[Effect of Fertilization on Soil Respiration and Its Temperature Sensitivity in a Sorghum Field].

The characteristics of soil respiration under the condition of fertilization have not been fully understood,especially for a long-term fertilization condition. In this study we measured both soil respiration using an LI-COR-6400-09 soil chamber attached to LI-COR-6400 portable photosynthesis system, and the vegetation spectrum using an ASD FieldSpec HandHeld2, in five different fertilization treatment fields. The soil respiration () and vegetation spectrum were simultaneously measured with two samples per month in the growing season in 2016 and 2017. The soil temperature at 10 cm depth () and moisture () for the surface of 10 cm were also measured simultaneously. The five different fertilization treatments included no fertilization (CK), inorganic fertilizer (INF), inorganic fertilizer+organic fertilizer (INF+M), inorganic fertilizer+organic fertilizer+straw turnover (INF+M+S) and organic fertilizer+straw turnover (M+S), and all treatments had been conducted since 2011. Based on those observation data, we made an analysis of and its temperature sensitivity () in the five different fertilization treatments. The results showed that no significant temporal change in among the five treatments was found. No significant difference was found in between the CK and INF treatments. Compared with the values of in CK and INF, the values in INF+M, M+S, and INF+M+S treatments increased by 28.2%-39.1%, 47.9%-76.0%, and 46.2%-50.8%, respectively. This indicated that use of organic fertilization and straw application increased . Both the and showed 14%-96% and 6%-37% in seasonal variations, respectively. Among the treatments, the correlation coefficient of the fitted equations between and was higher in the INF+M, INF+M+S and M+S treatment than in CK and INF, but was not between and . For the relationship between and vegetation indexes we found that the correlation coefficients between and the difference vegetation index (DVI), ratio vegetation index (RVI), and enhanced vegetation index (EVI), respectively, were higher than that of and the normalized differential vegetation index (NDVI); and that the correlation coefficients between and the red edge slope () and red edge area () were higher than between and the red edge position (). This indicated that the treatments in INF+M+S increased the correlation coefficient between and the spectrum characteristics index. The determination coefficient of the fitted equations including the feature spectral parameters, , and variables was higher than that of the equations only including both and variables, or a single variable of or . Compared with CK, the value increased by 26%, 39%, 21%, and 37% for the INF, INF+M, INF+M+S, and M+S treatments, respectively. This indicated that temperature sensitivity increased under the condition of fertilization treatments. The Shannon diversity index, bulk density, and soil organic matter were the main factors causing the difference in , , and , i.e., at a temperature of 10℃, in the different treatments, which could explain the 97.6%, 78.2%, and 92.8% variations in , , and , respectively.