Simulated acid rain impact on growth, yield and leaf anatomy of Dioscorea rotundata (L.)

Acid rain causes damage to crops and also has adverse effect on the soil and the environment. These have led to the abandonment of farmlands in affected areas. Southern Nigeria which is known for yam cultivation is subjected to acid rain resulting from gas flaring activities, importation of fairly used vehicles, power generation and industrial activities. The growth, yield and leaf anatomy response of Dioscorea rotundata (L.) exposed to simulated acid rain (SAR) of pH 2.0, 3.0, 4.0 and 6.0 (control) was investigated. Acid rain exposure caused morphological changes in plants including chlorosis, necrosis, and leaf folding. Acidic precipitation inhibited vine length, leaf number, chlorophyll content index and leaf area at pH 2.0; while growth was encouraged at pH 6.0. 22% of leaf surface area of D. rotundata L, was injured after simulated acid rain treatment at pH 2.0 while necrosis was absent at the (control) pH 6.0. Harvest index of D. rotundata was not significantly different (p>0.05) between the pH treatment groups; however, was slightly higher at the (control) pH 6.0. Percentage dry matter partitioning of D. rotundata leaf and stem was not affected by the acid rain exposure; nevertheless, maximum percentage dry matter of tuber was obtained at pH 4.0 and pH 6.0. Transverse sections of D. rotundata leaves showed cuticle wax damage and rupture of epidermis at lower pH 2.0 and 3.0. Mesophyll degradation and cytoplasm depletion was also observed in the treated leaves. The plant leaves revealed dark tissues in necrotic areas which may be phenolic compounds secretion. However, it became clear that significant increases in the growth parameters considered occurred at pH 6.0 (control).