Surface reflectance properties of Antarctic moss and their relationship to plant species, pigment composition and photosynthetic function
2002; Wiley; Volume: 25; Issue: 10 Linguagem: Inglês
10.1046/j.1365-3040.2002.00916.x
ISSN1365-3040
AutoresCatherine E. Lovelock, Sharon A. Robinson,
Tópico(s)Biocrusts and Microbial Ecology
ResumoPlant, Cell & EnvironmentVolume 25, Issue 10 p. 1239-1250 Free Access Surface reflectance properties of Antarctic moss and their relationship to plant species, pigment composition and photosynthetic function C. E. Lovelock, Corresponding Author C. E. Lovelock Smithsonian Environmental Research Center, PO Box 28, Edgewater MD 21037, USA and Dr Catherine Lovelock. Fax: +1 443 4822380; e-mail: [email protected]Search for more papers by this authorS. A. Robinson, S. A. Robinson Institute for Conservation Biology, University of Wollongong, Northfields Avenue, Wollongong, NSW 2522, AustraliaSearch for more papers by this author C. E. Lovelock, Corresponding Author C. E. Lovelock Smithsonian Environmental Research Center, PO Box 28, Edgewater MD 21037, USA and Dr Catherine Lovelock. Fax: +1 443 4822380; e-mail: [email protected]Search for more papers by this authorS. A. Robinson, S. A. Robinson Institute for Conservation Biology, University of Wollongong, Northfields Avenue, Wollongong, NSW 2522, AustraliaSearch for more papers by this author First published: 19 September 2002 https://doi.org/10.1046/j.1365-3040.2002.00916.xCitations: 77AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Abstract In this study the variations in surface reflectance properties and pigment concentrations of Antarctic moss over species, sites, microtopography and with water content were investigated. It was found that species had significantly different surface reflectance properties, particularly in the region of the red edge (approximately 700 nm), but this did not correlate strongly with pigment concentrations. Surface reflectance of moss also varied in the visible region and in the characteristics of the red edge over different sites. Reflectance parameters, such as the photochemical reflectance index (PRI) and cold hard band were useful discriminators of site, microtopographic position and water content. The PRI was correlated both with the concentrations of active xanthophyll-cycle pigments and the photosynthetic light use efficiency, Fv/Fm, measured using chlorophyll fluorescence. Water content of moss strongly influenced the amplitude and position of the red-edge as well as the PRI, and may be responsible for observed differences in reflectance properties for different species and sites. All moss showed sustained high levels of photoprotective xanthophyll pigments, especially at exposed sites, indicating moss is experiencing continual high levels of photochemical stress. Introduction Solar radiation is essential for photosynthesis and growth of plants. The surface reflectance characteristics of leaves is key in determining both the quantity and quality of solar radiation that is incident on leaf internal organs (Vogelmann 1993). Although solar radiation in the visible region drives photosynthesis, absorptance of high levels of visible radiation and radiation at other wavelengths can be damaging. At shorter wavelengths, absorbed UV-B (280–320 nm) radiation can cause lesions to nucleic acid and proteins. Excess levels of visible radiation (400–750 nm) can cause photo-inhibition of photosynthesis (Cornic, Woo & Osmond 1982). High absorptance at longer wavelengths (> 750 nm) leads to increases in temperature that can be detrimental in arid environments where it is important for plants to conserve water by limiting transpiration and to maintain leaf temperatures close to that of air temperatures (Gates et al. 1965; Ehleringer 1981). Variation in absorptance of leaves has been observed (Ehleringer & Björkman 1978; Vogelmann 1993) and specialized adaptation of surface reflectance properties in plants is known to facilitate photosynthetic carbon gain. For example, in desert ecosystems pubescent or waxy leaf surfaces that increase reflectance are common (Billings & Morris 1951; Ehleringer 1981) and have been demonstrated to be important in protection from photo-inhibition of photosynthesis (e.g. Robinson, Lovelock & Osmond 1993). Moreover, epidermal tissues often accumulate compounds that are effective screens against UV-B radiation, thereby decreasing their reflectance in the UV region (e.g. Tevini 1993). In this study we surveyed the natural variability of surface reflectance in moss in continental Antarctica. At the study site in Wilkes Land, eastern Antarctica, conditions are cold and usually very arid, resulting in lichens dominating the rocky, ice-free areas. The moss community is well developed for the region, but it is restricted to melt lakes, melt streams and other locations where free water is available for at least some of the summer (November–March) (Melick, Hovendon & Seppelt 1997). In winter the moss is covered with snow and ice and is subject to disturbance from cryo-perturbation, which causes highly complex microrelief of ridges and valleys within the moss turves. In comparison with lower latitudes, levels of UV radiation are low in Antarctica. But, Antarctica is experiencing large increases in incident UV-B radiation due to reductions in concentrations of stratospheric ozone (Frederick & Snell 1988). Increases in UV radiation are having large effects on the primary production of the oceans (Neale, Davis & Cullen 1998), and could also be affecting terrestrial vegetation. The heat balance of moss, photosynthetic processes and the impacts of enhanced UV radiation are likely to be partially dependent on moss surface reflectance characteristics and pigment composition. Thus, the first aim of this study was to test the hypothesis that moss species and moss inhabiting different environments have different surface reflectance characteristics. We measured the surface reflectance, at approximately 1 nm intervals from 200 to 900 nm, of three dominant moss species over three sites with differing water availabilities, and over differences in microtopography. Surface reflectance properties of vegetation are often used as indicators of photosynthetic function in remote sensing of vegetation (reviewed in Field, Gamon & Penuelas 1994). Variation in reflectance has been observed among plant taxa (e.g. Gates et al. 1965; Peñuelas et al. 1993; Gamon et al. 1995), due to differences in water and nutrient availability (e.g. Peñuelas et al. 1994; Gamon, Serrano & Surfus 1997), environmental stress (e.g. Rock, Hoshizaki & Millar 1988), and both seasonally (Running & Nemani 1988; Gamon et al. 1995) and diurnally (Gamon et al. 1990; Peñuelas et al. 1994; Gamon et al. 1997). Changes in surface reflectance of intact leaves have been directly correlated with leaf chemical composition (Jacquemoud et al. 1996) and changes in photosynthetic processes in some higher plant taxa (Gamon et al. 1990, 1997; Gilmore & Ball 2000). However, it is often difficult to reconcile physiological measurements, which are usually made at the scale of individual leaves and remotely sensed measurements, which are often made at the scale of whole canopies (Williams 1991; Field et al. 1994). Some of the difficulty arises because canopies are complex. Canopies are composed of layers of leaves of different species that can have a range of properties. Leaves within canopies can have varying distributions, orientations, morphologies, internal structures, pigment compositions, and epidermal characteristics, all properties that could influence the surface reflectance of the canopy (Rock et al. 1988; Field et al. 1994; Vose et al. 1995). At the leaf level, mosses are very simple consisting of a few cell layers. But at a higher level of organization, moss turves, although small in comparison to the canopies of trees, are relatively complex, composed of many leafy gametophytes packed together to form what can be thought of as a ‘microcanopy’. In mosses, measurement of photosynthetic processes and surface reflectance can be made at the same scale. Thus, the second aim of our study was to test the hypothesis that the spectral properties of moss are directly related to photosynthetic processes and pigment composition. We wished to understand whether non-destructive hyperspectral measurements could potentially be used to map distributions of moss species and physiological activity both spatially and temporally. Herein we describe tests of correlations among surface reflectance properties and commonly used reflectance indices and pigment concentrations, water contents and photosynthetic function of Antarctic moss. Materials and methods Moss was obtained from three sites around the Australian base Casey, Wilkes Land, continental Antarctica (66°17′ S, 110°32′ E). Two sites were directly adjacent to the base (Red Shed and Science), whereas the other site was 20 km west at Robinson Ridge. Water availability varies across the sites. The Red Shed site is directly adjacent to a large summer melt lake, the Robinson Ridge site is adjacent to a melt stream that flows intermittently over the summer months, whereas at the Science site water is only available when overlying snow melts early in the summer. Temperature also varies over the sites. Robinson Ridge is cooler and more exposed, than the Red Shed and Science sites (Melick et al. 1997). In the early 1990s the Science site was exposed to contamination due to deposition of cement dust during construction (Adamson, Adamson & Seppelt 1994). At each site representative samples, approximately 3 cm2 were cut from the turves over three summer seasons (October to February) from 1996 to 1999. The three most common species, Grimmia antarctici Card., Ceratodon purpureus (Hedw.) Brid., and Bryum pseudotriquetrum (Hedw.) Gaertn., Meyer and Scherb. were sampled. The necessity of minimizing the impacts of the study, the extent of the moss beds (smaller at Science) and the natural distribution of the three moss species resulted in different representations of each species at each site (Table 1). We tested for differences between moss species and the influence of site on pigment and surface reflectance parameters using samples from all sites. We used a subset of the Robinson Ridge and Red Shed Grimmia antarctici samples to test for effects of microtopography. Table 1. Details of species and site for moss samples used in the study Species Number of samples per site Robinson Ridge Red Shed Science Ceratodon purpureus 4 4 5 Bryum pseudotriquetrum 7 3 2 Grimmia antarctici 24 36 2 Total 35 43 9 In addition we tested the influence of moss water content on surface reflectance. We used four samples of G. antarctici from microtopographic ridges at Robinson Ridge. We measured the surface reflectance of the samples when they were dry, and after they had been rehydrated with a fine mist of water for 5 min. Excess water was blotted from the moss before measurements. Moss re-hydrate rapidly, regaining full physiological activity in 1 to 2 min (Robinson et al. 2000). Measuring surface reflectance We used an integrating sphere fitted to a scanning spectrophotometer (sphere diameter 63 mm; sample aperture size 3 cm2; GBC UV-Vis 918; GBC, Melbourne, Australia) to measure spectral reflectance of moss between 200 and 900 nm at approximately 1 nm intervals. The moss turf samples were large enough to completely fill the sample aperture of the integrating sphere. To maintain the moss canopy architecture (gametophyte arrangement) the samples were held in place within a 1 cm deep highly reflective sample holder. For some samples this required shaving tissue from the basal portion of the sample using a razor blade until the turf was 1 cm thick. The depth and packing of the samples resulted in transmittance through the sample being negligible. Reflectance measured therefore represents the moss canopy with green photosynthetic tissue of between 2 and 5 mm depth and 8–5 mm of non-photosynthetic tissue below. From the entire reflectance spectra, using subsets of the total 87 spectra (Table 1), we present mean reflectance at key wavelengths and also calculate reported indices used in remote sensing vegetation (Table 2). The cold hard band (CHB; Gilmore & Ball 2000) has been found to correlate with the formation of a chlorophyll-protein complex in leaves that protects against freezing damage. The photosynthetic reflectance index (PRI; Gamon et al. 1990, 1997) was developed to reflect changes in concentrations of the xanthophyll cycle pigments that are formed when plants are stressed. The amplitude of the reflectance change at the red-edge (δRE) and the position of the red-edge (δλRE) were calculated from the first derivative of the spectra (Horler, Dockray & Barber 1983). Other reflectance indices used by a range of researchers were also calculated (e.g. Carter 1991, 1993; Vogelmann, Rock & Moss 1993; Lichtenthaler, Gitelson & Lang 1996; Gitelson & Merzlyak 1997). Table 2. Calculation of reflectance indices Parameter Index Calculation Cold hard banda CHB (R750 − R710)/(R750 + R710) Normalized difference between the first derivative in the red and greenb EGFN (1st R530 − 1st R710)/(1st R530 − 1st R710) Ratio of first derivative in the green to first derivative in the redb EGFR (1st R530/1st R710) Normalized difference vegetation indexc NDVI (R850 − R680)/(R850 + R680) Normalized pigment chlorophyll ratio indexb NPCI (R680 − R430)/(R680 + R430) Photosynthetic reflectance indexd PRI (R531 − R570)/(R531 + R570) a Gilmore & Ball 2000; bPeñuelas et al. 1994; cRouse et al. 1973; dGamon et al. 1997. Pigment, water and photosynthetic characteristics Prior to measurement of the reflectance spectra, a subset of the G. antarctici samples were dark-adapted for 20 min after which the chlorophyll fluorescence parameter Fv/Fm was measured using a PAM 2000 (H. Walz, Effeltrech, Germany). After the reflectance spectra were measured, the photosynthetically active apices of the moss were removed using a razor blade and the tissue was frozen in liquid nitrogen. Samples were returned to Australia in liquid nitrogen and then stored at −80 °C in a freezer prior to pigment analysis. For chlorophyll and carotenoid determination, samples [50–100 mg fresh weight (FW)] were ground with liquid nitrogen and sand in a mortar and pestle and then extracted in (1·5 mL) 100% acetone. The samples were transferred to a microcentrifuge tube containing 1 mg sodium bicarbonate and kept on ice in the dark for 20 min After centrifugation (13 600 × g for 5 min) the pellet was re-extracted in 0·5 mL 80% acetone using a polypropylene tissue grinder (Crown Scientific, Sydney, Australia). After a further 20 min on ice, the sample was centrifuged as above and the supernatants from each extraction combined and made up to 3 mL with 100% acetone. Chlorophylls and carotenoids were then quantified by high-pressure liquid chromatography (HPLC) using a method adapted from Gilmore & Yamamoto (1991). The samples (30–70 µL) were injected into a Shimadzu HPLC system (Shimadzu, Sydney, Australia) at a flow rate of 2 mL min−1. Solvent A (acetonitrile : methanol : Tris HCL buffer 0·1 m, pH 8·0; 79 : 8 : 3) ran isocratically from 0 to 4 min followed by a 2·5 min linear gradient to 100% Solvent B (methanol : hexane; 4 : 1) which then ran isocratically from 6·5 to 15 min Flow rate was decreased from 2 to 1·5 mL min−1 between 6 and 12 min and then ran at 1·5 mL min−1 until 15 min, to maintain stable pressure. The column was re-equilibrated with solvent A between samples. Pigments were separated on an Spherisorb ODS1 column (Alltech, Sydney, Australia) and quantified by integration of peak areas, detected at 440 nm using a photodiode array detector (Model SPD-M10AVP; Shimadzu), relative to pure chlorophyll (Sigma, Sydney, Australia) and carotenoid (Extrasynthase, Genay, France and VKI, Horsholm, Denmark) standards. Anthocyanin concentrations were determined using the differential pH method of Fuleki & Francis (1968) and Francis (1982). Moss tissue (0·1–0·2 g FW) was ground with liquid nitrogen and sand in a mortar and pestle and then extracted in (1·5 mL) of 1% HCl in methanol. Samples were centrifuged at 13 600 × g for 6 min and absorbance of the supernatant measured at 526 nm One hundred microlitres of sodium acetate buffer (pH 5·0) was then added to 1 mL of the supernatant and after 3 min this sample was centrifuged for 10 min at 13 600 × g before a second measurement of absorbance at 526 nm. Anthocyanin concentration was calculated from the difference in these two absorbance measures. Water content of samples was measured after oven drying at 80 °C to stable weight and is expressed as g H2O g [dry weight (DW)]−1 as described in Robinson et al. (2000). Concentration of UV-B absorbing pigments was determined from 15 to 60 mg of dry moss tips. Dry tissue was weighed, ground in liquid nitrogen with acid-washed sand and then extracted in 1·5 mL of acidified methanol (methanol–H2O–HCl; 79 : 20 : 1). The sample was transferred to a microfuge tube and allowed to stand on ice in the dark, with vortexing every 20 min After 1 h the tube was centrifuged (13 600 × g, 4 min) and the supernatant removed. The final volume of supernatant was made up to 1·5 mL with acidified methanol. Absorbance across the UV-B region (280–320 nm) was scanned spectrophotometrically. Values are expressed as mean absorbance for this wavelength range. Data analysis Correlations among surface reflectance indices, pigments, chlorophyll fluorescence parameter Fv/Fm and water content were tested using the non-parametric Spearman rank correlation (Rho) using the statistical computing package Data Desk 6·1 (Version 6·1; Data Descriptions, Ithaca, NY, USA). Rho detects consistently increasing or decreasing trends but does not assume variables are linearly related. Linear regression was also used to test for significant relationships between moss chlorophyll concentrations and reflectance indices, and among other variables. Tests of the influence of site, species and microtopography on pigments and reflectance parameters were performed using analysis of variance (anova). For tests of sites and species anovas were unbalanced (unequal sample sizes), therefore post hoc tests of differences between individual means were adjusted for the unequal sample sizes using the Bonferroni test. The adequacy of the anova models was assessed by inspecting residual plots. Paired t-tests were used to assess the influence of hydration on reflectance parameters. Results Differences between species in reflectance and pigments Reflectance spectra of mosses were similar in shape to those observed for intact leaves of angiosperms with the major features of the spectra those indicative of chlorophyll (Fig. 1). Examination of the first derivative of the spectra (Fig. 1b) showed typical peaks at the green (approximately 525 nm) and red edge (approximately 700 nm). Moss species did not significantly differ in their UV reflectance (R320), but they differed significantly at 526, 550 and 850 nm, in both δRE and δλRE, and tended to have different CHB (Table 3). In all cases, B. pseudotriquetrum had greater reflectance values. Figure 1Open in figure viewerPowerPoint Mean reflectance spectra (a) and first derivative (b) of all samples of the three common Antarctic moss species: Bryum pseudotriquetrum (dotted line, n = 3), Ceratodon purpureus (dashed line, n = 5) and Grimmia antarctici (solid line, n = 25) collected during the 1997–98 season from the Robinson Ridge and Red shed sites. Table 3. Surface reflectance characteristics and pigment concentrations for three common moss species in Continental Antarctica, (n=11, 12, 63, respectively) Bryum pseudotriquetrum Ceratodon purpureus Grimmia antarctici F P Reflectance R320 0·0070 ± 0·0008 0·0071 ± 0·0010 0·0070 ± 0·0003 NS R526 0·049 ± 0·005 0·022 ± 0·006 0·023 ± 0·001 28·40 < 0·0001 R550 0·055 ± 0·007 0·034 ± 0·008 0·034 ± 0·002 5·84 0·0074 R850 0·388 ± 0·037 0·275 ± 0·020 0·311 ± 0·012 4·29 0·0170 δRE 0·0101 ± 0·0001 0·0060 ± 0·0001 0·0068 ± 0·0001 8·74 0·0004 δλRE 705·4 ± 1·9 700·6 ± 1·0 700·4 ± 0·5 7·33 0·0012 PRI −0·160 ± 0·028 −0·160 ± 0·015 −0·172 ± 0·009 NS NDVI 0·835 ± 0·047 0·800 ± 0·029 0·868 ± 0·012 NS NPCI 0·442 ± 0·057 0·484 ± 0·043 0·398 ± 0·024 EGFR 6·04 ± 1·58 8·82 ± 2·43 8·03 ± 0·85 NS EGFN 0·643 ± 0·042 0·784 ± 0·072 0·701 ± 0·021 NS CHB 0·349 ± 0·058 0·229 ± 0·021 0·261 ± 0·015 2·74 0·0708 Pigments Anthocyanins (A526 diff g−1 FW) 1·2 ± 0·2 1·3 ± 0·2 1·2 ± 0·2 NS Anthocyanins/TChl. (A526 diff mol−1) 2·9 ± 0·3 5·7 ± 1·2 3·0 ± 0·2 7·42 0·0011 UV absorbing pigments Mean A(320−280nm) (g−1 DW) 266 ± 42 127 ± 22 110 ± 9 15·34 < 0·0001 Total chlorophyll (nmol g−1 FW) 475 ± 60 241 ± 40 453 ± 44 2·50 0·0882 Chl a : b ratio 3·2 ± 0·2 3·6 ± 0·3 3·2 ± 0·1 NS VAZ/TChl (mmol mol−1) 64 ± 5 132 ± 36 103 ± 6 3·64 0·0305 %(AZ/VAZ) 18·0 ± 3·9 39·4 ± 4·9 37·4 ± 2·5 6·37 0·0026 Tcar./Tchl. (mmol mol−1) 443 ± 15 643 ± 96 631 ± 31 2·86 0·0629 NS signifies a non-significant difference at the P=0·10 level. Pigment concentrations also varied among species (Table 3). Bryum pseudotriquetrum had higher levels of UV-absorbing pigments but lower carotenoid levels (total carotenoid and xanthophyll concentrations) in comparison with C. purpureus and G. antarctici. Ceratodon purpureus had lower total chlorophyll concentrations than G. antarctici or B. pseudotriquetrum but higher levels of anthocyanins. Many of the moss pigments concentrations tended to co-vary with each other. For example, total chlorophyll concentration was highly correlated with the total carotenoid content (Rho = 0·91). Additionally, concentrations of all the carotenoids tended to be highly correlated (e.g. correlation among lutein and the xanthophyll cycle pigments Rho = 0·726). Anthocyanins, measured as absorptance of extracts at 526 nm and expressed on a fresh weight basis, were also correlated with total chlorophyll (Rho = 0·625). The proportion of xanthophyll-cycle pigments in the de-epoxidated photoprotective forms, zeaxanthin and antheraxanthin, was negatively correlated with total chlorophyll (Rho = −0·482) and positively correlated with the total pool size of the xanthophyll-cycle pigments (Rho = 0·588). Microtopography The PRI was strongly influenced by whether moss was growing on a ridge or valley, but no other reflectance parameter was significantly affected by microtopographic position (Table 4). Samples from ridges had lower values of PRI (more negative) than those in the valleys. Total chlorophyll concentrations were approximately half on the ridges compared to the valleys, whereas the concentration of xanthophyll-cycle pigments per chlorophyll was 50% higher. There was also a significantly higher proportion of the xanthophyll-cycle present in the photoprotective forms on ridges. Table 4. Surface reflectance properties and pigment concentrations of Grimmia antarctici over different microtopographic positions. Moss is from ridges or valleys at Robinson Ridge and Red Shed sites, n = 8 Ridge Valley F P Reflectance R320 0·0058 ± 0·0003 0·0066 ± 0·0006 NS R526 0·027 ± 0·003 0·0022 ± 0·001 NS R550 0·035 ± 0·004 0·042 ± 0·003 NS R850 0·362 ± 0·016 0·374 ± 0·023 NS δRE 0·0079 ± 0·0001 0·0084 ± 0·0001 NS δλRE 700·75 ± 1·26 700·25 ± 1·19 NS PRI −0·213 ± 0·009 −0·117 ± 0·011 48·79 0·0001 NDVI 0·849 ± 0·013 0·882 ± 0·031 NS NPCI 0·333 ± 0·064 0·425 ± 0·069 NS EGFR 8·90 ± 1·77 9·33 ± 2·16 NS EGFN 0·761 ± 0·032 0·780 ± 0·043 NS CHB 0·295 ± 0·025 0·256 ± 0·036 NS Pigments Anthocyanins (A526 diff g−1 FW) 1·0 ± 0·4 1·9 ± 0·3 NS Anthocyanins/TChl. (A526 diff mol−1) 2·7 ± 0·5 2·6 ± 0·6 NS Total chlorophyll (nmol g−1 FW) 375 ± 73 791 ± 66 17·88 0·0008 Chl a : b ratio 3·3 ± 0·2 3·1 ± 0·2 NS VAZ/TChl (mmol mol−1) 130 ± 12 81 ± 6 12·87 0·0030 %(AZ/VAZ) 40·9 ± 5·4 27·1 ± 3·3 4·82 0·0454 Tcar./Tchl. (mmol mol−1) 761 ± 87 465 ± 18 10·98 0·0051 NS signifies a non-significant difference at the P=0·10 level. Sites Over the three sites we observed significant difference in many of the reflectance parameters, but there were no significant effects of site on R320, PRI, NDVI or NPCI (Table 5). The Science site had higher reflectance at 526 and 550 nm, but lower reflectance at 850 nm in comparison with moss growing at the Red Shed and Robinson Ridge sites. Moss at the Red Shed site exhibited greater δRE and δλRE values than the moss at the Robinson Ridge and Science sites. The CHB was also higher at Robinson Ridge than at the other two sites. Moss at the Red Shed site had lower EGFR and EGFN than moss at Robinson Ridge and Science. Table 5. Surface reflectance characteristics and pigment concentrations of moss over three sites in Continental Antarctica. n = 34, 43, 9, respectively Robinson Ridge Red Shed Science F P Reflectance R320 0·0068 ± 0·0004 0·0070 ± 0·0004 0·0086 ± 0·0011 NS R526 0·0027 ± 0·0004 0·0023 ± 0·0004 0·0038 ± 0·0011 4·94 0·0094 R550 0·035 ± 0·002 0·034 ± 0·001 0·052 ± 0·004 3·43 0·0371 R850 0·351 ± 0·017 0·289 ± 0·015 0·331 ± 0·024 4·28 0·0170 δRE 0·0081 ± 0·0001 0·0063 ± 0·0001 0·0070 ± 0·0001 3·93 0·0235 δλRE 703·8 ± 1·1 699·3 ± 0·2 700·1 ± 0·4 11·91 < 0·0001 PRI −0·165 ± 0·014 −0·177 ± 0·010 −0·146 ± 0·011 NS NDVI 0·857 ± 0·019 0·864 ± 0·015 0·808 ± 0·042 NS NPCI 0·454 ± 0·035 0·391 ± 0·027 0·370 ± 0·051 NS EGFR 10·19 ± 1·43 5·86 ± 0·58 9·30 ± 2·99 4·62 0·0127 EGFN 0·764 ± 0·032 0·651 ± 0·023 0·742 ± 0·062 4·36 0·0159 CHB 0·324 ± 0·029 0·226 ± 0·008 0·256 ± 0·026 4·52 0·0137 Pigments Anthocyanins (A526 diff g−1 FW) 1·5 ± 0·2 1·1 ± 0·2 1·3 ± 0·1 NS Anthocyanins/TChl. (A526 diff mol−1) 3·5 ± 0·5 3·3 ± 0·4 3·3 ± 0·3 NS UV absorbing pigments Mean A(320−280nm) (g−1 DW) 213 ± 37 132 ± 20 104 ± 17 4·29 0·0224 Total chlorophyll (nmol g−1 FW) 500 ± 58 374 ± 49 393 ± 39 NS Chl a : b ratio 3·2 ± 0·2 3·3 ± 0. 1 3·4 ± 0·2 NS VAZ/TChl (mmol mol−1) 124 ± 14 93 ± 6 61 ± 7 4·72 0·0114 %(AZ/VAZ) 29·7 ± 3·0 40·4 ± 3·0 28·5 ± 6·3 3·68 0·0292 Tcar./Tchl. (mmol mol−1) 677 ± 55 586 ± 29 458 ± 16 3·19 0·0462 NS signifies a non-significant difference at the P=0·10 level. Differences in reflectance indices corresponded to changes in pigment contents over the sites. Total chlorophyll and anthocyanin concentrations were not significantly different among sites, although the mosses tended to have higher concentrations of these pigments at Robinson Ridge than at the Science and Red Shed sites (Table 5). Xanthophyll pigment concentrations, total carotenoids and concentrations of UV absorbing pigments were all greater at Robinson Ridge than at the other two sites. Relationships among reflectance, plant pigments, water content and photosynthesis Overall, correlation between surface reflectance indices and plant pigment contents was low. Concentration of total chlorophyll was correlated significantly, but not strongly with many of the key reflectance wavelengths and indices (Table 6). The strongest linear regression was between total chlorophyll and reflectance indices calculated with reflectance measured at 850 and 680 nm (either R850, R850–680, and NDVI) and with δRE (Fig. 2). There was no significant relationship between total chlorophyll and EGFR, EGFN or NPCI. Table 6. Reflectance signals of moss over all sites and species, and their Spearman rank correlation (Rho) and linear relationship with chlorophyll concentrations. Reflectance signals are from key wavelengths over the spectra measured. Regressions were carried out on logarithmically transformed data where appropriate Reflectance parameter Rho Regression R2 R280 0·087 NS R320 0·057 NS R476 0·044 NS R526 0·298 LogR526 = −1·72 + 0·000193 × TChl 0·060** R550 0·362 LogR550 = −1·60 + 0·000242 × TChl 0·080*** R680 −0·168 NS R850 0·486 R850 = 0·261 + 0·000134 × TChl 0·166*** R850-280 0·484 R850-280 = 0·254 + 0·000133 × TChl 0·161*** R850-320 0·482 R850-320 = 0·253 + 0·000133 × TChl 0·163*** R850-480 0·485 R850-480 = 0·251 + 0·000134 × TChl 0·166*** R850-526 0·475 R850-526 = 0·239 + 0·000125 × TChl 0·161*** R850-550 0·483 R850-550 = 0·259 + 0·000125 × TChl 0·171*** R850-680 0·488 R850-680 = 0·239 + 0·000132 × TChl 0·179*** R850/480 0·292 R850/480 = 31·83 + 0·0140 × TChl 0·050** R850/526 0·063 NS R850/550 −0·007 NS R850/680 0·462 R850/550 = 13·46 + 0·0139 × TChl 0·107*** R680/850 −0·498 R680/850 = 0·103 + 0·00000651 × TChl 0·122*** δ λRE 0·335 RλRE = 698·8 + 0·00139 × TChl 0·069** δ RE 0·488 RRE = 0·00562 + 0·00000365 × TChl 0·147*** PRI 0·273 PRI = − 0·194 + 0·00000596 × TChl 0·059** NDVI 0·498 NDVI = 0·813 + 0·000113 × TChl 0·125*** EGFR 0·196 NS EGFN 0·107 NS NPCI −0·146 NS CHB 0·408 CHB = 0·198 + 0·000162 × TChl 0·151*** Le
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