摘要:

AbstractTerrestrial higher plants exchange large amounts of CO2with the atmosphere each year; c. 15% of the atmospheric pool of C is assimilated in terrestrial‐plant photosynthesis each year, with an about equal amount returned to the atmosphere as CO2in plant respiration and the decomposition of soil organic matter and plant litter. Any global change in plant C metabolism can potentially affect atmospheric CO2content during the course of years to decades. In particular, plant responses to the presently increasing atmospheric CO2concentration might influence the rate of atmospheric CO2increase through various biotic feedbacks. Climatic changes caused by increasing atmospheric CO2concentration may modulate plant and ecosystem responses to CO2concentration. Climatic changes and increases in pollution associated with increasing atmospheric CO2concentration may be as significant to plant and ecosystem C balance as CO2concentration itself. Moreover, human activities such as deforestation and livestock grazing can have impacts on the C balance and structure of individual terrestrial ecosystems that far outweigh effects of increasing CO2concentration and climatic change.In short‐term experiments, which in this case means on the order of 10 years or less, elevated atmospheric CO2concentration affects terrestrial higher plants in several ways. Elevated CO2can stimulate photosynthesis, but plants may acclimate and (or) adapt to a change in atmospheric CO2concentration. Acclimation and adaptation of photosynthesis to increasing CO2concentration is unlikely to be complete, however. Plant water use efficiency is positively related to CO2concentration, implying the potential for more plant growth per unit of precipitation or soil moisture with increasing atmospheric CO2concentration. Plant respiration may be inhibited by elevated CO2concentration, and although a naive C balance perspective would count this as a benefit to a plant, because respiration is essential for plant growth and health, an inhibition of respiration can be detrimental. The net effect on terrestrial plants of elevated atmospheric CO2concentration is generally an increase in growth and C accumulation in phytomass. Published estimations, and speculations about, the magnitude of global terrestrial‐plant growth responses to increasing atmospheric CO2concentration range from negligible to fantastic. Well‐reasoned analyses point to moderate global plant responses to CO2concentration. Transfer of C from plants to soils is likely to increase with elevated CO2concentrations because of greater plant growth, but quantitative effects of those increased inputs to soils on soil C pool sizes are unknown.Whether increases in leaf‐level photosynthesis and short‐term plant growth stimulations caused by elevated atmospheric CO2concentration will have, by themselves, significant long‐term (tens to hundreds of years) effects on ecosystem C storage and atmospheric CO2concentration is a matter for speculation, not firm conclusion. Long‐term field studies of plant responses to elevated atmospheric CO2are needed. These will be expensive, difficult, and by definition, results will not be forthcoming for at least decades. Analyses of plants and ecosystems surrounding natural geological CO2degassing vents may provide the best surrogates for long‐term controlled experiments, and therefore the most relevant information pertaining to long‐term terrestrial‐plant responses to elevated CO2concentration, but pollutants associated with the vents are a concern in some cases, and quantitative knowledge of the history of atmospheric CO2concentrations near vents is limited.On the whole, terrestrial higher‐plant responses to increasing atmospheric CO2concentration probably act as negative feedbacks on atmospheric CO2concentration increases, but they cannot by themselves stop the fossil‐fuel‐oxidation‐driven increase in atmospheric CO2concentration. And, in the very long‐term, atmospheric CO2concentration is controlled by atmosphere‐ocean C equilibrium rather than by terrestrial plant and ecosystem response

ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1995.tb00025.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractChanges in land use between 1850 and 1980 are estimated to have increased the global areas in croplands, pastures, and shifting cultivation by 891, 1308, and 30 × 106ha, respectively, reducing the area of forests by about 600 × 106ha, releasing about 100 PgC to the atmosphere, and transferring about 23 PgC from live vegetation to dead plant material and wood products. Another 1069 × 106ha are estimated to have been logged during this period, and the net release of carbon from the combined processes of logging and regrowth contributed 23 PgC to the 100‐PgC release. Annual rates of land‐use change and associated emissions of carbon have decreased over the last several decades in temperate and boreal zones and have increased in the tropics. The average release of carbon from global changes in land use over the decade of the 1980s Is estimated to have been 1.6 ± 0.7 PgC y−1almost entirely from the tropics. This estimate of carbon flux is higher than estimates reported in recent summaries because it is limited here to studies concerned only with changes in land use. Other recent analyses, based on data from forest inventories, have reported net accumulations of carbon as high as 1.1 PgC y−1in temperate and boreal zones. Because the accumulation of carbon in forests may result from natural processes unrelated to land‐use change, estimates based on these inventories should be distinguished from estimates based on changes in land use. Both approaches identify terrestrial sinks of carbon. The argument is made here, however, that differences between the two approaches may help identify the location and magnitude of heretofore ‘missing’ sinks. Before different estimates can be used in this way, analyses must consider similar geographical regions and dates, and they must account for the accumulation and loss of carbon in forest products in a c

ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1995.tb00026.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe possible responses of the terrestrial biosphere to future CO2increases and associated climatic change are being investigated using dynamic global vegetation models (DG VMs) which include the Farquharet al.(1980) biochemical model of leaf assimilation as the primary means of carbon capture. This model requires representative values of the maximum rates of Rubisco activity, Vmax, and electron transport, Jmax, for different vegetation types when applied at the global scale. Here, we describe an approach for calculating these values based on measurements of the maximum rate of leaf photosynthesis (Amax)13C discrimination. The approach is tested and validated by comparison with measurements of Rubisco activity assayed directly on wild‐type and transgenicNicotiana tabacum(tobacco) plants with altered Rubisco activity grown under ambient and elevated CO2mole fractions with high and low N‐supply.VmaxandJmaxvalues are reported for 18 different vegetation types with global coverage. Both variables were linearly related reinforcing the idea of optimal allocation of resources to photosynthesis (light harvesting vs. Rubisco) at the global scale. The reported figures should be of value to the further development of vegetation and ecosystem models employing mechanistic DG

ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1995.tb00027.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractArbutus unedois a sclerophyllous evergreen, characteristic of Mediterranean coastal scrub vegetation. In Italy, trees ofA. unedohave been found close to natural CO2vents where the mean atmospheric carbon dioxide concentration is about 2200 μmol mol−1. Comparisons were made between trees growing in elevated and ambient CO2concentrations to test for evidence of adaptation to long‐term exposure to elevated CO2. Leaves formed at elevated CO2have a lower stomatal density and stomatal index and higher specific leaf area than those formed at ambient CO2, but there was no change in carbon to nitrogen ratios of the leaf tissue. Stomatal conductance was lower at elevated CO2during rapid growth in the spring. In mid‐summer, under drought stress, stomatal closure of all leaves occurred and in the autumn, when stress was relieved, the conductance of leaves at both elevated and ambient CO2increased. In the spring, the stomatal conductance of the new flush of leaves at ambient CO2was higher than the leaves at elevated CO2, increasing instantaneous water use efficiency at elevated CO2. Chlorophyll fluorescence measurements suggested that elevated CO2provided some protection against photoinhibition in mid‐summer. Analysis ofA/Cicurves showed that there was no evidence of either upward or downward regulation of photosynthesis at elevated CO2. It is therefore anticipated thatA. unedowill have higher growth rates as the ambient CO2concentrations

ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1995.tb00028.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractDaily samples between 1964 and 1991 from suction traps throughout Great Britain were used to study the migration phenologies of five aphid species:Brachycaudus helichrysi, Elatobium abietinum, Metopolophium dirhodum, Myzus persicaeandSitobion avenae, and their relationship with temperature. Regression relationships have been established between characteristics of aphid phenology and temperature, latitude and longitude for each species. There were differences between species in the period for which temperature was most strongly associated with aphid phenology. The study indicates that temperature, especially winter temperature, is the dominant factor affecting aphid phenology, for all five species. A 1 °C increase in average winter temperature advanced the migration phenology by 4–19 days depending on species. Effects of temperature on the aphid phenology are similar between holocyclic and anholocyclic species, unlike the effects of temperature on date of first flight record which have been previously shown to be important only in anholocyclic speci

ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1995.tb00029.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY