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Graminoids are typically the dominant plants in certain grassland communities, and their clonal growth is considered an important method of evaluating their adaptation to environmental disturbances. Whether disturbances caused by small burrowing herbivores influence clonal growth in graminoids is not well documented. A field experiment was conducted to investigate the effects of disturbances by small burrowing herbivores, the plateau pika, on the clonal growth of the tussock-forming Kobresia pygmaea and the rhizomatous K. humilis across three sites. This study showed that disturbance by plateau pikas increased the shoot number, spacer number and tiller bud number per clonal fragment of both the tussock-forming K. pygmaea and the rhizomatous K. humilis across three sites. This study also showed that disturbance by plateau pikas increased the rhizome branch number, rhizome length, and rhizome bud number per clonal fragment of rhizomatous K. humilis at each site, while the effects of disturbance by plateau pikas on the rhizome branch number, rhizome length, and rhizome bud number per clonal fragment of the tussock-forming K. pygmaea were different among the three sites. These results suggested that disturbance by plateau pikas benefits for current and potential population recruitment in the tussock-forming K. pygmaea and the rhizomatous K. humilis due to the resulting higher shoot number and tiller bud number per clonal fragment.

Plateau pikas (Ochotona curzoniae) often clip tall plants near active burrow entrances to detect and avoid predators. This clipping behavior influencing plant communities near active burrow entrances has not been well documented. A field experiment was conducted to investigate the effects of this clipping behavior on plant communities across three sites in the Qinghai-Tibetan Plateau by comparing plant communities near active burrow entrances with communities near abandoned burrow entrances. This study showed that the clipping behavior decreased plant community height and increased plant cover and species richness of the community and had no effect on plant community biomass across three sites or at each site. This study further showed that clipping behavior decreased the plant biomass of the graminoid group and had no effect on the plant species richness of the graminoid group, whereas it increased the plant biomass and plant species richness of the forb group across the three sites or at each site. These findings suggest that a general pattern concerning the effect of the clipping behavior can increase plant species richness and decrease the grazing quality of alpine meadows near active burrow entrances.

Small semi-fossorial herbivores can affect plant aboveground biomass (AGB) in grasslands and possibly alter the allocation of AGB and belowground biomass (BGB). In this study, plateau pika (Ochotona curzoniae) was used to investigate such effects at three alpine meadow sites on the Eastern Tibetan Plateau, where pairs of disturbed vs. undisturbed plots were randomly selected and sampled. We also explored the relationships between soil properties and BGB/AGB across the plots in the presence and absence of plateau pikas, respectively. We found that BGB and BGB/AGB were 11.40 and 8.20% lower in the presence of plateau pikas than in their absence, respectively. We also found that the BGB/AGB was positively related to soil moisture and soil total nitrogen (STN) in the absence of plateau pikas. In contrast, BGB/AGB was positively related to STN, soil organic carbon (SOC), soil carbon/nitrogen (C/N), and soil total phosphorus in the presence of plateau pikas. These factors indicated plateau pika disturbance increased AGB allocation. The relationship between AGB and BGB of alpine meadow plants to soil variables was also different between sites with and without plateau pika disturbance. In conclusion, small semi-fossorial herbivore disturbance is likely to alter grassland carbon stock and should be well controlled for sustainable conservation and management of alpine meadows on the Tibetan Plateau.

Although partial root-zone drying irrigation (PRD) has been proven to be applicable to alfalfa production, the physiological mechanism of how PRD improves water use efficiency without biomass loss in alfalfa has not been well documented. We designed a field experiment with two irrigation modes (PRD and conventional furrow irrigation (CFI)) and four irrigation volumes (70%-I1, 85%-I2, 100%-I3, and 115%-I4 of alfalfa water requirement (ET)) to determine the effect of PRD on gas exchange and antioxidant enzymatic activities. Our study showed that PRD did not markedly affect the biomass but reduced the leaf area of alfalfa plants at the first and second harvest times. Whether for the first or second harvest time, PRD had no significant effect on net photosynthetic rate (Pn) but decreased the stomatal conductance (Gs) and transpiration rate (Tr), resulting in higher leaf water use efficiency (LWUE). PRD significantly increased the superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities, as well as the soluble sugar, proline, and malondialdehyde (MDA) concentrations, and decreased the soluble protein concentration at the first and the second harvest times. These results suggest that PRD could improve photosynthetic characteristics, increase oxidation resistance, and regulate osmotic adjustment. This would conserve irrigation water volumes and maintain a relatively steady biomass of alfalfa plants. Our findings present physiological evidence that PRD can be successfully applied to alfalfa production.

Herbivore disturbance can affect the grassland ecosystem services though creating extensive disturbances vegetation and soil. This study focused on plateau pika (Ochotona curzoniae) disturbance to investigate the effect of disturbance by small burrowing herbivores on ecosystem services of alpine grasslands though five sites. In this study, the palatable plant biomass, plant species richness, soil water storage, soil organic carbon, total nitrogen, phosphorus and potassium stocks were used to estimate the forage availability, biodiversity conservation, water conservation, carbon sequestration and soil nutrient maintenance. This study showed that plateau pika disturbance was related to higher plant species richness and soil organic carbon stock, associated with lower palatable plant biomass and soil water storage, and had no effect on total potassium stock, whereas the responses of soil total nitrogen and phosphorus stocks to plateau pika disturbance were different among sites. The palatable plant biomass, plant species richness, soil organic carbon, total nitrogen and phosphorus stocks showed downward parabolas, whereas the soil water storage showed a decreasing trend with increasing plateau pika disturbance intensity. These results indicated that the role of plateau pikas is dependent not only on the management target of alpine grasslands but also on the plateau pika disturbance intensity.

The plateau pika (Ochotona curzoniae) is known to influence the plant diversity and biomass of the alpine meadow, and it is regarded as a pest. The species has been subject to extensive controls without a clear target density in the Qinghai‐Tibetan Plateau. We investigated the effects of different plateau pika disturbance levels on plant composition, species diversity and biomass. The density of active burrow entrances was used as an index of disturbance levels I, II, III and IV (corresponding to 8, 19, 27 and 39 active burrow entrances per 625 m²). We found that the plant community composition differed with different disturbance levels. The plant replacements were mainly related to associate plants rather than dominant plants. With the increase in the plateau pika disturbance levels, the plant cover decreased, and the plant height first increased and then decreased. The plant evenness index was higher in the levels II and III disturbance conditions, while the plant diversity index and plant richness index were highest in the level IV disturbance condition. The disturbance levels had no effect on the total plant biomass; however, the intermediate disturbance levels (II and III) increased the palatable plant biomass. The total plant biomass was mainly dependent on the unpalatable plant biomass. The total plant biomass showed a positive correlation with the richness index and a negative correlation with the evenness index. The palatable plant biomass showed a positive correlation with the evenness index and a negative correlation with the richness index. These results imply that the intermediate disturbance levels are beneficial to livestock production as they increase the alpine meadow quality, and the higher disturbance level is better for plant diversity conservation in the alpine meadows of the Qinghai‐Tibetan Plateau.

Do semi-fossorial herbivores influence the trajectory of plant community succession by altering belowground bud density in alpine meadows? Field surveys were carried out to investigate the effect of disturbance and disturbance intensity of the plateau pika (Ochotona curzoniae) on the belowground bud density in alpine meadows at two sites. The Linear Mixed Model (LMM) test and Linear Model (LM) test were used to analyze the relative effect of plateau pika disturbance on bud density and to clarify the response of belowground bud density to disturbance intensity. Our results showed that disturbance by the plateau pika increased belowground bud density of graminoids and plants from the grass and sedge families, including Kobresia pygmaea and Elymus nutans, but had no effect on forbs bud density. The bud density of graminoids, grass and sedge plants, and K. pygmaea and E. nutans showed a downward parabolic trend in response to increased disturbance intensity of the plateau pika, implying that there was an optimal level of disturbance intensity that maximized belowground bud density of graminoids. These results suggest that disturbance by the plateau pika has different effects on belowground bud densities of graminoids versus forbs. Additionally, disturbance by plateau pika up to the optimal intensity may improve grazing quality of alpine meadow in the long term through increasing graminoid bud density, resulting in a higher proportion of graminoids in pasture, while higher levels of disturbance by plateau pika may deteriorate alpine meadows through a reduction in graminoid bud density.

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), NO 3 − -N and NH 4 + -N of bare land. Moderate disturbance intensities increased the SOC, TN and TP of both vegetated land and bare land and reduced the NO 3 − -N, NH 4 + -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.

Bioturbation by small burrowing herbivores can affect soil organic carbon (C), total nitrogen (N) and total phosphorus (P) concentrations mainly by creating visible bare soil patches that are interspersed within vegetated surfaces in grasslands. This study focused on plateau pikas (Ochotona curzoniae) to investigate the effects of bioturbation by these small burrowing herbivores on the soil C, N, and P concentrations and their stoichiometry in bare and vegetated soils in alpine meadows. This study showed that plateau pika bioturbation was related to lower organic C concentrations in bare soil in the 0–10 cm and 10–20 cm layers than in vegetated soil and to lower total N concentrations in bare soil than in vegetated soil only in the 0–10 cm layer, whereas no significant differences were observed for the P concentrations. This study also showed that plateau pika bioturbation results in lower C:N and C:P ratios in bare soil than in vegetated soil at two soil depths and lower N:P ratios only in the 0–10 cm layer. These results presented a pattern of how bioturbation by small burrowing herbivores influences soil stoichiometry (C:N:P). The findings of this study imply that lower C:N and C:P ratios are a possible mechanism by which bare soil patches caused by small burrowing herbivores can naturally recover.

The plateau pika ( Ochotona curzoniae ), one of the main bioturbators, creates extensive disturbances in the soil of the alpine meadow of the Qinghai-Tibet Plateau (QTP). This study investigated the effects of the presence and intensity of plateau pika disturbances on the main soil nutrients of the Kobresia pygmaea meadow across three study sites in the QTP by using the method of counting the active burrow entrance densities of plateau pika in the field as a representation of the disturbance intensity. Our results showed that the presence of plateau pika significantly increased the soil total nitrogen (TN), soil organic carbon (SOC) and total phosphorus (TP) concentrations and decreased the available phosphorus (AP) concentrations across the three study sites. The presence of plateau pika increased the NO 3 − -N and NH 4 + -N concentrations in Luqu County and Maqu County, but had no significant effect on these concentrations in Gonghe County. The soil TN, SOC and TP concentrations showed a downward parabola and the NO 3 − -N, NH 4 + -N and AP concentrations showed an upward parabola as the intensity of the disturbances increased in Luqu County and Maqu County. These soil nutrients had a threshold (inflection point) of 475 (475 ± 90) burrow entrances per ha. However, the soil TN, SOC and TP concentrations increased linearly while the NO 3 − -N, NH 4 + -N and AP concentrations decreased linearly with the increasing intensity of disturbances in Gonghe County (≤512 burrow entrances per ha). These results implied that the soil nutrient changes induced by plateau pika disturbances are not only related to their presence but are also related to the intensity of the disturbances, and that the most appropriate disturbance intensity (475 (475 ± 90) burrow entrances per ha) of plateau pika was beneficial to the storage of soil carbon and nitrogen in the alpine meadow in the QTP.

Although grassland degradation simultaneously affects plant productivity and soil nutrient concentrations, the relationship between plant productivity and soil nutrient concentrations during the process of grassland degradation is not yet well documented. A 4-year survey in the Qinghai-Tibetan Plateau was conducted to simultaneously investigate the relationships between plant productivity and soil nutrient concentrations in an alpine grassland at an overall degradation level and individual degradation levels. Our results showed that the total plant, sedge, and forb biomasses decreased, whereas the grass and legume biomasses first increased and then decreased as the level of alpine grassland degradation increased. Soil organic carbon (C), total nitrogen (N), total phosphorus (P), available N, and available P concentrations also decreased with the increase in degradation level. Our results also showed that plant productivity was positively correlated with soil nutrient concentrations (soil organic C, total T, total P, available N, available P) at an overall degradation level, whereas plant productivity was positively correlated with only the soil organic C concentration at each degradation level. Our findings suggested that the alpine grassland degradation conditions had different effects on the plant productivity of four functional groups (sedges, grasses, legumes, forbs) and affected the relationship between plant productivity and soil nutrient concentrations.

Partial root-zone drying irrigation (PRDI) can influence carbon (C), nitrogen (N), and P (phosphorus) allocations in annual crop plants. This study consisted of a two-factorial split-plot field experiment conducted on Huanghua farmland in western China, and it was focused on investigating the effects of PRDI on the biomass; water productivity; and C, N and P allocations in a perennial plant (alfalfa) from 2016-2017. The two factors were the irrigation mode (PRDI and conventional furrow irrigation (CFI)) and irrigation volume (70 %-I1, 85 %-I2, 100 %-I3 and 115 %-I4 of the alfalfa water requirement), in which the irrigation mode was the primary plot and the irrigation volume was the subplot. This study showed that PRDI decreased the alfalfa leaf biomass and increased the alfalfa root, stem biomass and water productivity but that it had no effect on the alfalfa shoot biomass at the end of the vegetative growth period in 2016 and 2017. PRDI increased the C and P concentrations in the roots and the N concentration in the roots, stems and leaves, and it led more C and P to be allocated to the roots and more N to be allocated to the leaves in 2016 and 2017. These results implied that C, N, and P allocation changes in different organs induced by PRDI may be one of the possible ways for alfalfa plants to adapt to the changing environmental conditions caused by PRDI.

The presence of small burrowing herbivores often cause extensive disturbance to the grassland soil nutrient stocks. This study investigated the effect of small burrowing herbivore presence, the plateau pika (Ochotona curzoniae), and variation in disturbance intensity on soil nitrogen stocks at five alpine meadow sites. Disturbed plots occupied by plateau pikas consist of burrows and their associated bare soil patches in a matrix of continuous alpine meadow. The percentage of the bare soil area in a disturbed plot was used as a proxy for disturbance intensity of plateau pikas. This study showed that the soil total nitrogen stock was lower of bare soil than vegetated soil within disturbed plots, while ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3−-N), inorganic nitrogen and ammonium nitrogen/nitrate nitrogen ratio (ANR) were higher in bare soil than vegetated soil within the disturbed plots. This study further showed that the NH4+-N, inorganic nitrogen and ANR of disturbed plots were higher than those of undisturbed plots, whereas soil total nitrogen and the NO3−-N stock was not different between disturbed plots and undisturbed plots. This study also showed that the soil total nitrogen, NH4+-N and inorganic nitrogen stocks of disturbed plots were higher at intermediate disturbance intensities of plateau pikas, whereas the NO3−-N stock and ANR were not related to disturbance intensities. These results suggest that the NH4+-N and inorganic nitrogen stocks were higher in the presence of plateau pikas, and intermediate disturbance intensity of plateau pikas was beneficial for soil quality due to higher soil total nitrogen, NH4+-N and inorganic nitrogen stocks. The findings of this study present a possible approach for estimating how the presence of a small burrowing herbivore influences grassland soil nitrogen stock.

Alternate furrow irrigation is considered a water-saving technique to improve water use efficiency without considerable yield reduction in horticultural crops and field crops. We investigated the effects of alternate furrow irrigation on the biomass and quality of alfalfa (Medicago sativa) in this study. A field experiment was designed with two irrigation modes (alternate furrow irrigation-AFI and conventional irrigation-CI) and four irrigation volumes (70%-I1, 85%-I2, 100%-I3 and 115%-I4 of alfalfa water requirement (ET)). Alternate furrow irrigation increased the water use efficiency based on the total biomass and aboveground biomass of alfalfa by 40–46% and 36–42%, respectively. This approach maintained comparable aboveground biomass at the first and the second harvest times but significantly decreased the aboveground biomass at the third harvest time, which contributed to the seasonal drop in aboveground biomass compared to conventional irrigation. Alternate furrow irrigation increased the number of branches per plant, but decreased the leaf numbers per plant at the first harvest time and the plant height at the second harvest time. This trade-off was comparable to the aboveground biomass at the first and the second harvest times compared to conventional irrigation. Meanwhile, the reduction in plant height and leaf numbers per plant caused by alternate furrow irrigation at the third harvest time contributed to the aboveground drop in biomass. The results also demonstrated that alternate furrow irrigation increased the root biomass and root volume, which reduced the ratio of aboveground biomass to root biomass and decreased the stem-to-leaf ratio compared to conventional irrigation. Our findings indicate that alternate furrow irrigation not only increases the water use efficiency of alfalfa without trading off aboveground biomass before the second harvest time but also improves the forage quality of alfalfa in the study region.

Leaf traits have been proven to reflect the adaptation of individual plants to disturbance environments in a grassland ecosystem. A field survey was conducted to investigate the effects of the disturbance intensity of plateau pika on the leaf traits of a dominant (Kobresia pygmaea) and two common plants (Elymus nutans and Anemone rivularis var. flore-minore) in an alpine meadow. This study indicated that the plateau pika disturbance enables the individuals of three plants to exhibit respective plasticity because the three plants had different leaf indices (LI) as the disturbance intensity increased. K. pygmaea, E. nutans and A. rivularis var. flore-minore had high specific leaf area (SLA), leaf dry mass content (LDMC), and leaf nitrogen content (LNC) at relatively low, moderate, and high disturbance intensities of plateau pika, respectively. K. pygmaea, E. nutans and A. rivularis var. flore-minore suffered low nutrient stress at low, moderate and high disturbance intensities due to high N : P at corresponding disturbance intensities. These results indicated that K. pygmaea, E. nutans and A. rivularis var. flore-minore grew well at relatively low, moderate, and high disturbance intensity conditions, respectively, which contributed to the improvement of alpine meadows with a higher proportion of E. nutans at a moderate disturbance intensity or the deterioration of alpine meadows with a higher proportion of A. rivularis var. flore-minore at a high disturbance intensity. Our findings suggest that leaf traits are effective tools to explain how small burrowing herbivore disturbances often lead to the improvement or deterioration of alpine meadows under different disturbance intensities.

Plateau pika (Ochotona curzoniae) is an endemic mammal in the Qinghai-Tibetan Plateau, and its activities create extensive disturbances on vegetation and soil of alpine meadow. Field surveys at two sites were conducted to determine the effects of plateau pika disturbances on important soil factors and plant biomass of vegetated land, and their relationships of the same alpine meadow type. Our study showed that plateau pika disturbances significantly increased soil organic carbon, soil total nitrogen, graminoid biomass and the number of plant species, and significantly decreased soil moisture and forb biomass, although they had no significant impacts on soil total phosphorus, soil total potassium and total biomass on vegetated land. Our study further showed that soil organic carbon, soil total nitrogen, graminoid biomass and the number of plant species were much higher at intermediate disturbance intensities than those at low and high disturbance intensities in the disturbed areas, and soil moisture showed a decreasing trend with the increase of disturbance intensity. Plateau pika disturbances altered the contribution of some important soil nutrients and moisture to plant biomass, and had different impact on the best models between plant biomass (total biomass, graminoid biomass and forb biomass) and predominant soil factors. Our results demonstrated that the optimal disturbance intensities of plateau pika were beneficial to alpine meadow. These results highlighted the influence of the presence of plateau pika and its disturbance intensity on key soil nutrients and plant productivity on vegetated land of the same alpine meadow type, which will help us better understand the role of plateau pika in the alpine meadow ecosystem.

Soil salinity is an increasingly serious problem worldwide that reduces agricultural output potential. Selected beneficial soil bacteria can promote plant growth and augment tolerance to biotic and abiotic stresses. Bacillus subtilis strain GB03 has been shown to confer growth promotion and abiotic stress tolerance in the model plant Arabidopsis thaliana. Here we examined the effect of this beneficial soil bacterium on salt tolerance in the legume forage crop, white clover. Plants of white clover (Trifolium repens L. cultivar Huia) were grown from seeds with or without soil inoculation of the beneficial soil bacterium Bacillus subtilis GB03 supplemented with 0, 50, 100, or 150 mM NaCl water into soil. Growth parameters, chlorophyll content, malondialdehyde (MDA) content and osmotic potential were monitored during the growth cycle. Endogenous Na(+) and K(+) contents were determined at the time of harvest. White clover plants grown in GB03-inoculated soil were significantly larger than non-inoculated controls with respect to shoot height, root length, plant biomass, leaf area and chlorophyll content; leaf MDA content under saline condition and leaf osmotic potential under severe salinity condition (150 mM NaCl) were significantly decreased. Furthermore, GB03 significantly decreased shoot and root Na(+) accumulation and thereby improved K(+)/Na(+) ratio when GB03-inoculated plants were grown under elevated salt conditions. The results indicate that soil inoculation with GB03 promotes white clover growth under both non-saline and saline conditions by directly or indirectly regulating plant chlorophyll content, leaf osmotic potential, cell membrane integrity and ion accumulation.