•Divergent shift of normal alpine meadows altered the soil and meadow properties.•Ks of topsoil significantly reduced by normal meadow transition into severely degraded meadow.•Ks of sub topsoil ...significantly reduced by normal meadow transition into shrub meadow.•Divergent shift towards shrub and degraded meadows both decreased water retention and storage.
Soil saturated hydraulic conductivity (Ks) is a critical ecohydrological parameter for assessing the capacity of soil layers in grassland ecosystems to respond to precipitation efficiency, recharge groundwater and supply freshwater to rivers, which is significantly impacted by shifts in vegetation composition. Nevertheless, few studies focused on the effects of the shifts in vegetation composition on Ks of alpine grassland ecosystems. This study examined the effects of normal alpine meadow transition into shrub and severely degraded meadow stages on Ks and further qualified the driving processes. The results showed that the divergent shift of normal alpine meadows altered the soil and meadow properties. Soil water retention and storage capacity of the topsoil was reduced due to the divergent shift of the normal meadow transition into shrub meadow or severely degraded meadow. Ks and field moisture capacity (FMC) reduced by 73.1% and 64.9% in the 0–10 cm soil layer during the transition from normal to degraded meadow, while their variation in the 0–10 cm soil layer were not significant but water consumption increased during the shift from normal to shrub meadow. At the state of normal alpine meadow shift toward severely degraded meadow, the dominant factors affecting Ks were meadow cover (MC), root mass density (RMD), clay content and total porosity, with total effect coefficients of 0.48, 0.42, 0.39 and 0.69, respectively. Meanwhile, when normal alpine meadow shift toward shrub meadow, dominant factors affecting Ks were MC, non-capillary porosity, clay and sand contents, with total effect coefficients of 0.47, −0.86, −0.54 and −0.50, respectively. This study helps understanding the impacts of the shifts in vegetation composition on the ecohydrological processes in alpine meadow ecosystems in response to climate change and overgrazing.
Uncertainty about the effects of warming and grazing on soil nitrogen (N) availability, species composition, and aboveground net primary production (ANPP) limits our ability to predict how global ...carbon sequestration will vary under future warming with grazing in alpine regions. Through a controlled asymmetrical warming (1.2/1.7°C during daytime/nighttime) with a grazing experiment from 2006 to 2010 in an alpine meadow, we found that warming alone and moderate grazing did not significantly affect soil net N mineralization. Although plant species richness significantly decreased by 10% due to warming after 2008, we caution that this may be due to the transient occurrence or disappearance of some rare plant species in all treatments. Warming significantly increased graminoid cover, except in 2009, and legume cover after 2008, but reduced non-legume forb cover in the community. Grazing significantly decreased cover of graminoids and legumes before 2009 but increased forb cover in 2010. Warming significantly increased ANPP regardless of grazing, whereas grazing reduced the response of ANPP to warming. N addition did not affect ANPP in both warming and grazing treatments. Our findings suggest that soil N availability does not determine ANPP under simulated warming and that heavy grazing rather than warming causes degradation of the alpine meadows.
Plateau pikas (Ochotona curzoniae) bioturbation affects the soil nutrient concentrations of the alpine meadow in the Qinghai-Tibetan Plateau (QTP) by the arrangement of bare land. This study ...investigated the effect of the disturbance produced by plateau pika bioturbation on primary soil nutrient concentrations of the Kobresia pygmaea meadow in view of overall and site scale and further analyzed the effect of the disturbance intensity of plateau pika on the soil nutrient concentrations of vegetated land and bare land. Our results showed that the disturbance by plateau pika bioturbation significantly decreased the soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP), and increased the available phosphorus (AP), NO3−-N and NH4+-N of bare land. Moderate disturbance intensities increased the SOC, TN and TP of both vegetated land and bare land and reduced the NO3−-N, NH4+-N and AP of vegetated land while increasing those of bare land. Disturbance within the threshold disturbance intensities of plateau pika is beneficial to the soil C and N, accumulating higher available nutrient concentrations in the topsoil, which would provide good habitats for certain rare plants and supply nutrients for the nitrophilous graminoid plants to grow well in the QTP. These results suggest that the understanding of the responses of the soil nutrient concentrations to plateau pika bioturbation should consider the bare land under disturbance intensities of plateau pika and alpine meadow type.
•Disturbance and intensity present more information than only intensity.•Disturbance by plateau pika increased the soil NO3−-N and NH4+-N of bare land.•Different intensity has different influence on soil nutrients.•Bare land under moderate disturbed intensity is beneficial to the alpine meadow.
Nitrogen (N) availability is increasing dramatically in many ecosystems, but the influence of elevated N on the functioning of arbuscular mycorrhizal (AM) fungi in natural ecosystems is not well ...understood.
We measured AM fungal community structure and mycorrhizal function simultaneously across an experimental N addition gradient in an alpine meadow that is limited by N but not by phosphorus (P). AM fungal communities at both whole-plant-community (mixed roots) and single-plant-species (Elymus nutans roots) scales were described using pyro-sequencing, and the mycorrhizal functioning was quantified using a mycorrhizal-suppression treatment in the field (whole-plant-community scale) and a glasshouse inoculation experiment (single-plant-species scale).
Nitrogen enrichment progressively reduced AM fungal abundance, changed AM fungal community composition, and shifted mycorrhizal functioning towards parasitism at both whole-plant-community and E. nutans scales. N-induced shifts in AM fungal community composition were tightly linked to soil N availability and/or plant species richness, whereas the shifts in mycorrhizal function were associated with the communities of specific AM fungal lineages.
The observed changes in both AM fungal community structure and functioning across an N enrichment gradient highlight that N enrichment of ecosystems that are not P-limited can induce parasitic mycorrhizal functioning and influence plant community structure and ecosystem sustainability.
The nitrogen‐fixing legume Lupinus polyphyllus invaded semi‐natural mountainous grasslands across Europe during the last decades. This invasion resulted in degraded habitats through changes in the ...structure and function of the mountain meadow vegetation. In our study, we analyzed (1) the effects of increasing cover of L. polyphyllus on the seed bank of mountain meadows, and (2) the potential of the seed bank of these stands for active restoration of mountain meadows in terms of species composition and number. We conducted a seed bank analysis on 84 plots with increasing cover of L. polyphyllus in three mountain‐meadow types of the Rhön Biosphere Reserve, Germany. Seedlings from 119 species germinated from the seed bank samples, including 17 Red List species but only a few seedlings of L. polyphyllus. The species composition of the seed bank matched distinct patterns of the three meadow types, but differed from the species composition of the current aboveground vegetation in a nonmetric multidimensional scaling ordination. While the influence of L. polyphyllus on the current vegetation was visible, no effects on the seed bank were apparent. L. polyphyllus had no influence on total seed density, seed density of typical mountain‐meadow species, or species numbers in the seed bank. Only the seeds of the Red List species were significantly related to the cover of L. polyphyllus. We conclude that the seed bank offers potential for active restoration of species‐rich mountain meadows, but species absent from the seed bank have to be added by other measures.
•Meadow patch coverage (MPC) regulates the magnitude of soil erosion processes.•MPC can maintain runoff and reduce sediment under different rainfall intensities.•Alpine meadow degradation can be ...evaluated by quantifying the decrease of MPC.•Meadow and bald patches decreased runoff coefficient in the 60% MPC.
Meadow patches are caused by the fragmentation and disappearance of mattic epipedons, and can serve as evidence of degradation. This is a gradual decline in meadow patch coverage, which can result in soil and surface water loss due to increased bare soil surface. However, little is known about how the loss of mattic epipedons alters soil erosion processes in alpine regions. This study sheds light on this topic by conducting simulated rainfall experiments with different rainfall intensities to assess runoff and sediment generation. We selected representative degraded alpine meadows on the eastern Qinghai-Tibetan Plateau in China. The observed temporal variations of runoff and soil loss rates were explained by the presence of two stages of meadow patch coverage decline: an increasing and a relatively stable stage. Compared to 30% and 60% meadow patch coverage, 90% meadow patch coverage displayed an extended increasing stage with delayed entrance into the stable stage during the rainfall period. The runoff coefficients were significantly higher in 90% and 30% meadow patch coverage than in 60%. The sediment concentrations were significantly lower in 90% and 60% meadow patch coverage than in 30%. It is worth stressing that 90% meadow patch coverage could prompt more rainfall flowing as runoff and reduce sediment under different rainfall intensities. The complex mosaic-pattern formed by meadow and bald patches changed the hydrological response of the soil, decreasing runoff coefficient in 60% meadow patch coverage. The destruction, reduction or even disappearance of some mattic epipedons led to a higher sediment concentration in 30% meadow patch coverage. The meadow patch coverage exerted a greater influence on sediment yield than on runoff volume, although it was generally affected by rainfall intensity. Our findings highlight the importance of maintaining runoff and reducing sediment through the presence of mattic epipedons. Mattic epipedons appear as an effective soil erosion control feature, and this study offers a theoretical guidance for planning adaptive management strategies for degraded alpine meadows on the Qinghai-Tibetan Plateau.
•Meadow patch coverage (MPC) regulated runoff and sediment under natural rainfall.•MPC had a greater impact on sediment yield than runoff volume in alpine area.•The greater MPC, the greater runoff ...coefficient and the lower sediment concentration.•Maintaining runoff is crucial to water conservation capacity of alpine meadow.
Soil and water conservation is the most important among ecological functions of alpine meadow on the Qinghai-Tibetan Plateau. Quantitative assessment of the effects of meadow patch coverage (MPC) on the runoff and sediment processes in alpine meadow is urgent for predicting the water conservation function of this special alpine ecosystem. Here, a field experiment was conducted to determine the effects of different meadow patch coverage through runoff and sediment processes in a typical alpine meadow on the eastern Qinghai-Tibetan Plateau. The results showed that runoff in 30% and 60% MPC plots were 39.4% and 37.9% less than in 90% MPC plot, respectively. The sediment yield in 60% and 90% MPC plots were 77.9% and 82.1% less than in 30% MPC plot, respectively. The sediment concentration in 30% MPC in heavy rainfall scenario is 4.34 times and 6.51 times higher than that in light rainfall scenario and moderate rainfall scenario, respectively. Our results indicated that MPC presented a greater impact on sediment yield than runoff volume, although runoff was greatly affected by rainfall. The higher MPC followed the greater runoff coefficient and the lower sediment concentration. The influences of MPC on runoff and sediment yield in light rainfall scenario and moderate rainfall scenario were weaker than those in heavy rainfall scenario. It is necessary to maintain surface runoff while controlling soil loss for realizing the sustainability of alpine meadow ecosystems. Therefore, these findings may conducive to offer a theoretical guidance to achieve the combined goal of soil erosion regulation during alpine meadow degradation on the Qinghai-Tibetan Plateau.
The biological nitrogen input is essential for nutrient enrichment in natural grassland ecosystems. This process is carried out by diazotrophic microbes. However, the patterns and assembly processes ...of diazotrophic communities in grassland soil are not fully understood, especially in alpine meadows of high-altitude Qinghai-Tibet Plateau (QTP). In this study, the diversity patterns and community assembly processes of soil diazotrophic communities were investigated in QTP alpine meadows. The results showed that different diazotrophic taxa responded differentially to the increase of soil pH, and α-diversity increased linearly with pH values. Diazotrophic community turnover was enhanced by the increased variation in soil pH, moreover, it also showed strong response to mean annual temperature. Null model analysis showed that deterministic processes were most important in shaping the phylogenetic community structure and assembly of diazotrophs. Diazotrophic communities of each sampling site tended to be phylogenetically clustered, while communities at high pH soils (pH 7.00 to 8.00) showed more clustering than those of low pH (pH 5.02 to 7.00). The soil pH is a main driver in structuring soil diazotrophic community assembly by regulating the relative importance of deterministic and stochastic processes in QTP alpine meadows.
•Soil diazotrophic community assembly in alpine meadows was studied.•Soil pH is a main driver shaping diazotrophic community assembly.•Diazotrophic communities show more phylogenetic clustering at high pH soils.•Deterministic processes govern phylogenetic structure and turnover of diazotrophs.
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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.
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