Soil Humus Compositions and The Influence on Soil Acidity in Larix olgensis plantation of NE China

Variation in soil humus compositions (SHC) and the effect on soil acidity (SA) were studied in LOP of NE China. The results showed that for rhizosphere soil (RS) and non-rhizosphere soil (NRS), soil organic matter (SOM), carbon (C) in humic acid (HA) and humin increased from young stand (YS) to near mature stand (NMS) over ages, however, SUM, C in fulvic acid (FA) and humin decreased from NMS to mature stand (MS). Soil humification degree (SHD) were higher in secondary forests than in YS and NMS. As compared with young stand in the first rotation (YSFR), for RS, SUM, C in FA and humin decreased by 4.53%, 35.8% and 1.98% in young stand in the second rotation (YSSR), respectively, but for NRS, SUM, C in HA, FA and humin increased by 46.44%, 43.69%, 47.45% and 49.5%, respectively, Correlation between SHC and SA changed over ages. In RS, close correlation existed among SHC, active acidity (pH, AA), exchange and hydrolytic acidity at different development stages (DDS).