Effects of drought and N level on the interactions of the root hemiparasite Rhinanthus alectorolophus with a combination of three host species

• Increasing nitrogen deposition and more frequent drought events are likely to change plant interactions in natural grasslands. Both factors may also influence the interactions between hemiparasitic plants, regarded as keystone species in many grasslands, and their host species.
• We grew a combination of three suitable hosts, a grass, a forb and a legume, with and without the hemiparasite Rhinanthus alectorolophus at three levels of nitrogen (N) and two levels of water availability in a factorial design.
• Biomass of the hemiparasite and host community increased with N level and was reduced by drought to a similar degree. Larger plants in fertilised pots started to wilt earlier, and the presence of a hemiparasite further increased drought sensitivity. The hemiparasite strongly reduced biomass of the host community and overall productivity, and affected the competitive balance among host plants because it particularly reduced biomass of the dominant grass. These effects were the opposite of those of high N. The hemiparasite increased the root mass fraction of the hosts at all levels of N and water availability, indicating that the effect of the hemiparasite on the hosts was mainly due to loss of belowground resources.
• Our results indicate that hemiparasites will not always respond more strongly to increased N availability and drought than autotrophic plants, and that hemiparasites can have similarly strong effects on grassland communities as soil fertility and drought. By preferentially attacking dominant species the hemiparasites might alleviate the negative effects of nutrient enrichment on grassland diversity.

     

Experimental investigation of drought induced acidification in a rich fen soil

Intact rich fen soil cores with controlled water levels near thesurface were installed in an open greenhouse. To simulate short termsummer drought, water levels were lowered (20 cm) after two weeks inhalf of the cores (experimental cores) and remained near the surface inthe other half (blanks). After two more weeks, the water levels werebrought back to the surface in the experimental cores and remainedthere for another two weeks. In the blanks, reduction and alkalinizationof the top peat layer occurred. In the experimental soil cores oxidationand acidification started within one week after drawdown. An indicationfor a drought induced rise in soluble reactive phosphorus has beenfound. The velocity of the acidification process illustrates the dynamicnature of the hydrochemical conditions in fen soils during drought. Theprocesses controlling the acid/base status of rich fen, the effect ofdrought induced acidification on P availability and the significance forthe vegetation are discussed.     

Epiphytic bromeliads in a changing world: the effect of elevated CO2 and varying water supply on growth and nutrient relations

• Global climate change is likely to impact all plant life. Vascular epiphytes represent a life form that may be affected more than any other by possible changes in precipitation leading to water shortage, but negative effects of drought may be mitigated through increasing levels of atmospheric CO₂.
• We studied the response of three epiphytic Aechmea species to different CO₂ and watering levels in a full‐factorial climate chamber study over 100 days. All species use crassulacean acid metabolism (CAM). Response variables were relative growth rate (RGR), nocturnal acidification and foliar nutrient levels (N, P, K, Mg).
• Both elevated CO₂ and increased water supply stimulated RGR, but the interaction of the two factors was not significant. Nocturnal acidification was not affected by these factors, indicating that the increase in growth in these CAM species was due to higher assimilation in the light. Mass‐based foliar nutrient contents were consistently lower under elevated CO₂, but most differences disappeared when expressed on an area basis.
• Compared to previous studies with epiphytes, in which doubling of CO₂ increased RGR, on average, by only 14%, these Aechmea species showed a relatively strong growth stimulation of up to +61%. Consistent with earlier findings with other bromeliads, elevated CO₂ did not mitigate the effect of water shortage.

     

基于全球气候模式集合的鄱阳湖流域未来潜在蒸散量及其干旱效应研究

鄱阳湖流域近年来旱涝灾害频发,原有的水量平衡被打破。因此,开展鄱阳湖地区潜在蒸散量及干旱效应研究具有重要意义。潜在蒸散量（Reference Evapotranspiration,ET₀）是评价区域水资源配置和计算干旱指数的重要指标。以我国的鄱阳湖流域为研究区,依托统计降尺度模型,基于站点观测数据、气候模式数据以及美国环境中心再分析数据,运用遗传算法构建多模式集合,模拟未来情景下流域潜在蒸散量和干旱指数（Drought Index,DI）时空演变特征。结果表明：基于遗传算法构建的模式集合较单一气候模式或等权模式集合,模拟性能佳;RCP4.5、8.5情景下流域ET₀均呈上升趋势,ET₀变化的第一主周期分别为20年和4年,流域ET₀未来空间变化特征表现为东高西低;RCP8.5情景下,鄱阳湖流域DI在年际上呈显著上升趋势,9-11月是干旱风险防范的关键时期;流域年DI变化的主周期为8年,流域的中东部地区将是未来干旱风险防范的重点区域。本研究为认识区域尺度下气候变化对潜在蒸散量的影响提供借鉴,同时为政府部门科学应对鄱阳湖流域未来时期可能出现的旱情提供的决策支持。     

Robust ecological drought projections for drylands in the 21st century

Dryland ecosystems may be especially vulnerable to expected 21st century increases in temperature and aridity because they are tightly controlled by moisture availability. However, climate impact assessments in drylands are difficult because ecological dynamics are dictated by drought conditions that are difficult to define and complex to estimate from climate conditions alone. In addition, precipitation projections vary substantially among climate models, enhancing variation in overall trajectories for aridity. Here, we constrain this uncertainty by utilizing an ecosystem water balance model to quantify drought conditions with recognized ecological importance, and by identifying changes in ecological drought conditions that are robust among climate models, defined here as when >90% of models agree in the direction of change. Despite limited evidence for robust changes in precipitation, changes in ecological drought are robust over large portions of drylands in the United States and Canada. Our results suggest strong regional differences in long‐term drought trajectories, epitomized by chronic drought increases in southern areas, notably the Upper Gila Mountains and South‐Central Semi‐arid Prairies, and decreases in the north, particularly portions of the Temperate and West‐Central Semi‐arid Prairies. However, we also found that exposure to hot‐dry stress is increasing faster than mean annual temperature over most of these drylands, and those increases are greatest in northern areas. Robust shifts in seasonal drought are most apparent during the cool season; when soil water availability is projected to increase in northern regions and decrease in southern regions. The implications of these robust drought trajectories for ecosystems will vary geographically, and these results provide useful insights about the impact of climate change on these dryland ecosystems. More broadly, this approach of identifying robust changes in ecological drought may be useful for other assessments of climate impacts in drylands and provide a more rigorous foundation for making long‐term strategic resource management decisions.     

Hydro-climate and ecological behaviour of the drought of Amazonia in 2005

In 2005, southwestern Amazonia experienced the effects of an intense drought that affected life and biodiversity. Several major tributaries as well as parts of the main river itself contained only a fraction of their normal volumes of water, and lakes were drying up. The consequences for local people, animals and the forest itself are impossible to estimate now, but they are likely to be serious. The analyses indicate that the drought was manifested as weak peak river season during autumn to winter as a consequence of a weak summertime season in southwestern Amazonia; the winter season was also accompanied by rainfall that sometimes reached 25% of the climatic value, being anomalously warm and dry and helping in the propagation of fires. Analyses of climatic and hydrological records in Amazonia suggest a broad consensus that the 2005 drought was linked not to El Niño as with most previous droughts in the Amazon, but to warming sea surface temperatures in the tropical North Atlantic Ocean.     

Response of an old‐growth tropical rainforest to transient high temperature and drought

Tropical rainforests have experienced episodes of severe heat and drought in recent decades, and climate models project a warmer and potentially drier tropical climate over this century. However, likely responses of tropical rainforests are poorly understood due to a lack of frequent long‐term measurements of forest structure and dynamics. We analyzed a 12‐year record (1999–2010) of 47 817 annual measurements of canopy height to characterize the response of an old‐growth Neotropical rainforest to the severe heat and drought associated with the 1997–1998 El Niño. Well‐drained soils on slopes and plateaus experienced a threefold increase in the fraction of the landscape in gaps (≤2 m) and a reduction in the fraction in high canopy (>15 m) causing distributions of canopy height to depart from equilibrium for a period of 2–3 years. In contrast, forests on low‐lying alluvial terraces remained in equilibrium and were nearly half as likely to experience upper canopy (>15 m) disturbance over the 12 years of observation. Variation in forest response across topographic positions suggests that tropical rainforests are more sensitive to moisture deficits than high temperature and that topography likely structures landscape‐level variation in the severity of drought impacts.     

氮沉降对森林生态系统碳吸存的影响

工业化带来的大气氮沉降增加是影响森林生态系统碳吸存的重要因素。将森林碳库分为地上和地下两部分,从3个方面综述了国内外氮沉降对森林生态系统碳吸存影响的研究现状。(1)地上部分:氮限制的温带森林,氮沉降增加了地上部分碳吸存。氮丰富的热带森林,氮沉降对地上部分碳吸存没有影响。过量的氮输入会造成森林死亡率的上升,从而降低地上部分碳吸存。(2)地下部分:相比地上部分研究得少,表现为增加、降低和没有影响3种效果。(3)目前的结论趋向于认为氮沉降促进森林生态系统碳吸存,然而氮沉降所带来的森林生态系统碳吸存能力到底有多大依然无法确定,这也将成为未来氮碳循环研究的重点问题。分析了氮沉降影响森林生态系统碳吸存的机理,介绍了氮沉降对森林生态系统碳吸存影响的4种研究方法。探讨了该领域研究的不足及未来的研究方向。     

干旱胁迫对大丽花生理生化指标的影响

以大丽花品种'粉西施'扦插苗为试材,研究不同程度干旱胁迫及复水处理对大丽花品种'粉西施'叶片生理生化指标的影响.结果表明:随着干旱胁迫程度的增加和时间的延长,大丽花叶片的相对含水量、水势和叶绿素含量显著下降;叶片相对电导率、丙二醛含量显著增加,质膜遭到损害,大量离子外渗,严重胁迫下质膜的损害最严重,复水后无法恢复到对照水平;可溶性糖、脯氨酸含量显著增加,脯氨酸含量在中度和重度胁迫后期增加显著,说明其对干旱亏缺的敏感性较低;可溶性蛋白呈降-升-降的变化趋势;抗氧化酶SOD、POD和CAT活性先上升后下降,3种酶对干旱胁迫和活性氧的响应存在一定差异,表现为相互协调的作用.     

The photosynthetic drought physiology of a diverse group of southern hemisphere conifer species is correlated with minimum seasonal rainfall

1. The instantaneous and integrated leaf gas exchange of 13 species of southern hemisphere conifers grown under identical glasshouse conditions were examined to determine whether there was any correlation between the characteristics of water use at the leaf level and environmental water availability.
2. In the conifer species examined, the minimum ratio of internal to ambient CO₂ measured in leaves during artificially imposed drought [( c _i/ c _a)_min] was strongly correlated with the minimum rainfall observed within the natural range of each species. This suggests that the distributions of these species are constrained by the drought tolerance of their photosynthetic apparatus.
3. A good correlation was found between the ratio of internal to ambient CO₂ measured in leaves under optimal conditions ( c _i/ c _a)_max and leaf δ¹³C (and hence inferred ∫[ c _i/ c _a]). Neither of these, however, correlated with the environmental parameters considered most likely to be limiting species distribution, i.e. precipitation and altitude.
4. These data suggest that decreasing water availability may have been the major factor responsible for the restriction and extinction of conifers in the southern hemisphere.     

The impacts of increasing drought on forest dynamics,structure, and biodiversity in the United States

We synthesize insights from current understanding of drought impacts at stand‐to‐biogeographic scales, including management options, and we identify challenges to be addressed with new research. Large stand‐level shifts underway in western forests already are showing the importance of interactions involving drought, insects, and fire. Diebacks, changes in composition and structure, and shifting range limits are widely observed. In the eastern US, the effects of increasing drought are becoming better understood at the level of individual trees, but this knowledge cannot yet be confidently translated to predictions of changing structure and diversity of forest stands. While eastern forests have not experienced the types of changes seen in western forests in recent decades, they too are vulnerable to drought and could experience significant changes with increased severity, frequency, or duration in drought. Throughout the continental United States, the combination of projected large climate‐induced shifts in suitable habitat from modeling studies and limited potential for the rapid migration of tree populations suggests that changing tree and forest biogeography could substantially lag habitat shifts already underway. Forest management practices can partially ameliorate drought impacts through reductions in stand density, selection of drought‐tolerant species and genotypes, artificial regeneration, and the development of multistructured stands. However, silvicultural treatments also could exacerbate drought impacts unless implemented with careful attention to site and stand characteristics. Gaps in our understanding should motivate new research on the effects of interactions involving climate and other species at the stand scale and how interactions and multiple responses are represented in models. This assessment indicates that, without a stronger empirical basis for drought impacts at the stand scale, more complex models may provide limited guidance.     

基于NDVI的云南省2009-2010年干旱遗产效应研究

气候变化正导致干旱事件发生的强度、频度显著改变,极端气候事件发生的不确定性直接影响陆地生态系统关键生态过程。我国西南地区在2009-2010年发生百年一遇的极端干旱,目前关于植被生长在长时间尺度对此次干旱事件的响应尚不明确。以云南省为研究区,基于多年Normalized difference vegetation index(NDVI)影像数据以及长时间序列气象资料对此次极端事件的干旱遗产效应开展研究,分析了干旱遗产效应的持续时间以及不同植被类型的响应差异。结果表明:1)云南省植被生长在极端干旱事件发生后受到的抑制时间大约持续1-2年,受影响区域主要集中在遭遇降水严重减少的地区;2)海拔2000 m附近为植被对干旱响应最为敏感的区域,海拔高于4000 m的植被生长几乎未受到干旱影响;3)较之草地和农田,森林植被受到的抑制作用更为强烈。研究揭示了极端干旱对云南省植被生长造成的影响,为该地区未来应对极端干旱并有效开展植被恢复提供理论依据。     

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.     

信号分子水杨酸减缓干旱胁迫对紫御谷光合和膜脂过氧化的副效应

为研究信号分子水杨酸(SA)对干旱胁迫下紫御谷光合和膜脂过氧化的影响,为SA应用于紫御谷抗旱育苗提供理论依据,测定分析了SA处理对干旱胁迫下紫御谷幼苗叶片光合和膜脂过氧化相关指标的变化。结果表明:(1)干旱胁迫破坏了紫御谷叶绿体的膜结构,使基粒数量明显减少,垛叠不明显,排列比较松散,而SA处理能在一定程度上保护叶绿体的膜结构。(2)干旱胁迫降低了紫御谷幼苗叶片的叶绿素b和总叶绿素含量,而SA处理能提高干旱胁迫下紫御谷幼苗叶片的叶绿素a、叶绿素b、总叶绿素和胡萝卜素含量。(3)干旱胁迫降低了叶片的净光合速率、气孔导度、蒸腾速率、光饱和点和暗呼吸速率,增加了叶片的光补偿点、CO₂饱和点、CO₂补偿点和光呼吸速率,而SA处理则增加了紫御谷幼苗叶片的净光合速率、气孔导度、光饱和点和暗呼吸速率,降低了紫御谷幼苗叶片的光补偿点、CO₂饱和点、CO₂补偿点和光呼吸速率。(4)干旱胁迫降低了紫御谷幼苗叶片的F_v/F_m和Φ_PSⅡ,显著增加了叶片的相对电导率和丙二醛含量,而SA处理则增加了幼苗叶片的F_v/F_m和Φ_PSⅡ,降低了叶片的相对电导率和丙二醛含量。表明:信号分子水杨酸能够有效减缓干旱胁迫对紫御谷光合和膜脂过氧化的影响。     

Properties,morphogenesis, and effect of acidification on spines of the cidaroid sea urchin Phyllacanthus imperialis

Cidaroid sea urchins are the sister clade to all other extant echinoids and have numerous unique features, including unusual primary spines. These lack an epidermis when mature, exposing their high‐magnesium calcite skeleton to seawater and allowing the settlement of numerous epibionts. Cidaroid spines are made of an inner core of classical monocrystalline skeleton and an outer layer of polycrystalline magnesium calcite. Interestingly, cidaroids survived the Permian‐Triassic crisis, which was characterized by severe acidification of the ocean. Currently, numerous members of this group inhabit the deep ocean, below the saturation horizon for their magnesium calcite skeleton. This suggests that members of this taxon may have characteristics that may allow them to resist ongoing ocean acidification linked to global change. We compared the effect of acidified seawater (pH 7.2, 7.6, or 8.2) on mature spines with a fully developed cortex to that on young, growing spines, in which only the stereom core was developed. The cortex of mature spines was much more resistant to etching than the stereom of young spines. We then examined the properties of the cortex that might be responsible for its resistance compared to the underlying stereomic layers, namely morphology, intramineral organic material, magnesium concentration, intrinsic solubility of the mineral, and density. Our results indicate that the acidification resistance of the cortex is probably due to its lower magnesium concentration and higher density, the latter reducing the amount of surface area in contact with acidified seawater. The biofilm and epibionts covering the cortex of mature spines may also reduce its exposure to seawater.     

各种属性森林对干旱胁迫的响应研究进展

全球气候变化的背景下,干旱事件的发生频率、强度和持续时间不断增加,增加了森林生态系统面临的风险,探讨森林对干旱胁迫响应的规律与特征是生态学领域研究的热点。以干旱的定量表达为切入点,总结和归纳了评估森林对干旱响应的常见指标、评估方法和应用案例,特别是梳理了各种属性(如林龄、冠层高度等)的森林对干旱胁迫响应的差异性。基于当前研究进展和问题,提出在未来研究中,亟待发展多尺度综合解析各种属性森林对干旱胁迫响应差异的驱动机制研究;各种属性森林生态系统稳态转换临界点的探测;森林对干旱的响应规律在森林管理和模型优化的实践应用。     

The impact of shrub encroachment on savanna bird diversity from local to regional scale

Aim  Evidence is accumulating of a general increase in woody cover of many savanna regions of the world. Little is known about the consequences of this widespread and fundamental ecosystem structural shift on biodiversity.
Location  South Africa.
Methods  We assessed the potential response of bird species to shrub encroachment in a South African savanna by censusing bird species in five habitats along a gradient of increasing shrub cover, from grassland/open woodland to shrubland dominated by various shrub species. We also explored historical bird species population trends across southern Africa during the second half of the 20th century to determine if any quantifiable shifts had occurred that support an ongoing impact of shrub encroachment at the regional scale.
Results  At the local scale, species richness peaked at intermediate levels of shrub cover. Bird species composition showed high turnover along the gradient, suggesting that widespread shrub encroachment is likely to lead to the loss of certain species with a concomitant decline in bird species richness at the landscape scale. Finally, savanna bird species responded to changes in vegetation structure rather than vegetation species composition: bird assemblages were very similar in shrublands dominated by Acacia mellifera and those dominated by Tarchonanthus camphoratus .
Main conclusions  Shrub encroachment might have a bigger impact on bird diversity in grassland than in open woodland, regardless of the shrub species. Species recorded in our study area were associated with historical population changes at the scale of southern Africa suggesting that shrub encroachment could be one of the main drivers of bird population dynamics in southern African savannas. If current trends continue, the persistence of several southern African bird species associated with open savanna might be jeopardized regionally.     

森林土壤微生物对干旱和氮沉降的响应

干旱和氮沉降深刻影响着人类世森林生态系统的生命活动与物质循环,进而影响全球碳平衡、并反馈作用于气候变化。土壤微生物驱动元素的生物地球化学循环和关键土壤生态过程,在气候变化生物学研究方面具有核心地位和全球重要性。本文综述了干旱和氮沉降对森林土壤细菌和菌根真菌的影响。提出未来应加强全球变化多因子交互作用对土壤微生物多样性、活性与生态功能的研究;建立野外长期定位站,强化亚热带森林生态系统与全球变化研究;注重土壤生物之间互作及网络研究;利用微生物大数据建立相关的机理模型等。从认识微生物多样性和群落组成对全球变化的响应与适应,逐步发展为调控利用微生物群落服务于森林的优化管理、生态资源的合理保护与可持续利用,为充分发挥微生物减缓全球气候变化的作用提供理论基础。     

The oceans are changing: impact of ocean warming and acidification on biofouling communities

Climate change (CC) is driving modification of the chemical and physical properties of estuaries and oceans with profound consequences for species and ecosystems. Numerous studies investigate CC effects from species to ecosystem levels, but little is known of the impacts on biofilm communities and on bioactive molecules such as cues, adhesives and enzymes. CC is induced by anthropogenic activity increasing greenhouse emissions leading to rises in air and water temperatures, ocean acidification, sea level rise and changes in ocean gyres and rainfall patterns. These environmental changes are resulting in alterations within marine communities and changes in species ranges and composition. This review provides insights and synthesis of knowledge about the effect of elevated temperature and ocean acidification on microfouling communities and bioactive molecules. The existing studies suggest that CC will impact production of bioactive compounds as well as the growth and composition of biofouling communities. Undoubtedly, with CC fouling management will became an even greater challenge.     

Predicting shifts in the functional composition of tropical forests under increased drought and CO2 from trade‐offs among plant hydraulic traits

Tropical forest responses are an important feedback on global change, but changes in forest composition with projected increases in CO₂ and drought are highly uncertain. Here we determine shifts in the most competitive plant hydraulic strategy (the evolutionary stable strategy or ESS) from changes in CO₂ and drought frequency and intensity. Hydraulic strategies were defined along a spectrum from drought avoidance to tolerance by physiology traits. Drought impacted competition more than CO₂, with elevated CO₂ reducing but not reversing drought‐induced shifts in the ESS towards more tolerant strategies. Trait plasticity and/or adaptation intensified these shifts by increasing the competitive ability of the drought tolerant relative to the avoidant strategies. These findings predict losses of drought avoidant evergreens from tropical forests under global change, and point to the importance of changes in precipitation during the dry season and constraints on plasticity and adaptation in xylem traits to forest responses.