acidification. Diatoms have unique cell walls made from silica and are responsible
for 25–45% of ocean primary productivity and export roughly 40% of particulate
carbon to the deep ocean for storage (Boyd et al. 2019). Ongoing acidification,
however, hinders their ability to form strong shells making them smaller and less
effective at carbon sequestration (Petrou et al. 2019).
Looking forward, increased rates of melting of sea ice means more sunlight
penetrating ocean waters in the Arctic. This will lengthen the growing season of
phytoplankton at high latitudes, and lead to higher phytoplankton biomass, which in
turn will further warm surface waters by pigment-induced changes in radiant
heating, triggering additional positive feedbacks (Park et al. 2015). In response to
increasing temperatures and changes in circulation, entire communities of common
cool-adapted phytoplankton are projected to move poleward before 2100, which
may have large effects on food webs (Barton et al. 2016). Assemblages of foraminifera (zooplankton), which live in darker, cooler waters, have already moved
poleward relative to pre-industrial distributions (Jonkers et al. 2019). In addition to
relocation, some species have been shown to adapt to modest increases in temperature and acidification, but often with costs, such as smaller, carbon-depleted cells
(Schlüter et al. 2014; Irwin et al. 2015). Acidification may also alter competition
among phytoplankton species, as well as antagonistic interactions. For example,
acidification may select for nuisance species, such as toxic microalga over those
providing ecosystem services, or impact the composition of viruses attacking phytoplankton, which are key factors controlling blooms (Riebesell et al. 2018;
Highfield et al. 2017). Continued inaction leading to sustained warming may result
in changes in wind patterns, water temperatures, ice cover, and circulation that
would transfer nutrients from surface waters into the deep ocean, starving current
ecosystems (Moore et al. 2018).
In terrestrial systems plant cells contain chloroplasts, photosynthesizing organelles of endosymbiotic origin that facilitated the dominance of this group with
respect to biomass and primary production (Bar-On et al. 2018). Vegetation and
soils are major carbon sinks, absorbing roughly 25% of anthropogenic CO 2 . Plant
communities also perform key roles in oxygen, nitrogen, and water cycles, and
strongly impact the diversity and distribution of land animals. The thermal tolerances
of plants are governed by biogeographic and evolutionary histories as well as local
environments and species interactions, and are generally predicted to become
increasingly threatened by GCC (Lancaster and Humphreys 2020).
Ecological research networks, synthesizing long-term vegetation data, show
strong effects of GCC on primary productivity, carbon flux, and advancing spring
phenological events (Franklin et al. 2016). Shorter scale analyses show rapid shifts
in plant distributions, mostly to higher latitudes and elevations (Kelly and Goulden
2008; Corlett and Westcott 2013). Changes in land use, and associated effects on
succession dynamics, have also reduced the resilience of forest communities
(Franklin et al. 2016). While growth is increasing in forests that are temperature
limited, widespread mortality is also increasing due to “hot droughts” where warmer
temperatures extract water from plants even without net changes in precipitation;
conditions that also contribute to wildfires and insect-mediated disease outbreaks
16 Symbiosis in a Rapidly Changing World
279
for 25–45% of ocean primary productivity and export roughly 40% of particulate
carbon to the deep ocean for storage (Boyd et al. 2019). Ongoing acidification,
however, hinders their ability to form strong shells making them smaller and less
effective at carbon sequestration (Petrou et al. 2019).
Looking forward, increased rates of melting of sea ice means more sunlight
penetrating ocean waters in the Arctic. This will lengthen the growing season of
phytoplankton at high latitudes, and lead to higher phytoplankton biomass, which in
turn will further warm surface waters by pigment-induced changes in radiant
heating, triggering additional positive feedbacks (Park et al. 2015). In response to
increasing temperatures and changes in circulation, entire communities of common
cool-adapted phytoplankton are projected to move poleward before 2100, which
may have large effects on food webs (Barton et al. 2016). Assemblages of foraminifera (zooplankton), which live in darker, cooler waters, have already moved
poleward relative to pre-industrial distributions (Jonkers et al. 2019). In addition to
relocation, some species have been shown to adapt to modest increases in temperature and acidification, but often with costs, such as smaller, carbon-depleted cells
(Schlüter et al. 2014; Irwin et al. 2015). Acidification may also alter competition
among phytoplankton species, as well as antagonistic interactions. For example,
acidification may select for nuisance species, such as toxic microalga over those
providing ecosystem services, or impact the composition of viruses attacking phytoplankton, which are key factors controlling blooms (Riebesell et al. 2018;
Highfield et al. 2017). Continued inaction leading to sustained warming may result
in changes in wind patterns, water temperatures, ice cover, and circulation that
would transfer nutrients from surface waters into the deep ocean, starving current
ecosystems (Moore et al. 2018).
In terrestrial systems plant cells contain chloroplasts, photosynthesizing organelles of endosymbiotic origin that facilitated the dominance of this group with
respect to biomass and primary production (Bar-On et al. 2018). Vegetation and
soils are major carbon sinks, absorbing roughly 25% of anthropogenic CO 2 . Plant
communities also perform key roles in oxygen, nitrogen, and water cycles, and
strongly impact the diversity and distribution of land animals. The thermal tolerances
of plants are governed by biogeographic and evolutionary histories as well as local
environments and species interactions, and are generally predicted to become
increasingly threatened by GCC (Lancaster and Humphreys 2020).
Ecological research networks, synthesizing long-term vegetation data, show
strong effects of GCC on primary productivity, carbon flux, and advancing spring
phenological events (Franklin et al. 2016). Shorter scale analyses show rapid shifts
in plant distributions, mostly to higher latitudes and elevations (Kelly and Goulden
2008; Corlett and Westcott 2013). Changes in land use, and associated effects on
succession dynamics, have also reduced the resilience of forest communities
(Franklin et al. 2016). While growth is increasing in forests that are temperature
limited, widespread mortality is also increasing due to “hot droughts” where warmer
temperatures extract water from plants even without net changes in precipitation;
conditions that also contribute to wildfires and insect-mediated disease outbreaks
16 Symbiosis in a Rapidly Changing World
279