(Overpeck 2013). As with phytoplankton, increased CO 2 can contribute to enhanced
growth in plants, called CO 2 fertilization, which if widespread would exert mitigating effects on GCC. However, forests appear limited in their ability to use the excess
CO 2 . Carbon intake depends on nutrient and water availability, and changes in these
factors are predicted to slow carbon sequestration going forward (Jiang et al. 2020;
Green et al. 2019).
In addition to the domesticated chloroplasts, virtually all plant species interact
with microbes that retain at least some independence. Many of these emerge from the
soil microbiota, which itself is highly diverse and plays key roles in climate feedback
via the cycling of soil organic carbon and other nutrients; although uncertainty
remains regarding whether soils will ultimately be a sink or a source of greenhouse
gasses in the future (Jansson and Hofmockel 2020). Warming can change the
composition of soil microbiota, favoring specific bacterial species or fungi, which
in turn can influence system function (DeAngelis et al. 2015; Classen et al. 2015).
The rhizosphere, the soil zone surrounding plant roots, contains a number of plant
beneficial or conditionally beneficial microbes that play important roles in mitigating
drought, nutrient, and thermal stress and may enhance plant fitness in climateaffected soils (Mendes et al. 2013; Jansson and Hofmockel 2020).
The most widespread plant symbioses involve their mostly obligate associations
with mycorrhizal fungi (MF). About 90% of plants receive MF-mediated benefits
such as water, nutrients, or protection in exchange for organic carbon derived from
plant photosynthesis. Four types of MF are recognized (Tedersoo et al. 2020;
Steidinger et al. 2019; Brundrett and Tedersoo 2018): (1) Arbuscular
endomycorrhiza; AMF are found in roughly 78% of plant species, are common in
warm tropical forests, and produce structures called arbuscules that form in root
cortex cells and facilitate nutrient, especially phosphorous, transfer.
(2) Ectomycorrhiza; EcMF occur in only 2% of (mostly) woody plant species yet
occupy the roots of nearly 60% of tree stems, especially those in nitrogen-poor
boreal and temperate forests. EcMF are characterized by a Hartig net of in-growing
hyphae that penetrate the root epidermis and cortex mobilizing nitrogen and other
nutrients. (3) Orchid MF are found in the largely epiphytic Orchidaceae (ca. 10% of
plants) and are characterized by coiled structures called pelotons that colonize root
cells. (4) Ericoid MF occur in acidic soils associating with 1.4% of plants in the
Ericaceae (heaths) and characterized by hyphal coils in root epidermal cells. Vegetation with MF store about 350 gigatons of carbon globally, mostly by AMF and
EcMF, compared to 29 GT in non-MF plants (Soudzilovskaia et al. 2019).
Belowground, extensive networks of MF connect conspecific and heterospecific
plants facilitating nutrient transfer among plants (Tedersoo et al. 2020). Remarkably,
up to 40% of the carbon in the fine roots of any given individual plant can be
obtained from the photosynthetic products of its neighbors (Klein et al. 2016). Intraand interspecific plant communication, such as warning signals and kin recognition,
also occurs through MF networks (Tedersoo et al. 2020). Together, nutrient
exchange and communication influence plant–plant interactions and community
dynamics, and by increasing the number of trading partners, the costs of nutrients
can be lowered while increasing the stability of the association (Wyatt et al. 2014;
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K. M. Oliver and C. H. V. Higashi
growth in plants, called CO 2 fertilization, which if widespread would exert mitigating effects on GCC. However, forests appear limited in their ability to use the excess
CO 2 . Carbon intake depends on nutrient and water availability, and changes in these
factors are predicted to slow carbon sequestration going forward (Jiang et al. 2020;
Green et al. 2019).
In addition to the domesticated chloroplasts, virtually all plant species interact
with microbes that retain at least some independence. Many of these emerge from the
soil microbiota, which itself is highly diverse and plays key roles in climate feedback
via the cycling of soil organic carbon and other nutrients; although uncertainty
remains regarding whether soils will ultimately be a sink or a source of greenhouse
gasses in the future (Jansson and Hofmockel 2020). Warming can change the
composition of soil microbiota, favoring specific bacterial species or fungi, which
in turn can influence system function (DeAngelis et al. 2015; Classen et al. 2015).
The rhizosphere, the soil zone surrounding plant roots, contains a number of plant
beneficial or conditionally beneficial microbes that play important roles in mitigating
drought, nutrient, and thermal stress and may enhance plant fitness in climateaffected soils (Mendes et al. 2013; Jansson and Hofmockel 2020).
The most widespread plant symbioses involve their mostly obligate associations
with mycorrhizal fungi (MF). About 90% of plants receive MF-mediated benefits
such as water, nutrients, or protection in exchange for organic carbon derived from
plant photosynthesis. Four types of MF are recognized (Tedersoo et al. 2020;
Steidinger et al. 2019; Brundrett and Tedersoo 2018): (1) Arbuscular
endomycorrhiza; AMF are found in roughly 78% of plant species, are common in
warm tropical forests, and produce structures called arbuscules that form in root
cortex cells and facilitate nutrient, especially phosphorous, transfer.
(2) Ectomycorrhiza; EcMF occur in only 2% of (mostly) woody plant species yet
occupy the roots of nearly 60% of tree stems, especially those in nitrogen-poor
boreal and temperate forests. EcMF are characterized by a Hartig net of in-growing
hyphae that penetrate the root epidermis and cortex mobilizing nitrogen and other
nutrients. (3) Orchid MF are found in the largely epiphytic Orchidaceae (ca. 10% of
plants) and are characterized by coiled structures called pelotons that colonize root
cells. (4) Ericoid MF occur in acidic soils associating with 1.4% of plants in the
Ericaceae (heaths) and characterized by hyphal coils in root epidermal cells. Vegetation with MF store about 350 gigatons of carbon globally, mostly by AMF and
EcMF, compared to 29 GT in non-MF plants (Soudzilovskaia et al. 2019).
Belowground, extensive networks of MF connect conspecific and heterospecific
plants facilitating nutrient transfer among plants (Tedersoo et al. 2020). Remarkably,
up to 40% of the carbon in the fine roots of any given individual plant can be
obtained from the photosynthetic products of its neighbors (Klein et al. 2016). Intraand interspecific plant communication, such as warning signals and kin recognition,
also occurs through MF networks (Tedersoo et al. 2020). Together, nutrient
exchange and communication influence plant–plant interactions and community
dynamics, and by increasing the number of trading partners, the costs of nutrients
can be lowered while increasing the stability of the association (Wyatt et al. 2014;
280
K. M. Oliver and C. H. V. Higashi