Abstract:

【Objective】 The aims of this research are to elucidate the effects of simulated nitrogen (N) and phosphorus (P) deposition and litter treatment on soil organic carbon (SOC) components in Pinus koraiensis forests, to provide a theoretical basis for improving soil fertility, ecosystem productivity and stability of P. koraiensis forests. 【Method】 Taking broad-leaved P. koraiensis forest and P. koraiensis piantation in Liangshui National Nature Reserve of Heilongjiang Province were studied. Each forest type was set with three plots of 20 m×30 m, and 12 quadrats were set in each plot. Each quadrat was subjected to treatments. (1) Litter treatment: three levels were removed (R), addition (A) and unchanged (CK1) were tested in October 2017, and three replicates were set for each level. (2) Simulated N and P deposition treatment: from May to October in 2018 and 2019, the experiment was carried out once a month. Four levels were set: low (L) (N and P supplemental levels are 5 g/m²), middle (M) (N is 15 g/m², P is 10 g/m²), high (H) (N is 30 g/m²,P is 20 g/m²), and no N and P (CK2), and three replicates were set for each level. The amounts of N and P were 2 L for each quadrat, and the same volume of stream water was sprayed for the control. In May, August and October of 2018 and 2019, three sampling sites were randomly selected in each quadrat. Collected the soil samples at 0-20 cm soil layer, and pick out plant roots, rocks larger than 2 mm and soil animals, then put it in a cool and ventilated place for natural air drying. After that it was extracted according to the extraction method of SOC for each component and measured using a TOC elemental analyzer. Finally, SPSS 21.0 and Canoco 5.0 were used for statistical analysis. 【Result】 (1) In the first year of the experiment, the low dose N and P deposition treatments significantly affected the SOC components. (2) In the second year, the middle dose significantly affected the SOC components. (3) For the two years, the SOC content was the highest in the broad-leaved P. koraiensis forest. The contents of mineral-bound, easily oxidized organic carbon, and total organic carbon were the highest in August. Litter removal and addition treatments had no effect on the SOC components. 【Conclusion】 (1) In the first year of the experiment, the low dose of N and P promoted the accumulation of SOC components. (2) In the second year, the middle dose treatments promoted the mineralization of SOC components. (3) In the second year of the experiment, the broad-leaved P. koraiensis forest was beneficial to the accumulation of SOC components. Environmental conditions in August is favorable for the formation of mineral-bound, easily oxidized organic carbon and total organic carbon. Litter removal and addition can promote the release of SOC components.

Key words: N and P deposition, litter, soil organic carbon, broad-leaved Pinus koraiensis forests, P. koraiensis plantation