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Investigating Soil Acidification Mechanisms for Inhibiting Phytophthora

Firs grown as Christmas trees are susceptible to a root disease called phytophthora root rot. Experiments started in 2016 have demonstrated that the addition of elemental sulfur to acidify the soil to a pH of 4 has a dramatic effect in improving the health of susceptible trees when grown in a soil harboring this disease, and reduces losses of Canaan fir by two-thirds compared to soil with a pH of 6. The current best non-mutually exclusive explanations for the improved growth and survival of trees under low pH conditions are (1) enhanced mineral nutrient availability to the tree, resulting in better tree color and growth, (2) direct inhibition at low pH of Phytophthora spp growth, and (3) a dramatically changed microbial community associated with the roots of these fir trees, which might favor better root health. There are remarkably diverse bacteria found associated with fir roots that are antagonistic to the growth of Phytophthora spp. These need to be further studied to determine whether they can become a practical tool as a root dip at the time of planting to protect the roots from infection.