Light dependence in the phototrophy–phagotrophy balance of constitutive and non-constitutive mixotrophic protists

SCHENONE, L.; BALSEIRO, E; MODENUTTI, B

Oecologia

Springer Science and Business Media Deutschland GmbH

Año: 2022 vol. 200 p. 295 - 306

Mixotrophic protists display contrasting nutritional strategies and are key groups connecting planktonic food webs. Theycomprise constitutive mixotrophs (CMs) that have an innate photosynthetic ability and non-constitutive mixotrophs (NCMs)that acquire it from their prey. We modelled phototrophy and phagotrophy of two mixotrophic protists as a function ofirradiance and prey abundance. We hypothesised that differences in their physiology (constitutive versus non-constitutivemixotrophy) can result in different responses to light gradients. We fitted the models with primary production and bacterivorydata from laboratory and field experiments with the nanoflagellate Chrysochromulina parva (CM) and the ciliateOphrydium naumanni (NCM) from north Andean Patagonian lakes. We found a non-monotonic response of phototrophyand phagotrophy to irradiance in both mixotrophs, which was successfully represented by our models. Maximum valuesfor phototrophy and phagotrophy were found at intermediate irradiance coinciding with the light at the deep chlorophyllmaxima in these lakes. At lower and higher irradiances, we found a decoupling between phototrophy and phagotrophy inthe NCM while these functions were more coupled in the CM. Our modelling approach revealed the difference betweenboth mixotrophic functional types on the balance between their nutritional strategies under different light scenarios. Thus,our proposed models can be applied to account how changing environmental conditions affect both primary and secondaryproduction within the planktonic microbial food web.