| 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 (Rs) 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 (T10) and moisture (Ws) 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 Rs and its temperature sensitivity (Q10) in the five different fertilization treatments. The results showed that no significant temporal change in Rs among the five treatments was found. No significant difference was found in Rs between the CK and INF treatments. Compared with the values of Rs in CK and INF, the Rs 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 Rs. Both the Ts and Ws showed 14%-96% and 6%-37% in Rs seasonal variations, respectively. Among the treatments, the correlation coefficient of the fitted equations between Rsand Ts was higher in the INF+M, INF+M+S and M+S treatment than in CK and INF, but was not between Rsand Ws. For the relationship between Rs and vegetation indexes we found that the correlation coefficients between Rs and the difference vegetation index (DVI), ratio vegetation index (RVI), and enhanced vegetation index (EVI), respectively, were higher than that of Rs and the normalized differential vegetation index (NDVI); and that the correlation coefficients between Rsand the red edge slope (Dred) and red edge area (Sred) were higher than between Rs and the red edge position (λred). This indicated that the treatments in INF+M+S increased the correlation coefficient between Rs and the spectrum characteristics index. The determination coefficient of the fitted equations including the feature spectral parameters, T10, and Wsvariables was higher than that of the equations only including both T10 and Ws variables, or a single variable of T10 or Ws. Compared with CK, the Q10 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 Q10 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 Rs, Q10, and R10, i.e., Rs at a temperature of 10℃, in the different treatments, which could explain the 97.6%, 78.2%, and 92.8% variations in Rs, Q10, and R10, respectively. |
