Soil respiration within riparian buffers and adjacent crop fields
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3 We quantified rates of soil respiration among sites within an agricultural 4 landscape in central Iowa, USA. The study was conducted in riparian cool-season grass 5 buffers, in re-established multispecies (switchgrass + poplar) riparian buffers and in 6 adjacent crop (maize and soybean) fields. The objectives were to determine the 7 variability in soil respiration among buffer types and crop fields within a riparian 8 landscape, and to identify those factors correlating with the observed differences. Soil 9 respiration was measured approximately monthly over a two-year period using the soda- 10 lime technique. Mean daily soil respiration across all treatments ranged from 0.14-8.3 g 11 C m-2 d-1. There were no significant differences between cool-season grass buffers and 12 re-established forest buffers, but respiration rates beneath switchgrass were significantly 13 lower than those beneath cool-season grass. Soil respiration was significantly greater in 14 both buffer systems than in the cropped fields. Seasonal changes in soil respiration were 15 strongly related to temperature changes. Over all sites, soil temperature and soil moisture 16 together accounted for 69 % of the seasonal variability in soil respiration. Annual soil 17 respiration rates correlated strongly with soil organic carbon (R =0.75, P<0.001) and fine 18 root (<2 mm) biomass (R=0.85, P<0.001). Annual soil respiration rates averaged 1140 C 19 m-2 for poplar, 1185 g C m-2 for cool-season grass, 1020 g C m-2 for switchgrass, 750 g 20 C m-2 for soybean and 740 g C m-2 for corn. Overall, vegetated buffers had significantly 21 higher soil respiration rates than did adjacent crop fields, indicating greater soil biological 22 activity within the buffers.