Interannual Variability in Global Soil Respiration on a 0.5 Degree Grid Cell Basis (1980-1994)

We used a climate-driven regression model to develop spatially resolved estimates of soil-CO{sub 2} emissions from the terrestrial land surface for each month from January 1980 to December 1994, to evaluate the effects of interannual variations in climate on global soil-to-atmosphere CO{sub 2} fluxes. The mean annual global soil-CO{sub 2} flux over this 15-y period was estimated to be 80.4 (range 79.3-81.8) Pg C. Monthly variations in global soil-CO{sub 2} emissions followed closely the mean temperature cycle of the Northern Hemisphere. Globally, soil-CO{sub 2} emissions reached their minima in February and peaked in July and August. Tropical and subtropical evergreen broad-leaved forests contributed more soil-derived CO{sub 2} to the atmosphere than did any other vegetation type ({approx}30% of the total) and exhibited a biannual cycle in their emissions. Soil-CO{sub 2} emissions in other biomes exhibited a single annual cycle that paralleled the seasonal temperature cycle. Interannual variability in estimated global soil-CO{sub 2} production is substantially less than is variability in net carbon uptake by plants (i.e., net primary productivity). Thus, soils appear to buffer atmospheric CO{sub 2} concentrations against far more dramatic seasonal and interannual differences in plant growth. Within seasonally dry biomes (savannas, bushlands, and deserts), interannual variability in soil-CO{sub 2} emissions correlated significantly with interannual differences in precipitation. At the global scale, however, annual soil-CO{sub 2} fluxes correlated with mean annual temperature, with a slope of 3.3 PgCY{sup -1} per degree Celsius. Although the distribution of precipitation influences seasonal and spatial patterns of soil-CO{sub 2} emissions, global warming is likely to stimulate CO{sub 2} emissions from soils

Biomass, carbon and nitrogen dynamics of multi-species riparian buffers within an agricultural watershed in Iowa,USA

This study was conducted to determine biomass dynamics, carbon sequestration and plant nitrogen immobiliza- tion in multispecies riparian buffers, cool-season grass buffers and adjacent crop ?elds in central Iowa. The seven-year-old multispecies buffers were composed of poplar (Populus × euroamericana ‘Eugenei’) and switch- grass (Panicum virgatum L.). The cool-season grass buffers were dominated by non-native forage grasses (Bro- mus inermis Leysser., Phleum pratense L. and Poa pratensis L). Crop ?elds were under an annual corn-soybean rotation. Aboveground non-woody live and dead biomass were determined by direct harvests throughout two growing seasons. The dynamics of ?ne (0–2 mm) and small roots (2–5 mm) were assessed by sequentially col- lecting 35 cm deep, 5.4 cm diameter cores (125 cm deep cores in the second year) from April through Novem- ber. Biomass of poplar trees was estimated using allometric equations developed by destructive sampling of trees. Poplar had the greatest aboveground live biomass, N and C pools, while switchgrass had the highest mean aboveground dead biomass, C and N pools. Over the two-year sampling period, live ?ne root biomass and root C and N in the riparian buffers were signi?cantly greater than in crop ?elds. Growing-season mean biomass, C and N pools were greater in the multispecies buffer than in either of the crop ?elds or cool-season grass buffers. Rates of C accumulation in plant and litter biomass in the planted poplar and switchgrass stands averaged 2960 and 820 kg C ha-1 y-1, respectively. Nitrogen immobilization rates in the poplar stands and switchgrass sites averaged 37 and 16 kg N ha-1 y-1, respectively. Planted riparian buffers containing native perennial species therefore have the potential to sequester C from the atmosphere, and to immobilize N in biomass, therefore slow- ing or preventing N losses to the atmosphere and to ground and surface waters

Soil respiration within riparian buffers and adjacent crop fields

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