【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.
【Objective】 Inorganic carbon constitutes a large proportion of soil carbon storage in the coastal area of northern Jiangsu; therefore, estimating the soil inorganic carbon (SIC) content with precision and accuracy is a prerequisite for further study.【Method】Soil samples at different depths (i.e., 0-10, ≥10-20, ≥20-40, ≥40-60, ≥60-80, and ≥80-100 cm) were collected from a poplor plantation and a Spartina alterniflora wetland. The SIC content as well as its recovery rate were then estimated using a calcimeter, carbon dioxide (CO2) absorption and indirect methods, respectively. This was done to compare the precision and accuracy of the three methods. 【Result】 The ranges of the SIC content estimated by the calcimeter, CO2 absorption and indirect methods were 4.25-9.93, 6.18-11.50 and 5.50-12.60 g/kg with the average of 8.11, 9.58 and 9.54 g/kg, respectively. When the amendment rate of exogenous calcium carbonate was 2.35-12.90 g/kg, the averaged recovery rates of SIC content estimated by the calcimeter, CO2 absorption and indirect methods were 96.9%, 105.0% and 71.5%, respectively. According to the SIC content corrected by the recovery, the SIC contents measured by the indirect method were significantly higher than those measured by the other two methods, indicating that the recovery of SIC measured by the indirect method was underestimated. The coefficients of variation of the SIC content in the parallel soil samples estimated by the calcimeter, CO2 absorption and indirect methods were 1.19%-4.99%, 0.52%-3.34% and 1.51%-6.79% with averages of 2.44, 1.36 and 3.25 g/kg, respectively. 【Conclusion】 The calcimeter, CO2 absorption and indirect methods can all be used to determine the SIC content of coastal soils from Northern Jiangsu, although the SIC estimated by the CO2 absorption and indirect methods were both higher than those measured by the calcimeter method. However, the SIC recovery rate estimated by the indirect method was underestimated, and this was mainly due to the overestimation of the organic carbon content of the acid-treated soils by the potassium dichromate oxidation method. The accuracy of the CO2 absorption method was the highest, followed by that of the calcimeter and indirect methods. However, the calcimeter method is time-saving, whereas the indirect method can quantify the contents of soil organic carbon and SIC simultaneously. In the future, researchers should choose a method that is in line with their specific research purposes.
【Objective】 This research aims to investigate the effects of different organic matters on soil organic carbon and soil respiration in Pinus tabuliformis forest. The results can provide reference for predicting soil carbon budget of P. tabuliformis forest ecosystem in Taiyue Mountain, Shanxi Province, China.【Method】A random block design was used to add biochar (BC), maize straw (JG), Quercus mongolica leaf (LD) and P. tabuliformis leaf (YS) to 0-20 cm soil of P. tabuliformis forest in Taiyue Mountain, with no addition as control check (CK). Li-8100 automatic measurement system for CO2 flux was used to continuously measure soil respiration rate under organic matter addition, and the contents of soil organic carbon (SOC), microbial biomass carbon (MBC), readily oxidized carbon (ROC) and dissolved organic carbon (DOC) in each treatment were monitored. Based on the relationship between soil respiration and soil organic carbon and its components, the effects of organic matter addition on soil respiration and soil carbon components of P. tabuliformis forest in Taiyue Mountain were investigated. 【Result】 (1)The addition of biochar significantly reduced the soil respiration rate, and the soil respiration rate was significantly increased by 11.67% after adding JG compared with CK, while there was no significant difference between other treatments and CK. (2)In August 2014, the addition of JG significantly increased the soil SOC, MBC, ROC and DOC contents, the addition of BC significantly increased the soil MBC content, and the addition of LD and YS significantly increased the soil SOC and MBC contents. In October 2014, the addition of JG significantly increased soil SOC, MBC, ROC and DOC contents, the addition of LD significantly increased soil MBC and ROC contents, and the addition of YS significantly increased soil SOC and MBC contents. In March 2015, the addition of JG significantly increased soil SOC, MBC and ROC contents, while the addition of LD significantly increased soil ROC contents. In May 2015, JG supplementation significantly increased soil MBC content.(3) Compared with CK, soil respiration at 10 (R10) was significantly decreased by 18.01% after BC addition, and increased by 30.88% after YS leaf addition. Other organic compounds had no significant effect on soil respiration temperature sensitivity (Q10) and R10. (4) Soil respiration rate was significantly positively correlated with soil temperature, SOC, MBC, ROC and DOC. 【Conclusion】 The addition of organic matter significantly affected soil carbon dynamics and soil temperature and humidity, which all had significant effects on soil CO2 emissions. The addition of JG had the most significant effect on soil organic carbon and its carbon components, but the soil respiration rate was the highest, which was not conducive to carbon storage. The addition of LD could increase soil active organic carbon content and significantly improve soil organic carbon pool quality in a short term, while the addition of BC could increase soil microbial biomass carbon content in a short term, and significantly reduce soil respiration rate, which has the best effect on reducing soil CO2 emission.
