Effects of pH and mineralisation on nitrification in a subtropical acid forest soil

Effects of pH on nitrification have been explored widely; however, few researchers have investigated the compound effects of pH and mineralisation on nitrification and responsible nitrifiers in subtropical forest soils. An acid subtropical forest soil was subjected to pH treatments by liming for 40 days at 25°C and 60% water holding capacity. After 40 days, gross N transformation rates in the samples were evaluated using the 15N tracing technique and model. Ammonia-oxidising bacteria (AOB) and ammonia-oxidising archaea (AOA) were quantified by quantitative polymerase chain reaction. The results showed that gross rates of mineralisation (P < 0.01), NH4+ oxidation to NO3− (P < 0.01), and dissimilatory NO3− reduction to ammonium (DNRA, P < 0.05) significantly increased with elevated soil pH. The NH4+ oxidation to NO3− rates and N mineralisation rates were significantly correlated (P < 0.05). The abundance of AOB (P < 0.05) but not AOA amoA genes dramatically increased in the elevated pH treatments after 40 days. We suggest that the N mineralisation was sensitive to elevated pH in the subtropical acid forest soil, which increased the supply rate of nitrification substrate and the favourable pH microsites for nitrifiers. Interactions between elevated pH and mineralisation have a synergistic and stimulatory effect on development of AOB and their associated nitrifying activity.

The biological activity of soil in Norway spruce forests and in fern Athyrium distentifolium Tausch ex Opiz stands on deforested polluted sites in the Beskydy Mts.

The study is focussed on the biological activity of acid forest soil with aim to characterize some of its parameters. Activity of acidic soil phosphatase, basal and potentional respiration were compared and viable plate counts of microorganism colonies were evaluated. The soils of the Kněhyně region in the Moravian-Silesian Beskids Mts. are intensively influenced by acid deposition. They were sampled from area where often occurrence of fernAthyrium distentifoliumTausch ex Opiz was recorded. Above mentioned characteristics (values of parameters) were determined in soil samples collected in fern stands (close to the periphery of fern individuals with rich root system), from site between individual ferns and from the rest of neighbouring spruce community without distinct herbage layer. In majority of studied cases, increased values of all monitored parameters were found in space ofA. distentifoliumroots accumulated close by fern base. Bare soil between individual fern plants often shows on a lower biological soil activity, however these differences were mostly not statistically significant. On the contrary, values of studied soil parameters recorded in the rest of neighbouring forest community without distinct herbage layer, reached mostly the lowest values and they often differ significantly from values assessed in soil taken near theA. distentifoliumroots.