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Summary: The plant cuticle is an important plant‐atmosphere boundary, the synthesis and maintenance of which represents a significant metabolic cost. Only limited information regarding cuticle dynamics is available.We determined the composition and dynamics of Clusia rosea cuticular waxes and matrix using 13CO2 labelling, compound‐specific and bulk isotope ratio mass spectrometry. Collodion was used for wax collection; gas exchange techniques to test for any collodion effects on living leaves.Cutin matrix (MX) area density did not vary between young and mature leaves and between leaf sides. Only young leaves incorporated new carbon into their MX. Collodion‐based sampling discriminated between epicuticular (EW) and intracuticular wax (IW) effectively. Epicuticular differed in composition from IW. The newly synthetised wax was deposited in IW first and later in EW. Both young and mature leaves synthetised IW and EW. The faster dynamics in young leaves were due to lower wax coverage, not a faster synthesis rate. Longer‐chain alkanes were deposited preferentially on the abaxial, stomatous leaf side, producing differences between leaf sides in wax composition.We introduce a new, sensitive isotope labelling method and demonstrate that cuticular wax is renewed during leaf ontogeny of C. rosea. We discuss the ecophysiological significance of the new insights. [ABSTRACT FROM AUTHOR]

Summary: Stomata exert control on fluxes of CO2 and water (H2O) in the majority of vascular plants and thus are pivotal for planetary fluxes of carbon and H2O. However, in mosses, the significance and possible function of the sporophytic stomata are not well understood, hindering understanding of the ancestral function and evolution of these key structures of land plants.Infrared gas analysis and 13CO2 labelling, with supporting data from gravimetry and optical and scanning electron microscopy, were used to measure CO2 assimilation and water exchange on young, green, ± fully expanded capsules of 11 moss species with a range of stomatal numbers, distributions, and aperture sizes.Moss sporophytes are effectively homoiohydric. In line with their open fixed apertures, moss stomata, contrary to those in tracheophytes, do not respond to light and CO2 concentration. Whereas the sporophyte cuticle is highly impermeable to gases, stomata are the predominant sites of 13CO2 entry and H2O loss in moss sporophytes, and CO2 assimilation is closely linked to total stomatal surface areas.Higher photosynthetic autonomy of moss sporophytes, consequent on the presence of numerous stomata, may have been the key to our understanding of evolution of large, gametophyte‐independent sporophytes at the onset of plant terrestrialization. [ABSTRACT FROM AUTHOR]

The plant cuticle is an important plant-atmosphere boundary, the synthesis and maintenance of which represents a significant metabolic cost. Only limited information regarding cuticle dynamics is available. We determined the composition and dynamics of Clusia rosea cuticular waxes and matrix using 13 CO 2 labelling, compound-specific and bulk isotope ratio mass spectrometry. Collodion was used for wax collection; gas exchange techniques to test for any collodion effects on living leaves. Cutin matrix (MX) area density did not vary between young and mature leaves and between leaf sides. Only young leaves incorporated new carbon into their MX. Collodion-based sampling discriminated between epicuticular (EW) and intracuticular wax (IW) effectively. Epicuticular differed in composition from IW. The newly synthetised wax was deposited in IW first and later in EW. Both young and mature leaves synthetised IW and EW. The faster dynamics in young leaves were due to lower wax coverage, not a faster synthesis rate. Longer-chain alkanes were deposited preferentially on the abaxial, stomatous leaf side, producing differences between leaf sides in wax composition. We introduce a new, sensitive isotope labelling method and demonstrate that cuticular wax is renewed during leaf ontogeny of C. rosea. We discuss the ecophysiological significance of the new insights., (© 2023 The Authors. New Phytologist © 2023 New Phytologist Foundation.)