Literature values for photosynthetic rates in Cladophora glomerata vary widely. There are several possible reasons for this, including light-limitation in certain types of experiments. Photosynthesis and respiration in Cladophora appear to be strongly pH dependent. Photosynthesis in Cladophora samples from Lake Erie show a pH optimum of about pH 8.2, with rates decreasing to near zero by pH 9.6. Respiration shows a bimodal pH response curve, with optima at about pH 7.6 and pH 9.2. Thus, experiments performed in unbuffered systems can greatly underestimate photosynthesis in Cladophora due to pH changes caused by CO 2 uptake. Choice of buffers is an important consideration. Tricine is considered to be biologically unreactive and has a pK of 8.15, making it an ideal buffer for use in slightly alkaline systems. Tris buffer, however, shifts the pH optimum for photosynthesis in Cladophora (measured as oxygen evolution) to about pH 9.0. The response curve for respiration is the same in either buffer. Photosynthesis in Cladophora is depressed in a 100% oxygen atmosphere, suggesting that these cells photorespire. This further complicates estimates of net photosynthesis.