Respiration Rates of Organic Soil Depending on Changes of Moisture and Aeration

Abstract

This paper aims at analyzing changes in soil respiration depending on the levels of soil moisture and aeration. Organic forest soil was used in the experiments. Watering of the soil was applied starting from two initial moisture contents: 1) GWC > 0.1, desiccated soil, respiration equals to zero; 2) GWC between 0.46 - 0.78, moisture of the soil approximately the same as at the time of sample collection. Watering of the soil was applied once or continuously during the experiment. The experiments were conducted under both: unrestricted air-supply and anoxic conditions. Measurements of: oxygen consumption, carbon dioxide emission, and RQ were determined with a volumetric respirometer. Soil desiccation, which occurs under good access of the air, and leads to the increase of respiration rate (the “Birch effect”), is predominantly related to aerobic respiration following the change in soil aeration. If respiration of non-desiccated soil is assumed as 100%, the oxygen consumption of desiccated soil equaled to 209.90% of such value in the non-desiccated soil at the lowest moisture level, and only to 51% at the highest. Carbon dioxide emission equaled to 191.92% and 111% at the lowest and the highest moisture levels, respectively. Desiccation did not increase the respiration rate under anoxic conditions. It either decreased or remained statistically unchanged. However, obtained values of RQ index suggest that under anoxic conditions desiccation affects fermentation processes in the soil. The value of RQ index at the moisture level lower than GWC 1 was very low attaining merely 0.3 - 0.4, which suggests active fermentation processes. At higher moisture content yet, RQ value exceeded 2.