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

Abstract

By influencing belowground processes, streamside vegetation affects soil processes important to surface water quality. We conducted this study to compare root distributions and dynamics, and total soil respiration among six sites comprising an agricultural buffer system: poplar (Populus × euroamericana‘ Eugenei), switchgrass, cool-season pasture grasses, corn (Zea mays L.), and soybean (Glycine max (L.) Merr.). The dynamics of fine (0--2 mm) and small roots (2--5 mm) were assessed by sequentially collecting 35 cm deep, 5.4 cm diameter cores from April through November. Coarse roots were described by excavating 1 × 1 × 2 m pits and collecting all roots in 20 cm depth increments. Root distributions within the soil profile were determined by counting roots that intersected the walls of the excavated pits. Soil respiration 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 switchgrass sites while root biomass in the crop fields was < 2.3 Mg ha^-1 at its maximum. Roots of trees, cool-season grasses, and switchgrass extended to more than 1.5 m in depth, with switchgrass roots being more widely distributed in deeper horizons. Root density was significantly greater under switchgrass and cool-season grasses than under corn or soybean. Soil respiration rates, 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 fields. Abundant fine roots, deep rooting depths, and high soil respiration rates in the multispecies riparian buffer zones suggest that these buffer systems added more organic matter to the soil profile, and therefore provided better conditions for nutrient sequestration within the riparian buffers.