Effects of Climate Change and a Doubling of CO2 on Vegetation Diversity

A model is presented for predicting the response of global familydiversity to global environmental change. The model assumesthat three primary mechanisms determine diversity: the capacityto survive the absolute minimum temperature of a site, the abilityto complete the life cycle in a given length and warmth of thegrowing season, and the capacity to expand leaves in a definedregime of precipitation and vegetation transpiration. The directeffects of CO₂ on vegetation transpiration are also included. About one-third of the floristic regions of the world exhibitincreased diversity with a 3°C increase in temperature,a 10% increase in precipitation, and a doubling of the CO2 concentration.The addition of CO₂ offsets the increased rates of transpiration,caused by global warming through its capacity to reduce transpiration.As a consequence, the diversity of dry regions displayed thegreatest increase in diversity due to increased CO₂.     

Climate Change,Water Practices and Relational Worlds in the Andes

Climate change translates into insecure water provision and produces new uncertainties for farmers and politicians in Colca Valley, Southern Peru. Anthropological studies of climate change have mainly focused on adaptation, resilience and so-called indigenous traditional knowledge. This article argues that a stronger ethnographic focus on material practices – including knowledge practices – can contribute to a more nuanced understanding of climate change effects, responses and forms of water management. The author aims to see responses to climate change as more than cultural representations, and therefore focuses on water practices and the realities that these practices make, as well as the relational webs of humans, environment, infrastructure and other-than-human beings. The article explores different practices that enact multiple versions of water, and multiple – yet related and entangled – water worlds. The author suggests that this has implications for how we understand politics of climate and water: as tensions between singularizing practices and multiplicity.     

Development of Water Stress under Increased Atmospheric CO2 Concentration

The increase in water use efficiency (the ratio of photosynthetic to transpiration rates) is likely to be the commonest positive effect of long-term elevation in CO₂ concentration (CE). This may not necessarily lead to decrease in long-term water use owing to increased leaf area. However, some plant species seem to cope better with drought stress under CE, because increased production of photosynthates might enhance osmotic adjustment and decreased stomatal conductance and transpiration rate under CE enable plants to maintain a higher leaf water potential during drought. In addition, at the same stomatal conductance, internal CO₂ concentration might be higher under CE which results in higher photosynthetic rate. Therefore plants under CE of the future atmosphere will probably survive eventual higher drought stress and some species may even be able to extend their biotope into less favourable sites. This revised version was published online in July 2006 with corrections to the Cover Date.     

Climate Change and Microbiological Water Quality at California Beaches

Daily microbiological water quality and precipitation data spanning 6?years were collected from monitoring stations at southern California beaches. Daily precipitation projected for the twenty-first century was derived from downscaled CNRM CM3 global climate model. A time series model of Enterococcus concentrations that was driven by precipitation, matched the general trend of empirical water quality data; there was a positive association between precipitation and microbiological water contamination (P?相似文献   

Effects of City Expansion on Heat Stress under Climate Change Conditions

We examine the joint contribution of urban expansion and climate change on heat stress over the Sydney region. A Regional Climate Model was used to downscale present (1990–2009) and future (2040–2059) simulations from a Global Climate Model. The effects of urban surfaces on local temperature and vapor pressure were included. The role of urban expansion in modulating the climate change signal at local scales was investigated using a human heat-stress index combining temperature and vapor pressure. Urban expansion and climate change leads to increased risk of heat-stress conditions in the Sydney region, with substantially more frequent adverse conditions in urban areas. Impacts are particularly obvious in extreme values; daytime heat-stress impacts are more noticeable in the higher percentiles than in the mean values and the impact at night is more obvious in the lower percentiles than in the mean. Urban expansion enhances heat-stress increases due to climate change at night, but partly compensates its effects during the day. These differences are due to a stronger contribution from vapor pressure deficit during the day and from temperature increases during the night induced by urban surfaces. Our results highlight the inappropriateness of assessing human comfort determined using temperature changes alone and point to the likelihood that impacts of climate change assessed using models that lack urban surfaces probably underestimate future changes in terms of human comfort.     

Acclimation of CO(2) Assimilation in Cotton Leaves to Water Stress and Salinity

Cotton (Gossypium hirsutum L. cv Acala SJ2) plants were exposed to three levels of osmotic or matric potentials. The first was obtained by salt and the latter by withholding irrigation water. Plants were acclimated to the two stress types by reducing the rate of stress development by a factor of 4 to 7. CO₂ assimilation was then determined on acclimated and nonacclimated plants. The decrease of CO₂ assimilation in salinity-exposed plants was significantly less in acclimated as compared with nonacclimated plants. Such a difference was not found under water stress at ambient CO₂ partial pressure. The slopes of net CO₂ assimilation versus intercellular CO₂ partial pressure, for the initial linear portion of this relationship, were increased in plants acclimated to salinity of −0.3 and −0.6 megapascal but not in nonacclimated plants. In plants acclimated to water stress, this change in slopes was not significant. Leaf osmotic potential was reduced much more in acclimated than in nonacclimated plants, resulting in turgor maintenance even at −0.9 megapascal. In nonacclimated plants, turgor pressure reached zero at approximately −0.5 megapascal. The accumulation of Cl⁻ and Na⁺ in the salinity-acclimated plants fully accounted for the decrease in leaf osmotic potential. The rise in concentration of organic solutes comprised only 5% of the total increase in solutes in salinity-acclimated and 10 to 20% in water-stress-acclimated plants. This acclimation was interpreted in light of the higher protein content per unit leaf area and the enhanced ribulose bisphosphate carboxylase activity. At saturating CO₂ partial pressure, the declined inhibition in CO₂ assimilation of stress-acclimated plants was found for both salinity and water stress.     

Simulating Growth and Root-shoot Partitioning in Prairie Grasses Under Elevated Atmospheric CO2and Water Stress

We constructed a model simulating growth, shoot-root partitioning,plant nitrogen (N) concentration and total non-structural carbohydratesin perennial grasses. Carbon (C) allocation was based on theconcept of a functional balance between root and shoot growth,which responded to variable plant C and N supplies. Interactionsbetween the plant and environment were made explicit by wayof variables for soil water and soil inorganic N. The modelwas fitted to data on the growth of two species of perennialgrass subjected to elevated atmospheric CO₂and water stresstreatments. The model exhibited complex feedbacks between plantand environment, and the indirect effects of CO₂and water treatmentson soil water and soil inorganic N supplies were important ininterpreting observed plant responses. Growth was surprisinglyinsensitive to shoot-root partitioning in the model, apparentlybecause of the limited soil N supply, which weakened the expectedpositive relationship between root growth and total N uptake.Alternative models for the regulation of allocation betweenshoots and roots were objectively compared by using optimizationto find the least squares fit of each model to the data. Regulationby various combinations of C and N uptake rates, C and N substrateconcentrations, and shoot and root biomass gave nearly equivalentfits to the data, apparently because these variables were correlatedwith each other. A partitioning function that maximized growthpredicted too high a root to shoot ratio, suggesting that partitioningdid not serve to maximize growth under the conditions of theexperiment.Copyright 1998 Annals of Botany Company plant growth model, optimization, nitrogen, non-structural carbohydrates, carbon partitioning, elevated CO₂, water stress,Pascopyrum smithii,Bouteloua gracilis, photosynthetic pathway, maximal growth     

Projections of Water Stress Based on an Ensemble of Socioeconomic Growth and Climate Change Scenarios: A Case Study in Asia

The sustainability of future water resources is of paramount importance and is affected by many factors, including population, wealth and climate. Inherent in current methods to estimate these factors in the future is the uncertainty of their prediction. In this study, we integrate a large ensemble of scenarios—internally consistent across economics, emissions, climate, and population—to develop a risk portfolio of water stress over a large portion of Asia that includes China, India, and Mainland Southeast Asia in a future with unconstrained emissions. We isolate the effects of socioeconomic growth from the effects of climate change in order to identify the primary drivers of stress on water resources. We find that water needs related to socioeconomic changes, which are currently small, are likely to increase considerably in the future, often overshadowing the effect of climate change on levels of water stress. As a result, there is a high risk of severe water stress in densely populated watersheds by 2050, compared to recent history. There is strong evidence to suggest that, in the absence of autonomous adaptation or societal response, a much larger portion of the region’s population will live in water-stressed regions in the near future. Tools and studies such as these can effectively investigate large-scale system sensitivities and can be useful in engaging and informing decision makers.     

Modeling Forest Mortality Caused by Drought Stress: Implications for Climate Change

Climate change is expected to affect forest landscape dynamics in many ways, but it is possible that the most important direct impact of climate change will be drought stress. We combined data from weather stations and forest inventory plots (FIA) across the upper Great Lakes region (USA) to study the relationship between measures of drought stress and mortality for four drought sensitivity species groups using a weight-of-evidence approach. For all groups, the model that predicted mortality as a function of mean drought length had the greatest plausibility. Model tests confirmed that the models for all groups except the most drought tolerant had predictive value. We assumed that no relationship exists between drought and mortality for the drought-tolerant group. We used these empirical models to develop a drought extension for the forest landscape disturbance and succession model LANDIS-II, and applied the model in Oconto county, Wisconsin (USA) to assess the influence of drought on forest dynamics relative to other factors such as stand-replacing disturbance and site characteristics. The simulations showed that drought stress does affect species composition and total biomass, but effects on age classes, spatial pattern, and productivity were insignificant. We conclude that (for the upper Midwest) (1) a drought-induced tree mortality signal can be detected using FIA data, (2) tree species respond primarily to the length of drought events rather than their severity, (3) the differences in drought tolerance of tree species can be quantified, (4) future increases in drought can potentially change forest composition, and (5) drought is a potentially important factor to include in forest dynamics simulations because it affects forest composition and carbon storage.     

Bacteria and Fungi Respond Differently to Multifactorial Climate Change in a Temperate Heathland,Traced with 13C-Glycine and FACE CO2

It is vital to understand responses of soil microorganisms to predicted climate changes, as these directly control soil carbon (C) dynamics. The rate of turnover of soil organic carbon is mediated by soil microorganisms whose activity may be affected by climate change. After one year of multifactorial climate change treatments, at an undisturbed temperate heathland, soil microbial community dynamics were investigated by injection of a very small concentration (5.12 µg C g⁻¹ soil) of ¹³C-labeled glycine (¹³C₂, 99 atom %) to soils in situ. Plots were treated with elevated temperature (+1°C, T), summer drought (D) and elevated atmospheric carbon dioxide (510 ppm [CO2]), as well as combined treatments (TD, TCO2, DCO2 and TDCO2). The ¹³C enrichment of respired CO₂ and of phospholipid fatty acids (PLFAs) was determined after 24 h. ¹³C-glycine incorporation into the biomarker PLFAs for specific microbial groups (Gram positive bacteria, Gram negative bacteria, actinobacteria and fungi) was quantified using gas chromatography-combustion-stable isotope ratio mass spectrometry (GC-C-IRMS).Gram positive bacteria opportunistically utilized the freshly added glycine substrate, i.e. incorporated ¹³C in all treatments, whereas fungi had minor or no glycine derived ¹³C-enrichment, hence slowly reacting to a new substrate. The effects of elevated CO₂ did suggest increased direct incorporation of glycine in microbial biomass, in particular in G⁺ bacteria, in an ecosystem subjected to elevated CO₂. Warming decreased the concentration of PLFAs in general. The FACE CO₂ was ¹³C-depleted (δ¹³C = 12.2‰) compared to ambient (δ¹³C = ∼−8‰), and this enabled observation of the integrated longer term responses of soil microorganisms to the FACE over one year. All together, the bacterial (and not fungal) utilization of glycine indicates substrate preference and resource partitioning in the microbial community, and therefore suggests a diversified response pattern to future changes in substrate availability and climatic factors.     

Effect of Elevated CO2 Concentration on Leaf Structure of Brassica Juncea under Water Stress

Study on the effect of elevated CO₂ concentration on leaf structure of Brassica juncea L. cv. Bio-141 (95) under moisture stress revealed, that CO₂ elevated to 600 mol mol^–1 increased the length of epidermal cel and length of palisade parenchyma cells, and induced larger chloroplasts and more oval shaped starch granules in comparison with plants grown at ambient CO₂ concentration. This increase in structural sink size helped in check feedback inhibition by excessive photoassimilate which was subsequently used to compensate the adverse moisture stress effect in B. juncea leaves.     

Complex Spatiotemporal Responses of Global Terrestrial Primary Production to Climate Change and Increasing Atmospheric CO2 in the 21st Century

Quantitative information on the response of global terrestrial net primary production (NPP) to climate change and increasing atmospheric CO₂ is essential for climate change adaptation and mitigation in the 21^st century. Using a process-based ecosystem model (the Dynamic Land Ecosystem Model, DLEM), we quantified the magnitude and spatiotemporal variations of contemporary (2000s) global NPP, and projected its potential responses to climate and CO₂ changes in the 21^st century under the Special Report on Emission Scenarios (SRES) A2 and B1 of Intergovernmental Panel on Climate Change (IPCC). We estimated a global terrestrial NPP of 54.6 (52.8–56.4) PgC yr⁻¹ as a result of multiple factors during 2000–2009. Climate change would either reduce global NPP (4.6%) under the A2 scenario or slightly enhance NPP (2.2%) under the B1 scenario during 2010–2099. In response to climate change, global NPP would first increase until surface air temperature increases by 1.5°C (until the 2030s) and then level-off or decline after it increases by more than 1.5°C (after the 2030s). This result supports the Copenhagen Accord Acknowledgement, which states that staying below 2°C may not be sufficient and the need to potentially aim for staying below 1.5°C. The CO₂ fertilization effect would result in a 12%–13.9% increase in global NPP during the 21^st century. The relative CO₂ fertilization effect, i.e. change in NPP on per CO₂ (ppm) bases, is projected to first increase quickly then level off in the 2070s and even decline by the end of the 2080s, possibly due to CO₂ saturation and nutrient limitation. Terrestrial NPP responses to climate change and elevated atmospheric CO₂ largely varied among biomes, with the largest increases in the tundra and boreal needleleaf deciduous forest. Compared to the low emission scenario (B1), the high emission scenario (A2) would lead to larger spatiotemporal variations in NPP, and more dramatic and counteracting impacts from climate and increasing atmospheric CO₂.