Microcosm Bioassays Research Articles

Planetary Bioresources and Astroecology: 1. Planetary Microcosm Bioassays of Martian and Carbonaceous Chondrite Materials: Nutrients, Electrolyte Solutions, and Algal and Plant Responses

The biological fertilities of planetary materials can be assessed using microcosms based on meteorites. This study applies microcosm tests to martian meteorites and analogues and to carbonaceous chondrites. The biological fertilities of these materials are rated based on the soluble electrolyte nutrients, the growth of mesophile and cold-tolerant algae, and plant tissue cultures. The results show that the meteorites, in particular the Murchison CM2 carbonaceous chondrite and DaG 476 martian shergottite, contain high levels of water-extractable Ca, Mg, and SO 4–S. The martian meteorites DaG 476 and EETA 79001 also contain higher levels of extractable essential nutrients NO 3–N (0.013–0.017 g kg −1) and PO 4–P (0.019–0.046 g kg −1) than the terrestrial analogues. The yields of most of the water-extractable electrolytes vary only by factors of 2–3 under a wide range of planetary conditions. However, the long-term extractable phosphate increases significantly under a CO 2 atmosphere. The biological yields of algae and plant tissue cultures correlate with extractable NO 3–N and PO 4–P, identifying these as the limiting nutrients. Mesophilic algae and Asparagus officinalis cultures are identified as useful bioassay agents. A fertility rating system based on microcosm tests is proposed. The results rate the fertilities in the order martian basalts > terrestrial basalt, agricultural soil > carbonaceous chondrites, lava ash > cumulate igneous rock. The results demonstrate the application of planetary microcosms in experimental astroecology to rate planetary materials as targets for astrobiology exploration and as potential space bioresources. For example, the extractable materials in Murchison suggest that concentrated internal solutions in carbonaceous asteroids (3.8 mol L −1 electrolytes and 10 g L −1 organics) can support and disperse microorganisms introduced by natural or directed panspermia in early solar systems. The results also suggest that carbonaceous asteroids and martian basalts can serve as potential future resources for substantial biological populations in the Solar System.

Responses of Estuarine Phytoplankton Communities to Nitrogen Form and Mixing Using Microcosm Bioassays

We examined the effects of different forms of nitrogen and mixed versus static conditions on the structure and function of natural Neuse River estuary phytoplankton communities incubated in 66-liter microcosms in March, May, August, and November 1999. Significant differences were found between effects of mixed versus static treatments in three of four experiments, but no differences were observed between effects of different forms of nitrogen. Mixed incubations resulted in higher contributions of diatoms to total community biomass (measured as chlorophyll a) than in static tanks in May. Significantly higher rates of carbon fixation were also observed, likely due to increased suspension of diatoms in surface (illuminated) layers of the tanks. In August, we found significantly higher abundances of cyano- bacteria, total community biomass, and rates of carbon fixation in static tanks than in tanks that were mixed. In Novem- ber, static incubations showed significantly higher abundances of cryptophytes resulting in higher total community bio- mass and rates of carbon fixation in static tanks than in mixed tanks. Nitrogen additions significantly increased total community biomass relative to controls in May and August, indicating that the communities were nitrogen-limited at these times. We conclude that while nitrogen additions may result in increases in phytoplankton biomass when nitrogen is limiting, phytoplankton community structure in the Neuse River Estuary may be determined more by the hydrodynam- ics of the system (mixing versus stratification) than by the form of nitrogen available for growth.

Variability of community metrics: Detecting changes in structure and function

AbstractIncreased environmental realism in toxicity testing has been advocated to better predict ecological effects of toxic chemicals, and several aquatic microcosm bioassays have been developed that use both natural and synthetic organism assemblages. Additionally, greater emphasis is being placed on community changes as evidence of adverse effects on aquatic ecosystems. The ability to infer structural or functional changes in stressed vs. unstressed communities is linked to statistical power that arises from the combination of experimental design and the underlying variability in chosen metrics. We evaluated several community response variables (metrics) in aquatic laboratory microcosm experiments and field studies to estimate metric variability. Variability of community metrics under laboratory conditions was similar to that observed in the field. Power curves were constructed to estimate the detectability of significant responses with different experimental designs. Using the median C. V. for each measured response, we estimated the minimum detectable distance for power of 0.8 (β = 0.2) and α = 0.05 for each response. Community metrics with C.V.s <30% allow detection of differences between means of 20 to 60%, using as few as three replicates. Structural metrics such as species richness and standing crop are expected to prove more useful in detecting community and ecosystem changes. Process rates are affected by material supplies that may not change under stress.

Comparisons of single‐species, microcosm and experimental pond responses to atrazine exposure

AbstractResults from single‐species toxicity tests form the basis for guidance about concentrations of chemicals that are likely to be environmentally hazardous. Microcosm bioassays have been proposed as better tools for this purpose under some circumstances. Rarely have comparisons been made among the responses in the various test systems and those seen in natural communities. We compared the responses among single‐species algal assays, a synthetic microcosm (the Taub microcosm) and experimental ponds exposed to similar concentrations of atrazine by comparing concentrations of atrazine that reduced algal activity or biomass to 50% of control values (EC50). Eight algal species were examined; mean species EC50 values for 14C uptake ranged from 37 to 308 μg/L. For the Taub microcosm, EC50 values were 103 to 159 μg/L for 14C uptake, 126 to 165 μg/L for dissolved oxygen production and 106 to 164 μg/L for dissolved oxygen consumption. Values were dependent on the time intervals selected for calculations. In the ponds, EC50 values for 14C uptake were 100 μg/L and for chlorophyll a, 82 μg/L. The basic similarity among EC50 values across test systems suggests that results from a combination of single‐species assays, or the Taub microcosm, provided a reasonable estimate of the concentration of atrazine that produced similar direct effects on more natural communities.

COMPARISONS OF SINGLE-SPECIES, MICROCOSM AND EXPERIMENTAL POND RESPONSES TO ATRAZINE EXPOSURE

Results from single-species toxicity tests form the basis for guidance about concentrations of chemicals that are likely to be environmentally hazardous. Microcosm bioassays have been proposed as better tools for this purpose under some circumstances. Rarely have comparisons been made among the responses in the various test systems and those seen in natural communities. We compared the responses among single-species algal assays, a synthetic microcosm (the Taub microcosm) and experimental ponds exposed to similar concentrations of atrazine by comparing concentrations of atrazine that reduced algal activity or biomass to 50% of control values (EC50). Eight algal species were examined; mean species EC50 values for 14C uptake ranged from 37 to 308 μg/L. For the Taub microcosm, EC50 values were 103 to 159 μg/L for 14C uptake, 126 to 165 μg/L for dissolved oxygen production and 106 to 164 μg/L for dissolved oxygen consumption. Values were dependent on the time intervals selected for calculations. In the ponds, EC50 values for 14C uptake were 100 μg/L and for chlorophyll a, 82 μg/L. The basic similarity among EC50 values across test systems suggests that results from a combination of single-species assays, or the Taub microcosm, provided a reasonable estimate of the concentration of atrazine that produced similar direct effects on more natural communities.