Effect of added water and acidity of simulated rain on growth of field-grown radish

Abstract

Radish plants were grown in field plots and exposed to simulated rain at four levels of acidity: pH 5·6, pH 4·2, pH 3·5 and pH 2·8. Simulated rain solutions, containing background ions and acidified with a mixture of sulphuric and nitric acids, were applied intermittently between ambient rain events for 1-h periods. In order to test for the effect of the extra supply of water, the growth of plants that received only ambient rain was compared with that of those that received ambient rain and applications of simulated rain at pH 5·6. Applications of simulated rain at pH 5·6 did not affect the total accumulation of biomass but they did affect the distribution of dry matter among plant organs by increasing mass in the shoot and decreasing mass in the root. Because there was a significant effect of additions of simulated rain treatments at pH 5·6, the effect of acidity on plant growth was tested within simulated rain treatments. Plants were not visibly injured at the elevated levels of acidity but there were effects on allometric relationships. Root mass was positively correlated with increases in acidity but shoot mass was unaffected even at pH 2·8. These results indicate that increased acidity of simulated rain applied under field conditions may stimulate accumulation of dry matter in radish plants but that plant-soil water relationships may be an important factor in modifying plant response to acidic rain.