Mitigation of the stresses of acid sulfate soils by terrestrial and aquatic plants (Melaleuca armillaris and Phragmites australis) under varying moisture regimes

The long-term roles of live plant roots in mitigating acid sulfate soil stresses remain poorly understood. Three studies, each lasting twelve months, were conducted using Melaleuca armillaris and Phragmites australis. In the first study, alkaline sandy loam soil was mixed into the sulfuric soil to increase the pH to 6.7, and Melaleuca seedlings were planted. In the second and third studies, M. armillaris and P. australis were planted in sulfuric and sulfidic soils and maintained at 75% water-holding capacity and flooded soil conditions. All the studies were set using 300 mm stormwater tubes with sealed bottom ends. The treatments were replicated four times, set up under a glasshouse in a completely randomized design, and harvested after 12 months. The pH and root biomass were measured from the surface, middle, and deep profiles. Results showed that the neutralization obtained by mixing alkaline sandy loam soil with sulfuric soil was stable but deteriorated due to plant root penetration. In the sulfuric soil material (pH <4), M. armillaris produced more roots at the surface than in the deep soil under circumneutral pH and aerobic soil conditions. In sulfidic soil material (pH >4), more roots were produced in the deeper soils. In the sulfuric and sulfidic soil materials, P. australis produced more roots at the surface than at the deep under pH >4 and aerobic conditions. Under anaerobic conditions with a pH >4, root distribution was even. Our findings suggest that common terrestrial and aquatic plants maintain a characteristic distribution of roots to mitigate the stresses of acid sulfate soils.