138
unaffected, suggesting a more relevant contribution of cyclic electron flow when
compared to the Mehler reaction (Lakshmanan et al. 2015). Regarding seagrass, the
Mehler reaction has been investigated in the seagrass Z. marina, and its contribution
to the electron flow appears to be minor when compared to photorespiration (Buapet
and Björk 2016). Although alternative electron flows have been mentioned in several seagrass studies, the works focusing on their contribution and physiological
role remain scarce.
7.2 Photosynthesis in a Dynamic Environment: Research
Advances in Seagrasses
Seagrass meadows, particularly in the shallow water, are subjected to dynamic environmental conditions. Daily and seasonal fluctuations of various physicochemical
factors such as light, temperature, and salinity have been reported in many seagrass
habitats across the bioregions. In the global change scenarios, such fluctuations can
be exacerbated as extreme weather events become more frequent. Additionally,
interactions between these environmental factors and a future increase in dissolved
CO 2 might impose a profound effect on seagrass metabolisms. To successfully
maintain positive carbon balance and growth, seagrass must be able to adjust their
photosynthetic systems to these short- and long-term changes. Here, recent research
addressing effects of abiotic stress factors on photophysiology of seagrasses are
summarized.
7.2.1 Light: Photoacclimation and Photoprotection
Seasonal and daily fluctuation in light quantity and quality are common in seagrass
habitats (Kenworthy and Haunert 1991; Gallegos and Kenworthy 1996; Kahn et al.
2013). Furthermore, anthropogenic activities causing sedimentation and eutrophication can lead to a shift in light regimes (Schmidt et al. 2012; Yaakub et al. 2014).
The effects of varying light conditions on the photosynthetic activity of seagrasses
have been extensively studied. Early efforts have been invested in determining the
light requirement for seagrass to maintain its carbon balance (Dennison and Alberte
1982; Pérez and Romero 1992; Abal et al. 1994; Zimmerman et al. 1995; Kenworthy
and Fonseca 1996), while more recent works have focused on photoacclimation
mechanisms to both low light and high light in relation to depth distributions (Olivé
et al. 2013; Dattolo et al. 2013, 2014; Park et al. 2016). Pulse amplitude modulation
(PAM) fluorometry has been the most frequently used techniques for the investigation of photophysiology of seagrasses. The most common PAM parameters used to
describe photosynthetic activity are the effective photochemical efficiency of PSII
(Φ PSII ) which provides an estimation of the proportion of the light absorbed by PSII
that is utilized in photochemistry and the maximum photochemical efficiencies
of PSII (F v /F m ) which indicates stress associated with photoinhibition (Maxwell
P. Buapet
unaffected, suggesting a more relevant contribution of cyclic electron flow when
compared to the Mehler reaction (Lakshmanan et al. 2015). Regarding seagrass, the
Mehler reaction has been investigated in the seagrass Z. marina, and its contribution
to the electron flow appears to be minor when compared to photorespiration (Buapet
and Björk 2016). Although alternative electron flows have been mentioned in several seagrass studies, the works focusing on their contribution and physiological
role remain scarce.
7.2 Photosynthesis in a Dynamic Environment: Research
Advances in Seagrasses
Seagrass meadows, particularly in the shallow water, are subjected to dynamic environmental conditions. Daily and seasonal fluctuations of various physicochemical
factors such as light, temperature, and salinity have been reported in many seagrass
habitats across the bioregions. In the global change scenarios, such fluctuations can
be exacerbated as extreme weather events become more frequent. Additionally,
interactions between these environmental factors and a future increase in dissolved
CO 2 might impose a profound effect on seagrass metabolisms. To successfully
maintain positive carbon balance and growth, seagrass must be able to adjust their
photosynthetic systems to these short- and long-term changes. Here, recent research
addressing effects of abiotic stress factors on photophysiology of seagrasses are
summarized.
7.2.1 Light: Photoacclimation and Photoprotection
Seasonal and daily fluctuation in light quantity and quality are common in seagrass
habitats (Kenworthy and Haunert 1991; Gallegos and Kenworthy 1996; Kahn et al.
2013). Furthermore, anthropogenic activities causing sedimentation and eutrophication can lead to a shift in light regimes (Schmidt et al. 2012; Yaakub et al. 2014).
The effects of varying light conditions on the photosynthetic activity of seagrasses
have been extensively studied. Early efforts have been invested in determining the
light requirement for seagrass to maintain its carbon balance (Dennison and Alberte
1982; Pérez and Romero 1992; Abal et al. 1994; Zimmerman et al. 1995; Kenworthy
and Fonseca 1996), while more recent works have focused on photoacclimation
mechanisms to both low light and high light in relation to depth distributions (Olivé
et al. 2013; Dattolo et al. 2013, 2014; Park et al. 2016). Pulse amplitude modulation
(PAM) fluorometry has been the most frequently used techniques for the investigation of photophysiology of seagrasses. The most common PAM parameters used to
describe photosynthetic activity are the effective photochemical efficiency of PSII
(Φ PSII ) which provides an estimation of the proportion of the light absorbed by PSII
that is utilized in photochemistry and the maximum photochemical efficiencies
of PSII (F v /F m ) which indicates stress associated with photoinhibition (Maxwell
P. Buapet