| Soil respiration plays a crucial role in global carbon (C) budget. It is important to conduct the research in the typical agricultural regions, China to understand its spatial and temporal variations and their controlling factors. This will benefit not only quantitative evaluation of soil respiration at a regional scale, but also the agricultural C budget in China and even in the world. In this study, we had a field observation on soil respiration in Changle, Taicang, Changwu, Baodi and Heilongjiang which respected five typical agricultural regimes in China. We also integrated soil respiration data in agricultural ecosystems between 2000 and 2012 in China, and analyzed the seasonal and spatial variations and the factors influencing soil respiration in five agricultural regions (Southeast, Southwest, North, Northwest, and Northeast China).Soil respiration changed obviously with the seasons in five typical agricultural regions. In summer, soil respiration rate reached the highest value in regions without rice-planting, and exhibited an obvious downward trend during rice growing reason. Soil respiration rate stayed a low value in winter. The annual mean rate of soil respiration in Taicang, Changle, Baodi, Heilongjiang and Changwu was 881.8±48.4 g C m-2 a1,853.4±108.5 g Cm-2a-1,733.4±66.6gCm-2a-1,603.5±13.2gCm-2 a-1, and 556.0±27.5gCm-2a-1, respectively.We extracted data from 112 published field studies that studied the soil respiration in China farmland ecosystems. Our results indicated that the annual mean rate of soil respiration in farmland ecosystems of China was 682.8±18.3gCm-2 a-1, and total C efflux from soil respiration in agricultural region of China was about 0.90 PgCa-1. The order of soil respiration rate in five agricultural regions was Southeast> Southwest> North> Northeast> Northwest. Southeast had a significant difference in soil respiration rate between Northeast, North and Northwest, respectively. The significant difference in soil respiration rates was found between water-cultivation and dry-cultivation regions (p<0.05). Soil respiration in dry-cultivation regions was 1.3 times higher than that in water-cultivation ones. Soil respiration rate was significantly affected by crop types (p<0.05), with an order of cotton> corn> soybean> rice> wheat.At Changle, soil respiration rate was significantly correlated with soil temperature during dry farming (p< 0.01, R2=0.52). Soil respiration rate was mainly driven by soil temperature when soil moisture was lower than 30%. When soil moisture was in the range of 30-60%, soil respiration rate was significantly correlated with soil moisture (p<0.01, R2=0.57), while the relationship between soil respiration and soil moisture became significant negative linear correlation when soil moisture was higher than 60%(p<0.01, R2=0.40). At Taicang, soil respiration rate was significantly correlated with soil temperature (p< 0.01, R2=0.62). When soil moisture was higher than 30%, soil respiration rate showed a significantly correlation with soil moisture (p< 0.01, R2=0.49). But soil respiration was mainly influenced by soil temperature when soil moisture was lower than 30%. At Baodi, soil respiration rate had a significantly correlation with soil temperature and soil moisture (p<0.01, correlation coefficient was 0.95 and 0.33 respectively). Soil moisture did not significantly affect soil respiration when soil temperature was lower than 10℃. When soil temperature was in the range of 20～30℃, soil respiration rate significantly correlated with soil moisture (p< 0.01, R2=0.74). At Heilongjiang, soil respiration rate showed a significant correlation with soil temperature (p< 0.05, R2=0.34) when both soil temperature and soil moisture stayed in low level. At Changwu, soil respiration rate was significantly correlated with soil temperature (p< 0.05, R2=0.97), and the correlation with soil moisture became significant only when soil temperature within 20～30℃.Significant correlations were found in soil respiration with annual mean temperature and NPP (p<0.05). But there was no significant correlation between soil respiration and annual precipitation. Soil respiration rate had a significant correlation with soil temperature during crop growing season except rice growing season in Southwest of China (p< 0.05). There was a significant correlation between soil respiration and soil moisture during corn growing season (p< 0.05), but the correlation was not significant during wheat growing season. |
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