Abstracts on Global Climate Change

Aug 2004

High-resolution vegetation and climate change associated with Pliocene Australopithecus afarensis

Bonnefille, R Potts, R Chalie, F Jolly, D Peyron, O


Plio-Pleistocene global climate change is believed to have had an important influence on local habitats and early human evolution in Africa. Responses of hominin lineages to climate change have been difficult to test, however, because this procedure requires well documented evidence for connections between global climate and hominin environment. Through high-resolution pollen data from Hadar, Ethiopia, we show that the hominin Australopithecus afarensis accommodated to substantial environmental variability between 3.4 and 2.9 million years ago. A large biome shift, up to 5degreesC cooling, and a 200- to 300-mm/yr rainfall increase occurred just before 3.3 million years ago, which is consistent with a global marine delta(18)O isotopic shift.

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The gypsy moth life stage model: landscape-wide estimates of gypsy moth establishment using a multi-generational phenology model

Gray, DR


A multi-generational model of gypsy moth phenology was developed from existing literature and used to assess the risk of establishment of this exotic pest across North America based on the suitability of 4457 locations in satisfying the temperature requirements for seasonal development. Approximately 595 million hectares of North America is estimated to be climatically suitable for gypsy moth establishment. Limits to the potential range exist in the southern United States because of limits to diapause development, and in northern Canada because of slower prediapause and larval development. A 1.5 degreesC increase in mean daily maximum and minimum temperatures, as might occur with global climate change, would result in a range expansion in the north, a range contraction in the south, and a net increase in range of approximately 16%. The model is described and the probable limitations to establishment are discussed. Crown Copyright (C) 2004 Published by Elsevier B.V. All rights reserved.

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Environmental magnetic record of paleoclimate change from the Eocene-Oligocene stratotype section, Massignano, Italy

Jovane, L Florindo, F Dinares-Turell, J Turell, S


A high-resolution environmental magnetic study of the Massignano section, Italy (Global Stratotype Section and Point for the Eocene-Oligocene boundary), has been performed to test whether a clear magnetic signature associated with climatic change is recognizable in this record. Our results reveal the existence of alternating intervals with high and low magnetic mineral concentrations similar to the pattern of rock magnetic property variations observed from an environmental magnetic study of the CIROS-1 sediment core from Antarctica. These results suggest that an external forcing mechanism drove the sedimentary response to global climate change prior to the major Oi-1 cooling event at the Eocene-Oligocene boundary.

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Nitrate assimilation in plant shoots depends on photorespiration

Rachmilevitch, S Cousins, AB Bloom, AJ


Photorespiration, a process that diminishes net photosynthesis by approximate to25% in most plants, has been viewed as the unfavorable consequence of plants having evolved when the atmosphere contained much higher levels of carbon dioxide than it does today. Here we used two independent methods to show that exposure of Arabidopsis and wheat shoots to conditions that inhibited photorespiration also strongly inhibited nitrate assimilation. Thus, nitrate assimilation in both dicotyledonous and monocotyledonous species depends on photorespiration. This previously undescribed role for photorespiration (i) explains several responses of plants to rising carbon dioxide concentrations, including the inability of many plants to sustain rapid growth under elevated levels of carbon dioxide; and (h) raises concerns about genetic manipulations to diminish photorespiration in crops.

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Larval salamander response to uv radiation and predation risk: Color change and microhabitat use

Garcia, TS Stacy, J Sih, A


Adaptations to avoid or cope with harmful ultraviolet radiation (UVR) have evolved in many amphibian species. Sublethal levels of UVR can select for simple responses in larval amphibians, such as dark pigmentation or preference for UVR-protected microhabitats (i.e., under cover or in deep water). This Study focuses on color response to UVR, and whether avoidance behaviors like refuge use and depth choice depend on larval body color. We quantified responses to ambient levels of UVR in four experiments in semi-field conditions using two sister species of salamander larvae that differ in their evolutionary history of UVR exposure. Both Ambystoma barbouri and A. texanum larvae darkened in response to UVR, and when given the choice of refuge, significantly increased the proportion of time spent in hiding. Additionally, both species used deeper microhabitats when exposed to UVR, but only A. barbouri larvae showed a preference for shallow waters when UVR was blocked out. Neither of these behaviors seemed to be color dependent, with larvae from both species taking refuge and preferring deep water in the presence of UVR, regardless of body color. Interesting behavioral trade-offs arose when larvae were confronted with conflicting selection pressures from UVR and predation risk. Risk from predatory fish forces larvae to shallow areas, while UVR forces larvae into deeper water. Thus, the combination of the two selection pressures creates a conflict in optimal depth choice. Faced with this conflict, A. barbouri preferred deeper, risky areas to shallow water with high UVR exposure. Ambystoma texanum responded to predation risk with a preference for shallow water, but did not significantly alter depth in response to UVR. Given the opportunity to mediate exposure to UVR and predation risk by altering depth choices, neither species changed color in response to either UVR or predation risk. Overall, these changes in behavior and color may affect larval feeding, competition, and predation rates and could thus alter aquatic community structure.

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Biodiversity, biosphere reserves, and the big apple - A study of the New York Metropolitan Region

Solecki, WD Rosenzweig, C


The objectives of this article were to assess the dimensions of biodiversity-urban society interactions within the New York Metropolitan Region, a 31-county area with a population of 21.5 million, and to explore pathways to reconcile dysfunctional relationships between these two ever-entwined systems. The article builds on the premise that urban biodiversity exists at a crucial nexus of ecological and societal interactions, linking local, regional, and global scales, and that urban ecologies are projected to become even more dynamic in the future, particularly as a result of global climate change. The pathway proposed to reconcile the biodiversity-urban society relationships is the incorporation of biosphere reserve strategies into regional environmental planning efforts focused on the New York/New Jersey Harbor/Estuary specifically and on the greater New York Metropolitan Region in general. The concepts of the “ecological footprint” and vulnerability to global environmental change are used to analyze the current interactions between biodiversity and urban society, and to evaluate the efficacy of adopting biosphere reserve strategies in the region. New York has long been at the forefront of American environmentalism and landscape planning. Coupled with this history is a still small but growing interest in regional environmental planning efforts (e.g., the U.S. EPA Harbor Estuary Program) and green infrastructure (e.g., the 2002 Humane Metropolis Conference organized by the Ecological Cities Project). The research presented here aims to contribute to these nascent activities. As a megacity, New York may serve as a model for other major cities of the world.

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Photosynthetic down-regulation over long-term CO2 enrichment in leaves of sour orange (Citrus aurantium) trees

Adam, NR Wall, GW Kimball, BA Idso, SB Webber, AN

NEW PHYTOLOGIST 163:2 341-347

Understanding how trees are affected by a long-term increase in atmospheric CO2 is crucial to understanding the future impact of global climate change. Measurements of photosynthetic characteristics were made in sour orange trees (Citrus aurantium) growing under an enhanced CO2 atmosphere and N-replete soil for 14 yr to determine whether photosynthetic down-regulation had occurred. Photosynthesis, A : C-i gas exchange relationships and Rubisco activity and content were measured throughout the 14th year of the experiment. The CO2-induced enhancement ratio of photosynthesis was calculated and compared with estimates of the enhancement of cumulative wood biomass production. Content of the large subunit of Rubisco was significantly reduced by CO2 enrichment indicating that down-regulation had occurred. A high correlation between the CO2-induced enhancement of photosynthesis and the enhancement of cumulative wood biomass production suggested that the decline in wood biomass production was closely related to the decline in photosynthesis. These results indicate that long-term CO2 enrichment can result in photosynthetic down-regulation in leaves of trees, even under nonlimiting N conditions. (C) New Phytologist (2004). No claim to original US government works.

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Response of different decomposer communities to the manipulation of moisture availability: potential effects of changing precipitation patterns

Taylor, AR Schroter, D Pflug, A Wolters, V


The potential impacts of changes in precipitation patterns associated with global climate change on the relationship between soil community diversity and litter decomposition were investigated. For a period of ca. 5 months, two decomposer communities in litterbags (1000 and 45 mum mesh size) containing spruce litter were subjected to two irrigation treatments: constant and fluctuating (drying/rewetting) moisture conditions. The latter were expected to induce moisture stress on the decomposer communities. The two mesh sizes were used to exclude different faunal components from the decomposer communities. The 1000 mum mesh excluded only the macrofauna, whereas the 45 mum mesh excluded both the macro- and mesofauna. In the short-term perspective of the present study, mesofauna abundance showed no response to imposed fluctuating moisture conditions. Irrespective of the presence of mesofauna, mass loss, microbial biomass and the control mechanisms, regulating carbon mineralization appeared unaffected by fluctuating moisture conditions. The reduction in the functional/structural diversity of the decomposer communities in the 45 mum litterbags resulted in strongly increased Nematoda abundance but it did not alter the response of Nematoda to fluctuating moisture conditions. Processes in the nitrogen (N)-cycle and mass loss were sensitive indicators of changes in the structural and functional complexity of decomposer communities. However, a negative effect of fluctuating moisture conditions on extractable N was coupled to the presence of mesofauna. Extremes in rainfall patterns, generated by climate change, may have a negative impact on the availability of nutrients, particularly N, for plants. This effect could be amplified by an additional impoverishment in the structural and functional complexity of the respective decomposer communities.

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Global climate change and infectious disease

Parola, R Raoult, D


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Cell death and degeneration in the symbiotic dinoflagellates of the coral Stylophora pistillata during bleaching

Franklin, DJ Hoegh-Guldberg, P Jones, RJ Berges, JA


Rising sea temperatures are increasing the incidences of mass coral bleaching (the dissociation of the coral-algal symbiosis) and coral mortality. In this study, the effects of bleaching (induced by elevated light and temperature) on the condition of symbiotic dinoflagellates (Symbiodinium sp.) within the tissue of the hard coral Stylophora pistillata (Esper) were assessed using a suite of techniques. Bleaching of S. pistillata was accompanied by declines in the maximum potential quantum yield of photosynthesis (F-v/F-m, measured using pulse amplitude modulated [PAM] fluorometry), an increase in the number of Sytox-green-stained algae (indicating compromised algal membrane integrity and cell death), an increase in 2’,7’-dichlorodihydrofluroscein diacetate (H(2)DCFDA)stained algae (indicating increased oxidative stress), as well as ultrastructural changes (vacuolisation, losses of chlorophyll, and an increase in accumulation bodies). Algae expelled from S. pistillata exhibited a complete disorganisation of cellular contents; expelled cells contained only amorphous material. In situ samples taken during a natural mass coral bleaching event on the Great Barrier Reef in February 2002 also revealed a high number of Sytox-labelled algae cells in symbio. Dinoflagellate degeneration during bleaching seems to be similar to the changes resulting from senescence-phase cell death in cultured algae. These data support a role for oxidative stress in the mechanism of coral bleaching and highlight the importance of algal degeneration during the bleaching of a reef coral.

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Identity and diversity of coral endosymbionts (zooxanthellae) from three Palauan reefs with contrasting bleaching, temperature and shading histories

Fabricius, KE Mieog, JC Colin, PL Idip, D Van Oppen, MJH

MOLECULAR ECOLOGY 13:8 2445-2458

The potential of corals to associate with more temperature-tolerant strains of algae (zooxanthellae, Symbiodinium) can have important implications for the future of coral reefs in an era of global climate change. In this study, the genetic identity and diversity of zooxanthellae was investigated at three reefs with contrasting histories of bleaching mortality, water temperature and shading, in the Republic of Palau (Micronesia). Single-stranded conformation polymorphism and sequence analysis of the ribosomal DNA internal transcribed spacer (ITS)1 region was used for genotyping. A chronically warm but partly shaded coral reef in a marine lake that is hydrographically well connected to the surrounding waters harboured only two single-stranded conformation polymorphism profiles (i.e. zooxanthella communities). It consisted only of Symbiodinium D in all 13 nonporitid species and two Porites species investigated, with the remaining five Porites harbouring C.. Despite the high temperature in this lake (> 0.5degrees above ambient), this reef did not suffer coral mortality during the (1998) bleaching event, however, no bleaching-sensitive coral families and genera occur in the coral community. This setting contrasts strongly with two other reefs with generally lower temperatures, in which 10 and 12 zooxanthella communities with moderate to low proportions of clade D zooxanthellae were found. The data indicate that whole coral assemblages, when growing in elevated seawater temperatures and at reduced irradiance, can be composed of colonies associated with the more thermo-tolerant clade D zooxanthellae. Future increases in seawater temperature might, therefore, result in an increasing prevalence of Symbiodinium phylotype D in scleractinian corals, possibly associated with a loss of diversity in both zooxanthellae and corals.

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Quantifying the water vapour feedback associated with post-Pinatubo global cooling

Forster, PMD Collins, M


There is an ongoing important debate about the role of water vapour in climate change. Predictions of future climate change depend strongly on the magnitude of the water vapour feedback and until now models have almost exclusively been relied upon to quantify this feedback. In this work we employ observations of water vapour changes, together with detailed radiative calculations to estimate the water vapour feedback for the case of the Mt. Pinatubo eruption. We then compare our observed estimate with that calculated from a relatively large ensemble of simulations from a complex coupled climate model. We calculate an observed water vapour feedback parameter of -1.6 Wm(-2) K-1, with uncertainty placing the feedback parameter between -0.9 to -2.5 Wm(-2) K-1. The uncertain is principally from natural climate variations that contaminate the volcanic cooling. The observed estimates are consistent with that found in the climate model, with the ensemble average model feedback parameter being -2.0 Wm(-2) K-1, with a 5-95% range of -0.4 to -3.6 Wm(-2) K-1 (as in the case of the observations, the spread is due to an inability to separate the forced response from natural variability). However, in both the upper troposphere and Southern Hemisphere the observed model water vapour response differs markedly from the observations. The observed range represents a 40%-400% increase in the magnitude of surface temperature change when compared to a fixed water vapour response and is in good agreement with values found in other studies. Variability, both in the observed value and in the climate model’s feedback parameter, between different ensemble members, suggests that the long-term water vapour feedback associated with global climate change could still be a factor of 2 or 3 different than the mean observed value found here and the model water vapour feedback could be quite different from this value; although a small water vapour feedback appears unlikely. We also discuss where in the atmosphere water vapour changes have their largest effect on surface climate.

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Mycorrhizal fungi as drivers of ecosystem processes in heathland and boreal forest biomes

Read, DJ Leake, JR Perez-Moreno, J


The importance of mycorrhizas in heathland and boreal forest biomes, which together cover much of the landmass of the Northern Hemisphere and store most of the global stocks of carbon, is reviewed. The taxonomic affinities of the organisms forming these symbiotic partnerships are assessed, and the distinctive structural features of the ericoid mycorrhizas of heathland dwarf shrubs and the ectomycorrhizas of boreal forest trees are described. It is stressed that neither in terms of the geographical distribution of the plants nor in terms of the occurrence of their characteristic mycorrhizas in the soil profile should these biomes be considered to be mutually exclusive. What unites them is their apparent affinity for acidic organic soils of inherently low accessibility of the major nutrients nitrogen (N) and phosphorus (P). These properties relate directly to the nature of the nutrient-poor recalcitrant litter produced by their host plants and through positive-feedback mechanisms that are reinforced by selective removal of labile nutrients by the mycorrhizas. We suggest that coevolution of these plant litter traits with mycorrhizal associations that are adapted to them has been one of the defining features of these ecosystems. Ericoid and ectomycorrhizal fungi have biochemical and physiological attributes that make them highly efficient at scavenging for organic sources of N and P in surface soil horizons. In so doing, they restrict supplies of these elements to the decomposer communities. Case studies involving exploitation of N and P in defined organic substrates are described. In both biomes the dominant plants depend upon the abilities of their fungal partners to recover nutrients, so the symbioses control nutrient cycles, productivity, species composition, and functioning of these ecosystems. It is in this context that the fungal symbionts are here considered to be drivers of nutritional processes in their respective biomes. Through their influences upon the quality of carbon residues mycorrhizal fungi must also affect the sink-source balance for this key element in soil. There is an urgent need for the evaluation of the relative contributions of symbiotic and saprotrophic components of the microflora to the processes of carbon storage and cycling in these biomes, particularly in the context of global climate change and impacts of anthropogenic pollutant N deposition.

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Adaptation to temperate climates

Bradshaw, WE Zani, PA Holzapfel, CM

EVOLUTION 58:8 1748-1762

Only model organisms live in a world of endless summer. Fitness at temperate latitudes reflects the ability of organisms in nature to exploit the favorable season, to mitigate the effects of the unfavorable season, and to make the timely switch from one life style to the other. Herein, we define fitness as Ry, the year-long cohort replacement rate across all four seasons, of the mosquito, Wyeomyia smithii, reared in its natural microhabitat in processor-controlled environment rooms. First, we exposed cohorts of W. smithii, from southern, midlatitude, and northern populations (30-50degreesN) to southern and northern thermal years during which we factored out evolved differences in photoperiodic response. We found clear evidence of evolved differences in heat and cold tolerance among populations. Relative cold tolerance of northern populations became apparent when populations were stressed to the brink of extinction; relative heat tolerance of southern populations became apparent when the adverse effects of heat could accumulate over several generations. Second, we exposed southern, midlatitude, and northern populations to natural, midlatitude day lengths in a thermally benign midlatitude thermal year. We found that evolved differences in photoperiodic response (1) prevented the timely entry of southern populations into diapause resulting in a 74% decline in fitness, and (2) forced northern populations to endure a warm-season diapause resulting in an 88% decline in fitness. We argue that reciprocal transplants across latitudes in nature always confound the effects of the thermal and photic environment on fitness. Yet, to our knowledge, no one has previously held the thermal year constant while varying the photic year. This distinction is crucial in evaluating the potential impact of climate change. Because global warming in the Northern Hemisphere is proceeding faster at northern than at southern latitudes and because this change represents an amelioration of the thermal environment and a concomitant increase in the duration of the growing season, we conclude that there should be more rapid evolution of photoperiodic response than of thermal tolerance as a consequence of global warming among northern, temperate ectotherms.

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Elevated CO2 alters birch resistance to Lagomorpha herbivores

Mattson, WJ Kuokkanen, K Niemela, P Julkunen-Tiitto, R Kellomaki, S Tahvanainen, J


We studied the three-way interaction of elevated CO2, nitrogen (N), and temperature (T), and the two-way interaction of elevated CO2 and early-season defoliation on the secondary chemistry and resistance of Eurasian silver birch (Betula pendula) and North American paper birch (B. papyrifera) against the Eurasian hare (Lepus timidus) and the North American eastern cottontail rabbit (Sylvilagus floridanus), respectively. Elevated CO2 decreased the palatability of winter-dormant silver and paper birch stems to both hares and rabbits, respectively. But the effect on hares was only apparent at intermediate levels of N fertilization. Elevated T had no effect on palatability. The effects of elevated CO2, N, and T on levels of silver birch bark phenolics and terpenoids were dominated by two-way interactions between N and CO2, and N and T. Generally, however, N amendments elicited a parabolic response in carbon partitioning to most biosynthetic classes of silver birch phenolics (i.e. highest concentrations occurring at intermediate N). CO2 elevation was most enhancing at highest levels of N. On the other hand, T increases, more often than not, elicited reductions in phenolics, but especially so at the highest N level. In the case of B. papyrifera, elevated CO2 increased carbon partitioning to Folin-Denis stem and branch phenolics and condensed tannins. Early-season defoliation, on the other hand, had no effect on phenolics and tannins but lowered both N and energy levels of branches. Elevated CO2 substantially ameliorated the negative effects of severe defoliation on tree growth. These results support the hypothesis that continuing anthropogenic alterations of the atmosphere may trigger significant changes in plant phenotypic resistance to mammalian herbivores owing to an increasing net carbon balance between the highly vagile supply and demand capacities of plant carbon sources and sinks.

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Determination of black carbon in natural organic matter by chemical oxidation and solid-state C-13 Nuclear Magnetic Resonance spectroscopy

Simpson, MJ Hatcher, PG


Black carbon is an important component of natural organic matter that may play a significant role in global climate change. However, the complexity of natural organic matter has resulted in a milieu of methods and accompanying black carbon values that make it difficult to delineate the proportion of black carbon in soil and sedimentary total carbon budgets, Here we report on a chemical oxidation method that removes lignin and then facilitates black carbon to be estimated from solid-state C-13 Nuclear Magnetic Resonance (NMR) spectroscopy. The resulting black carbon values are lower in comparison to those reported by other researchers but may be a more accurate method for estimating black carbon in a range of natural organic matter samples from different environments. (C) 2004 Elsevier Ltd. All rights reserved.

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Simulated long-term changes in river discharge and soil moisture due to global warming

Manabe, S Milly, PCD Wetherald, R


By use of a coupled ocean-atmosphere-land model, this study explores the changes of water availability, as measured by river discharge and soil moisture, that could occur by the middle of the 21st century in response to combined increases of greenhouse gases and sulphate aerosols based upon the “IS92a” scenario. In addition, it presents the simulated change in water availability that might be realized in a few centuries in response to a quadrupling of CO2, concentration in the atmosphere. Averaging the results over extended periods, the radiatively forced changes, which are very similar between the two sets of experiments, were successfully extracted. The analysis indicates that the discharges from Arctic rivers such as the Mackenzie and Ob’ increase by up to 20% (of the pre-Industrial Period level) by the middle of the 21st century and by up to 40% or more in a few centuries. In the tropics, the discharges from the Amazonas and Ganga-Brahmaputra rivers increase substantially. However, the percentage changes in runoff from other tropical and many mid-latitude rivers are smaller, with both positive and negative signs. For soil moisture, the results of this study indicate reductions during much of the year in many semiarid regions of the world, such as the southwestern region of North America, the northeastern region of China, the Mediterranean coast of Europe, and the grasslands of Australia and Africa. As a percentage, the reduction is particularly large during the dry season. From middle to high latitudes of the Northern Hemisphere, soil moisture decreases in Summer but increases in winter.

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The effects of infrared loading and water table on soil energy fluxes in northern peatlands

Noormets, A Chen, JQ Bridgham, SD Weltzin, JF Pastor, J Dewey, B LeMoine, J

ECOSYSTEMS 7:5 573-582

Increased radiative forcing is an inevitable part of global climate change, yet little is known of its potential effects on the energy fluxes in natural ecosystems. To simulate the conditions of global warming, we exposed peat monoliths (depth, 0.6 m; surface area, 2.1 m(2)) from a bog and fen in northern Minnesota, USA, to three infrared (IR) loading (ambient, +45, and +90 W m(-2)) and three water table (-16, -20, and -29 cm in bog and -1, -10 and -18 cm in fen) treatments, each replicated in three mesocosm plots. Net radiation (Rn) and soil energy fluxes at the top, bottom, and sides of the mesocosms were measured in 1999, 5 years after the treatments had begun. Soil heat flux (G) increased proportionately with IR loading, comprising about 3%-8% of Rn. In the fen, the effect of IR loading on G was modulated by water table depth, whereas in the bog it was not. Energy dissipation from the mesocosms occurred mainly via vertical exchange with air, as well as with deeper soil layers through the bottom of the mesocosms, whereas lateral fluxes were 10-20-fold smaller and independent of IR loading and water table depth. The exchange with deeper soil layers was sensitive to water table depth, in contrast to G, which responded primarily to IR loading. The qualitative responses in the bog and fen were similar, but the fen displayed wider seasonal variation and greater extremes in soil energy fluxes. The differences of G in the bog and fen are attributed to differences in the reflectance in the long waveband as a function of vegetation type, whereas the differences in soil heat storage may also depend on different soil properties and different water table depth at comparable treatments. These data suggest that the ecosystem-dependent controls over soil energy fluxes may provide an important constraint on biotic response to climate change.

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