首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   8篇
  完全免费   1篇
  2010年   1篇
  2009年   1篇
  2003年   1篇
  2002年   1篇
  2001年   1篇
  2000年   1篇
  1997年   1篇
  1991年   1篇
  1989年   1篇
排序方式: 共有9条查询结果,搜索用时 15 毫秒
1
1.
We measured porewater profiles of inorganic (NH4 +, NO3 (+NO2 ), PO4 3– (hereafter referred to as DIP)) and organic (DON, DOP) nutrients in seagrass-vegetated sediments at two sites in a shallow bay in Bermuda within close proximity (200 m) but subject to different nutrient loading. At both sites, total dissolved and inorganic nutrient concentrations were usually 1–2 orders of magnitude higher in the sediments than in the water column, with the exception of NO3 . Organic N and P were significant components of the total dissolved nutrient pools both in the sediment porewater and in the overlying water column (up to 75% for DON and 40% for DOP), and may be important in meeting plant nutrient demands. We used two approaches to examine how well porewater nutrient concentrations reflected the relative availabilities of N and P for seagrasses: (1) a simple stoichiometric nutrient regeneration model based on the N:P ratio of decomposing organic matter and porewater NH4 + concentrations to predict porewater DIP, and (2) fitting of the porewater profiles to estimate rates of net nutrient production (or consumption), which reflects the balance between nutrient sources and sinks in the rhizosphere. The stoichiometric model indicated that sediment porewaters were depleted in P relative to N in the low-nutrient outer bay site, and enriched in P relative to N in the higher-nutrient inner bay site. These results are consistent with the mechanism of carbonate sediments in oligotrophic tropical environments being a strong sink for dissolved inorganic P and our previous work suggesting that nutrient enrichment causes P to become disproportionately more available than N. Net nutrient production rates of porewater P at both sites and N at the inner bay site were low (typically < 2%) relative to the nutrient demands of the seagrasses. The implications of the profile interpretation are two-fold: (1) the low rates of net nutrient production indicate diffusive losses from the root zone were insignificant and that nutrient turnover rates were high, except in the P-limited outer bay where N accumulated in sediment porewaters; and (2) because standing stock nutrient concentrations often represent a small fraction of the total nutrients cycled in the sediments, they are in many cases a poor indicator of nutrient availability. Based on our estimates of losses from the root zone, decomposition, and plant uptake we have constructed a rough budget for the cycling of P and N at our two sites.  相似文献
2.
In 1998, the concentration of phosphomonoesters, a biologically available fraction of the dissolved organic phosphorus pool, was measured along Palmones River (a small Mediterranean river in Southern Spain) and its estuary. Due to the extremely low phosphomonoester concentration in the river (usually under detection limits by analytical procedures), a method using chromatographic cartridges to concentrate this compound was used. Phosphomonoester concentration was usually in the nanomolar range, although values up to 6 m were measured in a sampling station near an effluent of domestic sewage and a cellulose pulp plant. Concentrations were always lower than the dissolved reactive phosphorus (mostly orthophosphate). Phosphomonoesters represented a variable percentage of the dissolved organic phosphorus, from negligible percentages up to 56%. Besides, a highly significant correlation between these two phosphorus fractions was found.In addition, phosphomonoesterase (alkaline phosphatase) activity was measured in the water and macrophytobenthos (both algae and aquatic phanerogams) along the river and the estuary. In water, most of the phosphatase activity upstream was regarded as soluble. This was confirmed by the difficulty of performing kinetic studies in the unfiltered samples. On the contrary, the phosphomonoesterase activity in the estuary was attributed to different size fractions, suggesting that phosphomonoesters are used actively as a phosphate source by bacteria and phytoplankton, with relative contributions depending on the sampling period.  相似文献
3.
Winter and summer water column profiles from a transect co-inciding with the 54° N parallel across the Irish Sea were examined for relationships between the fractions of total dissolved nitrogen and phosphorus. Inorganic nitrogen and phosphorus gave the expected seasonal variation. As inorganic nitrogen concentrations decreased during the summer, dissolved organic nitrogen concentrations increased. Dissolved organic phosphorus showed little seasonal variation and formed a smaller fraction of the total dissolved pool compared to nitrogen. Winter inorganic nitrogen and phosphorus salinity relationships were conservative: winter organic nitrogen and phosphorus salinity relationships were not conservative. In the winter, dissolved organic nitrogen and phosphorus formed a significant fraction of the total dissolved pool.  相似文献
4.
一株可溶性有机磷去除菌的分离及其生物学特性   总被引:1,自引:1,他引:0       下载免费PDF全文
以甘油磷酸钠(Sodium Glycerophosphate, 以下简称NaGly)作为外源可溶性有机磷, 从富营养化的养殖池污泥中分离到5株可溶性有机磷去除菌株, 通过除磷率比较, 筛选出一株最为高效的菌株D2, 其对初始浓度为5 mg/L甘油磷酸盐磷(Phosphorus Glycerophosphate, 以下简称GP-P)的去除率可达99.0%。此外, 对其进行了16S rRNA基因序列测定, 并进一步研究了其生长特性与除磷特性。试验结果表明, 菌株D2为肠球菌(Enterococcus sp.), 与屎肠球菌(Enterococcus faecium)菌株KT4S13 (登录号: AB481104)和CICC6078 (登录号: DQ672262)的16S rRNA 基因序列相似性近100%; 其生长周期为: 0-4 h为生长迟缓期, 4-8 h为对数生长期, 8-28 h为稳定期, 28 h以后为衰亡期; 且在15°C-40°C、pH 4.0-9.0以及5-40 mg/L GP-P条件下均能够生长, 其中菌株D2最适生长的温度范围和pH范围分别为30°C-35°C、6.0-7.0, 而且20-30 mg/L GP-P能显著促进菌株D2生长。此外, 菌株D2在进入衰亡期之前随着作用时间的延长, 对20 mg/L GP-P的除磷率逐渐升高, 在进入衰亡期后的28-32 h内对20 mg/L GP-P的除磷效果趋于稳定, 其在15°C-40°C、pH 4.0-9.0以及5-40 mg/L GP-P条件下均具有除磷作用, 其最适除磷温度范围、pH范围和GP-P浓度范围分别为25°C-35°C、6.0-7.0和5-10 mg/L。  相似文献
5.
Dissolved organic matter (DOM) plays several important roles in forest ecosystem development, undergoing chemical, physical and/or biological reactions that affect ecosystem nutrient retention. Very few studies have focused on gross rates of DOM production, and we know of no study that has directly measured DOM production from root litter. Our objectives were to quantify major sources of total potentially water-soluble organic matter (DOMtps) production, with an emphasis on production from root litter, to quantify and compare total potentially soluble organic C, N, and P (DOCtps, DONtps, and DOPtps) production, and to quantify changes in their production during forest primary succession and ecosystem development at the Mt. Shasta Mudflows ecosystem chronosequence. To do so, we exhaustively extracted freshly senesced root and leaf and other aboveground litter for DOCtps, DONtps, and DOPtps by vegetation category, and we calculated DOMtps production (g m−2 y−1) at the ecosystem level using data for annual production of fine root and aboveground litter. DOM production from throughfall was calculated by measuring throughfall volume and concentration over 2 years. Results showed that DOMtps production from root litter was a very important source of DOMtps in the Mount Shasta mudflow ecosystems, in some cases comparable to production from leaf litter for DONtps and larger than production from leaf litter for DOPtps. Total DOCtps and DONtps production from all sources increased early in succession from the 77- to the 255-year-old ecosystem. However, total DOPtps production across the ecosystem chronosequence showed a unique pattern. Generally, the relative importance of root litter for total fine detrital DOCtps and DONtps production increased significantly during ecosystem development. Furthermore, DOCtps and DONtps production were predominantly driven by changes in biomass production during ecosystem development, whereas changes in litter solubility due to changes in species composition had a smaller effect. We suggest that DOMtps production from root litter may be an important source of organic matter for the accumulation of SOM during forest ecosystem development. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Shauna M. Uselman, Robert G. Qualls, and Juliane Lilienfein conceived of or designed the study and performed research. SMU analyzed data and wrote the article. SMU and RGQ contributed new methods or models.  相似文献
6.
Organically bound phosphorus (P) is a mobile form of phosphorus in many soils and thus its dynamics relevant for the leaching and cycling of this element. Despite its importance, little is known about the chemical composition of dissolved organic P. We studied the concentrations, fluxes, and chemical composition of organic P in forest floor leachates and soil solutions in a Rendzic Leptosol under a 90-year-old European beech (Fagus sylvatica L.) forest over a 27-month period (1997–1999). The chemical composition of organic P was analysed using XAD-8 fractionation and 31P-nuclear magnetic resonance (NMR) spectroscopy. Organic P was the dominant P form in forest floor leachates as well as in porewaters of the mineral soil. The largest concentrations of organic P were observed during summer and peaked (330–400 g dissolved organic P l–1) after rain storms following short dry periods, concurrently with the concentrations of organic carbon (OC). Because of high rainfall, fluxes of organic P (and C) were greatest in autumn although concentrations of organic C and P were lower than in summer. In forest floor leachates, the hydrophilic fraction of dissolved organic matter contained 83 ± 13% of the bulk organic P. In soil solutions from 90 cm depth, organic P was almost exclusively in the hydrophilic fraction. Because of the low retention of the hydrophilic fraction of dissolved organic matter in the mineral soils, concentrations of organic P in soil water remained almost constant with depth. Consequently, organic P contributed > 95% of the total P leached into deeper subsoils. The overall retention of organic P in the weakly developed mineral soils was little and so the average annual fluxes of organic P in subsoils at 90 cm depth (38 mg m–2) comprised 67% of those from the forest floors (57 mg m–2) during the study period. Hence, organic P proved to be mobile in the studied soil. 31P-NMR spectroscopy confirmed the dominance of organic P species in soil water. Signals due to inorganic P occurred only in spectra of samples collected in winter and spring months. Spectra of samples from summer and autumn revealed traces of condensed phosphates. Due to low P contents, identification of organic P species in samples from winter and spring was not always possible. In summer and autumn, monoester and diester phosphates were the dominant organic species and varied little in their relative distributions. The distribution of organic species changed little from forest floor leachates to the subsoil solutions indicating that the composition of P-containing compounds was not influenced by sorptive interactions or biological transformation.  相似文献
7.
Cultures of the soil bacterium Serratia liquifaciens grimesii were grown with32 P labelled phosphate, to produce a uniformly32 P labelled source of microbial P. Extracts of the bacteria were prepared by sonication, dialysis and filtration to provide a clear sterile solution which was characterised in terms of dissolved organic and condensed P (DOP and DCP) and molecular weight range. The extract was used as a source of P to Agrostis capillaris L. seedlings in nutrient solution from which orthophosphate was omitted. In a time course experiment, root surface phosphatase activity increased as soon as extract was added to the root medium, DOP was rapidly hydrolysed and orthophosphate concentration increased rapidly. These processes were complete within about 8 h, after which phosphatase activity fell to its original level, and the plants absorbed molybdate reactive P from the nutrient solution so that it reached its original concentration over 48 h. DCP concentrations did not change significantly throughout the experiment. This work clearly demonstrated that DOP but not DCP, as a component of a bacterial extract produced by a relatively straightforward method, was quickly hydrolysed and the P made available for plant uptake.  相似文献
8.
Release of soluble reactive phosphorus (SRP) from dissolved organic phosphorus (DOP), concentrated by reverse osmosis of water samples from Lough Neagh Northern Ireland, was measured in the presence of enzymes and cultures of lake water bacteria in a basal liquid medium adjusted to the pH of lake water (7.6). No hydrolysis of unfractionated DOP was observed in the presence of alkaline phosphatase but a combination of alkaline phosphatase and phosphodiesterase mineralized 14% of DOP in a 30 day incubation period at 15 °C. A similar amount of mineralization was attained by phytase. Phytase induced the same degree of mineralization in a range of DOP fractions varying from MW > 100 000 to c. 500. A mixed culture of lake water bacteria mineralized 12% of unfractionated DOP. Single cultures of lake water bacteria displayed low mineralizing activity (mean of 49 cultures = 5% DOP hydrolysed). Results indicate that DOP from Lough Neagh in the above molecular weight range is predominantly recalcitrant to bacterial mineralization under natural lake conditions.  相似文献
9.
Shuji Hino 《Hydrobiologia》1989,174(1):49-55
The molecular weight distribution of dissolved organic phosphorus (DOP) and the possible mechanisms of orthophosphate (Pi) release were examined by gel filtration and incubation with some hydrolytic enzymes. Sixty five percent of the DOP appeared to have apparent molecular weights between 300 to 10000 daltons. Less than 10% of the DOP estimated higher molecules greater than 10000 daltons. Alkaline phosphatase released Pi more easily from low molecular weight (< 1500 daltons) DOP than from high molecular weight fractions. While, addition of nucleases or phosphodiesterase alone did not appear Pi release from high molecular weight DOP compounds. Pi release from those DOP compounds increased markedly (more than 30%) when alkaline phosphatase was incubated with nucleases or phosphodiesterase. However, 60% of DOP did not release Pi when alkaline phosphatase was incubated with either enzymes.  相似文献
1
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号