Biological activity in soil from forest stands in Central Sweden, as related to site properties

The relationship between biological activities in samples from the forest floor and, respectively, stand (site quality class, tree age, and latitude) and soil (pH, carbon, carbon/nitrogen, and available phosphorus) properties was examined in a multi-site study performed in Central Sweden. The biological activities measured were respiration and phosphatase and dehydrogenase activity. The incubations were made in the laboratory on sieved and homogenized samples. When the biological activities were expressed on a dry matter weight basis, the concentration of organic C was the strongest predictor of respiration and phosphatase activity. In contrast, the strongest predictor of dehydrogenase activity was the pH value. Respiration and dehydrogenase activity were not significantly correlated. When excluding the influence of C concentration by expressing the activities on a C weight basis, respiration and phosphatase activity were not significantly correlated with any of the independent variables studied. Curvilinear models (polynomial equations of second and third order) gave significantly better descriptions of the relationship between respiration and, respectively, pH and C/N ratio, than linear models. Optimum conditions for respiration were indicated at intermediate pH (4-5 in 0.01 M CaCl2) and C/N ratio (20-30). The dehydrogenase activity on a C weight basis was correlated with the pH value even more strongly than it was on a dry matter basis. The phosphatase activity was not significantly correlated with the content of available P either on a dry matter basis or on a C weight basis.