Caiping Zhou

Simulated distribution of vegetation types in response to climate change on the Tibetan Plateau

Abstract Questions: What is the relationship between alpine vegetation patterns and climate? And how do alpine vegetation patterns respond to climate changes? Location: Tibetan Plateau, southwestern China. The total area is 2 500 000 km2 with an average altitude over 4000 m. Methods: The geographic distribution of vegetation types on the Tibetan Plateau was simulated based on climatology using a small set of plant functional types (PFTs) embedded in the biogeochemistry-biography model BIOME4. The paleoclimate for the early Holocene was used to explore the possibility of simulating past vegetation patterns. Changes in vegetation patterns were simulated assuming continuous exponential increase in atmospheric CO2 concentration, based on a transient ocean-atmosphere simulation including sulfate aerosol effects during the 21st century. Results: Forest, shrub steppe, alpine steppe and alpine meadow extended while no desert vegetation developed under the warmer and humid climate of the early Holocene. In the fut...Abstract Questions: What is the relationship between alpine vegetation patterns and climate? And how do alpine vegetation patterns respond to climate changes? Location: Tibetan Plateau, southwestern China. The total area is 2 500 000 km2 with an average altitude over 4000 m. Methods: The geographic distribution of vegetation types on the Tibetan Plateau was simulated based on climatology using a small set of plant functional types (PFTs) embedded in the biogeochemistry-biography model BIOME4. The paleoclimate for the early Holocene was used to explore the possibility of simulating past vegetation patterns. Changes in vegetation patterns were simulated assuming continuous exponential increase in atmospheric CO2 concentration, based on a transient ocean-atmosphere simulation including sulfate aerosol effects during the 21st century. Results: Forest, shrub steppe, alpine steppe and alpine meadow extended while no desert vegetation developed under the warmer and humid climate of the early Holocene. In the future climate scenario, the simulated tree line is farther north in most sectors than at present. There are also major northward shifts of alpine meadows and a reduction in shrub-dominated montane steppe. The boundary between montane desert and alpine desert will be farther to the south than today. The area of alpine desert would decrease, that of montane desert would increase. Conclusions: The outline of changes in vegetation distribution was captured with the simulation. Increased CO2 concentration would potentially lead to big changes in alpine ecosystems.

Uptake of organic nitrogen by eight dominant plant species in Kobresia meadows

Abstract15N-labelled glycine experiments were carried out in both a Kobresia pygmaea meadow and a Kobresia humilis meadow to investigate whether alpine plants can take up organic nitrogen directly from the soil and whether different plant species differ in this respect. Eight plant species were selected in the two meadows, five in the Kobresia humilis meadow and four in the Kobresia pygmaea meadow, with one common species. After 4 h following 15N injection, atom% excess 15N in the aboveground parts of Ptilagrostis concinna was about 0.012, higher than in the aboveground parts of the other three species in the Kobresia pygmaea meadow, while that in the aboveground parts of Festuca ovina was higher than in the aboveground parts of the other four species in the Kobresia humilis meadow. After 1 day all the values for atom% excess 15N were substantially higher, except in the aboveground parts of Gentiana straminea in the Kobresia pygmaea meadow and in the aboveground parts of Festuca ovina and Gentiana aristata in the Kobresia humilis meadow. One day after 15N injection, atom% excess 15N in the roots was higher than that in any of the aboveground parts. In the first 4 h, uptake rates of organic nitrogen by the four species in the Kobresia pygmaea meadow were in the range of 0–0.83 µmol g–1 h–1, with a value of 1.43 µmol g–1 h–1 for the roots. In contrast, those of five species and the roots in the Kobresia humilis meadows varied between 1.34–8.08 µmol g–1 h–1. Key species such as Kobresia pygmaea and Kobresia humilis showed a greater capacity to take up organic nitrogen than non-key species over a 5-day period. This implies that alpine plants can take up organic nitrogen from the soil, but uptake capacity varies widely among different species, and for the same species from different Kobresia meadows.

Carbon Balance in an Alpine Steppe in the Qinghai-Tibet Plateau

Carbon fluxes were measured using a static chamber technique in an alpine steppe in the Qinghai-Tibet Plateau from July 2000 to July 2001. It was shown that carbon emissions decreased in autumn and increased in spring of the next year, with higher values in growth seasons than in winters. An exponential correlation (E(carbon)= 0.22(exp(0.09T) + ln(0.31P+ 1)), R(2)= 0.77, P < 0.001) was shown between carbon emissions and environmental factors such as temperature (T) and precipitation (P). Using the daily temperature (T) and total precipitation (R), annual carbon emission from soil to the atmosphere was estimated to be 79.6 g C/m(2), 46% of which was emitted by microbial respiration. Considering an average net primary production of 92.5 g C/m(2) per year within the 2 year experiment, alpine steppes can take up 55.9 g CO(2)-C/m(2) per year. This indicates that alpine steppes are a distinct carbon sink, although this carbon reservoir was quite small.

Litter species traits, but not richness, contribute to carbon and nitrogen dynamics in an alpine meadow on the Tibetan Plateau

AimsLitter, as afterlife of plants, plays an important role in driving belowground decomposition processes. Here we tested effects of litter species identity and diversity on carbon (C) and nitrogen (N) dynamics during litter decomposition in N-limited alpine meadow soil from the Qinghai–Tibet Plateau.MethodsWe incubated litters of four meadow species, a sedge (“S”, Kobresia humilis), a grass (“G”, Elymus nutans), a herb (“H”, Saussurea superba), and a legume (“L”, Oxytropis falcata), in monoculture and in mixture with meadow soil. CO2 release was measured 21 times during the incubation, and soil available N and microbial biomass C and N were measured before and after the experiment.ResultsThe organic C decay rate did not differ much among soils amended with monocultures or mixtures of litter, except in the H, S, L, and S+H treatments, which had much higher decay rates. Potential decomposable C pools were lowest in the control, highest in the L treatment, and intermediate in the S treatment. Mineralized N was completely immobilized by soil microbes in all treatments except the control, S+L, and S+G+L treatments. Litter mixtures had both additive and non-additive effects on CO2-C emission (mainly antagonistic effects), net N mineralization (mainly synergistic), and microbial biomass C and N (both). Overall, these parameters were not significantly correlated with litter species richness. Similarly, microbial C or N was not significantly correlated with litter N content or C/N. However, cumulative CO2-C emission and net N mineralization were positively correlated with litter N content and negatively correlated with litter C/N.ConclusionsLitter N content and C/N rather than litter species richness drove the release of CO2-C and net available N in this ecosystem. The antagonistic effects of litter mixtures contributed to a modest release of CO2-C, but their synergistic effects enhanced net available N. We suggest that in alpine meadow communities, balancing species with high and low N contents will benefit soil carbon sequestration and plant competition for available N with soil microbes.