Biomass and valve length of diatoms living on tree bark as novel indicators of atmospheric environment changes.

Diatoms, an important group of primary producers, are valuable indicators of environment changes in aquatic ecosystems. Presently, limited knowledge is available on diatoms living on tree bark and their responses to atmospheric environmental changes. Mosses such as Hypnum callichroum living on the bark of Cinnamomum camphora were collected monthly in a 9-year period to explore temporal changes in composition, biomass and valve length of diatoms in a subtropical evergreen broadleaf forest. A total of 20 diatom species from 14 genera were identified in tree-bark moss samples, with limited seasonal and monthly variations in diatom communities. Diatom biomass fluctuated between 0.25 × 10 and 1.58 × 10 valves g dry mosses, typically peaking in winter and spring. Monthly anomalies in diatom biomass were significantly correlated with the concentrations of SO, PM10, and PM2.5, suggesting that atmospheric environmental changes might influence diatom biomass through altering acidity and nutrients adsorbed on atmospheric dust. Pinnularia borealis was the dominant species, with a mean monthly percentage of 68.1 %. Its monthly mean valve length (25.1-32.1 μm) generally declined with a decrease in O, rainfall, and humidity, suggesting that low ozone concentration and drought may cause diatom cell-size reduction. Taken together, biomass and valve length of diatoms living on tree-bark mosses can serve as novel indicators of atmospheric environmental changes. Long-term monitoring of aerophilic diatoms can provide new insights into algal diversity and their ecosystem functioning in terrestrial ecosystems.