The effect of acid rain, soil temperature and humidity on C-mineralization rates in organic soil layers under spruce

Abstract

The biological activity in organic soil layers under spruce was determined by measuring rates of carbon dioxide emission. Under laboratory conditions, biological activity was found to be optimal at temperatures ranging from 20°C to 35°C and at water contents ranging from 40% to 60%. Weakly acidic to neutral pH values of organic materials stimulated microbial CO2 formation whereas high acidity (pH < 2.4) inhibited it. Low CO2 emission rates were observed at pH < 2.4 and therefore populations of microorganisms highly resistant to acid must be present in the organic materials. The OL horizon was found to contribute 50% of the total potential C-mineralization with the lower horizons OF and OH contributing 25 % each. In simulating "acid rain" experiments, analysis of water percolating through the organic layers was shown to cause constant leaching of cations at the pH 3 to 6.5 range. In this respect, the OL horizon exerts a buffering effect. It can be postulated that the acidification of soil organic material under spruce by acid rain inhibits C-mineralization and decreases the release of mineral nutrients. In the long run this can be expected to affect the turnover of mineral nutrients in forest ecosystems.

Nitrogen mineralization and H+ transfers in a Scots pine (Pinus sylvestris L.) forest soil as affected by liming

“…The soil moisture content may influence the mineralization rate (Clarholm et al, 1981;Wilhelmi and Rothe, 1990). However, in the present research the moisture content probably did not seriously affect the N transformations: there was no correlation between the incubation cores' initial MC, final MC or average MC, on the one hand, and ammonification, nitrification (or their sum) or NO3-, NHa-and Ni concentrations per sampling spot, on the other hand.…”