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The surface concentration of ozone ([O(3)]) has risen from less than 10 ppb prior to the industrial revolution to a day-time mean concentration of approximately 40 ppb over much of the northern temperate zone. If current global emission trends continue, surface [O(3)] is projected to rise a further 50% over this century, with larger increases in many locations including Northern Hemisphere forests. This review uses statistical meta-analysis to determine mean effects, and their confidence limits, of both the current and projected elevations of [O(3)] on light-saturated photosynthetic CO(2) uptake (A(sat)) and stomatal conductance (g(s)) in trees. In total, 348 measurements of A(sat) from 61 studies and 266 measures of g(s) from 55 studies were reviewed. Results suggested that the elevation of [O(3)] that has occurred since the industrial revolution is depressing A(sat) and g(s) by 11% (CI 9-13%) and 13% (CI 11-15%), respectively, where CI is the 95% confidence interval. In contrast to angiosperms, gymnosperms were not significantly affected. Both drought and elevated [CO(2)] significantly decreased the effect of ambient [O(3)]. Younger trees (<4 years) were affected less than older trees. Elevation of [O(3)] above current levels caused progressively larger losses of A(sat) and g(s), including gymnosperms. Results are consistent with the expectation that damage to photosynthesis depends on the cumulative uptake of ozone (O(3)) into the leaf. Thus, factors that lower g(s) lessen damage. Where both g(s) and [O(3)] were recorded, an overall decline in A(sat) of 0.21% per mmol m(-2) of estimated cumulative O(3) uptake was calculated. These findings suggest that rising [O(3)], an often overlooked aspect of global atmospheric change, is progressively depressing the ability of temperate and boreal forests to assimilate carbon and transfer water vapour to the atmosphere, with significant potential effects on terrestrial carbon sinks and regional hydrologies. 相似文献
95.
Daniel Obrist 《Biogeochemistry》2007,85(2):119-123
Plants accumulate significant amounts of atmospheric mercury (Hg) in aboveground biomass, likely sequestering over 1,000 Mg
of atmospheric Hg every year. This large mercury uptake could be strong enough to affect tropospheric Hg levels and might
be partially responsible for seasonal variations in atmospheric Hg observed at Mace Head, Ireland. The fluctuations of Hg
concentrations coincide temporally with the annual oscillation of carbon dioxide (CO2) in the Northern Hemisphere, which is a result of seasonal growth of vegetation. Therefore, declining Hg concentrations in
spring and summer may be attributed in part to plant uptake of atmospheric Hg. Further, the increase of Hg concentrations
during non-active vegetation periods might partially be due to plant-derived Hg emitting back to the atmosphere during carbon
mineralization. The implications of these propositions are that past and future changes in biomass productivity and organic
carbon pools may have had—and may continue to have—significant effects on atmospheric Hg levels. Specifically, large losses
in soil and biomass carbon pools in the last 150 years could have contributed significantly to observed increases in atmospheric
Hg pollution. The roles of vegetation and terrestrial carbon pools should receive detailed consideration on how they might
attenuate or exacerbate atmospheric Hg pollution. 相似文献
96.
Herbivores influence nutrient cycling and primary production in terrestrial plant communities. However, both empirical and
theoretical studies have indicated that the mechanisms by which herbivores influence nutrient availability, and thus their
net effects on primary production, might differ between time scales. For a grassland in southeast England, we show that the
effects of rabbits on primary production change over time in a set of grazed plots paired with exclosures ranging from 0 to
14 years in age. Herbivore exclusion decreased net aboveground primary production (APP) in the short term, but increased APP
in the long term. APP was closely correlated with N mineralization rates in both grazed and ungrazed treatments, and accumulation
of litter within the grazing exclosures led to higher N mineralization rates in exclosures in the long run. Rabbit grazing
did not influence litter quality. The low contrast in palatability between species and the presence of grazing-tolerant plants
might prevent rabbits from favoring unpalatable plant species that decompose slowly, in contrast to results from other ecosystems.
Our results indicate that it is essential to understand the effects on N cycling in order to predict the effect of rabbit
grazing on APP. Rabbits might decrease N mineralization and APP in the long term by increasing losses of N from grasslands. 相似文献
97.
Simulating the effects of N availability, straw particle size and location in soil on C and N mineralization 总被引:2,自引:0,他引:2
Predicting the C and N mineralization of straw added to soil is important for forecasting subsequent soil N availability during
and between crop growth cycles. The decomposition module of the STICS model, parameterized under optimal conditions, was used
to predict straw decomposition in sub-optimal conditions, i.e. when contact between soil and residue was poor (due to large
size residues or surface placement) or when mineral N availability was restricted. The data used in the simulations were obtained
from published studies of effects of residue size, location and N availability on C and N mineralization from straw under
controlled laboratory conditions. We selected studies in which the dynamics of C and N mineralization were measured simultaneously.
The dynamics of straw mineralization could be well predicted by the model under optimal conditions with standard parameter
values as derived from measured C/N ratios of the residues, but not under sub-optimal conditions which required a new parameterization. A good fit could be obtained
on these treatments by a marked reduction in the rate constants of residue and microbial biomass decomposition and a marked
increase in the microbial biomass C/N ratio. Our results show the need to include in decomposition models routines for simulating effects of spatial heterogeneity
of residue distribution, different particle sizes and limiting N availability. 相似文献
98.
Karin Karlson Rutger Rosenberg 《Journal of experimental marine biology and ecology》2007,344(2):123-135
This study focused on effects from Monoporeia affinis reworking and ventilation activities on benthic fluxes and mineralization processes during a simulated bloom event. The importance of M. affinis density for benthic solute (O2, ΣNO2− + NO3−, NH4+ and HPO42−) fluxes and sediment reactivity (mobilization of NH4+ and HPO42−) following additions of organic material to the sediment surface was experimentally investigated using sediment-water and closed sediment (jar) incubations. Three different densities of M. affinis were used to resemble a low, medium and high density situation (1300, 2500 and 6400 ind. m− 2, respectively) of a natural amphipod community. The degradation of phytodetritus (Tetraselmis sp., 5 g C m− 2) added to the sediment surface was followed over a period of 20 days. Benthic solute fluxes of O2, ΣNO2− + NO3− and NH4+ were generally progressively stimulated with increasing number of M. affinis, while no such correlation was found for HPO42−. Solute fluxes were initially enhanced 1 to 2 days after the addition of phytodetritius, caused by mineralization of the most labile organic material and a food-stimulated irrigation by the amphipods. There was no effect from the activity of M. affinis on total denitrification (Dtot = Dn + Dw) or denitrification utilizing nitrate from coupled nitrification/denitrification (Dn) for any of the densities examined. Denitrification utilizing overlying water nitrate (Dw) was only about 10% of Dtot. Dw was significantly enhanced for the highest M. affinis density investigated. The reactivity of the sediment decreased progressively with increasing density of M. affinis and with time of the experiment. However, enhanced ammonium production at least 6 days after the organic addition indicated excretion of N-containing organic compounds by M. affinis. In conclusion, large spatial and temporal variations in density of M. affinis may be of significant importance for benthic solute fluxes and overall mineralization of organic material in Baltic Sea sediments. 相似文献
99.
Andrew J. Dugmore Douglas M. Borthwick Mike J. Church Alastair Dawson Kevin J. Edwards Christian Keller Paul Mayewski Thomas H. McGovern Kerry-Anne Mairs Guðrún Sveinbjarnardóttir 《Human ecology: an interdisciplinary journal》2007,35(2):169-178
In order to assess possible contributions of climate change to the human ecology of the North Atlantic islands we evaluate
the utility of cumulative deviations from the mean, calculated for the Greenland ice core storm frequency proxy (GISP2 Na+) and sea ice proxy (GISP2 chloride excess). Our aim is to identify episodes of unpredictable change in the context of long-term
trends of cultural and environmental development. Key changes are identified in the proxy climate records in 975 and 980 ad, 1025 and 1040 ad, 1180 ad, 1425 and 1450 ad, and 1520 and 1525 ad. Some of these changes are consistent with those inferred from new studies of the palaeoecological record of the Faroes.
This indicates that the cumulative deviation measure could give greatest prominence to the most important climate changes
affecting landscapes and settlement (such as the changes of 1425 and 1450 ad and their immediate aftermath), rather than extreme events, such as great single storms. 相似文献
100.