Marion Island bryophytes: evidence for functional types based on traits related to photosynthesis and desiccation tolerance

Abstract

There is currently a worldwide interest in grouping species on the basis of their functional characteristics into plant functional types (PFTs). This reduces the complexity of models that predict the effects of global change on vegetation and ecosystem processes. Marion Island has vegetation dominated by bryophytes and is experiencing intense climate change. However, there is no accepted scheme and no consensus on the most useful traits for a bryophyte PFT classification. This study aimed at grouping 38 of the island bryophyte species into functional groups. A suite of 14 photosynthetic characteristics related to light or desiccation response were obtained from chlorophyll fluorescence quenching analysis. The characteristics were subjected to principal component and clustering analyses to group the species into functional types. Seven light response groups and nine desiccation response groups were recognised. Six groups were recognised in the combined analysis of the light and desiccation response traits. The species with the highest photosynthetic capacity and lowest photoinhibition had low or moderate saturated moisture content, dried out slowly, low or moderate photoprotection capability in high light and when desiccated and moderate recovery of photochemistry upon rehydration. The species with the lowest photosynthetic capacity and highest photoinhibition had the highest saturated moisture content, dried out very fast, had low photoprotective capability in high light and when desiccated and showed very low to moderate recovery. The group of species with low photosynthetic capacity was distinguished from the group with the lowest photosynthetic capacity by having a higher quantum yield of electron transport at the optimal photosynthetically active radiation (PAR). The two groups consisting of moderate or high photosynthetic capacity species were distinguished by the fraction of open reaction centres in high light and the ability to recover photochemistry upon rehydration. The group consisting of species with moderate photosynthetic capacity had a moderate fraction of open reaction centres in high light, moderate photoprotective capability when desiccated and high recovery of photochemistry upon rehydration. Correspondence analysis shows that the groupings are related to phylogeny, especially at the phylum level, and the species belonging to the same genus mostly had similar light and desiccation response characteristics. There is a strong correspondence between functional groupings, light regime and habitat moisture. The light response traits, particularly photoinhibition, are strongly associated with light regime. Photosynthetic capacity, moisture content and ability to recover photochemistry upon rehydration, correspond to habitat moisture. Life form was also strongly associated with functional groupings, particularly with the desiccation response traits.