Physiological ecology of selected Hawaiian mosses across environmental gradients

Ph.D. University of Hawaii at Manoa 2010.Includes bibliographical references.Mosses are an understudied group of plants that can potentially confirm or expand principles of plant function described for tracheophytes, from which they diverge strongly in structure. Resaerch was undertaken to assess whether mosses follow patterns already observed in vascular plants such as optimization of performance by modification of functional "clusters" of trait-trait and trait-environment correlations, increase of tissue δ13C associated with greater microhabitat irradiance and altitude, and nutrient content and stoichiometry associated with soil fertiliy and other environmental gradients. A total of 40 physiological and morphological traits were measured from 17 ground-, trunk-and branch-dwelling Hawaiian moss species and one liverwort species to test the hypotheses that 1) trait values would reflect the distinctive growth form and slow growth of mosses, but also that trait correlations would be analogous to those of tracheophytes, 2) moss carbon isotope ratios would correlate with irradiance and elevation, and 3) moss nutrient concentrations would follow stoichiometric patterns found in vascular plants. The moss species had low leaf mass per area (LMA) and low gas exchange rates, but unlike tracheophytes, light-saturated photosynthetic rate per mass (Amass) did not correlate with habitat irradiance. Other photosynthetic parameters and structural traits were aligned with microhabitat irradiance, driving inter-correlation of traits including leaf area, cell size, cell wall thickness, and canopy density. Across species, Amass and nitrogen concentration correlated negatively with canopy mass per area (CMA), analogous to linkages found for the "leaf economic spectrum," with CMA replacing LMA. Bryophytes were remarkably similar to vascular plants in exhibiting greater δ13C with increasing elevation and microhabitiat irradiance. Results supported stoichiometric theory: mass-based nutrient concentrations increased with nutrient availability; area-based nutrient concentrations increased with irradiance as mediated by bryophyte canopy mass per area; N and P followed the general scaling shown previously for tracheophytes; and P increased and N:P decreased with elevation consistent with increasing cold tolerance. These findings extend the generality of stoichiometric theory, pointing to convergent physiological responses across distantly related lineages, operating across local and global resource gradients. Despite divergence of mosses and tracheophytes in leaf size and function, analogous trait coordination has arisen during ecological differentiation