Climate change 2014 - Synthesis Report

Microbial degradation of hydrocarbons in the environment.

Mechanisms of membrane toxicity of hydrocarbons.

Nature And Properties Of Soils

Antibiotics and antibiotic resistance in water environments

We conducted a study of the relationship between the dissolution rates of organic compounds that are sparingly soluble in water and the biodegradation of these compounds by mixed cultures of bacteria. The rates of dissolution of naphthalene and 4-chlorobiphenyl were directly related to their surface areas. The bacteria caused a decline in the concentration of the soluble substrate. The rate of bacterial growth fell abruptly when 4-chlorobiphenyl or naphthalene was no longer detectable in solution. The population continued to increase in media with different surface areas of insoluble 4-chlorobiphenyl, but the final counts were higher in media in which the surface areas of the substrate were larger. The rates of dissolution of palmitic acid, octadecane, di(2-ethylhexyl) phthalate, and 1-naphthyl N-methylcarbamate were determined in the absence of microorganisms. A mixed culture of microorganisms mineralized palmitic acid, di(2-ethylhexyl) phthalate, and Sevin (1-naphthyl N-methylcarbamate) at a logarithmic rate, but octadecane mineralization was linear. The rates of mineralization at the end of the active phase of the biodegradation were lower than the rate of dissolution of palmitic acid but higher than the rate of dissolution of octadecane in the uninoculated medium. We suggest that spontaneous dissolution rates are only one of the factors that govern the rates of biodegradation.

https://aem.asm.org/content/aem/52/2/290.full.pdf

Rates of dissolution and biodegradation of water-insoluble organic compounds.

Riparian forest zones are used for mitigation of agricultural and urban nonpoint source pollution. Phosphatase activity is ubiquitous in soil and sensitive to environmental perturbations, and hence, it may serve as an indicator of soil quality in riparian areas. We examined the relationship betw

Spatial distribution of soil phosphatase activity within a riparian forest1

The effects of phosphate and ammonium additions on microbial respiration were determined using three peat soils with similar total N content (25–38 g kg−1) and different total P (TP) content: low (231 mg P kg−1), intermediate (385 mg P kg−1), and high (1.473 g P kg−1). These soils, obtained from Everglades National Park, Florida, had been formed predominantly from the partial decomposition of sawgrass (Cladium jamaicense). Soil respiration was measured by gas chromatography. Amendment of the soils with 0–100 mm PO4 or NH4 resulted in changes in the C-to-nutrient ratio that ranged from 4 to 2042 for C:P and 11.5 to 14.1 for C:N. Kinetic parameters for soil respiration were obtained by fitting the data to a kinetic model that describes soil C mineralization as the sum of an exponential decay function for readily mineralizable C and a zero-order decay function for stable C. Estimates of the zero-order rate constant for endogenous respiration in unamended soil samples increased with TP content of the soil (in mmol CO2 kg−1 d−1): low TP (36–40) < intermediate TP (49–52) < high TP (107–114). Addition of phosphate stimulated the respiration rate of the low and intermediate TP soil, but had no effect on the rate of soil respiration of the high TP soil. Ammonium additions inhibited soil respiration in the low and intermediate TP soils at most concentrations tested; the rate of respiration was inversely proportional to the amount of NH4 added. Addition of ammonium to the high TP soil stimulated respiration. Microbial respiration in the low and intermediate TP soils is limited by P availability, whereas N appears to limit respiration in the high TP soil. These results suggest that P pollution may have a marked, long-term effect on microbial respiration in organic soils with low TP content.

Nutrient limitations on microbial respiration in peat soils with different total phosphorus content

The spatial distribution of C mineralization, nematode density, organic matter content and soil moisture were determined for a forest and an old field soil in the northeastern U.S.A. over the course of a year. The data were analyzed using univariate, multivariate and geostatistical methods. The forest soil had a higher C mineralization rate, soil moisture content and nematode density than the old field soil throughout the year. High C mineralization rates and nematode density coincided with a brief January thaw in the forest, but not in the old field soil. Multiple regression analysis identified different components as significant for C mineralization depending on sampling date. In the old field, soil moisture and organic matter content were significant regression components for C mineralization at different times of the year. In the forest, organic matter, root mass (>2 mm) and bulk density were significant regression components on different dates. For nematodes, the multiple regression analysis identified soil moisture and bulk density as significant in both soils at different times of the year. Maps for each property were estimated with block kriging for each sampling date. In the forest, areas of maximal C mineralization and nematode density coincided with areas of high organic matter and moisture content only on some sampling dates. In the old field, maximal C mineralization generally coincided with areas of high moisture and organic matter content. Spatial structure in both forest and old field changed through the year. Our results suggest that dynamics and spatial patterns of C mineralization in the old field may be more susceptible to changes in soil moisture than in the forest soil. By contrast, temporal and spatial patterns of nematode density in both ecosystems appear to be susceptible to soil moisture dynamics. Organic matter appears to be important in controlling the spatial distribution of C mineralization, but not that of nematodes.

José A. Amador

Papers

Rates of dissolution and biodegradation of water-insoluble organic compounds.

Spatial distribution of soil phosphatase activity within a riparian forest1

Nutrient limitations on microbial respiration in peat soils with different total phosphorus content

Spatial and temporal patterns of soil biological activity in a forest and an old field

Extraction of chromophoric humic substances from seawater