排序方式: 共有24条查询结果,搜索用时 15 毫秒
1.
2.
BAOZHANG CHEN † T. ANDREW BLACK† NICHOLAS C. COOPS PRAVEENA KRISHNAN† RACHHPAL JASSAL† CHRISTIAN BRÜMMER† ZORAN NESIC† 《Global Change Biology》2009,15(8):1962-1981
This study analyzes 9 years of eddy‐covariance (EC) data carried out in a Pacific Northwest Douglas‐fir (Pseudotsuga menzesii) forest (58‐year old in 2007) on the east coast of Vancouver Island, Canada, and characterizes the seasonal and interannual variability in net ecosystem productivity (NEP), gross primary productivity (GPP), and ecosystem respiration (Re) and primary climatic controls on these fluxes. The annual values (± SD) of NEP, GPP and Re were 357 ± 51, 2124 ± 125, and 1767 ± 146 g C m?2 yr?1, respectively, with ranges of 267–410, 1592–2338, and 1642–2071 g C m?2 yr?1, respectively. Spring to early summer (March–June) accounted for more than 80% of annual NEP while late spring to early autumn (May–August) was mainly responsible for its interannual variability (~80%). The major drivers of interannual variability in annual carbon (C) fluxes were annual and spring mean air temperatures (Ta) and water deficiency during late summer and autumn (July–October) when this Douglas‐fir forest growth was often water‐limited. Photosynthetically active radiation (Q), and the combination of Q and soil water content (θ) explained 85% and 91% of the variance of monthly GPP, respectively; and 91% and 96% of the variance of monthly Re was explained by Ta and the combination of Ta and θ, respectively. Annual net C sequestration was high during optimally warm and normal precipitation years, but low in unusually warm or severely dry years. Excluding 1998 and 1999, the 2 years strongly affected by an El Niño/La Niña cycle, annual NEP significantly decreased with increasing annual mean Ta. Annual NEP will likely decrease whereas both annual GPP and Re will likely increase if the future climate at the site follows a trend similar to that of the past 40 years. 相似文献
3.
4.
5.
6.
7.
Mitochondria from Orobanche were analysed for the activities of aconitate hydratase, isocitrate dehydrogenase, succinate dehydro-genase, fumarate hydratase, malate dehydrogenase, NADH oxidase, substrate-cytochrome c oxidoreductases, glutamate dehydrogenase, aminotransferases, ATPase and “malic” enzyme. The specific activities of isocitrate dehydrogenase, NADH oxidase, substrate-cytochrome c oxidoreductases and glutamate dehydrogenase in the mitochondria) fraction from parasite tissue compared favourably with those reported for most of the mitochondria from growing and storage tissues. Succinate dehydrogenase, fumarate hydratase and aspartate aminotransferase were of intermediate activity, while aconitate hydratase and malate dehydrogenase had rather low activity, and “malic” enzyme had very low activity in comparison with other preparations. The relevance of these findings in relation to mitochondrial metabolism in the parasite is discussed. No evidence was obtained to suggest any basic abnormality in the biochemical properties of the mitochondria from Orobanche centua which may be correlated with its obligatorily parasitic existence. 相似文献
8.
The Effects of Habitat Geometry on Territorial Defense Costs: Intruder Pressure in Bounded Habitats 总被引:1,自引:0,他引:1
STAMPS JUDY A.; BUECHNER MARYBETH; KRISHNAN V.V. 《Integrative and comparative biology》1987,27(2):307-325
Computer simulation models were used to explore the effect ofhabitat geometry on intruder pressure for territories in differentlocations within a patch of uniformly high quality habitat,for territories in patches of different shapes and sizes, andfor patches surrounded by different types of suboptimal habitats. In models in which the edges of the habitat patch are impermeable(hard-edged), intruders do not leave the central territorialhabitat, H, and intruder pressure is lower for territories onthe edge of H than for more centrally located territories. Averageintruder pressure for any given loop of territories (, for loop = i) is positively relatedto both the proportion of territories on the edge of the patch(ESR) and the average distance moved by intruders. In models in which the edges of H are permeable (soft-edged),intruders are able to move between H and the surrounding habitats,which were of two types: sinks (no intruders generated there)and reserves (a source of intruders). The presence of sinksdramatically reduces both and average intruder pressure over H () as compared to hard-edged habitats, and both and are negatively related to the proportion of territories on theedge of the patch (ESR). Conversely, and are positively related to ESR when the surrounding habitat acts as an intruder-reserve. Data from empirical studies of territorial species agree withmany of the direct and indirect qualitative predictions of thesemodels. The effects of habitat geometry on defense costs maybe important in many territorial species, and should be takeninto account in future studies. 相似文献
9.
Distribution of Glycosidases and Acid Invertase Activities in Relation to Elongation Growth in Pearl Millet Internode 总被引:1,自引:0,他引:1
CHANDA S. V.; JOSHI A. K.; KRISHNAN P. N.; SINGH Y. D. 《Journal of experimental botany》1986,37(9):1406-1415
The mean cell length along a differentiating internode and alliedchanges in the activities of ß-glucosidase, - andß-galactosidase. -mannosidase and acid invertase,together with the contents of reducing and non-reducing sugars,were examined in pearl millet (Pennisetum americanum L. Leekecv. BJ-104). The specific activities of cytoplasmic -mannosidase,wall ß-glucosidase, and cytoplasmic and wall acidinvertase showed close relationships with the rate of cell elongation.The linear regressions of the rate of cell elongation, and thespecific activities of wall ß-glucosidase and cytoplasmicand wall invertase showed significant positive correlations(P<0·05), whereas cytoplasmic -mannosidase was negativelycorrelated (P<0·01). The results are discussed in the light of cell wall looseningand the provision of carbon substrates for cell elongation. Key words: Glycosidases, acid invertase, sugars, cell elongation, Pennisetum americanum L., Leeke 相似文献
10.
KRISHNAN PS 《Archives of biochemistry and biophysics》1951,32(1):230-231