The aboveground biomass of desert steppe and its spatiotemporal variation in western Inner Mongolia

A precise understanding of the aboveground biomass of desert steppe and its spatio-temporal variation is important to understand how arid ecosystems respond to climate change and to ensure that scarce grassland resources are used rationally. On the basis of 756 ground survey quadrats sampled in western Inner Mongolia steppe in 2005-2011 and remote sensing data from the Moderate Resolu- tion Imaging Spectroradiometer （MODIS）--the normalized difference vegetation index （NDVI） dataset for the period of 2001-2011--we developed a statistical model to estimate the aboveground biomass of the desert steppe and further explored the rela- tionships between aboveground biomass and climate factors. The conclusions are as follows： （1） the aboveground biomass of the steppe in the research area was 5.27 Tg （1 Tg=1012 g） on average over 11 years; between 2001 and 2011, the aboveground biomass of the western Inner Mongolia steppe exhibited fluctuations, with no significant trend over time; （2） the aboveground biomass of the steppe in the research area exhibits distinct spatial variation and generally decreases gradually from southeast to northwest; and （3） the important factor causing intemnnual variations in aboveground biomass is precipitation during the period from January to July, but we did not find a significant relationship between the aboveground biomass and the corresponding temperature changes. The precipitation in this period is also an important factor influencing the spatial distribution of aboveground biomass （R2=0.39, P〈0.001）, while the temperature might be a minor factor （R2=0.12, P〈0.01 ）. The uncertainties in our estimate are primarily due to uncertainty in converting the fresh grass yield estimates to dry weight, underestimates of the biomass of shrubs, and error in remote sensing dataset.

Efficient synthesis of cyclic carbonates under atmospheric CO_(2) by DMAP-based ionic liquids: the difference of inert hydrogen atom and active hydrogen atom in cation

The coupling reaction of carbon dioxide(CO_(2)) and epoxides is one of the most efficient pathways to achieve the carbon balance.However,to accomplish it under the mild conditions,especially under the atmospheric pressure,is still a perplexing problem.Three novel ionic liquids(ILs),[DMAPBrPC][TMGH],[DMAPBrPC][DBUH],and[DMAPBrPC][BTMA],are designed and synthesized.All of them display the excellent catalytic activity for the title reaction achieving the yield over 96.6% under the atmospheric CO_(2) pressure at 60℃.Interestingly,[DMAPBrPC][BTMA]with the inert hydrogen atom in cation exhibits the superior catalytic activity as compared to other two ILs with the protic hydrogen atom in cation along with the same anion.The active hydrogen atom in[DMAPBrPC][TMGH]and[DMAPBrPC][DBUH]would impede the–COO^(-)group to absorb CO 2,which is an unfavorable item for the reaction.Moreover,the strong hydrogen bond in[DMAPBrPC][TMGH]and[DMAPBrPC][DBUH]would lessen the nucleophilic ability of Br^(-) anion resulting in the inferior catalytic performance,which is further confirmed by the density functional theory(DFT)calculations.The cation without the active hydrogen atom could also be employed to design the ILs with the excellent catalytic feature when it is combined with the suitable anion.

遥感技术在鸟类生态学研究中的应用

获取鸟类活动及生境信息是鸟类生态学研究的基础,而遥感技术弥补了传统野外调查方法的缺陷,提供了获取多种信息的新途径。应用遥感技术的鸟类生态学研究热点从最初的种群行为观察,到栖息地选择,再到生境适宜性、破碎化及人为干扰探究等,随着技术的不断发展也在扩展和变化。不同波段或组合下的遥感技术各有所长。光学遥感应用广泛,尤其是信息量较大的红外波段图像和作为野外鸟巢及物种活动监测常用工具的红外相机;多光谱图像常用于栖息地制图以及地物识别,高空间分辨率的数据甚至可对鸟类种群进行直接计数;高光谱数据则可对光谱特征相似的地物进行更为精确的区分和反演;激光雷达遥感主要用于栖息地植被结构的三维探测,为了解鸟类栖息地选择提供更好的依据。微波遥感在飞鸟探测上应用颇多,近年来多极化数据在复杂栖息地精确制图上也具有优势,但成本较高、解译复杂且推广度较低。在实际应用中,遥感数据时空尺度的选择会影响研究结果,部分遥感反演参数也缺乏生态学意义。多源遥感数据的结合应用能够提升制图分类的精度,实现数据的时空分辨率互补,优化鸟类生态研究所需参数。未来的遥感技术在鸟类生态学中的应用应致力于提供更加明确的光谱信息、相对简便的解译方法,以及更为合理的多源数据组合方式等。