Life at the boundary: photosynthesis at the soil-fluid interface. A synthesis focusing on mosses

Mosses are among the earliest branching embryophytes and probably originated not later than the early Ordovician when atmospheric CO₂ was higher and O₂ was lower than today. The C₃ biochemistry and physiology of their photosynthesis suggests, by analogy with tracheophytes, that growth of extant bryophytes in high CO₂ approximating Ordovician values would increase the growth rate. This occurs for many mosses, including Physcomitrella patens in suspension culture, although recently published transcriptomic data on this species at high CO₂ and present-day CO₂ show down-regulation of the transcription of several genes related to photosynthesis. It would be useful if transcriptomic (and proteomic) data comparing growth conditions are linked to measurements of growth and physiology on the same, or parallel, cultures. Mosses (like later-originating embryophytes) have been subject to changes in bulk atmospheric CO₂ and O₂ throughout their existence, with evidence, albeit limited, for positive selection of moss Rubisco. Extant mosses are subject to a large range of CO₂ and O₂ concentrations in their immediate environments, especially aquatic mosses, and mosses are particularly influenced by CO₂ generated by, and O₂ consumed by, soil chemoorganotrophy from organic C produced by tracheophytes (if present) and bryophytes.