1a. Objectives (from AD-416):
1. Overcome yield reductions due to the negative impacts on indigenous arbuscular mycorrhizal [AM] fungi of repetitive tillage and cultivation to control weeds in organic farming through inoculation with AM fungi produced via the on-farm system. 2. Optimize utilization of arbuscular mycorrhizal symbiosis to enhance crop growth and yield. 2.1) Develop greenhouse media and nutrient regimes for the production of AM fungus colonized seedlings in organic management. 2.2) Develop methods for the production of AM fungus colonized sweet corn seedlings in the greenhouse and quantify growth and yield response after outplanting. 2.3) Examine the functioning of AM fungi in high P soil in the field by determining the response to inoculation with AM fungi in field plots with greatly reduced AM fungus populations due to long term bare fallow. 3. Increase the acquisition of nitrogen by crop plants via mycorrhizal symbiosis by manipulating the regulatory processes of N uptake by arbuscular mycorrhizal fungus hyphae.
1b. Approach (from AD-416):
Arbuscular mycorrhizal [AM] fungi form a mutualistic symbiosis with the roots of the majority of crop plants. Among the benefits the plant receives are enhanced mineral nutrient uptake, drought resistance, and disease resistance. These benefits make optimal utilization of the symbiosis important to ensure the economic and environmental sustainability of US agriculture. One way to utilize the symbiosis is to inoculate vegetable seedlings with AM fungi in the greenhouse, prior to out planting in the field. This allows plants to benefit from the symbiosis immediately. We will develop inoculation strategies and greenhouse culture regimes for organic farmers to produce well colonized seedlings. Further, we will examine two farming practices that should benefit from inoculation: growth of sweet corn seedlings in the greenhouse for early transplant to the field and transplant of vegetable seedlings into soil repetitively cultivated to produce a stale weed seedbed to control weeds. Throughout, we will utilize AM fungi produced via our system for the on-farm production of inoculum. In addition, we will study the functioning of AM fungi. We will study how the nitrogen uptake and transfer to the host plant is regulated by the photosynthetic capacity of the plant. Phosphorus (P) availability is the most important regulator of development and efficacy of the symbiosis. We will conduct field experiments at the Rodale Institute to determine if plant response to the symbiosis in high P soil is affected more by the vigor of the native population of AM fungi or by intrinsic properties of the host plant which determine responsiveness. These studies will yield targeted strategies for utilization of AM fungus inoculum.
3. Progress Report:
This project “Function of arbuscular mycorrhizal fungi in organic and conventional agriculture” completed the OSQR Peer Review Process and was approved on April 5, 2011. Arbuscular mycorrhizal (AM) fungi are soil fungi which form a symbiosis with the majority of crop plants, assisting roots in nutrient uptake, drought tolerance, and disease resistance. Better utilization of this symbiosis in agriculture through the contributions of this project should result in decreased synthetic chemical input, and increased profits and sustainability, as per the Focus Area of the National Program Component. A number of field experiments were initiated for the 2012 growing season to examine the utilization of AM fungus inoculum produced on-farm in real world situations. These include inoculation of sweet corn seedlings prior to planting in the field; inoculation of leek seedlings prior to transplant into a field repeatedly cultivated to suppress weed populations; and continuation of our work utilizing AM fungus inoculum in tomato, pepper, and sweet potato production. We initiated another Ri T-DNA transformed carrot root culture over the winter to replace our declining, 15+ year-old culture. This new root culture will be used for in vitro studies of production of signals under zinc and copper limitation and for the axenic production of spores of Glomus intraradices for metabolic studies. Metabolic studies over the past year, with collaborators at South Dakota State Univ., have focused on how sugar availability to the fungus affects its ability to take up and transport nitrogen to the host plant.
1. Using soil fungi to enhance crop production. Nitrogen is the most commonly limiting nutrient in agricultural soils, and nitrogen fertilizer application is a significant expense to the farmer and a potential hazard to water resources. Arbuscular mycorrhizal fungi are naturally-occurring soil fungi that can transport nitrogen from the soil to roots of most crop plants. ARS researchers at Wyndmoor, Pennsylvania in collaboration with researchers at South Dakota State University discovered that nitrogen transport from the fungus to the plant is dependent upon sugar transport from the plant to the fungus. This understanding of how these fungi transport nitrogen to plants can help farmers apply nitrogen when it can be more efficiently utilized by the plant, thereby helping reduce the amount of nitrogen fertilizer used.
Fellbaum, C., Gachomo, E.W., Beesetty, Y., Choudhari, S., Strahan, G.D., Pfeffer, P., Kiers, T., Bucking, H. 2012. Carbon availability for the fungus triggers nitrogen uptake and transport in the arbuscular mycorrhizal symbiosis. Proceedings of the National Academy of Sciences. Available: http://www.pnas.org/content/early/2012/01/27/1118650109.full.pdf+html.