δ13C and δ15N of moss Haplocladium microphyllum (Hedw.) Broth. for indicating growing environment variation and canopy retention on atmospheric nitrogen deposition

Abstract

Mosses have been recognized as a useful tool for biomonitoring atmospheric deposition and assessing regional environment. This study was carried on whether the same moss growing in areas with identical regional atmospheric deposition while under different growing environments would have the same indicating signals. Similar variations in mean δ 13C and δ 15N signatures were found between mosses collected from five habitats, with an increasing sequence from mosses under canopies to epilithic mosses, indicating that habitats were potentially regulating δ 13C and δ 15N values of mosses. Dryer habitats (lower water availability) and input of more aerosol N were the main reasons for higher δ 13C and δ 15N values of mosses at open sites (especially for epilithic species), while more negative values of mosses under canopies were attributed to their wetter habitats and less uptake of aerosol N. Additionally, δ 15N values not δ 13C varied linearly with canopy thickness from −7.84‰ (1 m) to −4.71±0.7‰ (4 m), suggesting δ 15N was more sensitive for indicating canopy retention. Consequently, isotopic data of mosses under different environments could not be compared for atmospheric deposition research with each other even collected at the same site. Moss δ 13C and δ 15N were affected not only by regional atmospheric N sources but also by their growing environments. δ 15N of epilithic Haplocladium microphyllum at open sites can be taken as confident bio-indicator of atmospheric N deposition, which would deepen the application of stable nitrogen isotope of bryophytes in atmosphere–plant system study.