The alpine meadow ecosystem on the Qinghai–Tibetan Plateau (QTP) is very sensitive to warming and plays a key role in regulating global carbon (C) cycling. However, how warming affects the soil ...organic carbon (SOC) pool and related C inputs and outputs in alpine meadow ecosystems on the QTP remains unclear. Here, we combined two field experiments and a meta‐analysis on field experiments to synthesize the responses of the SOC pool and related C cycling processes to warming in alpine meadow ecosystems on the QTP. We found that the SOC content of surface soil (0–10 cm) showed a minor response to warming, but plant respiration was accelerated by warming. In addition, the warming effect on SOC was not correlated with experimental and environmental variables, such as the method, magnitude and duration of warming, initial SOC content, mean annual temperature, and mean annual precipitation. We conclude that the surface SOC content is resistant to climate warming in alpine meadow ecosystems on the QTP.
The soil organic carbon (SOC) content of surface soil (0–10 cm) showed a minor response to warming, although plant respiration was accelerated by warming. We conclude that the surface SOC content is resistant to climate warming in alpine meadow ecosystems on the Qinghai–Tibetan Plateau.
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We measured the influences of soil fertility and plant community composition on Glomeromycota, and tested the prediction of the functional equilibrium ...hypothesis that increased availability of soil resources will reduce the abundance of arbuscular mycorrhizal (AM) fungi.
Soil CO2 emission is a key part of the terrestrial carbon cycle. Grazing exclusion by fencing is often considered a beneficial grassland management option to restore degraded grassland, but its ...effect on soil CO2 emission on the northeastern Tibetan Plateau is equivocal and is the subject of this study. Using a closed static chamber, we measured diurnal soil CO2 flux weekly from July, 2008, to April, 2009, in response to grazing and grazing exclusion in the alpine meadow and alpine shrub meadow. Concomitantly, soil temperature was measured at depths of 5 cm, 10 cm, 15 cm and 20 cm with digital temperature sensors. It emerged that: 1) non-grazed grasslands emitted more soil CO2 than grazed grasslands over the growing season; 2) the alpine shrub meadow emitted more soil CO2 than the alpine meadow; the annual cumulative soil CO2 emissions of alpine meadow and alpine shrub meadow were 241.5–326.5 g C/m2 and 429.0–512.5 g C/m2, respectively; 3) seasonal patterns were evident with more soil CO2 flux in the growing than in the non-growing season; and 4) the diurnal soil CO2 flux exhibited a single peak across all sampling sites. In addition, soil CO2 flux was correlated positively with soil temperature at 5 cm, but not at the other depths. We concluded that grazing exclusion enhanced soil CO2 emission over the growing season, and decreased carbon sequestration of alpine meadow and alpine shrub meadow on the northeastern Tibetan Plateau. Since an increase in soil temperature increased soil CO2 flux, global warming could have an effect on soil CO2 emission in the future.
•Non-grazed grasslands emitted more soil CO2 than grazed grasslands over the growing season.•Seasonal patterns were evident with more soil CO2 flux in the growing than in the non-growing season.•The diurnal soil CO2 flux exhibited a single peak across all sampling sites.•Soil CO2 flux was correlated positively with soil temperature at 5 cm.•Grazing exclusion enhanced soil CO2 emission over the growing season on the Tibetan Plateau.
Seagrass phenophases are crucial in understanding their reproductive biology but are seldom documented. We studied flowering and fruiting phenophases of Enhalus acoroides from a mixed-species ...intertidal seagrass meadow in Ritchie’s archipelago, Andaman Islands, India. The estimated mean densities of pistillate and staminate flowers were 16.0 ± 12.0/ m2 and 12.7 ± 7.3/ m2, respectively. We observed the bloom of free-floating male flowers (961.7 ± 360.4/ m2) during the spring low tides (at mean sea surface temperature ~30°C). Seagrass cover, shoot density, and canopy height of E. acoroides, along with flowering densities, showed a zonal variation within the sampled meadow. We report the first-time observations of several phenophases of E. acoroides, such as female inflorescence buds, male inflorescence, a bloom of released male flowers, pollination, and fertilized flowers from the Indian waters. We also report the prevailing threats to seagrass meadows, such as meadow scarring done by boat anchorage in the Andaman Islands.
Seagrass meadows are globally threatened by anthropogenic and natural pressures that cause habitat fragmentation and ecosystem degradation. Seagrass fragmentation is manidested by the loss of ...vegetation in gaps within a meadow. Depending on the degree of fragmentation, the ecological services provided by theseagrass meadows may be compromised. This study aims to understand the effect meadow fragmentation hason the shoot density of the canopy (large-scale or meadow-scale effect), as well as the effect the local gap size has on the shoot density at the edge of the gap (local-scale or gap-scale effect). In other woerd, determine whether the effects on the large scale can impact the local scales of the gap. This study demonstrates that the greater the gap area is, the lower the shoot density of the vegetation surrounding the gap. Moreover, the effect of fragmentation at the meadow-scale has been proved: the higher the fragmentation degree of the meadow is, the lower the shoot density is in the surrounding vegetation near the gap. Hence, the differences in shoot density at the edges of a gap are proven to be produced by both meadow fragmentation and gap characteristics.
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•Meadows fragmentation impacts on the canopy density at both gap- and canopy-scales.•The larger the gap size the sparser the canopy density of the on-shore canopy nearby.•The higher the meadow fragmentation the sparser the canopy density at gap edges.
Background and aims
Long-term nitrogen (N) addition can affect soil organic carbon (SOC) pool within different soil fractions with different turnover rates. However, the mechanisms of these effects, ...particularly in alpine grassland ecosystems, are not clear.
Methods
We studied the responses of SOC content in different soil fractions to N addition based on a six-year N addition field experiment in an alpine meadow ecosystem on the Tibetan Plateau. We measured soil chemical and microbial properties, and SOC content in bulk soil, particular organic matter (POM) and mineral-associated organic matter (MAOM) fractions in response to N addition.
Results
N addition increased soil N availability, decreased soil pH and microbial biomass, but had minimal effect on plant biomass, soil enzyme activity, and SOC content in bulk soil. With increasing levels of N addition, SOC in the POM fraction (POC) showed a significant negative trend, while SOC in the MAOM fraction (MAOC) did not change significantly.
Conclusions
As plant biomass input and soil enzyme activity were not significantly altered with N addition, the decline in POC was likely caused by changes in microbial physiology (carbon use efficiency), while the insignificant change in MAOC may be determined by the balance between input (from microbial necromass) and output (from microbial decomposition). Taken together, our study showed that the less-protected POC fraction is more vulnerable to N addition than the more-protected MAOC fraction in the alpine grassland. This finding may improve the prediction of soil C dynamics in response to N deposition in alpine grassland ecosystems on the Tibetan Plateau.
The Tibetan Plateau has undergone significant climate warming in recent decades, and precipitation has also become increasingly variable. Much research has explored the effects of climate change on ...vegetation on this plateau. As potential vegetation buried in the soil, the soil seed bank is an important resource for ecosystem restoration and resilience. However, almost no studies have explored the effects of climate change on seed banks and the mechanisms of these effects. We used an altitudinal gradient to represent a decrease in temperature and collected soil seed bank samples from 27 alpine meadows (3,158–4,002 m) along this gradient. A structural equation model was used to explore the direct effects of mean annual precipitation (MAP) and mean annual temperature (MAT) on the soil seed bank and their indirect effects through aboveground vegetation and soil environmental factors. The species richness and abundance of the aboveground vegetation varied little along the altitudinal gradient, while the species richness and density of the seed bank decreased. The similarity between the seed bank and aboveground vegetation decreased with altitude; specifically, it decreased with MAP but was not related to MAT. The increase in MAP with increasing altitude directly decreased the species richness and density of the seed bank, while the increase in MAP and decrease in MAT with increasing altitude indirectly increased and decreased the species richness of the seed bank, respectively, by directly increasing and decreasing the species richness of the plant community. The size of the soil seed bank declined with increasing altitude. Increases in precipitation directly decreased the species richness and density and indirectly decreased the species richness of the seed bank with increasing elevation. The role of the seed bank in aboveground plant community regeneration decreases with increasing altitude, and this process is controlled by precipitation but not temperature.
Soil seed bank is an important resource for ecosystem restoration and resilience. However, almost no studies have explored the effects of climate change on seed banks and the mechanisms of these effects. We found increases in precipitation directly decreased the species richness and density and indirectly decreased the species richness of the seed bank with increasing elevation. The role of the seed bank in aboveground plant community regeneration decreases with increasing altitude, and this process is controlled by precipitation but not temperature.
Alpine meadow and alpine steppe are the two most widely distributed nonzonal vegetation types in the Qinghai-Tibet Plateau. In the context of global climate change, the differences in ...spatial-temporal variation trends and their responses to climate change are discussed. It is of great significance to reveal the response of the Qinghai-Tibet Plateau to global climate change and the construction of ecological security barriers. This study takes alpine meadow, alpine steppe and the overall vegetation of the Qinghai-Tibet Plateau as the research objects. The normalized difference vegetation index (NDVI) data and meteorological data were used as the data sources between 2000 and 2018. By using the mean value method, threshold method, trend analysis method and correlation analysis method, the spatial and temporal variation trends in the alpine meadow, alpine steppe and the overall vegetation of the Qinghai-Tibet Plateau were compared and analyzed, and their differences in the responses to climate change were discussed. The results showed the following: (1) The growing season length of alpine meadow was 145~289 d, while that of alpine steppe and the overall vegetation of the Qinghai-Tibet Plateau was 161~273 d, and their growing season lengths were significantly shorter than that of alpine meadow. (2) The annual variation trends of the growing season NDVI for the alpine meadow, alpine steppe and the overall vegetation of the Qinghai-Tibet Plateau increased obviously, but their fluctuation range and change rate were significantly different. (3) The overall vegetation improvement in the Qinghai-Tibet Plateau was primarily dominated by alpine steppe and alpine meadow, while the degradation was primarily dominated by alpine meadow. (4) The responses between the growing season NDVI and climatic factors in the alpine meadow, alpine steppe and the overall vegetation of the Qinghai-Tibet Plateau had great spatial heterogeneity in the Qinghai-Tibet Plateau. These findings provide evidence towards understanding the characteristics of the different vegetation types in the Qinghai-Tibet Plateau and their spatial differences in response to climate change.
An essential ecosystem service is the dilution effect of biodiversity on disease severity, yet we do not fully understand how this relationship might change with continued climate warming and ...ecosystem degradation. We designed removal experiments in natural assemblages of Tibetan alpine meadow vegetation by manipulating plotâlevel plant diversity to investigate the relationship between different plant biodiversity indices and foliar fungal pathogen infection, and how artificial fertilization and warming affect this relationship. Although pathogen group diversity increased with host species richness, disease severity decreased as host diversity rose (dilution effect). The dilution effect of phylogenetic diversity on disease held across different levels of host species richness (and equal abundances), meaning that the effect arises mainly in association with enhanced diversity itself rather than from shifting abundances. However, the dilution effect was weakened by fertilization. Among indices, phylogenetic diversity was the most parsimonious predictor of infection severity. Experimental warming and fertilization shifted species richness to the most supported predictor. Compared to planting experiments where artificial communities are constructed from scratch, our removal experiment in natural communities more realistically demonstrate that increasing perturbation adjusts natural community resistance to disease severity.
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