Nitrogen mineralization in volcanic soil under grassland, shrub and forest vegetation in the Aegean region of Turkey

Abstract

Net nitrogen mineralization of a grassland-, Quercus coccifera shrub- and Pinus brutia forest-site within the Aegean region was investigated continuously through a year by field and standard incubation methods. Seasonal fluctuations resulting from field incubation are marked in grassland and shrub, but less pronounced in the forest. They are mainly associated with the changes in soil moisture being at minimum in the mediterranean summer. The annual yield of N mineralization is high in grassland and shrub (7.5 and 6.6 h·m), but low in the forest (2.8 g·m), where nitrification is inconspicuous. The reasons for this surprising phenomenon are discussed. N-mineralization is highly elevated in all sites under the favourable conditions of standard incubation (potential mineralization) and the seasonal differences as well as those between the sites are largely diminished.

Conifer invasion of forest meadows transforms soil characteristics in the Pacific Northwest

“…This, along with faster decomposition in grasses, may explain why N mineralization rates in grasslands are typically higher than those in forests (Göceoglu, 1988;Hixson et al, 1990;Ross et al, 1996). Both direct measures of N in our study (PMN and extractable NH 4 + ) were higher in meadow than in forest mineral soil, but these differences were not statistically significant.…”

“…Lignin in tree litter tends to protect cellulose from microbial attack. This, along with the higher N levels (Daubenmire and Prusso, 1963;Henzell, 1973;Aber and Melillo, 1980), may explain why grass litter decomposes faster than tree litter (Göceoglu, 1988;Hixson et al, 1990;Ross et al, 1996).…”

“…The relatively large allocation of fixed C to the rhizosphere by grasses may account for the elevated SOM often found in grassland A horizon soils (Göceoglu, 1988;Hixson et al, 1990;Jenkinson, 1991;Popenoe et al, 1992;Feige et al, 1995;Ross et al, 1996;Yakimenko, 1997). In the Popenoe et al (1992) study, however, no significant differences were found between meadows and forest soil SOM concentrations in the top 10 cm of mineral soil.…”

“…Grasslands and forests differ greatly in soil chemistry (Göceoglu, 1988;Popenoe et al, 1992;Hart et al, 1993;Ross et al, 1996;Yakimenko, 1997), rates of litter decomposition (Hunt et al, 1988;Köchy and Wilson, 1997), and food web composition (Hunt et al, 1987;Ingham et al, 1989). Our study was designed to measure changes in both chemical and biological characteristics of high-elevation mountain meadows as they are invaded by adjacent forests.…”