Plant Physiology and Biochemistry 86 (2015) 147e154
Contents lists available at ScienceDirect
Plant Physiology and Biochemistry journal homepage: www.elsevier.com/locate/plaphy
Research article
Responses of the photosynthetic apparatus to winter conditions in broadleaved evergreen trees growing in warm temperate regions of Japan Chizuru Tanaka a, Takashi Nakano b, Jun-ya Yamazaki a, *, Emiko Maruta a a b
Department of Biology, Faculty of Science, Toho University, Miyama 2-2-1, Funabashi, Chiba 274-8510, Japan Mount Fuji Research Institute, Yamanashi Prefectural Government (MFRI), Kenmarubi 5597-1, Kamiyoshida, Fujiyoshida City, Yamanashi 403-0005, Japan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 September 2014 Accepted 2 December 2014 Available online 3 December 2014
Photosynthetic characteristics of two broadleaved evergreen trees, Quercus myrsinaefolia and Machilus thunbergii, were compared in autumn and winter. The irradiance was similar in both seasons, but the air temperature was lower in winter. Under the winter conditions, net photosynthesis under natural sunlight (Anet) in both species dropped to 4 mmol CO2 m2 s1, and the quantum yield of photosystem II (PSII) photochemistry in dark-adapted leaves (Fv/Fm) also dropped to 0.60. In both species the maximum carboxylation rates of Rubisco (Vcmax) decreased, and the amount of Rubisco increased in winter. A decline in chlorophyll (Chl) concentration and an increase in the Chl a/b ratio in winter resulted in a reduction in the size of the light-harvesting antennae. From measurements of Chl a fluorescence parameters, both the relative fraction and the energy flux rates of thermal dissipation through other nonphotochemical processes were markedly elevated in winter. The results indicate that the photosynthetic apparatus in broadleaved evergreen species in warm temperate regions responds to winter through regulatory mechanisms involving the downregulation of light-harvesting and photosynthesis coupled with increased photoprotective thermal energy dissipation to minimize photodamage in winter. These mechanisms aid a quick restart of photosynthesis without the development of new leaves in the following spring. © 2014 Elsevier Masson SAS. All rights reserved.
Keywords: Broadleaved evergreens Energy flux Energy partition Quercus myrsinaefolia Machilus thunbergii
1. Introduction
Abbreviations: Amax, the potential photosynthetic rate; Anet, the net photosynthesis under natural sunlight; Chl, Chlorophyll; F, steady-state fluorescence; Fm, Fo and Fv, the maximum, minimum and variable fluorescence yields, respectively; Fm0 , Fo0 and Fv0, the maximum, minimum and variable fluorescence yields, respectively, during energization; Fv/Fm, the quantum yield of PSII photochemistry in darkadapted leaves; gs, stomatal conductance; JNPQ, energy flux rate of NPQ associated with the xanthophyll cycle; JONP, energy flux rate of non-photochemical processes not associated with the xanthophyll cycle; JPSII, energy flux rate of PSII photochemistry; NPQ, non-photochemical quenching of chlorophyll fluorescence; PPFD, photosynthetic photon flux density; PSI and PSII, photosystem I and photosystem II, respectively; qL, the fraction of open PSII reaction centers based on the lake model; TBARS, thiobarbituric acid reaction substance; Vcmax, the maximum carboxylation rates of Rubisco; 4, the apparent quantum yield of CO2 fixation on an illuminatedlight basis; FNPQ, the quantum yield of non-photochemical quenching associated with the xanthophyll cycle; FONP, the quantum yield of non-photochemical processes not associated with the xanthophyll cycle; FPSII, the quantum yield of PSII photochemistry. * Corresponding author. E-mail address: [email protected] (J.-y. Yamazaki). http://dx.doi.org/10.1016/j.plaphy.2014.12.002 0981-9428/© 2014 Elsevier Masson SAS. All rights reserved.
Broadleaved evergreen species grown in the monsoonal region originated in warm regions and spread from central Japan westwards across a large belt of southern China, including Taiwan, to the southern side of the Himalayan mountains (Ohsawa, 1990). The species growing in this region have large, very thick, often shiny leaves. In this region, the climate features high levels of precipitation and high temperatures in summer, but is somewhat xeric with low temperatures in winter. The trees endemic to this area are confined exclusively to oceanic, mild winter areas such as those in Japan (Sakai, 1975). Quercus species, which are distributed from the southern end to 38 N in Japan, are the major canopy components of warm temperate broadleaved evergreen forests. The distribution of Machilus overlaps with that of Quercus, and the Machilus species observed in warmer coastal regions are exposed to warm currents (the Black Current on the Pacific Ocean side and the Tsushima Current on the Japan Sea side) that reach as far north as the Tohoku
148
C. Tanaka et al. / Plant Physiology and Biochemistry 86 (2015) 147e154
district (below 40 N), which is the northern limit of the Machilus species. There have been two major findings with respect to the determinants of the distribution of broadleaved evergreen trees. Sakai (1975) determined the freezing tolerance of these trees on the basis of the freezing temperatures in the stems, leaves, and buds, and concluded that cold tolerance is the main determinant of the distribution of broadleaved evergreen trees. Taneda and Tateno (2005) reported that evergreen broadleaved trees with large-diameter vessels were significantly more vulnerable to freezeethaw embolism than were evergreen conifers with small-diameter tracheids. This result suggested that the cross-sectional diameter of the xylem elements is one of the important determinants of the distribution of evergreen woody species. Photosynthetic activities are lower at low temperatures in winter than at optimal or high temperatures in the primary growing season. Evergreen conifers growing under harsh winter conditions in subalpine regions exhibit downregulation in both capacity of photosynthesis and efficiency of photosystem (PS) II (Zarter et al., 2006a, 2006b; Yamazaki et al., 2003, 2007). In contrast, those at lower altitudes may or may not exhibit downregulation of photosynthetic capacity in winter (Adams et al., 2004; Zarter et al., 2006a) but invariably experience downregulation of PSII efficiency (Adams and Demmig-Adams, 1994; Adams et al., 1995, 2004; Ebbert et al., 2005; Zarter et al., 2006a). Broadleaved evergreen trees show lowered photosynthetic activity in winter (Adams and Demmig-Adams, 1995; Adams et al., 1995; Verhoeven et al., 1996). In addition, given that broadleaved trees continue to perform photosynthesis under direct sunlight throughout winter, winter photosynthesis may exceed that in the growing season and account for a large part of the annual photosynthesis (Miyazawa and Kikuzawa, 2005). Winter stress induces suppression of the photochemical effi€ ciency of PSII and the CalvineBenson-cycle enzymes (Oquist and Huner, 2003). Excessive photons reduce molecular oxygen, resulting in the production of harmful active oxygen species and severe photoinhibition of photosynthesis (Ottander et al., 1995; Yamazaki et al., 2007). The photosynthetic apparatus of overwintering evergreen trees must accordingly develop protective mechanisms against these stresses to survive the winter and recover their capacity for photosynthesis by the following spring (Ottander et al., 1995; Miyazawa and Kikuzawa, 2005; Yamazaki et al., 2003, 2007). However, in winter, broadleaved evergreen species in warm temperate regions of East Asia are exposed to milder winter conditions than those in boreal and continental climate regions. Under mild winter conditions, the PSII complexes are not degraded but phosphorylated, owing to the fast recovery of overall photosynthesis when the climate becomes warm (Ebbert et al., 2005; Demmig-Adams and Adams, 2006; Verhoeven et al., 2009). Studies of xanthophyll cycle-related energy dissipation from antennae attached to the PSII complexes in winter have been performed (Adams et al., 1995, 2004; Yamazaki et al., 2011). We previously reported the involvement of thermal dissipation and changes in chlorophyll (Chl) forms in overwintering broadleaved evergreen species (Yamazaki et al., 2011). The present study, by comparing leaves in autumn with those in winter, attempts to elucidate in further detail how mechanisms of thermal energy dissipation are involved in the protection of the photosynthetic apparatus in overwintering broadleaved evergreens in warm temperate regions of Japan.
2. Materials and methods 2.1. Study site and plant materials All measurements were performed on the campus of Toho University, Funabashi, Japan (latitude 35 410 N, longitude 140 20 E; altitude 20 m), located in a warm temperate region. Two evergreen species [Quercus myrsinaefolia (Fagaceae) and Machilus thunbergii (Lauraceae)] were used. The heights of the Machilus and Quercus trees included in the survey were approximately 8 and 10 m, respectively, and their diameters at breast height were approximately 30 and 20 cm, respectively. Photosynthetic photon flux density (PPFD) was measured with a photon sensor (IKS-27; Koito Co., Japan) mounted on a horizontal plane with respect to the earth's surface, and the data obtained were recorded by a data logger (KADEC-UP; KONA system, Japan) at 10-min intervals. Maximum and minimum air temperatures were 31.1 C (October 5, 2007)/2.2 C (February 18, 2008) and 29.6 C (October 12, 2013)/ 3.1 C (January 11, 2014), obtained from an automated meteorological data acquisition system (AMeDAS) at Funabashi Meteorological Observatory (latitude 35 420 N, longitude 140 20 E, altitude: 28 m) provided by the Japan Meteorological Agency (JMA; http:// www.jma.go.jp/). Between the gap of the two experiments (2007e2014) there were no environmental and characteristic differences such as light conditions, the features of the campus, and current year's leaf characteristics at the study site. In addition, the significant climate changes were not observed from the data obtained from the JMA about the gap of multiple years between the two experiments (2007e2014). Hereafter, the data of November 13, 2007 and October 26, 2013 will be referred to as autumn data, and the data of February 1, 2008 and February 7, 2014 as winter data. 2.2. Measurements of photosynthetic parameters Photosynthetic parameters were measured on sun-exposed current-year leaves on November 13, 2007 and February 1, 2008. Under field conditions, net photosynthesis (Anet) of the leaves was measured between 11:00 and 14:00 (local time) with a portable gas-exchange analyzer (LI-6400; LI-COR, Inc., USA) attached to a transparent standard leaf chamber (6400-08; LI-COR, Inc.). The potential photosynthetic rate (Amax), the apparent quantum yield of CO2 fixation on an illuminated-light basis (4), and the potential rate of carboxylation by Rubisco (Vcmax) were measured under ambient temperature with an LI-6400 attached to an LED light and CO2 concentration control unit (6400-02B; LI-COR, Inc.). For the determination of Amax, the net photosynthetic rates at 10 stepwise actinic light intensity intervals from 0 to 1500 mmol photons m2 s1 were measured under a cuvette CO2 concentration of 370 mmol mol1. It took 3e4 min to obtain a stable photosynthetic rates at each reduction in the LED intensity. Using these data, Amax was calculated by the equation of Johnson and Thornley (1984). The value of 4 was estimated by linear regression at PPFD
Contents lists available at ScienceDirect
Plant Physiology and Biochemistry journal homepage: www.elsevier.com/locate/plaphy
Research article
Responses of the photosynthetic apparatus to winter conditions in broadleaved evergreen trees growing in warm temperate regions of Japan Chizuru Tanaka a, Takashi Nakano b, Jun-ya Yamazaki a, *, Emiko Maruta a a b
Department of Biology, Faculty of Science, Toho University, Miyama 2-2-1, Funabashi, Chiba 274-8510, Japan Mount Fuji Research Institute, Yamanashi Prefectural Government (MFRI), Kenmarubi 5597-1, Kamiyoshida, Fujiyoshida City, Yamanashi 403-0005, Japan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 September 2014 Accepted 2 December 2014 Available online 3 December 2014
Photosynthetic characteristics of two broadleaved evergreen trees, Quercus myrsinaefolia and Machilus thunbergii, were compared in autumn and winter. The irradiance was similar in both seasons, but the air temperature was lower in winter. Under the winter conditions, net photosynthesis under natural sunlight (Anet) in both species dropped to 4 mmol CO2 m2 s1, and the quantum yield of photosystem II (PSII) photochemistry in dark-adapted leaves (Fv/Fm) also dropped to 0.60. In both species the maximum carboxylation rates of Rubisco (Vcmax) decreased, and the amount of Rubisco increased in winter. A decline in chlorophyll (Chl) concentration and an increase in the Chl a/b ratio in winter resulted in a reduction in the size of the light-harvesting antennae. From measurements of Chl a fluorescence parameters, both the relative fraction and the energy flux rates of thermal dissipation through other nonphotochemical processes were markedly elevated in winter. The results indicate that the photosynthetic apparatus in broadleaved evergreen species in warm temperate regions responds to winter through regulatory mechanisms involving the downregulation of light-harvesting and photosynthesis coupled with increased photoprotective thermal energy dissipation to minimize photodamage in winter. These mechanisms aid a quick restart of photosynthesis without the development of new leaves in the following spring. © 2014 Elsevier Masson SAS. All rights reserved.
Keywords: Broadleaved evergreens Energy flux Energy partition Quercus myrsinaefolia Machilus thunbergii
1. Introduction
Abbreviations: Amax, the potential photosynthetic rate; Anet, the net photosynthesis under natural sunlight; Chl, Chlorophyll; F, steady-state fluorescence; Fm, Fo and Fv, the maximum, minimum and variable fluorescence yields, respectively; Fm0 , Fo0 and Fv0, the maximum, minimum and variable fluorescence yields, respectively, during energization; Fv/Fm, the quantum yield of PSII photochemistry in darkadapted leaves; gs, stomatal conductance; JNPQ, energy flux rate of NPQ associated with the xanthophyll cycle; JONP, energy flux rate of non-photochemical processes not associated with the xanthophyll cycle; JPSII, energy flux rate of PSII photochemistry; NPQ, non-photochemical quenching of chlorophyll fluorescence; PPFD, photosynthetic photon flux density; PSI and PSII, photosystem I and photosystem II, respectively; qL, the fraction of open PSII reaction centers based on the lake model; TBARS, thiobarbituric acid reaction substance; Vcmax, the maximum carboxylation rates of Rubisco; 4, the apparent quantum yield of CO2 fixation on an illuminatedlight basis; FNPQ, the quantum yield of non-photochemical quenching associated with the xanthophyll cycle; FONP, the quantum yield of non-photochemical processes not associated with the xanthophyll cycle; FPSII, the quantum yield of PSII photochemistry. * Corresponding author. E-mail address: [email protected] (J.-y. Yamazaki). http://dx.doi.org/10.1016/j.plaphy.2014.12.002 0981-9428/© 2014 Elsevier Masson SAS. All rights reserved.
Broadleaved evergreen species grown in the monsoonal region originated in warm regions and spread from central Japan westwards across a large belt of southern China, including Taiwan, to the southern side of the Himalayan mountains (Ohsawa, 1990). The species growing in this region have large, very thick, often shiny leaves. In this region, the climate features high levels of precipitation and high temperatures in summer, but is somewhat xeric with low temperatures in winter. The trees endemic to this area are confined exclusively to oceanic, mild winter areas such as those in Japan (Sakai, 1975). Quercus species, which are distributed from the southern end to 38 N in Japan, are the major canopy components of warm temperate broadleaved evergreen forests. The distribution of Machilus overlaps with that of Quercus, and the Machilus species observed in warmer coastal regions are exposed to warm currents (the Black Current on the Pacific Ocean side and the Tsushima Current on the Japan Sea side) that reach as far north as the Tohoku
148
C. Tanaka et al. / Plant Physiology and Biochemistry 86 (2015) 147e154
district (below 40 N), which is the northern limit of the Machilus species. There have been two major findings with respect to the determinants of the distribution of broadleaved evergreen trees. Sakai (1975) determined the freezing tolerance of these trees on the basis of the freezing temperatures in the stems, leaves, and buds, and concluded that cold tolerance is the main determinant of the distribution of broadleaved evergreen trees. Taneda and Tateno (2005) reported that evergreen broadleaved trees with large-diameter vessels were significantly more vulnerable to freezeethaw embolism than were evergreen conifers with small-diameter tracheids. This result suggested that the cross-sectional diameter of the xylem elements is one of the important determinants of the distribution of evergreen woody species. Photosynthetic activities are lower at low temperatures in winter than at optimal or high temperatures in the primary growing season. Evergreen conifers growing under harsh winter conditions in subalpine regions exhibit downregulation in both capacity of photosynthesis and efficiency of photosystem (PS) II (Zarter et al., 2006a, 2006b; Yamazaki et al., 2003, 2007). In contrast, those at lower altitudes may or may not exhibit downregulation of photosynthetic capacity in winter (Adams et al., 2004; Zarter et al., 2006a) but invariably experience downregulation of PSII efficiency (Adams and Demmig-Adams, 1994; Adams et al., 1995, 2004; Ebbert et al., 2005; Zarter et al., 2006a). Broadleaved evergreen trees show lowered photosynthetic activity in winter (Adams and Demmig-Adams, 1995; Adams et al., 1995; Verhoeven et al., 1996). In addition, given that broadleaved trees continue to perform photosynthesis under direct sunlight throughout winter, winter photosynthesis may exceed that in the growing season and account for a large part of the annual photosynthesis (Miyazawa and Kikuzawa, 2005). Winter stress induces suppression of the photochemical effi€ ciency of PSII and the CalvineBenson-cycle enzymes (Oquist and Huner, 2003). Excessive photons reduce molecular oxygen, resulting in the production of harmful active oxygen species and severe photoinhibition of photosynthesis (Ottander et al., 1995; Yamazaki et al., 2007). The photosynthetic apparatus of overwintering evergreen trees must accordingly develop protective mechanisms against these stresses to survive the winter and recover their capacity for photosynthesis by the following spring (Ottander et al., 1995; Miyazawa and Kikuzawa, 2005; Yamazaki et al., 2003, 2007). However, in winter, broadleaved evergreen species in warm temperate regions of East Asia are exposed to milder winter conditions than those in boreal and continental climate regions. Under mild winter conditions, the PSII complexes are not degraded but phosphorylated, owing to the fast recovery of overall photosynthesis when the climate becomes warm (Ebbert et al., 2005; Demmig-Adams and Adams, 2006; Verhoeven et al., 2009). Studies of xanthophyll cycle-related energy dissipation from antennae attached to the PSII complexes in winter have been performed (Adams et al., 1995, 2004; Yamazaki et al., 2011). We previously reported the involvement of thermal dissipation and changes in chlorophyll (Chl) forms in overwintering broadleaved evergreen species (Yamazaki et al., 2011). The present study, by comparing leaves in autumn with those in winter, attempts to elucidate in further detail how mechanisms of thermal energy dissipation are involved in the protection of the photosynthetic apparatus in overwintering broadleaved evergreens in warm temperate regions of Japan.
2. Materials and methods 2.1. Study site and plant materials All measurements were performed on the campus of Toho University, Funabashi, Japan (latitude 35 410 N, longitude 140 20 E; altitude 20 m), located in a warm temperate region. Two evergreen species [Quercus myrsinaefolia (Fagaceae) and Machilus thunbergii (Lauraceae)] were used. The heights of the Machilus and Quercus trees included in the survey were approximately 8 and 10 m, respectively, and their diameters at breast height were approximately 30 and 20 cm, respectively. Photosynthetic photon flux density (PPFD) was measured with a photon sensor (IKS-27; Koito Co., Japan) mounted on a horizontal plane with respect to the earth's surface, and the data obtained were recorded by a data logger (KADEC-UP; KONA system, Japan) at 10-min intervals. Maximum and minimum air temperatures were 31.1 C (October 5, 2007)/2.2 C (February 18, 2008) and 29.6 C (October 12, 2013)/ 3.1 C (January 11, 2014), obtained from an automated meteorological data acquisition system (AMeDAS) at Funabashi Meteorological Observatory (latitude 35 420 N, longitude 140 20 E, altitude: 28 m) provided by the Japan Meteorological Agency (JMA; http:// www.jma.go.jp/). Between the gap of the two experiments (2007e2014) there were no environmental and characteristic differences such as light conditions, the features of the campus, and current year's leaf characteristics at the study site. In addition, the significant climate changes were not observed from the data obtained from the JMA about the gap of multiple years between the two experiments (2007e2014). Hereafter, the data of November 13, 2007 and October 26, 2013 will be referred to as autumn data, and the data of February 1, 2008 and February 7, 2014 as winter data. 2.2. Measurements of photosynthetic parameters Photosynthetic parameters were measured on sun-exposed current-year leaves on November 13, 2007 and February 1, 2008. Under field conditions, net photosynthesis (Anet) of the leaves was measured between 11:00 and 14:00 (local time) with a portable gas-exchange analyzer (LI-6400; LI-COR, Inc., USA) attached to a transparent standard leaf chamber (6400-08; LI-COR, Inc.). The potential photosynthetic rate (Amax), the apparent quantum yield of CO2 fixation on an illuminated-light basis (4), and the potential rate of carboxylation by Rubisco (Vcmax) were measured under ambient temperature with an LI-6400 attached to an LED light and CO2 concentration control unit (6400-02B; LI-COR, Inc.). For the determination of Amax, the net photosynthetic rates at 10 stepwise actinic light intensity intervals from 0 to 1500 mmol photons m2 s1 were measured under a cuvette CO2 concentration of 370 mmol mol1. It took 3e4 min to obtain a stable photosynthetic rates at each reduction in the LED intensity. Using these data, Amax was calculated by the equation of Johnson and Thornley (1984). The value of 4 was estimated by linear regression at PPFD
