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Though aboveground biomass (AGB) has an important contribution to the global carbon cycle, the information about storage and climatic effects of AGB is scare in Three-River Source Region (TRSR) shrub ecosystems. This study investigated AGB storage and its climatic controls in the TRSR alpine shrub ecosystems using data collected from 23 sites on the Tibetan Plateau from 2011 to 2013. We estimated the AGB storage (both shrub layer biomass and grass layer biomass) in the alpine shrubs as 37.49 Tg, with an average density of 1447.31 g m<sup>-2</sup>. Biomass was primarily accumulated in the shrub layer, which accounted for 92% of AGB, while the grass layer accounted for only 8%. AGB significantly increased with the mean annual temperature (<i>P</i> < 0.05). The effects of the mean annual precipitation on AGB were not significant. These results suggest that temperature, rather than precipitation, has significantly effects on of aboveground vegetation growth in the TRSR alpine shrub ecosystems. The actual and potential increase in AGB density was different due to global warming varies among different regions of the TRSR. We conclude that long-term monitoring of dynamic changes is necessary to improve the accuracy estimations of potential AGB carbon sequestration across the TRSR alpine shrub ecosystems.
Although large amounts of soil organic carbon (SOC) stored in the shrublands, information about SOC storage was little on the Tibetan Plateau. This study aims to evaluate the spatial patterns and storage of SOC in the shrublands and the relationships of climatic variables and soil pH on the Tibetan Plateau.<br>We used 177 profiles of soil samples obtained from 59 shrubland sites on the northeast Tibetan Plateau from 2011 to 2013. Ordinary least squares regressions, curve estimation, and multiple linear regressions were used to evaluate controlling factors on SOC stock. Kriging interpolation was used to upscale sit-level measurements to the whole study area.<br>We found that SOC storage in the northeast Tibetan shrublands was 1.36 Pg C in the top 1 m with an average SOC stock of 12.38 kg m<sup>−2</sup>. SOC stock decreased from east to west and south to north but generally increased significantly with the mean annual temperature (MAT) and the mean annual precipitation (MAP), and tended to decrease with soil pH. Although similar relationships were also observed in alpine shrublands, the trends among SOC stock, MAP, and MAT were not observed in desert shrublands. Our results indicate that a reduction in soil pH accelerates the C sequestration potential. Furthermore, global warming contributed to C sequestration in alpine shrublands, specifically, SOC stock increased 8.44 kg m<sup>−2</sup> with an increased unit of MAT in alpine shrublands just considering temperature effects. Meanwhile, the C sequestration was different among different regions due to the uneven increases in precipitation. However, in desert shrublands, MAP and MAT did not significantly affect SOC stock.<br>The results indicate that though a reduction in soil pH could contribute to C sequestration, MAT and MAP have different effects on SOC stock in different Tibetan Plateau shrublands. Increased MAT and MAP were 0.05 °C and 1.67 mm every year on the Tibetan Plateau, which will increase C sequestration in alpine shrublands, but might have limited impacts on desert shrublands, which help us comprehend soil C cycling in the global climate change scenario.
Background Rheum tanguticum Maxim. ex Balf is one of the plants generically known as rhubarb, a culinary vegetable that has long been used as a herbal remedy both in China and Europe. Increasing demand for rhubarb has triggered the overexploitation of Rh. tanguticum. Cultivation is therefore necessary for quality control and protection of wild resources. Nitrogen fertilizer plays an important role in cultivation. This study aimed to explore how nitrogen fertilizer affects the growth and quality of rhubarb on the Qinghai-Tibetan plateau. Results Nitrogen fertilizer promoted growth but had no significant influence on the active compounds of Rh. tanguticum. Generally, the N2 (150 kg ha(-1)) and N3 (225 kg ha(-1)) levels showed the most improved growth indexes, with no significant differences between them. The growth index and the amounts of eight of the nine studied active compounds in Rh. tanguticum increased from each year to the next and differed among growth stages. The contents of the active compounds were higher at the green stage and lower at the growth stage, which was opposite to the seasonal trends in root dry matter ratio. Gallic acid levels decreased with the growth of the plant. Conclusion The N2 level (150 kg ha(-1)) was the recommended nitrogen fertilizer level in this study. It was revealed that seasonal changes rather than nitrogen fertilizer influenced active compounds in the root of Rh. tanguticum. (c) 2018 Society of Chemical Industry
Alpine shrubland ecosystems in the Three Rivers Source Region (TRSR) store substantial soil organic carbon (SOC), but the storage, patterns and control of SOC in those ecosystems have rarely been investigated. In this study, using data from 66 soil profiles surveyed from 22 sites between 2011 and 2013, we estimated the storage and patterns of SOC, and their relationships with climatic factors, elevation, ground cover and slope. Our results showed that SOC storage in the top 100 cm across the TRSR shrubland was 0.68 ± 0.38 Pg C, with an average SOC density (soil carbon storage per area) of 26.21 ± 14.58 kg m−2. Spatially, SOC density increased with longitude and latitude. Vertically, SOC in the topsoil at 30 cm and 50 cm accounted for 56% and 75%, respectively, of the total at 100 cm. SOC density showed a decreasing trend with increasing elevation, but it was greater in regions of higher ground cover. The density had no relationship with either mean annual precipitation or slope. Increasing mean annual temperature had positive effects on SOC density, which is inconsistent with the global trend. With increasing soil depth, however, the effects of temperature on SOC density were not significant. Therefore, in a global warming scenario, increasing temperature gives shrubland considerable C sink potential on the topsoil, and the regions of C sequestration differ as a result of uneven increases in temperature. Hence, further monitoring of dynamic changes is necessary to provide a more accurate assessment of potential C sequestration in TRSR shrubland.<br>• Storage and patterns of SOC were investigated in the TRSR shrubland. • SOC has no relationship with both precipitation and slope. • SOC was decreasing with elevation, but larger with both ground cover and temperature.