Organic Acid Changes In Bermudagrass Root Exudates Under Aluminum Stress.

Root exudates can act as root zone chelators to reduce harmful effects when plants are under heavy metal stress. Aluminum toxicity in acidic soils is a common problem in bermudagrass areas across Oklahoma. Therefore, a growth unit study was developed to evaluate organic acid changes of ‘Princess-77’ bermudagrass root exudates under Al stress. Aluminum (AlK(SO₄)₂^.12H₂O) treatments were applied at 100 ppm and 200 ppm to bermudagrass growing in a 4.5 pH sand profile. Treatments also including a 4.5 pH treatment with no Al and a 7.0 pH control with no Al. Each treatment was replicated three times in a randomized complete block design. Relative root mass significantly decreased 60.5% and 65.3% at Al concentrations of 100 ppm and 200 ppm separately compared to the 4.5 pH treatment with no Al. Leaf tissue samples were analyzed for mineral nutrients (P, Ca, K, Mg, Na, S, Fe, Zn, Cu, Mn, Ni, and B) and Al concentrations. Aluminum accumulated in bermudagrass leaf tissues under Al stress. There was a significant (p = 0.01) negative linear relationship (r² = 0.61) between Al leaf accumulation and bermudagrass root mass where root mass decreased as Al accumulation increased. Root exudates were analyzed by High Performance Liquid Chromatography (HPLC) for five target organic acids (oxalic, malic, citric, malonic and succinic acid). It was hypothesized that the secretion of oxalic, malic and citric acids in bermudagrass root exudates would increase in response to Al stress. This preliminary work will provide insight for future development and selection of more Al tolerant bermudagrass cultivars for Oklahoma.

Key words: Bermudagrass (Cynodon dactylon var. dactylon), aluminum stress; root exudates; organic acids