Li Yingnian

CO2 flux in alpine wetland ecosystem on the Qinghai-Tibetan Plateau, China

Abstract Using the CO 2 flux data measured by the eddy covariance method in the northeast of Qinghai-Tibetan Plateau in 2005, we analyzed the carbon flux dynamics in relation to meteorological and biotic factors. The results showed that the alpine wetland ecosystem was the carbon source, and it emitted 316.02 gCO 2 · m −2 to atmosphere in 2005 with 230.16 gCO 2 · m −2 absorbed in the growing season from May to September and 546.18 gCO 2 · m −2 released in the non-growing season from January to April and from October to December. The maximum of the averaged daily CO 2 uptake rates and release rates was (0.45 ± 0.0012) mgCO 2 · m −2 · s −1 (Mean ± SE) in July and (0.22 ± 0.0090) mgCO 2 · m −2 · s −1 in August, respectively. The averaged diurnal variation showed a single-peaked pattern in the growing season, but exhibited very small fluctuation in the non-growing season. Net ecosystem exchange ( NEE ) and gross primary production ( GPP ) were all correlated with some meteorological factors, and they showed a negatively linear correlation with aboveground biomass, while a positive correlation existed between the ecosystem respiration ( R es ) and those factors.

Seasonal variations and mechanism for environmental control of NEE of CO2 concerning the Potentilla fruticosa in alpine shrub meadow of Qinghai-Tibet Plateau

The study by the eddy covariance technique in the alpine shrub meadow of the Qinghai-Tibet Plateau in 2003 and 2004 showed that the net ecosystem carbon dioxide exchange (NEE) exhibited noticeable diurnal and annual variations, with more distinct daily changes during the warmer seasons. The CO2 emission of the shrub ecosystem culminated in April and September while the CO2 absorption capacity reached a maximum in July and August. The absorbed carbon dioxide during the two consecutive years was 231.4 and 274.8 g CO2·m−2 respectively, yielding an average of 253.1 gCO2·m−2 per year: that accounts for a large proportion of absorbed CO2 in the region. Obviously, the diurnal carbon flux was negatively related to temperature, radiation and other atmospheric factors. Still, minute discrepancies in kurtosis and duration of carbon emission/absorption were detected between 2003 and 2004. It was found that the CO2 flux in the daytime was similarly affected by photosynthetic photon flux density in both years. Temperature appears to be the most important determinant of CO2 flux: specifically, the high temperature during the plant growing season inhibits the carbon absorption capacity. One potential explanation is that soil respiration is enhanced under such condition. Analysis of biomass revealed that the annual net carbon fixed capacity of aboveground and belowground biomass was 544.0 in 2003 and 559.4 g C·m−2 in 2004, which coincided with the NEE absorption capacity (63.1 g C·m−2 in 2003 and 74.9 g C·m−2 in 2004) in the corresponding plant growing season.

Monitoring and simulation of water, heat, and CO2 fluxes in terrestrial ecosystems based on the APEIS-FLUX system

The Integrated Environmental Monitoring (IEM) project, part of the Asia-Pacific Environmental Innovation Strategy (APEIS) project, developed an integrated environmental monitoring system that can be used to detect, monitor, and assess environmental disasters, degradation, and their impacts in the Asia-Pacific region. The system primarily employs data from the moderate resolution imaging spectrometer (MODIS) sensor on the Earth Observation System-(EOS-) Terra/Aqua satellite, as well as those from ground observations at five sites in different ecological systems in China. From the preliminary data analysis on both annual and daily variations of water, heat and CO2 fluxes, we can confirm that this system basically has been working well. The results show that both latent flux and CO2 flux are much greater in the crop field than those in the grassland and the saline desert, whereas the sensible heat flux shows the opposite trend. Different data products from MODIS have very different correspondence, e.g. MODIS-derived land surface temperature has a close correlation with measured ones, but LAI and NPP are quite different from ground measurements, which suggests that the algorithms used to process MODIS data need to be revised by using the local dataset. We are now using the APEIS-FLUX data to develop an integrated model, which can simulate the regional water, heat, and carbon fluxes. Finally, we are expected to use this model to develop more precise high-order MODIS products in Asia-Pacific region.

Relations between Carbon Dioxide Fluxes and Environmental Factors of Kobresia humilis Meadows and Potentilla fruticosa Meadows

Carbon dioxide fluxes of Kobresia humilis and Potentilla fruticosa shrub meadows, two typical ecosystems in the Qinghai-Tibet Plateau, were measured by eddy covariance technology and the data collected in August 2003 were employed to analyze the relations between carbon dioxide fluxes and environmental factors of the ecosystems. August is the time when the two ecosystems reach their peak leaf area indexes and stay stable, and also the period when the net carbon absorptions of Kobresia humilis and Potentilla fruticosa shrub meadows reach 56.2 g C·m−2 and 32.6 g C·m−2, with their highest daily carbon dioxide absorptions standing at 12.7 μmol·m−2·s−1 and 9.3 μmol·m−2·s−1, and their highest carbon discharges at 5.1 μmol·m−2·s−1 and 5.7 μmol·m−2·s−1, respectively. At the same photosynthetic photo flux densities (PPFD), the carbon dioxide-uptake rate of the Kobresia humilis meadow is higher than that of the Potentilla fruticosa shrub meadow; where the PPFD are higher than 1,200 μmol·m−2·s−1. The carbon dioxide uptake rates of the two ecosystems declined as air temperature increased, but the carbon dioxide uptake rate of the Kobresia humilis meadow decreased more quickly (−0.086) than that of the Potentilla fruticosa shrub meadow (−0.016). Soil moistures exert influence on the soil respirations and this varies with the vegetation type. The daily carbon dioxide absorptions of the ecosystems increase with increased diurnal temperature differences and higher diurnal temperature differences result in higher carbon dioxide exchanges. There exists a negative correlation between the vegetation albedos and the carbon dioxide fluxes.

Predicting plant traits and functional types response to grazing in an alpine shrub meadow on the Qinghai-Tibet Plateau

The identification of easily measured plant functional types (PFTs) that consistently predict grazing response would be a major advance. The responses to grazing of individual traits and PFTs were analyzed along a grazing gradient in an alpine shrub meadow on the Qinghai-Tibet Plateau, China. Three response types were identified; grazing increaser (GI), grazing decreaser (GD), and neutral (NE) for both traits and PFTs. Seven traits were measured: plant height, economic group, cotyledon type, plant inclination, growth form, life cycle, and vegetative structure. The first five were significantly affected by grazing. Ordinal regressions for grazing response of the seven traits showed that the best single predictors of response were growth form (including the attributes “Scattered”, “Bunched” or “Closely Bunched”), and plant inclination (“Rosette”, “Prostrate”, or “Erect”), followed by economic group (“Shrub”, “Grass”, “Sedge”, “Legume”, “Forb”, or “Harmful”) and plant height (“Tall”, “Medium”, or “Small”). Within the four optimal traits, the summed dominance ratio (SDR) of small plants, forbs, rosette and bunched plants, invariably increased, while that of tall plants, shrubs, grasses, and erect plants decreased, when grazing pressure was enhanced. Canonical correspondence analysis (CCA) identified eleven explanatory PFTs based on 195 defined PFTs, by combining the different attributes of the four optimal traits. Among explanatory PFTs, the most valuable in predicting the community response to grazing were Tall×Shrub×Erect×Scattered and Small×Forb×Rosette, as these have the closest connections with grazing disturbance and include fewer species. Species richness, diversity, and community evenness, did not differ among grazing treatments because turnover occurred in component species and their relative abundances along the grazing gradient. We have demonstrated that a minimum set of PFTs resulting from optimal individual traits can provide consistent prediction of community responses to grazing in this region. This approach provides a more accurate indicator of change within a changing environment than do univariate measures of species diversity. We hope to provide a link between management practices and vegetation structure, forming a basis for future, large scale, plant trait comparisons.

Assembly patterns of plant functional traits in alpine meadow under disturbances by mowing and fertilization

Aims Fully understanding the assembly patterns of plant functional traits in plant communities is a big challenge in the study of community ecology. The assembly patterns in alpline meadow and driving factors are still poorly known. In this study, experiments with different mowing intensities and various treatments of fertilization were conducted in alpline meadow for the purpose of improving the understanding of the assembly patterns of plant functional traits in plant community. Methods Data on functional diversity of 10 traits for 33 species from 108 quadrats (with varying combinations of mowing and fertilization) were analyzed by randomizations tests, ANCOVA and regression analysis, respectively, for the trait convergence/divergence. Important findings None of the traits studied showed consistently significant convergence or divergence pattern in integral gradients of fertilization and mowing treatments, while the ratios of quadrats assembled under deterministic and stochastic processes were 82.7% and 17.3%, respectively. Among the functional traits tested, growth form, life cycle, aboveground dry mass per plant, leaf area and leaf dry mass showed a stochastic pattern of assembly, but they were not affected by variations in mowing treatments and community characteristics (i.e. aboveground net primary productivity, biomass loss and vegetation height). Convergence or divergence patterns were shown in traits such as plant inclination, reproductive modes, nitrogen fixation, plant height and specific leaf area, which were affected by variations in mowing treatments and community characteristics. Among them, assembly patterns of plant inclination and specific leaf area were only affected by community characteristics, while nitrogen fixation, reproductive modes and plant height were affected by both mowing treatments and community characteristics. Moreover, the patterns of assembly varied by traits. Aboveground net primary productivity and biomass 吕美强等: 刈割与施肥干扰下高寒草甸植物功能性状的构建模式 917 doi: 10.3724/SP.J.1258.2014.00086 loss well explained variations in the assembly pattern of plant functional traits. Mowing and fertilization showed the reversed effects on the assembly pattern of plant height, while no significant interaction was found between mowing and fertilization. The results suggested that there were different assembly patterns of functional traits in the community: stochastic pattern of assembly was the primary, and the deterministic pattern was secondary. Deterministic pattern was trait-dependent and correlated with variations in mowing treatments and community characteristics. The balancing effect of opposite selection forces, on the other hand, could lead to stochastic assembly patterns in plant functional traits.