The influence of incubation periods on photosynthesis–irradiance curves

Abstract

In phytoplankton primary production studies, samples for the determination of photosynthesis versus irradiance relationship ( P -I) are usually incubated at several irradiance levels during a fixed time period, commonly 2 -4 h. However, it is not clear if the use of this fixed incubation time is appropriate to study the P -I relationship in any given ecosystem. The aim of this work was to study the influence of incubation time on the P -I relationship in natural phytoplankton populations from three different coastal ecosystems: an open coastal area, an estuary, and a coastal lagoon. Physical and chemical variables, phytoplankton biomass, species composition, and P -I curves were analysed. The results showed that, in the coastal area and in the estuary, P -I relationships were time dependent, whereas in the coastal lagoon different incubation periods produced the same P -I curve. An underestimation of daily primary production, ranging from 13% to 42.5%, was calculated when data from standard incubation times (2 -4 h) were used in ecosystems where P -I curves present a dynamic time-dependent behaviour. This work suggests that the response of the P -I curves to the incubation time varies with the characteristics of the ecosystem and is related to the light regime to which phytoplankton cells are adapted. D

Phytoplankton production modelling in three marine ecosystems—static versus dynamic approach

“…1). The sampling location has a depth of 15 m and chlorophyll concentration (Chla) mean values are around 1 mg Chla m −3 (Macedo et al, 2002). The water is very turbid, with annual values of suspended matter ranging from 45 to 120 mg l −1 .…”

“…It consisted of using a towing net with three filtering cones with different gauze (200, 41 and 15 m) nested inside each other. Photosynthetic parameters were calculated from the P-E curves obtained (see Macedo et al, 2002).…”

“…The values used to initialise the model regarding phytoplankton biomass, salinity, temperature and nutrient concentrations are presented in Table 4 and were determined by Macedo et al (2002).…”

“…On the other hand, production stops shortly after light is switched off, while recovery from photoinhibition takes longer (Kok, 1956;Belay, 1981). Previous model and experimental results suggest that static P-E curves might lead to a significant underestimation of phytoplankton primary productivity (Duarte and Ferreira, 1997;Macedo et al, 2002).…”

“…Experimental evidence suggests that in many cases the static description of the P-E relationship is not appropriate (Marra, 1978;Neale and Marra, 1985;Pahl-Wostl, 1992;Macedo et al, 1998Macedo et al, , 2002. In fact, the photosynthetic parameters depend on light intensities recently experienced by the organisms.…”