Managing Global Resources for a Secure Future

Arbuscular mycorrhizal fungi (AMF) impart growth benefits to water-stressed plants, contributing to resilience under moisture-limited conditions. While AMF communities are diverse and abundant in natural systems, they may be altered by agricultural management strategies, including over-fertilization, fungicide application, and monoculture cropping. Organic systems can improve soils by stimulating increased species diversification through cultivation of beneficial soil microbes such as AMF. However, optimization of symbiotic relationships between crops and microbes through selections of crop and microbe genetics remains unclear. Our work begins to elucidate these relationships. Using carrot as a model crop, we seek to determine whether cultivar and AMF isolate selection contribute to increased plant benefits, measured in improved growth and system resilience. Under well-watered and water-stressed conditions, our present study screened four carrot cultivars in low-nutrient organic soils inoculated with AMF isolates from geographically distinct locations.

Carrots were greenhouse grown in pasteurized organic field soils amended with perlite and whole inoculants of eight AMF isolates. Mock inoculant served as a negative control. Carrots were well watered during establishment and water-stressed during root maturation. Experiments were repeated in organic field trials, where water was controlled through drip irrigation under rain-excluding caterpillar tunnels. Biometric data were recorded for roots and shoots. AMF colonization was quantified in fine roots.

Cultivars differed in their tolerance to water-stress in response to AMF inoculation, with heirloom cultivars of carrot more tolerant to water-limited conditions than hybrids. Inoculation with several AMF isolates increased root growth while decreasing shoot growth. Colonization patterns differed between geographically-unique isolates of a single species of AMF. Genetic tolerance to water stress by certain carrot cultivars likely influenced root growth response to AMF symbiosis. The proportion of fungal structures in roots may provide insight as to which isolates will likely improve host root growth.