Improvement of moss photosynthesis by humic acids from Antarctic tundra soil

There have been several published reports regarding the growth promoting effect of humic acids (HA) on vascular plants; however, the effect of HA on bryophytes is still unknown. Due to the ecological importance of mosses, which dominate the Antarctic flora, we assessed the effectiveness of HA as a biostimulant using three moss species: Antarctic Ceratodon purpureus KMA5038, Arctic Bryum sp. KMR5045, and Physcomitrella patens which inhabits temperate regions. Natural HA (KS1-3_HA) were extracted through acidic precipitation of alkaline extracts from Antarctic tundra soil. Spectroscopic structural properties of KS1-3_HA were characterized and determined to possess several functional groups such as hydroxyl (R-OH) and carboxyl (R-COOH), implying they could have a growth-related biological function. For two polar mosses, increasing HA concentrations correlated with increased growth and photosynthesis. The efficiency for temperate moss increased at lower concentrations tested, but rather began to reduce at the highest HA concentration, indicating that effective concentrations of HA vary depending on the moss species and habitat. Based on these results, Antarctic HA may have ecological role in enhancing the growth and photosynthesis of Antarctic mosses. We believe this is the first study to establish a positive physiological effect of HA on mosses and hope it may serve as a basis for studying the role of HA in preserving the terrestrial ecosystem of Antarctica.