Fine root dynamics, coarse root biomass, root distribution, and soil respiration in a multispecies riparian buffer in Central Iowa, USA

By influencing belowground processes, streamside vegetation affects soil pr ocesses important to surface water quality. We conducted this study to comp are root distributions and dynamics, and total soil respiration among six s ites comprising an agricultural buffer system: poplar (Populus x euroameric ana' Eugenei), switchgrass, cool-season pasture grasses, corn (Zea mays L.) , and soybean (Glycine max (L.) Merr.). The dynamics of fine (0-2 mm) and s mall roots (2-5 mm) were assessed by sequentially collecting 35 cm deep, 5. 4 cm diameter cores from April through November. Coarse roots were describe d by excavating 1 x 1 x 2 m pits and collecting all roots in 20 cm depth in crements. Root distributions within the soil profile were determined by cou nting roots that intersected the walls of the excavated pits. Soil respirat ion was measured monthly from July to October using the soda-lime technique . Over the sampling period, live fine-root biomass in the top 35 cm of soil averaged over 6 Mg ha(-)1 for the cool-season grass, poplar, and switchgra ss sites while root biomass in the crop fields was < 2.3 Mg ha(-)1 at its m aximum. Roots of trees, cool-season grasses, and switchgrass extended to mo re than 1.5 m in depth, with switchgrass roots being more widely distribute d in deeper horizons. Root density was significantly greater under switchgr ass and cool-season grasses than under corn or soybean. Soil respiration ra tes, which ranged from 1.4-7.2 g C m(-2) day(-1), were up to twice as high under the poplar, switchgrass and cool-season grasses as in the cropped fie lds. Abundant fine roots, deep rooting depths, and high soil respiration ra tes in the multispecies riparian buffer zones suggest that these buffer sys tems added more organic matter to the soil profile, and therefore provided better conditions for nutrient sequestration within the riparian buffers.