Abstract:Soil carbon stored on the Tibetan Plateau appears to be stable under current temperature, but it may be sensitive to global warming. In addition, different grazing systems may alter carbon emission from subalpine meadow ecosystems in this region. Using a chamber-closed dynamic technique, we measured ecosystem respiration (ER) and soil respiration (SR) rates with an infrared gas analyzer on a perennial grazing meadow (PM) and a seasonal grazing meadow (SM) of Shangri-La in the Hengduan Mountain area. Both PM and SM showed strong unimodal seasonal variations, with the highest rates in July and the lowest in January. Significant diurnal variations in respiration were also observed on PM, affected mainly by air and soil temperatures, with the highest rates at 14:00 and the lowest before dawn. Both ER and SR rates were higher on PM than on SM from June to October, suggesting that the higher grazing pressure on PM increased respiration rates on subalpine meadows. The exponential model F = ae^bT of soil temperature (T) explained the variation in respiration better than the model of soil moisture (W) (R² = 0.50–0.78, P < 0.0001), while the multiple model F = ae^bTW^c gave better simulations than did single-factor models (R² = 0.56–0.89, P < 0.0001). Soil respiration was the major component of ER, accounting for 63.0%–92.7% and 47.5%–96.4% of ER on PM and SM, respectively. Aboveground plant respiration varied with grass growth. During the peak growing season, total ecosystem respiration may be dominated by this above-ground component. Long-term (annual) Q₁₀ values were about twice as large as short-term (one day) Q₁₀. Q₁₀ at different time scales may be controlled by different ecological processes. The SM had a lower long-term Q₁₀ than did the PM, suggesting that under increased temperature, soil carbon may be more stable with reduced grazing pressure.

Abstract:C. microphylla, C. davazamcii and C. korshinskii exhibit a geographical replacement series from east to west on the Inner Mongolia Plateau. Currently, there is still a debate about the taxonomic and genetic relationship among these 3 species. We studied the genetic diversity and genetic relationship among these 3 species by analyzing DNA samples of individual plants from within 10 populations with random amplified polymorphic DNA (RAPD) markers. We identified 678 RAPD loci in total, of which all were polymorphic (PPB = 100%). There were 41 unique loci (6.05%). In general, a trend presented that the genetic diversity of these species decreased from east to west. Further, the genetic diversity was significantly negatively correlated with the local annual mean temperature. Analysis of molecular variation (AMOVA) showed that the genetic variation among these 3 species was only 6.08% of the total genetic variation. Between the species, the genetic variation was insignificant (P = 0.9961). The proportion of genetic variation among populations within each species was 11.90% (P < 0.001) of the total genetic variation, and the total genetic variation mainly existed within the populations (82.02%). Estimated with Shannon's index, genetic differentiation within the populations (Hpop/Hsp) was 0.8013, the coefficient of gene differentiation (Gst) was 0.1603, and the gene flow index (Nm) was 2.6192. This, thus, indicates that there is relatively high gene flow among these populations, and that these 3 species are crossbreeding. The genetic diversity level and the population distribution pattern showed geographic continuity to some extent.

Abstract:One major challenge in agro-meteorological research is to accurately predict the impacts of global climate warming on future agricultural production. So the effects of climate warming over the past decades need to be assessed. We analyzed the effects of climate warming on crop planting, structure and yield in 5 northwestern provinces of China with a focus on Gansu Province, utilizing accumulated temperature (≥ 10°C, AT), accumulated negative temperature (< 0°C, ANT) and crop data collected from 1981 to 2003. The analysis led to the following conclusions: 1) climate warming is the main driving force for the expansion of winter wheat toward the north and the west in China, for the rapid increase in cotton planting acreage, and for the expansion of annually multi-crop areas toward the north in China and higher altitude; 2) Climate warming is the direct cause for early seeding of spring crops, prolonged growth duration for thermophilic crops and shortened growth duration for overwinter crops; 3) Climate warming is largely attributed to the dramatic increase in cotton yield.

Abstract:By means of fixed-point monitoring and comparative analysis, soil water deficient situation, soil moisture dynamic variation laws, soil aridization and soil water compensation features under condition of different artificial vegetations were studied on 35–45° steep slope of loess region in North Shaanxi Province, China. The results showed that soil water was extremely deficient under condition of perennial artificial vegetation on steep slope, soil water storage (0–10 m) was only equal to 26.2%–42.0% of the field capacity in dry years, and in rainy years it was also only equal to 27.0%–43.3% of the field capacity. The order of soil water deficit was Caragana microphylla > locust > alfalfa > Chinese arborvitae > poplar > Chinese pine > wild land > apricot > Chinese date > farm land. Annual variations of soil moisture with the same vegetation were weakened with soil depth increasing, and occurred mainly in 0–200 cm soil layers. In the same growth season, all CVs (coefficients of variation) of soil moisture under condition of different vegetations were bigger and concentrated comparatively in 0–120 cm soil layers, but difference of CVs in different vegetations was small. Below 120 cm soil layers, CVs were smaller, but difference of CVs in different vegetations was bigger. Permanent dry soil layers always occurred under condition of perennial vegetation on steep slope, but the difference of soil aridization intensity was obvious among different vegetations and growth years. Soil water compensation and recovery depths in rainy seasons were 1.0–1.4 m, but the soil water storage increment and compensation degree in different vegetations were dramatically different. Soil water compensation depth in the same vegetation in rainy years was over 60 cm more than that in dry years, while the soil water storage increment in 5 m soil layers increased over 3 times. Under natural precipitation, the soil water deficit in artificial vegetation on steep slope cannot be ameliorated, and the soil aridization also can't be relieved.