Differential growth response of Ulva lactuca to ammonium and nitrate assimilation

Abstract

Controlled cultivation of marine macroalgal biomass such as Ulva species, notably Ulva lactuca, is currently studied for production of biofuels or functional food ingredients. In a eutrophic environment, this macrophyte is exposed to varying types of nutrient supply, including different and fluctuating levels of nitrogen sources. Our understanding of the influences of this varying condition on the uptake and growth responses of U. lactuca is limited. In this present work, we examined the growth response of U. lactuca exposed to different sources of nitrogen (NH 4 + ; NO 3 − ; and the combination NH 4 NO 3 ) by using photo-scanning technology for monitoring the growth kinetics of U. lactuca. The images revealed differential increases of the surface area of U. lactuca disks with time in response to different N-nutrient enrichments. The results showed a favorable growth response to ammonium as the nitrogen source. The NH 4 Cl and NaNO 3 rich media (50 μM of N) accelerated U. lactuca growth to a maximum specific growth rate of 16.4±0.18% day −1 and 9.4±0.72% day −1 , respectively. The highest biomass production rate obtained was 22.5±0.24 mg DW m −2 ·day −1 . The presence of ammonium apparently discriminated the nitrate uptake by U. lactuca when exposed to NH 4 NO 3 . Apart from showing the significant differential growth response of U. lactuca to different nitrogen sources, the work exhibits the applicability of a photo-scanning approach for acquiring precise quantitative growth data for U. lactuca as exemplified by assessment of the growth response to two different N-sources.

Uptake kinetics and storage capacity of dissolved inorganic phosphorus and corresponding N:P dynamics in Ulva lactuca (Chlorophyta)

“…), which aligns with reported results for U. lactuca by other authors (Ale et al. ). This decrease in growth may be caused by a shift to a reproductive state, inhibiting vegetative growth in U. lactuca (Bruhn et al.…”

“…Determination of SA, as a nondestructive method to infer growth, showed a gradual decrease in growth (Fig. 2), which aligns with reported results for U. lactuca by other authors (Ale et al 2011). This decrease in growth may be caused by a shift to a reproductive state, inhibiting vegetative growth in U. lactuca (Bruhn et al 2011).…”

“…Ale et al. () reported nitrate uptake of ~70 μmol · g DW −1 · d −1 for U. lactuca , which is an equivalent to ~3.5 μmol · cm −2 · d −1 , given our correlation factors (Fig. ).…”

“…It should be noted that the presence of ammonium (NH 4 + ) can influence the uptake of nitrate in U. lactuca (Ale et al. , Holdt and Kraan ). In our study, daily DIN uptake was not significantly affected ( R = −0.027) by the presence of ammonium (NH 4 + ).…”

Macroalgal blooms favor heterotrophic diazotrophic bacteria in nitrogen-rich and phosphorus-limited coastal surface waters in the Yellow Sea

“…We found that the concentrations of NH 4 þ were significantly lower at sites with canopies than at those without, suggesting that NH 4 þ is a favorable N source for the growth of Ulva (Ale et al, 2011) and for macroalgal canopies that had not undergone massive decomposition; otherwise, there should have higher NH 4 þ concentrations in CC than in CF waters. This observation is largely in line with previous studies indicating the importance of DIN during the growth of macroalgae and a large nitrogen storage capability in their tissues (Valiela et al, 1992(Valiela et al, , 1997Pedersen and Borum, 1996;Men endez et al, 2002).…”