Addition Of Mineral Nutrients Research Articles

Effect of combined application of inorganic nitrogen and phosphorus to an organic-matter poor soil on soil organic matter cycling.

Sequestering carbon dioxide (CO2) in agricultural soils promises climate change mitigation as well as sustainable ecosystem services. In order to stabilize crop residues as soil carbon (C), addition of mineral nutrients in excess to crop needs is suggested as an inevitable practice. However, the effect of two macronutrients i.e., nitrogen (N) & phosphorus (P), on C cycling has been found contradictory. Mineral N usually decreases whereas mineral P increases the soil organic C (SOC) mineralization and microbial biomass. How the addition of these macronutrients in inorganic form to an organic-matter poor soil affect C cycling remains to be investigated. To reconcile this contradiction, we tested the effect of mineral N (120 kg N ha-1) and/or P (60 kg N ha-1) in presence or absence of maize litter (1 g C kg-1 soil) on C cycling in an organic-matter poor soil (0.87% SOC) in a laboratory incubation. Soil respiration was measured periodically during the incubation whereas various soil variables were measured at the end of the incubation. Contrary to literature, P addition stimulated soil C mineralization very briefly at start of incubation period and released similar total cumulative CO2-C as in control soil. We attributed this to low organic C content of the soil as P addition could desorb very low amounts of labile C for microbial use. Adding N with litter built up the largest microbial biomass (144% higher) without inducing any further increase in CO2-C release compared to litter only addition. However, adding P with litter did not induce any increase in microbial biomass. Co-application of inorganic N and P significantly increased C mineralization in presence (19% with respect to only litter amended) as well as absence (41% with respect to control soil) of litter. Overall, our study indicates that the combined application of inorganic N and P stabilizes added organic matter while depletes the already unamended soil.

Cow Manure Disposal Using an Earthworm Bio-Bed and the Development of a Vermicompost-Based Substrate for Capsicum Seedlings

ABSTRACTVermicompost is becoming an important substitute for peat in horticulture due to the negative consequences of peat depletion. There is no aerobic fermentation pretreatment in the process of direct digestion of fresh cow manure by earthworms, which resulted in different properties of vermicompost compared with traditional treatment methods. However, there is limited knowledge on the properties of vermicompost in the direct earthworm digestion process. In the present study, a large-scale earthworm bio-bed was used to convert fresh cow manure into vermicompost, and then the physical, chemical, and microbial properties of the vermicompost were determined. To study the influence of mineral nutrient additions, vermicompost was mixed with vermiculite at a ratio of 4:1 (v/v), and was then used as the growth medium for capsicum seedlings. The results showed that nitrate nitrogen (243.39 mg/kg), ammonium nitrogen (50.38 mg/kg), total phosphorus (47.61 g/kg), available phosphorus (41.68 g/kg), catalase activity (2.17 mL/g·h), bacterial biomass (3.60 × 107 cfu/g), actinobacterial biomass (2.40 × 107 cfu/g), and fungal biomass (1.55 × 106 cfu/g) measurements were significantly higher in vermicompost than in the parent material. However, moisture (50.01%), electrical conductivity (2.07 mS/cm), total nitrogen (8.52 g/kg), organic matter (28.47%), and urease activity (0.63 mL/g·h) were significantly lower in the vermicompost compared to the parent material. The shoot and root morphological indices and the capsicum biomass accumulation measurements in the vermicompost treatments were superior to those found in the commercial peat medium (CK). Leaf expansion (14.83 cm), shoot height (24.20 cm), stem diameter (4.38 cm), leaf number (16.20 No.), root length (352.83 cm), root surface area (60.30 cm2), root diameter (0.61 mm), and root volume (0.92cm3) significantly higher in vermicompost-vermiculite mixed media with added urea (0.5 kg/m3), superphosphate (10.0 kg/m3), and potassium chloride (1.0 kg/m3) than in CK at the late seedling growth stage. The addition of mineral nutrients (NPK) had little effect on the physical properties of the vermicompost media, but it improved the available nutrients. In summary, fresh cow manure without pre-treatment can be processed into vermicompost using a large-scale earthworm bio-bed. Vermicompost could serve as an alternative for commercial peat media in the cultivation of capsicum plug seedlings, and the beneficial effects of adding NPK gradually emerged as the seedling growth time increased.

Soil microbial CNP and respiration responses to organic matter and nutrient additions: Evidence from a tropical soil incubation

Soil nutrient availability has a strong influence on the fate of soil carbon (C) during microbial decomposition, contributing to Earth's C balance. While nutrient availability itself can impact microbial physiology and C partitioning between biomass and respiration during soil organic matter decomposition, the availability of labile C inputs may mediate the response of microorganisms to nutrient additions. As soil organic matter is decomposed, microorganisms retain or release C, nitrogen (N) or phosphorus (P) to maintain a stoichiometric balance. Although the concept of a microbial stoichiometric homeostasis has previously been proposed, microbial biomass CNP ratios are not static, and this may have very relevant implications for microbial physiological activities. Here, we tested the hypothesis that N, P and potassium (K) nutrient additions impact C cycling in a tropical soil due to microbial stoichiometric constraints to growth and respiration, and that the availability of energy-rich labile organic matter in the soil (i.e. leaf litter) mediates the response to nutrient addition. We incubated tropical soil from French Guiana with a 13C labeled leaf litter addition and with mineral nutrient additions of +K, +N, +NK, +PK and +NPK for 30 days. We found that litter additions led to a ten-fold increase in microbial respiration and a doubling of microbial biomass C, along with greater microbial N and P content. We found some evidence that P additions increased soil CO2 fluxes. Additionally, we found microbial biomass CP and NP ratios varied more widely than CN in response to nutrient and organic matter additions, with important implications for the role of microorganisms in C cycling. The addition of litter did not prime soil organic matter decomposition, except in combination with +NK fertilization, indicating possible P-mining of soil organic matter in this P-poor tropical soil. Together, these results point toward an ultimate labile organic substrate limitation of soil microorganisms in this tropical soil, but also indicate a complex interaction between C, N, P and K availability. This highlights the difference between microbial C cycling responses to N, P, or K additions in the tropics and explains why coupled C, N and P cycle modeling efforts cannot rely on strict microbial stoichiometric homeostasis as an underlying assumption.

Maize productivity dynamics in response to mineral nutrient additions and legacy organic soil inputs of contrasting quality

Residual effects of organic inputs of contrasting quality on maize productivity were investigated as a function of soil degradation in the highlands of western Kenya. Tithonia (Tithonia diversifolia (Hemsl.) A. Gray) green manure, cypress sawdust (Cupressus lusitanica Mill.), and biochar made from eucalyptus wood (Eucalyptus saligna Sm.) were applied at a rate of 6tCha−1 for three cropping seasons, both with and without mineral fertilizer additions (120kgNha−1, 100kgKha−1, 100kgPha−1). Maize grain yield was monitored for six years beyond the initial organic matter additions. During the years when amendments were added, tithonia applications resulted in the greatest yield increases, between 153 and 183% more than the unamended control in comparison to increases by136% with biochar and by 107% with sawdust additions. In contrast to application of tithonia, peak yields with sawdust or biochar in most cases occurred 1–2 years after additions had ended. Yet during the same period, yields in fields that had previously received tithonia were on average still 71% of peak yields. Four years later, yields declined to between 28 and 22% of peak yields, whereas yields after biochar and sawdust applications declined to between 57 and 25% of peak values. Six years after organic matter additions ended, maize yields were not significantly different irrespective of additions of the quality of organic amendments. The data indicate that yield responds in the short-term to input quality and specifically the amount of applied N; while the residual effects of organic matter additions on yield dynamics may relate more to legacy effects of high crop residue return, input C quality and increasing soil C.

Synergistic and antagonistic interactions among organic amendments of contrasted stability, nutrient availability and soil organic matter in the regulation of C mineralisation

Organic amendments to agricultural soils may increase soil organic matter reserves. However, manure amendment may stimulate soil microbial activity and soil organic matter decomposition. The stability of manure and soil organic matter and the availability of nutrients are crucial for the regulation of soil organic matter decomposition. Therefore, we aimed to study the effects of adding stabilised or unstabilised manures combined with mineral nutrients (N–NO3, P–PO4, K and S–SO4) on carbon mineralisation in two agricultural (sandy loam) soils with contrasted organic matter stocks and N availability. These two soils were incubated alone and after adding unstabilised farmyard manure (FYM) or stabilised manure (compost), combined with the addition of mineral nutrients. Mineralisation of C (CO2 evolution) increased after FYM addition while it decreased after compost addition as compared to the control soils. When mineral nutrients were added to soils amended with FYM, C mineralisation synergistically increased only in soils with low nitrogen availability. In these soils, the addition of nutrients may promote the mobilization of soil C, while in soils with high N availability the synergistic mobilization of C on adding FYM may be reduced. In contrast, the depressed C mineralisation after the addition of compost was little affected by nutrient availability. We suggest that recalcitrant compounds in compost may be stabilised in soil particles and humic substances with little effects of nutrient availability. In contrast, the incorporation of FYM was mainly driven by microbial transformations and affected by nutrient availability. Finally, we conclude that the application of stabilised organic matter may be a good practice for the built up of humus in a wide range of arable lands with particular significance for land reclamation in organic matter depleted soils.

Production of ethanol from raw juice and thick juice of sugar beet by continuous ethanol fermentation with flocculating yeast strain KF-7

Sugar beet juice can serve as feedstock for ethanol product due to its high content of fermentable sugars and high energy output/input ratio. Batch ethanol fermentation of raw juice and thick juice proved that addition of mineral nutrients could not improve ethanol concentration, but could accelerate the fermentation rate. Fermentation of thick juice with an initial pH of 9.1 did not affect the fermentation process. The continuous ethanol fermentation of raw juice was performed at 35 °C with a dilution rate of 0.3 h−1, resulting in ethanol concentration, ethanol yield and productivity of 70.7 g L−1, 89.8% and 21.2 g L−1 h−1, respectively. A two-stage reactor was used in the continuous ethanol fermentation of thick juice by feeding fresh yeast cells into the second reactor. This process was stable at a total process dilution rate of 0.11 h−1 with an overall sugar concentration of 190 g L−1 in the influent. The ethanol concentration was kept at approximately 80 g L−1, corresponding to ethanol yield of 82.5% and productivity of 8.8 g L−1 h−1.

矿质养分输入对森林生物固氮的影响

矿质养分输入对森林生物固氮的影响

Do soil fertilization and forest canopy foliage affect the growth and photosynthesis of Amazonian saplings?

Most Amazonian soils are highly weathered and poor in nutrients. Therefore, photosynthesis and plant growth should positively respond to the addition of mineral nutrients. Surprisingly, no study has been carried out in situ in the central Amazon to address this issue for juvenile trees. The objective of this study was to determine how photosynthetic rates and growth of tree saplings respond to the addition of mineral nutrients, to the variation in leaf area index of the forest canopy, and to changes in soil water content associated with rainfall seasonality. We assessed the effect of adding a slow-release fertilizer. We determined plant growth from 2010 to 2012 and gas exchange in the wet and dry season of 2012. Rainfall seasonality led to variations in soil water content, but it did not affect sapling growth or leaf gas exchange parameters. Although soil amendment increased phosphorus content by 60 %, neither plant growth nor the photosynthetic parameters were influenced by the addition of mineral nutrients. However, photosynthetic rates and growth of saplings decreased as the forest canopy became denser. Even when Amazonian soils are poor in nutrients, photosynthesis and sapling growth are more responsive to slight variations in light availability in the forest understory than to the availability of nutrients. Therefore, the response of saplings to future increases in atmospheric [CO2] will not be limited by the availability of mineral nutrients in the soil.

Lipase production by Aspergillus ibericus using olive mill wastewater

Olive mill wastewater (OMW) characteristics make it a suitable resource to be used as a microbial culture media to produce value-added compounds, such as enzymes. In this work, the ability of the novel species Aspergillus ibericus to discolor OMW and produce lipase was studied. An initial screening on plates containing an OMW-based agar medium and an emulsified olive oil/rhodamine-B agar medium was employed to select the strain A. ibericus MUM 03.49. Then, experiments in conical flasks with liquid OMW-based media showed that the fungus could growth on undiluted OMW, with a chemical oxygen demand (COD) of 97±2g/L, and to produce up to 2,927±54U/L of lipase. When pure OMW was used in the media, the maximum COD and color reduction achieved were 45 and 97%, respectively. When OMW diluted to 10% was used, A. ibericus was able to reduce phenolic and aromatic compounds by 37 and 39%, respectively. Additionally, lipase production was found to be promoted by the addition of mineral nutrients. When the fermentations were scaled up to a 2-L bioreactor, A. ibericus produced up to 8,319±33U/L of lipase, and the maximum COD and color reduction were 57 and 24%, respectively.

No growth stimulation by CO2 enrichment in alpine glacier forefield plants

AbstractSince 1850, glaciers in the European Alps have lost around 40% of their original area, releasing bare forefields, which are colonized by alpine pioneer species, setting the scene for later successional stages. These expanding pioneer communities are likely less restricted by resources and competition than late‐successional systems. We thus hypothesized that rising atmospheric CO2 concentration will enhance plant growth in these high‐elevation communities. Nine characteristic, perennial glacier forefield species were assembled in microcosms and grown at a nearby experimental site in the Swiss Alps (2440 m a.s.l.). The communities were exposed to an elevated CO2 concentration of 580 ppm by free‐air CO2 enrichment for three seasons. Four study species were additionally grown in isolation in containers, half of which received a low dose of mineral fertilizer (25 kg N ha‐1 a‐1) in order to explore a potential nutrient limitation of the CO2 response. Responses of growth dynamics and peak season biomass of the two graminoid species, four forbs and three cushion forming species were analysed by repeated nondestructive assessments and a final biomass harvest. After three seasons, none of the species were stimulated by elevated CO2, irrespective of mineral nutrient addition, which by itself enhanced growth in the fertilized plants by +34% on average. Increased CO2 concentration did not affect total (above‐ plus belowground) biomass but reduced aboveground biomass by −35% across all species, even in the fast growing ones. This reduced aboveground biomass was associated with higher biomass partitioning to roots. Foliar nonstructural carbohydrate concentration increased and nitrogen concentration in leaves decreased under elevated CO2. We observed downward adjustment of photosynthetic capacity by on average −26% under long‐term exposure to 580 ppm CO2 (assessed in graminoids only). Our results indicate that glacier forefield pioneers, growing under harsh climatic conditions are not carbon limited at current atmospheric CO2 concentration.

Ability of a “minimum” microbial food web model to reproduce response patterns observed in mesocosms manipulated with N and P, glucose, and Si

We compared an idealised mathematical model of the lower part of the pelagic food web to experimental data from a mesocosm experiment in which the supplies of mineral nutrients (nitrogen and phosphorous), bioavailable dissolved organic carbon (BDOC, as glucose), and silicate were manipulated. The central hypothesis of the experiment was that bacterial consumption of BDOC depends on whether the growth rate of heterotrophic bacteria is limited by organic-C or by mineral nutrients. In previous work, this hypothesis was examined qualitatively using a conceptual food web model. Here we explore the extent to which a “simplest possible” mathematical version of this conceptual model can reproduce the observed dynamics. The model combines algal–bacterial competition for mineral nutrients (phosphorous) and accounts for alternative limitation of bacterial and diatom growth rates by organic carbon and by silicate, respectively. Due to a slower succession in the diatom–copepod, compared to the flagellate–ciliate link, silicate availability increases the magnitude and extends the duration of phytoplankton blooms induced by mineral nutrient addition. As a result, Si interferes negatively with bacterial consumption of BDOC consumption by increasing and prolonging algal–bacterial competition for mineral nutrients. In order to reproduce the difference in primary production between Si and non-Si amended treatments, we had to assume a carbon overflow mechanism in diatom C-fixation. This model satisfactorily reproduced central features observed in the mesocosm experiment, including the dynamics of glucose consumption, algal, bacterial, and mesozooplankton biomass. While the parameter set chosen allows the model to reproduce the pattern seen in bacterial production, we were not able to find a single set of parameters that simultaneously reproduces both the level and the pattern observed for bacterial production. Profound changes in bacterial morphology and stoichiometry were reported in glucose-amended mesocosms. Our “simplest possible” model with one bacterial population with fixed stoichiometry cannot reproduce this, and we suggest that a more elaborate representation of the bacterial community is required for more accurate reproduction of bacterial production.

Temperature Controls a Dependence of Barley Plant Growth on Mineral Nutrition Level

The effect of temperature regime on growth and other morphological characteristics of barley plants (Hordeum distichum L., cv. Andrei) as dependent on the level of mineral nutrition was investigated in a controlled experiment. Plants were raised hydroponically at a high (0.22 g/(g day)) and low (0.05 g/(g day)) relative rates of the addition of mineral nutrients (R A). Mineral nutrients were daily added to the nutrient solutions in exponentially increased amounts to provide steady-state plant growth. At the optimum temperature regime (21/17°C, day/night), the plant relative growth rate (RGR) was proportional to the preset R A during the entire exponential period. Low R A led to a decrease in the nitrogen content in plants, plant weight, and respiratory activity, as well as to the increase in the relative root weight. Biomass accumulation at lowered temperature regime (13/8°C) and a high R A was 1.8-fold lower than at optimum temperature regime. Although under these conditions, the ratio of respiration to gross photosynthesis reduced threefold due to the decrease in the respiration rate, RGR of plants was equal to 0.11 ± 0.02 g/(g day), which was twice lower than the preset R A. These pointed to the decrease in plant ability to maintain a certain ratio of photosynthesis to respiration within a day. At a deficiency of mineral nutrition and low temperature, RGR reached the preset R A. Plants adapted to lowered temperature by a shift of the temperature optimum of their metabolism (heat production) to lower values. As a whole, a low variability of such growth parameters as RGR, C/N, and root to shoot weight ratio at different R A and lowered temperatures testified to the lessening of growth limitation by the mineral nutrition.

Effect of indigenous bacterial activity on arsenic mobilization under anaerobic conditions

Batch biochemical leaching tests were carried out to investigate the mobility of arsenic from a contaminated soil collected from a French gold mining site. The specific objective of this research was to examine the effect of indigenous bacterial activity on arsenic mobilization under anaerobic conditions. In a first step, physical and chemical characterizations were performed to provide data concerning the liquid–solid partitioning and mobility of arsenic and other inorganic constituents. In a second step, batch bioleaching tests were conducted in shaker flasks to determine the effect of indigenous bacterial activity under different anaerobic conditions (i.e., addition of mineral nutrients and carbon sources) on arsenic mobilization. Results indicated that arsenic release during contact with deionized water was limited by its very low solubility in the interstitial solution and by the stability of the different arsenic compounds formed with the amorphous solid phases of the soil (mainly iron (oxy)hydroxides). However, an increased mobilization potential was observed over the long term under anaerobic conditions with indigenous bacterial activity enhanced by the addition of carbon sources.

Temporary cyst formation of Heterocapsa triquetra (Dinophyceae) in natural populations

Heterocapsa triquetra (Ehrenberg) Stein is a phototrophic marine dinoflagellate with wide coastal distribution. It is known to be capable of mixotrophy and diel vertical migration. The species was particularly abundant in the Gulf of Finland (the Baltic Sea) during the summers of 1996 and 1998, leading to discolouration of water on the south-west coast of Finland. Large-scale (50 m3) coastal mesocosm experiments in the north-west Gulf of Finland (the Baltic Sea) in the summers of 1996 and 1998 with daily mineral nutrient additions provoked a biomass increase of phytoplankton dominated by H. triquetra. From the first days of the experiment temporary cysts of H. triquetra were found in the bottom sediment water of the mesocosms. Maximum temporary cyst production rates reached values up to 20×106 cysts m−2 day−1, accounting for <1% of the depth-integrated motile population size. The environmental features favouring temporary cyst production remain uncertain; zooplankton grazing and nutrient stress are potential factors. Temporary cysts of H. triquetra were observed in a unialgal culture (f/2 medium) isolated in summer 1999 from Eel Pond (Woods Hole, Mass., USA).

Methanogenic Activity and Repression on Hydrogen Sulfide Evolved During High Rate Thermophilic Methane Fermentation of Municipal Solid Waste.

High rate thermophilic methane fermentation using a gas circulation-type reactor was explored for its potential to reduce the volume of and make beneficial use of municipal solid waste (MSW) . Treatment without addition of mineral nutrients allowed for a maximum TS volumetric loading rate of only 1 g/l⋅d. However, with addition of mineral nutrients, a high TS volumetric loading rate of 8 g/l⋅d was achieved. At a TS loadingrate of 1 g/l⋅d, the methanogenic activity with addition of mineral nutrients was 4-fold higher than that without mineral nutrients. The concentrations of coenzymes F430 and corrinoids were 0.12 μmol/g-VSS and 0.07 μmol/g-VSS, respectively, at a TS volumetric loading rate of 8 g/l⋅d. Carbon recovery at each TS volumetric loading was nearly 100%, and about 50% of the carbon in raw waste was converted to methane gas. The degradation efficiency of lipid, protein, holocellulose and lignin were 90.7%, 59.4%, 91.9% and 66.0%, respectively. To repress the evolution of hydrogen sulfide, air was supplied to the anaerobic reactor, by which the concentration of hydrogen sulfide in biogas was reduced nearly 100% when air at 7.5% of the amount of evolved biogas was used.

Morphological Evaluation of Apical Meristem Decline in Greenhouse-grown Tomato Transplants and the Effect of Mineral Nutrition on Its Occurrence

Tomato (Lycopersicon esculentum Mill.) transplants can be affected by an intermittent physiological problem manifested by loss of apical meristem function and retarded growth rates, referred to herein as apical meristem decline (AMD). Production losses associated with this condition can be substantial. Similar abnormal and arrested development of the shoot apex has been observed in a number of other species, and referred to as blindness, budlessness, toplessness, blindwood, and bud abortion. A developmental study using scanning electron microscopy was conducted in `Agriset' tomato during an occurrence of AMD to evaluate and compare normal and afflicted plants. The AMD condition was associated with cessation of leaf primordia development and lack of flower initiation. The shoot apex of plants with AMD remained vegetative compared to normal plants which at the same age had well-differentiated flower primordia. No evidence of abortion, die back, or necrosis of the shoot apex was observed. The effects of mineral nutrient additions on symptom development varied with year. In year 1, N fertilization reduced the incidence of both AMD and retarded bud growth (i.e., the percentage of normal plants increased from 29% to 97% with N applications). Preplant applications of P, alone or in conjunction with CaCO3 and trace elements, also ameliorated AMD. In year 2, AMD was observed only at very low levels, i.e., 4% or less, and mineral nutrition had no apparent effect on AMD or normal plant number.

High elevation pioneer plants are sensitive to mineral nutrient addition

Alpine pioneer plant species on recently deglaciated land reach low levels of ground cover and receive lots of nutrients with meltwater over a very short season. Whether such high elevation ruderals might still respond to further nutrient addition was unknown. Their ruderal nature predestines them to high responsiveness, but the cold climate and short seasonal cycle may constrain such responses, which are well documented for late successional well-established alpine vegetation. After three seasons of fertilizer application (NPK and trace elements, 100–200 kg N ha −1 a −1 ), we found pioneer plant communities at 2500 m a.s.l. in the Swiss Central Alps to exhibit massive biomass stimulations (+177%). This response was largely due to increased fractions of plant-covered ground (gap filling). On patches, which had nearly full plant cover already before the treatment, biomass was not significantly affected by additional nutrients. Graminoids took the greatest advantage from elevated nutrient availability. The relative biomass contributions and reproduction efforts differed in extent and direction from species to species, with tall species such as Poa alpina being most responsive. Thus, we conclude that many of the studied alpine pioneers can indeed utilize more nutrients for enhanced growth including their investments in reproductive structures. Given that our third and last experimental season was very untypical, with late snowcover until early August, we consider our results as conservative, with even more pronounced effects to be expected in average seasons. Alpine Pionierpflanzen auf Flächen, welche erst vor kurzem vom Gletscher freigegeben wurden und wo die Bodenbedeckung mit Pflanzen gering ist, werden während einer sehr kurzen Vegetationszeit aus dem Schmelzwasser reichlich mit Nährstoffen versorgt. Bisher war es unbekannt, ob solche Ruderalpflanzen auf zusätzliche Nährstoffzufuhr reagieren können. Der ruderale Charakter dieser Pflanzen scheint sie für eine starke Reaktionsfähigkeit zu prädestinieren, das kalte Klima und die kurze Saison hingegen könnten derartige Reaktionen, wie sie für alpine Vegetationen in späten Sukzessionsstadien gut dokumentiert sind, stark einschränken. Drei Jahre Düngung (NPK und Spurenelemente, 100–200 kg N ha −1 a −1 ) bewirkten bei Pionierpflanzengesellschaften in den Schweizer Zentralalpen auf 2500 m ü. M. eine massive Erhöhung der Biomasse (+177%), welche vor allem durch erhöhten Anteil der pflanzenbedeckten Bodenfläche verursacht wurde (Auffüllen von Lücken). An Stellen, welche vor der Düngung bereits beinahe vollständig mit Pflanzen bedeckt waren, hatte die erhöhte Nährstoffzufuhr keinen signifikanten Einfluss auf die Biomasse. Grasartige konnten von der erhöhten Nährstoffverfügbarkeit am meisten profitieren. Die untersuchten Arten reagierten bezüglich ihres Anteils an der Gesamtbiomasse und der Investition in die Reproduktion unterschiedlich, wobei große Arten wie Poa alpina die stärkste Düngereaktion zeigten. Viele der untersuchten alpinen Pionierpflanzen können in der Tat zusätzliche Nährstoffe für erhöhtes Wachstum und Reproduktion nutzen. Da die dritte und letzte Saison dieses Experiments sehr untypisch war (Schnee bis in den frühen August), beurteilen wir unsere Ergebnisse eher als konservativ und würden in einer durchschnittlichen Saison noch ausgeprägtere Reaktionen erwarten.

Vertical niche separation of phytoplankton: large-scale mesocosm experiments

Vertical distribution patterns of Heterocapsa triquetra, Mesodinium rubrum, Aphani- zomenon sp., Anabaena lemmermannii, Monoraphidium contortum and chlorophyll a were analyzed in large-scale mesocosms extending throughout the euphotic layer and manipulated with low and high levels of mineral nutrient additions. Using an ordination method, quantitative comparisons of the variability in the vertical distribution due to species differences, to experimental treatments, and to inter-annual variation were made. The inter-specific variance component was largest. The signifi- cance of inter-specific differences was verified by a randomization test. There was also significant inter-annual variability in the species-specific vertical distribution patterns, but the inter-annual effect was less pronounced than the differences between species. Differences in the nutrient loads to the mesocosm did not have significant effects on species-specific vertical distribution patterns. The results demonstrate that the vertical segregation patterns of phytoplankton are species-specific and robust, not overly sensitive to changes in environmental conditions, but appear to be persistent bio- logical phenomena. The implications of these findings to co-existence, competition, and diversity in the plankton are discussed.

Effect of water, temperature and fertilizers on soil nitrogen net transformations and tree growth in an elfin cloud forest of Colombia

(Accepted 31st July 1999)In the ‘elfin’ cloud forest of Serrania de Macuira, exchangeable ammonium and nitrate, and the rates of soil nitrogen mineralization and nitrification were measured in soil samples under different water, temperature and mineral nutrient additions. The effects of nitrogen, phosphorus and nitrogen plus phosphorus fertilization on radial trunk growth were measured in three tree species. In the cloud forest soils, concentrations of ammonium were much higher than those of nitrate. Nitrate was higher in samples collected during the afternoon than during the morning, probably as a result of leaching during the night or nitrification during the day. When samples were incubated under different water and temperature treatments, rates of nitrogen mineralization and nitrification increased more with changes in soil water content than with changes in temperature. Nitrification was significantly increased in soils amended with ammonium or with ammonium plus phosphorus, suggesting that nitrification is substrate-limited. Fertilization with nitrogen and phosphorus resulted in significantly increased girth increments in Guapira fragrans (Dum. -Cours.) Little and Rapanea guianensis Aublet. Myrcianthes fragrans (Sw.) D.C. did not respond to the fertilization. The results of this study support the hypothesis that the characteristics of montane rain forest in small and large tropical mountains (the ‘Massenerhebung’ effect) are greatly controlled by soil water conditions and related soil nitrogen availability.

Nutrient and surfactant enhancement for the biodegradation of chlorinated hydrocarbons in the wastewater from a Louisiana Superfund site

Surfactant based soil washing and flushing is an emerging technology for Superfund site remediation in the United States. The presence of surfactants in the wastewater, however, poses challenging problems for subsequent biological or physical–chemical processes. The objective of this research is to evaluate the potential effects of selected surfactants on the biodegradation of chlorinated hydrocarbons in the wastewater from the Petro Processors (PPI) Superfund site north of Baton Rouge, LA. Results from this study showed that biodegradation of a real world waste containing a broad array of hazardous contaminants was significantly enhanced by the amendment of mineral nutrients and surfactants, especially a nonionic surfactant Witconol. The enhancement based on TOC reduction was 49% higher for the mixture of PPI wastewater with Witconol than the combined biodegradation of PPI wastewater and Witconol alone, whereas a similar enhancement was observed with an anionic surfactant sodium dodecylsulfate (SDS). The addition of mineral nutrients was also shown to further enhance the biodegradation of PPI wastewater, with a 13% increase in TOC reduction as compared to the nutrient limited controls. Nutrient addition significantly increased microbial growth, biodegradation, and foam degradation of surfactant-laden PPI wastewater.