143
Interestingly, an increase in the expressions of the genes encoding Rubisco small
subunit was observed in parallel with an increase in the expressions of the genes
encoding Rubisco activase. The positive effect of high temperature (27–33°C) has
also been demonstrated in a tropical seagrass, H. uninervis, in which photosynthesis
and growth increased with increased temperature while respiration remained constant (Collier et al. 2011). These works indicate that responses to heat stress vary
considerably depending on the plant history.
7.2.4 Effect of CO 2 Enrichment on Seagrass Primary
Production
Considering the projected increase in dissolved CO 2 in the global change scenarios, seagrass is expected to benefit from an increase in carbon availability.
Therefore, the effects of CO 2 enrichment on photosynthesis have been intensively
investigated in seagrasses for the past few years (Alexandre et al. 2012; Campbell
and Fourqurean 2013a,b; Martínez-Crego et al. 2014; Ow et al. 2015, 2016; Cox
et al. 2016; Borum et al. 2016). Additionally, the more ecological relevant experimental setting using in situ mesocosms has become increasingly common
(Campbell and Fourqurean 2013a,b; Cox et al. 2016). These studies, however,
focused on comparing photosynthetic and growth rates between control and CO 2 -
enriched plants, while only a few works have addressed the mechanistic adaptation of seagrass photobiology to high CO 2 .
The positive effects of increased CO 2 have been reported in various seagrass species such as Z. noltii, C. serrulata, H. uninervis, T. hemprichii, and Amphibolis
antarctica (Alexandre et al. 2012; Burnell et al. 2014; Ow et al. 2015, 2016). In
these seagrasses, growth rates, net primary productivity, the maximum photosynthetic rates and the photosynthetic efficiency of CO 2 -enriched plants were higher
than controls. Additionally, synergistic effects between an increase in dissolved CO 2
and irradiance have been reported by Ow et al. (2016). Therefore seagrass responses
to an increase in CO 2 might vary depending on the light environments. It was suggested that the seagrass C. serrulata grown under low light, being short of ATP
production, is more dependent on the passive CO 2 uptake and thus benefits more
from an increase in dissolved CO 2 (Ow et al. 2016). This is confirmed by a greater
increase in the maximum photosynthetic rates (P max ) and photosynthetic efficiency
(α) as a response to high CO 2 in C. serrulata under low light. Similarly, other studies have suggested that species with low HCO 3
− utilizing efficiency would respond
more positively to an increase in dissolved CO 2 more than the efficient HCO 3
− users
(Campbell and Fourqurean 2013b; Borum et al. 2016). Borum et al. (2016) examined the HCO 3
− utilization efficiency of nine seagrass species and their subsequent
responses to CO 2 enrichment. Here A. antarctica which appeared to be among the
least efficient HCO 3
− users exhibited the strongest response to an increase in CO 2 .
7 Photobiology of Seagrasses: A Systems Biology Perspective
Interestingly, an increase in the expressions of the genes encoding Rubisco small
subunit was observed in parallel with an increase in the expressions of the genes
encoding Rubisco activase. The positive effect of high temperature (27–33°C) has
also been demonstrated in a tropical seagrass, H. uninervis, in which photosynthesis
and growth increased with increased temperature while respiration remained constant (Collier et al. 2011). These works indicate that responses to heat stress vary
considerably depending on the plant history.
7.2.4 Effect of CO 2 Enrichment on Seagrass Primary
Production
Considering the projected increase in dissolved CO 2 in the global change scenarios, seagrass is expected to benefit from an increase in carbon availability.
Therefore, the effects of CO 2 enrichment on photosynthesis have been intensively
investigated in seagrasses for the past few years (Alexandre et al. 2012; Campbell
and Fourqurean 2013a,b; Martínez-Crego et al. 2014; Ow et al. 2015, 2016; Cox
et al. 2016; Borum et al. 2016). Additionally, the more ecological relevant experimental setting using in situ mesocosms has become increasingly common
(Campbell and Fourqurean 2013a,b; Cox et al. 2016). These studies, however,
focused on comparing photosynthetic and growth rates between control and CO 2 -
enriched plants, while only a few works have addressed the mechanistic adaptation of seagrass photobiology to high CO 2 .
The positive effects of increased CO 2 have been reported in various seagrass species such as Z. noltii, C. serrulata, H. uninervis, T. hemprichii, and Amphibolis
antarctica (Alexandre et al. 2012; Burnell et al. 2014; Ow et al. 2015, 2016). In
these seagrasses, growth rates, net primary productivity, the maximum photosynthetic rates and the photosynthetic efficiency of CO 2 -enriched plants were higher
than controls. Additionally, synergistic effects between an increase in dissolved CO 2
and irradiance have been reported by Ow et al. (2016). Therefore seagrass responses
to an increase in CO 2 might vary depending on the light environments. It was suggested that the seagrass C. serrulata grown under low light, being short of ATP
production, is more dependent on the passive CO 2 uptake and thus benefits more
from an increase in dissolved CO 2 (Ow et al. 2016). This is confirmed by a greater
increase in the maximum photosynthetic rates (P max ) and photosynthetic efficiency
(α) as a response to high CO 2 in C. serrulata under low light. Similarly, other studies have suggested that species with low HCO 3
− utilizing efficiency would respond
more positively to an increase in dissolved CO 2 more than the efficient HCO 3
− users
(Campbell and Fourqurean 2013b; Borum et al. 2016). Borum et al. (2016) examined the HCO 3
− utilization efficiency of nine seagrass species and their subsequent
responses to CO 2 enrichment. Here A. antarctica which appeared to be among the
least efficient HCO 3
− users exhibited the strongest response to an increase in CO 2 .
7 Photobiology of Seagrasses: A Systems Biology Perspective