160
et al. 2019). Under P limitation, cultures of both Trichodesmium and Crocosphaera
exhibit higher growth and N 2 fixation rates when Fe is also limiting than when it is
replete. Several strains of the unicellular marine diazotroph, Crocosphaera have
also been assessed for their responses to increasing CO 2 (Hutchins et al. 2013) and
temperature (Fu et al. 2014). Results indicated that strains of each showed distinct
temperature and CO 2 optima. Fe-limited Trichodesmium cells exhibit a 5 °C higher
optimum growth temperature as a result of enhanced iron use efficiency (Jiang
et al. 2018).
Irradiance fields of plankton populations will be altered with greater upper ocean
stratification: deeper convective mixing will be reduced in some biomes, exposing
upper water column populations to higher integrated daily levels of light (Table 9.1).
Light itself can effect differential N 2 fixation responses to CO 2 concentration, CO 2
fixation, growth and photosynthetic efficiency in Trichodesmium: higher irradiances
reduce the stimulatory effect of CO 2 on N 2 fixation while the opposite occurs with
CO 2 fixation (Garcia et al. 2011; see also Boatman et al. 2017, 2019). Elevated NO 3
-
concentrations, as might result from climate change, were inhibitory to N 2 fixation
at low light levels, but not at higher irradiance and led to overall higher growth rates
(Garcia and Hutchins 2014).
While many studies have examined changes in CO 2 concentrations or pCO 2 , and
have reported concurrent changes in pH (Eichner et al. 2014b; Hutchins et al. 2007),
far fewer have explicitly isolated the effects of pCO 2 and pH. One study reported
stronger negative effects of decreasing pH which offset positive enrichment effects
of CO 2 increases in Trichodesmium (Hong et al. 2017).
Hence, the relative composition of the upper ocean diazotrophic flora could shift
substantially as all of these various physical and chemical factors co-vary (Fu et al.
2014). Recent studies have focused on elucidating the underlying mechanisms for
these responses using transcriptomics (Hong et al. 2017; Walworth et al. 2016a) and
modeling (Luo et al. 2019). Other studies have considered the longer term adaptation and evolution of diazotrophic populations. For instance, long-term exposure of
Trichodesmium to elevated CO 2 results in adaptive responses encoded in their
underlying genome (Hutchins et al. 2015; Walworth et al. 2016a, b).
Harmful algal blooms (HABs) are another increasing global phenomenon in
marine coastal waters (Gobler 2020)(Table 9.1). The expansion of these blooms
which include eukaryotic dinoflagellate and diatom species as well as cyanobacterial taxa have been linked to various aspects of environmental change including
eutrophication, surface warming and increasing CO 2 concentrations (among other
factors)(Gobler 2020; Wurtsbaugh et al. 2019). The large potentially toxic diazotrophic blooms of Nodularia and Nostoc in the Baltic Sea which have occurred seasonally for many decades have been mentioned in Chaps. 4 and 7 (Gobler 2020;
Wurtsbaugh et al. 2019). Other highly toxic cyanobacterial species also appear to be
expanding in their extent and frequency of blooms. In several coastal systems of
Australia, including Moreton Bay off Brisbane and the Peel- Harvey estuary in
southwest Australia, blooms of the benthic cyanobacteria, Lyngbya majuscule, have
become common (O’Neil et al. 2012).
9 Marine N 2 Fixation, Global Change and the Future
et al. 2019). Under P limitation, cultures of both Trichodesmium and Crocosphaera
exhibit higher growth and N 2 fixation rates when Fe is also limiting than when it is
replete. Several strains of the unicellular marine diazotroph, Crocosphaera have
also been assessed for their responses to increasing CO 2 (Hutchins et al. 2013) and
temperature (Fu et al. 2014). Results indicated that strains of each showed distinct
temperature and CO 2 optima. Fe-limited Trichodesmium cells exhibit a 5 °C higher
optimum growth temperature as a result of enhanced iron use efficiency (Jiang
et al. 2018).
Irradiance fields of plankton populations will be altered with greater upper ocean
stratification: deeper convective mixing will be reduced in some biomes, exposing
upper water column populations to higher integrated daily levels of light (Table 9.1).
Light itself can effect differential N 2 fixation responses to CO 2 concentration, CO 2
fixation, growth and photosynthetic efficiency in Trichodesmium: higher irradiances
reduce the stimulatory effect of CO 2 on N 2 fixation while the opposite occurs with
CO 2 fixation (Garcia et al. 2011; see also Boatman et al. 2017, 2019). Elevated NO 3
-
concentrations, as might result from climate change, were inhibitory to N 2 fixation
at low light levels, but not at higher irradiance and led to overall higher growth rates
(Garcia and Hutchins 2014).
While many studies have examined changes in CO 2 concentrations or pCO 2 , and
have reported concurrent changes in pH (Eichner et al. 2014b; Hutchins et al. 2007),
far fewer have explicitly isolated the effects of pCO 2 and pH. One study reported
stronger negative effects of decreasing pH which offset positive enrichment effects
of CO 2 increases in Trichodesmium (Hong et al. 2017).
Hence, the relative composition of the upper ocean diazotrophic flora could shift
substantially as all of these various physical and chemical factors co-vary (Fu et al.
2014). Recent studies have focused on elucidating the underlying mechanisms for
these responses using transcriptomics (Hong et al. 2017; Walworth et al. 2016a) and
modeling (Luo et al. 2019). Other studies have considered the longer term adaptation and evolution of diazotrophic populations. For instance, long-term exposure of
Trichodesmium to elevated CO 2 results in adaptive responses encoded in their
underlying genome (Hutchins et al. 2015; Walworth et al. 2016a, b).
Harmful algal blooms (HABs) are another increasing global phenomenon in
marine coastal waters (Gobler 2020)(Table 9.1). The expansion of these blooms
which include eukaryotic dinoflagellate and diatom species as well as cyanobacterial taxa have been linked to various aspects of environmental change including
eutrophication, surface warming and increasing CO 2 concentrations (among other
factors)(Gobler 2020; Wurtsbaugh et al. 2019). The large potentially toxic diazotrophic blooms of Nodularia and Nostoc in the Baltic Sea which have occurred seasonally for many decades have been mentioned in Chaps. 4 and 7 (Gobler 2020;
Wurtsbaugh et al. 2019). Other highly toxic cyanobacterial species also appear to be
expanding in their extent and frequency of blooms. In several coastal systems of
Australia, including Moreton Bay off Brisbane and the Peel- Harvey estuary in
southwest Australia, blooms of the benthic cyanobacteria, Lyngbya majuscule, have
become common (O’Neil et al. 2012).
9 Marine N 2 Fixation, Global Change and the Future