THE SHORT‐TERM EFFECT OF IRRADIANCE ON THE PHOTOSYNTHETIC PROPERTIES OF ANTARCTIC FAST‐ICE MICROALGAL COMMUNITIES¹

Abstract

Although sea-ice represents a harsh physicochemical environment with steep gradients in temperature, light, and salinity, diverse microbial communities are present within the ice matrix. We describe here the photosynthetic responses of sea-ice microalgae to varying irradiances. Rapid light curves (RLCs) were generated using pulse amplitude fluorometry and used to derive photosynthetic yield (ΦPSII ), photosynthetic efficiency (α), and the irradiance (Ek ) at which relative electron transport rate (rETR) saturates. Surface brine algae from near the surface and bottom-ice algae were exposed to a range of irradiances from 7 to 262 μmol photons · m(-2) · s(-1) . In surface brine algae, ΦPSII and α remained constant at all irradiances, and rETRmax peaked at 151 μmol photons · m(-2) · s(-1) , indicating these algae are well acclimated to the irradiances to which they are normally exposed. In contrast, ΦPSII , α, and rETRmax in bottom-ice algae reduced when exposed to irradiances >26 μmol photons · m(-2) · s(-1) , indicating a high degree of shade acclimation. In addition, the previous light history had no significant effect on the photosynthetic capacity of bottom-ice algae whether cells were gradually exposed to target irradiances over a 12 h period or were exposed immediately (light shocked). These findings indicate that bottom-ice algae are photoinhibited in a dose-dependent manner, while surface brine algae tolerate higher irradiances. Our study shows that sea-ice algae are able to adjust to changes in irradiance rapidly, and this ability to acclimate may facilitate survival and subsequent long-term acclimation to the postmelt light regime of the Southern Ocean.

Can bottom ice algae tolerate irradiance and temperature changes?

“…(Martin et al, 2012;McMinn et al, 2010;Ryan et al, 2009Ryan et al, , 2012. The explanation for this is unclear, and yield values recovered to more normal levels in low temperature incubations.…”

“…Three to five replicate cores were collected at each location. During collection, the cores were protected from PAR exposure by performing all operations underneath a black sheet, then immediately transferring them into opaque black plastic bags and placing into insulated boxes (Ryan et al, 2009. The bottom of each core was then cut into a standard size (width × height × length of 4 × 4 × 10 cm) in a dimly lit room (1-10 μmol m − 2 s − 1 ), and melted into three times the quantity of filtered seawater (35‰, 0.22 μm, − 1.8°C) in the dark over a period of 12 h (Mundy et al, 2011;Ryan et al, 2006).…”

“…As the ϕ PSII value is a ratio and ETR is derived from this parameter, it is termed relative ETR (rETR). An RLC permits derivation of different parameters that can be used to describe the photosynthetic properties of an algal sample, including rETR max (the maximum value for rETR), photosynthetic efficiency (α) and saturation irradiance (E k ) (Ryan et al, 2009). To determine these parameters, the rETR data were imported into Microsoft Excel v 10.0 (Microsoft, USA) and the curve was fitted with a "waiting-in-line" function (Ritchie, 2008).…”

“…Antarctic bottom ice algal communities are thought to be extremely shade-adapted, with low E k values (saturation irradiance, a measure of the intensity of PAR required to permit maximum photosynthesis), and are able to adjust photosynthetic rates to suit changing diurnal irradiance levels (Arrigo et al, 1997;Ryan et al, 2009). Low PAR conditions are typical of the underice environment (Lizotte, 2001).…”

Effects of temperature and irradiance on photosynthesis and growth of a green-tide-forming species (Ulva linza) in the Yellow Sea

“…Error bars=SD ambiguous problem involves controversial issues in chlorophyll fluorescence measurements. Therefore, rETR values were calculated by multiplying the Φ PSII by the irradiance applied (Ryan et al 2009). Steady-state light curves (LCs) were constructed with full light adapted for 1-h and long-term (7-d) examination.…”