Abiotic factors regulating nitrogen transformations in the organic layer of acid forest soils: Moisture and pH

Abstract

The relationships between nitrogen transformations and moisture and pH in coniferous forest litter were determined using laboratory incubation experiments.A linear relation between gravimetric moisture content and nitrification was found within the whole studied range of moisture conditions (10-290% ODW). Net nitrogen mineralization increased linearly with moisture content up to 140% ODW. At higher moisture contents, net mineralization was found to be independent of moisture. Relative nitrification was found to be a linear function of moisture content. The dependence of the CO 2 production rates on moisture in the coniferous litter decreased from low to high moisture availability. Due to a nearly linear relationship between gravimetric moisture content and log-(water potential) within the investigated moisture range, the same type of relationships were found with this latter parameter as well. The relationship between nitrogen transformations and pH was studied by means of the addition of different amounts of HC1 and NaOH during short incubation experiments (1 week). Nitrification was found to be a negative linear function of the H-ion concentration within the range of 0.04 (pH 4.40) and 0.36 (pH 3.45) mmol H-ion L -1. At a higher H-ion concentration and thus at a lower pH than 3.45, no nitrate was produced any more. No relationship between net mineralization and pH was found.

Effects of a clear-cut on the in situ nitrogen mineralisation and the nitrogen cycle in a 67-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) plantation

“…The acidity of the soil had no inhibiting effect on the nitrifying capacity, as previously found in many other studies [19,39,62,81]. Marques [53] hypothesised that the change in vegetation via the introduction of Douglas-fir has led to the destabilisation of the organic matter.…”

Nitrogen mineralization and gaseous nitrogen losses from waterlogged and drained organic soils in a black alder (<i>Alnus glutinosa</i> (L.) Gaertn.) forest

“…Beside substrate chemistry, moisture content together with temperature are considered as the most important abiotic factors influencing biogeochemical transformation processes (Tietema et al, 1992). In general, increasing moisture contents stimulate the biogeochemical processes up to a threshold value where anaerobicity can limit microbial activity (Tietema et al, 1992).…”

“…In general, increasing moisture contents stimulate the biogeochemical processes up to a threshold value where anaerobicity can limit microbial activity (Tietema et al, 1992). Temperature has a similar effect on microbial activity, due to the fact that rates of enzymatic processes generally increase with increasing temperature (Michaelis and Menten, 1913).…”

The relationship between N mineralization or microbial biomass N with micromorphological properties in beech forest soils with different texture and pH

“…However, part of the decline is also attributed to lower efficiency of N-mineralization per unit microbe. In the organic layer of earthworm-and bacteriadominated soil, low efficiency of N-mineralization may be due to the relatively fresh litter with low N-content, which may induce N-immobilization rather than net release (Swift et al 1979). In contrast, the organic layer of fungi-dominated soil may show high net N-mineralization per unit microbe because substrate quality of the more-decomposed organic matter is higher (higher N-content).…”

“…Soil conditions such as pH and texture are important factors regulating C and N dynamics, and lead to substantial differences in litter decay, humus form, and N-release (Swift et al 1979;Green et al 1993;Ponge 2003). Acid and/or sandy soils have low rates of decomposition, low depolymerization of N-containing polymers by microbial enzymes, and presumably also low net N-release to the vegetation (e.g., Aerts and Chapin 2000;Ponge 2003;Schimel and Bennett 2004).…”