Dead or alive? Testing the use of C:N ratios and chlorophyll fluorescence in vertical shoot profiles to determine depth of vitality and point of senescence in populations of bryophytes.

Bryophytes with indeterminate growth rarely exhibit clearly identifiable modules or age segments, but can be vertically divided into different physiologically active zones, since physiological activity normally declines vertically along the shoot profile depth. The aim of this study was to investigate whether it is possible to use C:N ratios (C/N) and/or parameters from chlorophyll fluorescence measurements (e.g. Fv/Fm, Fm or qN) to determine if bryophyte tissue is alive, senescent or dead, and at what distance along the shoot segment profile the moss tissue cease to live. Variation in C:N ratios and chlorophyll fluorescence between sites was also examined. This study shows that it is possible to separate alive, senescing and dead parts of the moss shoots in Pleurozium schreberi, and that chlorophyll fluorescence is a good method to use, whereas C/N varies between sites and species (for Hylcomium splendens and Racomitrium lanuginosum) and does not seem to reflect physiological activity to the same degree.