Zhao Xinquan

Large scale patterns of forage yield and quality across Chinese grasslands

Understanding the patterns of forage quantity and quality and investigating the factors influencing these patterns are essential for the development of animal husbandry. However, there is very little field evidence focused on these issues at a large spatial scale. In the current study, we analyzed forage quantity and quality at 177 sites distributed in all the major grassland types across China, and explored the relationship between forage quantity and quality based on consistent sampling protocols. We also investigated potential factors influencing forage quality patterns across China. Our study indicates the Tibetan grasslands had both higher quantity and quality forage than the Inner Mongolian grasslands, and alpine meadow had the best quantity and quality forage because of the meadow’s high productivity and the crude protein and nitrogen free extract content of the meadow forage. For the main vegetation formations, Kobresia tibetica meadows and Achnatherum splendens steppes had the highest quantity, while Kobresia pygmaea meadows and Kobresia humilis meadows had the best quality. We also found that although environmental factors, such as temperature and soil fertility, could affect physiological processes and so influence forage quality, the large scale patterns of change were mainly a result of the differences in vegetation types. Finally, we reported a negative relationship between forage quantity and quality: higher forage quantity means more crude fiber but less ether extract and crude protein. These findings improve our understanding on the spatial patterns of forage quantity and quality, and provide solid evidence related to the future development of animal husbandry.

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.

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.

Nitrogen uptake and allocation characteristics of alpine meadow main species under water and nitrogen additions based on 15 N isotope

Aims Resource-use differentiation among species, which can reduce species competition for the same resources, is the main mechanism to maintain species diversity. Changes in soil temperature and moisture conditions, in the context of global change, may affect nitrogen (N) nutrition of plants of alpine meadow ecosystems. Our objective is to compare the characteristics of N uptake and resource allocation of dominant species of alpine meadow with changes in soil N and water. Methods An alpine meadow was treated with N and water addition for three years using the method of 15 N iso- tope injection. We determined the growth responses of dominant species to the N and water additions, as well as the features of N uptake capacity, N allocation and root to shoot ratio. Important findings The species showed significantly different responses to the N and water treatments, with respect to functional traits of species in N absorption capacity, root N content and root to shoot ratio. There was no significant relationship between N absorption capacity and root N content, whereas N absorption capacity was negatively correlated with root to shoot ratio across all plant species. These results indicated there was ecological niche differentiation in N uptake and a trade-off between the N absorption capacity and resource allocation strate- gies among species.

Characteristics of soil respiration in different degraded alpine grassland in the source region of Three-River

摘 要 为了研究高寒草原退化对土壤呼吸的影响, 对三江源区不同退化程度的高寒草原土壤呼吸进行了测定, 分析了土壤 呼吸与生物量、土壤温度以及土壤湿度的相关性, 结果表明: 1)不同退化程度的高寒草原土壤呼吸均表现出一定的月动态, 这 种月动态在不同退化程度间各有不同。2)高寒草原在退化演替序列上生长季平均土壤呼吸速率呈先增加后降低的变化趋势, 其中在中度退化程度下达到最高值((2.46 ± 0.27) μmol·m·s), 显著高于未退化((1.92 ± 0.11) μmol·m·s)和重度退化((1.30 ± 0.16) μmol·m·s)水平(p 0.05), 重度退化程度下呼吸速率显著 低于其他退化水平(p < 0.01)。3)地上生物量和土壤呼吸存在极显著线性正相关关系(p = 0.004), 而地下生物量与土壤呼吸的相 关性不很显著(p = 0.056)。4)除重度退化外, 未退化、轻度退化和中度退化高寒草原土壤呼吸与土壤温度显著正相关; 土壤呼 吸与土壤湿度的二项式拟合方程在轻度退化程度下达到显著水平(p < 0.05), 而在未退化、中度退化和重度退化程度下均达到 极显著水平(p < 0.01)。 关键词 高寒草原, 草地退化, 土壤湿度, 土壤呼吸, 三江源区, 温度