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T. E. Huxman E. P. Hamerlynck M. E. Loik & S. D. Smith 《Plant, cell & environment》1998,21(12):1275-1283
The ability of seedlings to tolerate temperature extremes is important in determining the distribution of perennial plants in the arid south-western USA, and the manner in which elevated CO2 impacts the ability of plants to tolerate high temperatures is relatively unknown. Whereas the effects of chronic high temperature (30–38°C) and elevated CO2 are comparatively well understood, little research has assessed plant performance in elevated CO2 during extreme (> 45 °C) temperature events. We exposed three species of Yucca to 360 and 700 μmol CO2 mol–1 for 8 months, then 9 d of high temperature (up to 53 °C) to evaluate the impacts of elevated CO2 on the potential for photosynthetic function during external high temperature. Seedlings of a coastal C3 species (Yucca whipplei), a desert C3 species (Yucca brevifolia), and a desert CAM species (Yucca schidigera), were used to test for differences among functional groups. In general, Yuccas exposed to elevated CO2 showed decreases in carboxylation efficiency as compared with plants grown at ambient before the initiation of high temperature. The coastal species (Y. whipplei) showed significant reductions (33%) in CO2 saturated maximum assimilation rate (Amax), but the desert species (Y. brevifolia and Y. schidigera) showed no such reductions in Amax. Stomatal conductance was lower in elevated CO2 as compared with ambient throughout the temperature event; however, there were species-specific differences over time. Elevated CO2 enhanced photosynthesis in Y. whipplei at high temperatures for a period of 4 d, but not for Y. brevifolia or Y. schidigera. Elevated CO2 offset photoinhibition (measured as Fv/Fm) in Y. whipplei as compared with ambient CO2, depending on exposure time to high temperature. Stable Fv/Fm in Y. whipplei occurred in parallel with increases in the quantum yield of photosystem II (ΦPSII) at high temperatures in elevated CO2. The value of ΦPSII remained constant or decreased with increasing temperature in all other treatment and species combinations. This suggests that the reductions in Fv/Fm resulted from thermal energy dissipation in the pigment bed for Y. brevifolia and Y. schidigera. The greater efficiency of photosystem II in Y. whipplei helped to maintain photosynthetic function at high temperatures in elevated CO2. These patterns are in contrast to the hypothesis that high temperatures in elevated CO2 would increase the potential for photoinhibition. Our results suggest that elevated CO2 may offset high-temperature stress in coastal Yucca, but not in those species native to drier systems. Therefore, in the case of Y. whipplei, elevated CO2 may allow plants to survive extreme temperature events, potentially relaxing the effects of high temperature on the establishment in novel habitats. 相似文献
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Effect of soil water stress on soil respiration and its temperature sensitivity in an 18-year-old temperate Douglas-fir stand 总被引:5,自引:0,他引:5
RACHHPAL S. JASSAL T. ANDREW BLACK MICHAEL D. NOVAK DAVID GAUMONT-GUAY ZORAN NESIC 《Global Change Biology》2008,14(6):1305-1318
We analyzed 17 months (August 2005 to December 2006) of continuous measurements of soil CO2 efflux or soil respiration (RS) in an 18‐year‐old west‐coast temperate Douglas‐fir stand that experienced somewhat greater than normal summertime water deficit. For soil water content at the 4 cm depth (θ) > 0.11 m3 m?3 (corresponding to a soil water matric potential of ?2 MPa), RS was positively correlated to soil temperature at the 2 cm depth (TS). Below this value of θ, however, RS was largely decoupled from TS, and evapotranspiration, ecosystem respiration and gross primary productivity (GPP) began to decrease, dropping to about half of their maximum values when θ reached 0.07 m3 m?3. Soil water deficit substantially reduced RS sensitivity to temperature resulting in a Q10 significantly < 2. The absolute temperature sensitivity of RS (i.e. dRS/dTS) increased with θ up to 0.15 m3 m?3, above which it slowly declined. The value of dRS/dTS was nearly 0 for θ < 0.08 m3 m?3, thereby confirming that RS was largely unaffected by temperature under soil water stress conditions. Despite the possible effects of seasonality of photosynthesis, root activity and litterfall on RS, the observed decrease in its temperature sensitivity at low θ was consistent with the reduction in substrate availability due to a decrease in (a) microbial mobility, and diffusion of substrates and extracellular enzymes, and (b) the fraction of substrate that can react at high TS, which is associated with low θ. We found that an exponential (van't Hoff type) model with Q10 and R10 dependent on only θ explained 92% of the variance in half‐hourly values of RS, including the period with soil water stress conditions. We hypothesize that relating Q10 and R10 to θ not only accounted for the effects of TS on RS and its temperature sensitivity but also accounted for the seasonality of biotic (photosynthesis, root activity, and litterfall) and abiotic (soil moisture and temperature) controls and their interactions. 相似文献
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YUNSHENG LOU KAZUYUKI INUBUSHI TAKAYUKI MIZUNO TOSHIHIRO HASEGAWA YANHUNG LIN HIDEMITSU SAKAI WEIGUO CHENG KAZUHIKO KOBAYASHI 《Global Change Biology》2008,14(11):2678-2687
A pot experiment was conducted to investigate CH4 emissions from a sandy paddy soil as influenced by rice cultivars and atmospheric CO2 elevation. The experiment with two CO2 levels, 370 μL L−1 (ambient) and 570 μL L−1 (elevated), was performed in a climatron, located at the National Institute for Agro‐Environmental Sciences, Tsukuba, Japan. Four rice cultivars were tested in this experiment, including IR65598, IR72, Dular and Koshihikari. Tiller number, root length and grain yield were clearly larger under elevated CO2 than under ambient CO2. IR72 and Dular showed significantly higher tiller number, root length and grain yield than Koshihikari and IR65598. Average daily CH4 fluxes under elevated CO2 were significantly larger by 10.9–23.8% than those under ambient CO2, and varied with the cultivars in the sequence Dular ≧ IR72>IR65598 ≧ Koshihikari. Dissolved organic C (DOC) content in the soil was obviously higher under elevated CO2 than under ambient CO2 and differed among the cultivars, in the sequence IR72>Dular>Koshihikari>IR65598. The differences in average daily CH4 fluxes between CO2 levels and among the cultivars were related to different root exudation as DOC content, root length and tiller number. This study indicated that Koshihikari should be a potential cultivar for mitigating CH4 emission and simultaneously keeping stable grain yield, because this cultivar emitted lowest CH4 emission and produced medium grain yield. 相似文献
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Adoption of reduced‐impact logging (RIL) methods could reduce CO2 emissions by 30–50% across at least 20% of remaining tropical forests. We developed two cost effective and robust indices for comparing the climate benefits (reduced CO2 emissions) due to RIL. The indices correct for variability in the volume of commercial timber among concessions. We determined that a correction for variability in terrain slope was not needed. We found that concessions certified by the Forest Stewardship Council (FSC, N = 3), when compared with noncertified concessions (N = 6), did not have lower overall CO2 emissions from logging activity (felling, skidding, and hauling). On the other hand, FSC certified concessions did have lower emissions from one type of logging impact (skidding), and we found evidence of a range of improved practices using other field metrics. One explanation of these results may be that FSC criteria and indicators, and associated RIL practices, were not designed to achieve overall emissions reductions. Also, commonly used field metrics are not reliable proxies for overall logging emissions performance. Furthermore, the simple distinction between certified and noncertified concessions does not fully represent the complex history of investments in improved logging practices. To clarify the relationship between RIL and emissions reductions, we propose the more explicit term ‘RIL‐C’ to refer to the subset of RIL practices that can be defined by quantified thresholds and that result in measurable emissions reductions. If tropical forest certification is to be linked with CO2 emissions reductions, certification standards need to explicitly require RIL‐C practices. 相似文献
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Metabolic rate in diapause and nondiapause brown locust eggs correlated with embryonic development 总被引:1,自引:0,他引:1
INNOCENT N. KAMBULE SHIRLEY A. HANRAHAN FRANCES D. DUNCAN 《Physiological Entomology》2011,36(4):299-308
Insects use dormancy to survive adverse conditions. Brown locust Locustana pardalina (Walk.) eggs offer a convenient model to study dormancy (diapause and quiescence), which contributes to their survival under arid conditions. The metabolic rates of developing nondiapause, diapause and quiescent eggs are compared in the present study using closed‐system respirometry. The embryo becomes committed to continue development and hatch or to enter diapause 6 days after the eggs are placed on moist soil. The metabolic rate of nondiapause eggs increases exponentially until hatching, whereas that of diapause eggs is low and stable. The metabolic rate of diapause laboratory eggs (1.9 ± 0.6 µL CO2 mg?1 h?1) is significantly higher than that of field eggs (0.5 ± 0.3 µL CO2 mg?1 h?1), although the ranges of metabolic rate overlap and the embryos are all in late anatrepsis. The metabolic rate of quiescent eggs is similar to that of diapause eggs but decreases with time. Low metabolic rates during arrested development allow eggs to persist over long periods before hatching. 相似文献
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