Photosynthetically active radiation is required for seedling growth promotion by volcanic dacitic tuff breccia (Azomite)

A plant's growth and development are shaped by its genome and the capacity to negotiate its environment for access to light, water, and nutrients. There is a vital need to understand the interactions between the plant, its physical environment, and the fertilizers used in agriculture. In this study, a commercially available volcanic ash fertilizer, Azomite (R), characterized as dacitic (rhyolitic) tuff breccia, was tested for its effect on promoting early seedling vigor. Early growth and photomorphogenesis processes are well studied in Arabidopsis. Seedling assays under different light conditions were used to dissect the underlying mechanisms involved. These assays are well established and can be translated to agriculturally important crop plants. The volcanic ash fertilizer was tested at different concentrations on seedlings grown on basic media lacking sucrose either in continuous darkness (Dc), continuous Red (Rc), Far-Red (FRc), or White Light (WLc). Micronutrients in the volcanic ash significantly increased seedling growth under Rc and WLc, but not under Dc and FRc, indicating that photosynthetically active radiation was required for the observed growth increase. Furthermore, red-light photoreceptor mutant, phyB-9, lacked the growth response, and higher amount of fertilizer reduced growth in all conditions tested. These data suggest that light triggers the ability of the seedling to utilize micronutrients in volcanic ash in a dose-dependent manner. The methods described here can be used to establish mechanisms of activity of various nutrient inputs and, coupled with whole-genome expression profiling, can lead to better insights into optimizing nutrient field applications to improve crop production.