Drought sensitivity shapes species distribution patterns in tropical forests

Although patterns of tree species distributions along environmental gradients have been amply documented in tropical forests, mechanisms causing these patterns are seldom known. Efforts to evaluate proposed mechanisms have been hampered by a lack of comparative data on species' reactions to relevant axes of environmental variation. Here we show that differential drought sensitivity shapes plant distributions in tropical forests at both regional and local scales. Our analyses are based on experimental field assessments of drought sensitivity of 48 species of trees and shrubs, and on their local and regional distributions within a network of 122 inventory sites spanning a rainfall gradient across the Isthmus of Panama. Our results suggest that niche differentiation with respect to soil water availability is a direct determinant of both local- and regional-scale distributions of tropical trees. Changes in soil moisture availability caused by global climate change and forest fragmentation are therefore likely to alter tropical species distributions, community composition and diversity.     

Arabian Sea tropical cyclones intensified by emissions of black carbon and other aerosols

Throughout the year, average sea surface temperatures in the Arabian Sea are warm enough to support the development of tropical cyclones, but the atmospheric monsoon circulation and associated strong vertical wind shear limits cyclone development and intensification, only permitting a pre-monsoon and post-monsoon period for cyclogenesis. Thus a recent increase in the intensity of tropical cyclones over the northern Indian Ocean is thought to be related to the weakening of the climatological vertical wind shear. At the same time, anthropogenic emissions of aerosols have increased sixfold since the 1930s, leading to a weakening of the southwesterly lower-level and easterly upper-level winds that define the monsoonal circulation over the Arabian Sea. In principle, this aerosol-driven circulation modification could affect tropical cyclone intensity over the Arabian Sea, but so far no such linkage has been shown. Here we report an increase in the intensity of pre-monsoon Arabian Sea tropical cyclones during the period 1979-2010, and show that this change in storm strength is a consequence of a simultaneous upward trend in anthropogenic black carbon and sulphate emissions. We use a combination of observational, reanalysis and model data to demonstrate that the anomalous circulation, which is radiatively forced by these anthropogenic aerosols, reduces the basin-wide vertical wind shear, creating an environment more favourable for tropical cyclone intensification. Because most Arabian Sea tropical cyclones make landfall, our results suggest an additional impact on human health from regional air pollution.     

基于模拟土壤含水量的干旱监测技术

为实现大范围干旱的实时监测,开发了基于模拟土壤含水量的干旱监测技术.采用VIC(variable infiltration capacity)大尺度水文模型模拟了30 km网格尺度的逐日土壤含水量,建立了土壤含水量距平指数(SMAPI),分析了其在2002年山东干旱和2010年西南地区干旱监测中的作用.结果表明,SMAPI具有较明确的物理意义,能够反映大范围干旱在时间和空间上的发生、发展及变化趋势.基于模拟土壤含水量的干旱监测技术,可为全面认识干旱,有效预防和减轻干旱灾害提供技术支持.     

锶及其同位素在环境地球化学研究中的应用

近年来.随着同位素地球化学理论和测试分析技术的逐步发展和完善.锶及其同位素应用越来越广泛,目前已在很多领域的研究中显示出莺要的作用.本文主要从环境生物地球化学角度加以论述.其应用主要包括四个方面:(1)用Rb-Sr系统进行地质测年;(2)利用锶同位素进行古环境的研究;(3)用锶同位素进行物源示踪;(4)用锶同位素计算流域的风化速率.文章最后.简要地对锶及其同位索的研究作了总结和展望.     

西双版纳热带森林碳循环中土壤呼吸对次生演替的响应

【目的】探明热带森林次生演替过程中土壤呼吸速率的季节变化及其主要调控因素,分析土壤微生物生物量碳及理化性质对土壤呼吸速率时间动态的影响,为精确评估热带森林恢复对土壤碳库变化的影响提供参考。【方法】采用LI-6400-09便携式土壤呼吸测定仪对西双版纳热带森林演替前期的白背桐(Mallotus paniculatus)群落与演替后期的高檐蒲桃(Syzygium oblatum)群落土壤呼吸速率进行连续定位观测,结合相关分析和主成分分析,探讨热带森林演替过程中土壤微生物生物量碳、容重、pH及碳氮库各组分含量变化对土壤呼吸速率的影响。【结果】研究区白背桐与高檐蒲桃群落土壤呼吸具有明显的单峰型季节变化特征,最大值出现在湿季(6月),其中高檐蒲桃群落土壤呼吸速率[3.80~6.19 μmol/(m²·s)]显著高于白背桐群落[2.40~4.35 μmol/(m²·s)],但恢复前期土壤呼吸变幅(1.81倍)显著高于恢复后期(1.63倍);土壤呼吸速率随土壤温度和水分季节变化呈非线性显著或极显著增加的趋势(P<0.01或P<0.05),其中,高檐蒲桃群落温度、水分对土壤呼吸的解释率分别为49.00%~65.30%、2.96%~53.00%,显著高于白背桐群落的6.40%~49.10%、2.48%~43.70%;两群落土壤呼吸速率均与碳库(总碳、土壤微生物生物量碳)及氮库(硝态氮、全氮、铵态氮)含量显著或极显著正相关(P<0.01或0.05),并与pH呈极显著负相关 (P<0.01);土壤易氧化碳、硝态氮、含水量对土壤呼吸变化的贡献最大,而土壤温度、土壤微生物生物量碳、全氮、铵态氮及水解氮的影响次之。【结论】西双版纳热带森林次生演替显著促进了土壤呼吸,土壤呼吸时间动态主要受土壤微气候(如含水量)及土壤碳库(如易氧化碳)、氮库(如硝态氮)组分含量所调控。     

Increased soil emissions of potent greenhouse gases under increased atmospheric CO2

Increasing concentrations of atmospheric carbon dioxide (CO(2)) can affect biotic and abiotic conditions in soil, such as microbial activity and water content. In turn, these changes might be expected to alter the production and consumption of the important greenhouse gases nitrous oxide (N(2)O) and methane (CH(4)) (refs 2, 3). However, studies on fluxes of N(2)O and CH(4) from soil under increased atmospheric CO(2) have not been quantitatively synthesized. Here we show, using meta-analysis, that increased CO(2) (ranging from 463 to 780 parts per million by volume) stimulates both N(2)O emissions from upland soils and CH(4) emissions from rice paddies and natural wetlands. Because enhanced greenhouse-gas emissions add to the radiative forcing of terrestrial ecosystems, these emissions are expected to negate at least 16.6 per cent of the climate change mitigation potential previously predicted from an increase in the terrestrial carbon sink under increased atmospheric CO(2) concentrations. Our results therefore suggest that the capacity of land ecosystems to slow climate warming has been overestimated.     

Atmospheric science: marine aerosols and iodine emissions

O'Dowd et al. describe the formation of marine aerosols from biogenic iodine and the growth of these aerosols into cloud-condensation nuclei (CCN). Based on chamber and modelling results, the authors suggest that biogenic organic iodine compounds emitted from macroalgae may be responsible for coastal particle bursts and that production of these compounds in the open ocean could increase CCN there too. It has since been shown that coastal particles are more likely to be produced from the photooxidation of molecular iodine. Moreover, I contend that open-ocean particle production and cloud enhancement do not result from emissions of organic iodine at atmospheric levels. For iodine particles to affect cloud properties over the remote ocean, an additional source of iodine is necessary as organic precursors cannot be responsible.