177
the energy-based metabolic processes (black arrows) already incorporated into
GrassLight with feedback controls on physiological potential mediated by differential
gene expression (red arrows). Genetically controlled responses to environmental forcing are identified by key pathways that control, e.g., the function of chloroplast LHCs,
carbon fixation by Rubisco, the allocation of sucrose to growth and respiration, as well
as translocation between shoots and root/rhizomes. This integrated approach to environmental forcing through differential transcriptomics that control physiology leading
to whole-plant performance will provide a powerful tool for future field investigations
of seagrass responses to climate change.
8.3 Seagrasses as Ecosystem Engineers
In addition to representing complex biological systems in their own right, seagrasses
interact with a larger ecosystem of sedimentary, surficial, and planktonic microbes,
epiphytic algae, several trophic levels of grazers and predators (Duffy 2006), and
even pathogens (Lamb et al. 2017). As will be discussed below, seagrasses are more
than just another “brick in the wall”—they are true engineers of ecosystems that
would not exist in their absence, as evidenced by the disappearance of associated
services in the wake of local extirpations (Short and Wyllie-Echeverria 1996; Lamb
et al. 2017). This appreciation of seagrass connectivity led to the early adoption of
the ecosystems approach to the study of seagrass interactions with their environment and other trophic levels (McRoy and Hellfrich 1977; Phillips and McRoy
1980).
8.3.1 Seagrass-Sediment Interactions
In addition to their importance as a source of organic carbon for higher trophic levels and burial, seagrasses are significant biogeochemical agents in their own right
(Fig 8.4). By transporting as much as 6% of the photosynthetically produced O 2
below ground to support aerobic respiration of roots and rhizomes, seagrasses stimulate oxidative remineralization of organic carbon buried in the sediment (Smith
et al. 1984; Bodensteiner 2006; Hu and Burdige 2008), potentially limiting their
role as blue carbon sinks. However, the corrosive environment generated by the
release of respiratory CO 2 stimulates the dissolution of sedimentary carbonates,
thereby increasing alkalinity and trapping the remineralized C as HCO 3
− that does
not re-equilibrate with the atmosphere upon release from the sediment (Burdige and
Zimmerman 2003; Burdige et al. 2008; Burdige et al. 2010). Sulfate reduction in
sediments also generates alkalinity, but the low iron content of most carbonate sediments limits pyrite formation, and virtually all of the sulfide is oxidized back to
sulfate upon contact with O 2 in the overlying bottom water, consuming alkalinity in
the process.
8 Systems Biology and the Seagrass Paradox…
the energy-based metabolic processes (black arrows) already incorporated into
GrassLight with feedback controls on physiological potential mediated by differential
gene expression (red arrows). Genetically controlled responses to environmental forcing are identified by key pathways that control, e.g., the function of chloroplast LHCs,
carbon fixation by Rubisco, the allocation of sucrose to growth and respiration, as well
as translocation between shoots and root/rhizomes. This integrated approach to environmental forcing through differential transcriptomics that control physiology leading
to whole-plant performance will provide a powerful tool for future field investigations
of seagrass responses to climate change.
8.3 Seagrasses as Ecosystem Engineers
In addition to representing complex biological systems in their own right, seagrasses
interact with a larger ecosystem of sedimentary, surficial, and planktonic microbes,
epiphytic algae, several trophic levels of grazers and predators (Duffy 2006), and
even pathogens (Lamb et al. 2017). As will be discussed below, seagrasses are more
than just another “brick in the wall”—they are true engineers of ecosystems that
would not exist in their absence, as evidenced by the disappearance of associated
services in the wake of local extirpations (Short and Wyllie-Echeverria 1996; Lamb
et al. 2017). This appreciation of seagrass connectivity led to the early adoption of
the ecosystems approach to the study of seagrass interactions with their environment and other trophic levels (McRoy and Hellfrich 1977; Phillips and McRoy
1980).
8.3.1 Seagrass-Sediment Interactions
In addition to their importance as a source of organic carbon for higher trophic levels and burial, seagrasses are significant biogeochemical agents in their own right
(Fig 8.4). By transporting as much as 6% of the photosynthetically produced O 2
below ground to support aerobic respiration of roots and rhizomes, seagrasses stimulate oxidative remineralization of organic carbon buried in the sediment (Smith
et al. 1984; Bodensteiner 2006; Hu and Burdige 2008), potentially limiting their
role as blue carbon sinks. However, the corrosive environment generated by the
release of respiratory CO 2 stimulates the dissolution of sedimentary carbonates,
thereby increasing alkalinity and trapping the remineralized C as HCO 3
− that does
not re-equilibrate with the atmosphere upon release from the sediment (Burdige and
Zimmerman 2003; Burdige et al. 2008; Burdige et al. 2010). Sulfate reduction in
sediments also generates alkalinity, but the low iron content of most carbonate sediments limits pyrite formation, and virtually all of the sulfide is oxidized back to
sulfate upon contact with O 2 in the overlying bottom water, consuming alkalinity in
the process.
8 Systems Biology and the Seagrass Paradox…