Soluble organic nitrogen in forest soils of northeast China

Abstract

Soluble organic nitrogen (SON) is recognized as a sensitive indicator of soil nitrogen status. The present work was conducted in the temperate forests of northeast China where soils are typically characterized by high organic matter and high organic nitrogen content, and soil sampling was made in early spring just after the freeze-thaw period. The water extracted SON pools in the organic layer of forest soils were measured within the range from 156.0 mg·kg−1 to 292.6 mg·kg−1, a similar magnitude of salt solution extracted SON pools reported in literatures. However, the water soluble SON pools in 0–15 cm mineral soils in present study were much higher (3–10 times) than any other reports, ranging from 58.6 mg·kg−1 to 125.2 mg·kg−1. Water soluble SON varied markedly among the soils under different forests and at different sites. The SON in water extracts were positively and significantly correlated to soil organic matter and total nitrogen contents, but negatively correlated to microbial biomass nitrogen (MBN). The reasons of the abnormally large SON pools and the negative correlations between SON and MBN in the 0–15cm mineral soils in this study were specially discussed.