| Hydrology of wetland control and maintain the structure and function of wetland ecosystem. The change of hydrological will impact soil respiration rate. Meanwhile, the rise of global temperature will impact the structure and function of wetland ecosystem. So, it is necessary to study the effect of water table and warming on wetland soil respiration and its mechanism.The study took the reclaimed tidal wetland at the Dongtan of Chongming Island in Shanghai as object, analyzed total soil respiration, root respiration, root-free soil CO2 release and litter layer CO2 release along a gradient of water table and in warming and control site from April to October 2014. Meanwhile, soil temperature and humidity, soil physical and chemical properties and biological factors were measured in all sites. We studied the effects of elevated temperature and water table variation on soil respiration and discussed their mechanism in order to provide reference to predict wetland carbon sequestration ability under different water table and warming in this area, and provide basic data and basis for scientific management of wetland. The result shows that:1. The effect of water table on soil respiration and its components(1) Daily dynamic of soil respiration and its components represented unimodal curve in different water tables, and medium water table> low water table>high water table. The maximum appeared in 12:00～14:00, and the minimum appeared in 00:00～03:00. Soil respiration and its components represented obvious seasonal variation. RSL represented unimodal curve, but the other components and RST represented polymodal curve. Total soil respiration of low, medium and high water table is 3.14,3.48,2.16μmol·m-2·s-1 respectively. Total soil respiration of low water table was significantly higher than high water table, but was lower than medium water table. This result demonstrated that soil respiration didn’t increase all along water table decreasing, but deceased when the water table was lower than the threshold.(2) There were significant exponential relationship between the daily dynamics of soil respiration, its components and temperature of soil 5cm depth (P<0.05), but there wasn’t significant relationship between soil volumetric moisture and soil respiration (P>0.05). Throughout the growing season, there were not significant relationship between the seasonal dynamics of soil respiration, its components and soil temperature. No water on the ground, the RST of all water tables and soil temperature represented significant exponential relationship (P<0.05), only RSR one of the components of soil respiration and soil temperature represented significant exponential relationship (P<0.05). Soil temperature can explain 51.9%～68.8% and 46.9%～58.3% of the RST and RSR seasonal variation respectively. When there was water on the ground, soil respiration, its components and soil temperature have no significant relationship (P>0.05).(3) In three water tables, contribution rates of soil respiration components were significantly different, whose order is:RSR> RSS> RSL (P<0.05). But contribution rates of RSR, RSS and RSL represent no significant difference along the gradient of water table (P>0.05).(4) Q10 of low, medium and high water table RST were 1.51,2.51 and 1.63 respectively, and Q10 of low, medium and high water table RSR were 1.70,3.73 and 1.85 respectively. These results indicated that the medium water table had strongest temperature sensitivity of total soil respiration and root respiration, and the temperature sensitivity of root respiration was stronger than total soil respiration.2. The effect of warming on soil respiration and its components(1) On season scale, OTC had obvious warming effect, the air temperature averagely increased by 1.61±0.16℃ (P<0.01), the temperature of soil 5cm depth averagely increased by 1.09±0.15℃ (P<0.01). On day scale, warming effect of OTC appeared only in the daytime, and night soil temperature of OTC is lower than CK.(2) Daily dynamic of soil respiration and its components in CK and OTC all represented unimodal curve, whose peaks showed in the same time. Overall, the daily soil respiration rate of warming treatment was greater than the control (P<0.05). Soil respiration and its components in CK and OTC all had significant seasonal dynamics, RSL represented unimodal curve, the other components and RST represented polymodal curve. In the growing season, OTC significantly increased RST, RSR and RSS respectively (P<0.05).(3) In OTC and CK, the daily dynamics of soil respiration, its components and temperature of soil 5cm depth represent significant exponential relationship (P<0.05), but there were no significant relationship between seasonal dynamics of soil respiration, its components and soil temperature (P>0.05). When there was no water on the ground, RST, RSR, RSS in warming treatment represented significant exponential relationship with soil temperature (P<0.05), RST and RSR in the control represented significant exponential relationship with soil temperature (P<0.05). When there was water on the ground, soil respiration, its components and soil temperature represent no significant relationship (P>0.05).(4) In OTC and CK, contribution rates of soil respiration components were significantly different, whose order is:RSR> RSS> RSL (P<0.05), but there was no significant difference of contribution rates of soil respiration components between OTC and CK (P>0.05).(5) Q10 of RST, RSR and RSS in OTC were 2.86,3.25 and 2.61 respectively, and Q10 of RST and RSR in CK were 2.51 and 3.73 respectively. These results illuminated that warming increased temperature sensitivity of total soil respiration, but decreased temperature sensitivity of root respiration, and the temperature sensitivity of root respiration was stronger than total soil respiration. |
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