Diurnal variation in photochemical dynamics and surface reflectance of thedesiccation-tolerant moss, Tortula ruralis

Most desiccation-tolerant plants alter shoot structure during drying, makin g it possible to use changes in surface reflectance as a proxy measure of p lant water status. Diurnal courses of surface reflectance (albedo) and chlo rophyll fluorescence parameters of the ectohydric moss, Tortula ruralis (He dw.) Gaertn, were measured to assess the coordination between anatomical an d physiological features under field conditions. Albedo showed a sigmoidal relationship with relative humidity and the deviation of moss mat temperatu re from dew point. Maximum photosynthetic quantum yield (F-v/F-m) also disp layed a sigmoidal relationship pooled across three days differing in light, temperature, and relative humidity. Depending on the light conditions and rapidity of drying during the morning, there were distinct differences in t he ability of T. ruralis to establish thermal dissipation of excess light e nergy (NPQ) across a range of light levels following rehydration through th e day. These findings suggest that there is a coordinated suite of architec tural and physiological characteristics maintaining the photosynthetic inte grity of these plants in highly variable arid and semi-arid environments.