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Research

Blackwell Science, Ltd

Light interception and dry matter conversion efficiency of miscanthus genotypes estimated from spectral reflectance

measurements

Uffe Jørgensen, Jørgen Mortensen and Christer Ohlsson

Danish Institute of Agricultural Sciences (DIAS), Department of Crop Physiology and Soil Science, Research Centre Foulum, PO Box 50, 8830 Tjele, Denmark

Summary

• Relationships between crop reflectance in the visible and the near infrared wave-lengths are closely correlated with the amount of photosynthetically active tissue inthe crop. Reflectance measurements were used to quantify genotypic differencesin light interception, dry matter (DM) conversion efficiency and senescence patternwithin the genus

Miscanthus.

The aim was to verify this method as a selection toolin plant breeding programmes.• Spectral reflectance of nine genotypes was measured weekly throughout theirsecond and third growing seasons in a field experiment conducted in Denmark. Leafgreenness was assessed by visual scoring.• Significant differences between genotypes in the calculated fraction of PAR inter-cepted in green tissue (f

ipar

) occurred mainly early and late in the growing season.The f

ipar

values correlated well with visual estimates of leaf greenness. Within geno-types accumulated intercepted PAR ranged from 632 to 737 MJ m

−

2

in the thirdyear, while the DM : radiation quotient,

ε

, ranged from 1.06 to 2.53 g MJ

−

1

.• Yield variation between genotypes was mainly caused by differences in

ε

.Measuring spectral reflectance was less time consuming than visual leaf scoring. Thesignificant physiological variation within the genus

Miscanthus

gives good prospectsfor future breeding.

Key words:

spectral reflectance, vegetation index, light interception, biomassconversion efficiency, radiation use efficiency, miscanthus, senescence, energy crop.

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Author for correspondence:

U. JørgensenTel: +45 89991762Fax: +45 89991619Email: uffe.jorgensen@agrsci.dk

Received:

2 July 2002

Accepted:

14 October 2002

Introduction

The perennial C

4

-grass miscanthus originating from south-east Asia has been extensively investigated for its biomassproduction-potential in Europe in the 1980s and 1990s(Lewandowski

et al

., 2000; Jones & Walsh, 2001). Comparedwith other C

4

-genera, miscanthus is more tolerant to thecool climate of north-west Europe (Beale & Long, 1995).Once established, miscanthus is harvested annually and inDenmark needs a rotation of minimum 10–12 yr in order todepreciate establishment costs (Parsby, 1996). The Europeaninvestigations during the first decade were almost exclusivelyconducted with one genotype, the sterile, triploid hybrid

M.

×

giganteus

Greef & Deuter ex Hodkinson & Renvoize(Hodkinson & Renvoize, 2001; similar to

M.

×

ogiformis

Honda ‘Giganteus’ (Linde-Laursen, 1993)). In northernEurope

M.

×

giganteus

was difficult to establish and had arather poor combustion quality because it did not senesce,which delayed leaching of minerals from the crop duringwinter ( Jørgensen, 1997; Venendaal

et al

., 1997). Therefore,the genetic base of miscanthus has been broadened in Europeby collecting and screening existing genotypes ( Jørgensen,1997; Eppel-Hotz

et al

., 1998; Jones & Walsh, 2001) and bydeveloping breeding methods for miscanthus (Deuter &Abraham, 1998).

During the ‘European Miscanthus Improvement’ (EMI)project, 15 genotypes were grown at five sites from Portugalto Sweden, and their biomass production and chemical com-position were measured (Clifton-Brown

et al

., 2001). Spectralreflectance of the genotypes established at the Danish site was

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measured in 1998 and 1999. The aim was to quantify geno-typic differences in light interception and senescence pattern.The ultimate goal was to use the method as a selection tool inplant breeding. Spectral reflectance measurements of miscant-hus genotypes have not been reported before.

Relationships between reflectance in the visible and inthe near infrared spectral regions (Vegetation Indices (VI))are closely correlated with the amount of photosyntheticallyactive tissue in plant canopies (Wiegand & Richardson, 1990;Myneni & Williams, 1994). The fraction of photosyntethi-cally active radiation intercepted (f

ipar

), which is an importantparameter for crop growth modelling, may be directly derivedfrom VI (Christensen, 1992; Christensen & Goudriaan,1993). We have confirmed the relationship between VI andf

ipar

in miscanthus and have shown that, compared with thetraditional use of line quantum sensors, spectral reflectancemeasurements provided a better estimate of PAR-interceptionin green leaves during the late part of the growing season(Vargas

et al

., 2002).Hand-held equipment for remote sensing of spectral

reflectance has been developed and the VI of one experimentalunit can be measured and logged in less than 1 min. Remotesensing of canopy spectral reflectance is a rapid, accurate andnondestructive tool for screening genotypes for their develop-ment and production capacity (Christensen, 1992). Further-more, spectral reflectance may be used to describe differencesin the course of senescence, which influences biomass qualityfor combustion (Jørgensen, 1997). In this article we presentmiscanthus seasonal f

ipar

, accumulated intercepted PAR,biomass yield, DM : radiation quotient and crop greenness ofnine miscanthus genotypes.

Materials and Methods

Design and management of field experiments

The study was conducted on a sandy loam soil (typicFragiudalf (USDA soil taxonomy)), at the Danish Instituteof Agricultural Sciences, Research Centre Foulum, Jutland,Denmark (56

°

30

′

N, 9

°

35

′

E). Fifteen genotypes wereplanted in 1997 in a randomised complete block design inthree replications. The plants were evenly distributed in25 m

2

plots at a density of two plants m

−

2

. Weeds weremanaged manually/mechanically in 1997 and 1998. In 1999the area was treated with glyphosate before emergence ofthe miscanthus shoots. Later, miscanthus was sprayed twicewith 1 l ha

−

1

of ‘Flux Extra’ herbicide (80 g l

−

1

Fluroxypyr,

40 g l

−

1

Clopyralid, 100 g l

−

1

MCPA and 50 g l

−

1

Dicamba).Miscanthus was harvested on 19 November, 1998 and18 October, 1999 for determination of above-ground DM.Further details regarding soil composition and harvestprocedure are provided in Clifton-Brown

et al

. (2001).Climatic data were collected at a meteorological station 1 kmfrom the research site. The mean air temperature during the1998 growing season was slightly below the long-termaverage, while it was 0.7

°

C above the long-term average in1999 (Table 1). Precipitation was close to normal in 1998 andabove normal in 1999.

Plant material

The experiment included four acquisitions of

M.

×

giganteus

(genotype 1–4), which did not survive the first winter inDenmark (Jørgensen & Schwarz, 2000). Genotypes 5 and 9poorly survived the first winter, which resulted in 33 and40% of the original plant stands, respectively. Therefore, themeasurements of spectral reflectance in 1998 and 1999 onlyincluded nine genotypes (Table 2).

Canopy measurement

‘Crop greenness’ was determined as a measure of cropsenescence by measuring the leaves on the tallest shoot ofthree randomly selected plants within a plot. Leaves werescored as green if they had more than 60% green leaf area.‘Greenness’ was estimated as the relation between number of‘green leaves’ and the total number of leaves on the shoot.

Canopy reflectance was measured weekly, beginning at firstleaf development and stopping at first severe frost (<

−

2

°

C at2 m height). Measurements were obtained by using a SDL1800 two-band sensor from Skye Instruments Ltd, Llandrin-dod Wells, Wales, UK and logged on a Hewlett PackardHP95LX computer. The SDL 1800 was fitted with two sen-sors each consisting of two silicon photodiodes equippedwith specific interference filters for the wavelength intervals640–660 nm (red) and 790–810 nm (infrared). The sensorswere mounted on a portable retractile mast. One sensor wascosine-corrected and used to measure the incoming radiation.The other sensor without diffuser had a restricted view angleof 15

°

. The sensor was kept inverted and was used for meas-urements of reflected radiation. The sensors were placed4.5 m above ground to be able to cover a 1.1-m

2

ground-level area. In each plot, four repeated measurements weretaken centred above each of two plants in the plot centre to

Air temp. (°C) Precipitation (mm) Global radiation (MJ m−2)

1998 13.2 286 22411999 14.2 372 24971961–90 13.5 299 2436

Table 1 Climatic data for the growing seasons (May–September) 1998 and 1999 compared with the long-term mean (1961–90)

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reduce the effect of leaf flutter. For each plot, only the meanof the eight measurements was used in the forthcoming cal-culations of statistical differences. Reflectance of radiationfrom the soil in 1999 was measured in a plot kept free of veg-etation by repetitive soil rotary cultivation. Canopy reflect-ance was subsequently corrected for reflectance from the soil.

Calculations

The Ratio Vegetation Index (RVI) was calculated as the ratiobetween the reflection of incoming infrared radiation (

ρ

i

) andthe reflection of incoming red (

ρ

r

) radiation. The fractionof PAR intercepted (f

ipar

) was subsequently calculated byiteration from the theoretically based model derived byChristensen & Goudriaan (1993):

Eqn 1

where:

Eqn 2

Eqn 3

and

ρ

i,s

and

ρ

r,s

are the reflectance from bare soil.

ρ

i,

∞

and

ρ

r,

∞

are the reflectance from the crop at maximumleaf area.

The incoming PAR (S

p

) was estimated as 50% of themeasured global radiation. The daily intercepted PAR (IPAR)during the growing season was calculated for each genotypeby multiplication of S

p

with estimates of f

ipar

obtained bylinear interpolation between measurement dates. AccumulatedIPAR (AIPAR) was summed over the growing season for eachgenotype:

AIPAR

=

Σ

S

p

f

ipar

Eqn 4

The DM : radiation quotient (

ε

, sometimes called radiationuse efficiency) was calculated for each genotype from theabove-ground DM yield harvested in autumn:

ε

=

DM/AIPAR Eqn 5

Genotypic differences were evaluated on the basis ofmeasurement standard deviation and of Tukey’s minimumsignificant difference calculated by the GLM procedure (SASInstitute, ver. 6.12).

Results

Fraction of PAR intercepted in green leaves

To calculate f

ipar

from eqn 1, the reflectance of bare soil andof crop at maximum leaf area was estimated (Table 3). Thebare soil values were means of measurements in anunvegetated plot throughout 1999, and the maximum cropvalues were means of genotype 13 on 23 July and 12 August1999.

All miscanthus genotypes were still in the establishmentphase in 1998 and matured in 1999. Accordingly, meancanopy development was

c.

30 d earlier in the third thanin the second growth period thus resulting in a higher maxi-mum PAR interception (Fig. 1). The initial decline of f

ipar

in1998 was due to an early weed cover. Weeds were removed

EMI Genotype no Description

6 M. sinensis triploid hybrid from cross pollination in a miscanthus population7 Hybrid between two M. sinensis8 Hybrid between M. sacchariflorus and M. sinensis10 Hybrid between M. sacchariflorus and M. sinensis11 M. sinensis genotype collected in central Honshu, Japan (88–110*)12 M. sinensis genotype collected in central Honshu, Japan (88–111*)13 M. sinensis genotype collected in central Honshu, Japan (90–5*)14 M. sinensis genotype collected in central Honshu, Japan (90–6*)15 M. sinensis genotype collected in central Hokkaido, Japan

*These codes were used in the study of Jørgensen (1997).

Table 2 Genotypes planted at Foulum, Denmark, 1997 and measured for spectral reflectance in 1998 and 1999

RVIf f

f fi

r

i, i i, ipar r ipar

r, r r, ipar i ipar

[ ( / )( )] [ ( ) ]

[ ( / )( ) ] [ ( )]= =

+ − × + −+ − × + −

∞ ∞

∞ ∞

ρρ

ρ η ρ ηρ η ρ η

1 1 1

1 1 1

2

2

ηρ ρ

ρ ρrr, r,s

r,s r,

=−

−∞

∞

/1

ηρ ρ

ρ ρii, i,s

i,s i,

=−

−∞

∞

/1

Table 3 Parameter values for Eqn 1 estimated from reflectance measurements above bare soil and above miscanthus at maximum leaf area in 1999

Near infrared Red RVI

Reflectance from bare soil ρi,s = 0.174 ρr,s = 0.111 1.57Reflectance at max. leaf area ρi,∞ = 0.469 ρr,∞ = 0.0262 17.9

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Research266

by row cultivation on day 153 and by hand-weeding onday 159.

The fipar in green leaves of genotype 10 was higher than thatof other genotypes in 1998. Genotype 10 differed signific-antly from the other genotypes from the third measurementdate (19 June) until 12 August (Fig. 2). Genotypes 10 and 15started senescing before other genotypes after the measure-ment on day 267 (24 September). On day 286 (13 October)fipar of genotype 15 was significantly lower than that of othergenotypes. On day 303 (30 October), just before the firstfrost, fipar of genotypes 10 and 15 was significantly lower thanthat of all other genotypes.

In 1999, crop development was again earliest in genotype10, but also genotype 8 had significantly higher fipar than theremaining genotypes in May and early June (Fig. 2). Frommid-July to the end of August, genotype 13 had the signi-ficantly highest fipar reaching 0.89 on Day 224 (12 August). Aslight reduction in fipar occurred for all genotypes in lateAugust followed by a more significant reduction in October.Genotype 15 senesced first and had significantly lower fiparthan the remaining genotypes on day 291–298 (18–25October), while on day 306 (2 November) genotypes 8 and10 reached a similarly low level as genotype 15. First frostoccurred on day 314 (10 November).

Accumulated intercepted PAR (AIPAR)

There was a nearly two-fold increase in AIPAR, calculatedaccording to eqn 4, from 1998 to 1999 (Table 4). In 1998,genotype 10 from the beginning of the season differed fromall other genotypes by intercepting more PAR, and at the endof the season it had accumulated more than 100 MJ m−2

more than any other genotype (Table 4). In 1999, the highestaccumulation of intercepted PAR occurred in genotypes 8, 13and 10.

Yield and dry matter : radiation quotient (ε)

DM yield in autumn increased in most genotypes with afactor of c. 3 from 1998 to 1999 (Table 4). The yield washighest in genotype 10 in both years. However, in 1999 geno-types 6, 8 and 11 also yielded 15 t DM ha−1 or more. Thesegenotypes were amongst those that intercepted the mostPAR. However, genotype 13 intercepted the second highestamount of PAR in 1999, but was only ranked sixth withrespect to yield. Accordingly, when calculating the DM :radiation quotient (eqn 5) genotype 13 had a significantly

Fig. 1 Mean fraction of PAR intercepted (fipar) in green leaf area of nine genotypes in 1998 and 1999.

Fig. 2 Fraction of PAR intercepted (fipar) in green leaf area of selected genotypes during 1998 and 1999. Bars indicate standard deviation (n = 3) at each measurement date.

Table 4 Dry matter yield at harvest in autumn (DM), accumulated intercepted PAR (AIPAR) and DM:radiation quotient (ε) of nine genotypes in 1998 and 1999. The Tukey minimum significant difference (P = 0.05) is given for each parameter

DM (g m−2) AIPAR (MJ m−2) ε (g MJ−1)

Genotype No. 1998 1999 1998 1999 1998 1999

6 523 1641 353 694 1.48 2.367 473 1036 326 632 1.46 1.648 412 1587 375 737 1.09 2.1510 775 1823 483 720 1.59 2.5311 522 1496 378 695 1.37 2.1612 313 1236 344 684 0.91 1.8113 327 1118 346 722 0.95 1.5314 238 988 342 646 0.70 1.5315 193 680 298 643 0.64 1.06

Mean 420 1289 361 686 1.13 1.86Tukey MSD 346 573 54 79 0.82 0.85

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lower ε of 1.53 g MJ−1 compared with the value of 2.53 g MJ−1

in genotype 10 (Table 4).The ε-value increased from 1998 to 1999, but the ranking

of the genotypes was similar regardless of year. Genotypes 14and 15 had the lowest ε-values.

Crop senescence

The visually scored ‘greenness’ values are plotted next to thefipar-values in Fig. 3. Some graphs show mean greenness oftwo to three genotypes, which were very similar. The shape ofthe two curves in each graph is similar until day 300, when the‘greenness’ decreases at a higher rate.

Discussion

The fraction of intercepted PAR in green tissue wassuccessfully estimated from the measured spectral reflectanceof the miscanthus genotypes. Vargas et al. (2002) showedthat the use of VI in M. sinensis ‘Goliath’ provided a betterdescription of green leaf area development than did the use ofsolarimeters, especially late in the growing period when leavessenesced. Solarimeters inserted above and below the canopy

or a ‘Sunfleck Ceptometer’ have hitherto been the methodsused for fipar estimation in miscanthus (van der Werf et al.,1993; Beale & Long, 1995; Greef, 1996; Bullard et al., 1997;Vleeshouwers, 1998; Clifton-Brown et al., 2000). By usingthese methods, however, radiation intercepted by nonphoto-synthetically active tissues (senescent leaves, stems, andflowers) is included. Greef (1996) kept the lower solarimeterabove the senesced leaves at the bottom of the crop so thatthey did not influence the measurement. Beale & Long(1995) in addition made a visual estimation of percentagesenesced shoots and flowers in the upper canopy to correct themeasured interception. Neither of these methods accountedfor dynamic changes in the canopy of leaves, shoots andinflorescences. Like Gallo et al. (1993), we recommend spectralreflectance measurements for the estimation of interceptedPAR in photosynthetically active tissue.

The fipar-values calculated from the measured spectralreflectance reached a maximum of c. 0.8, which was con-siderably lower than the values obtained by the solarimeter/Sunfleck Ceptometer in other studies (van der Werf et al.,1993; Beale & Long, 1995; Greef, 1996; Bullard et al., 1997;Vleeshouwers, 1998; Clifton-Brown et al., 2000), where fiparvalues above 0.95 were reached in the late part of the growing

Fig. 3 The development of fipar and of crop greenness during 1999. Genotypes 11–13 and 14 + 15 are shown as mean of genotypes.

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season. Senescence of leaves generally starts in mid- to latesummer in M. × giganteus and M. sinensis (Greef, 1996;Jørgensen, 1997), which is probably the main reason for thelower fipar calculated from spectral reflectance compared withthe solarimeter-based values (Vargas et al., 2002). Also, develop-ment of flowers may reduce the PAR interception in greentissue significantly, such as in rape (Andersen et al., 1996).However, in miscanthus fipar-values decreased only slightlyafter initial flowering around day 240 in 1999 (Fig. 2).

The changes in leaf greenness followed changes in fipar veryclosely (Fig. 3). Making visual estimates took six to seventimes longer to determine than those of spectral reflectance.Furthermore, spectral reflectance is better suited to integrateuneven patterns of senescence. Physiological senescencebefore the crop is killed by frost is essential to mediate removalof the elements K and Cl by leaching of the plant tissue( Jørgensen, 1997). These elements are harmful to biomasscombustion processes (Sander, 1997). Most genotypes senescedbefore the first frost, but genotype 7 still had c. 40% greenleaves at the time of frost. This stay-green trait of genotype 7was also observed at the other European sites (Clifton-Brownet al., 2001).

In 1999, the DM : radiation quotient (ε) calculated fromabove-ground harvested biomass in the autumn was higherthan that in 1998. The main reason was probably that mis-canthus allocates a large proportion of DM into roots andrhizomes below ground in the establishment phase (Greef,1996). It is likely that the ceiling yield level of a fully estab-lished crop was almost reached in 1999. Therefore, ε was notmuch affected by augmented below-ground translocation.The average yield of October and February harvest of the ninegenotypes in 1999–2000 was 11.0 t DM ha−1, in January2001 it was 11.4 t DM ha−1, and in January 2002 it was 12.8t DM ha−1 (U. Jørgensen, unpublished). Another reason for theincreased ε from 1998 to 1999 might have been the highertemperatures in 1999 (Table 1). Photosynthesis in miscant-hus is very temperature sensitive in the range from 7 to 25°C(Sawada & Iwaki, 1978; van der Werf et al., 1993; Beale et al.,1996). Finally, the contribution from weeds to AIPAR early in1998 (Fig. 1) might also have contributed to the difference inε-value between years.

The calculated ε-values ranged from 1.06 g MJ−1 in geno-type 15 to 2.53 g MJ−1 in genotype 10 in 1999. This is a veryhigh intraspecies variation compared with the results of 12cultivars of spring barley (Hordeum vulgare L.) grown inDenmark (Christensen & Goudriaan, 1993). Significant differ-ences in the above-ground growth rate of cultivars during theseason were calculated, but no significant difference in ε overthe whole season was detected (Christensen, 1992). The mis-canthus genotypes differed in time of onset of senescence. Wemeasured biomass yield at one point in time during cropsenescence (18 October 1999), and the genotypes might havetranslocated different proportions of reserve material torhizomes at that time. It is likely that a 1-month difference

in the onset of DM translocation to rhizomes could result ina difference of up to 20% in the measured above-ground DM(based on Bullard et al., 1995; Greef, 1996; Jørgensen,1997). However, even with a 20% change in DM yield-difference between genotype 10 and 15, ε would still be c. twotimes higher in genotype 10.

The genotypes 14 and 15 were the first ones to start flower-ing in July (Clifton-Brown et al., 2001) and also had thelowest ε, which might indicate that flowering uncoupled photo-synthesis in still green leaves similar to the effect of droughtin certain miscanthus genotypes (Clifton-Brown et al., 2002).However, genotype 11 flowering in August had a higher εthan genotypes 7 (did not flower) and 8 (flowering in Octo-ber). The genotypes 6 and 10, flowering in September had thehighest ε. Whether there is a causal relation between floweringtime and the size of ε therefore needs further investigation.

It is difficult to compare ε from different studies becauseof differences in the methods for measuring PAR intercep-tion, different periods of biomass accumulation (Gallo et al.,1993), and the impacts of other limiting factors such as water,temperature and nutrients (Demetriades-Shah et al., 1992).However, interspecies variation in ε of C4-grasses grownunder similar conditions and measured by similar methodshas been demonstrated by Beale & Long (1995), who esti-mated ε of Spartina cynosuroides to 2.1 g MJ−1 and of M. ×giganteus to 3.3 g MJ−1. Kiniry et al. (1999) measured ε offour grasses and reported three to four times higher values inswitchgrass (Panicum virgatum) compared with sideoats grama(Bouteloua curtipendula).

In a detailed study of M. sinensis ‘Goliath’ at Research CentreFoulum in 1996, Vargas et al. (2002) estimated an ε-valueof 1.90 g MJ−1 from VI-calculated fipar. This value was similarto the average value of the genotypes in 1999 (Table 4). Otherinvestigations in temperate, but warmer climates than theDanish, have reported higher ε-values of M. × giganteuseven when PAR-interception was measured by solarimeters or‘Sunfleck Ceptometer’, which reflects the high temperatureresponse of the photosynthetic production of a C4-crop in acool climate: 2.6 g MJ−1 in the Netherlands (van der Werfet al., 1993), 3.3 g MJ−1 in south-eastern England (Beale &Long, 1995), 2.4 g MJ−1 in northern Germany (Greef, 1996),3.3 g MJ−1 in the Netherlands (Vleeshouwers, 1998) and2.4 g MJ−1 in Ireland (Clifton-Brown et al., 2000).

Genotype 10, which was a hybrid between M. sinensis andM. sacchariflorus showed some remarkable advantages com-pared with the other genotypes. Firstly, genotype 10 survivedwell and provided a complete plant cover. Secondly, it had anearly vigorous growth in the second growing season and thehighest shoot density (U. Jørgensen, unpublished), whichresulted in significantly higher accumulation of interceptedPAR. Under practical agronomic conditions, early leaf devel-opment is important for the crop to compete successfully withweeds and to reduce the need of weed management. Thirdly,genotype 10 had the highest calculated ε-values in both years.

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The last important observation was that even though geno-type 10 remained green throughout the autumn, the greenleaf area decreased rapidly just before the first frost.

Miscanthus is a wild grass that only recently has beencultivated for agricultural purposes ( Jørgensen & Schwarz,2000). ‘The developmental stage of the dedicated energycrops is at stone-age level compared with conventionalagricultural crops, which have been bred and investigated forcenturies’, said the late professor David Hall, Kings College,London, at the first European Energy Crops Conference in1996. Our results showed that even within the current Euro-pean gene pool there is a high physiological variation, whichprovides good prospects for future breeding of improvedmiscanthus genotypes adapted to different climatic regionsin Europe. When comparing the 1999 AIPAR and ε of thelowest yielding genotype 15 with genotype 10 it appeared thatAIPAR was only 12% higher in the high yielding genotype,while ε was 139% higher (Table 4) and thus clearly moreimportant to the 168% yield increase. Similarly, Tollenaar &Aguilera (1992) attributed 80% of the yield increase of a newmaize hybrid to improved ε and only 20% to improved PARabsorption.

The use of spectral reflectance seemingly is an efficientselection tool for miscanthus genotypes with optimal traits asthe spectral technique offers the possibility to distinguishbetween PAR interception and conversion efficiency. Further-more, a description of green canopy development during thegrowing season may reveal and quantify important traits, suchas early leaf area development and course of senescence.

Acknowledgements

This study was funded by the EU contract no. FAIR3 CT-96–1392. We thank Kaj Eskesen and Jens Bonderup Kjeldsenfor their measurements in the miscanthus field.

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