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Temperate Forest Soils (temperate + forest_soil)

Distribution by Scientific Domains

Life Sciences	75%

Selected Abstracts

Vertical partitioning of CO2 production within a temperate forest soil

GLOBAL CHANGE BIOLOGY, Issue 6 2006
ERIC A. DAVIDSON
Abstract The major driving factors of soil CO2 production , substrate supply, temperature, and water content , vary vertically within the soil profile, with the greatest temporal variations of these factors usually near the soil surface. Several studies have demonstrated that wetting and drying of the organic horizon contributes to temporal variation in summertime soil CO2 efflux in forests, but this contribution is difficult to quantify. The objectives of this study were to partition CO2 production vertically in a mixed hardwood stand of the Harvard Forest, Massachusetts, USA, and then to use that partitioning to evaluate how the relative contributions of CO2 production by genetic soil horizon vary seasonally and interannually. We measured surface CO2 efflux and vertical soil profiles of CO2 concentration, temperature, water content, and soil physical characteristics. These data were applied to a model of effective diffusivity to estimate CO2 flux at the top of each genetic soil horizon and the production within each horizon. A sensitivity analysis revealed sources of uncertainty when applying a diffusivity model to a rocky soil with large spatial heterogeneity, especially estimates of bulk density and volumetric water content and matching measurements of profiles and surface fluxes. We conservatively estimate that the O horizon contributed 40,48% of the total annual soil CO2 efflux. Although the temperature sensitivity of CO2 production varied across soil horizons, the partitioning of CO2 production by horizon did not improve the overall prediction of surface CO2 effluxes based on temperature functions. However, vertical partitioning revealed that water content covaried with CO2 production only in the O horizon. Large interannual variations in estimates of O horizon CO2 production indicate that this layer could be an important transient interannual source or sink of ecosystem C. [source]

Calibration model of microbial biomass carbon and nitrogen concentrations in soils using ultraviolet absorbance and soil organic matter

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2008
X. Xu
Summary There is a need for a rapid, simple and reliable method of determining soil microbial biomass (SMB) for all soils because traditional methods are laborious. Earlier studies have reported that SMB-C and -N concentrations in grassland and arable soils can be estimated by measurement of UV absorbance in soil extracts. However, these previous studies focused on soils with small soil organic matter (SOM) contents, and there was no consideration of SOM content as a covariate to improve the estimation. In this study, using tropical and temperate forest soils with a wide range of total C (5,204 mg C g,1 soil) and N (1,12 mg N g,1 soil) contents and pH values (4.1,5.9), it was found that increase in UV absorbance of soil extracts at 280 nm (UV280) after fumigation could account for 92,96% of the variance in estimates of the SMB-C and -N concentrations measured by chloroform fumigation and extraction (P < 0.001). The data were combined with those of earlier workers to calibrate UV-based regression models for all the soils, by taking into account their varying SOM content. The validation analysis of the calibration models indicated that the SMB-C and -N concentrations in the 0,5 cm forest soils simulated by using the increase in UV280 and SOM could account for 86,93% of the variance in concentrations determined by chloroform fumigation and extraction (P < 0.001). The slope values of linear regression equations between measured and simulated values were 0.94 ± 0.03 and 0.94 ± 0.04, respectively, for the SMB-C and -N. However, simulation using the regression equations obtained by using only the data for forest profile soils gave less good agreement with measured values. Hence, the calibration models obtained by using the increase in UV280 and SOM can give a rapid, simple and reliable method of determining SMB for all soils. [source]

Carbon monoxide uptake kinetics in unamended and long-term nitrogen-amended temperate forest soils

FEMS MICROBIOLOGY ECOLOGY, Issue 3 2006
Alvarus S. K. Chan
Abstract The effect of nitrogen (N) additions on the dynamics of carbon monoxide consumption in temperate forest soils is poorly understood. We measured soil CO profiles, potential rates of CO consumption and uptake kinetics in temperate hardwood and pine control plots and plots amended with 50 and 150 kg N ha,1 year,1 for more than 15 years. Soil profiles of CO concentrations were above atmospheric levels in the high-N plots of both stands, suggesting that in these forest soils the balance between consumption and production may be shifted so that either production is increased or consumption decreased. Highest rates of CO consumption were measured in the organic horizon and decreased with soil depth. In the N-amended plots, CO consumption increased in all but one soil depth of the hardwood stand, but decreased in all soil depths of the pine stand. CO enzyme affinities increased with soil depth in the control plots. However, enzyme affinities in the most active soil depths (organic and 0,5 cm mineral) decreased in response to low levels of N in both stands. In the high-N plots, affinities dramatically-increased in the hardwood stand, but decreased in the organic horizon and increased slightly in the 0,5 cm mineral soil in the pine stand. These findings indicate that long-term N addition either by fertilization or deposition may alter the size, composition and/or physiology of the community of CO consumers so that their ability to act as a sink for atmospheric CO has changed. This change could have a substantial effect on the lifetime of greenhouse gases such as CH4 and therefore the future of Earth's climate. [source]