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1.
MATS G. ÖQUIST TOBIAS SPARRMAN† LEIF KLEMEDTSSON‡ STINA HARRYSSON DROTZ HARALD GRIP JÜRGEN SCHLEUCHER§ MATS NILSSON 《Global Change Biology》2009,15(11):2715-2722
Soil processes in high-latitude regions during winter are important contributors to global carbon circulation, but our understanding of the mechanisms controlling these processes is poor and observed temperature response coefficients of CO2 production in frozen soils deviate markedly from thermodynamically predicted responses (sometimes by several orders of magnitude). We investigated the temperature response of CO2 production in 23 unfrozen and frozen surface soil samples from various types of boreal forests and peatland ecosystems and also measured changes in water content in them after freezing. We demonstrate that deviations in temperature responses at subzero temperatures primarily emanates from water deficiency caused by freezing of the soil water, and that the amount of unfrozen water is mainly determined by the quality of the soil organic matter, which is linked to the vegetation cover. Factoring out the contribution of water limitation to the CO2 temperature responses yields response coefficients that agree well with expectations based on thermodynamic theory concerning biochemical temperature responses. This partitioning between a pure temperature response and the effect of water availability on the response of soil CO2 production at low temperatures is crucial for a thorough understanding of low-temperature soil processes and for accurate predictions of C-balances in northern terrestrial ecosystems. 相似文献
2.
Sanna Saarnio Jukka Alm Pertti J. Martikainen & Jouko Silvola 《Journal of Ecology》1998,86(2):261-268
1 In a glasshouse experiment we studied the effect of raised CO2 concentration (720 p.p.m.) on CH4 emission at natural boreal peat temperatures using intact cores of boreal peat with living vascular plants and Sphagnum mosses. After the end of the growing season half of the cores were kept unnaturally warm (17–20 °C). The potential for CH4 production and oxidation was measured at the end of the emission experiment.
2 The vascular cores ('Sedge') consisted of a moss layer with sedges, and the moss cores (' Sphagnum ') of Sphagnum mosses (some sedge seedlings were removed by cutting). Methane efflux was 6–12 times higher from the Sedge cores than from the Sphagnum cores. The release of CH 4 from Sedge cores increased with increasing temperature of the peat and decreased with decreasing temperature. Methane efflux from Sphagnum cores was quite stable independent of the peat temperatures.
3 In both Sedge and Sphagnum samples, CO2 treatment doubled the potential CH4 production but had no effect on the potential CH4 oxidation. A raised concentration of CO2 increased CH4 efflux weakly and only at the highest peat temperatures (17–20 °C).
4 The results suggest that in cool regions, such as boreal wetlands, temperature would restrict decomposition of the extra substrates probably derived from enhanced primary production of mire vegetation under raised CO2 concentrations, and would thus retard any consequent increase in CH4 emission. 相似文献
2 The vascular cores ('Sedge') consisted of a moss layer with sedges, and the moss cores (' Sphagnum ') of Sphagnum mosses (some sedge seedlings were removed by cutting). Methane efflux was 6–12 times higher from the Sedge cores than from the Sphagnum cores. The release of CH
3 In both Sedge and Sphagnum samples, CO
4 The results suggest that in cool regions, such as boreal wetlands, temperature would restrict decomposition of the extra substrates probably derived from enhanced primary production of mire vegetation under raised CO
3.
Snow depth, soil freezing, and fluxes of carbon dioxide, nitrous oxide and methane in a northern hardwood forest 总被引:14,自引:0,他引:14
PETER M. GROFFMAN JANET P. HARDY† CHARLES T. DRISCOLL‡ TIMOTHY J. FAHEY§ 《Global Change Biology》2006,12(9):1748-1760
Soil–atmosphere fluxes of trace gases (especially nitrous oxide (N2 O)) can be significant during winter and at snowmelt. We investigated the effects of decreases in snow cover on soil freezing and trace gas fluxes at the Hubbard Brook Experimental Forest, a northern hardwood forest in New Hampshire, USA. We manipulated snow depth by shoveling to induce soil freezing, and measured fluxes of N2 O, methane (CH4 ) and carbon dioxide (CO2 ) in field chambers monthly (bi-weekly at snowmelt) in stands dominated by sugar maple or yellow birch. The snow manipulation and measurements were carried out in two winters (1997/1998 and 1998/1999) and measurements continued through 2000. Fluxes of CO2 and CH4 showed a strong seasonal pattern, with low rates in winter, but N2 O fluxes did not show strong seasonal variation. The snow manipulation induced soil freezing, increased N2 O flux and decreased CH4 uptake in both treatment years, especially during winter. Annual N2 O fluxes in sugar maple treatment plots were 207 and 99 mg N m−2 yr−1 in 1998 and 1999 vs. 105 and 42 in reference plots. Tree species had no effect on N2 O or CO2 fluxes, but CH4 uptake was higher in plots dominated by yellow birch than in plots dominated by sugar maple. Our results suggest that winter fluxes of N2 O are important and that winter climate change that decreases snow cover will increase soil:atmosphere N2 O fluxes from northern hardwood forests. 相似文献
4.
Located at northern latitudes and subject to large seasonal temperature fluctuations, boreal forests are sensitive to the changing climate, with evidence for both increasing and decreasing productivity, depending upon conditions. Optical remote sensing of vegetation indices based on spectral reflectance offers a means of monitoring vegetation photosynthetic activity and provides a powerful tool for observing how boreal forests respond to changing environmental conditions. Reflectance-based remotely sensed optical signals at northern latitude or high-altitude regions are readily confounded by snow coverage, hampering applications of satellite-based vegetation indices in tracking vegetation productivity at large scales. Unraveling the effects of snow can be challenging from satellite data, particularly when validation data are lacking. In this study, we established an experimental system in Alberta, Canada including six boreal tree species, both evergreen and deciduous, to evaluate the confounding effects of snow on three vegetation indices: the normalized difference vegetation index (NDVI), the photochemical reflectance index (PRI), and the chlorophyll/carotenoid index (CCI), all used in tracking vegetation productivity for boreal forests. Our results revealed substantial impacts of snow on canopy reflectance and vegetation indices, expressed as increased albedo, decreased NDVI values and increased PRI and CCI values. These effects varied among species and functional groups (evergreen and deciduous) and different vegetation indices were affected differently, indicating contradictory, confounding effects of snow on these indices. In addition to snow effects, we evaluated the contribution of deciduous trees to vegetation indices in mixed stands of evergreen and deciduous species, which contribute to the observed relationship between greenness-based indices and ecosystem productivity of many evergreen-dominated forests that contain a deciduous component. Our results demonstrate confounding and interacting effects of snow and vegetation type on vegetation indices and illustrate the importance of explicitly considering snow effects in any global-scale photosynthesis monitoring efforts using remotely sensed vegetation indices. 相似文献
5.
We investigated the relationship between stomatal frequency and a range of atmospheric CO2 concentrations ([CO2 ]atm ) in Betula pubescens and Pinus sylvestris , two important boreal trees in Scandinavia. If strong relationships exist, they can be used to reconstruct past [CO2 ]atm from stomatal frequency of fossil Betula and Pinus leaves. Responses of epidermal characters (stomatal density (SD), epidermal cell density (ED), stomatal index (SI)) to different CO2 concentrations were investigated utilising (1) the lower partial pressure of CO2 at increasing altitudes for B. pubescens , and in herbarium specimens of B. pubescens and P. sylvestris collected during the post-industrial rise of [CO2 ]atm from c. 280 ppmv to c. 360 ppmv in 1997 and (2) concentrations (560 ppmv) and temperatures (3° summer) above present day in the CLIMEX greenhouse experiment. All the results show no clear relationship between SD or SI and [CO2 ] atm for either B. pubescens or P. sylvestris. Most likely there are stronger genetically and environmentally induced factors that affect the development of the leaves. Problems with collecting representative samples from herbarium specimens are discussed. Since the effects of changes in [CO2 ]atm cannot be statistically modelled, B. pubescens and P. sylvestris are not suitable for reconstructing past atmospheric CO2 concentrations from fossil leaves using stomatal density or stomatal index 相似文献
6.
Abstract. Very little attention has been directed at the responses of tropical plants to increases in global atmospheric CO2 concentrations and the potential climatic changes. The available data, from greenhouse and laboratory studies, indicate that the photosynthesis, growth and water use efficiency of tropical plants can increase at higher CO2 concentrations. However, under field conditions abiotic (light, water or nutrients) or biotic (competition or herbivory) factors might limit these responses. In general, elevated atmospheric CO2 concentrations seem to increase plant tolerance to stress, including low water availability, high or low temperature, and photoinhibition. Thus, some species may be able to extend their ranges into physically less favourable sites, and biological interactions may become relatively more important in determining the distribution and abundance of species. Tropical plants may be more narrowly adapted to prevailing temperature regimes than are temperate plants, so expected changes in temperature might be relatively more important in the tropics. Reduced transpiration due to decreased stomatal conductance could modify the effects of water stress as a cue for vegetative or reproductive phenology of plants of seasonal tropical areas. The available information suggests that changes in atmospheric CO2 concentrations could affect processes as varied as plant/herbivore interactions, decomposition and nutrient cycling, local and geographic distributions of species and community types, and ecosystem productivity. However, data on tropical plants are few, and there seem to be no published tropical studies carried out in the field. Immediate steps should be undertaken to reduce our ignorance of this critical area. 相似文献
7.
Terrestrial export of highly bioavailable carbon from small boreal catchments in spring floods 总被引:1,自引:0,他引:1
1. We assessed the terrestrial export of organic carbon, which effectively supported aquatic bacterial production (BP), from small boreal catchments during spring flood. We analysed stream runoff from nine small catchments with different proportions of peat mires and coniferous forests by monitoring the dissolved organic carbon (DOC) flux in combination with conducting bacterial bioassays.
2. Multiple linear regression analysis showed that BP during 7-day-dark bioassays (BP7 ; μg C L−1 day−1 ) was explained by both the quantity and quality (low-molecular weight fractions) of the DOC. BP7 can be used as a measure of export of terrestrial organic carbon that is highly bioavailable.
3. Total export of DOC during spring flood from the different catchments ranged from 20 to 27 kg ha−1 and was negatively correlated to forest cover (%). However, the export of BP7 carbon was positively correlated to forest cover and varied from about 0.1 kg ha−1 in mire-dominated streams to about 0.2 kg ha−1 in forest-dominated streams.
4. The high bioavailability of forest carbon suggests that forests are the main contributors of BP-supporting carbon in boreal streams although mires have higher area-specific export of DOC. 相似文献
2. Multiple linear regression analysis showed that BP during 7-day-dark bioassays (BP
3. Total export of DOC during spring flood from the different catchments ranged from 20 to 27 kg ha
4. The high bioavailability of forest carbon suggests that forests are the main contributors of BP-supporting carbon in boreal streams although mires have higher area-specific export of DOC. 相似文献
8.
Soil CO2 efflux in a boreal pine forest under atmospheric CO2 enrichment and air warming 总被引:3,自引:0,他引:3
The response of forest soil CO2 efflux to the elevation of two climatic factors, the atmospheric concentration of CO2 (↑CO2 of 700 μmol mol−1 ) and air temperature (↑ T with average annual increase of 5°C), and their combination (↑CO2 +↑ T ) was investigated in a 4-year, full-factorial field experiment consisting of closed chambers built around 20-year-old Scots pines ( Pinus sylvestris L.) in the boreal zone of Finland. Mean soil CO2 efflux in May–October increased with elevated CO2 by 23–37%, with elevated temperature by 27–43%, and with the combined treatment by 35–59%. Temperature elevation was a significant factor in the combined 4-year efflux data, whereas the effect of elevated CO2 was not as evident. Elevated temperature had the most pronounced impact early and late in the season, while the influence of elevated CO2 alone was especially notable late in the season. Needle area was found to be a significant predictor of soil CO2 efflux, particularly in August, a month of high root growth, thus supporting the assumption of a close link between whole-tree physiology and soil CO2 emissions. The decrease in the temperature sensitivity of soil CO2 efflux observed in the elevated temperature treatments in the second year nevertheless suggests the existence of soil response mechanisms that may be independent of the assimilating component of the forest ecosystem. In conclusion, elevated atmospheric CO2 and air temperature consistently increased forest soil CO2 efflux over the 4-year period, their combined effect being additive, with no apparent interaction. 相似文献
9.
Elevated concentrations of atmospheric
CO2 protect against and compensate for
O3 damage to photosynthetic tissues of
field-grown wheat 总被引:2,自引:0,他引:2
I. F. McKEE B. J. MULHOLLAND J. CRAIGON C. R. BLACK & S. P. LONG 《The New phytologist》2000,146(3):427-435
The effects of elevated concentrations of atmospheric carbon dioxide and ozone on diurnal patterns of photosynthesis have been investigated in field-grown spring wheat ( Triticum aestivum ). Plants cultivated under realistic agronomic conditions, in open-top chambers, were exposed from emergence to harvest to reciprocal combinations of two carbon dioxide and two ozone treatments: [CO2 ] at ambient (380 μmol mol−1 , seasonal mean) or elevated (692 μmol mol−1 ) levels, [O3 ] at ambient (27 nmol mol−1 , 7 hr seasonal mean) or elevated (61 nmol mol−1 ) levels. After anthesis, diurnal measurements were made of flag-leaf gas-exchange and in vitro Rubisco activity and content. Elevated [CO2 ] resulted in an increase in photoassimilation rate and a loss of excess Rubisco activity. Elevated [O3 ] caused a loss of Rubisco and a decline in photoassimilation rate late in flag-leaf development. Elevated [CO2 ] ameliorated O3 damage. The mechanisms of amelioration included a protective stomatal restriction of O3 flux to the mesophyll, and a compensatory effect of increased substrate on photoassimilation and photosynthetic control. However, the degree of protection and compensation appeared to be affected by the natural seasonal and diurnal variations in light, temperature and water status. 相似文献
10.
THOMAS HICKLER BENJAMIN SMITH I. COLIN PRENTICE† KRISTINA MJÖFORS PAUL MILLER ALMUT ARNETH MARTIN T. SYKES 《Global Change Biology》2008,14(7):1531-1542
Results from free-air CO2 enrichment (FACE) experiments in temperate climates indicate that the response of forest net primary productivity (NPP) to elevated CO2 might be highly conserved across a broad range of productivities. In this study, we show that the LPJ-GUESS dynamic vegetation model reproduces the magnitude of the NPP enhancement at temperate forest FACE experiments. A global application of the model suggests that the response found in the experiments might also be representative of the average response of forests globally. However, the predicted NPP enhancement in tropical forests is more than twice as high as in boreal forests, suggesting that currently available FACE results are not applicable to these ecosystems. The modeled geographic pattern is to a large extent driven by the temperature dependence of the relative affinities of the primary assimilation enzyme (Rubisco) for CO2 and O2 . 相似文献
11.
Sensing of atmospheric CO2 by plants 总被引:15,自引:12,他引:3
K. A. MOTT 《Plant, cell & environment》1990,13(7):731-737
Abstract. Despite recent interest in the effects of high CO2 on plant growth and physiology, very little is known about the mechanisms by which plants sense changes in the concentration of this gas. Because atmospheric CO2 concentration is relatively constant and because the conductance of the cuticle to CO2 is low, sensory mechanisms are likely to exist only for intercellular CO2 concentration. Therefore, responses of plants to changes in atmospheric CO2 will depend on the effect of these changes on intercellular CO2 concentration. Although a variety of plant responses to atmospheric CO2 concentration have been reported, most of these can be attributed to the effects of intercellular CO2 on photosynthesis or stomatal conductance. Short-term and long-term effects of CO2 on photosynthesis and stomatal conductance are discussed as sensory mechanisms for responses of plants to atmospheric CO2 . Available data suggest that plants do not fully realize the potential increases in productivity associated with increased atmospheric CO2 . This may be because of genetic and environmental limitations to productivity or because plant responses to CO2 have evolved to cope with variations in intercellular CO2 caused by factors other than changes in atmospheric CO2 . 相似文献
12.
MICHAEL J. WILKINSON RUSSELL K. MONSON NICOLE TRAHAN STANFIELD LEE ERIN BROWN ROBERT B. JACKSON‡ H. WAYNE POLLEY§ PHILIP A. FAY§ RAY FALL†¶ 《Global Change Biology》2009,15(5):1189-1200
There is considerable interest in modeling isoprene emissions from terrestrial vegetation, because these emissions exert a principal control over the oxidative capacity of the troposphere. We used a unique field experiment that employs a continuous gradient in CO2 concentration from 240 to 520 ppmv to demonstrate that isoprene emissions in Eucalyptus globulus were enhanced at the lowest CO2 concentration, which was similar to the estimated CO2 concentrations during the last Glacial Maximum, compared with 380 ppmv, the current CO2 concentration. Leaves of Liquidambar styraciflua did not show an increase in isoprene emission at the lowest CO2 concentration. However, isoprene emission rates from both species were lower for trees grown at 520 ppmv CO2 compared with trees grown at 380 ppmv CO2 . When grown in environmentally controlled chambers, trees of Populus deltoides and Populus tremuloides exhibited a 30–40% reduction in isoprene emission rate when grown at 800 ppmv CO2 , compared with 400 ppmv CO2 . P. tremuloides exhibited a 33% reduction when grown at 1200 ppmv CO2 , compared with 600 ppmv CO2 . We used current models of leaf isoprene emission to demonstrate that significant errors occur if the CO2 inhibition of isoprene is not taken into account. In order to alleviate these errors, we present a new model of isoprene emission that describes its response to changes in atmospheric CO2 concentration. The model logic is based on assumed competition between cytosolic and chloroplastic processes for pyruvate, one of the principal substrates of isoprene biosynthesis. 相似文献
13.
J. Carlos Cervera José Luis Andrade Eric A. Graham Rafael Durán Paula C. Jackson J. Luis Simá 《Biotropica》2007,39(5):620-627
Mammillaria gaumeri , an endemic cactus from Yucatan, is threatened due to human-mediated habitat fragmentation but knowledge regarding factors that would inform management plans is limited, including information on optimal microhabitats and growth. We studied seasonal patterns of microclimate, net CO2 uptake and growth of adult individuals during the dry, rainy and northwind (late fall to winter) seasons in separate populations located in a coastal dune and in a dry forest. To provide an assay of primary productivity, we measured the production of new axillary buds (areoles) from the apex. We found that patterns of net CO2 uptake in the three seasons were consistent with obligate crassulacean acid metabolism. The reduction in soil water potential and the increase in water vapor pressure deficit led to a reduction in 24-h net CO2 uptake from 18.0 to 1.3 mmol CO2 /m2 , after 30 d of drought. Dry-weight gain was maximal during the rainy season and there was no growth during the dry season, thus seasonal patterns of net CO2 uptake and growth for M. gaumeri reflected soil and atmospheric water contents. Annual dry-weight gain increased linearly with plant size and with total daily photosynthetic photon flux density (PPFD) up to 80 percent of ambient. Maximal growth was in exposed microhabitats receiving 60–80 percent of total ambient PPFD. We hypothesize that low-magnitude disturbances, resulting in more exposed microhabitats, might be beneficial for growth and conservation of adult individuals of this rare species. 相似文献
14.
The cellular basis of guard cell sensing of rising CO2 总被引:5,自引:1,他引:4
S. M. ASSMANN 《Plant, cell & environment》1999,22(6):629-637
Numerous studies conducted on both whole plants and isolated epidermes have documented stomatal sensitivity to CO2 . In general, CO2 concentrations below ambient stimulate stomatal opening, or an inhibition of stomatal closure, while CO2 concentrations above ambient have the opposite effect. The rise in atmospheric CO2 concentrations which has occurred since the industrial revolution, and which is predicted to continue, will therefore alter rates of transpirational water loss and CO2 uptake in terrestrial plants. An understanding of the cellular basis for guard cell CO2 sensing could allow us to better predict, and perhaps ultimately to manipulate, such vegetation responses to climate change. However, the mechanisms by which guard cells sense and respond to the CO2 signal remain unknown. It has been hypothesized that cytosolic pH and malate levels, cytosolic Ca2+ levels, chloroplastic zeaxanthin levels, or plasma-membrane anion channel regulation by apoplastic malate are involved in guard cell perception and response to CO2 . In this review, these hypotheses are discussed, and the evidence for guard cell acclimation to prevailing CO2 concentrations is also considered. 相似文献
15.
Kristen R. Freeman Monte Y. Pescador Sasha C. Reed Elizabeth K. Costello Michael S. Robeson Steven K. Schmidt 《Environmental microbiology》2009,11(3):674-686
Soil-dominated ecosystems, with little or no plant cover (i.e. deserts, polar regions, high-elevation areas and zones of glacial retreat), are often described as 'barren', despite their potential to host photoautotrophic microbial communities. In high-elevation, subnival zone soil (i.e. elevations higher than the zone of continuous vegetation), the structure and function of these photoautotrophic microbial communities remains essentially unknown. We measured soil CO2 flux at three sites (above 3600 m) and used molecular techniques to determine the composition and distribution of soil photoautotrophs in the Colorado Front Range. Soil CO2 flux data from 2002 and 2007 indicate that light-driven CO2 uptake occurred on most dates. A diverse community of Cyanobacteria , Chloroflexi and eukaryotic algae was present in the top 2 cm of the soil, whereas these clades were nearly absent in deeper soils (2–4 cm). Cyanobacterial communities were composed of lineages most closely related to Microcoleus vaginatus and Phormidium murrayi , eukaryotic photoautotrophs were dominated by green algae, and three novel clades of Chloroflexi were also abundant in the surface soil. During the light hours of the 2007 snow-free measurement period, CO2 uptake was conservatively estimated to be 23.7 g C m−2 season−1 . Our study reveals that photoautotrophic microbial communities play an important role in the biogeochemical cycling of subnival zone soil. 相似文献
16.
The distribution pattern of C3 and C4 grasses was studied in eight sites located between 350 m and 2100 m along an altitudinal gradient in Central Argentina. Of 139 taxa fifty-nine are C3 and eighty C4 . Species of the C3 tribes (Stipeae, Poeae, Meliceae, Aveneae, Bromeae and Triticeae) and C3 Paniceae species increase in number at higher elevations; only one C3 species was found below 650 m. C4 Aristideae, Pappophoreae, Eragrostideae, Cynodonteae, Andropogoneae and Paniceae increase at lower altitudes. The floristic crossover point is at about 1500 m; the ground cover cross-over point is at about 1000 m. Analysis of the relationships between % C4 species along the gradient and nine climatic and environmental variables showed the highest correlation with July mean temperature, but all temperature variables show highly significant correlations with % C4 . Correlation with annual rainfall is lower but also significant. These results are consistent with previous research showing the relative importance of C4 grasses as temperature increases. C3 species make a high contribution to relative grass coverage below the C3 /C4 floristic crossover point but are rare below 1000 m. 相似文献
17.
N. N. ARTUS MSU-DOE 《Plant, cell & environment》1990,13(6):575-580
Abstract. Two nonallelic, nuclear recessive mutants of Arabidopsis thaliana (L.) Heynh. which become chlorotic when grown in an atmosphere enriched to 20000 cm3 CO2 m-3 have been isolated. For one of the mutants, chlorosis begins at the veins and gradually spreads to the interveinal regions. A minimum photon flux density of ca 50 μmol m-2 s-1 is required for this response. For the other mutant, the yellowing is independent of the light intensity and begins at the basal regions of the leaves and spreads to the tips. The injurious effects of CO2 seem to be restricted to photosynthetic tissues, since root elongation and callus growth were not inhibited by a high atmospheric CO2 concentration for either mutant. Neither mutant became chlorotic in a low O2 atmosphere that suppressed photorespiration as effectively as the elevated CO2 does. Thus, the mutations do not impose a requirement for photorespiration. The possibilities that the high CO2 -sensitive phenotypes are caused by an effect of CO2 in stomata, on ethylene synthesis, or on mineral uptake are discussed but are considered unlikely. 相似文献
18.
Aims Light-use efficiency (LUE) is an important tool for scaling up local CO2 flux (F CO2) tower observations to regional and global carbon dynamics. Using a data set including F CO2 and environmental factors obtained from an alpine meadow on the Tibetan Plateau, we examined both diurnal and seasonal changes in LUE and the environmental factors controlling these changes. Our objectives were to (i) characterize the diurnal and daily variability of LUE in an alpine meadow, (ii) clarify the causes of this variability, and (iii) explore the possibility of applying the LUE approach to this alpine meadow by examining the relationship between daily LUE and hourly LUE at satellite visiting times.Methods First, we obtained the LUE—the ratio of the gross primary production (GPP) to the absorbed photosynthetically active radiation (APAR)—from the flux tower and meteorological observations. We then characterized the patterns of diurnal and seasonal changes in LUE, explored the environmental controls on LUE using univariate regression analyses and evaluated the effects of diffuse radiation on LUE by assigning weights through a linear programming method to beam photosynthetically active radiation (PAR) and diffuse PAR, which were separated from meteorological observations using an existing method. Finally, we examined the relationships between noontime hourly LUE and daily LUE and those between adjusted noontime hourly and daily LUE because satellites visit the site only once or twice a day, near noon.Important findings The results showed that (i) the LUE of the alpine meadow generally followed the diurnal and seasonal patterns of solar radiation but fluctuated with changes in cloud cover. (ii) The fraction of diffuse light played a dominant role in LUE variation. Daily minimum temperature and vapor pressure deficit also affected LUE variation. (iii) The adjusted APAR, defined as the weighted linear sum of diffuse APAR and beam APAR, was linearly correlated with GPP on different temporal scales. (iv) Midday adjusted LUE was closely related to daily adjusted LUE, regardless of the cloud cover. The results indicated the importance of considering radiation direction when developing LUE-based GPP-estimating models. 相似文献
19.
The global vegetation response to climate and atmospheric CO2 changes between the last glacial maximum and recent times is examined using an equilibrium vegetation model (BIOME4), driven by output from 17 climate simulations from the Palaeoclimate Modelling Intercomparison Project. Features common to all of the simulations include expansion of treeless vegetation in high northern latitudes; southward displacement and fragmentation of boreal and temperate forests; and expansion of drought‐tolerant biomes in the tropics. These features are broadly consistent with pollen‐based reconstructions of vegetation distribution at the last glacial maximum. Glacial vegetation in high latitudes reflects cold and dry conditions due to the low CO2 concentration and the presence of large continental ice sheets. The extent of drought‐tolerant vegetation in tropical and subtropical latitudes reflects a generally drier low‐latitude climate. Comparisons of the observations with BIOME4 simulations, with and without consideration of the direct physiological effect of CO2 concentration on C3 photosynthesis, suggest an important additional role of low CO2 concentration in restricting the extent of forests, especially in the tropics. Global forest cover was overestimated by all models when climate change alone was used to drive BIOME4, and estimated more accurately when physiological effects of CO2 concentration were included. This result suggests that both CO2 effects and climate effects were important in determining glacial‐interglacial changes in vegetation. More realistic simulations of glacial vegetation and climate will need to take into account the feedback effects of these structural and physiological changes on the climate. 相似文献
20.
Maxim Dorodnikov Evgenia Blagodatskaya Sergey Blagodatsky reas Fangmeier & Yakov Kuzyakov 《FEMS microbiology ecology》2009,69(1):43-52
Increased root exudation under elevated atmospheric CO2 and the contrasting environments in soil macro- and microaggregates could affect microbial growth strategies. We investigated the effect of elevated CO2 on the contribution of fast- ( r -strategists) and slow-growing ( K -strategists) microorganisms in soil macro- and microaggregates. We fractionated the bulk soil from the ambient and elevated (for 5 years) CO2 treatments of FACE-Hohenheim (Stuttgart) into large macro- (>2 mm), small macro- (0.25–2.00 mm), and microaggregates (<0.25 mm) using 'optimal moist' sieving. Microbial biomass (Cmic ), the maximum specific growth rate (μ), growing microbial biomass (GMB) and lag-period ( t lag ) were estimated by the kinetics of CO2 emission from bulk soil and aggregates amended with glucose and nutrients. Although Corg and Cmic were unaffected by elevated CO2 , μ values were significantly higher under elevated than ambient CO2 for bulk soil, small macroaggregates, and microaggregates. Substrate-induced respiratory response increased with decreasing aggregate size under both CO2 treatments. Based on changes in μ, GMB and lag period, we conclude that elevated atmospheric CO2 stimulated the r- selected microorganisms, especially in soil microaggregates. Such an increase in r -selected microorganisms indicates acceleration of available C mineralization in soil, which may counterbalance the additional C input by roots in soils in a future elevated atmospheric CO2 environment. 相似文献