Importance of organic phosphate hydrolyzed in stalks of the lotic diatom <Emphasis Type="Italic">Didymosphenia geminata</Emphasis> and the possible impact of atmospheric and climatic changes

The aquatic colonial stalked diatom, Didymosphenia geminata, has acquired notoriety in recent years because of huge increases in many rivers of temperate regions. However, in some streams in northern England it has probably or, in the case of the R. Coquet (Northumberland), certainly been abundant for many decades. The paper describes the nutrient environment and phosphatase activities of Didymosphenia in Stony Gill (N. Yorkshire), a fast-flowing stream draining an upland catchment with peaty soils overlying limestone. Organic phosphate formed 85% of the filtrable phosphate in the water during the study (January–August 2000), with a maximum in April. Colonies were most abundant in June, but had disappeared by August. Surface phosphomonoesterase (PMEase) and phosphodiesterase activities assayed from March to July showed low PMEase activity in early March, but otherwise both were high throughout the period and especially so in June and July. Use of BCIP-NBT staining procedure showed that PMEase activity occurred in the stalks. A more detailed study of colony structure and staining with material from the R. Coquet in June 2006 also showed marked PMEase activity, with staining localized in the upper part of the stalks and the cells remaining unstained. It is suggested that organic phosphate is hydrolyzed in the stalk and the inorganic phosphate passes to the cell via a central tube in the stalk. It seems likely that organic phosphate as a major P source is a key factor favouring the success of Didymosphenia. The possible impact of environmental changes in the catchment such as climatic warming, C loss from peat and atmospheric N deposition is discussed. Handling editor: L. Naselli-Flores     

Seasonal phosphatase activities of mosses from Upper Teesdale,northern England

Abstract

Changes in tissue nutrient concentrations and surface phosphatase activities of eight moss species were measured over one year in terrestrial and semi-aquatic environments on Widdybank Fell, Upper Teesdale National Nature Reserve, northern England. Rates of phosphatase activity in apical regions of moss shoots differed markedly between species, but were generally greatest in the winter and least in the summer in most species. Mean values for phosphomonoesterase activity (µmol para-nitrophenol g^-1 d.wt h^-1) ranged from 18.2 for Polytrichum commune to 85.8 for Palustriella commutata var. falcata. Mean phosphodiesterase activity ranged from 3.1 for Polytrichum commune to 86.2 for Hylocomium splendens. In contrast, tissue nitrogen and phosphorus concentrations remained relatively constant throughout the year. Phosphatase activities were negatively correlated with tissue phosphorus concentration for several species, although few relationships were detected between ambient nutrient concentrations and phosphatase activity, tissue nitrogen, or tissue phosphorus concentration. These results demonstrate that phosphatase activities can provide a sensitive indicator of nutrient stress in terrestrial and semi-aquatic mosses, notably in the ectohydric Hylocomium splendens. However, further studies at sites with a wide range of nutrient levels are required to determine whether the technique can be used to indicate ambient nutrient status.     

Priming and microbial nutrient limitation in lowland tropical forest soils of contrasting fertility

Priming is an increase in soil organic carbon decomposition following input of labile organic carbon. In temperate soils where biological activity is limited commonly by nitrogen availability, priming is expected to occur through microbial acquisition of nitrogen from organic matter or stimulated activity of recalcitrant-carbon degrading microorganisms. However, these priming mechanisms have not yet been assessed in strongly weathered tropical forest soils where biological activity is often limited by the availability of phosphorus. We examined whether microbial nutrient limitation or community dynamics drive priming in three lowland tropical forest soils of contrasting fertility (‘low’, ‘mid’ and ‘high’) by applying C₄-sucrose (alone or in combination with nutrients; nitrogen, phosphorus and potassium) and measuring (1) the δ¹³C-signatures in respired CO₂ and in phospholipid fatty acid (PLFA) biomarkers, and (2) the activities of enzymes involved in nitrogen (N-acetyl β-glucosaminidase), phosphorus (phosphomonoesterase) and carbon (β-glucosidase, cellobiohydrolase, xylanase, phenol oxidase) acquisition from organic compounds. Priming was constrained in part by nutrient availability, because priming was greater when sucrose was added alone compared to when added with nutrients. However, the greatest priming with sucrose addition alone was detected in the medium fertility soil. Priming occurred in parallel with stimulated activity of phosphomonoesterase and phenol oxidase (but not N-acetyl β-glucosaminidase); when sucrose was added with nutrients there were lower activities of phosphomonoesterase and phenol oxidase. There was no evidence according to PLFA δ¹³C-incorporation that priming was caused by specific groups of recalcitrant-carbon degrading microorganisms. We conclude that priming occurred in the intermediate fertility soil following microbial mineralization of organic nutrients (phosphorus in particular) and suggest that priming was constrained in the high fertility soil by high nutrient availability and in the low fertility soil by the low concentration of soil organic matter amenable to priming. This first study of priming mechanisms in tropical forest soils indicates that input of labile carbon can result in priming by microbial mineralization of organic nutrients, which has important implications for understanding the fate of organic carbon in tropical forest soils.     

The effects of nutrient supply,predominantly addition of iron,and rhizobial inoculation on the tolerance of Lupinus pilosus genotypes to a calcareous soil

Two glasshouse experiments were conducted to examine the effects of nutrient supply and rhizobial inoculation on the performance of Lupinus pilosus genotypes differing in tolerance to calcareous soils. In experiment 1, plants were grown for 84 days in a calcareous soil (50% CaCO₃; soil water content 90% of field capacity) at four nutrient treatments (no-added nutrients, added nutrients without Fe, added nutrients with soil applied FeEDDHA, added nutrients with foliar applied FeSO₄). In experiment 2, plants were grown for 28 days with supply of NH₄NO₃ without inoculation or inoculated with Bradyrhizobium sp. (Lupinus). Chlorosis in the youngest leaves was a good indicator of the relative tolerance of the genotypes to the calcareous soil in both experiments, except the treatment with FeEDDHA at 5 mg kg^–1 soil which was toxic to all genotypes. Chlorosis scores correlated with chlorophyll meter readings and chlorophyll concentrations. The foliar application of FeSO₄ did not fully alleviate chlorotic symptoms despite concentrations of active or total Fe in the youngest leaves being increased. Adding nutrients and chemical nitrogen did not change the severity of chlorosis or improve the growth of the plant. The nutrient supply did not alter the ranking of tolerance of genotypes to the calcareous soil. The results suggest that nutrient deficiency or poor nodulation was not a major cause of poor plant growth on calcareous soils and that bicarbonate may exert a direct effect on chlorophyll synthesis. The mechanism for tolerance is likely to be related to an ability to exclude bicarbonate or prevent its transport to the leaves.     

Identification of alkaline phosphatase genes for utilizing a flame retardant,tris(2-chloroethyl) phosphate,in Sphingobium sp. strain TCM1

Tris(2-chloroethyl) phosphate (TCEP) is a haloalkyl phosphate flame retardant and plasticizer that has been recognized as a global environmental contaminant. Sphingobium sp. strain TCM1 can utilize TCEP as a phosphorus source. To identify the phosphomonoesterase involved in TCEP utilization, we identified four putative alkaline phosphatase (APase) genes, named SbphoA, SbphoD1, SbphoD2, and SbphoX-II, in the genome sequence. Following expression of these genes in Escherichia coli, APase activity was confirmed for the SbphoA and SbphoX-II gene products but was not clearly observed for the SbphoD1 and SbphoD2 gene products, owing to their accumulation in inclusion bodies. The single deletion of either SbphoA or SbphoX-II retarded the growth and reduced the APase activity of strain TCM1 cells on medium containing TCEP as the sole phosphorus source; these changes were more marked in cells with the SbphoX-II gene deletion. In contrast, the deletion of either SbphoD1 or SbphoD2 had no effect on cell growth or APase activity. The double deletion of SbphoA and SbphoX-II resulted in the complete loss of cell growth on TCEP. These results show that SbPhoA and SbPhoX-II are involved in the utilization of TCEP as a phosphorus source and that SbPhoX-II is the major phosphomonoesterase involved in TCEP utilization.

     

Alteration of phytoplankton phosphorus status during enrichment experiments: implications for interpreting nutrient enrichment bioassay results

We compared the results of phosphorus-enrichment bioassay experiments with alkaline phosphatase activity (APA) assays as indicators of phosphorus (P) limitation of in situ phytoplankton growth. In 4-d experiments, phytoplankton APA decreased or remained unchanged in P-enriched samples, but increased in unenriched samples, indicating a rapid alteration of the P status of the unenriched algae during the experimental incubations. In direct comparisons of enrichment bioassays and APA assays of reservoir phytoplankton samples, the results of the two methods corresponded in general, although contradictory results were not uncommon. Our data support the conclusion that enrichment experiments can indicate the potential for nutrient limitation of algal growth in the absence of other limiting factors, but do not necessarily demonstrate the occurrence of in situ nutrient limitation of phytoplankton production.     

Phosphatases ofAcinetobacter lwoffi. Localization and regulation of synthesis by orthophosphate

Several phosphomonoesterases and diesterases with various pH optima have been observed inAcinetobacter lwofi JW11. The osmotic shock fluids contained only those with an alkaline pH optimum. The synthesis of these phosphatases was regulated by external Pi concentrations. The shock fluids were fractionated by chromatography, yielding three fractions, two of which had hydrophobic properties. One of these contained an alkaline phosphatase that specifically required Ca²⁺ for activity. The diesterases required various divalent cations for their function. Mutants that lack phosphomonoesterase or both phosphomonoesterase and phosphodiesterase activities were isolated.     

石灰土演替过程中颗粒态有机质和矿物结合态有机质的微生物群落特征

碳酸盐岩经风化作用并在地形、植被、气候、时间及生物等因素的影响下逐渐演替出黑色石灰土、棕色石灰土、黄色石灰土和红色石灰土。【目的】研究不同演替阶段石灰土颗粒态有机质(particulate organic matter, POM)和矿物结合态有机质(mineral-associated organic matter, MAOM)的微生物群落特征,为岩溶土壤有机质稳定机制研究提供理论依据。【方法】以广西弄岗国家级自然保护区的黑色石灰土、棕色石灰土、黄色石灰土和红色石灰土为研究对象,运用湿筛法将土壤有机质(soil organic matter, SOM)分为POM和MAOM,分析其理化性质以及微生物群落特征。【结果】石灰土演替过程中POM和MAOM的有机碳、总氮、交换性钙含量均呈下降趋势,且MAOM的C/N均大于POM,POM的C/P均大于MAOM。细菌α多样性在黑色石灰土POM和MAOM中最高,且四类石灰土MAOM的真菌多样性比POM要高。Acidobacteria、Proteobacteria、Ascomycota均为石灰土演替过程中POM和MAOM的优势菌门。总磷是影响石灰土演替过...     

RETENTION OF P-NITROPHENOL AND 4-METHYLUMBELLIFERONE BY MARINE MACROALGAE AND IMPLICATIONS FOR MEASUREMENT OF ALKALINE PHOSPHATASE ACTIVITY1

During standardization of the methodology for estimating “cell-bound” alkaline phosphatase activity (APA: phosphomonoesterase) in Fucus spiralis L. (Phaeophyta), some of the nonphosphate moiety of the original phosphomonoester was found to be released to the medium subsequent to completion of the routine assays. This occurred with the two substrates generally employed in APA measurements: p-nitrophenyl phosphate (pNPP) and 4-methylumbelliferyl phosphate (MUP). Other marine macrophytes tested showed the same phenomenon. The conditions influencing retention were investigated to establish the simplest procedure for measuring APA. When using pNPP, the release of the product (p-nitrophenol) after the assays was maximum when assays were run for longer than 20 min and at slightly acid pH or at high pNPP concentrations. When using MUP, the leakage of the product (4-methylumbelliferone) after the assays was maximum when APA measurements were run for longer than 40 min and at neutral pH or at high MUP concentrations. The significance of the leakage of the nonphosphate moiety after APA assays is discussed.     

Surface phosphomonoesterase activity of a natural immobilized system: Chroococcidiopsis in an Antarctic desert rock

The phosphomonoesterase activity of a microbialcommunity dominated by Chroococcidiopsis in arock sample from the Antarctic dry desert was comparedwith that of a non-axenic culture of thecyanobacterium isolated from the same rock in order toestablish whether the organism differed in itsproperties when immobilized in the rock. The pHoptimum (9.5) was the same, but the response totemperature and light both differed. In the case oftemperature, the optimum was much higher in culture. Light flux at the low value of 8 mol photonm^-2 s^-1 was slightly inhibitory for acrushed rock sample, but enhanced activity of thecultured material. Although materials both showeda typical (apparent) Michaelis-Menten relationship,the values for Km and V_max differed. Itis suggested that study of natural immobilized systemsis important for the development of procedures to useimmobilized phototrophs for practical purposes.     

Phosphatase activities of the aquatic moss <Emphasis Type="Italic">Warnstorfia fluitans</Emphasis> (Hedw.) Loeske from an acidic stream in North-East England

A study was made of the aquatic environment, tissue nutrient composition and surface phosphatase activities of the aquatic moss Warnstorfia fluitans in Brandon Pithouse Stream, a small acidic stream in N-E England. The water, which originates from an underground spring, had been pH 2.6 for at least 30 years, but about 3.9 during the present study. The moss was by far the most abundant phototroph during all this period. Seasonal changes in aqueous nitrogen and phosphorus fractions were measured over a 2-year period near the source. Most of the filtrable N and P were at times organic, but the very high N:P ratio (even if organic N is excluded) suggests that only organic phosphate is likely to be important for the moss. There was a high peak in organic phosphate in late spring in both study years. Surface phosphomonoesterase (PMEase) and phosphodiesterase (PDEase) activities were highly correlated in the field and in axenic culture, though there were some differences in response to environmental factors. Axenic material showed higher PMEase and PDEase activities when grown with organic P than with inorganic P. Although the data suggest that internal P content is an important factor influencing phosphatase activities, PDEase activity was especially marked when the moss was grown with the diester, DNA, as P source, indicating that at least one of its surface phosphatases can also respond directly to the environment. Handling editor: S. M. Thomaz     

3种菊科入侵植物不同生长时期的土壤酶活性和养分变化

【目的】黄顶菊、三叶鬼针草和豚草是我国危害较严重的3种菊科入侵植物。了解3种菊科植物生长过程中土壤养分和酶活性的变化,可以为研究其入侵机制提供依据。【方法】在中国农业科学院植物保护研究所廊坊中试基地开展同质园实验,比较分析了黄顶菊、三叶鬼针草和豚草3种菊科入侵植物在幼苗期、旺盛生长期和生殖生长期根际土壤养分和酶活性的变化。【结果】3种外来菊科植物的生长时期对土壤养分和酶活性存在显著影响。3种外来植物入侵域的土壤速效磷、硝态氮含量以及磷酸酶活性随生长时期变化都表现出先升高后降低的趋势,均在旺盛生长期达到最大值。入侵域土壤速效磷和硝态氮含量的变化趋势与狗尾草明显不同。3种外来植物入侵降低了土壤速效钾含量,提高了土壤脲酶、磷酸酶活性。【结论】3种外来菊科植物的入侵改变了土壤养分和酶活性,创造出更有利于自身生长和繁殖的条件,以利于其进一步扩张。     

Phototrophic Biofilms on Ancient Mayan Buildings in Yucatan, Mexico

Buildings at the important archaeological sites of Uxmal and Kabah, Mexico, are being degraded by microbial biofilms. Phospholipid fatty acid (PLFA) and chlorophyll a analyses indicated that phototrophs were the major epilithic microorganisms and were more prevalent on interior walls than exterior walls. Culture and microscopical techniques showed that Xenococcus formed the major biomass on interior surfaces, but the stone-degrading genera Gloeocapsa and Synechocystis were also present in high numbers. Relatively few filamentous algae and cyanobacteria were detected. The fatty acid analysis also showed that complex biofilms colonize these buildings. Circular depressions observed by scanning electron microscopy (SEM) on stone and stucco surfaces beneath the biofilm corresponded in shape and size to coccoid cyanobacteria. SEM images also demonstrated the presence of calcareous deposits on some coccoid cells in the biofilm. Phototrophic biofilms may contribute to biodegradation by (1) providing nutrients that support growth of acid-producing fungi and bacteria and (2) active “boring” behavior, the solubilized calcium being reprecipitated as calcium carbonate. Received: 15 March 1999 / Accepted: 24 June 1999     

Phosphatase activity of benthic marine algae. An overview

This review provides an account of the phosphatase activities of benthicmarine algae and is based on reports for more than a hundred species, includingcyanobacteria, red, brown and green algae. Particular emphasis is given to theuse of phosphomonoesterase activity as a rapid means of assessing thephosphorusstatus of the alga and thus indirectly that of the environment. Anunderstandingof the influence of environmental factors and the growth pattern of theparticular alga is important in carrying out assays. For instance, the responseto light differs markedly between species, especially in short-term assays,whenthe effect can be obvious or none. Considerations about the methodology formeasuring "alkaline phosphatase activity" are discussed, particularly whethertosimulate field conditions or to use optimum conditions. Recommendations aresuggested concerning the best methodology for routine use, followed by adiscussion of the future prospects for the method.     

Phosphatase Activities of Endolithic Communities in Rocks of the Antarctic Dry Valleys

Abstract Phosphorus is scarce in Beacon Sandstone of the McMurdo Dry Valleys, Antarctica, and any input from precipitation is minimal. In endolithic microbial communities recycling of P by the action of phosphatases may therefore be important. The phosphatase activities of three different types of endolithic communities in the McMurdo Dry Valley, Antarctica, were studied in the laboratory. The dominant phototrophs were Chroococcidiopsis, mixed Gloeocapsa and Trebouxia, and Trebouxia. Bacteria were also visually conspicuous in the latter two communities, and the Trebouxia in both cases formed a lichenized association with fungal hyphae. In each case marked phosphomonoesterase (PMEase) activity was found in assays with 4-methylumbelliferyl phosphate (MUP) or p-nitrophenyl phosphate as substrate, and phosphodiesterase activity with bis-p-nitrophenyl phosphate as substrate. The pH optimum of PMEase (assayed at 0.5 pH intervals) of the Chroococcidiopsis, Gloeocapsa–Trebouxia, and Trebouxia communities was 9.5, 5.5, and 8.0, respectively. These values are similar for aqueous extracts of the respective rocks (pH 9.2, 6.2, 7.5). All three communities showed significantly higher PMEase activity at 5° than 1°C, and the first two also showed much higher activity at 5° than 10°C. All three communities also showed slightly lower activity in the light (7 μmol photon m^-2 s^-1) than the dark; this was found with all substrates and substrate concentrations. Prior exposure of a moistened sample to light for 2 h led to a reduction in activity even when the subsequent assay was done in the dark. The rate of PMEase activity (using 100 μM MUP) in the Gloeocapsa–Trebouxia and Trebouxia communities was approximately linear with time up to 24 h, whereas the Chroococcidiopsis community showed a marked decrease after 6 h. At least part of this was due to retention of the 4-methylumbelliferone (MU) hydrolysis product. In spite of the assays being conducted on a whole community, the activity–substrate relationship in each case quite closely resembled a typical Michaelis–Menten relationship. Estimates were made of the apparent half-saturation value and the concentration of MUP required to support half-maximal rates. The apparent K _m values were: Chroococcidiopis, 230 μM; Gloeocapsa–Trebouxia 169 μM; Trebouxia, 135 μM. The respective values for apparent V _max were 0.053, 0.55, and 0.35 μmol MU g^-1 h^-1. In view of the greater dependence of these communities on the rock for their sole supply of P than for C and probably N, it is suggested that the cycling of P within the communities is a key factor influencing their overall metabolic activity when moisture permits their activation. Received: 16 June 1999; Accepted: 23 August 1999; Online Publication: 24 March 2000     

Changes in alkaline phosphatase activity and phosphate uptake in P-limited phytoplankton,induced by light intensity and spectral quality

Alkaline phosphatase activity and P uptake were determined in P-limited Dunaliella tertiolecta, Thalassiosira pseudonana, Phaeodactylum tricornumtum, and Prymnesium parvum grown under different light intensities and colors. Both intracellular and extracellular enzyme activities varied with the intensity and quality of light in a species-specific manner. The spectral composition of the light also affected P uptake kinetics. No correlation was found between enzyme activity and V_max both within a species and for pooled data for all four species, indicating that the change in uptake kinetics and enzyme activity was not related to P limitation, but induced by the light conditions. Changes in the optimum N:P ratio induced by light were also not related to P uptake kinetics or enzyme activity. These data suggest that light conditions may in themselves have profound effects on species competition for limiting nutrients. Furthermore, since both alkaline phosphatase activity and P uptake were influenced by the prevailing light conditions we suggest that these parameters be used cautiously when determining the P nutritional status of phytoplankton in nature.Address for reprint requests     

Response of root and sediment phosphatase activity to increased nutrients and salinity

Wetlands of northern Belize, distributed along a salinity gradient, are strongly phosphorus limited and dominated largely by three species of emergent macrophytes: Eleocharis cellulosa, Cladium jamaicense, and Typha domingensis. We assessed changes in root and sediment phosphatase activities of each species to simultaneous changes of nutrients (N, P) and salinity in a mesocosm experiment. Phosphorus and nitrogen treatment effects on both root and sediment phosphatase were highly significant for all the species, while salinity significantly affected root phosphatase activity in Cladium only. All species showed a significant negative correlation between root phosphatase activity and increasing tissue P content until a threshold of 0.2% P, 0.15% P and 0.12% P in Eleocharis, Cladium and Typha, respectively. There was also a significant negative correlation between soil available P and root and sediment phosphatases in all species. Activity of root phosphatases of Eleocharis and Typha were positively correlated with root tissue N. Both root and sediment phosphatases of all three species were positively correlated with soil available N. The strongest (positive) correlation was found between phoshatase activites and N/P ratios. The results confirmed that these systems are P-limited and that extracellular phosphatases respond to P enrichment by decreasing their activities. Expression of root phosphatase activity by dry root weight, sediment volume, or whole plant biomass gave very different relative results across nutrient treatments and species, suggesting that root phosphatase activities need to be interpreted in a wider context that considers root density.     

漓江流域海拔、土壤及植被对土壤养分和酶化学计量比的影响

漓江流域海拔、土壤类型和植被类型多样。为研究其土壤养分和土壤酶活性特征,该研究以漓江流域石灰性土壤及酸性土壤的典型植被类型(自然林、毛竹林、马尾松林、果园、水稻田)的表层土壤(0～20 cm)为研究对象,测定土壤养分含量及碳氮转化相关胞外酶(淀粉酶、蔗糖酶、脲酶、蛋白酶、过氧化氢酶)活性及化学计量比特征。结果表明:(1)高海拔土壤的全氮(TN)、全磷(TP)、有效磷(AP)含量和淀粉酶、蔗糖酶、脲酶、蛋白酶活性相对较高,而过氧化氢酶活性则正好呈现相反的趋势。(2)相对于酸性土壤,石灰性土壤有较高的TP和AP含量。在酸性土壤中,植被类型对氮磷养分影响较大,总体上人工植被使得土壤氮素降低而使磷素增加; 而石灰性土壤养分在不同植被类型间差异相对较小。(3)相比自然林,人工植被的土壤氮转化酶活性极大降低,而土壤碳转化酶活性受人为影响程度相对较小,土壤氮磷酶活性化学计量比显示自然林呈现氮限制而人工林呈现碳限制。(4)典范对应分析(CCA)显示土壤理化性质在第Ⅰ轴和第Ⅱ轴解释了86.56%的土壤酶活性变异,土壤理化性质解释贡献率排序为TN>pH>铵态氮(NH₄⁺)>AP>TP>硝态氮(NO₃^-),其中前3个因子是造成土壤酶活性差异的主要因子。综上结果表明,漓江流域的酸性土壤对人为干扰的生态敏感性较高,植被变化易导致养分失衡,应注重土壤养分管理,防止土壤有机质的损失,提高漓江流域景观资源可持续利用的价值。该研究为当地生态系统的科学保育和开发提供了理论依据。     

Nutrient regeneration by zooplankton: effects on nutrient limitation of phytoplankton in a eutrophic lake

We tested the hypothesis that excretion of nutrients by zooplanktoncan reduce the severity of nutrient limitation of phytoplankton,and determine whether the phytoplankton community is limitedby nitrogen or phosphorus. In situ experiments were conductedin eutrophic Lake Mendota (Wisconsin, USA) during the summerof 1988, where phytoplankton were limited by N and P, but periodsof nutrient limitation were transitory Increased zooplanktonbiomass and the consequent increased excretion of nutrientsby zooplankton reduced P limitation (as measured by specificalkaline phosphatase activity) in all experiments Excretionof nutrients also reduced N limitation (as measured by ammoniumenhancement response) in one of three experiments. In additionalexperiments in the more highly eutrophic Lake Wingra, excretionof nutrients by zooplankton reduced both N and P limitationThese results support the hypothesis that zooplankton have potentiallyimportant indirect effects on phytoplankton communities throughrecycling of nutrients     

Impact of eutrophication on shallow marine benthic foraminifers over the last 150 years in Osaka Bay, Japan

High-resolution foraminiferal analysis was conducted on a short sediment core from the inner part of Osaka Bay, Japan. Changes in foraminiferal assemblages were associated with eutrophication, bottom water hypoxia, and changes in red tide-causing algae. Before the 1920s, the calcareous species Ammonia beccarii, and the agglutinated species Eggerella advena and Trochammina hadai were rare, but calcareous foraminifers in general were abundant. Between the 1920s and 1940s, calcareous foraminifers decreased abruptly in abundance, while A. beccarii, E. advena and T. hadai increased in abundance. This faunal change corresponded in time to an increase in nutrients flowing in through the Yodo River, and bottom water hypoxia related to eutrophication. In the 1960s and 1970s, A. beccarii, E. advena and T. hadai further increased in abundance to become dominant, and many calcareous foraminifers nearly disappeared, corresponding to increasing bottom water hypoxia related to the rapid increase in discharged nutrients during the high economic growth period from 1953 to 1971. After the 1990s, A. beccarii decreased rapidly in abundance and E. advena and Uvigerinella glabra increased in abundance. The main components of red tide-causing algae changed from dinoflagellates to diatoms in the 1980s through 1990s, thus there was a change in the food supply to the benthos, which may have caused the increase in abundance of E. advena and U. glabra.