Spectral Signatures of Photosynthesis. I. Review of Earth Organisms

“, 1993) and estimate plant productivity (Potter et al., 1993).”

“The refractive index in crop plants has been measured as 1.333–1.48, with averages around 1.43 (the refractive index of air is 1.0, of water is 1.333, and of soybean oil is 1.48) (Gausman, 1974) [wavelength-dependent refractive index (Jacquemoud and Baret, 1990)].”

“Thus, cold, dry environments favor needleleaf plants, wet, temperate environments favor broadleaf species, and hot, dry environments favor succulents with low surface-to-volume ratios (Holdridge, 1967; Schuepp, 1993; Larcher, 1995; Foley et al., 1996).”

“The resulting difference in spectral signatures can be distinguished by satellites (Tucker et al., 1985; Defries and Townshend, 1994).”

“The resulting difference in spectral signatures can be distinguished by satellites (Tucker et al ., 1985; Defries and Townshend, 1994).”

“…the foundation for virtually all life on Earth, with the annual amount of carbon fixed from CO 2 into organic form by land plants and by ocean phytoplankton being each approximately (cid:2) 45–60 Pg-C/year (Cramer et al ., 1999, 2001), or 6–8% of the atmospheric carbon content (Reeburgh, 1997).”

“It does not deal with horizontal variations (wavelengths of critical features) such as variation in other pigments that affect the visible spectrum, observations that the NIR end of the red edge may broaden in curvature and shift in location, and observations that the water absorbance bands may blue- or red-shift with…”

“Chl a In vitro spectra were stretched/shifted in In vitro spectra from wavelengths to match in vivo peaks by linear Junzhong Li (Du et al., 1998) transformation Chl b In vitro spectra were stretched/shifted in In vitro spectra from wavelengths to match in vivo peaks by linear Junzhong Li (Du et al.”

“It does not deal with horizontal variations (wavelengths of critical features) such as variation in other pigments that affect the visible spectrum, observations that the NIR end of the red edge may broaden in curvature and shift in location, and observations that the water absorbance bands may blue- or red-shift with…”

“, 2006) and possibly as high as 120°C (Kashefi and Lovley, 2003).”

“This two-step sequence is known as the “Z-scheme” for the zig-zag in redox potential at each step [first proposed by Hill and Bendall (1960); first proven by Duysens et al .”

“Nitrogen is the main limiting nutrient, and its content in photosynthesizers is the prime correlating variable with photosynthetic capacity (Schulze et al., 1994), since the Chls are tetrapyrroles with four nitrogen atoms surrounding a magnesium atom (Nobel, 1999), and the other pigments and proteins of the photosynth…”

“Components of plant leaf spectral reflectance: physical explanation Grant (1987) and Vogelmann (1993) reviewed in detail the optical properties of plant leaves, so only a brief summary from these reviews is provided here.”

“…with the nonvascular Bryophyta (mosses and liv-erworts) being the earliest, did not occur until 460 Myr ago, after which the abundance of plant life exploded, reaching a first peak of productivity by the end of the Devonian 360 Myr ago (Bambach, 1999; Carroll, 2001; Igamberdiev and Lea, 2006).”

“Other Chls (Chl b/c/d) provide light harvesting roles, but very recently Chl d, which was discovered in cyanobacteria (Miyashita et al., 1996; Miller et al., 2005), may replace Chl a in the RCs in some cyanobacteria that live in environments with little visible light (Chen et al.”

“1 (Kakani et al ., 2003)].”

“Thus, cold, dry environments favor needleleaf plants, wet, temperate environments favor broadleaf species, and hot, dry environments favor succulents with low surface-to-volume ratios (Holdridge, 1967; Schuepp, 1993; Larcher, 1995; Foley et al ., 1996).”

“…theoretical work on the chemical evolution of Chl and the PS II oxygen-evolving complex is based on ancient ocean chemistry (Mauzerall, 1976; Blankenship et al ., 1998; Dismukes et al ., 2001; Dasgupta et al ., 2004) and provides energetic constraints on the steps toward the development of PS II.”

“Thus, with these organisms being less dependent on the heat of the hydrothermal vents, their habitats gradually expanded to shallower waters where solar light could be utilized (Nisbet and Fowler, 1999; Des Marais, 2000).”

“For example, on Earth, the inefficiency of Rubisco (the carbon-fixing enzyme on which all photosynthesis depends and which sometimes is rendered useless for carbon fixation, because it also functions as an oxygenase) is the subject of much lament and agricultural biotechnological research (Parry et al., 2003).”

“The evolution of ocean chemistry could have played a major role in the evolution of Chl (Mauzerall, 1976; Blankenship and Hartman, 1998; Dismukes, 2001; Dasgupta et al., 2004).”

“This two-step sequence is known as the “Z-scheme” for the zig-zag in redox potential at each step [first proposed by Hill and Bendall (1960); first proven by Duysens et al .”

“Recently, Beatty et al .”

“The red edge is so different spectrally from other matter that it has been measured by satellites to identify vegetation cover (Tucker, 1976; Grant, 1987; Sagan et al ., 1993) and estimate plant productivity (Potter et al ., 1993).”

“P680 of PS II is at a higher potential than the water, allowing it to be a strong oxidant of water (Tommos and Babcock, 2000; Blankenship, 2002).”

“, 1995), low-light plants (Marschall and Proctor, 2004), red algae and cyanobacteria absorbing in green wavelengths (Samsonoff and MacColl, 2001), and, recently discovered, cyanobacteria that perform oxygenic photosynthesis utilizing NIR radiation (Chen et al.”

“The fossil record seems to support that the early photosynthesizers were anoxygenic purple bacteria and green sulfur bacteria that used reducing substrates other than water, such as H2 and H2S (Olson, 2006).”

“In C4 photosynthesis, which arose 20–35 Myr ago, CO 2 is similarly concentrated in an intermediate that is transported to an internal bundle of cells that allow stomates to draw in atmospheric CO 2 through a smaller aperture (Sage, 2001).”

“1 ) (additional characterization by Manske et al ., 2005).”

“The theoretical unicellular light limit has been estimated by Raven (1984) to be (cid:2) 0.1 (cid”

“…is produced instead of oxygen, and that sulfur may be further oxidized to sulfate (Van Gemerden and Mas, 1995): When the reductant is H 2 (Vignais et al ., 1985) or Fe 2 (cid:2) (Ehrenreich and Widdel, 1994; Jiao et al ., 2005), the reactions are: (cid:2) 4Fe(OH) 3 (cid:2) 8H (cid:2) (5) (In Eq.”

“A l g a e f r o m L a r k u m a n d V e s k ( 2003 ) .”

“( (cid:5) water (cid:2) (cid:6) algae (cid:5) algae ) z (6) For (cid:5) water ( (cid:4) ), we used water spectral absorption coefficient values as measured by the following sources: 200–380 nm, Segelstein (1981); 380–640 nm, Sogandares and Fry (1997); and 640–2,500 nm, Kou et al .”

“The non–light harvesting pigment anthocyanin, which accumulates at the surface of shade-adapted leaves and makes them red, may provide photoprotection under high light by shading Chl b in chloroplasts from green light (Gould et al ., 2002; Pietrini et al ., 2002).”

“Chl d has its major peak absorbance in the NIR at !720 nm (Manning and Strain, 1943; Larkum and Kühl, 2005), and thus oxygenic photosynthesis is being performed in the NIR! In nonoxygenic bacteria, BChls play the role of primary donor, with a great variety having distinct absorption spectra; a variety of electron dono…”

“When the reductant is H2 (Vignais et al., 1985) or Fe2! (Ehrenreich and Widdel, 1994; Jiao et al.”

“Allen and Martin (2007) provide a nice review of these ideas of the origins of oxygenic photosynthesis.”

“Other Chls (Chl b/c/d) provide light harvesting roles, but very recently Chl d, which was discovered in cyanobacteria (Miyashita et al., 1996; Miller et al., 2005), may replace Chl a in the RCs in some cyanobacteria that live in environments with little visible light (Chen et al.”

“For the upper limit of photon flux density, Wolstencroft and Raven (2002) summarized the literature and found a theoretical tolerance for land plants against photodamage at 6–9 mmol of photons m (cid”

“The first land plants, with the nonvascular Bryophyta (mosses and liverworts) being the earliest, did not occur until 460 Myr ago, after which the abundance of plant life exploded, reaching a first peak of productivity by the end of the Devonian 360 Myr ago (Bambach, 1999; Carroll, 2001; Igamberdiev and Lea, 2006).”

“The latter is so-called because plant photosynthetic pigments absorb strongly in the visible or PAR, which strongly contrasts with high scattering in the NIR due to refraction be-tween leaf mesophyll cell walls and air spaces inside the leaf.”

“…most of the discussion on UV effects on habitability focuses on protection against UV by ozone or microenvironments (Kasting, 1997; Cockell, 1999; Cockell and Raven, 2004), behaviors such as photomotility to avoid the harmful UV (Bebout and Garcia-Pichel, 1995), and specialized screening…”

“…b/c/d) provide light harvesting roles, but very recently Chl d, which was discovered in cyanobacteria (Miyashita et al ., 1996; Miller et al ., 2005), may replace Chl a in the RCs in some cyanobacteria that live in environments with little visible light (Chen et al ., 2005; Larkum and Kühl, 2005).”

“Cyanobacteria are observed to form crusts on dry, hot sand dunes in deserts (Karnieli et al. , 1999).”

“Oxygenic photosynthesis on Earth is limited to photosystems that operate at 400–730 nm, but anoxygenic photosynthesis occurs at wave-lengths as long as 1,015–1,020 nm (Trissl, 1993; Scheer, 2003).”

“7°C, the survival limit for arctic snow algae and arctic ice shelf cyanobacteria (but they require liquid water for growth) (Gorton et al., 2001; Mueller et al., 2005), and as high as !75°C for bacteria in hot springs (Miller et al.”

“…of UV light into the cell [scy-tonemin in arctic cyanobacteria (Mueller et al ., 2005), phenolics in snow algae (Gorton and Vogelmann, 2003), and mycosporine-like amino acids in response to UVB photoreceptors in cyanobacteria and algae (Portwich and Garcia-Pichel, 2000; Hernando et al ., 2006)].”

“The non–light harvesting pigment anthocyanin, which accumulates at the surface of shade-adapted leaves and makes them red, may provide photoprotection under high light by shading Chl b in chloroplasts from green light (Gould et al., 2002; Pietrini et al., 2002).”

“A low pH extreme has been observed for the alga Cyanidium caldarium living at pH 0 (and at 56°C) (Schleper at al ., 1995), and a high pH of 10 for cyanobacteria (Finlay et al ., 1987).”

“Chl a fluorescence spectrum, from spinach chloroplasts, is from Govindjee and Yang (1966).”

“One theory about the origin of photosynthesis is that it began as a fortuitous adaptation of primitive pigments for infrared thermotaxis of chemolithotrophic bacteria in hydrothermal ocean vents [early Archean, possibly 3.8 Ga ago (Nisbet et al ., 1995)].”

“196°C for some methanogenic bacteria) (Junge et al ., 2006) and possibly as high as 120°C (Kashefi and Lov-ley, 2003).”

“Thus, with these organisms being less dependent on the heat of the hydrothermal vents, their habitats gradually expanded to shallower waters where solar light could be utilized (Nisbet and Fowler, 1999; Des Marais, 2000).”

“, 1995), low-light plants (Marschall and Proctor, 2004), red algae and cyanobacteria absorbing in green wavelengths (Samsonoff and MacColl, 2001), and, recently discovered, cyanobacteria that perform oxygenic photosynthesis utilizing NIR radiation (Chen et al.”

“It is also possible that photosynthesis arose first in shallow waters and, before there was oxygenic photosynthesis to provide an ozone shield, ultraviolet (UV) screening proteins led to the transfer of excitation energy to the porphyrin (Mulkidjanian and Junge, 1997).”

“They are often the first colonizers on rock substrate and can be the dominant source of net primary productivity and a source of food for animals in some land ecosystems (Ager and Milton, 1987; Rees et al., 2004), in some cases accounting for 70% of the land cover (Solheim et al.”

“In contrast, Sphagnum mosses increase rather than decrease NIR reflectance when dried (dried spectra not shown), because their means of water supply to the plant’s capitula is not through internal conducting cells but through precipitation or capillary rise only (Harris et al ., 2005).”

“Therefore, most of the discussion on UV effects on habitability focuses on protection against UV by ozone or microenvironments (Kasting, 1997; Cockell, 1999; Cockell and Raven, 2004), behaviors such as photomotility to avoid the harmful UV (Bebout and Garcia-Pichel, 1995), and specialized screening pigments or phenoli…”

“Therefore, most of the discussion on UV effects on habitability focuses on protection against UV by ozone or microenvironments (Kasting, 1997; Cockell, 1999; Cockell and Raven, 2004), behaviors such as photomotility to avoid the harmful UV (Bebout and Garcia-Pichel, 1995), and specialized screening pigments or phenoli…”

“More than eight photons are generally required [experiments have shown up to about 12 photons (Govindjee, 1999)] because some are unsuccessful, and some in addition are used in the processes of cyclic photophosphorylation [which occurs in Photosystem I (PS I) generation of ATP, described later…”

“They are often the first colonizers on rock substrate and can be the dominant source of net primary productivity and a source of food for animals in some land ecosystems (Ager and Milton, 1987; Rees et al ., 2004), in some cases accounting for 70% of the land cover (Solheim et al ., 2000).”

“, 1999, 2001), or 6–8% of the atmospheric carbon content (Reeburgh, 1997).”

“tance) in the NIR [transmittance %15% (Bechtel et al., 2002)].”

“…that prevent the penetration of UV light into the cell [scy-tonemin in arctic cyanobacteria (Mueller et al ., 2005), phenolics in snow algae (Gorton and Vogelmann, 2003), and mycosporine-like amino acids in response to UVB photoreceptors in cyanobacteria and algae (Portwich and…”

“, 1995), and a high pH of 10 for cyanobacteria (Finlay et al., 1987).”

“(1961); see Blankenship and Prince, 1985)].”

“7°C, the survival limit for arctic snow algae and arctic ice shelf cyanobacteria (but they require liquid water for growth) (Gorton et al., 2001; Mueller et al., 2005), and as high as !75°C for bacteria in hot springs (Miller et al.”

“…of all pigments are influenced by the protein complexes in which they are bound, such that there can be variations in the same type of pigment and the peak absorbances in vivo tend to be broadened and shifted compared to those of the pure pigments extracted in solution (Vasil’ev and Bruce, 2006).”

“The first land plants, with the nonvascular Bryophyta (mosses and liverworts) being the earliest, did not occur until 460 Myr ago, after which the abundance of plant life exploded, reaching a first peak of productivity by the end of the Devonian 360 Myr ago (Bambach, 1999; Carroll, 2001; Igamberdiev and Lea, 2006).”

“But, thus, we are still left with the question, why—on Earth—is P680 at 680 nm, or, more generally, why are the other RCs at their exact wavelengths?”

“15.7°C, the survival limit for arctic snow algae and arctic ice shelf cyanobacteria (but they require liquid water for growth) (Gorton et al ., 2001; Mueller et al ., 2005), and as high as (cid:2) 75°C for bacteria in hot springs (Miller et al ., 1998).”

“In general, the literature on light harvesting has focused on excitation energy transfer kinetics, while the literature on RCs has focused on figuring out the molecular structure and mechanisms, genetic lineage, and molecular evolution (Xiong et al., 2000; Dismukes et al., 2001; Ferreira et al., 2004; McEvoy et al., 2…”

“…theoretical work on the chemical evolution of Chl and the PS II oxygen-evolving complex is based on ancient ocean chemistry (Mauzerall, 1976; Blankenship et al ., 1998; Dismukes et al ., 2001; Dasgupta et al ., 2004) and provides energetic constraints on the steps toward the development of PS II.”

“Cyanobacteria and other photosynthetic bacteria are also known to form mutualistic communities in microbial mats in benthic (Decker et al., 2005) and freshwater aquatic environments (Wiggli et al.”

“…a sensible explanation for the uphill exciton transfer from BChl b at 1,013 nm to the RC at 980 nm. Mauzerall and co-workers (Boichenko et al ., 2001; Hou et al ., 2001a,b) quantified, in detail, the entropy changes that occur in PS I, PS II, and cyanobacteria, and found them to be very small.”

“, 2004), in some cases accounting for 70% of the land cover (Solheim et al., 2000).”

“Work on kinetics of exciton transfer (Trissl, 1993; Trissl et al., 1999; Bernhard and Trissl, 2000) implies the optimality of arrangements between the RCs and the light harvesting antennas to ensure efficient transport and trapping of the excitons.”

“This seems to provide a sensible explanation for the uphill exciton transfer from BChl b at 1,013 nm to the RC at 980 nm. Mauzerall and co-workers (Boichenko et al ., 2001; Hou et al ., 2001a,b) quantified, in detail, the entropy changes that occur in PS I, PS II, and cyanobacteria, and found them…”

“4e are in situ measurements of whole mat layers (but outside the water) of species from the same microbial mat in an alpine bog pond (Wiggli et al ., 1999; data courtesy of Reinhard Bachofen).”

“Lean (Lean and Rind, 1998); 400–2,500 nm, Brian Cairns (Cairns et al., 2003).”

“Kiang et al. (2007) note that the red-edge shifts of IPP from shorter to longer wavelengths for species ranging from algae, lichens, mosses, to aquatic and terrestrial plants.”

“This is evident by the spectral signature of our planet (96), which is colored by the pigments engaged in harvesting sunlight.”

“Not unexpectedly, the wavelengths that the pigments of antenna systems have evolved to absorb follow a set of rules (Kiang et al., 2007).”

“The different spectral quality of M stars compared to G stars, for instance, may require phototrophs that process pigments with different absorption characteristics to those on Earth to match the spectrum (Kiang et al. , 2007a, 2007b).”

“Also, the exact location of the light absorption peak of B. viridis is probably sensitive to temperature, and the range of measurements on lab cultures may not be exactly the same as in the bacterium’s native environment (Kiang et al., 2007).”

“Kiang et al. (2007b) calculated photon flux densities reaching the surface on land and underwater (Table 1), and found that the photon surface flux density on planets orbiting M-dwarf stars would peak in particular near-IR wavebands at 0.93-1.1 µm, 1.1-1.4 µm, 1.5-1.8 µm, and 1.8-2.5 µm.”

“Previous work suggested that chlorphyll a evolved to absorb the peak solar photon flux onto the planetary surface (Kiang et al., 2007a, 2007b), which could potentially be predicted for different star–planet combinations.”

“Furthermore, the P680 referred to by Kiang et al. (2007a, b) is the special cluster of 4 Chl a molecules in PS II (see Dekker and van Grondelle 2000, and cited literature) while antenna pigments (which have evolved already at the anoxygenic stage) have, in general, absorption bands at shorter…”

“During our survey of Earth-based photosynthetic organisms, we observed that a number of molecular-scale chemical constraints and global scale environmental pressures determine the optimum wavelength of peak absorbance of PAR (Kiang et al ., 2007).”

“ple, light-harvesting pigments should absorb at wavelengths where there is available light and with sufficient energy per photon to perform the necessary tasks of charge separation or proton pumping (Kiang et al. 2007b; Stomp et al. 2007). Bacteria such as the radiotolerant Deinococcus radiodurans manufacture anti-oxi…”

“…and expensive to repeatedly detect, monitor and document the Figure 2 Major groups of photosynthetic organisms have distinct spectral signatures in the visible and near infrared spectrum, making them potentially distinguishable with hyperspectral remote sensing (reproduced from Kiang et al., 2007).”

“Many photosynthetic microorganisms, including algae and bacterial mats, produce similar characteristic reflectivity rises but at different wavelengths (Kiang et al., 2007a; Hegde et al., 2015).”

“The presence of biological pigments and the distinctive red-edge of chlorophyll have been proposed as potentially useful biosignatures (15, 16).”

“On planets around stars with a different spectral energy distribution (color spectrum) from the Sun, photosynthetic organisms may create features analogous to the VRE but at other wavelengths (Kiang et al., 2007a, 2007b; Kiang, 2008).”

“Kiang et al. 2007a).”

“Each group of photosynthetic organisms has been shown to possess photopigments adapted to their specific light regime ( e.g., Seager et al., 2005; Kiang et al., 2007).”

“For example, some photosynthetic microorganisms, particularly the nonoxygenic bacteria, have light capture systems allowing them to extend the PAR range into the near infrared (up to *1,100 nm; Kiang et al. 2007).”

“Discussing the results of Kiang et al. (2007a, 2007b) and Stomp et al. (2007), Raven (2007) also concluded that photosynthesis can occur on exoplanets in the HZ of M dwarfs.”

“ectral quality of surface irradiance, protecting it from ultra-violet radiation and allowing the emergence of advanced life on land, as well as altering the color balance of light for photosynthesis (Kiang et al., 2007a). Many of the evolutionary developments that brought about these transformations remain enigmatic.…”

“…sunlight, and water, respectively, are widely distributed, yield larger biological productivity, and can modify a whole planetary environment in a detectable way (Léger et al ., 1993; Wolstencroft and Raven, 2002; Raven and Wols-tencroft, 2004; Kiang et al ., 2007a, 2007b; Cockell, 2008).”

“The generality of the red edge depends on the photosynthesis system of exovegetation and the wavelength of that “edge” is likely to shift according to the spectral type of the host star (Wolstencroft & Raven 2002; Kiang et al. 2007a, 2007b).”

“…(e.g., Owen 1980; Angel et al. 1986; Leger et al. 1993; Selsis et al. 2002; Kaltenegger et al. 2010, and references therein) and the vegetation’s red edge(e.g., Arnold et al. 2002; Woolf et al. 2002; Seager et al. 2005; Montañés-Rodŕıguez et al. 2006; Hamdani et al. 2006; Kiang et al. 2007a,b).”

“Kiang et al. (2007) investigated potential photosynthesis on planets orbiting, for example, cool M stars.”

“To absorb energy, most algae use chlorophyll a and carotenoids, whereas green algae use chlorophyll b and diatoms and brown algae use chlorophyll c [83].”

“The first method relies on surface-dwelling life having molecules that absorb in regions of the spectrum to yield spectral features not expected from known abiotic materials (Hegde and Kaltenegger 2013; Kiang et al. 2007a, 2007b).”

“The focus is switching to 2nd or even 3rd generation biofuels (6).”

“uld be like ours is unsubstantiated. In fact, alien vegetation on planets orbiting other star types may photosynthesize at different wavelengths and manifest different colors than terrestrial plants ([272,273]). Previous work has modeled what the expected biosignatures over geologic history for a habitable planet migh…”

“IC PIGMENTS AS POTENTIAL BIOSIGNATURES 355 on the wavelength for the peak photon-flux at the planetary surface if the incident stellar spectrum and the planetary atmospheric parameters are well known (Kiang et al., 2007a, 2007b). However, if the most widespread or detectable surface organisms are not photosynthetic, th…”

“…blue bands subsequently drove more cryptic anoxygenic PS bacteria to adopt BChl which can harvest visible light but just as importantly can harvest far-red radiation, depending on the organism, up to 1050 nm (Larkum 1991, 2003, 2006, 2008; Kiang et al. 2007a,b; Stomp 2007, Ritchie et al. 2017).”

“…as oxygen, ozone, water, methane (e.g. Des Marais et al. 2002; Kaltenegger et al. 2010, and references therein) and a characteristic feature of plants known as the red edge (e.g. Seager et al. 2005; Kiang et al. 2007b,a) will play a key role in searching for life on habitable planet candidates.”

“…properties, which allow organisms to specialize toward different spectral niches, most notably as a function of depth in the water column (Glaeser et al. 2002; Manske et al. 2005; Gomez Maqueo Chew et al. 2007; Kiang, Siefert, et al. 2007; Kiang et al. 2007; Stomp et al. 2007; Chen et al. 2010).”

“Such studies have investigated the vegetation red edge in the Earthshine and in disk-integrated spectra, a near-IR ‘‘edge’’ that might dominate on an M star planet, and even an Archean ‘‘purple Earth’’ due to purple anoxygenic phototrophs (Montanes Rodriguez et al., 2004; Tinetti et al., 2006; Kiang et al., 2007b; Arn…”

“It has also been pointed out that under certain circumstances water splitting may be possible at wavelengths >700 nm in stepped photosynthetic systems (Kiang et al. 2007a, b) but at a cost of lower overall efficiency (Wolstencroft &Raven 2002).”

“Photons of even lower energies (∼1,000 nm) are used by purple anoxygenic bacteria (Kiang et al. 2007).”

“Prior research has furnished an elaborate summary of plant photosynthesis (Jones 2014; Kiang et al. 2007; Lambers, Chapin, and Pons 2008; Porcar-Castell et al. 2014).”

“Absorbance above 700 nm is negligible in most bound Chl a (Kiang et al. 2007), although Photosystem I (PS I) can weakly absorb further into the near infra-red region up to about 730 nm (Gobets and van Grondelle 2001).”

“Some authors have argued that it is a natural consequence of the ready availability of liquid water (H2O) and carbon dioxide (CO2) (e.g., Kiang et al. 2007; Léger et al. 2011).”

“…context, predominantly for black body radiation from red dwarf (M) stars which are cooler than the sun and have a longer wavelength of maximum photon emission (Wolstencroft and Raven 2002; Raven and Wolstencroft 2004; Kiang et al. 2007a, b; Stomp et al. 2007; Raven and Donnelly 2013).”

“Both atmospheric oxygen buildup (Des Marais et al. 2002) and flux spectral signatures of biological pigments (Kiang et al. 2007a, b) arising from photosynthesis have been proposed as biosignatures on extra-solar planets.”

“In the latter category of spectral signatures, the ‘red edge’, which is characteristic of terrestrial vegetation, has received considerable attention (e.g. Seager et al., 1995, Tinetti et al 2006, Kiang et al 2007a).”

“…with increasing severity of thrips damage (high with severe and low with healthy), presumably manifesting the very strong absorption by chlorophyll in this region of the electromagnetic spectrum (Malthus and Madeira 1993, Kumar et al. 2003, Mutanga et al. 2003, Cho 2007, Kiang et al. 2007).”

“This particular signature of vegetation has been proposed as a possible biomarker in Earth-like planets (e.g., Seager et al. 2005; Montañés-Rodŕıguez et al. 2006; Kiang et al. 2007a).”

“It may represent photosynthetic (Kiang et al., 2007) or UV-protective (Mueller et al., 2005; Zenoff et al., 2006) pigments, both of which are likely to exist on other planets, and their structure and function need not be pre-supposed when fluorescent detection is used.”

“For other (exo)planets, we may also expect that photosynthesis is essential in sustaining life over long periods of time (Seager et al. , 2005; Kiang et al. , 2007).”

“…is consistent with results of similar calculations and falls within the range of values quoted in recent literature (Wolstencroft and Ra-ven, 2002; Nobel, 2005; Kiang et al., 2007b; Milo, 2009); the conclusions drawn here would not be significantly altered by using other values within this range.”

“Oxygen has strong absorption bands at 688 and 761 nm (Wolstencroft & Raven 2002; Segura et al. 2005; Kiang et al. 2007a, b, Stomp et al. 2007; Kaltenegger & Traub 2009; Kaltenegger et al. 2010; von Paris et al. 2013; Seager & Bains 2015) but the absence of detectable O 2 does not necessarily mean…”

“The red-edge has been proposed as a possible biomarker in Earth-like planets (Tinetti et al. 2006c; Kiang et al. 2007a,b).”

“A major regular seasonal phenomenon in the oceans are phytoplankton blooms, which will cause spectral alterations of underwater light conditions 66,67 , and are themselves often important food sources.”

“There is a wide variety of chlorophylls allowing its makers to utilize a cornucopia of light environments (Kiang et al. 2007; Stomp et al. 2007).”

“Indeed, Kiang et al. (2007a) showed that Earth-like organisms may be ∼10% as productive around an M dwarf star, where 400–700 nm photons are in short supply, but could produce Earth-like amounts of biomass if the PAR range extends to ∼1100 nm.”

“The second assumption is plausible for planets around stars that have enough high-energy radiation to provide sufficient energy for photosynthesis, such as Solar twins, but becomes less plausible for cooler stars (Kiang et al. , 2007).”