Alpine Grassland Of Qinghai-Tibetan Plateau Research Articles

Precipitation affects soil nitrogen fixation by regulating active diazotrophs and nitrate nitrogen in an alpine grassland of Qinghai-Tibetan Plateau

Soil asymbiotic nitrogen (N) fixation provides a critical N source to support plant growth in alpine grasslands, and precipitation change is expected to lead to shifts in soil asymbiotic N fixation. However, large gaps remain in understanding the response of soil asymbiotic N fixation to precipitation gradients. Here we simulated five precipitation gradients (10 % (0.1P), 50 % (0.5P), 70 % (0.7P), 100 % (1.0P) and 150 % (1.5P) of the natural precipitation) in an alpine grassland of Qinghai-Tibetan Plateau and examined the soil nitrogenase activity and N fixation rate for each gradient. Quantitative PCR and high-throughput sequencing were used to measure the abundance and community composition of the soil nifH DNA (total diazotrophs) and nifH RNA reverse transcription (active diazotrophs) gene. Our results showed that the soil diazotrophic abundance, diversity and nifH gene expression rate peaked under the 0.5P. Soil nitrogenase activity and N fixation rate varied in the range 0.032–0.073 nmol·C2H4·g−1·h−1 and 0.008–0.022 nmol·N2·g−1·h−1 respectively, being highest under the 0.5P. The 50 % precipitation reduction enhanced the gene expression rates of Azospirillum and Halorhodospira which were likely responsible for the high N fixation potential. The 0.5P treatment also possessed a larger and more complex active diazotrophic network than the other treatments, which facilitated the resistance of diazotrophic community to environmental stress and thus maintained a high N fixation potential. The active diazotrophic abundance had the largest positive effect on soil N fixation, while nitrate nitrogen had the largest negative effect. Together, our study suggested that appropriate precipitation reduction can enhance soil N fixation through promoting the abundance of the soil active diazotrophs and decreasing soil nitrate nitrogen, and soil active diazotrophs and nitrate nitrogen should be considered in predicting soil N inputs in the alpine grassland of Qinghai-Tibetan Plateau under precipitation change.

In-depth characterization of phytase-producing plant growth promotion bacteria isolated in alpine grassland of Qinghai-Tibetan Plateau.

The use of plant growth promoting bacteria (PGPB) express phytase (myo-inositol hexakisphosphate phosphohydrolase) capable of hydrolyzing inositol phosphate in soil was a sustainable approach to supply available phosphorus (P) to plants. A total of 73 bacterial isolates with extracellular phytase activity were selected from seven dominant grass species rhizosphere in alpine grassland of Qinghai-Tibetan Plateau. Then, the plant growth promoting (PGP) traits of candidate bacteria were screened by qualitative and quantitative methods, including organic/inorganic Phosphorus solubilization (P. solubilization), plant hormones (PHs) production, nitrogen fixation, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity and antimicrobial activity. Further experiment were conducted to test their growth promoting effect on Lolium perenne L. under P-limitation. Our results indicated that these bacteria as members of phyla Proteobacteria (90.41%) and Actinobacteria (9.59%) were related to 16 different genera. The isolates of Pseudomonas species showed the highest isolates number (36) and average values of phytase activity (0.267 ± 0.012 U mL-1), and showed a multiple of PGP traits, which was a great candidate for PGPBs. In addition, six strains were positive in phytase gene (β-propeller phytase, bpp) amplification, which significantly increased the shoot length, shoot/root fresh weight, root average diameter and root system phytase activity of Lolium perenne L. under P-limitation, and the expression of phytase gene (bppP) in root system were verified by qPCR. Finally, the PHY101 gene encoding phytase from Pseudomonas mandelii GS10-1 was cloned, sequenced, and recombinantly expressed in Escherichia coli. Biochemical characterization demonstrated that the recombinant phytase PHY101 revealed the highest activity at pH 6 and 40°C temperature. In particular, more than 60% of activity was retained at a low temperature of 15°C. This study demonstrates the opportunity for commercialization of the phytase-producing PGPB to developing localized microbial inoculants and engineering rhizobacteria for sustainable use in alpine grasslands.

Livestock grazing impacts on plateau pika (Ochotona curzoniae) vary by species identity

Livestock and small burrowing mammals are potential ecosystem engineers and major drivers of ecosystem processes. Small mammals, often considered competitors with livestock, have been reported to increase in recent years and have been identified for their negative impacts on ecosystem services such as plant production and soil carbon sequestration. However, these increases and impacts by small mammals have rarely been studied with respect to how they may be influenced by livestock grazing. Here we experimentally manipulated large enclosures on the alpine grassland of Qinghai-Tibetan plateau, each with different livestock assemblages: yak (Bos grunniens), Tibetan sheep (Ovis aries), mixed populations of yak and sheep, and a control plot containing no livestock to study the potential impacts of livestock on the dominant small mammalian herbivore in the region, the plateau pikas (Ochotona curzoniae). We found that during the period of peak vegetative growth all pika populations in livestock experimental plots increased compared with those in the control plots. Additionally, pika populations and active pika burrow density increased more in experimental plots containing yaks compared with the sheep-only experimental plots. These results provide evidence that livestock grazing can increase the risk of pika outbreaks, which has led to this species being classified as a pest and subject to widespread control measures. We suggest explicitly incorporating livestock species identity in addition to grazing intensity and duration into management considerations to ensure maintenance of native biodiversity and long-term sustainability on the alpine grasslands of the Qinghai-Tibetan plateau.

The spatial and temporal dynamics of carbon budget in the alpine grasslands on the Qinghai-Tibetan Plateau using the Terrestrial Ecosystem Model

Grasslands in Tibetan Plateau play an important role in carbon emission reduction. Accurately evaluating the carbon budget of alpine grassland ecosystems is of great importance. Based on the parameterization and validation of a process-based ecosystem model (Terrestrial Ecosystem Model, TEM5.0), we analyze temporal and spatial dynamics and patterns of grassland ecosystem carbon emission and sequestration of Tibetan Plateau in China from 1961 to 2010. Alpine grasslands act as a carbon sink with mean annual value of 10.12 Tg C yr−1 during the past 50 years. The alpine meadow contributes most to the sink at 9.04 Tg C yr−1, while the alpine steppe only contributes 2.03 Tg C yr−1. 83.7% of the total area trends to be carbon sink and only 0.2% of the region showed no significant trend. Furthermore, the annual net ecosystem productivity shows significantly positive relationship with increasing temperature and atmosphere CO2 concentration, but it shows no significant relationship with precipitation. Alpine grasslands in Qinghai-Tibetan Plateau is a carbon sink and sequestrate totally 520 Tg C from 1961 to 2010. The carbon budget of alpine experienced dramatically spatial and temporal dynamics during past 50 years. Inter-annual variability of the net ecosystem productivity mainly depends on different sensitivities of net primary productivity and heterotrophic respiration to temperature and precipitation variability. Temperature and atmosphere CO2 concentration are main driving forces of carbon budget dynamics of grassland ecosystems in Qinghai-Tibetan Plateau during 1961–2010.

Optimization yak grazing stocking rate in an alpine grassland of Qinghai-Tibetan Plateau, China

A simple yak (Bos grunniens) production model developed in this study was to evaluate the health of the intensive livestock production system in the three rivers headwaters region, on the Qinghai-Tibetan Plateau. An experiment conducted for 3 years showed that individual yak liveweight gain (kg/head) was negatively related to stocking rate (Sr) (head/ha). Yak liveweight gain per hectare (kg/ha) was modeled as a quadratic function of Sr, with an apparent optimum yak stocking rate (Sr-op). Following the model, the Sr-op rate was 1.67 heads/ha for the warm-season pasture (WSP), 0.72 head/ha for the cool-season pasture (CSP), and 0.63 head/ha for the yearlong periods grazing pastures, respectively. The corresponding maximum carrying capacity (when individual yak live weight gain was equal to zero) was 3.34, 1.44, and 1.26 head/ha for warm-season, cool-season, and yearlong periods grazing pasture, respectively. In comparison with modeled maximum stock carrying capacity, all the cold-season pasture in the three rivers headwaters region were overgrazed. By contrast, only 37.5 % of the warm-season rangeland area overgrazed. It indicated that reconstruction of the proportion of the seasonal rangeland area may be an effective strategy to prevent serious rangeland degradation in this alpine region. Moreover, adjustment of the stoking rate at optimum values may likely improve the income for local herders.