[Response of the artificial cyanobacterial crusts to low temperature and light stress and the micro-structure changes under laboratory conditions].

ABSTRACT

Low temperature and light are noticeable environmental conditions commonly experienced by cyanobacterial crusts growing in desert areas. Here we reported the effects of low temperature and light on the morphology, physiological characteristics and ultrastructural changes of artificial cyanobacterial crust. Firstly artificial cyanobacterial crusts were formed by inoculating Microcoleus vaginatus Gom. and Scytonema javanicum (Kütz.) Born et Flah onto shifting sand in Petri dishes. Then, the artificial cyanobacterial crusts were selected as the experimental materials and subjected to the following treatments 28 degrees C + 60 microE x (m2 x s)(-1) (control), 10 degrees C + 60 microE x (m2 x s)(-1), 2 degrees C +60 microE x (m2 x s)(-1) and 2 degrees C + dark. On the 0th, 5th and 12th days during the experimental period, biomass (expressed as Chl-a), photosynthetic activities (optimal quantum yield, Fv/Fm), exopolysaccharide (EPS), scytonemin, carotenoid and C-phycocyanin contents of the crusts in different treatments were determined. We also observed the ultrastructural changes of the cyanobacterial crusts in the control and 2 degrees C treatments by means of scan electron microscope (SEM). Moreover, the morphological properties such as crust color, crust thickness and crust dry weight etc. were also examined. The results indicated that the morphology of the treated crusts suffered unfavorable effect under light and low temperature stress, and Chl-a, Fv/Fm, EPS, scytonemin and carotenoid contents as well as C-phycocyanin content of the treated crusts were all significantly lower than those of the crusts under control conditions (P < 0.05). When the cyanobacterial crusts were treated for 12 days under 2 degrees C + 60 microE (m2 x s)(-1), Chl-a, Fv/Fm, EPS, scytonemin and carotenoid contents as well as C-phycocyanin content within the crusts decreased by 61.48%, 94.89%, 66.37%, 31.01%, 59.38%, and 65.91%, respectively. Obvious destruction in ultrastructure was observed in the cyanobacterial crust under cold stress, such as the presence of numerous honeycombs within the crusts and the sparse and loose appearance of the algal filaments, etc. The research verified that the acquired treatments had negative effects on the morphology, growth and microstructures of the cyanobacterial crusts, and the cooperation of low temperature and dark could provide effective protection for the morphological, physiological and microstructural features of the crust subjected to cold and light stress. The aim of this study was to primarily discuss the responses of cyanobacterial crusts to low temperature and light stress, and to offer a basic understanding of cyanobacterial crusts against extreme environments in fields, which may have certain academic significance for researches interested in cyanobactrial crusts.