Effect of warming and drought on grassland microbial communities

The soil microbiome is responsible for mediating key ecological processes; however, little is known about its sensitivity to climate change. Observed increases in global temperatures and alteration to rainfall patterns, due to anthropogenic release of greenhouse gases, will likely have a strong influence on soil microbial communities and ultimately the ecosystem services they provide. Therefore, it is vital to understand how soil microbial communities will respond to future climate change scenarios. To this end, we surveyed the abundance, diversity and structure of microbial communities over a 2-year period from a long-term in situ warming experiment that experienced a moderate natural drought. We found the warming treatment and soil water budgets strongly influence bacterial population size and diversity. In normal precipitation years, the warming treatment significantly increased microbial population size 40–150% but decreased diversity and significantly changed the composition of the community when compared with the unwarmed controls. However during drought conditions, the warming treatment significantly reduced soil moisture thereby creating unfavorable growth conditions that led to a 50–80% reduction in the microbial population size when compared with the control. Warmed plots also saw an increase in species richness, diversity and evenness; however, community composition was unaffected suggesting that few phylotypes may be active under these stressful conditions. Our results indicate that under warmed conditions, ecosystem water budget regulates the abundance and diversity of microbial populations and that rainfall timing is critical at the onset of drought for sustaining microbial populations.     

Effect of latitude and acclimation on the lethal temperatures of the peach‐potato aphid Myzus persicae

• 1 Aphids, similar to all insects, are ectothermic and, consequently, are greatly affected by environmental conditions. The peach potato aphid Myzus persicae (Sulzer) has a global distribution, although it is not known whether populations display regional adaptations to distinct climatic zones along its distribution and vary in their ability to withstand and acclimate to temperature extremes. In the present study, lethal temperatures were measured in nine anholocyclic clones of M. persicae collected along a latitudinal cline of its European distribution from Sweden to Spain. The effects of collection origin and intra‐ and intergenerational acclimation on cold and heat tolerance, as determined by upper and lower lethal temperatures (ULT₅₀ and LLT₅₀, respectively), were investigated.
• 2 Lethal temperatures of M. persicae were shown to be plastic and could be altered after acclimation over just one generation. Lower lethal temperatures were significantly depressed in eight of nine clones after acclimation for one generation at 10°C (range: ?13.3 to ?16.2°C) and raised after acclimation at 25°C (range: ?10.7 to ?11.6°C) compared with constant 20°C (range: ?11.9 to ?12.9°C). Upper lethal temperatures were less plastic, although significantly increased after one generation at 25°C (range: 41.8–42.4°C) and in five of nine clones after acclimation at 10°C. There was no evidence of intergenerational acclimation over three generations.
• 3 Thermal tolerance ranges were expanded after acclimation at 10 and 25°C compared with constant 20°C, resulting in aphids reared at 10°C surviving over a temperature range that was approximately 2–6°C greater than those reared at 25°C.
• 4 There was no clear relationship between lethal temperatures and latitude. Large scale mixing of clones may occur across Europe, thus limiting local adaption in thermal tolerance. Clonal type, as identified by microsatellite analysis, did show a relationship with thermal tolerance, notably with Type O clones being the most thermal tolerant. Clonal types may respond independently to climate change, affecting the relative proportions of clones within populations, with consequent implications for biodiversity and agriculture.

     

Response of Locusta migratoria tibetensis Chen (Orthoptera: Acrididae) to climate warming over the Tibetan plateau

As a region with one of the most important terrestrial ecosystems, the Tibetan plateau is both sensitive to and vulnerable to climate warming. Locusta migratoria tibetensis Chen, an endemic species on the Tibetan plateau, is likely to be affected by climatic warming. In our studies, accumulated degree‐days (ADD) of L. Migratoria T.C. were calculated based on data from 90 weather stations over the Tibetan plateau from 1961 to 2005. Trend lines show that across weather stations, ADD increased at a rate of 1.17 DD/a during climate warming. The majority of weather stations (82.2%) showing increases in ADD were located towards the west of the Tibetan plateau. At higher elevations, the increase in the ratio of annual ADD to the station mean ADD was higher relative to those at lower elevations. A linear regression model between ADD and geographical position was established to create raster maps of ADD in ArcGIS 9.2. The area of potential locust distribution (APD) was estimated to be 42 420 km², mostly distributed along major rivers on the Tibetan plateau. In warmer years, the APD increased sharply over study periods. A new area of potential distribution would appear in the north Tibetan plateau if the climate warming continued. In the south‐east Tibetan plateau, the locust would expand its range northwards or westwards along the river valleys, and the locust APD would also rise in elevation.     

Linking community size structure and ecosystem functioning using metabolic theory

Understanding how biogeochemical cycles relate to the structure of ecological communities is a central research question in ecology. Here we approach this problem by focusing on body size, which is an easily measured species trait that has a pervasive influence on multiple aspects of community structure and ecosystem functioning. We test the predictions of a model derived from metabolic theory using data on ecosystem metabolism and community size structure. These data were collected as part of an aquatic mesocosm experiment that was designed to simulate future environmental warming. Our analyses demonstrate significant linkages between community size structure and ecosystem functioning, and the effects of warming on these links. Specifically, we show that carbon fluxes were significantly influenced by seasonal variation in temperature, and yielded activation energies remarkably similar to those predicted based on the temperature dependencies of individual-level photosynthesis and respiration. We also show that community size structure significantly influenced fluxes of ecosystem respiration and gross primary production, particularly at the annual time-scale. Assessing size structure and the factors that control it, both empirically and theoretically, therefore promises to aid in understanding links between individual organisms and biogeochemical cycles, and in predicting the responses of key ecosystem functions to future environmental change.     

Shifts in soil microorganisms in response to warming are consistent across a range of Antarctic environments

Because of severe abiotic limitations, Antarctic soils represent simplified systems, where microorganisms are the principal drivers of nutrient cycling. This relative simplicity makes these ecosystems particularly vulnerable to perturbations, like global warming, and the Antarctic Peninsula is among the most rapidly warming regions on the planet. However, the consequences of the ongoing warming of Antarctica on microorganisms and the processes they mediate are unknown. Here, using 16S rRNA gene pyrosequencing and qPCR, we report highly consistent responses in microbial communities across disparate sub-Antarctic and Antarctic environments in response to 3 years of experimental field warming (+0.5 to 2 °C). Specifically, we found significant increases in the abundance of fungi and bacteria and in the Alphaproteobacteria-to-Acidobacteria ratio, which could result in an increase in soil respiration. Furthermore, shifts toward generalist bacterial communities following warming weakened the linkage between the bacterial taxonomic and functional richness. GeoChip microarray analyses also revealed significant warming effects on functional communities, specifically in the N-cycling microorganisms. Our results demonstrate that soil microorganisms across a range of sub-Antarctic and Antarctic environments can respond consistently and rapidly to increasing temperatures.     

INTERACTIONS BETWEEN OCEAN ACIDIFICATION AND WARMING ON THE MORTALITY AND DISSOLUTION OF CORALLINE ALGAE1

Coralline algae are among the most sensitive calcifying organisms to ocean acidification as a result of increased atmospheric carbon dioxide (pCO₂). Little is known, however, about the combined impacts of increased pCO₂, ocean acidification, and sea surface temperature on tissue mortality and skeletal dissolution of coralline algae. To address this issue, we conducted factorial manipulative experiments of elevated CO₂ and temperature and examined the consequences on tissue survival and skeletal dissolution of the crustose coralline alga (CCA) Porolithon (=Hydrolithon) onkodes (Heydr.) Foslie (Corallinaceae, Rhodophyta) on the southern Great Barrier Reef (GBR), Australia. We observed that warming amplified the negative effects of high pCO₂ on the health of the algae: rates of advanced partial mortality of CCA increased from <1% to 9% under high CO₂ (from 400 to 1,100 ppm) and exacerbated to 15% under warming conditions (from 26°C to 29°C). Furthermore, the effect of pCO₂ on skeletal dissolution strongly depended on temperature. Dissolution of P. onkodes only occurred in the high‐pCO₂ treatment and was greater in the warm treatment. Enhanced skeletal dissolution was also associated with a significant increase in the abundance of endolithic algae. Our results demonstrate that P. onkodes is particularly sensitive to ocean acidification under warm conditions, suggesting that previous experiments focused on ocean acidification alone have underestimated the impact of future conditions on coralline algae. Given the central role that coralline algae play within coral reefs, these conclusions have serious ramifications for the integrity of coral‐reef ecosystems.     

云杉种子萌发和幼苗生长对气候变暖与UV B辐射增强的响应

采用开顶式有机玻璃罩(OTCs)及紫外灯分别模拟气候变暖和UV-B增强,对位于气候变暖和UV-B增强突出的青藏高原东缘的高山峡谷地云杉种子萌发、幼苗生长和光合色素含量的变化进行测定分析,探讨云杉对气候变暖和UV-B增强的响应机理。结果显示:(1)UV-B辐射增强对云杉种子萌发无显著影响,但显著抑制萌发幼苗的生长、降低其针叶叶绿素含量,并造成幼苗大量死亡(P<0.05)。(2)气候变暖使云杉种子提前萌发,并提高了发芽势、发芽率和发芽指数,促进幼苗生长和叶绿素的积累,显著降低幼苗死亡率(P<0.05)。(3)气候变暖缓解了UV-B增强对云杉萌发幼苗生长和叶绿素含量的抑制作用,并降低了UV-B胁迫下幼苗的死亡率。研究表明,在未来气候变暖和UV-B辐射增强同时存在时,气候变暖能够在一定程度上缓解UV-B增强对云杉林早期更新带来的抑制作用。     

长江源区高山嵩草物候与生物量动态及其对气候变化的响应

利用青藏高原腹地江河源头的曲麻莱县气象站1994～2004年观测的高寒嵩草草甸优势种高山嵩草的生育期、高度、产量等指标与同期气象资料,通过定量分析研究较长时段的物候及生物量变化特征,以揭示其对气候变化的响应.结果表明:(1)高山嵩草返青期和开花期的变化总体均呈"W"形,在区域气候变暖背景下,植物物候表现为返青期提前,开花期和枯黄期推迟,整个生长季延长.(2)高山嵩草的生物量变化在10年间呈明显的波动趋势,各月最高生物量均出现在1999年,最低生物量出现在1994年.(3)高山嵩草物候期与生长季各月气温呈显著的正相关关系(P<0.001),与月降水量呈弱正相关关系(P>0.05);月均气温成为本区草本植物发芽生长的先决条件,且6～8月气温与植物萌动的相关性最大.(4)生长季6～8月高山嵩草生物量鲜重和干重均与月均气温呈显著正相关,鲜重仅与月降水量呈显著正相关关系,在青藏高原的高寒区,温度比降水对植物产量的影响更大.     

红树林湿地有机碳研究进展

红树林湿地是地球上生产力最高的区域之一,尽管红树林的面积相对较少,但其单位面积的固碳能力很强,是重要的"蓝碳"碳库,其有机碳储量及动态对于全球碳平衡有重要影响。本文对红树林湿地有机碳(包括植被生物量碳和沉积物有机碳)的碳储量及计量方法,沉积物中有机碳的组成、来源及溯源方法,以及影响红树林湿地有机碳动态的因素等方面的研究进行了综述,并对其存在的问题和今后的研究趋势进行了分析。基于红树林湿地的固碳潜力和资源快速减少的现状,准确评估红树林碳库及其动态,有助于气候变化框架条约下的滨海湿地碳计量和价值评价,可以揭示红树林生态系统与全球变化的反馈关系,为红树林生态恢复和保护提供依据。