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本文基于ChinaFLUX的定位观测数据,研究了二种典型森林生态系统、二种典型草地生态系统和一种典型农田生态系统碳固定价值年内流量和累积过程。研究结果揭示了不同类型生态系统碳固定价值总量的差异,以及价值流量过程和累积曲线的不同变化趋势。5种生态系统按碳固定年价值由大到小的排序为:禹城〉千烟洲〉长白山〉海北〉当雄。千烟洲碳固定日价值和月价值年内变异最小,其次为长白山,禹城再次之,年内变异最大的为当雄和海北。5种生态系统碳固定日价值的累积过程都能很好地拟合为三次方曲线。 相似文献
74.
Dinitrogen (N2) fixed by a group of prokaryotes (diazotrophs) is the dominant process adding bioavailable nitrogen into the ocean. Although it has been intensively studied how N2 fixation is controlled by resources (bottom-up factors), it is unclear whether the grazing (top-down control) effectively impacts growth and distribution of different diazotroph groups. In this study, we evaluate this question by conducting log-log regression of diazotroph biomass onto corresponding N2 fixation rates in the global ocean. The slope of the regression for Trichodesmium is ~0.8, indicating that a small portion of the increase in N2 fixation does not accumulate as its biomass. This leads to a conclusion that Trichodesmium is under a substantial top-down control, although bottom-up control still dominates. We also analyze the residuals of the regression in the North Atlantic, concluding that free trichomes of Trichodesmium are subject to stronger top-down control than its colonies. The weak correlation between the biomass and N2 fixation of unicellular cyanobacterial diazotrophs indicates that the degree of top-down control on this type of diazotrophs varies greatly. The analyses obtain unrealistic results for diatom-diazotroph assemblages due to complicated nitrogen sources of these symbioses. Our study reveals the variability of top-down control among different diazotroph groups across time and space, suggesting its importance in improving our understandings of ecology of diazotrophs and predictions of N2 fixation in biogeochemical models. Measurements of size-specific N2 fixation rates and growth rates of different diazotroph groups can be useful to more reliably analyze the top-down control on these key organisms in the global ocean. 相似文献
75.
At a time when the concept of ‘human and environmental symbiosis’ has taken on much significance, protection of suburban forests
(i.e. forests adjacent to or near developed areas) is a topic that has drawn much attention. Suburban forests have, since
ancient times, been places where people have gathered firewood and cultured trees. As a result, the vegetation of suburban
forests is only partially natural and continues to change as the forms of human activity in and around them changes. Accurate
forecasts of how suburban forests will change are, therefore, an important element in the debate over how to protect them.
In this study, a suburban forest was analyzed with laser radar sensing, multi-spectrum scanning, digital photogrammetry analysis,
aerial photograph interpretation, and a field survey. Data gathered using these techniques were compiled on a GIS to forecast
future changes in the forest. Aerial photographs taken over the past 50 years were analyzed to illuminate changes in the forest
over that period. Specifically, comparisons of precise Digital Elevation Models (DEMs) measured by using digital photogrammetry
workstations made it possible to estimate growth in forest height. The possible future conversion of such results to estimates
of amounts of carbon dioxide consolidated by forests should be very significant for discussions of global environmental problems.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
76.
Cyanobacteria in New Zealand inland waters: Experimental studies 总被引:1,自引:1,他引:0
Anthony B. Viner 《新西兰海洋与淡水研究杂志》2013,47(3):503-507
A small volume of experimental work with cyanobacteria in New Zealand has been produced through the last two decades. Except for some studies with geothermal organisms biased to New Zealand conditions, most work has followed the world‐wide trends in cyanobacterial research. There has been some emphasis on N2‐fixing species, but symbiotic relationships, metabolic kinetics, nutrient and other environmental factors promoting ecological dominance, and toxicity have been investigated. 相似文献
77.
Chemoautotrophic organisms have once been excluded from the development of universally applicable CO2 fixation technology due to its low production yields of biomass. In this study, we used Acidithiobacillus ferrooxidans (A.f.) as a model chemoautotrophic microorganism to test the hypothesis that exogenetic photoelectrons from semiconducting mineral photocatalysis can enable the regeneration of Fe2+ that could be then used by A.f. and support its growth. In a simulated electrochemical system, where exogenetic electrons were provided by an electrochemical approach, an accelerated growth rate of A.f. was observed as compared with that in traditional batch cultivation. In a coupled system, where light-irradiated natural rutile provided the primary electron source to feed A.f., the bacterial growth rate as well as the subsequent CO2 fixation rate was demonstrated to be in a light-dependent manner. The sustaining flow of photogenerated electrons from semiconducting mineral to bacteria provided an inexhaustible electron source for chemoautotrophic bacteria growth and CO2 fixation. This finding might contribute to the development of novel effective CO2 fixation technology. 相似文献
78.
为了研究大口径瓦斯抽排钻井注浆固管过程中套管的稳定性,应用伯努利方程分析了注浆固管过程中浆液的动压力的变化规律。分析认为:注浆固管期间,若注浆管内过流面积小于套管与孔壁之间的过流面积,随着泵量的增加,导致套管外流体压力增加;当套管外与套管内压力差大于套管抗外挤强度时,套管发生失稳(瘪管)。结合工程实例,对套管失稳机理进行分析,提出了在固管过程中要控制泵量的建议。 相似文献
79.
The natural abundance15N/14N method was used to estimate the influence of silvicultural and P fertilization treatments on N accretion, N2fixation and N partitioning among tissues in a mature mesquiteProsopis glandulosavar.glandulosastand in Texas. The silvicultural treatments consisted of understory removal, herbicide treatment of brushy resprouts, thinning trees to single stems and 100 kg ha−1P fertilization. The trees had a mean basal diameter of 17·8 cm with 8 to 35 cm range. The stand was slow growing with the increase in dry matter ranging from 0·465 Mg ha−1year−1to 0·701 Mg ha−1year−1for the 8 years after the treatments were applied. N accretion after 8 years ranged from 3·1 kg ha−1year−1to 4·4 kg ha−1year−1.Due to the range in δ15N of the leaves, twigs, branches and trunk, we used the weighted (by biomass) average δ15N per tree in calculations of the percent N derived from N2fixation (%Ndfa). There was considerable variability in δ15N of the reference plants, i.e. from 3·3 to 5·9. In contrast there was low variability in the background δ15N of nearby soils (7·0±1·0). As the total above-ground biomass δ15N of a grass grown outside the influence of mesquite (7·8±0·58) had the same δ15N as the soil (7·5±1·0), we used the grass outside the influence of mesquite and the weighted tree mean δ15N to calculate % of N derived from N2fixation.The decrease in intraspecific competition by thinning multistemed trees to single stemmed trees was the only treatment that significantly (p= 0·0001) increased growth. Interspecific competition, i.e. understory removal, did not increase growth. There were no significant differences in total N production or N fixation among treatment means. The most striking result was the highly positive correlation between tree δ15N and total N per tree and biomass per tree (R2= 0·90,F= 164·4, df. = 18, mean square error (MSE) = 0·155,p= 0·0001). This implies that the younger trees colonizing infertile soils relied more heavily on N2fixation than larger trees which accumulated 1200 kg ha−1more N under their canopies. The percentage N derived from N2fixation ranged from 63 to 73% in the various treatments. Despite the high percentage of N derived from N2fixation, the N2fixation of the stand was very low, i.e. 1·98 to 2·80 kg N ha−1year−1, due to the low growth of the stand. We believe that comparisons of the whole tree weighted δ15N to background soil δ15N provides a more reasonable approach to estimate % N2fixation than comparisons of leaves of fixers and reference plants. 相似文献
80.
Measurements of nitrogen fixation (acetylene reduction) showed greatest rates in the saltmarsh pans with a benthic layer of cyanobacteria present. The smallest amount of nitrogen fixation occurred on the marsh surface where a Puccinellia maritima/Halimione portulacoides plant association shaded the underlying sediment. Phototrophic nitrogen fixation was always greater than dark, chemotrophic, bacterial fixation.Only a small proportion of the total amount of ammonium, which was formed during detrital breakdown, was nitrified to nitrate. Although there is a high capacity for bacterial nitrate reduction in these sediments, the process is limited by low nitrate availability and most nitrate upon reduction is converted to ammonium rather than being denitrified to gaseous products. Denitrification does not, therefore, result in any great loss of nitrogen from the saltmarsh.There was little net import or export of nitrogen on an annual basis, although nitrate and organic-N in small particulate material was removed from tidal water by the marsh, and there was net annual export of ammonium, dissolved organic-N and organic-N in large particulate material. Losses of nitrogen by the small net tidal export and by denitrification were approximately balanced by nitrogen fixation. It was concluded that the nitrogen cycle of the Colne Point saltmarsh was balanced on an annual basis, with most nitrogen being recycled within the marsh. The saltmarsh did not apparently act as a net source of nitrogen for the adjacent estuary, although it may act as an important processor of nitrogen, removing some forms of nitrogen such as nitrate from tidal water while exporting other forms of nitrogen such as dissolved organic-N. 相似文献