Gao-Lin Wu

Effect of fencing and grazing on a Kobresia-dominated meadow in the Qinghai-Tibetan Plateau

Grazing is one of the most important factors influencing community structure and productivity in natural grasslands. Fencing to exclude grazers is one of the main management practices used to protect grasslands. Can fencing improve grassland community status by restraining grazing? We conducted a field community study and indoor soil analyses to determine the long-term effects of fencing and grazing on the above-ground community and soil in a Kobresia-dominated meadow in the Qinghai-Tibetan Plateau, NW China. Our results showed that fencing significantly improved above-ground vegetation productivity but reduced plant density and species diversity. Long-term fencing favored the improvement of forage grass functional groups and restrained the development noxious weed functional groups. There were significant positive effects of fencing on below-ground organic matter, total nitrogen, available nitrogen, total phosphorus and available phosphorus. The productivity of grazed meadow showed a weak decrease over time. There were long-term decreasing trends for plant density both in fenced and grazed meadows. Our study suggests that grazing can be considered as a useful management practice to improve species diversity and plant density in long-term fenced grasslands and that periodic grazing and fencing is beneficial in grassland management.

Long-term fencing improved soil properties and soil organic carbon storage in an alpine swamp meadow of western China

Overgrazing significantly affects alpine meadows in ways similar to grasslands in other areas. Fencing to exclude grazers is one of the main management practices used to protect alpine meadows. However, it is not known if fencing can improve soil properties and soil organic carbon storage by restraining grazing in alpine meadows. We studied the long-term (nine-year) effects of fencing on soil properties, soil organic carbon and nitrogen storage compared with continued grazing in an alpine swamp meadow of the Qinghai–Tibetan Plateau, NW China. Our results showed that fencing significantly improved vegetation cover and aboveground biomass. There were significant effects of fencing on pH value, soil bulk density, and soil moisture. Long-term fencing favored the increase of soil total nitrogen, soil organic matter, soil organic carbon, soil microbial biomass carbon and soil carbon storage compared with grazed meadows. Our study suggests that long-term fencing to prevent disturbance could greatly affect soil organic carbon and nitrogen storage with regard to grazed meadows. Therefore, it is apparent from this study that fencing is an effective restoration approach of with regard to the soil’s storage ability for carbon and nitrogen in alpine meadow of the Qinghai–Tibetan Plateau.

Species-abundance–seed-size patterns within a plant community affected by grazing disturbance

Seed size has been advanced as a key factor that influences the dynamics of plant communities, but there are few empirical or theoretical predictions of how community dynamics progress based on seed size patterns. Information on the abundance of adults, seedlings, soil seed banks, seed rains, and the seed mass of 96 species was collected in alpine meadows of the Qinghai-Tibetan Plateau (China), which had different levels of grazing disturbance. The relationships between seed-mass-abundance patterns for adults, seedlings, the soil seed bank, and seed rain in the plant community were evaluated using regression models. Results showed that grazing levels affected the relationship between seed size and abundance properties of adult species, seedlings, and the soil seed bank, suggesting that there is a shift in seed-size--species-abundance relationships as a response to the grazing gradient. Grazing had no effect on the pattern of seed-size-seed-rain-abundance at four grazing levels. Grazing also had little effect on the pattern of seed-size--species-abundance and pattern of seed-size--soil-seed-bank-abundance in meadows with no grazing, light grazing, and moderate grazing), but there was a significant negative effect in meadows with heavy grazing. Grazing had little effect on the pattern of seed-size--seedling-abundance with no grazing, but had significant negative effects with light, moderate, and heavy grazing, and the |r| values increased with grazing levels. This indicated that increasing grazing pressure enhanced the advantage of smaller-seeded species in terms of the abundances of adult species, seedlings, and soil seed banks, whereas only the light grazing level promoted the seed rain abundance of larger-seeded species in the plant communities. This study suggests that grazing disturbances are favorable for increasing the species abundance for smaller-seeded species but not for the larger-seeded species in an alpine meadow community. Hence, there is a clear advantage of the smaller-seeded species over the larger-seeded species with increases in the grazing level.

Legume Grasslands Promote Precipitation Infiltration better than Gramineous Grasslands in arid Regions

Precipitation infiltration is the most important process for soil water supply of vegetation in the arid regions. Higher infiltration rate is advantageous for vegetation growth and maintenance in the arid areas. Four grassland types (Medicago sativa, Agropyron cristatum, Caragana korshinskii and Stipa capillata ) were selected in this study. Results showed that the infiltration capacity in the legume grasslands was about 30% higher than in the gramineous grasslands and the difference was significant (P   0.05). The below-ground biomass, total porosity, capillary porosity, soil organic matters and soil aggregate were the main factors to determine the soil infiltration rates. The capillary porosity and soil aggregate of the top soil presented significant negative effects on soil infiltration rate (P < 0.05). The below-ground biomass in 10-30 cm soil layer was the most important factor, which significantly and positively correlates with the soil infiltration rate (P < 0.01). It is possible to conclude that the legume grasslands presented the higher soil infiltration rate and promote precipitation infiltration in the studied area. And the legume grasslands might be a more suitable option for vegetation restoration from the perspective of soil infiltration and water supply in the arid regions.

Legume grasslands are in favour of promoting precipitation infiltration than Gramineous grasslands in the arid regions

Precipitation infiltration is the most important process for soil water supply of vegetation in the arid regions. Higher infiltration rate is advantageous for vegetation growth and maintenance in the arid areas. Four grassland types (Medicago sativa, Agropyron cristatum, Caragana korshinskii and Stipa capillata ) were selected in this study. Results showed that the infiltration capacity in the legume grasslands was about 30% higher than in the gramineous grasslands and the difference was significant (P   0.05). The below-ground biomass, total porosity, capillary porosity, soil organic matters and soil aggregate were the main factors to determine the soil infiltration rates. The capillary porosity and soil aggregate of the top soil presented significant negative effects on soil infiltration rate (P < 0.05). The below-ground biomass in 10-30 cm soil layer was the most important factor, which significantly and positively correlates with the soil infiltration rate (P < 0.01). It is possible to conclude that the legume grasslands presented the higher soil infiltration rate and promote precipitation infiltration in the studied area. And the legume grasslands might be a more suitable option for vegetation restoration from the perspective of soil infiltration and water supply in the arid regions.

Germination strategies of 20 alpine species with varying seed mass and light availability

Seed germination is a central component of plant life history. To investigate the proposed role of seed size on germinationstrategyinplantcommunities,asemifieldexperimentwasconductedinalpinemeadowoftheQinghai-Tibetan Plateau, China. Interspecies relationships of seed mass and seed germination characteristics were studied under semifield conditions with different light availability. Light availability and seed mass had significant effects on final germination percentage and time to germination for studied species. There was a significant negative correlation between the strength of lightrequiredforgerminationandseedmass.Fifteenstudyspecies(e.g.Ligulariaprzewalskii,ArtemisiasieversianaWilld, Tripolium vulgare Ness. and Saussurea morifolia Chen) exhibited a synchronous germination strategy. Seeds from large- seededspecies,suchasDracocephalumruyschiana,Laniophlomisrotate(Benth.)andSalviaprzewalskiiMaxim.,wereless likelytorequirelightforgerminationthanthoseofsmall-seededspecies,suchasA.sieversianaWilld,Seneciodiversipinnus Ling andSaussurea mongolica (Franch.). We propose that germination strategies of small-seeded species are well suited to unpredictable environmental variation in this alpine grassland community.

Response of soil properties to yak grazing intensity in a Kobresia parva-meadow on the Qinghai-Tibetan Plateau, China

Grazing intensity is one of the most important factors influencing soil properties variations in rangeland ecosystem. This research aimed to study the features of soil properties under different grazing intensity in a Kobresia parva-meadow on the Qinghai-Tibetan Plateau, China. Results showed that soil organic matter (SOM), soil organic carbon (SOC), and total nitrogen (N) significantly decreased with an increase grazing intensity and total and available potassium (K), and C/N ratio exhibited a similar pattern. However, there were not significant differences between warm-season pasture (WSP) and cool-season pasture (CSP). In addition, results indicated that soil P was a limited factor, and N was sensitive to grazing intensity in Kobresia parva alpine meadow grazing ecosystem. Therefore, our study demonstrated that soil properties, such as soil carbon and nitrogen, generally decreased with the increasing of grazing intensity in studied Kobresia parva-meadow on the Qinghai-Tibetan Plateau.

Above- and below-ground response to soil moisture change on an alpine wetland ecosystem in the Qinghai-Tibetan Plateau, China

Abstract. Climate change is expected to affect plant communities worldwide. However, less is known about the consequences of global warming-induced decrease of soil moisture on alpine wetland ecosystem in the Qinghai-Tibetan Plateau. To determine response of natural alpine wetland community to decrease of soil moisture, we did a gradient analysis of soil moisture by sequence space-series variation. We used sequence space-series variation of soil moisture to reflect potential time-series variation of soil moisture in alpine wetland community, by examining the effects of spatial heterogeneity of soil moisture on wetland community, as well as by determining how shifts in above- and below-ground properties of alpine wetland community. We found that vegetation aboveground biomass, cover and height all significantly increased with increase of soil moisture, but species richness was decreased. Soil organic carbon, total nitrogen, available nitrogen, total phosphorus and available phosphorus all significantly increased with increase of soil moisture, but soil pH value, total potassium and available potassium were significantly decreased. Meanwhile, species richness showed significantly positive correlations to aboveground biomass, covers and height. Aboveground biomass, vegetation covers and height were all significant positively related to soil organic carbon, total N, P, and available N, P, but negatively related to total K. But, species richness were significant negatively related to soil organic carbon, total N, P, and available N, P, but positively related to total K. Our observation indicates that decreasing of soil moisture may potentially negatively impact on the above- and below-ground properties in alpine wetland community.

Post-fire species recruitment in a semiarid perennial steppe on the Loess Plateau

Offspring recruitment is an important part of population dynamics, as well as for plant-community structure and succession. One generality regarding grasses and fire is that clonal grasses tolerate fire extremely well and in most cases reach their maximum production in the immediate post-fire years. One qualification to this statement is that post-fire offspring, recruitment mode is very important. However, respective data are scare in the semiarid perennial steppe. We studied the relative importance of asexual v. sexual recruitment in the post-fire recovery in semiarid steppe on the Loess Plateau of north-western China. We observed differences in regeneration strategy after different times post-fire (burnt in 2008, burnt in 1999, and no fire history for at least 30 years). Results showed that fire significantly increased offspring recruitment numbers, but not species richness. The increase of asexual recruitment after a fire made a major contribution to the increase of total offspring number. Meanwhile, there was no significant difference for the ratio of asexual to sexual recruitment among sites with different times since fire. The asexual to sexual recruitment ratio was significantly different for different species, with some species not recruiting offspring via sexual recruitment. Our results indicated that seedling recruitment contributed little to post-fire recovery of the perennial-steppe community. Lack of sexual recruitment is not related to fire management but to inherent traits of the occurring plants.

Effects of biotic and abiotic factors on soil organic carbon in semi-arid grassland

Carbon sequestration in grassland soil has been paid considerable attention in recent decades. However, the changes of soil organic carbon (SOC) still need clarification under the effect of environmental factors in semiarid area. Here, twenty sampling sites were selected to study the effects of plant community (plant cover, biomass, litter, composition and diversity) and environmental factors (i.e. mean annual precipitation, mean annual temperature) on SOC sequestration in the semi-arid grasslands. The results showed that SOC was significant positively related to mean annual precipitation, soil water content and soil pH. The higher aboveand below-ground biomass, species evenness and diversity presented the higher SOC. Specially, the species richness and proportion of gramineous species functional group significantly increased SOC. Below-ground biomass affected SOC mainly in the top 30 cm soil. Our results suggest that higher plant species richness and gramineous species proportion play a positive role in increasing the potential of soil carbon sequestration in semi-arid grassland.