

Soil water dynamics in the active layers under different land-cover types in the permafrost regions of the Qinghai–Tibet Plateau, China

The mechanisms of hydrological processes, biochemical cycles, and permafrost revolution, and the potential impacts of climate change on these, are still poorly quantified in alpine regions, partly due to a lack of understanding of soil water dynamics in the permafrost active layer. In this study, soil water in the active layer was monitored in-situ at nine sites, including wet meadow (WM), alpine meadow (AM), alpine steppe (AS), transitional area-steppe (TA-S), transitional area-meadow (TA-M), bare land (BL), extremely degraded wet meadow (EDWM), alpine steppe on south-facing slope (ASSF), and alpine meadow on north-facing slope (AMNF) regions. These sites are located in the hinterland of the Qinghai–Tibet Plateau (QTP). Ground-ice distributions and isotope variations under different alpine ecosystems were also examined. The results demonstrate that soil water content was low at 0.5-m depth and high at the surface and at 1.0-m depth in the soil profiles from the TA-S, BL, EDWM, ASSF, and AMNF sites. However, denser vegetation coverage masked the effects of the freeze–thaw processes, which leading soil water content increased gradually with soil depth. Moreover, rainfall infiltration for recharging soil water in the lower layers was hampered due to the buffering action of mattic epipedons and the existence of clayed layers. Additionally, preferential flow often occurred in the degraded alpine meadows, which supplied deeper soil water. The Pearson correlation coefficients between soil water in the deeper layers and ground-ice were above 0.67 (significance <0.05), suggesting that deep soil water had a stronger effect on the formation of ground-ice near the permafrost table than soil water at the surface and middle root layers. Furthermore, results from the analysis of isotopic tracers suggest that precipitation directly recharged more ground-ice near permafrost table at the EDWM, ASSF, and AWNF sites, but less so at the WM, AM, AS, and BL sites, due to greater evapotranspiration and land cover. These results provide insights into the effect future climate warming can have on ecological succession and regional hydrological processes.