| Larix principis-rupprechtii Mayr was the main afforestation tree species in temperate and alpine areas in china, but its plantation in partial areas appeared potential soil fertility decline since planted shaanxi province. Forest soil(0~20 cm) of young-aged(8 and 13 year) and middle-aged(23 year) and near mature-aged(33 year) and mature-aged(43 year) stands of Larix principis-rupprechtii Mayr plantations of the Qinling Mountains were conducted to studying the mass fraction of soil nutrients and soil enzyme activities characteristic of phenological and seasonal dynamics, meanwhile, difference comparison of the mass fraction of soil nutrition and soil microbial populations and soil enzyme activities for five stands and theirs relationships, in addition, the effect of applying nitrogen and phosphorus on the mass fraction of soil nutrition and soil microbial populations and soil enzyme activities of principis-rupprechtii Mayr plantation soil fertility degradation, in order to provide basic theories and guidelines for rational application of fertilizer in an artificial forest. The result indicated:(1) The mass fraction of soil nutrients(available nitrogen, available phosphorus and available potassium) ranked near mature-aged and mature-aged stand > young-aged stand > middle-aged stand, which displayed up-down-up tendency with the increase of age stands. The mass fraction of total organic carbon ranked near mature-aged and mature-aged stand > middle-aged stand > young-aged stand, which kept rising tendency the increase of age stands. Soil pH ranked young-aged stand > middle-aged stand > near mature-aged and mature-aged stand, which indicated falling tendency with the increase of age stands. Soil microbial populations(bacteria, actinomycetes, fungi and microbial total count) ranked near mature-aged and mature-aged stands > young-aged stand > middle-aged stand, which appeared up-down-up tendency with the increase of age stands. Soil enzymes activity(urease, invertase and calatase) ranked near mature-aged and mature-aged stand > young-aged stand > middle-aged stand, the enzymes activity manifested up-down-up tendency with the increase of age stands. Soil phosphatase indicated near mature-aged and mature-aged stand > young-aged stand > middle-aged stand, which appeared rising with the increase of age stands. Hence, soil nutrients decreased under middle-aged(23 year) stands of Larix principis-rupprechtii Mayr. In addition, significant correlations were observed among soil nutrients, soil enzyme activities and soil microbial(P<0.05), soil enzymes and soil microbial could be used as positive biological indicators for weighing soil fertility.(2) By different fertilization treatments for four years the result showed that: All fertilization treatments improved the mass fraction of soil available nitrogen, the mass fraction of soil available nitrogen of N1 treatment was the highest in all fertilization treatments, it was higher than CK treatment by 6.47 mg/kg, which was increased by 76.16%. All fertilization treatments improved the mass fraction of soil available phosphorus, the mass fraction of soil available phosphorus of P treatment was the highest in all fertilization treatments, it was higher than CK treatment by 6.09 mg/kg, which was increased by 206.51%. P treatment significantly promoted the mass fraction of soil available potassium compared to CK treatment by 17.33 mg/kg, which was increased by 15.11%(P<0.05). Except N2 treatment, the other treatments improved the mass fraction of soil total organic carbon, the mass fraction of soil total organic carbon of N2 +P treatment was the highest in all fertilization treatments, it was higher than CK treatment by 10.57 g/kg, which was increased by 105.27%. All fertilization treatments reduced soil pH, soil pH of N2+P treatment was the lowest in all fertilization treatments, it was lower than CK treatment by 0.42, which was decreased by 7.09%. All fertilization treatments reduced the quantity of soil bacteria, the quantity of soil bacteria of N2 treatment was the lowest in all fertilization treatments, it was lower than CK treatment by 3.43×106/g, which was decreased by 50.00%. All fertilization treatments reduced the quantity of soil actinomycetes, the quantity of soil actinomycetes of N2+P treatment was the lowest in all fertilization treatments, it was lower than CK treatment by 4.34×104/g, which was decreased by 50.00%. All fertilization treatments improved the quantity of soil fungi, the quantity of soil fungi of N1 treatment was the highest in all fertilization treatments, it was higher than CK treatment by 6.66×103/g, which was increased by 400.00%. All fertilization treatments improved the activity of soil urease, the activity of soil urease of N2+P treatment was the highest in all fertilization treatments, it was higher than CK treatment by 0.50 mg/g, which was increased by 173.79%. Except P treatment, the other treatments improved the activity of soil invertase, the activity of soil invertase of N1 treatment was the highest in all fertilization treatments, it was higher than CK treatment by 78.47 mg/g, which was increased by 107.97%. Except P treatment, the other treatments improved the activity of soil phosphatase, the activity of soil phosphatase of N2 treatment was the highest in all fertilization treatments, it was higher than CK treatment by 0.31 mg/g, which was increased by 52.69%. All fertilization treatments improved the activity of soil calatase, the activity of soil calatase of N2+P treatment was the highest in all fertilization treatments, it was higher than CK treatment by 5.08 mL/g, which was increased by 179.65%. N2+P fertilization treatment was more powerful than other fertilization treatments about increasing the soil fertility according to the principal component analysis.(3) Except soil total organic carbon, there were significant for soil nutrients and soil enzyme activities characteristic of seasonal dynamics under five stand aged plantation(8 year, 13 year, 23 year, 33 year, 43 year, as the same below)(P<0.05). Throughout the growing season, the mass fraction of soil available nitrogen, soil available phosphorus, soil available potassium and soil pH possessed some similar seasonal variation rules under five age stands, the mass fraction of soil available nitrogen and soil available phosphorus in sprout leaves stage(May to June) and leaf fall stage(September to October) were higher than in exuberant growth stage(July to August), which manifested up-down-up tendency, the mass fraction of soil available potassium and soil pH in exuberant growth stage(July to August) was higher than in sprout leaves stage(May to June) and leaf fall stage(September to October), which indicated down-up-down trend among various months. Accompanying seasonal variations, seasonal variation rules of five soil enzymes activity appeared the same regularities under five age stands, soil urease activity and soil invertase activity reached the highest peak in the end of leaf fall stage(October) and it were higher than the other stages, which kept slowly rising tendency along seasonal changes. Soil phosphatase activity in exuberant growth stage(July to August) was higher than in sprout leaves stage(May to June) and leaf fall stage(September to October), which displayed down-up-down tendency. Soil calatase activity in preliminary exuberant growth stage(July) was higher than in sprout leaves stage(May to June) and leaf fall stage(September to October), which exhibited down-up-down tendency with seasonality processes. Thus, the mass fraction of soil nutrients in five age stands decreased in exuberant growth stage(July to August), it was significant difference compared to the other stages(P<0.05), which provided theoretical basis for forest fertilization of Larix gmelinii plantation. |
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