Response of carbon mineralization to combined changes in soil moisture and carbon-phosphorus ratio in a low phosphorus histosol

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We conducted a laboratory study to evaluate the hypothesis that the effects of soil moisture on aerobic and anaerobic carbon mineralization in a histosol from a phosphorus-limited ecosystem depend on both C:P ratio of the soil and carbon availability. The effects of varying soil moisture and soil C:P ratio on carbon mineralization were studied in a pristine histosol with low P content (C:P = 2000). Relative water content (Θ(rel) = Θ(V)/ε, where Θ(V) is volumetric water content and E is the saturated water content) varied from 0.14 to 1.00, corresponding to soil water potentials (Ψ) of -188 to 0 bars, respectively. The C:P ratio was varied from 2000 to 20 by addition of PO4 to the soil. At the highest C:P value (2000), changes in water content had no significant effect on respiration rate (α). As the C:P ratio decreased, respiration became increasingly sensitive to changes in relative water content, with maximum respiration rates (α(max)) observed at Θ(rel) between 0.60 and 1.00 and C:P values between 20 and 200. There was a negative statistically significant linear relationship between relative respiration rate (α/α(max) and soil water potential at C:P < 2000, described by the equation: α/α(max) = -0.077 log Ψ + 0.898. Respiration in glucose-amended pristine soil showed little response to water content; however, combined addition of glucose and phosphorus to the soil resulted in a shift in the values of Θ(rel) at which maximum respiration rate was observed to between 0.2 and 0.4, depending on the C:P ratio of the soil. Methane evolution from glucose-amended soil was sensitive to changes in C:P and soil moisture, with CH4 production observed at increasingly lower values of Θ(rel) with decreasing C:P. These results suggest that the effects of soil moisture on carbon metabolism in these soils are dependent on both C:P ratio of the soil and carbon availability.

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Soil Science