Zhi-Yun Jiang

Contrasting water use pattern of introduced and native plants in an alpine desert ecosystem, Northeast Qinghai-Tibet Plateau, China.

Plant water use patterns reflect the complex interactions between different functional types and environmental conditions in water-limited ecosystems. However, the mechanisms underlying the water use patterns of plants in the alpine desert of the Qinghai-Tibet Plateau remain poorly understood. This study investigated seasonal variations in the water sources of herbs (Carex moorcroftii, Astragalus adsurgens) and shrubs (Artemisia oxycephala, Hippophae rhamnoides) using stable oxygen-18 isotope methods. The results indicated that the native herbs (C. moorcroftii, A. adsurgens) and one of the shrubs (A. oxycephala) mainly relied on water from the shallow layer (0-30 cm) throughout the growing season, while the introduced shrub (H. rhamnoides) showed plasticity in switching between water from shallow and deep soil layers depending on soil water availability. All studied plants primarily depended on water from shallow soil layers early in the season. The differences of water use patterns between the introduced and native plants are closely linked with the range of active root zones when competing for water. Our findings will facilitate the mechanistic understanding of plant-soil-water relations in alpine desert ecosystems and provide information for screening introduced species for sand fixation.

Evaporative enrichment of stable isotopes (δ18O and δD) in lake water and the relation to lake-level change of Lake Qinghai, Northeast Tibetan Plateau of China

Stable isotopic compositions (δ18O and δD) have been utilized as a useful indicator for evaluating the current and historical climatic and environmental changes. Therefore, it is vital to understand the relationship between the stable isotopic contents in lake water and the variations of lake level, particularly in Lake Qinghai, China. In this study, we analyzed the variations of isotope compositions (δ18O, δD and d-excess) in lake water and precipitation by using the samples that were collected from Lake Qinghai region during the period from 2009 to 2012. The results showed that the average isotopic contents of δ18O and δD in lake water were higher than those in precipitation, which were contrary to the variations of d-excess. The linear regression correlations between δ18O and δD in lake water and precipitation showed that the local evaporative line (LEL) in lake water (δD=5.88δ18O-2.41) deviated significantly from the local meteoric water line (LMWL) in precipitation (δD=8.26δ18O+16.91), indicating that evaporative enrichment had a significant impact on isotopic contents in lake water. Moreover, we also quantified the E/I ratio (evaporation-to-input ratio) in Lake Qinghai based on the lake water isotopic enrichment model derived from the Rayleigh equation. The changes of E/I ratios (ranging from 0.29 to 0.36 between 2009 and 2012) clearly revealed the shifts of lake levels in Lake Qinghai in recent years. The average E/I ratio of 0.40 reflected that water budget in Lake Qinghai was positive, and consistent with the rising lake levels and the increasing lake areas in many lakes of the Tibetan Plateau. These findings provide some evidences for studying the hydrological balance or water budget by using δ18O values of lake sedimentary materials and contribute to the reconstruction of paleolake water level and paleoclimate from an isotopic enrichment model in Lake Qinghai.

Shrub patch configuration in relation to precipitation and soil properties in Northwest China

Shrub patch configuration is a long-term evolutionary response to several environmental drivers and an equilibrium state in species competition. However, the variance in configuration along the precipitation gradient and its association with climate, soil, and adjacent vegetation remains unclear. Our study aimed to assess the variation of shrub patch configuration along a climatic gradient and the factors that affect shrub patch configuration, on the Inner Mongolia Plateau of Northwest China. Results showed that climate, soil, and vegetation contributed to 72.9% of the variance in shrub patch configuration. Interestingly, interspace/shrub radius ratio showed a decreasing trend with increasing precipitation transect. Patch size was positively correlated with aboveground biomass of interspace grass. Shrubs generally aggregated in high patches with low density on coarse soil texture, and vice versa. Moreover, shrub patches tended to occupy a larger percentage of landscape with increasing rainfall. To our knowledge, our study provides the first quantification of the effects of climate, soil, and vegetation on shrub patch configuration along a precipitation gradient in Northwest China, and may contribute to a better understanding of the structure and functions of shrub ecosystems with a broader ecological application in arid and semiarid regions.