Studies On Changing Rule Of Soil Quality, Adjustment And Control Measures In Larix Olgensis Plantations

Larix olgensis is main afforestation species in the northeastern China. The soil degradationin in Larix olgensis plantations, to a certain extent, has been found. However, rules and mechanism controlling the soil degradation were not very clear as yet. The study has investigated and compared soil physical, chemical, biochemical properties of eight stands on paired sites in mountainous regions of northeastern China, trying to look for the mechanism of soil degradation and the change trend of soil properties in different age of plantations in relations to forest productivity. The eight stands are 4 first rotation of Larix olgensis plantations with different age classes, the second rotation of Larix olgensis young stand, Pinus sylvestris var. mongolica young stand, secondary natural forest, and the mixed forest of Larix olgensis and Fraxinus mandshurica Rupr.. Countermeasures for controlling soil degradation were also recommended.The study got following results: (1) From young stand to mid-age of Larix olgensis, with the closure of canopy and the decrease of undergrowth vegetation cover, soil acidity, enzyme activity, total inorganic phosphorus, available K, soil moisture and total porosity decreased significantly; While soil organic matter content, humus component content, the amount of three main types of microbes, acid phosphatase activity, and bulk density in rhizosphere soil and non-rhizosphere soil increased with the increase of the amount of forest floor litter; From mid-age stand to near mature stand, with the decrease of stand density and crown cover as well as the restoration of undergrowth vegetation after preliminary thinning, soil organic matter content, fulvic acid, exchangeable acidity, exchangeable aluminium, neutral phosphatase activity, total amount of inorganic phosphorus, the amount of actinomycetes, soil moisture, and total porosity in rhizosphere soil and non-rhizosphere soil apparently increased; From near mature stand to mature stand, soil activity acidity, organic matter content, humus component content, available phosphorus, total amount of amino acid, available K, soil enzyme activity, soil moisture, and total porosity in rhizosphere soil and non-rhizosphere soil decreased, but total phosphorus, soil acidity (in particular, exchangeable aluminium), and bulk density increased. The reduction of soil nutrient content and enzyme activity, and the apparent increase of soil acidity and bulk density are likely the main reason for soil degradation in mature stand. (2) Compared to secondary natural forest, the amount of three main types of microbes in rhizosphere soil of different age of Larix olgensis plantation correspondingly decreased largely, enzyme activity in non-rhizosphere soilreduced, the biochemical activities abated, and soil physical and chemical properties deteriorated. Soil physical and chemical properties as well as biochemical activities deteriorated after secondary natural forest was replaced by Larix olgensis plantations. (3 ) Compared to young stand of the first rotation of Larix olgensis, activity acidity (pH value), organic matter content, humus component content, moisture, and total porosity in rhizosphere soil of the young stand of the second rotation of Larix olgensis decreased. Exchangeable aluminium, humic acid component content in rhizosphere soil and non-rhizosphere soil, activity acidity, organic matter content, humus component content, total amount of fifteen types of amino acid, the content of various forms of phosphorus, the amount of three main types of microbes, enzyme activity, and bulk density in non-rhizosphere soil increased. The new addition of cyaneus in actinomycetes group in rhizosphere soil and non-rhizosphere soil may be fundamental reason for the second rotation effect.(4) Compared to the young stand of Pinus sylvestris var. mongolica, soil acidity, humus component content, available K, total P, organic P, inorganic P, enzyme activity, and microbe amount of young stand olgensis of the second rotation of Larix olgensis in non-rhizosphere soi...