Temperature control of marine heterotrophic prokaryotes: a latitudinal gap between bottom-up and top-down controls

Abstract

Untangling the controlling factors of planktonic prokaryotes is paramount for better predict biogeochemical cycles in a changing ocean. The ecological question of when and where they are controlled by resource availability (bottom-up), protistan and viral losses (top-down) or temperature has long intrigued us. An extensive dataset of heterotrophic prokaryotes biomass and productivity from the Malaspina 2010 Circumnavigation Expedition was used in this study. Samples were collected from the surface down to 4000 m depth at 109 stations across the Atlantic, Indian and Pacific Oceans. We found a systematic negative relationship between bottom-up and temperature controls only lost under strong top-down control. Control by temperature could be seen as a gap opened in the solid wall of bottom-up and top-down regulation, peaking at moderate values of these two opposing controls. Our analysis also unveiled a remarkable latitudinal pattern in temperature control, which increased polewards regardless of the oceanic basin. Low temperature control between 20°N and 30°S suggests that global warming will have a limited effect on microbial standing stocks and activity in the tropics relative to higher latitude regions