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