Methods for determining microalgal nutrient limitation

The merits and methodological limitations of several main approaches for determining microalgal nutrient limitation are briefly reviewed and compared. (1) The elemental ratios of microalgae can reflect the status of nutrient limitation,but the result is far from constant and easily influenced by light,CO_(2) availability and nutrient status. (2) Enrichment experiments have been commonly used to determine the nutrient limitation in phytoplankton and natural water,but it can be influenced by the species composition of the seeding inocula phytoplankton sample and addition of one macronutrient may induce limitation of other nu trients. (3) Nutrient uptake kinetics can be used for detecting microalgal nutrient limitation, as nutrient limited cells exhibit increased uptake capacity or efficiency for the specific nutrient after it is re-supplied. But the uptake rates vary with a range of factors including microalgal species, nutrient history and nutrient status. (4) Biochemical approach has been used extensively in the study of N, P and Fe deprivation, but this method entails destruction of the sample and time consuming, and complicated process. (5) Fourier-transform infrared microspectroscopie analysis can reveal dramatic spectral differences between nutrient-limited and nutrient-replete microalgal cells and represents a novel method to investigate macromolecular synthesis in response to changes in nutrient supply. But this method has the limitation of requiring bulky and expensive equipment. (6) The chlorophyll fluorescence measurements are non-destructive and highly sensitive, thus require only small volumes and low concentration of experimental samples. These characteristics make it become an increasing potential approach for exploring nutrient status of microalgae and their physiological response to varying environmental conditions.