Total FAs (and SFAs and MUFAs) in all species showed click here significant negative correlations with N cell quota (QN) under N deficiency, but PUFAs had species-specific correlations with
QN. The results show that characteristic FA profiles of algal genus or species (representing particular algal classes) underlie fluctuations according to culture conditions. The significant correlation between FAs and QN under N deficiency suggests that elemental and biochemical limitation of phytoplankton should be considered mutually as determinants of food quality for zooplankton in marine ecosystems. The transfer of energy and matter across the plant–herbivore interface is of critical importance in aquatic food webs (Lindeman 1942, Brett and Müller-Navarra 1997). The factors regulating the trophic transfer efficiency have been widely studied. Of all limiting factors, elemental and biochemical limitation of phytoplankton have been suggested as major determinants of food quality for herbivorous zooplankton (Gulati and DeMott 1997, Sterner and Schulz 1998, Anderson et al. 2004, Müller-Navarra 2008). Elemental (especially HIF-1�� pathway phosphorus; P) versus biochemical (especially FAs) limitation of food quality for zooplankton is a well-known controversy, which has attracted more attention in limnology than in marine ecology (Lampert 2009).
To date, studies have considered these two limiting factors as mutually nonexclusive mechanisms in freshwater environments (Gulati and DeMott 1997, Lynn et al. 2000, Boersma et al. 2001, Gladyshev et al. 2007); however, there is no information on the relationship between elemental and biochemical limitation of phytoplankton in marine ecosystems. Nitrogen (N):P concentrations and supply ratios reveal a strong spatiotemporal variability in coastal seas and some oceanic areas (Karl et al. 1993, Cavender-Bares et al. 2001, Twomey and Thompson
2001, Ford et al. 2008, Lam and Kuypers 2011). Under a large variation in N and P supplies, nonhomeostasis of phytoplankton N:P stoichiometry was observed in several classic Y-27632 2HCl chemostat experiments (Rhee 1978, Goldman et al. 1979, Ahlgren 1985), as well as in our previous study (Bi et al. 2012), which analyzed how the intracellular concentrations (cell quota) of N and P (QN and QP) varied in dependence of N:P supply ratios and μ. The results in our previous study show that the relationship between QN (and QP) and μ can be interpreted from biochemical considerations (Bi et al. 2012). FAs are key biochemicals in the regulation of trophic interactions (Müller-Navarra 2008). FAs as basic constituents of lipids play an important role in cellular membrane functions, energy storage, and metabolic processes (Mourente et al. 1990, Roessler 1990, Guschina and Harwood 2009).