Background and aims
Seasonal grazing is a traditional grassland management practice in alpine swamp meadows on the Tibetan Plateau, but little information is available on the interactions between ...plant diversity and soil carbon and nitrogen sequestration in warm- and cold- season grazed alpine swamp meadows.
Methods
A multisite survey was conducted to investigate the plant characteristics and soil properties of Tibetan alpine swamp meadows under warm-season grazing (WG) and cold-season grazing (CG).
Results
Our study showed that plant biomass, litter mass, soil water content (SW), soil available nitrogen, soil microbial biomass carbon and nitrogen were significantly lower in the WG meadows than in the CG meadows (
P
< 0.05). However, plant diversity, species richness and the evenness index tended to increase in the WG meadows. Soil C and N storage were significantly lower in the WG meadows than in the CG meadows (
P
< 0.01). Grazing-induced changes in SW, plant diversity, plant biomass and litter mass were the major factors resulting in the decrease in soil C and N storage.
Conclusions
Our results indicate that warm-season grazing is beneficial for species diversity conservation, whereas cold-season grazing is suitable for soil C and N sequestration in alpine swamp meadows. Grazing-induced changes in litter mass greatly contributed to variations in plant diversity and soil C and N storage. In view of the accelerated vegetation and soil degradation in alpine grasslands, periodic warm- and cold-season grazing strategies should be considered to maintain alpine swamp meadow sustainability.
Background
Alpine ecosystem underlain by permafrost is considered as one of the most vulnerable ecosystems to disturbance, especially the alpine grassland on the Tibetan plateau with an altitude ...above 4000 m. Plateau pika (
Ochotona curzoniae
) burrowing can create distinctive bare grounds and cause micro-topographical heterogeneity in alpine grasslands. The burrowing-induced changes in microtopography may directly alter plant and soil interactions as well as ecosystem carbon cycle, which have rarely been studied in Tibetan alpine grasslands.
Methods
To test the responses of ecosystem respiration (Re) to pika burrowing-induced changes in microtopography, we investigated plant characteristics, soil properties and Re from the bare grounds and vegetated grounds in the alpine meadow and steppe on the Tibetan Plateau.
Results
Our study showed that vegetation cover, species richness, plant biomass, soil moisture (SM), soil organic carbon (SOC), total nitrogen (STN), soil microbial biomass carbon (MBC) and nitrogen (MBN) in the bare grounds were significantly lower than in the vegetated grounds in both alpine meadow and alpine steppe (
P
< 0.05). However, soil temperature and inorganic nitrogen tended to increase in the bare grounds. The growing season Re was significantly lower in the bare grounds than that in the vegetated grounds (
P
< 0.01). Pika burrowing had negative effects on Re and its temperature sensitivity in both alpine vegetations (
P
< 0.05). The relative changes in Re due to burrowing-induced changes in microtopography were positively correlated with the burrowing caused changes of AGB, BGB, SOC and MBC (
P
< 0.05). Pika burrowing-induced changes in soil temperature, soil moisture, plant biomass and microbial biomass are the major factors for the decrease of Re in the bare grounds.
Conclusion
In view of the large number of pika burrows in the alpine grasslands and the loss of soil organic carbon due to pika bioturbation, the impacts of pika burrowing-induced changes in microtopography on Re must be considered in predicting the carbon cycle in alpine grasslands.
Long-term active restoration is often employed to restore degraded grasslands. The establishment of a viable soil seed bank is the key to successful restoration, as it enhances the resilience of ...vegetation. However, little is known of how the soil seed bank affects vegetation resilience following long-term active restoration of degraded grasslands. We determined seed abundance and species composition of the soil seed bank and soil properties and vegetation resilience of intact, degraded, and long-term (>10 years) actively restored grasslands on the Tibetan plateau (3900–4200 m a.s.l.). The plant-soil-seed bank quality index and structural equation modelling (SEM) were used to assess the effect of the soil seed bank on vegetation resilience. After long-term (>10 years) active restoration of degraded grasslands by sowing seeds of native plant species, the densities of transient and persistent seeds increased by 5%, but seed richness (number of species) decreased by 25% when compared with degraded grasslands. This occurred largely as a result of an increase in grass but decrease in forb seeds. Persistent seeds of grasses play an important role in the productivity of restored grasslands, while the density of persistent seeds serves as an indicator of the resilience of vegetation. A combination of the plant community and soil properties determined seed density. Here, we show for the first time that long-term active restoration enhances vegetation resilience of grasslands by altering the soil seed bank. A high seed density of sown Gramineae and a low seed density of forbs in the soil seed bank is a key to the successful active restoration of degraded grasslands.
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•Alhagi sparsifolia offers a variety of socio-ecological services in arid lands.•Unsustainable activities for agricultural purposes may threaten nutrient cycling.•Long-term burning ...and cutting affect the foliar nutrition of A. sparsifolia.•Long-term overexploitation can impact the nutritional quality of A. sparsifolia.•Sustainable management of A. sparsifolia is crucial for ecological restoration.
Arid ecosystems are characterized by low availability and mobility of soil nutrients and slow geochemical cycles. Management of native vegetation in such ecosystems for fuel, livestock grazing, and other agricultural activities (burning and cutting) may threaten semi-natural communities due to the changes in nutrient cycles and soil fertility. Alhagi sparsifolia is a dominant perennial legume in the Taklamakan Desert of northwestern China and has been used as fodder for livestock and plays a crucial ecological role in stabilizing dunes in the oasis-desert ecotone. We evaluated the effects of long-term (12 years) burning and cutting of plant biomass on the mineral nutrition of A. sparsifolia and associated soils at two depths (0–50 and 50–100 cm) in the field conditions following the block design experiment. We found that burning effects tended to be restricted to the topsoil (0–50 cm), and the concentration of many micro-and macronutrients was increased. Burning was associated with a decrease in plant nitrogen (N) and phosphorus (P) concentration, whereas concentrations of other micro-and macronutrients increased; overall, burning reduced foliar stocks of N, P, and potassium (K). Annual cutting elicited smaller increases in soil mineral (total sulfur, total P, calcium, magnesium, and available P and K) concentrations than burning, and soil enzymatic activities increased. There were contrasting response patterns of leaf N and P concentration and macro-and micronutrients between the two management approaches. Burning and cutting reduced leaf N and P concentrations, while changes in root and shoot N and P concentrations depended on treatments. Thus, burning and cutting of A. sparsifolia impact organ nutrient stoichiometry (increased losses of macronutrients from arid plant-soil ecosystems) and nutritional quality (for feeding livestock), particularly due to predicted rises in extreme climatic events under climate change that are expected to increase risks of soil erosion, however, impacts on native trophic webs remain unclear.
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•Bibliometric analysis of AMF-mediated soil carbon cycle over a 22-year period was performed.•The influence of authors, institutions, countries and the research trends are ...identified.•A comprehensive overview of the field is provided using bibliometric tools and visual figures.•The future directions of AMF-mediated soil carbon cycle are proposed.
Arbuscular mycorrhizal fungi (AMF) play an indispensable role in terrestrial ecosystem soil organic carbon (SOC) dynamics. Over the past 22 years, numerous researchers have studied the role of AMF on soil the carbon cycle, thereby producing a wealth of knowledge. However, a comprehensive summary and analysis of the basic characteristics, research outputs, and knowledge base is still lacking. To explore the authors, countries, institutions, and keywords involved in the study of AMF effects on the soil carbon cycle, publications between 2001 and 2022 were identified and extracted from the Web of Science Core Collection databases using specific keywords, and a bibliometric analysis conducted on this data using CiteSpace. The number of publications has gradually increased over time, with a notable acceleration from 2017 onward. Most of the authors did not cooperate on a regular basis, and a stable cooperative group had not yet been formed among the core authors. The Chinese Academy of Sciences produced the largest number of publications among research institutions. Specifically, China published the largest number of articles in terms of national contributions, but had less influence in collaborative networks. The most desirable research topics mainly included nitrogen and phosphorus nutrients, root colonization, diversity, organic matter and organic carbon, plant growth, and microbial community. In more recent years, research seemed to focus more on AMF-mediated carbon, nitrogen, phosphorus, nutrient exchange, alterations in microbial community structure, advancements in research techniques and methods, and in-depth studies into related mechanisms. This study serves as a valuable reference for future researchers interested in the effects of AMF on the soil carbon cycle, and provides guidelines for future innovative research.
Pasture biomass and quality are dependent on herbivore grazing and precipitation, but the responses of vegetation to the interactive effects of climate and grazing regimes remain unclear. We ...conducted an eight-year sheep grazing experiment with 4 stocking rates (0, 3.5, 5.5, and 7.5 sheep/ha) in an alpine meadow of the northeastern Tibetan Plateau. The above-ground net primary productivity (ANPP) and forage nutritional value (FNV) of four dominant species
and
were measured during a wet year (360 mm rainfall) and a drought year (216 mm rainfall). The FNV was used as indicator of forage quality and was calculated from the crude protein (CP) content,
true dry matter digestibility (IVTD), metabolic energy (ME) yield, and neutral detergent fiber (NDF) content of the plant. The stocking rate explained a minimum of 76% of the variations of ANPP, and the precipitation sub-additive effect for ANPP ranged from 5% to 12%. The interaction of sheep stocking rate and precipitation affected ANPP of the 4 species, except for
The FNV of the pasture increased with increasing grazing pressure, but ANPP and forage nutritional yield (FNY) decreased. In calculating FNY, the increase in FNV did not compensate for the decrease in ANPP. In non-grazed plots, the CP yield declined sharply (18%-55%) in response to drought, but there was no effect on ME yield. The interaction between stocking rate and precipitation affected forage quality of the 4 plant species differently. The grassland ANPP and FNY could be maintained at a grazing intensity of 3.5 sheep/ha in wet and dry years. Our results highlight that stocking density affects pasture ANPP and FNV, and is contingent on rainfall.
Root exudates and rhizosphere microorganisms play key roles in the colonization of toxic plants under climate change and land degradation. However, how root exudates affect the rhizosphere ...microorganisms and soil nutrients of toxic plants in degraded grasslands remains unknown. We compared the interaction of soil microbial communities, root exudates, microbial carbon metabolism, and environmental factors in the rhizosphere of toxic and non-toxic plants. Deterministic processes had a greater effect on toxic than non-toxic plants, as root exudates affected rhizosphere microorganisms directly. The 328 up-regulated compounds in root exudates of toxic plants affected the diversity of rhizosphere microorganisms. Rhizosphere bacteria-enriched enzymes were involved in the phenylpropanoid biosynthesis pathway. Root exudates of toxic plants form complex networks of rhizosphere microorganisms, provide high rhizosphere nutrients, and increase microbial carbon metabolism. The interaction between root exudates and rhizosphere microorganisms is the key mechanism that enables toxic plants to spread in degraded grassland habitats.
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•Root exudates are the main drivers for the spread of toxic plants in degraded grassland•Rhizosphere bacteria-enriched enzymes are involved in phenylpropanoid biosynthesis•Root exudates of toxic plants alter microbial network complexity•Root exudates provide nutrients and increase microbial carbon metabolism
Biological sciences; Interaction of plants with organisms; Plant biology.
Increase in nitrogen (N) deposition will cause changes of root morphological and functional traits, thus deeply affecting ecosystem carbon (C) and N cycles. However, the influence of N deposition to ...root traits under different climatic conditions, and with different N deposition rate and durations were still unclear. Here, a meta-analysis was conducted to evaluate the effects of simulated increase in N deposition on 11 root traits under different conditions. In general, N addition significantly increased root/shoot ratio, fine root diameter, total root biomass, fine root production, fine root turnover rate, root respiration, fine root N concentration, while decreased fine root C/N at the global scale. Under N addition, the increased extents of fine root biomass and total root biomass were significantly greater in grassland ecosystems, while the increased extent of fine root turnover was greater in forests. N addition significantly increased fine root production in snow climate zone where forests with ectomycorrhizae. A pattern may be inferred that with increases in mean annual temperature (MAT) and mean annual precipitation (MAP), N addition decreased fine root N concentration and fine root C/N, while increased fine root turnover at the high-MAT and high-MAP areas. In addition, it may be ascertained that fine roots became shorter in the low-rate and short-term N addition experiments, while roots became longer in the high-rate and long-term N addition experiments. Our study indicates that increase in N deposition will cause intricate changes of root traits due to the diversity of climatic conditions and the uncertainty of increase rate and duration of N deposition in future.
•Both fine and total root biomass increased greater in grasslands under N addition.•FRTR increased greater in forests under N addition.•N addition significantly increases fine root production in snow climate zone.•N addition made FRNC and C/N decrease and FRTR enhance in parts of the tropics.•Fine root was shorter in the low-rate and short-term N addition, and vice versa.
Asymbiotic nitrogen-fixing (ANF) bacteria contribute a substantial amount of nitrogen in ecosystems, especially in those with low symbiotic nitrogen fixation (SNF) capability. Degradation of alpine ...grassland is widespread on the Tibetan Plateau and sown grassland has become one of the main strategies for grassland restoration. However, the diversity and community structure of ANF bacteria in different grassland types remain unknown. The aim of this study was to fill this gap. Soil samples were obtained from 39 grassland plots selected from three counties in the eastern Tibetan Plateau. The plots were classified as natural grassland (NG), sown grassland (SG), lightly degraded grassland (LDG), and severely degraded grassland (SDG). ANF microbial communities of the four grassland types were compared at the level of community and species diversity by 16S rRNA high-throughput sequencing technology. The phylum Proteobacteria accounted for >72% of the ANF bacteria. The community structures of soil ANF bacteria differed significantly (
p
< 0.01) among grassland types. We concluded that: (1) planting gramineous forage could possibly mitigate the decrease in diversity of soil ANF bacteria caused by grassland degradation; and (2) the diversity of soil ANF bacteria in alpine grassland of the Tibetan Plateau is closely related to grassland degradation and restoration.
•Aboveground biomass and vegetation coverage decreased with degradation successions.•More forbs and less grasses and sedges occurred with degradation successions.•Significant differences in soil ...nutrients showed in 0–20 cm with degraded processes.•Non-grazing increased vegetation cover, aboveground biomass and soil nutrients.•Soil nutrients were affected by aboveground vegetation.
Understanding the changes in vegetation parameters and soil nutrients in the different stages of grasslands degradation and recovery is crucial for assessing and restoring degraded grasslands. Consequently, we determined above-ground vegetation and soil C, N and P concentrations and their stoichiometry in different degradation and recovery stages on the Tibetan Plateau. Four degradation succession stages, GKC: Grass-Kobresia community, KHC: Kobresia humilis community, KPC: Kobresia pygmaea community, and FBC: forbs - black soil beach community, and three recovery succession stages, FG: freely grazed, RG: restricted grazed, and NG: non-grazed, were identified. Above-ground biomass and vegetation coverage decreased with degradation succession and there was a concomitant shift of plant functional groups to more above-ground biomass of forbs and less biomass of grasses and sedges. The highest species diversity emerged in the K. pygmaea succession stage, mainly due to an influx of Compositae. Significant differences in soil total nitrogen (TN), total phosphorus (TP) and soil organic carbon (SOC) concentrations occurred in the 0–10 and 10–20 cm layers among degradation successions. Vegetation cover, above-ground biomass, soil TN and SOC, as well as C:N and C:P ratios increased in non-grazed grasslands when compared to grazed grasslands. Soil TN, TP and SOC concentrations decreased with increasing soil depths across all degradation and recovery successions. In addition, soil nutrients and their stoichiometry were affected by above-ground biomass. We concluded that grazing exclusion could improve the above-ground vegetation and soil nutrients of degraded alpine grasslands, but that the rate of recovery was related to the degree of degradation.
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