Effect of light on photosynthetic efficiency of sequestered chloroplasts in intertidal benthic foraminifera (iHaynesina germanica/i and iAmmonia tepida/i)

摘要

Some benthic foraminifera have the ability to incorporate functional chloroplasts from diatoms (kleptoplasty). Our objective was to investigate chloroplast functionality of two benthic foraminifera (iHaynesina germanica/i and iAmmonia tepida/i) exposed to different irradiance levels (0, 25, 70?μmol?photon?msup?2/sup?ssup?1/sup) using spectral reflectance, epifluorescence observations, oxygen evolution and pulse amplitude modulated (PAM) fluorometry (maximum photosystem II quantum efficiency (Fv/Fm) and rapid light curves (RLC)). Our results clearly showed that iH. germanica/i was capable of using its kleptoplasts for more than 1?week while iA. tepida/i showed very limited kleptoplastic ability with maximum photosystem II quantum efficiency (Fv/Fm??=??0.4), much lower than iH. germanica/i and decreasing to zero in only 1?day. Only iH. germanica/i showed net oxygen production with a compensation point at 24?μmol?photon?msup?2/sup?ssup?1/sup and a production up to 1000?pmol?Osub2/sub?cellsup?1/sup?daysup?1/sup at 300?μmol?photon?msup?2/sup?ssup?1/sup. iHaynesina germanica/i Fv/Fm slowly decreased from 0.65 to 0.55 in 7?days when kept in darkness; however, it quickly decreased to 0.2 under high light. Kleptoplast functional time was thus estimated between 11 and 21?days in darkness and between 7 and 8?days at high light. These results emphasize that studies about foraminifera kleptoplasty must take into account light history. Additionally, this study showed that the kleptoplasts are unlikely to be completely functional, thus requiring continuous chloroplast resupply from foraminifera food source. The advantages of keeping functional chloroplasts are discussed but more information is needed to better understand foraminifera feeding strategies.