Differential impacts of pH and acid type on Brassicaceae seed germination and seedling growth

Abstract

Elevated acidity can be a considerable stressor for plants. Acids can arise from anthropogenic sources such as acid rain, characterized by inorganic acids like sulphuric acid. Beyond anthropogenic influences, various habitats exhibit inherent acidity due to bedrock properties, such as granite's limited buffering capacity or low pH resulting from biological activity, featuring an abundance of weak organic acids. While low pH (<4) is generally considered stressful for plants, differential impacts of distinct acid types—organic versus inorganic, strong versus weak—on plant growth and function remain unclear. To address this knowledge gap, I conducted a controlled experiment to determine whether acid responses are solely pH-dependent or if acid type specificity plays a role in plant functional responses. I grew two Brassicaceae species under factorial combinations of four pH levels (pH 1-5.5) and three acids (hydrochloric, sulfuric, and acetic) with distilled water as control, and measured seed germination, seedling growth, leaf size, shoot and root length. Seed germination, growth, and morphology increased with increasing pH across all acids. However, acid type also influenced plant responses. Hydrochloric acid promoted higher seed germination but hindered seedling growth, while acetic and sulphuric acids had the opposite effects. These results highlight the influence of acid types on plant functions, specifically affecting distinct developmental stages. Understanding the differential effects of acid types on various growth parameters provides insight into acid stress and potential tolerance mechanisms. My study has implications for restoration efforts in acidimpacted environments, challenging the assumption that pH alone dictates plant stress responses.