Characterization of photosynthetic pathway of plant species growing in the eastern Tibetan plateau using stable carbon isotope composition

The photosynthetic pathway of plant species collected at Menyuan, Henan, and Maduo sites, east of Tibetan Plateau, China, during the growing season were studied using stable carbon isotopes in leaves. The 232 samples leaves analyzed belonged to 161 species, 30 families, and 94 genera. The delta(13)C values (from -24.6 to -29.2 %o) indicated that all the considered species had a photosynthetic C-3 pathway. The absence of plant species with C-4 photosynthetic pathway might be due to the extremely low air temperature characterizing the Tibetan Plateau. The average delta(13)C value was significantly (p < 0.05) different between annuals and perennials at the three considered study sites. Hence the longer-lived species had greater water-use efficiency (WUE) than shorter-lived species, that is, longer-lived species are better adapted to the extreme environmental conditions of the Tibetan Plateau.

Stable carbon isotope analyses show dominance of C3 grasses in the feed selected by small herbivores at the alpine meadow at the Tibetan Plateau

Muscle samples were collected from small herbivorous mammals (Ochotona curzoniae, Microtus oecnomus, Myospalax fontanierii and Lepus oiostolus) at the alpine meadow ecosystem at the Tibetan Plateau in order to address variability in stable carbon isotope composition. Stable carbon isotope values of muscles remain steady and show no significant variations (-25.72 to -27.04 parts per thousand) among the four small mammal species. Based on the mass balance theory of stable isotopes, it is proposed that small herbivorous mammals mainly (or totally) rely on C3 grasses as food supply, and there is few or no distribution of C4 grasses at the ecosystem. The results reflect our previous study on the isotope patterns of plant species. Thus, stable carbon isotope analysis of muscles provides a method to address dietary selection and dietary variability in herbivores. In addition, stable carbon isotopic analyses can be used to address changes in vegetation distributions in ecosystem and paleovegetaion and paleoclimate.

The effect of land management on carbon and nitrogen status in plants and soils of alpine meadows on the Tibetan plateau

Large-scale grassland rehabilitation has been carried out on the severely degraded lands of the Tibetan plateau. The grasslands created provide a useful model for evaluating the recovery of ecosystem properties. The purposes of this research were: (1) to examine the relative influence of various rehabilitation practices on carbon and nitrogen in plants and soils in early secondary succession; and (2) to evaluate the degree to which severely degraded grassland altered plant and soil properties relative to the non-disturbed native community. The results showed: (1) The aboveground tissue C and N content in the control were 105-97 g m(-2) and 3.356gm(-2), respectively. The aboveground tissue C content in the mixed seed treatment, the single seed treatment, the natural recovery treatment and the severely degraded treatment was 137 per cent, 98 per cent, 49 per cent and 38 per cent, respectively, of that in the control. The corresponding aboveground tissue N content was 109 per cent, 84 per cent, 60 per cent and 47 per cent, respectively, of that in the control. (2) Root C and N content in 0-20 cm depths of the control had an 2 2 average 1606 gm(-2) and 30-36 gm(-2) respectively. Root C and N content in the rehabilitation treatments were in the range of 26-36 per cent and 35-53 per cent, while those in the severely degraded treatment were only 17 per cent and 26 per cent of that in the control. (3) In the control the average soil C and N content at 0-20 cm was 11307 gm(-2) and 846 gm(-2), respectively. Soil C content in the uppermost 20 cm in the seeded treatments, the natural recovery treatment and the severely degraded treatment was 67 per cent, 73 per cent and 57 per cent, respectively, while soil N content in the uppermost 20cm was 72 per cent, 82 per cent and 79 per cent, respectively, of that in the control. The severely degraded land was a major C source. Restoring the severely degraded lands to perennial vegetation was an alternative approach to sequestering C in former degraded systems. N was a limiting factor in seeding grassland. It is necessary for sustainable utilization of seeding grassland to supply extra N fertilizer to the soil or to add legume species into the seed mix. Copyright (c) 2005 John Wiley & Sons, Ltd.

Nitrogen deposition and carbon sequestration in alpine meadows

Nitrogen deposition experiments were carried out in alpine meadow ecosystems in Qinghai-Xizang Plateau in China, in order to explore the contribution of nitrogen deposition to carbon sequestration in alpine meadows. Two methods were used in this respect. First, we used the allocation of N-15 tracer to soil and plant pools. Second, we used increased root biomass observed in the nitrogen-amended plots. Calculating enhanced carbon storage, we considered the net soil CO2 emissions exposed to nitrogen deposition in alpine meadows. Our results show that nitrogen deposition can enhance the net soil CO2 emissions, and thus offset part of carbon uptake by vegetation and soils. It means that we have to be cautious to draw a conclusion when we estimate the contribution of nitrogen deposition to carbon sequestration based on the partitioning of N-15 tracer in terrestrial ecosystems, in particular in N-limited ecosystems. Even if we assess the contribution of nitrogen deposition to carbon sequestration based on increased biomass exposed to nitrogen deposition in terrestrial ecosystems, likewise, we have to consider the effects of nitrogen deposition on the soil CO2 emissions.

珠穆朗玛峰东绒布冰川表层雪中的气候和环境记录

Snow chemistry research helps to found the basis of studying ice cores. Samples of fresh snow and snow pits were collected from East Rongbuk Glacier on the north slope of Mt. Qomolangma during October, 2002. Major soluble ions (Na~+, NH_4~+, K~+, Mg~(2+), Ca~(2+), Cl~-, NO_3~- and SO_4~(2-)) andδ~(18)O were detected for analysis. Source analysis showed that major sources contributing to the snow chemistry in Mt. Qomolangma region are remote Asian dust and salt lake dust, sea-salt aerosols from Indian monsoon, local rock-mineral dust, human activities and natural atmospheric procedures. Principal factor analysis indicated that high-concentration group was dominated by continental dust with little oceanic source, indicating continental or local precipitation, while the low group dominated by oceanic aerosols indicated oceanic precipitation. Local mineral dust was a minor a source characterized mainly by Ca~(2+), Mg~(2+) contribution. Ammonia related mainly with continental dusts and nitrogen-circulation processes in the atmosphere, it also had a peculiar source should be seasonal agriculture activities in the south Asia. Nitrate showed bad correlations with other ions for its special chemical characteristics. δ~(18)O and major soluble ions displayed obvious seasonal variations. The summer precipitation had very low ion loadings and relatively lower heavy oxygen isotope from the Indian Ocean with occasionally ion peaks formed by local evaporation. While the winter and spring precipitation had high ion loadings and δ~(18)O value for the great amount of continental dust and evaporated vapors. Frequent fluctuations of δ~(18)O and ion concentration occur during the transitional period, indicating alternated precipitations by various air mass types. Ion concentration in snow from the Qomolangma region is comparable with from the Antactica, representing relatively pure background of atmospheric environment on earth. While the high concentration is close to the glaciers' located near the major sources of Asian dust. Compared with the snow chemistry of South Slope of Mt. Qomolangma, the North Slope has lower sea-salt ion concentration during summer monsoon and higher concentration of all major ions during pre- and post-monsoon period due to it's special geophysical location.