| Due to it’s fast growing, Larch is one of the most important tree species in mountains region of North China. It had been introduced to Shaanxi Province before fifty years ago, and the proportion of the Larch in Qinling region is account for 90% of all Shaanxi Province larch. There has few report about the varies of soil biological activity in different aged Larix principis-rupprechtii plantations of this area with the season. In order to study the fertility of soil in different-aged Larix principis-rupprechtii plantations in this area, we chose young-(7 and 12 years old), middle-(22 years old), and near-mature-(32 and 42 years old) aged Larix principis-rupprechtii plantations in the Nantan Nursery Garden of Taibai and Huoditang of Ning-shan in Shannxi Province as the experimental sites, and established three 20 × 20-m plots in each age stand plantation in 2014. In each plot, soil samples were collected from three depths(0-20 cm, 20-40 cm, and 40-60 cm) at five randomly located points. We collected soil samples in the middles of May, July and September 2014. Using these samples, we examined the soil chemical properties(pH, available N, and available P), enzyme activities(phosphatase, urease, invertase, and catalase) and soil microbe quantity(bacteria, fungi and actinomyces) in the different-aged plantations. Also, we applied N and P fertilizers for middle-age plantation to study the effects of external nutrient on the above indexes, there were 6 treatments : N1(75kgN/hm2), N2(150kg N/hm2), P(75kg P/hm2), N1P(75kg N/hm2+75kg P/hm2) and N2P(150kg N/hm2+75kg P/hm2), every treatment had three repetitions. Main results were as follows:(1) The soil was slightly acidic in Qinling Mountain. The range of soil pH was 5.84-6.76. The soil pH was lower in young aged Larix plantations than that in near-mature aged plantations, and rose with the soil depth increased. The seasonal growth of Larix had significant influence on soil pH, and it was lowest t in vigorous growth period.The contents of soil available N and available P in this ares were at low levels, the range was 0.58mg/kg-3.29mg/kg in available P and 4.34 mg/kg-29.97 mg/kg in available N. They were higher in near-mature aged plantations than in young and middle aged plantations, with an increase in soil depth, there were significantly decrease in the contents of soil available N and available P. In vigorous growth period of Larix, available N was lower,while available P was higher.(2) Catalase and invertase activities in young aged plantations were higher than that in middle and near-mature aged plantations, phosphatase and urease activities in near-nature plantations were significant higher than other age’s. The activities of all enzymes reduced with soil depth increased. There had no homogeneous response to the season in the activities of enzymes. Catalase and urease activities decreased firstly and increased subsequently with month, appeared minimums in July while invertase and phosphatase activities had no significant regulation with month, varied with age and soil depth.Soil bacteria quantity occupied absolute advantage in soil microorganism quantity, actinomyces was in the second place while fungi was the last one. Middle aged plantation’s has maximum in bacteria quantity and minimum in actinomyces and fungi quantities among all the ages. There was an significant decrease in microorganism with an increase in soil depth. Microorganism quantities were most in the vigorous growth period of Larix.(3) Accordingly, on the basis of these findings, the statuses of nutrient and biological activity in middle aged plantation were poor, but plants demand plenty of nutrients to accumulate biomass in this age, so soil fertilization was not well to satisfy the large need of plant growth. The production will descend if there have no measure to solve this problem.(4) The effects of fertilizing treatments on soil pH, available P and available N were not significant until into July. All fertilizing treatments decreased pH, fertilizing N treatments significantly increased the content of available N, fertilizing P treatments rose the content of available P. As available nutrients, the reaction of soil enzyme activities to fertilizing treatment didn’t reflect until into July, compared to the control, all enzyme activities were significant higher in the N1 P and N2 P treatment. The effect of fertilizing treatment expressed from May, only fertilizing N treatment rose bacteria quantity while only fertilizing P treatment had a big impact on fungi quantity, applying nitrogen and phosphorus together could significantly increased three microorganism quantities.(5) In conclusion, the soil productivity decline of middle-aged plantation was more serious than other age, and fertilizing measure could relieve and improve this appearance, The result of applying nitrogen and phosphorus together was the best.(6) Available P was significantly positively correlative to phosphatase activity, bacteria and fungi quantities. Available N was significantly positively correlative to urease activity, bacteria and fungi quantities. Invertase and phosphatase were significantly positively correlative to bacteria quantity. There was a negative correlation between urease activity and bacteria quantity, catalase activity was positively correlative with fungi quantity, negatively correlative with bacteria and actinomyces quantities. |
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