title: Transplant experiments uncover Baltic Sea basin-specific responses in bacterioplankton community composition and metabolic activities.
abstract: Anthropogenically induced changes in precipitation are projected to generate increased river runoff to semi-enclosed seas, increasing loads of terrestrial dissolved organic matter and decreasing salinity. To determine how bacterial community structure and functioning adjust to such changes, we designed microcosm transplant experiments with Baltic Proper (salinity 7.2) and Bothnian Sea (salinity 3.6) water. Baltic Proper bacteria generally reached higher abundances than Bothnian Sea bacteria in both Baltic Proper and Bothnian Sea water, indicating higher adaptability. Moreover, Baltic Proper bacteria growing in Bothnian Sea water consistently showed highest bacterial production and beta-glucosidase activity. These metabolic responses were accompanied by basin-specific changes in bacterial community structure. For example, Baltic Proper Pseudomonas and Limnobacter populations increased markedly in relative abundance in Bothnian Sea water, indicating a replacement effect. In contrast, Roseobacter and Rheinheimera populations were stable or increased in abundance when challenged by either of the waters, indicating an adjustment effect. Transplants to Bothnian Sea water triggered the initial emergence of particular Burkholderiaceae populations, and transplants to Baltic Proper water triggered Alteromonadaceae populations. Notably, in the subsequent re-transplant experiment, a priming effect resulted in further increases to dominance of these populations. Correlated changes in community composition and metabolic activity were observed only in the transplant experiment and only at relatively high phylogenetic resolution. This suggested an importance of successional progression for interpreting relationships between bacterial community composition and functioning. We infer that priming effects on bacterial community structure by natural episodic events or climate change induced forcing could translate into long-term changes in bacterial ecosystem process rates.
authors.affiliation: Centre for Ecology and Evolution in Microbial Model Systems, Linnaeus University, Kalmar Sweden.
authors.forename: Markus V
authors.initials: MV
authors.lastname: Lindh
authors.affiliation: Department of Ecology and Environmental Science, Umeå University, Umeå Sweden ; Umeå Marine Sciences Centre, Umeå University, Umeå Sweden.
authors.forename: Daniela
authors.initials: D
authors.lastname: Figueroa
authors.affiliation: Centre for Ecology and Evolution in Microbial Model Systems, Linnaeus University, Kalmar Sweden.
authors.forename: Johanna
authors.initials: J
authors.lastname: Sjöstedt
authors.affiliation: Centre for Ecology and Evolution in Microbial Model Systems, Linnaeus University, Kalmar Sweden ; Department of Marine Science, University of Otago, Dunedin New Zealand.
authors.forename: Federico
authors.initials: F
authors.lastname: Baltar
authors.affiliation: Centre for Ecology and Evolution in Microbial Model Systems, Linnaeus University, Kalmar Sweden.
authors.forename: Daniel
authors.initials: D
authors.lastname: Lundin
authors.affiliation: Department of Ecology and Environmental Science, Umeå University, Umeå Sweden ; Umeå Marine Sciences Centre, Umeå University, Umeå Sweden.
authors.forename: Agneta
authors.initials: A
authors.lastname: Andersson
authors.affiliation: Centre for Ecology and Evolution in Microbial Model Systems, Linnaeus University, Kalmar Sweden.
authors.forename: Catherine
authors.initials: C
authors.lastname: Legrand
authors.affiliation: Centre for Ecology and Evolution in Microbial Model Systems, Linnaeus University, Kalmar Sweden.
authors.forename: Jarone
authors.initials: J
authors.lastname: Pinhassi
keywords: DOM; bacterial community functioning; bacterial diversity; climate change; marine bacteria; salinity; terrigenous carbon