Soil type and species diversity influence selection on physiology in Panicum virgatum

Authors: SHERRARD, MARK - University Of Northern Iowa; JOERS, LUCAS - University Of Wisconsin; CARR, CHRISTINA - University Of Northern Iowa; Cambardella, Cynthia

Submitted to: Evolutionary Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/18/2015
Publication Date: 5/29/2015
Citation: Sherrard, M.E., Joers, L.C., Carr, C.M., Cambardella, C.A. 2015. Soil type and species diversity influence selection on physiology in Panicum virgatum. Evolutionary Ecology. 29(5):679-702. doi: 10.1007/s10682-015-9770-y.

Interpretive Summary: Agricultural production and homogenization of land management practices over the past century have resulted in wide-spread loss of plant and animal biodiversity. Current and projected expansion of bioenergy crop production in the Midwestern USA has the potential to dramatically alter agricultural land use. This study provides field data on short-term physiological response of switchgrass(Panicum virgatum), a common perennial grown for bioenergy, to soil type and plant diversity when planted within several perennial bioenergy production systems established on two soil types in north-central Iowa. We found that soil characteristics influence selection on plant physiology via differences in available water capacity which suggests that soil type drives plant expression of genetic potential in stressful years (e.g., droughts, floods) and in regions with low annual precipitation. The findings also have important implications for grassland restoration and biodiversity conservation in landscapes dominated by agriculture. These results will provide information to land managers for development and implementation of bioenergy cropping systems that enhance biodiversity in the Midwest.

Technical Abstract: Species diversity influences the productivity and stability of plant communities, but its effect on the evolution of species within those communities is poorly understood. In this study, we tested whether species diversity and soil type influence selection on physiology in switchgrass (Panicum virgatum). Plants were grown in 0.33-0.55ha plots in eight full-factorial treatment combinations: four diversity treatments (1 species – switchgrass monoculture; 5 species – C4 grasses; 16 species – a mix of grasses, forbs, and legumes; 32 species – a mix of grasses, forbs, legumes, and sedges) and two soil types (Waukee loam “loam” and a Spillville-Coland alluvial complex “clay”). We measured selection on photosynthetic rate, chlorophyll concentration, and specific leaf area in each treatment combination and compared the strength of selection between soil types and diversity treatments. When significant, selection favored increased photosynthesis, increased chlorophyll concentration, and decreased specific leaf area in all treatment combinations. Selection for these attributes was stronger in the faster-draining loam soil than the slower-draining clay soil. Selection rarely differed significantly between diversity treatments; however, most instances in which selection differed between soil types occurred in the high-diversity mixes suggesting that species diversity alters the impact of soil type as an agent of selection. Selection may have been stronger in the loam soil because of its lower available water capacity. There was a lengthy summer drought during our experiment, and under these conditions, plants with high photosynthesis and chlorophyll concentration would have more resources to invest in their root system for water uptake. Increased capacity for water uptake would benefit plants in both soil types during drought but would have the greatest adaptive significance in the faster-draining loam soil.