THE INFLUENCE OF WATER-CONTENT ON THE LIGHT CLIMATE WITHIN ANTARCTIC MOSSES CHARACTERIZED USING AN OPTICAL MICROPROBE

The light climate within wet and dry samples of ten mosses from the ma ritime Antarctic was determined using a computer-controlled optical mi croprobe system. Irradiances decreased with increasing depth within th e moss. The rate of attenuation varied greatly between replicates refl ecting the heterogeneity of the moss macro-structure. Attenuation maxi ma were observed at wavelengths corresponding to the peaks of chloroph yll absorption around 675 nm and below 450 nm, although the inter-wave length differences were small compared to the inter-replicate variatio n. Wide inter-specific variations in light penetration were observed. These were dependent upon a number of factors, of which the most impor tant appeared to be stem orientation, with stem density, leaf size and orientation and pigment content possibly also affecting light absorpt ion. In most mosses the inter-wavelength variation was lost and the de pth of light penetration was increased on drying. The degree to which light penetration changed on dehydration was dependent upon the relati ve effects of structural and pigment changes. It is suggested that, as drying occurs, the increased penetration of light into the moss incre ases the photosynthetic potential of deeper layers, and hence reduces the loss of productivity by the moss.