ON THE DISSOLVED SOLIDS OF THE PONGOLO FLOOD PLAIN PANS

SUMMARY

The water retained in the Pongolo flood plain pans differs from that of the Pongolo River not only in having a higher TDS, but also in the composition of the solutes, which approximate to seawater in their equivalent ionic proportions at high concentrations. These solutes are shown to originate from very highly mineralised seepage water characteristic of soils overlying Cretaceous sediments of marine origin found elsewhere in South Africa. This feature of the soils of the flood plain precludes the use of irrigation seepage water to maintain the water levels in the pans, and stresses the need for the release of simulated floods from the Pongolo-poort Dam to flush the system if the present biological characteristics of the pans are to be maintained.     

PRELIMINARY RESULTS ON THE UPTAKE AND RELEASE OF 32P BY POTAMOGETON PECTINATUS

SUMMARY

The absorption and release of ³²PO₄, by Potamogeton pectinatus L during winter was investigated using a partitioned container in which the roots were separated from the stems and leaves. ³²PO₄ is absorbed by the roots as well as the stems and leaves under both light and dark conditions and transported to all parts of the plant. Transport rates (μg P plant^?1 24 hr^?1) show that more phosphorus is released by the roots than by the stems and leaves, indicating a nett movement of phosphorus from the surrounding water to the substrate. Foliar absorption of ³²P exceeds root absorption under both light and dark conditions.     

Supply of phosphorus to the water column of a productive hardwater lake: controlling mechanisms and management considerations

Onondaga Lake is a hypereutrophic, industrially polluted lake located in Syracuse, NY. High hypolimnetic concentrations of H₂S that develop after anoxia restrict the accumulation of total Fe²⁺ due to the formation of FeS, and may limit Fe-PO₄ interactions. High water column concentrations of Ca²⁺ and high rates of CaCO₃ deposition occur due to inputs of Ca²⁺ from an adjacent soda ash manufacturing facility. Patterns of P concentration and other water chemistry parameters in the lower waters, and results from chemical equilibrium calculations, suggest that Ca-PO₄ minerals may regulate the supply of P from sediments to the water column in Onondaga Lake. These findings have important management implications for Onondaga Lake. First, declines in water column Ca²⁺ concentrations due to reductions in industrial CaCl₂ input may result in conditions of undersaturation with respect to Ca-PO₄ mineral solubility and increases in the release of P from sediments to the water column. Second, introduction of O₂ from hypolimnetic oxygenation, as a lake remediation initiative, may enhance P supply from sediments, because of increased solubility of Ca-PO₄ minerals at lower pH.     

NOTES ON THE AVAILABILITY AND CHEMICAL COMPOSITION OF WATER FROM THE GRAVEL PLAINS OF THE NAMIB-NAUKLUFT PARK

SUMMARY

Data are presented on the occurrence of a surprising number of permanent water sources on the gravel plains of the Namib-Naukluft Park, South West Africa. As a consequence, no game animal is further than ca 25 km away from the nearest watering-place. Within a broad range of ionic contents, the surface waters of the desert display a marked similarity in their chemical composition, being mainly dominated by Na⁺>Ca⁺⁺>Mg⁺⁺: Cl^?>SO₄ ^?>HCO₃ ^??CO_3- ^?. Evaporation, precipitation and rock dominance seem to be the main controlling mechanisms involved in determining the chemical composition of the waters.     

HYDROCHEMISTRY OF THE UPPER ORANGE RIVER CATCHMENT

SUMMARY

A four year pre-impoundment study of the catchment of the Hendrik Verwoerd Dam was conducted. The Orange River was the major source of dissolved chemicals and suspended sediments, while the Caledon River contributed 24 and 30% respectively, and the Kraai River 9 and 8% respectively. The upper reaches of the Orange River catchment contributed mainly to the dissolved chemical and sediment loads, in contrast to the minimal contribution of the lower reaches. This was in spite of the relatively stable geological formations in the upper reaches and the erodable formations in the lower reaches. Dry-wet seasonal variations occurred in nutrient and sediment concentrations and loads, except for the Bell River where constant values were measured. The water was characterized by magnesium and bicarbonate dominance. Adsorption by the suspended sediments was dominated by calcium (potassium in the Bell River) and zinc among the trace elements. Due to its low salinity and sodium adsorption ratio, the water was suitable for irrigation. High magnesium levels made it, however, less attractive for irrigational purposes.

The phosphorus loading rate at the inflow of the Hendrik Verwoerd Dam was only 0,55 g P m^?2 a^?1, which was well below the 1,39 g P m^?2 a^?1 critical rate for eutrophic conditions, applying the Vollenweider Model. Therefore, this impoundment was classified as oligo-mesotrophic.     

Nitrogen and phosphorus interchange between sediments and overlying water of a wastewater retention pond

Nitrogen and P interchange between the sediments and the overlying water of a simulated retention pond used for wastewater treatment were evaluated under conditions of seasonal temperature fluctuations and varying physico-chemical conditions (exposing floodwater surface to daylight vs. dark and turbulent vs. quiscent floodwater). Natural sediment columns obtained from two types of field retention ponds were used. One type of retention pond consisted of calcareous clay loam sediment while the sediment of second retention pond contained organic soil. Nutrient interchange between sediments and the overlying water was measured once a month over a period of one year. Nitrogen removal rates from floodwater were controlled by the initial floodwater NH ₄ ⁺ and NO ₃ ^? concentration, rate of NH ₄ ⁺ diffusion from the sediments to the overlying water, ammonification in the sediments, NH₃ volatilization and nitrification at the sediment-water interface, and denitrification in the sediments. Under the conditions studied, NH ₄ ⁺ concentrations of the floodwater were in the range of 0.01 to 0.05 µg/ml, while NO ₃ ^? concentrations were in the range of 0.27 to 0.78 µg/ml. Sediments with organic soil were found to be less effective in the removal of floodwater organic N, organic C and P, compared to the sediments with calcareous clay loam. Phosphorus exchange rates were dependent on the capacity of the sediment to adsorb or desorb P. Total P exchange rates were in the range of ?1.04 to 0.34 mg P/m² day. Seasonal temperature fluctuations, turbulent vs. quiscent water conditions or exposing the floodwater surface to daylight or dark had very little effect on N and P exchange rates.     

Potential nitrogen and carbon processing in a landscape rich in milldam legacy sediments

Recent identification of the widespread distribution of legacy sediments deposited in historic mill ponds has increased concern regarding their role in controlling land–water nutrient transfers in the mid-Atlantic region of the US. At Big Spring Run in Lancaster, Pennsylvania, legacy sediments now overlay a buried relict hydric soil (a former wetland soil). We compared C and N processing in legacy sediment to upland soils to identify soil zones that may be sources or sinks for N transported toward streams. We hypothesized that legacy sediments would have high nitrification rates (due to recent agricultural N inputs), while relict hydric soils buried beneath the legacy sediments would be N sinks revealed via negative net nitrification and/or positive denitrification (because the buried former wetland soils are C rich but low in O₂). Potential net nitrification ranged from 9.2 to 77.9 g m^?2 year^?1 and potential C mineralization ranged from 223 to 1,737 g m^?2 year^?1, with the highest rates in surface soils for both legacy sediments and uplands. Potential denitrification ranged from 0.37 to 21.72 g m^?2 year^?1, with the buried relict hydric soils denitrifying an average of 6.2 g m^?2 year^?1. Contrary to our hypothesis, relict hydric layers did not have negative potential nitrification or high positive potential denitrification rates, in part because microbial activity was low relative to surface soils, as indicated by low nitrifier population activity, low substrate induced respiration, and low exoenzyme activity. Despite high soil C concentrations, buried relict hydric soils do not provide the ecological services expected from a wetland soil. Thus, legacy sediments may dampen N removal pathways in buried relict hydric soils, while also acting as substantial sources of NO₃ ^? to waterways.     

Shifts in the relative availability of phosphorus and nitrogen along estuarine salinity gradients

Phosphorus (P) availability in estuaries may increase with increasing salinity because sulfate from sea salt supports production of sulfide in sediments, which combines with iron (Fe) making it less available to sequester P. Increased P availability with increased salinity may promote the generally observed switch from P limitation of primary production in freshwater ecosystems to nitrogen (N) limitation in coastal marine waters. To investigate this hypothesis, we analyzed pore water from sediment cores collected along the salinity gradients of four Chesapeake Bay estuaries (the Patuxent, Potomac, Choptank, and Bush Rivers) with watersheds differing in land cover and physiography. At salinities of 1–4 in each estuary, abrupt decreases in pore water Fe²⁺ concentrations coincided with increases in sulfate depletion and PO₄ ^3? concentrations. Peaks in water column PO₄ ^3? concentrations also occur at about the same position along the salinity gradient of each estuary. Increases in pore water PO₄ ^3? concentration with increasing salinity led to distinct shifts in molar NH₄ ⁺:PO₄ ^3? ratios from >16 (the Redfield ratio characteristic of phytoplankton N:P) in the freshwater cores to <16 in the cores with salinities >1 to 4, suggesting that release of PO₄ ^3? from Fe where sediments are first deposited in sulfate-rich waters could promote the commonly observed switch from P limitation in freshwater to N limitation in mesohaline waters. Finding this pattern at similar salinities in four estuaries with such different watersheds suggests that it may be a fundamental characteristic of estuaries generally.     

Biogeochemical evolution of a sulfur-iron rich aquatic system in a reflooded wetland environment (Lake Agmon,northern Israel)

Major biogeochemical processes in the newly created, shallow Lake Agmon (Hula Valley, northern Israel) were investigated from 1994 to 1996. Sediment cores, lake water and porewater were analyzed for chemical composition and spatial distribution. Sediment analyses revealed that Lake Agmon has two different sediment types: peat sediments in the northern and central parts, and marls in the southern part. The basic composition of the lake's water was controlled mainly by the mixing of two distinct water types (Jordan River and water drainage), and by evaporation. About 3/4 of the lake water originated from the Jordan Inlet, a quarter through the Z Canal Inlet (peat drainage) and a minor amount from groundwater seepage. Lake Agmon is unique among freshwater wetlands owing to its high SO ₄ ^2– content, which is ca. 1/3 that of sea water. This characteristic is ascribed to the dissolution of secondary gypsum, formed in the peat soils since the drainage of the historic Hula Marsh. Leaching gypsum from the shallow sediments during the first few months after flooding was followed by a later stage of constant diffusion and advection of SO ₄ ^2– from gypsum dissolution in deeper sediments. Gypsum dissolution in lake sediments contributed ca. half of the SO₄ ^2– and Ca²⁺ inputs to the lake. The concomitant increase of Ca²⁺ combined with alkalinity release due to organic matter decomposition in the sediments led to the precipitation of CaCO₃. This precipitation was enhanced by photosynthesis, particularly during summers, and consumed about a tenth of the Ca²⁺ and third of the alkalinity outputs from the lake. Iron-hydroxide was the main agent for microbial oxidation of organic matter, surpassing by far the role of sulfate, nitrate and manganese as electron acceptors. The produced Fe²⁺ was transported upward by diffusion and advection and oxidized to ferric iron at the sediment-water interface. There is evidence, however, that some sulfate was reduced, but most of the produced sulfide reacted with ferrous iron and accumulated in the sediments as FeS minerals. Therefore, despite high sulfate concentrations, the high iron availability restricted release of toxic sulfides into the water and thereby served to maintain reasonable water quality.     

Spatial and seasonal variation in greenhouse gas and nutrient dynamics and their interactions in the sediments of a boreal eutrophic lake

Dynamics of greenhouse gases, CH₄, CO₂ and N₂O, and nutrients, NO ₂ ^– + NO ₃ ^– , NH ₄ ⁺ and P, were studied in the sediments of the eutrophic, boreal Lake Kevätön in Finland. Undisturbed sediment cores taken in the summer, autumn and winter from the deep and shallow profundal and from the littoral were incubated in laboratory microcosms under aerobic and anaerobic water flow conditions. An increase in the availability of oxygen in water overlying the sediments reduced the release of CH₄, NH ₄ ⁺ and P, increased the flux of N₂O and NO ₂ ^– + NO ₃ ^– , but did not affect CO₂ production. The littoral sediments produced CO₂ and CH₄ at high rates, but released only negligible amounts of nutrients. The deep profundal sediments, with highest carbon content, possessed the greatest release rates of CO₂, CH₄, NH ₄ ⁺ and P. The higher fluxes of these gases in summer and autumn than in winter were probably due to the supply of fresh organic matter from primary production. From the shallow profundal sediments fluxes of CH₄, NH₄ ⁺ and P were low, but, in contrast, production of N₂O was the highest among the different sampling sites. Due to the large areal extension, the littoral and shallow profundal zones had the greatest importance in the overall gas and nutrient budgets in the lake. Methane emissions, especially the ebullition of CH₄ (up to 84% of the total flux), were closely related to the sediment P and NH ₄ ⁺ release. The high production and ebullition of CH₄, enhances the internal loading of nutrients, lake eutrophication status and the impact of boreal lakes to trophospheric gas budgets.     

The evaluation of inorganic phosphate species in salt water lake sediments

Abstract

Surface sediments drawn from 10 shallow bays have been subjected to selective extraction in order to sub-divide the total P content into sub-categories such as water soluble P, Ca-P, Al-P and Fe-P. The reagents selected were similar to systems used in soil analysis, but evaluation of the procedures showed that the species values varied with time of extraction, weight of sediment taken, volume of extradant and chemical nature of the sediment. In water extractions, the P levels appeared to be determined by saturation with a sparingly soluble salt, while in acidic media P extract levels peaked (using different experimental conditions) due to loss of extracted P as a new phase (e.g. CaHPO₄) or through re-adsorption on other components.

The optimum conditions for P speciation in sediments must be determined from a series of preliminary studies because each of the five sediments studied in detail displayed individual characteristic behaviour.     

Phosphorus dynamics in shallow eutrophic lakes: an example from Zeekoevlei,South Africa

Zeekoevlei is the largest freshwater lake in South Africa and has been suffering from hyper-eutrophic conditions since last few decades. We have used total P (TP), dissolved phosphate (PO₄ ³⁻), organic P (OP), calcium (Ca) and iron (Fe) bound P fractions to investigate the relevant physical, chemical and biological processes responsible for sedimentation and retention of P and to study phosphorus (P) dynamics in this shallow lake. In addition, redox proxies (V/Cr and Th/U ratios) are used to study the prevailing redox conditions in sediments. Adsorption by CaCO₃ and planktonic assimilation of P are found to control P sedimentation in Zeekoevlei. Low concentration of the labile OP fraction in surface sediments restricts the release of P by bacterial remineralisation. Low molar Ca/P and Fe/P ratios indicate low P retention capacity of sediments, and P is most likely released by desorption from wind-induced resuspended sediments and mixing of pore water with the overlying water column. Handling editor: J. Saros     

Effects of temporary desiccation on the mobility of phosphorus and metals in sulphur-rich fens: differential responses of sediments and consequences for water table management

In the Netherlands, permanent damming of sulphate (SO₄ ^2–)-rich surface water, in order to rewet desiccated wetlands, has resulted in stagnation and eutrophication of surface water. Permanent damming of surface water prevents periodic drought during summer and leads to suppressed iron (Fe)-rich groundwater input and to stimulated SO₄ ^2– reduction, all likely stimulating depletion of reducible Fe in the sediment. A laboratory experiment was conducted to assess the importance of temporary desiccation, its differential effects on various sediment types and the consequences for water table management. Permanent high SO₄ ^2–-rich surface water tables above sediments that are indirectly affected by shallow groundwater flows, resulted in severe eutrophication. The effect of temporary desiccation on phosphorus (P) mobilization and immobilization strongly depended on the sediment Fe and P pools in combination with the buffering capacity of the sediment. Desiccation of sediment that is indirectly affected by shallow groundwater flows, led to a long-lasting reduction in phosphate (o-PO₄ ^3–) release from the sediment because a reduced Fe pool is present, resulting in the release of Fe upon oxidation. Formerly dry sediments that have not been influenced by groundwater for a long time do not possess such a reduced Fe pool and desiccation did not reduce P-release from these sediments resulting in considerable eutrophication of the water layer immediately after rewetting. In sediment of seepage zones that are directly and permanently influenced by deeper groundwater, reduced Fe and calcium levels are so high that o-PO₄ ^3– was effectively immobilized under oxidized as well as reduced conditions. The results indicate that restoration of desiccated wetlands can not be achieved by simply retaining water by means of constructed dams. If water retention is artificially increased, temporary drops in water level during the summer are necessary to recharge the reducible P-binding Fe pool in large zones of the wetlands in order to prevent eutrophication.     

Evidence for Anaerobic CH 4 Oxidation in Freshwater Peatlands

This study involved in vitro assays of peat soil to investigate the occurrence, importance and potential mechanism(s) of anaerobic methane oxidation (AOM) in several northern peatlands ranging from ombrotrophic bog to minerotrophic fen. Although strong evidence suggests that AOM is linked to sulfate reduction in marine sediments, very little is known about AOM in freshwater systems such as northern peatlands, which have large methane (CH ₄ ) production and are a significant source of atmospheric CH ₄ . Our results showed a mean net AOM rate of 17 ± 2.6 nmol kg ^{? 1} s ^{? 1} with a maximum rate of 176 nmol kg ^{? 1} s ^{? 1} for a minerotrophic fen in central New York. AOM was demonstrated with three independent methods to verify our results: (a) additions of methanogenic inhibitors, (b) stable isotope enrichment ( ¹³ C-CH ₄ ), and (c) natural abundance stable isotope analysis ( ¹³ C-CH ₄ ). These experiments confirmed that AOM occurs simultaneously with methanogenesis, consumes a significant portion of gross CH ₄ production, and significantly fractionates C isotopes (～ ?127‰). Experiments using a variety of potential electron acceptors demonstrated that Fe(III) and SO₄ ^{2 ?} are not quantitatively important, while the role of NO ₃ ^? is uncertain and deserves more attention. The exact mechanism(s) for AOM in peat soils remains unclear; however the AOM rates reported in this study are similar to those reported for CH ₄ production and aerobic CH ₄ oxidation in northern peatlands, suggesting that AOM may be an important control on CH ₄ fluxes in northern peatland ecosystems.     

Phosphorus fixation in lake sediments using LaCl3-modified clays

Fourteen types of clay, including soils and sediments from Lake Taihu, were modified by LaCl₃, and their abilities of phosphorus (P) sorption (the total P up-taken) and fixation (the unleachable P retained in modified clays) were investigated. Results showed that P sorption rates of LaCl₃-modified clays were all higher than 90%, while the fixation rates were raised from 3–14% to 52–95%. Kaolinite was selected to study the pH effect on P sorption and desorption of La³⁺ from the modified clays. In the pH range of 4–8, P sorption on LaCl₃-modified kaolinite could reach over 80%, with a maximum of 97% at pH 5. The desorption rate of La³⁺ decreased with the increase of pH, which was lower than <0.006% at pH > 6.12. This study may provide a solution for internal P pollution from lake sediments.     

Nutrient turnover studies in alpine ecosystems

Summary The nutrient relations of five treeless plant communities on acid soils above siliceous rock of the Central Alps are investigated. Three of these communities, situated on Mt. Patscherkofel, are dominated by dwarf shrubs of the Ericaceae family: Loiseleurietum (P 1, 2175 m NN), Loiseleuria heath (P 2, 2000 m NN), and Vaccinium heath (P 3, 1980 m NN). The other two are bound to higher elevations (2500 m NN, at Timmelsjoch): Caricetum curvulae (T 1), forming the mats, and Salicetum herbaceae (T 2), covering the snow-beds.Phytomass productivity decreases with increasing altitude in the sequence P 3-P 2, P 1-T 1-T 2.Compared with the turf communities of the Northern Calcareous Alps, nitrogen reserves and experimental net-mineralization of the soils (0–15 cm) are extremely low in P 1, P 2, and P 3 (<0.5 g N/m² mineralized per GS¹). The fluctuation of N in the living above-ground phytomass during the GS is also low (about 1.6 g/m² in P 1 and P 2; 2.2 g/m² in P 3, although it exceeds the values of net mineralization. Additional uptake through mycorrhizal fungi or activation of mineralizing microbes in the rhizosphere by exudation is assumed.The P- and K-reserves are extremely small in the humic soils of P 2 and P 3, but somewhat higher in the more mineral soil of P 1. Mean lactatesoluble P of the three sites is low (0.3 g/m² or less) whereas K_lact (2.7–3.3 g/m²) is higher than the lowest level found in some turf communities, e.g. Caricetum firmae. The amounts of P in the phytomass are in the range of those of the turf communities and agree with the gradation in the mean P_lact values (P 1 and P 3>P 2). There are, however, almost no discernible fluctuations of P in the phytomass, and the K-fluctuations are far below the mean K_lact level.The Timmelsjoch communities generally have higher N/C-, P/C-, and K/C-ratios in the soils compared with those of Mt. Patscherkofel, although the N-reserves (g/m²) and the K-reserves (of T 1 only) are lower. The P_lact values are higher than those from Mt. Patscherkofel and also exceed those of the calcareous turf communities. K_lact is low in T 1 whereas in T 2 it is in the range of P 1, P 2, and P 3. Compared with T 1, T 2 has distinctly higher amounts of the three nutrients in the soils and a higher net mineralization of N, as well as higher values in the phytomass components and in the fluctuation of the latter.In conclusion, a general view is given (Fig. 9) of the most important nutrient parameters of the communities represented in this series, including some others of lower altitudes.     

Review of methodologies for extracting plant-available and amorphous Si from soils and aquatic sediments

There is a variety of methodologies used in the aquatic sciences and soil sciences for extracting different forms of Si from sediments and soils. However, a comparison of the published extraction techniques is lacking. Here we review the methodologies used to extract different Si fractions from soils and sediments. Methods were classified in those to assess plant-available Si and those to extract Si from amorphous silica and allophane. Plant-available Si is supposed to comprise silicic acid in soil solution and adsorbed to soil particles. Extraction techniques for plant-available Si include extractions with water, CaCl₂, acetate, acetic acid, phosphate, H₂SO₃, H₂SO₄, and citrate. The extractants show different capabilites to desorb silicic acid, with H₂SO₃, H₂SO₄ and citrate having the greater extraction potential. The most common extractants to dissolve amorphous silica from soils and aquatic sediments are NaOH and Na₂CO₃, but both also dissolve crystalline silicates to varying degrees. In soils moreover Tiron is used to dissolve amorphous silica, while oxalate is used to dissolve allophanes and imogolite-type materials. Most techniques analyzing for biogenic silica in aquatic environments use a correction method to identify mineral derived Si. By contrast, in the soil sciences no correction methods are used although pedologists are well aware of the overestimation of amorphous silica by the NaOH extraction, which is most commonly used to extract silica from soils. It is recommended that soil scientists begin to use the techniques developed in the aquatic sciences, since it seems impossible to extract amorphous Si from soils completely without dissolving some of the crystalline silicates.     

TECHNICAL NOTE: NITROGEN FERTILIZATION EFFECTS ON THE DEGRADATION OF AGED DIESEL OIL IN COMPOSTED DRILLING WASTES

Hydrocarbon-contaminated wastes generated from oil and gas drilling activities may be used as a soil amendment once composted and further decomposition of residual hydrocarbons can be accomplished after the composts are applied to soils. To test if N fertilization may enhance hydrocarbon decomposition, we investigated the effects of N application on hydrocarbon degradation in different-aged composts (1-, 2-, 3-, and 4-year-old composts, coded as 1Y, 2Y, 3Y, and 4Y composts, respectively) through a pot experiment planted with white spruce (Picea glauca [Moench] Voss) seedlings. The percentage degradation of total petroleum hydrocarbon (TPH, C11 to C40) in the composts without N fertilization was correlated to initial NH₄ ⁺ concentrations (R = 0.99, P < 0.001). The percentage degradation of TPH was highest in the 3Y compost (41.1%) that had an initial level of 325.3 mg NH₄ ⁺-N kg^?1 and the lowest in the 1Y compost (9.3%) that had an initial level of 8.3 mg NH₄ ⁺-N kg^?1. The degradation of TPH was enhanced by N fertilization in the 1Y (from 9.3 to 15.3%) and 4Y composts (from 14.3 to 22.6%) that had low initial NH₄ ⁺ concentrations. Our results show that application of NH₄ ⁺-based fertilizers may enhance the degradation of TPH when initial NH₄ ⁺ concentrations in the compost are low.     

Development and application of a technique for estimating nutrient deficiency in soft sediments

A diffusion enrichment technique is presented which allows for chemical enrichment of soft surficial and shallow subsurface sediments and subsequent measurement of O₂ production. The sediment is enriched by inserting a perforated tube containing dialysis tubing filled with a nutrient/agar mixture. O₂ production by surficial sediment is measured using an inverted, translucent, polyethylene chamber over the sediment. The inside of the chamber contains a collapsible bag connected to the water outside the chamber. When water overlying the sediment is withdrawn from a sampling port, it is displaced with water from outside the chamber, thus preventing contamination of water samples with pore water from below. The technique was tested by enriching near-shore sediments in a large oligotrophic lake with inorganic N and P. NHinf4/^p+ additions significantly stimulated benthic primary production as measured by 0₂ production, whereas enrichment with POinf4/^3- had no effect.     

Shoot specific fungal endophytes alter soil phosphorus (P) fractions and potential acid phosphatase activity but do not increase P uptake in tall fescue

Aims

An experiment was performed to test how different fungal endophyte strains influenced tall fescue’s ability to access P from four P sources varying in solubility.

Methods

Novel endophyte infected (AR542E+ or AR584E+), common toxic endophyte infected (CTE+), or endophyte-free (E-) tall fescues were grown for 90 days in acidic soils amended with 30 mg kg^?1 P of potassium dihydrogen phosphate (KH₂PO₄), iron phosphate (FePO₄), aluminum phosphate (AlPO₄), or tricalcium phosphate ((Ca₃(PO₄)₂), respectively.

Results

Phosphorus form strongly influenced plant biomass, P acquisition, agronomic P use efficiency, microbial communities, P fractions. P uptake and vegetative biomass were similar for plants grown with AlPO₄, Ca₃(PO₄)₂, and KH₂PO₄ but greater than in control and FePO₄ soils. Infection with AR542E+ resulted in significantly less shoot biomass than CTE+ and E- varieties; there was no influence of endophyte on root biomass. The biomarker for arbuscular mycorrhizal fungi (AM fungi, 16:1ω5c) was selected as an effective predictor of variations in P uptake and tall fescue biomass. Potential acid phosphatase activity was strongly influenced by endophyte x P form interaction.

Conclusions

Endophyte infection in tall fescue significantly affected the NaOH-extractable inorganic P fraction, but had little detectable influence on soil microbial community structure, root biomass, or P uptake.