Predicting impacts of Arctic climate change: Past lessons and future challenges

General circulation models predict increases in temperature and precipitation in the Arctic as the result of increases in atmospheric carbon dioxide concentrations. Arctic ecosystems are strongly constrained by temperature, and may be expected to be markedly influenced by climate change. Perturbation experiments have been used to predict how Arctic ecosystems will respond to global climatic change, but these have often simulated individual perturbations (e.g. temperature alone) and have largely been confined to the short Arctic summer. The importance of interactions between global change variables (e.g. CO₂, temperature, precipitation) has rarely been examined, and much experimentation has been short-term. Similarly, very little experimentation has occurred in the winter when General circulation models predict the largest changes in climate will take place. Recent studies have clearly demonstrated that Arctic ecosystems are not dormant during the winter and thus much greater emphasis on experimentation during this period is essential to improve our understanding of how these ecosystems will respond to global change. This, combined with more long-term experimentation, direct observation of natural vegetation change (e.g. at the tundra/taiga boundary) and improvements in model predictions is necessary if we are to understand the future nature and extent of Arctic ecosystems in a changing climate.     

Impacts of climate change and environmental factors on reproduction and development in wildlife

The robustness of the growth of the human population in the face of environmental impacts is in contrast to the sensitivity of wildlife. There is a danger that the success of reproduction of humans provides a false sense of security for the public, media and politicians with respect to wildlife survival, the maintenance of viable ecosystems and the capacity for recovery of damaged ecosystems and endangered species. In reality, the success of humans to populate the planet has been dependent on the combination of the ability to reproduce successfully and to minimize loss of offspring through controlling and manipulating their own micro-environment. In contrast, reproduction in wildlife is threatened by environmental changes operating at many different physiological levels.     

Physiological ecology of Mesozoic polar forests in a high CO2 environment

Fossils show that coniferous forests extended into polar regions during the Mesozoic, a time when models and independent paleo-CO2 indicators suggest that the atmospheric CO2 concentration was at least double that of the present day. Consequently, such polar forests would have experienced high CO2 interacting with an extreme variation in light. Here we describe an experiment investigating this plant-environment interaction for extant tree species that were important components of polar forests, and give results from the first year of treatment. Specifically, we tested the hypotheses that growth in elevated CO2 (1) stimulates photosynthesis; (2) reduces photoinhibition during the polar summer; and (3) reduces respiration of above- and below-ground plant organs. Our results indicate that CO2 fertilization generally does not affect photosynthesis under continuous daylight characteristic of the polar summer but does increase it when the period of illumination is shorter. Growth in elevated CO2 did not alter the potential for photoinhibition. CO2 enrichment significantly reduced leaf and root respiration rates by 50 and 25 %, respectively, in a range of evergreen taxa. Incorporating these observed CO2 effects into numerical simulations using a process-based model of coniferous forest growth indicates that a high paleo-CO2 concentration would have increased the productivity of Cretaceous conifer forests in northern Alaska. This results from decreased respiratory costs that more than compensate for the absence of high CO2-high temperature interactions during the polar summer. The longer-term effects of CO2 enrichment on seasonal changes in the above- and below-ground carbon balance of trees are discussed.     

Simulation of the stomatal conductance of winter wheat in response to light, temperature and CO2 changes

BACKGROUND AND AIMS: The stomata are a key channel of the water cycle in ecosystems, and are constrained by both physiological and environmental elements. The aim of this study was to parameterize stomatal conductance by extending a previous empirical model and a revised Ball-Berry model. METHODS: Light and CO(2) responses of stomatal conductance and photosynthesis of winter wheat in the North China Plain were investigated under ambient and free-air CO(2) enrichment conditions. The photosynthetic photon flux density and CO(2) concentration ranged from 0 to 2000 micro mol m(-2) s(-1) and from 0 to 1400 micro mol mol(-1), respectively. The model was validated with data from a light, temperature and CO(2) response experiment. RESULTS: By using previously published hyperbolic equations of photosynthetic responses to light and CO(2), the number of parameters in the model was reduced. These response curves were observed diurnally with large variations of temperature and vapour pressure deficit. The model interpreted stomatal response under wide variations in environmental factors. CONCLUSIONS: Most of the model parameters, such as initial photon efficiency and maximum photosynthetic rate (P(max)), have physiological meanings. The model can be expanded to include influences of other physiological elements, such as leaf ageing and nutrient conditions, especially leaf nitrogen content.     

Carbon biogeochemistry and climate change

The rapid increase of atmospheric CO₂ resulting from anthropogenic activites has stimulated a great deal of interest in the carbon cycle. Important decisions need to be made about future tolerable levels of atmospheric CO₂ content, as well as the land and fossil fuel use strategies that will permit us to achieve these goals. The vast amount of new data on atmospheric CO₂ content and ancillary properties that has become available during the last decade, and the development of models to interpret these data, have led to significant advances in our capacity to deal with such issues. However, a major continuing source of uncertainty is the role of photosynthesis in providing a sink for anthropogenic emissions. It is thus appropriate that a new evaluation of the status of our understanding of this issue should be made at this time.The aim of this paper is to provide a setting for the papers that follow by giving an overview of the role of carbon dioxide in climate, the biogeochemical processes that control its distribution, and the evolution of carbon dioxide through time from the origin of the earth to the present. We begin with a discussion of relevant processes. We then proceed to a more detailed discussion of the time periods that are best documented: the late Pleistocene (during which time large continental ice sheets waxed and waned) and the modern era of anthropogenic impact on the carbon cycle.     

青藏高原高寒湿地生态系统CO2通量

依据涡度相关系统连续观测的2005年CO₂通量数据,对青藏高原东北隅的高寒湿地生态系统源/汇功能及其部分环境影响因素进行了分析。结果表明,高寒湿地生态系统为明显的碳源,在植物生长季（5~9月份）吸收230.16 gCO₂•m^-2,非生长季（1~4月份及10~12月份）释放546.18 gCO₂•m^-2,其中净排放最高在5月份,为181.49 gCO₂•m^-2,净吸收最高在8月份,为189.69 gCO₂•m^-2,年释放量为316.02 gCO₂•m^-2。在平均日变化中,最大吸收值出现在7月份12:00,为（0.45±0.0012） mgCO2•m^-2•s^-1,最大排放速率出现在8月份0:00,为（0.22±0.0090） mgCO₂•m^-2•s^-1。生长季中6~9月份表现为明显的单峰型日变化,非生长季的变化幅度较小。净生态系统交换量（NEE）和生态系统总初级生产力（GPP）与气温、空气水气饱和亏和地表反射率等环境因素呈现相似的相关性,与地上生物量和群落叶面积指数则为线性负相关,生态系统呼吸（Res）则与上述因子的相关性呈现相反的趋势。     

大豆主要株型和产量指标对大气CO2和温度升高的响应

针对当前气候变暖和大气CO_2浓度升高同步发生现实,以高光效大豆品种黑农41(HN41)和3个常规对照品种周豆16号(ZD16)、中豆35号(ZD35)和桂黄豆2号(GHD2)为研究对象,通过开顶式气室模拟高CO_2浓度(650μL/L)和温度升高(±0.5—0.6℃)研究了大气CO_2和温度升高对大豆的生长发育与产量影响。结果表明,CO_2浓度升高对株高、茎粗、单株干重和单株籽粒重影响极显著;温度、CO_2与品种互作极显著地影响单株籽粒重。CO_2浓度升高有增加大豆株高、茎粗、干重和单株籽粒重的趋势,且高温下CO_2浓度升高对株高和茎粗的促进作用更大,而正常温度水平下高CO_2浓度升高更有利于干物质积累。与对照CO_2浓度比,高CO_2浓度显著促进了高温下HN41、ZD16和GHD2的株高,并显著提高了正常温度下HN41、ZD16、ZD35和GHD2的单株干重。与正常温度相比,高温仅显著提高了高CO_2处理下HN41的茎粗,并显著提高了对照CO_2处理下HN41的单株籽粒重。此外,同一CO_2浓度和温度处理下,高光效大豆HN41的茎粗、根冠比和单株籽粒重等都显著高于ZD16、ZD35和GHD2;而仅在正常温度与高CO_2浓度处理下HN41的单株干重显著高于ZD16和GHD2。CO_2浓度和温度升高显著影响了高光效大豆的生长,其中,高温下CO_2浓度升高有利于其生长势,正常温度下CO_2浓度升高有利于其光合产物积累。     

大气CO2浓度升高对不同施氮土壤酶活性的影响

利用中国唯一的无锡FACE（Free-air CO₂ enrichment,开放式空气CO₂浓度升高）平台,研究了大气CO₂浓度升高对土壤β-葡糖苷酶、转化酶、脲酶、酸性磷酸酶、β-氨基葡糖苷酶的影响。研究发现,不同氮肥处理下大气CO₂浓度升高对某些土壤酶活性的影响不同。在低氮施肥处理中,大气CO₂浓度升高显著降低β-葡糖苷酶活性,但是在高氮施肥处理下,大气CO₂浓度升高显著增加β-葡糖苷酶活性。在低氮和常氮施肥处理中大气CO₂浓度升高显著增加了土壤脲酶活性,但在高氮水平下影响不显著。在低氮、常氮施肥处理中,大气CO₂浓度升高对土壤酸性磷酸酶活性没有影响,而在高氮施肥处理中显著增强了土壤中磷酸酶活性。大气CO₂浓度升高对土壤转化酶活性和β-氨基葡糖苷酶的活性有增加趋势,但影响不显著。研究还发现,在不同的CO₂浓度下,土壤酶活性对不同氮肥处理的响应也不同。在正常CO₂浓度下,土壤中β-葡糖苷酶活性随着氮肥施用量的增加而降低,而在大气CO₂浓度升高条件下,却随着氮肥施用量的增加而增加。在大气CO₂浓度升高条件下,高氮施肥显著增加了转化酶和酸性磷酸酶活性,而在正常CO₂浓度下,影响不显著。在大气CO₂浓度升高条件下,氮肥处理对脲酶活性的影响不大,但在正常CO₂浓度下,脲酶活性随着氮肥施用量的增加而增加。氮肥对β-氨基葡糖苷酶活性的影响不明显。     

超临界CO2提取甘草地上部分总黄酮

采用单因素试验对甘草地上部分（茎叶）的超临界CO₂提取工艺进行了研究。实验考察了压力、萃取时间、温度及CO₂流量对甘草地上部分总黄酮提取率的影响,以总黄酮提取率和含量为指标,系统的研究了超临界二氧化碳萃取法提取甘草地上部分总黄酮的提取效果。得出的最佳工艺参数为：采用40~60目原料,80%乙醇为夹带剂,萃取时间：1.5 h;萃取压力：30.0 MPa;萃取温度：50℃;CO₂流量：10 kg·h^-1;分离压力: 5.8 MPa;分离温度: 40℃。实验结果表明超临界二氧化碳萃取甘草总黄酮的提取率2.09%,含量5.42%,工艺具有提取率高,纯度高的特点,为规模化生产甘草总黄酮的提取提供了研究基础。     

An assessment of direct and indirect effects of climate change for populations of the Rocky Mountain Apollo butterfly (Parnassius smintheus Doubleday)

Abstract Climate change is occurring and insects are responding. Current challenges for ecologists and managers are predicting how organisms will respond to continuing climate change and determining how to mitigate potential negative effects. In contrast to broad scale predictions for climate change involving the distribution of species, in this article we highlight the many ways in which local populations of the Rocky Mountain Apollo butterfly (Parnassius smintheus Doubleday) are predicted to respond to climate change. Using experimental and observational data collected over the past 15 years, we detail both direct and indirect effects. In addition, we identify limitations in our knowledge restricting the ability to predict how populations will respond to climate change. Some changes, such as warmer winter temperatures, may have beneficial effects; however, most of the effects of climate change will be detrimental. Variability in snow cover during the overwintering period and habitat loss due to forest encroachment have the largest potential negative effects.     

Modelling Plant Responses to Elevated CO2: How Important is Leaf Area Index?

BACKGROUND AND AIMS: The problem of increasing CO(2) concentration [CO(2)] and associated climate change has generated much interest in modelling effects of [CO(2)] on plants. While variation in growth and productivity is closely related to the amount of intercepted radiation, largely determined by leaf area index (LAI), effects of elevated [CO(2)] on growth are primarily via stimulation of leaf photosynthesis. Variability in LAI depends on climatic and growing conditions including [CO(2)] concentration and can be high, as is known for agricultural crops which are specifically emphasized in this report. However, modelling photosynthesis has received much attention and photosynthesis is often represented inadequately detailed in plant productivity models. Less emphasis has been placed on the modelling of leaf area dynamics, and relationships between plant growth, elevated [CO(2)] and LAI are not well understood. This Botanical Briefing aims at clarifying the relative importance of LAI for canopy assimilation and growth in biomass under conditions of rising [CO(2)] and discusses related implications for process-based modelling. MODEL: A simulation exercise performed for a wheat crop demonstrates recent experimental findings about canopy assimilation as affected by LAI and elevation of [CO(2)]. While canopy assimilation largely increases with LAI below canopy light saturation, effects on canopy assimilation of [CO(2)] elevation are less pronounced and tend to decline as LAI increases. Results from selected model-testing studies indicate that simulation of LAI is often critical and forms an important source of uncertainty in plant productivity models, particularly under conditions of limited resource supply. CONCLUSIONS: Progress in estimating plant growth and productivity under rising [CO(2)] is unlikely to be achieved without improving the modelling of LAI. This will depend on better understanding of the processes of substrate allocation, leaf area development and senescence, and the role of LAI in controlling plant adaptation to environmental changes.     

Effect of climate change on mast-seeding species: frequency of mass flowering and escape from specialist insect seed predators

Global surface temperatures are expected to increase by several degrees in the next century, with potentially large but poorly understood impacts on ecological interactions. Here we propose potential effects of increased temperatures on ecologically dominant New Zealand grasses (Chionochloa spp.) that mass flower and mast seed. Twenty-two years’ data from five masting Chionochloa species in New Zealand showed that the cue for heavy flowering was unusually high temperature in the summer of the year before flowering. Attack by predispersal insect seed predators was much reduced in mast years, apparently because predator populations were satiated. Increased temperatures would greatly decrease interannual variation in Chionochloa flowering, allowing seed predator populations to increase and potentially to devastate the seed crop annually. Similar responses are likely in masting species worldwide. This previously unrecognized effect of global warming could have widespread impacts on temperate ecosystems.     

Plant respiration and elevated atmospheric CO2 concentration: cellular responses and global significance

BACKGROUND: Elevated levels of atmospheric [CO2] are likely to enhance photosynthesis and plant growth, which, in turn, should result in increased specific and whole-plant respiration rates. However, a large body of literature has shown that specific respiration rates of plant tissues are often reduced when plants are exposed to, or grown at, high [CO2] due to direct effects on enzymes and indirect effects derived from changes in the plant's chemical composition. SCOPE: Although measurement artefacts may have affected some of the previously reported effects of CO2 on respiration rates, the direction and magnitude for the effects of elevated [CO2] on plant respiration may largely depend on the vertical scale (from enzymes to ecosystems) at which measurements are taken. In this review, the effects of elevated [CO2] from cells to ecosystems are presented within the context of the enzymatic and physiological controls of plant respiration, the role(s) of non-phosphorylating pathways, and possible effects associated with plant size. CONCLUSIONS: Contrary to what was previously thought, specific respiration rates are generally not reduced when plants are grown at elevated [CO2]. However, whole ecosystem studies show that canopy respiration does not increase proportionally to increases in biomass in response to elevated [CO2], although a larger proportion of respiration takes place in the root system. Fundamental information is still lacking on how respiration and the processes supported by it are physiologically controlled, thereby preventing sound interpretations of what seem to be species-specific responses of respiration to elevated [CO2]. Therefore the role of plant respiration in augmenting the sink capacity of terrestrial ecosystems is still uncertain.     

Plants and climate change: complexities and surprises

Background Anthropogenic climate change (ACC) will influence all aspects of plant biology over coming decades. Many changes in wild species have already been well-documented as a result of increased atmospheric CO₂ concentrations, warming climate and changing precipitation regimes. A wealth of available data has allowed the use of meta-analyses to examine plant–climate interactions on more sophisticated levels than before. These analyses have revealed major differences in plant response among groups, e.g. with respect to functional traits, taxonomy, life-history and provenance. Interestingly, these meta-analyses have also exposed unexpected mismatches between theory, experimental, and observational studies.Scope We reviewed the literature on species’ responses to ACC, finding ∼42 % of 4000 species studied globally are plants (primarily terrestrial). We review impacts on phenology, distributions, ecophysiology, regeneration biology, plant–plant and plant–herbivore interactions, and the roles of plasticity and evolution. We focused on apparent deviations from expectation, and highlighted cases where more sophisticated analyses revealed that unexpected changes were, in fact, responses to ACC.Conclusions We found that conventionally expected responses are generally well-understood, and that it is the aberrant responses that are now yielding greater insight into current and possible future impacts of ACC. We argue that inconclusive, unexpected, or counter-intuitive results should be embraced in order to understand apparent disconnects between theory, prediction, and observation. We highlight prime examples from the collection of papers in this Special Issue, as well as general literature. We found use of plant functional groupings/traits had mixed success, but that some underutilized approaches, such as Grime''s C/S/R strategies, when incorporated, have improved understanding of observed responses. Despite inherent difficulties, we highlight the need for ecologists to conduct community-level experiments in systems that replicate multiple aspects of ACC. Specifically, we call for development of coordinating experiments across networks of field sites, both natural and man-made.     

Photoautotrophic culture of Coffea arabusta somatic embryos: photosynthetic ability and growth of different stage embryos

Coffea arabusta somatic embryos were cultured and development of stomata, rate of CO2 fixation or production, chlorophyll content and chlorophyll fluorescence were studied in embryos at different stages of development. Cotyledonary and germinated embryos have photosynthetic capacity, although pretreatment at a high photosynthetic photon flux (PPF) (100 micromol m(-2) s(-1)) for 14 d increased photosynthetic ability. Except in a very small number of cases, stomata did not develop fully in precotyledonary stage embryos and were absent in torpedo stage embryos. Low chlorophyll content (90-130 microg g(-1) fresh mass) was noted in torpedo and precotyledonary stage embryos compared with cotyledonary and germinated embryos (300-500 microg g(-1) fresh mass). Due to the absence of stomata and low chlorophyll content in the torpedo and precotyledonary stage embryos, the photosynthetic rate was low and, in some cases, CO2 production was observed. These data suggest that the cotyledonary stage is the earliest stage that can be cultured photoautotrophically to ensure plantlet development. When grown photoautotrophically (in a sugar-free medium with CO2 enrichment in the culture headspace and high photosynthetic photon flux), torpedo and precotyledonary stage embryos lost 20-25% of their initial dry mass after 60 d of culture. However, in cotyledonary and germinated embryos, the dry mass of each embryo increased by 10 and 50%, respectively. By using a porous supporting material, growth (especially root growth) was increased in cotyledonary stage embryos. In addition, photoautotrophic conditions, high PPF (100-150 micromol m(-2) s(-1)) and increased CO2 concentration (1100 micromol mol(-1)) were found to be necessary for the development of plantlets from cotyledonary stage embryos.     

Growth of regenerated tree seedlings associated with microclimatic change in a mature larch plantation after harvesting

In order to further develop methods of sustainable forest management, we evaluated the effects of logging practices during the winter on microclimatic factors and growth of four seral deciduous broad-leaved tree seedlings regenerated in a larch plantation in northern Japan. We found that winter logging practices drastically changed microclimatic factors, especially in terms of light intensity and the vertical distribution pattern of CO₂ concentration. Harvesting overstory larch trees increased photosynthetic photon flux (PPF), which may enhance the photosynthesis of understory plants. We examined the undergrowth for tree seedlings of the following species: two late successional species, Prunus ssiori and Carpinus cordata; one gap phase species, Magnolia hyporeuca; and one mid-late successional species, Quercus mongolica var. crispula. All of the four studied tree species responded well to the practices of winter logging after the second year of harvesting overstoried larch trees. The current shoot diameter and current shoot length increased significantly. Therefore, we conclude that winter logging practices should improve shoot growth of deciduous broad-leaved tree seedlings regenerated in a larch plantation through the change in environmental factors that accompanies larch harvest.