Effects of ultraviolet and photosynthetically active radiation on five seagrass species

摘要: Five seagrass species [Halophila ovalis (R.Br) Hook. f., Halodule uninervis (Forsk.) Aschers., Zostera capricorni Cymodocea serrulata Aschers. (ed.) and Syringodium isoetifolium (Aschers.) Dandy] from Moreton Bay, Australia, were grown under increased (+25%) ambient levels of ultraviolet (UV) radiation photosynthetically active (PAR), various morphological physiological responses examined. Leaf fluorescence ratio (variable:maximum fluorescence) in conjunction with xanthophyll pigment content (violaxanthin, antheraxanthin zeaxanthin) used as a measure photosynthetic efficiency. In addition, absorbance the UV spectrum, chlorophyll chloroplast density indicators capacity. The examined had varying degrees sensitivity to radiation. Halophila most sensitive species, exhibiting largest decrease efficiency smallest increase UV-blocking pigments response more UV-tolerant Z. capricorni, C. S. isoetifolium, only significantly affected by radiation, showing gradual decline increases pigment. corresponded leaf morphology, thicker leaves (as isoetifolium) providing greater protection for UV-sensitive organelles. Not all increasing PAR, decreases zeaxanthin observed isoetifolium. Sensitivity PAR plasticity; wide range growth forms (e.g. ovalis, capricorni) least PAR. Seagrass depth-distributions Bay appear be influenced other factors such epiphytes, shading nutrients also affecting species' tolerance. All some degree thus future changes intensity may have repercussions on distribution seagrasses.