Ammonium Depletion Research Articles

Rates of rhizodeposition and ammonium depletion in the rhizosphere of axenic oat roots

A multiple split root chamber and artificial soil were developed which allowed for maintenance of axenic conditions and for the isolation of soil from specific regions of single roots. A sterile minirhizotron was used to measure patterns and rates of root extension under sterile conditions. Carbon and nitrogen distributions in the rhizosphere of sterile oat roots were measured in combination with rates of root elongation to calculate specific rates of rhizodeposition and ammonium nitrogen uptake. The highest rates of rhizodeposition C production and N depletion occurred at the root tip (first day segment). Rhizodeposited soluble and insoluble C compounds represented up to 50% of the standing root biomass C. Within 48 hours after root entry, levels of rhizosphere ammonium-N decreased by 40–50%. The results were summarized in a simple model of root growth, rhizodeposition, and NH 4 + −H uptake.

Simulating the development of chlorophyll maxima in the celtic sea

A chlorophyll maximum is often present in shallow seas during periods of thermal stratification. Data from the Celtic Sea are used to support formulation of a dynamic model describing the vertical-temporal distribution of cyanobacteria, flagellates, diatoms, copepods, ammonium, and nitrate, given year-long background patterns for temperature and available solar radiation. Simulated results include the typical spring diatom peak coupled to mixed layer depletion of ammonium and nitrate, as well as subsequent peaks for other plankters and accumulation of chlorophyll within the thermocline.

KINETICS OF NITROGEN‐15 LABELLED AMMONIUM UPTAKE BY CAULERPA CUPRESSOIDES (CHLOROPHYTA)1,2,3

ABSTRACTThe incorporation of 15NH4+ as a function of time and concentration was used to estimate ammonium uptake by Caulerpa cupressoides (West) C. Agardh, taken from its habitat on the sediments of Tague Bay lagoon, St. Croix, U.S. Virgin Islands. 15N‐based uptake rates followed Michaelis‐Menten type saturation kinetics; the maximum uptake rate was 8.7 ± 3.0 μmol N/g dry wt·h at 26° C and the half‐saturation constant was 48 ± 10 μM (X̄± SE). The high half‐saturatiaon constant reflects the dependence of Caulerpa on sediment pore waters as a nitrogen source. Calculations of uptake from isotope time course data were compared to estimates made from ammonium depletion. More ammonium disappeared than could be accounted for by the incorporation of 15N in Caulerpa, and isotope dilution of the ammonium pool is shown not to be responsible for underestimates of uptake, primarily because large 15N additions (40–300 μM) were used. It is suggested that either (1) a secondary ammonium sink such as wall sorption or bacterial uptake significantly influenced ammonium concentrations, or (2) 15N was lost as labelled dissolved organic nitrogen or volatilized during 15N sample preparation.

Transformations of nitrogen following epilimnetic N-fertilization in Castle Lake, CA.: 2. Nitrate and ammonium depletion pathways

Transformations of nitrogen following epilimnetic N-fertilization in Castle Lake, CA.: 2. Nitrate and ammonium depletion pathways

Soil Characteristics and Nutrient Status in a Northern Australian Mangrove Forest

The results of a study of soil factors in relation to plant growth for a tropical mangrove forest in northern Australia are presented and discussed. Basic soil properties are described briefly in terms of particle size distribution, bulk density and total carbon, nitrogen and phosphorus. Soil redox potential, pH, salinity and extractable nitrogen and phosphorus were monitored monthly over a 14 month period commencing April 1979. Sampling was carried out at 9 sites along a 370 m transect which exhibits strong gradients in topography, above ground biomass, canopy height and species distribution. Statistical analysis of the data shows that above ground biomass correlates significantly with the following soil factors, averaged over depth within the rooting zone and over time: Extractable P (r=0.85, p<0.01), redox potential (r=0.89, p<0.01) and salinity (r=−0.79, p<0.05). The strong biomass-EH correlation may be partly due to oxygen translocation by the plants to the root zone. Soil ammonium levels were within the range of 1–14 μg N per g (dry wt) and, unlike the above parameters, showed only minor variation with position along the transect. Variation of ammonium levels with time was apparent, but no significant correlation with rate of new shoot growth could be demonstrated, although depth profiles indicated depletion of ammonium by plant uptake during rapid growth periods. In addition neither soil ammonium, extractable phosphorus nor rate of plant growth showed any definite seasonal periodicity in this tropical system.

Differences in Steady-State Net Ammonium and Nitrate Influx by Cold- and Warm-Adapted Barley Varieties

A flowing nutrient culture system permitted relatively rapid determination of the steady-state net nitrogen influx by an intact barley (Hardeum vulgare L. cv Kombar and Olli) plant. Ion-selective electrodes monitored the depletion of ammonium and nitrate from a nutrient solution after a single pass through a root cuvette. Influx at concentrations as low as 4 micromolar was measured. Standard errors for a sample size of three plants were typically less than 10% of the mean.When grown under identical conditions, a variety of barley bred for cold soils had higher nitrogen influx rates at low concentrations and low temperatures than one bred for warm soils, whereas the one bred for warm soils had higher influx rates at high concentrations and high temperatures. Ammonium was more readily absorbed than nitrate by both varieties at all concentrations and temperatures tested. Ammonium and nitrate influx in both varieties were equally inhibited by low temperatures.

The Importance of Regenerated Nitrogen to Phytoplankton Productivity to Phytoplankton Productivity in a Subalpine Lake

Experiments utilizing epilimnetic water were conducted to determine the rate of ammonium regeneration, due to zooplankton excretion and microbial mineralization processes, in relation to the rate of inorganic nitrogen assimilation by phytoplankton. The euphotic zone of dimictic, meso—oligotrophic Castle Lake is characterized by a rapid depletion of both nitrate and ammonium soon after spring thaw. External inputs of nitrogen are minimal during this period and levels of inorganic nitrogen remain low until fall overturn. The rate of ammonium assimilation was high relative to nitrate assimilation, and was significantly correlated with the rate of ammonium regeneration. The importance of this rapid turnover of nitrogen to phytoplankton growth is consistent with the results of previous Castle Lake studies, and with the current conceptual model of primary production in the mixed layer of nitrogen—deficient marine ecosystems.

The Effect of Ammonia and Ammonia‐sulfur Solutions on Nitrification Rates and Chemical Properties of a Calcareous Soil

AbstractNitrification rates and changes in chemical properties of a calcareous soil were investigated after injection of liquid anhydrous NH3 and anhydrous NH3‐S solutions.Nitrification rates (on a whole pot basis) of 15.7, 25.3, and 32.2 mg of N per pot per day were found with the application of 200, 400, and 600 mg of N/pot, respectively. These nitrification rates were recorded during the initial 14 days of the study when total NO3‐ accumulation appeared to be linear.Ammonium depletion from zones 1 cm in thickness measured outward from the injection point appear to obey a first‐order rate law. Half life values ranged from 12.4 to 1.4 days. They were longest at the injection point with the highest NH3 rate and decreased with decreasing rate of application and with increasing distance from the injection point. There were no differences in the nitrification rates of the two sources as measured by either nitrate accumulation on a whole pot basis or ammonium depletion of individual zones.Less than 10% of the applied sulfur was recovered as SO42‐ during the incubation period. Little difference was found in the effect of the two sources on pH, DTPA extractable Zn or Fe, or NaHCO3 extractable P. DTPA‐extractable Mn was higher near the injection point in the NH3‐S treatments.