| Abstrakt: |
The relationships between primary production and irradiance were analyzed over an annual cycle in natural BIOFILMS of two undisturbed streams: La Solana (LS), anopen calcareous stream, and Riero Major (RM), a shaded siliceous stream. In LS, low photosynthetic efficiency (α[SUPchl] And α[SUParea]) and high values of both the light saturation parameter (I[SUBk]) and the carotenoid / chlorophyll ratio indicated adaption to high light regimes. On the other hand, higer photosynthetic efficiency and lower I as well as photoinhibition at high irradiance found in the biofilms of RM indicated shade adaption. However, the lack of correlation between light availability in nature and the photosynthetic behavior in this stream. Both in the open and shaded streams, algal patches collected simultaneously exhibited different photosynthesis-irradiance (P-I) curves, showing that community composition influnced the P-I parameters, in the open stream (LS), however, significant negative correlations between P[SUBmax] and chlorophyll a and between α[SUParea] and chlorophyll a (r = -0.994, P < 0.001. and r = -0.929, P < 0.05, respectively) suggested that photosynthetic rates were maintained at the ambient high light environment, thus compensating for low photosysnthsis at low irrandiance. In the shaded stream (RM), because photosythesis was saturated at low irradiance, primary production was relatively high given the low light conditions. [ABSTRACT FROM AUTHOR] |
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