[Allelopathic effects of the humus soils from Betula platyphylla and Quercus liaotungensis pure plantations on 9 kinds of common shrubs and herbs].

The humus soils were collected from Betula platyphylla and Quercus liaotungensis pure plantations and woodless land separately where the site conditions were basically the same, and taken as medium for potting culture test of 9 kinds of shrubs or herbs in plastic greenhouse to assess the allelopathic effects of humus soils of pure plantations on shrubs or herbs. Humus soils from B. platyphylla plantation significantly inhibited the seed germinations of Medicago sativa and Melilotus officinalis, decreased the catalase (CAT) activity of M. officinalis, Coronilla varia, M. sativa and Lespedeza davurica, and improved malondialdehyde (MDA) contents in seedlings of Caragana kor-shinskii, C. varia and Astragalus adsurgens. The biomass growths of C. varia, Amorpha fruticosa, M. sativa, M. officinalis and A. adsurgens in humus soils from B. platyphylla plantation were significantly decreased by 48.2%, 45.1%, 44.3%, 37.3% and 36.0%, respectively. In addition, humus soil of Q. liaotungensis plantation significantly decreased the germination rates of M. sativa and A. adsurgens, the chlorophyll contents of Vicia villosa, A. fruticosa and M. sativa, and improved malondialdehyde (MDA) contents in seedlings of Lespedeza davurica, Caragana korshinskii, M. officinalis and A. adsurgens. The biomass growths of A. adsurgens, M. sativa, M. officinalis and A. fruticosa were significantly decreased by 52.6% , 43.8%, 35.5% and 34.6%, respective- ly. B. platyphylla plantation humus soil had obvious inhibition effects on M. sativa, M. officinalis and A. fruticosa, while Q. liaotungensis plantation humus soil had obvious inhibition effects on M. sativa, A. adsurgens and A. fruticosa.

[Soil humus differentiation and correlation with other soil biochemical properties in pure forests in semi-arid low-hilly area of Inner Mongolia, China].

Whether the content and composition of soil humus in pure forest change due to its simple component of litter and specificity of single-species dominant community is a key problem for forest sustainable management. In this study, soils from 6 kind of pure forests in semi-arid low-hilly area of Inner Mongolia were collected and their humus and other biochemical properties were measured to investigate the differentiation of soil humus and the impact factors. The results showed that the soil of Picea asperata and Betula platyphylla pure forests had the highest contents of humus and better condensation degrees and stabilities, followed by that of Populus simonii, Larix principis-rupprechtii and Ulmus pumila pure forests, while the soil of Pinus tabuliformis pure forest had the lowest content of humus, condensation degree and stability. There were significant positive correlations between soil microorganism biomass, activity of phosphatase and the content and stability of soil humus. In contrast, the soil peroxidate, dehydrogenase activity and soil humus content showed significant negative correlations with each other. Furthermore, the enhancement of dehydrogenase activity might decrease the stability of humus. There were significant positive correlations between available N and the content and stability of soil humus, but total Cu, Zn and Fe had negative correlations with them, and total Cu and Fe might reduce the stability of humus as well. The particularity of pure forest environment and litter properties might be the key inducement to soil humus differentiation, thus reforming the pure forest through mixing with other tree species or planting understory vegetation would be the fundamental way to improve the soil humus composition and stability.