Thermal discharge-created increasing temperatures alter the bacterioplankton composition and functional redundancy
Xiong et al. AMB Expr
Thermal discharge-created increasing temperatures alter the bacterioplankton composition and functional redundancy
Jinbo Xiong 0 3
Shangling Xiong 0 2
Peng Qian 0
Demin Zhang 0 3
Lian Liu 1
Yuejun Fei 1
0 School of Marine Sciences, Ningbo University , Ningbo 315211 , China
1 Marine Environmental Monitoring Center of Ningbo, SOA , Ningbo 315012 , China
2 College of Biological and Environmental Sciences, Zhejiang Wanli University , Ningbo 315000 , China
3 Collaborative Innovation Center for Zhejiang Marine High-efficiency and Healthy Aquaculture , Ningbo 315211 , China
Elevated seawater temperature has altered the coupling between coastal primary production and heterotrophic bacterioplankton respiration. This shift, in turn, could influence the feedback of ocean ecosystem to climate warming. However, little is known about how natural bacterioplankton community responds to increasing seawater temperature. To investigate warming effects on the bacterioplankton community, we collected water samples from temperature gradients (ranged from 15.0 to 18.6 °C) created by a thermal flume of a coal power plant. The results showed that increasing temperatures significantly stimulated bacterial abundance, grazing rate, and altered bacterioplankton community compositions (BCCs). The spatial distribution of bacterioplankton community followed a distance similarity decay relationship, with a turnover of 0.005. A variance partitioning analysis showed that temperature directly constrained 2.01 % variation in BCCs, while temperature-induced changes in water geochemical and grazing rate indirectly accounted for 4.03 and 12.8 % of the community variance, respectively. Furthermore, the relative abundances of 24 bacterial families were linearly increased or decreased (P < 0.05 in all cases) with increasing temperatures. Notably, the change pattern for a given bacterial family was in concert with its known functions. In addition, community functional redundancy consistently decreased along the temperature gradient. This study demonstrates that elevated temperature, combined with substrate supply and trophic interactions, dramatically alters BCCs, concomitant with decreases in functional redundancy. The responses of sensitive assemblages are temperature dependent, which could indicate temperature departures.
Thermal discharge; Bacterioplankton community compositions; Spatial distribution; Sensitive assemblages; Functional redundancy
Introduction
Climate warming has led to an accelerating pace of
elevated seawater temperature (EST)
(Brown et al.
2004)
, which is evidenced by long-term observations
and prediction model
(Pachauri et al. 2014; Vezzulli
et al. 2012)
. The EST has imposed negative effects on
ocean ecosystems (Hoegh-Guldberg and Bruno 2010),
such as expanded range of red tides
(McLeod et al.
2012)
, enhanced mass mortality of benthic organisms
(Coma et al. 2009)
, and increased virulence of bacterial
pathogens
(Bally and Garrabou 2007)
. The indoor
mesocosms studies have found that warming tightens the
coupling between phytoplankton production and
bacterial respiration, thus leading to an increased recycling of
organic matter (and CO2)
(Hoppe et al. 2008; Scheibner
et al. 2014; Wohlers et al. 2009)
. It is now recognized that
the biological carbon pool of the oceans largely relies on
the balance between primary production and microbial
respiration (Calleja et al. 2005), which is one of the major
uncertainties in predicting future climate warming.
However, despite its importance, the knowledge on how
bacterioplankton community responds to ocean warming is
scarce.
Long-term observational data have shown that ocean
warming significantly alters microbial community
composition
(Hoegh-Guldberg and Bruno 2010; Vezzulli
et al. 2012)
. However, this approach is restricted because
there are few long-term data sets available.
Alternatively, laboratory manipulation of temperature has been
adopted to address warming effects on microbial
activities, while the conclusions are contradictory
(Hoppe
et al. 2008; Sarmento et al. 2010; Wohlers et al. 2009)
. For
example, bacterial respiration is consistently accelerated
(Hoppe et al. 2008), or unaffected
(Wohlers et al. 2009)
along seawater temperature gradient. Interestingly, there
are similarly confusing results regarding the structures of
bacterioplankton community, with some cases showing
thermal sensitivity
(Dziallas and Grossart 2011;
Scheibner et al. 2014)
, and others not
(Shade et al. 2012b)
. It is
likely that the direct warming effects are overridden by
other abiotic and/or biotic factors, e.g., warming-induced
changes in nutrient levels and grazing rate.
Consistently, a few studies have shown that predation pressure
is the major driver of differences in bacterial assemblages
(Scheibner et al. 2014; Zöllner et al. 2009)
. However, the
stochastic nature of hydrology, i.e., daily tide and water
flow, could create pronounced (...truncated)