The Difference Of Soil Habitat Quality Of Six Forest Types And Niche Of Underground Resources Of Dominant Tree Species In Xiaoxing’an Mountains

Xiaoxing’an Mountains,as one of the important forest areas in China,plays an important role in ecological civilization construction,ecological environment protection and resource utilization.As the top zonal vegetation community in Xiaoxing’an Mountains,the original broad-leaved Korean pine forest has been degraded and caused a series of ecological problems due to abnormal interference.There are many weak links in the management research of natural secondary forests in Northeast China,and the research on the competition of underground resources and soil soil habitat and its changes needs to be strengthened urgently.In this study,six typical forest ecosystems in Xiaoxing’an Mountains area namely original Korean pine forest,Betula platyphylla secondary forest,Betula costata secondary forest,Populus davidiana secondary forest,Quercus mongolica secondary forest and miscellaneous wood secondary forest,were taken as research objects,and the changes of various habitat factors and the differences of soil habitat quality index under different soil habitat conditions were compared.Six dominant tree species,Korean pine,Betula platyphylla,Populus davidiana,Quercus mongolica,Fraxinus mandshurica and Tilia amurensis,were selected in the secondary forest with Korean pine regeneration,and their niche overlap and separation of underground resources were compared and analyzed.The main results were as follows:There were significant differences in soil habitat factors and soil habitat quality between the original Korean pine forest and the broad-leaved secondary forest.The specific performance was as follows:in terms of soil water and heat,the soil temperature and humidity of the original Korean pine forest and the broad-leaved secondary forest were basically the same with time;the soil temperature and humidity of the original Korean pine forest were significantly lower than that of the broad-leaved secondary forest in the early growth stage;The soil bulk density of the original Korean pine forest was 1.26 g/cm³,which was significantly higher than that of the broad-leaved secondary forest.The soil pH value of the original Korean pine forest was 5.0,the available nitrogen content was 612.57 mg/kg,the available potassium content was 143.26 mg/kg,and the microbial biomass carbon content was 230.08 mg/kg,which were significantly lower than those of the broad-leaved secondary forest.The soil organic matter content and available phosphorus content of the original Korean pine forest were 12.36 g/kg and 18.59 mg/kg,which were significantly lower than those of the four secondary forests of Betula platyphylla secondary forest,Betula costata secondary forest,Populus davidiana secondary forest and miscellaneous wood secondary forest,and significantly higher than those in the Quercus mongolica secondary forest.The soil habitat quality index SQI of broad-leaved secondary forest was 0.81,which was significantly higher than that of original Korean pine forest.There were different degrees of separation between Korean pine and broad-leaved tree species in the niche of underground nutrition space,the seasonal niche of absorbing soil moisture,seasonal niche and quantitative niche for absorbing soil nutrients,and niche for absorbing soil nutrient forms.The specific manifestations are as follows:The amount of roots absorbed by Korean pine in topsoil（0-20cm）was significantly lower than that of broad-leaf trees.However,in the lower soil（30-60cm）,Korean pine still had a considerable proportion of absorption roots,which was significantly higher than that of broad-leaved trees.The broad-leaved trees generally absorb soil moisture from mid-May to late September,while Korean pine still had transpiration from early April to late October.Broad-leaved trees absorbed nitrogen nutrients from early May to late September,with a short absorption period,and the peak of nutrient absorption in summer was steep and obvious,while Korean pine had been absorbing nitrogen nutrients from April to October,and the peak of nutrient absorption in summer was slow and not obvious.Compared with Korean pine,broad-leaf trees consumed more nitrogen nutrients and had lower utilization efficiency,which belonged to high consumption and low efficiency,while Korean pine belonged to low consumption and high efficiency.During the growing season,the average nitrate reductase activity of Korean pine leaves was 0.120μmol NO₃^-g^-1h^-1,which was significantly lower than that of broad-leaved trees.The niche overlap of underground resources between Pinus koraiensis and Betula platyphylla,Populus davidiana,Quercus mongolica and Fraxinus mandshurica were small,while that between Tilia amurensis and Pinus koraiensis was high.