Nutrient Amendment Experiments Research Articles

Regulation of phytoplankton dynamics by vitamin B12

Despite the biological necessity of vitamin B12 (cobalamin), its importance in phytoplankton ecology has been ignored for nearly three decades. Here we report strong and selective responses of phytoplankton communities to varying low levels (5–87 pM) of dissolved B12 in several coastal embayments. The ecological importance of this vitamin is inferred from observed declines in dissolved B12 levels as field populations of large (>5 μm) phytoplankton increased. In contrast, biomass of small (<5 μm) phytoplankton varied independently of B12 concentrations. These observations were corroborated by field‐based nutrient amendment experiments, in which B12 additions stimulated growth of large phytoplankton taxa 6‐fold over unamended controls. In contrast, small taxa (<5 μm) were largely unaffected. This study provides the first evidence of vitamin B12's influence on phytoplankton field population dynamics based on direct chemical measurements of cobalamin, and implicates B12 as an important organic regulator of photoautotrophic fertility in marine systems.

The use of saline mine water and municipal wastes to establish plantations on rehabilitated open-cut coal mines, Upper Hunter Valley NSW, Australia

Commercial forestry plantations as a post-mining land use in the Upper Hunter Valley NSW, Australia, have productivity limitations and are restricted by the poor nutrient quality of mining substrates and low regional rainfall. However, municipal waste products and saline groundwater from coal mining operations can assist in establishing and improving plantation growth rates. The aim of this study was to investigate the establishment and growth of four potentially commercial species in a saline irrigation and nutrient amendment experiment over 2 years. The experiment was designed as a split–split plot with irrigation being the main plot effect, nutrient amendments (overburden, fertiliser, biosolids, compost and topsoil) as the subplot effect and species ( Corymbia maculata Hook, Eucalyptus botryoides Smith, E. tereticornis Smith and E. occidentalis Endl.) as the sub-subplot effect. Survival, height, diameter, above-ground biomass, tree form and weed competition in each treatment were measured along with substrate electrical conductivity. Tree survival after 24 months improved with irrigation (89.8%) compared to the rain-fed treatment (78.6%). Irrigation did not significantly improve tree growth responses but there was an increasing trend after 24 months with irrigation producing better overall growth. Biosolids, compost and fertiliser produced significantly better growth than the topsoil and overburden treatments. However, weed growth was higher in biosolids and compost and was correlated with reduced tree growth but not less than topsoil and overburden treatments. Eucalyptus occidentalis performed significantly better than other species in relation to height (1.89 m), diameter at 30 cm (3.1 cm) and standing crop biomass (982 kg ha −1) after 2 years. Surface substrate EC 1:5 (0–10 cm) increased significantly following irrigation events but reduced over time by leaching from rainfall. Electrical conductivity in the lower horizon (10–30 cm) was not significantly different from the upper horizon in the irrigation treatment but was significantly higher in the rain-fed treatment after 2 years. Biosolids and compost increased EC 1:5 over the first 6 months but thereafter compost and overburden produced higher values during the second year of the study. These results show that saline mine water irrigation can be used to establish plantations without impacting deleteriously on tree growth and substrate EC 1:5. However, further research is required to determine whether growth rates will reach a commercial standard and that the long-term impacts of using saline irrigation water are avoided.

Meta-analysis of lotic nutrient amendment experiments: detecting and quantifying subtle responses

AbstractEcological theory predicts that multiple nutrients, added independently, could each stimulate algal community biomass. In contrast to this theoretical prediction, individual nutrient amendment experiments frequently detect significant increases in algal community biomass in response to addition of a single nutrient, whereas the independent addition of other nutrients often does not result in a statistically significant increase in biomass. However, because of the low replication and high variability typical of ecological field experiments, only large responses can be detected as statistically significant in any single experiment. It is therefore possible that smaller, yet still real and biologically important responses occur, but remain undetected because of the low statistical power of individual experiments. Meta-analysis of lotic nutrient (N and P) amendment experiments indicated that simultaneous stimulation of benthic algal community biomass by >1 nutrient was the rule, not the exception. Add...

Nutrient Limitation of Algal Biomass Accrual in Streams: Seasonal Patterns and a Comparison of Methods

In-situ, nutrient amendment experiments (nutrient-diffusing substrata, NDS) were con- ducted in 12 New Zealand gravel-bed streams to investigate seasonality of biomass accrual and nutrient limitation of benthic algal communities. Benthic algal biomass accrual rates exhibited sig- nificant (p = 0.019, repeated measures ANOVA) seasonal differences; rates were greatest in summer and least in winter. The degree of nutrient limitation also differed (p = 0.003) seasonally; periphyton community biomass was most responsive to nutrient amendments in summer and least responsive in winter. Temperature may be the underlying cause of these patterns. The ratios of dissolved inor- ganic nitrogen to soluble reactive phosphorus (DIN:SRP) in streamwater and of streambed periphyton communities were of limited use for predicting which nutrient limited NDS bioassays; cellular nu- trient content was weakly predictive. This study demonstrates the need to consider temporal changes (i.e., seasonality) when assessing the influence of nutrients on stream ecosystems, and indicates that the use of nutrient ratios to ascertain which nutrient may limit benthic algal biomass should be validated with field experiments.

Constraints of Nutrient Availability on Primary Production in Two Alpine Tundra Communities

A nutrient amendment experiment was conducted for two growing seasons in two alpine tundra communities to test the hypotheses that: (1) primary production is limited by nutrient availability, and (2) physiological and developmental constraints act to limit the responses of plants from a nutrient—poor community more than plants from a more nutrient—rich community to increases in nutrient availability. Experimental treatments consisted of N, P, and N + P amendments applied to plots in two physiognomically similar communities, dry and wet meadows. Extractable N and P from soils in nonfertilized control plots indicated that the wet meadow had higher N and P availability. Photosynthetic, nutrient uptake, and growth responses of the dominants in the two communities showed little difference in the relative capacity of these plants to respond to the nutrient additions. Aboveground production responses of the communities to the treatments indicated N availability was limiting to production in the dry meadow community while N and P availability colimited production in the wet meadow community. There was a greater production response to the N and N + P amendments in the dry meadow relative to the wet meadow, despite equivalent functional responses of the dominant species of both communities. The greater production response in the dry meadow was in part related to changes in community structure, with an increase in the proportion of graminoid and forb biomass, and a decrease in the proportion of community biomass made up by the dominant sedge Kobresia myosuroides. Species richness increased significantly in response to the N + P treatment in the dry meadow. Graminoid biomass increased significantly in the wet meadow N and N + P plots, while forb biomass decreased significantly, suggesting a competitive interaction for light. Thus, the difference in community response to nutrient amendments was not the result of functional changes at the leaf level of the dominant species, but rather was related to changes in community structure in the dry meadow, and to a shift from a nutrient to a light limitation of production in the wet meadow.

Stream Geomorphology: Effects on Periphyton Standing Crop and Primary Production

Anthropogenic changes in stream geomorphology have reduced the capacity of many North American streams to trap and retain sediments and organic matter. Significant losses of retentive structures from many small streams have resulted from beaver trapping. We compared algal standing crops and rates of primary production in two adjacent streams in the Zuni Mountains of New Mexico. Castor Creek has been worked by beaver and is a complex, highly retentive system with an extensive floodplain and accumulations of organic debris. Sawmill Creek is moderately incised, free of large organic debris, and poorly retentive. Clay tiles introduced into Castor Creek had average chlorophyll a standing crops 3-9× greater than Sawmill Creek (54.8-257.8 vs. 18.4-44.9 mg/m²). Chlorophyll a on natural substrates averaged 11× greater in Castor Creek than in Sawmill Creek (1679.4 vs. 154.2 mg/m²). Average standing crop of chlorophyll a per 250 m reach was 136× greater in Castor Creek than in Sawmill Creek due to its greater surface area (12.4×) and greater standing crop (11×). Extensive filamentous algal mats and the macro-alga Nitella gracilis in Castor Creek's beaver ponds exhibited the highest rates of primary production (85 mg C m^-2 hr^-1) while epilithic samples from both streams were similar (16.6 and 21.2 mg C m^-2 hr^-1 for Castor and Sawmill Creeks respectively). Nutrient amendment experiments revealed that both streams were nitrogen limited. Sediment samples taken in 1989 showed Castor Creek had 25× more dissolved NH₄ in the upper 5 cm of sediment than Sawmill Creek (1242 vs. 50 μg/L). We suggest that higher algal production in Castor Creek is linked to greater nutrient availability at the sediment/water interface due to greater retention and processing of organic matter in the hyporheic zone.

Edaphic limitations to growth and photosynthesis in Sierran and Great Basin vegetation.

Soils derived from hydrothermally altered andesite support unique communities of Sierran conifers (Pinus ponderosa Laws. and P. jeffreyi Grev. and Balf.) amongst sagebrush (Artemisia tridentata Nutt.) vegetation in the western Great Basin. Plants grown in soil derived from hydrothermally altered bedrock had lower growth rates, total biomass, and net photosynthetic rates than plants grown in soil derived from unaltered andesite of the same formation. Total dry mass was 10 to 28% lower for conifers grown in altered soil whereas dry mass of Artemisia tridentata and Bromus tectorum L. was reduced by over 90%. Results from a nutrient amendment experiment indicated that low phosphorus was the dominant limitation in altered soil, and phosphorus-deficiency affected growth primarily by limiting leaf area development rather than direct inhibition of photosynthesis. The proportionately greater reduction of biomass for Artemisia and Bromus grown in altered soil supports our hypothesis that Great Basin vegetation is excluded from altered soil by intolerance to nutrient deficiency. The Sierran conifers growing on this rock type are therefore free of competition for water with Great Basin vegetation and are able to persist in an exceptionally dry climate.

Changes in Soil Nitrogen-Mineralization and Nitrification Along an Altitudinal Transect in Tropical Rain Forest in Costa Rica

(1) Surface soils (0-15 cm) were collected from six sites in mature undisturbed tropical rain forest along an altitudinal transect (100 m-2600 m) on Volcan Barva, Costa Rica. The rates of nitrogen-mineralization and nitrification were measured under (a) field conditions, where the soils were incubated under the litter layer, and (b) laboratory conditions, where the incubations were done at higher temperatures, but at field moisture content. In addition, a measure of nitrogen-mineralization was made under 'improved' conditions, where the incubation temperature was increased, and aeration and moisture content improved. The moisture content, pH and the concentrations of a range of soil nutrients were also measured for each soil. A nutrient amendment experiment was also done, where selected nutrients were added to soils from three altitudes (100 m, 1000 m and 2600 m), and their effect on nitrogen mineralization and nitrification assessed. (2) The moisture content, total nitrogen and carbon, extractable potassium, calcium, magnesium and ammonium-nitrogen increased, and both extractable copper and nitratenitrogen decreased, with altitude. (3) Soil nitrogen-mineralization and nitrification both decreased with increasing altitude under field conditions, and both rates were not increased significantly by laboratory incubation, where the temperature alone was alleviated. However, where both temperature and aeration/moisture content were improved, then nitrogen-mineralization rate increased by between one and three orders of magnitude, and a positive relationship was found with altitude of origin. These combined results suggest that nitrogenmineralization may be limited under field conditions by the high moisture contents found in the montane soils. (4) Partial correlation analysis of these nitrogen turnover rates with other measures of soil chemistry showed that (a) under 'improved' conditions the mineralization rate was positively correlated with resource quality and negatively correlated with pH and perhaps reducing conditions, (b) under field and laboratory conditions the mineralization rate was correlated with the reaction product, and (c) nitrification was correlated with the reaction substrate, implying a resource limitation. (5) In the nutrient-addition experiment, ammonium-nitrogen increased nitrogenmineralization rates at low and high altitudes, but decreased rates at the intermediate altitude. Calcium carbonate addition increased mineralization rates at the low and intermediate altitude, whereas calcium sulphate increased these rates only at the highest altitude. Phosphorus addition had no effect on nitrogen-mineralization at any altitude. (6) Nitrification rates were increased by substrate addition, confirming that the reaction was substrate limited. However, the stimulation was much less than the amount of added substrate, and other limiting factors are clearly important. Calcium sulphate also increased nitrification, but only at the lowest altitude. (7) These findings agree with the general hypothesis that nitrogen-mineralization and nitrification rates are reduced in montane tropical rain forest, and may be a contributory factor controlling growth, species composition and stand structure. The significance of these results for future management of montane tropical rain forest is briefly discussed.