ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1996.tb00052.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractChanges in the trace gas composition of the atmosphere over glacial–interglacial cycles are linked to changes in the oceanic carbon cycle. This paper examines the role of biologically driven fluxes of organic and inorganic carbon in modifying the carbon dioxide chemistry of the oceans, and the corresponding implications for the partitioning of CO2between the atmosphere and ocean. Relevant details of the marine carbon system are presented together with an assessment of the significance of remineralization and dissolution processes. Recent estimates of the marine carbonate fluxes show significant uncertainties and inconsistencies which must be resolved in order to assess fully the role of the oceans' biota in the marine carbon system. Various types of ocean carbon cycle models have been developed in order to interpret the changes in past atmospheric carbon dioxide. Some take account of the role of the oceans' biota, focussing in the main on the cycling of organic matter. Relatively few have considered the role of the carbonate pump and the subtle interactions between organic and inorganic carbon cycling. The significance of carbonate formation and dissolution, and of the effects of global change on the marine carbonate system, for air–sea fluxes of CO2are discussed. Finally some recommendations for future research are made in order to improve our understanding of how spatial and temporal variation in marine carbonate fluxes, in conjunction with processes determining the oxidation and burial of organic matter in the oceans, affect levels of CO2in the atmosph

ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1996.tb00053.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractA strong correlation is observed between an El Niño index (anomalies in tropical Pacific sea surface temperature) and rainfall in the Judean foothills near Jerusalem over the past 20 years. These relationships clearly influenced the growth of local pine trees, as reflected in the width of their annual tree rings. The ability to predict El Niño events about a year in advance lend a special significance to relationships reported here for ecology, agriculture and water management in this climatic transition zone. To help explain the observed, long‐range teleconnection we propose a possible mechanism based on a newly identified direct cloud connection between equatorial Africa (more directly affected by El Niño) and the Southeastern Mediterranean shoreland. The penetration and contribution of the moisture current from equatorial Africa to this region may depend on a shift in the usual rain generating moisture currents to southwesterly trajectories (passing over north Africa). The occurrence of such shifts is supported by the observed decrease in the mean18O content of the local precipitation during El Nino win

ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1996.tb00054.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractTrees growing in natural systems undergo seasonal changes in environmental factors that generate seasonal differences in net photosynthetic rates. To examine how seasonal changes in the environment affect the response of net photosynthetic rates to elevated CO2, we grewPinus taedaL. seedlings for three growing seasons in open‐top chambers continuously maintained at either ambient or ambient + 30 Pa CO2. Seedlings were grown in the ground, under natural conditions of light, temperature nd nutrient and water availability. Photosynthetic capacity was measured bimonthly using net photosynthetic rate vs. intercellular CO2partial pressure (A‐Ci) curves. Maximum Rubisco activity (Vcmax) and ribulose 1,5‐bisphosphate regeneration capacity mediated by electron transport (Jmax) and phosphate regeneration (PiRC) were calculated fromA‐Cicurves using a biochemically based model. Rubisco activity, activation state and content, and leaf carbohydrate, chlorophyll and nitrogen concentrations were measured concurrently with photosynthesis measurements. This paper presents results from the second and third years of treatment.Mean leaf nitrogen concentrations ranged from 13.7 to 23.8 mg g−1, indicating that seedlings were not nitrogen deficient. Relative to ambient CO2seedlings, elevated CO2increased light‐saturated net photosynthetic rates 60–110% during the summer, but<30% during the winter. A relatively strong correlation between leaf temperature and the relative response of net photosynthetic rates to elevated CO2suggests a strong effect of leaf temperature. During the third growing season, elevated CO2reduced Rubisco activity 30% relative to ambient CO2seedlings, nearly completely balancing Rubisco and RuBP‐regeneration regulation of photosynthesis. However, reductions in Rubisco activity did not eliminate the seasonal pattern in the relative response of net photosynthetic rates to elevated CO2. These results indicate that seasonal differences in the relative response of net photosynthetic rates to elevated CO2are likely to occur in

ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1996.tb00055.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractTwo species of eucalypt (Eucalyptus macrorhynchaandE. rossii) were grown under conditions of high temperatures (45 °C, maximum) and high light (1500 μmol m−2s−1, maximum) at either ambient (350 μL L−1) or elevated (700 μL L−1) CO2concentrations for 8 weeks. The growth enhancement, in terms of total dry weight, was 41% and 103% forE. macrorhynchaandE. rossii, respectively, when grown in elevated [CO2]. A reduction in specific leaf area and increased concentrations of non‐structural carbohydrates were observed for leaves grown in elevated [CO2]. Plants grown in elevated [CO2] had an overall increase in photosynthetic CO2assimilation rate of 27%; however, when measured at the same CO2concentration a down‐regulation of photosynthesis was evident especially forE. macrorhyncha.During the midday period when temperatures and irradiances were maximal, photosynthetic efficiency as measured by chlorophyll fluorescence (Fv/Fm) was lower inE. macrorhynchathan inE. rossii.Furthermore,Fv/Fmwas lower in leaves ofE. macrorhynchagrown under elevated than under ambient [CO2]. These reductions inFv/Fmwere accompanied by increases in both photochemical (qP) and nonphotochemical quenching (qN and NPQ), and by increases in the concentrations of xanthophyll cycle pigments with an increased proportion of the total xanthophyll cycle pool comprising of antheraxanthin and zeaxanthin. Thus, increased atmospheric [CO2] may enhance photoinhibition when environmental stresses such as high temperatures limit the capacity of a plant to respond with growth to

ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1996.tb00056.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe impact of elevated [CO2] on seed germination was studied in different genotypesof Arabidopsis thalianafrom natural populations. Two generations of seeds were studied: the maternal generation was produced in the greenhouse (present‐day conditions), the offspring generation was produced in two chambers where the CO2concentration was either the present atmospheric concentration (about 350 ppm) or elevated (700 ppm). The seeds were tested for proportion of germinated seeds and mean germination time in both chambers to study the impact of elevated [CO2] during seed production and germination.Elevated [CO2] during maturation of seeds on the mother‐plants decreased the proportion of germinated seeds, while elevated [CO2] during germination had no effect on the proportion of germinated seeds. However, when seeds were both produced and germinated under elevated [CO2] (situation expected by the end of next century), germination was slow and low.Moreover, the effect of the [CO2] treatment differs among genotypes ofArabidopsis: there is a strong treatment × genotype interaction. This means that there is ample genetic variance for a selective response modiying the effects of high levels of [CO2] in natural populations ofArabidopsis thaliana.The outcome at the community level will depend on what seeds are available, when they germinate and the resulting competition following germina

ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1996.tb00057.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractAn archive of satellite and aircraft photographs of the western Sudan showed no longterm (1943–1994) trends in the abundance of trees despite several decades of recent drought in this region. These data extend the extant historical record of vegetation change in the African Sahel, where recent fluctuations in vegetation greenness have been monitored with the NOAA Advanced Very High Resolution Radiometer since 1980. Despite substantial population turnover, woody vegetation is not yet indicative of the recent climate changes in this regio

ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1996.tb00058.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractAtmospheric CO2concentration is rising and it has been suggested that a portion of the additional carbon is being sequestered in terrestrial vegetation and much of that in below‐ground structures. The objective of the present study was to quantify the effects of elevated atmospheric CO2on fine root length and distribution with depth with minirhizotrons in an open‐top chamber experiment in an oak‐palmetto scrub ecosystem at Kennedy Space Centre, Florida, USA. Observations were made five times over a period of one and a half years in three ambient chambers (350 p.p.m. CO2), three CO2enriched chambers (700 p.p.m. CO2), and three unchambered plots. Greater root length densities were produced in the elevated CO2chambers (14.2 mm cm−2) compared to the ambient chambers (8.7 mm cm−2). More roots may presumably lead to more efficient acquisition of resources. Fine root abundance varied significantly with soil depth, and there appeared to be enhanced proliferation of fine roots near the surface (0–12 cm) and at greater depth (49–61 cm) in the elevated CO2chambers. The vertical root distribution pattern may be a response to availability of nutrients and water. More studies are needed to determine if increased root length under CO2enriched conditions actually results in greater sequestering of carbon

ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1996.tb00059.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractIncreasing surface levels of UV‐B resulting from stratospheric ozone reduction directly affect tropospheric photochemistry. There may also be indirect tropospheric effects due to changes in emission of organic compounds from vegetation. We treated woody and herbaceous isoprene‐emitting species in the field with supplemental UV‐B simulating 30% ozone depletion. ForQuercus gambelii, photosynthesis and isoprene emission were significantly greater in elevated UV‐B treatments when expressed on a leaf area basis, but not on a leaf mass basis. Leaves ofMucuna pruriens, however, showed no significant differences in photosynthesis or isoprene emission between treatments, nor when exposed for 45 min to acute high levels of UV‐B. Elevated UV‐B during growth did not elicit significant isoprene emission fromAcer platanoides, a non‐emitting species. Other potential UV‐B effects, such as changes in leaf area or species composition, which may influence regional isoprene emissions, sho

ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1996.tb00060.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractHydraulic conductances of alfalfa and soybean plants grown in controlled environment chambers at the current ambient carbon dioxide concentration and at twice the current ambient concentration were determined from measurements of transpiration rate and leaf and stem water potentials in the growth conditions. Growth at elevated carbon dioxide concentration reduced both transpiration rate and hydraulic conductance from the soil to the leaf in both species. Hydraulic conductance from the soil to the base of the stem was also lower at elevated carbon dioxide in soybean, but not alfalfa. These measurements identified the stem to leaf hydraulic pathway as a major target of the carbon dioxide effect in both species. The conductance of excised stem segments was much less in plants grown at elevated carbon dioxide in soybeans.

ISSN:1354-1013    

DOI:10.1111/j.1365-2486.1996.tb00061.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY