ORIGINAL PAPER

Victoria Stokes Æ Gary Kerr

Relationships between growth and leaf-scale physiological parametersin five Wildstar� cherry clones (Prunus avium L.)

Received: 12 December 2005 / Accepted: 8 March 2006 / Published online: 25 April 2006� Springer-Verlag 2006

Abstract Infra-red gas exchange analysis was used tomeasure leaf-scale physiological parameters of fiveWildstar� cherry clones (Prunus avium L.) and twosources of unimproved stock. Assimilation rate (A),evapotranspiration rate (E), stomatal conductance (gs)and water use efficiency (WUE) were recorded to evaluatewhether the quick and simplemeasurements couldbe usedas a proxy for assessing growth potential of the cherryclones. Differences in A, E and gs were found betweenvarieties, with clone one always having higher rates thanclones two and three.Differences in growthhighlighted byan earlier study were linked to the physiological param-eters described here. Varieties with high A tended to havegood height increment and relative growth rate (RGR),while those with low A, E and gs had poor height incre-ment. However, clone 5, the clone with the largest heightincrement, did not have the highest A, suggesting that itsgood height growth reflected allocation of photoassimi-late to main stem growth relative to branches and roots.Likewise, clone 1 and clone 4 (with high A) were rankedonly second and third in height growth, indicating thatsome of the carbon gain was lost in branching. Clones 2and 3 performed poorly in both physiological parametersand height growth. Although a positive relationship wasfound between assimilation rate and growth, the rela-tionship was not strong enough to assess growth potentialof the cherry clones accurately, perhaps due to differencesin the allocation of dry matter within the plant.

Keywords Prunus avium Æ Physiology Æ Growth ÆPhotosynthesis Æ Evapotranspiration Æ Stomatalconductance Æ Relative growth rate

Introduction

One of the most significant developments in the avail-ability of broadleaved planting stock in Britain over thepast 20 years has been the development of Wildstarclones of Prunus avium L. developed by HorticultureResearch International (HRI). These clones are avail-able from three nurseries and come as mixtures of sevenor more clones (Russell 2002). The clones are signifi-cantly more expensive than normal planting stock beingthree to four times the price depending on the size andquantity ordered. The main advantages claimed are:

1. The clones are from genuine native cherry trees.2. Canker resistance is medium to high.3. Shortened rotation time of 45–55 years compared

with the normal 50 years on fertile sites and 65 yearson moderate sites for unimproved stock (Kerr andEvans 1993).

4. Rapid establishment.5. Good habit and vigour.

However, a recent evaluation of five of the clones byKerr and Rose (2004) has shown that some of theseclaims are not fully supported. Data from one of twotrial sites described by Kerr and Rose (2004) arereproduced as Tables 1 and 2. The growth of theWildstar clones was found to be significantly better thanthe unimproved stock in terms of height increment andrelative growth rate (RGR). However, some of theclones compared poorly with the normal planting stockin terms of form (scored as 1 is potentially excellenttimber tree, 2 is potential timber tree, 3 is candidate toremove in early thinning) and resistance to bacterialcanker (Pseudomonas syringae pv. morsprunorum) (Kerrand Rose 2004).

The purpose of this study was to determine whetherquick and simple Infra-red Gas Analyser (IRGA) mea-surements of leaf-scale physiological parameters couldbe used to evaluate the growth performance of the trees.Other studies have demonstrated a link between genetic

Communicated by Rainer Matyssek

V. Stokes (&) Æ G. KerrForest Research, Alice Holt Lodge, Wrecclesham,Farnham, Surrey GU10 4LH, UKE-mail: Victoria.Stokes@forestry.gsi.gov.ukTel.: +44-1420-22255Fax: +44-1420-520558

Eur J Forest Res (2006) 125: 369–375DOI 10.1007/s10342-006-0127-5

variation in physiological parameters and growth (Ledig1976; Fasehun 1978 in Populus X. euramericana, Ri-ikonen et al. 2003 in Betula pendula). However, thecorrelation between photosynthetic rate and growthparameters has been found by various studies to bepositive (e.g. Ceulemans and Impens 1983; Nelson andEhlers 1984) negative or non-existent (e.g. Pearcy andUnstin 1984) and probably depends on the growthparameter used and allocation or distribution of drymass within the plant.

The existence of a strong and robust relationshipbetween easily measured leaf-scale physiologicalparameters and growth could be used to distinguishsuperior clones for further tree breeding and improve-ment (Lapido et al. 1984; Ceulemans et al. 1987).

Methods

The Alice Holt experiment is situated in a researchenclosure near to the Forestry Commission ResearchStation in Hampshire, UK (Lat. 51:10:38N; Long.0:50:49W). The soil is a surface water gley (714daccording to Avery 1980) and supported a grass swardbefore the establishment of this experiment; the site issheltered by surrounding mature woodland on all sides.The site is at 120 m above sea level and is flat; averagerainfall is 700 mm per year measured at a nearbymeteorological station. The experiment is a completelyrandomised design with 20 single tree plots of each of

seven treatments (five clones; C1–C5, and two sources ofunimproved stock; S1 and S2). The experiment was laidout as a rectangle consisting of 7 rows·20 columns withtrees planted at 2 · 2 m2 spacing. The trees were plantedin April 1999 inside a deer and rabbit-proof fence, treeswere notch planted into screefed planting positions thatwere 1.0 · 1.0 m2 and further protection was providedwith 0.6 m treeshelters. Weed control was applied tokeep a 1 m diameter zone around each tree 90% weed-free by use of propyzamide and glyphosate, according tothe guidance of Willoughby and Dewar (1995). Heightincrements and RGR were calculated for years 1–4. TheRGR were calculated using the equation below fromHunt (1978).

RGR ¼ Log eH2 � Log eH1

where RGR is relative height growth rate, H1 is initialheight and H2 is final height.

Form was assessed using the scale of 1 for a poten-tially excellent timber tree, 2 for a potential timber treeand 3 for a candidate to remove in early thinning (seeKerr and Rose 2004).

During the summer of 2004 measurements of pho-tosynthetic assimilation rate (A, lmol m�2 s�1), evapo-transpiration (E, mmol m�2 s�1) and stomatalconductance (gs, mmol m�2 s�1) of the trees were madeusing a field-portable IRGA (TPS-1, PP-Systems, Hit-chin, Herts, UK). These measures allow comparison ofthe rates of carbon acquisition and concurrent water lossof the different clones under field conditions. The ma-chine also recorded photosynthetically active radiation(PAR, lmol m�2 s�1) and air temperature at eachmeasurement. The functioning and use of an IRGA isdescribed in more detail by Long et al. (1996) and Par-sons et al. (1997). The standard equations used to cal-culate A, E and gs are described by Postl and Bolhar-Nordenkampf (1993). The ratio of assimilation (A) toevapotranspiration (E) was calculated to determine wa-ter use efficiency (WUE, mmol mol�1); this is anexpression of the amount of carbon gained for each unitof water lost from the leaf.

Measurements were made on four dry days in Julyand early August 2004, on days with constant sky con-ditions. Measurements were made between 10:00 and14:00 h to minimise the influence of diurnal fluctuationsof physiological parameters and leaves from the differenttreatments were assessed at random to prevent anysystematic error. The weather conditions on each of thefour measurement days are described in Table 3.

Table 1 Summary of performance of Wildstar� clones and twounimproved stocks at the Alice Holt site: results

Meanheight(cm)April 1999

Meanheightincrementto December2002 (cm)

Meanrelativegrowth rate

Meanformscorea

Clone 1 14.1 262.8 3.0 2.6Clone 2 20.8 223.6 2.5 2.9Clone 3 7.6 207.1 3.4 2.4Clone 4 17.9 251.3 2.7 1.9Clone 5 8.3 285.5 3.6 1.4Polish (S1) 41.6 180.2 1.7 2.0Hungarian (S2) 28.5 188.1 2.0 2.2Mean of clones 246.1 3.0 2.2Mean of unimproved 184.2 1.8 2.1

a1 is potentially excellent timber tree, 2 is potential timber tree, 3 iscandidate to remove in early thinning (see Kerr and Rose 2004)

Table 2 Summary ofperformance of Wildstar�clones and two unimprovedstocks at the Alice Holt site:summary of analysis

Student’s t (P £ 0.05) = 1.98;ns not significant, SED stan-dard error of the differencesbetween means***P £ 0.001

Source/contrasts Degrees offreedom

Height increment RGR

Significance SED Significance SED

Clones versus unimproved stock 1 *** 8.3 *** 0.05Between unimproved stock 1 ns – *** 0.09Between clones 4 *** 14.0 *** 0.09Residual 133Total 139

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Individual fully expanded, healthy leaves of the same agewere selected from the South-facing, outer edges of thecanopy at mid-canopy height (1.5 m). One leaf wassampled from each tree (20 per clone) on each samplingdate, with different leaves being sampled on each date.Nine of the 140 trees had died (one each of C2, C4 andS1 and six of C3) but no duplicate measurements weremade to ensure that samples remained independent.Leaf chamber conditions were maintained as close aspossible to ambient and measurements were takenwithin 1 min of the leaf entering the chamber to mini-mise any influence of the chamber on the leaf processes.

Data were analysed using analysis of variance (Gen-stat 2003) with measurement day included as a split-plotin time factor. The five clones and two unimprovedstocks were treated as seven ‘varieties’ and t-tests werecarried out to examine the significance of differencesbetween (a) the clones and the unimproved stock and (b)between the two unimproved stocks.

Results

Variety differences

There were differences in A among varieties at the 6%significance level (Fig. 1a, Table 4) with C1 and C4having the highest A, both higher than those achieved byC2 and C3. There were no significant differences be-tween the clones and the unimproved stocks or betweenthe two unimproved stocks.

There were differences in E between the varieties(P = 0.005) with C1, C4 and S2 having higher E thanC2 and C3 (Fig. 1b, Table 4). Again, there were nosignificant differences in evapotranspiration rate be-tween the clones and the unimproved stocks or betweenthe two unimproved stocks.

A similar pattern was seen for stomatal conductancewith differences observed among the seven varieties(P < 0.001) (Fig. 1c and Table 4). Clones 2 and 3 hadlower stomatal conductance than C1 and S2.

There were no significant differences between varie-ties for WUE (Fig. 1d and Table 4) because although Aand E were different among varieties, the ratio betweenA and E was relatively constant overall.

Differences between assessment dates

There were differences for A, E, gs and WUE betweenassessment dates (all P < 0.001, Table 4). All sevenvarieties had a low A and high WUE on day 3 (Fig. 2)due to the overcast sky conditions, generally low levelsof PAR (Table 3) and low V (leaf to air vapour pressuredifference, kPa, Table 3). The highest mean overallassimilation rates were on day 2, the hottest andbrightest day.

The highest gs values for all varieties were recordedon day 1 (Fig. 3) which had the lowest temperatures and

thinly overcast skies, with medium-low PAR. The V ondays 1 and 3 was much lower than on days 2 and 4(Table 3) corresponding with high WUE. Therefore,despite the light levels on day 4 being double those onday 1, the mean overall A and WUE were higher on day1 (Table 3) as the low V did not induce stomatal limi-tation. C3 and S1 had particularly low A on days 2 and 4compared to day 1 (Fig. 2) indicating that stomatallimitation caused by high V on days 2 and 4 may havesignificantly reduced A for these varieties.

5

5.5

6

6.5

7

7.5

C1 C2 C3 C4 C5 S1 S2

Variety

C1 C2 C3 C4 C5 S1 S2

Variety

C1 C2 C3 C4 C5 S1 S2

Variety

mea

n A

(µm

ol m

–2 s

–1)

1.8

2

2.2

2.4

2.6

mea

n E

(m

mol

m–2

s–1

)

100

120

140

160

180

200

mea

n g s

(m

mol

m–2

s–1

)

2.60

2.70

2.80

2.90

3.00

3.10

3.20

C1 C2 C3 C4 C5 S1 S2

Variety

mea

n W

UE

(m

mol

mol

–1)

a

b

c

d

Fig. 1 Mean physiological parameters for the four measurementdays: a assimilation (A, lmol m�2 s�1), b evapotranspiration (E,mmol m�2 s�1), c stomatal conductance (gs, mmol m�2 s�1) and dwater use efficiency (WUE, mmol mol�1). Bars = ±1SE (0.3018,0.0810, 8.38 and 0.125, respectively)

371

Although for A, E and gs there were no significantinteractions between variety and day (P = 0.092,P = 0.085 and P = 0.195, respectively) for WUE therewas an interaction between variety and day (P = 0.017)

and between the two unimproved stocks across days(P = 0.039). This is particularly interesting becausethere was no overall significant effect of variety on WUE(P = 0.838). This was caused by a change in the A/E

Table 3 Weather conditions and physiological parameters recorded on the four measurement days

Measurement date Sky conditions Air Temperaturea PARb Vc Ad Ee gsf WUEg

28 July 2004, day 1 Hazy, thinly overcast 26.4 349 1.38 6.9 2.43 199.4 2.9029 July 2004, day 2 Clear 29.8 945 2.29 7.5 2.72 130.2 2.773 August 2004, day 3 Overcast 26.7 228 1.23 5.2 1.62 139.6 3.364 August 2004, day 4 Clear 29.0 846 1.85 6.2 2.20 134.4 2.82

a�C, recorded by the gas analyser for each measurementbMean photosynthetically active radiation, lmol m�2 s�1cMean V, leaf to air vapour pressure difference, kPadMean assimilation rate, lmol m�2 s�1eMean evapotranspiration rate, mmol m�2 s�1fMean stomatal conductance, mmol m�2 s�1gMean water use efficiency, mmol mol-1

Table 4 Analysis of physiological measurements

Source/contrast Degrees of freedom Aa sign. SED Eb sign. SED gsc sign. SED WUEd sign. SED

Variety 6 bs (P = 0.059) 0.427 ** 0.115 *** 11.84 ns 0.177Clone versus unimproved 1 ns ns ns nsUnimproved S1 versus unimproved S2 1 ns ns * nsResidual 133Day 3 *** 0.262 *** 0.066 *** 6.37 *** 0.120Clone versus day 18 ns 0.737 ns 0.189 ns 18.80 * 0.328Clone versus Unimproved day 3 ns ns ns nsUnimp S1 versus Unimproved S2 day 3 ** ns ns *Residual 399Total 559

ns not significant, bs borderline significant, SED standard error of the differences between means*P £ 0.05**P £ 0.01***P £ 0.001aAssimilation rate, lmol m�2 s�1bEvapotranspiration rate, mmol m�2 s�1cStomatal conductance, mmol m�2 s�1dWater use efficiency, mmol mol�1

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

C1 C2 C3 C4 C5 S1 S2

Variety

Mea

n A

(µm

ol m

–2 s

–1)

Day 1

Day 2

Day 3

Day 4

Fig. 2 Mean assimilation rate (lmol m�2 s�1) for clones 1–5 andthe two unimproved stocks showing variation between the fourmeasurement days. Bars = ±1SE (0.5210)

0

50

100

150

200

250

300

C1 C2 C3 C4 C5 S1 S2

Variety

Mea

n g s

(m

mol

m–2

s–1

)

Day 1

Day 2

Day 3

Day 4

Fig. 3 Mean stomatal conductance (gs, mmol m�2 s�1) for clones1–5 and the two unimproved stocks showing variation between thefour measurement days. Bars = ±1SE (13.29)

372

ratio (WUE) in some varieties that occurred on the dullday 3. Although the reduction in E on day 3 (due to thecooler, dull weather conditions and low V) was similarfor S1 and S2 (data not shown) the reduction in A wasgreater for S2 than for S1 (Fig. 2) resulting in low WUEfor S2.

In summary, although A, E and gs differed signifi-cantly between varieties, varietal differences did notdiffer between days. The WUE was not significantlydifferent between varieties. However, on particular days,small (non-significant) changes in A and E of somevarieties resulted in significantly different WUE, andhence interaction between variety and day and betweenS1 and S2 and day.

Link with growth rate

There were significant differences between varieties forA, E and gs that may be related to differences in early(years 1–4) height increment or RGR. Mean values ofthese parameters were ranked to facilitate comparison ofthe different varieties (Table 5).

The two best varieties for A (C1 and C4) had goodheight increments and RGR. C5, the third highestranking variety for A (although not significantly higherthan C2 and C3) had the largest height increment andRGR. Varieties with high A therefore tended to havegood growth rates.

The two varieties with the lowest A, E and gs were C2and C3. These two varieties had poor form and thelowest growth rates within the improved stocks; how-ever, C3 had high RGR due to its initial small size.

Relationships between early growth rate and sub-sequent physiological parameters were investigated,however, no clear relationships were observed betweenparameters.

Discussion

One of the objectives of the study described here was toexamine the physiology of young cherry trees. The rangeof assimilation values recorded was similar to, although

slightly lower than those from other studies, for exam-ple, Centritto et al. (2000) measured A of P. aviumsaplings at 14:00 h on a hot summer day in Italy andfound values in the range of 15 lmol m�2 s�1. Similarly,Niederleitner and Knoppik (1997) recorded A of 9–17 lmol m�2 s�1 for five different clones of P. avium inGermany. The WUE values were also similar to thisstudy, being 1.5–3 mmol mol�1. Quilot et al. (2004)measured Asat (maximum A under saturating light con-ditions) of peach clones derived from Prunus davidianaand found Asat to be highly variable between clones,with values from 7 to 18 lmol m�2 s�1.

Transpiration rates recorded in this study were lowerthan those of 4.5–5.5 mmol m�2 s�1 recorded by Nie-derleitner and Knoppik (1997) for five different clones ofP. avium in Germany in saturating light. Centritto et al.(2000) also recorded transpiration values of 3–6 mmol m�2 s�1 in shaded and 4–9 mmol m�2 s�1 inunshaded P. avium saplings, depending on time of year,again higher than values in this study. This could becaused by different conditions of temperature and soilmoisture. Stomatal conductance values were similar tothose of 50–650 mmol m�2 s�1 recorded for P. davidi-ana by Quilot et al. (2004).

The high gs values seen in all varieties on day 1 (whichhad low temperatures, thinly overcast skies, medium-lowPAR and low V) compared to days 2 and 4 (hot andbright with high V) may indicate that conductance wasreduced by stomatal closure on days 2 and 4 to preventexcessive water loss. This may have limited assimilationrates in C3 and S1, which achieved higher A on the hazyday 1 than on the hot, bright days 2 and 4. The highWUE seen on days 1 and 3 (cooler and duller) representsa strategy of maximising production in the often-dullBritish climate, enabling significant levels of photosyn-thesis to occur at relatively low light levels. A similarconservative water-use strategy was found by ChunYinget al. 2005) in which Populus przewalskii was found tohave a higher drought tolerance and WUE than P.cathayana.

The main findings from Kerr and Rose (2004) con-cerning the growth of the clones were: (1) the clones hadsuperior growth compared with the unimproved stock;(2) the two sources of unimproved stock had marginallydifferent RGR and (3) there were significant differencesin growth between clones. Each of these can be reviewedin the context of the results of this study.

Firstly, the clones did not necessarily achieve higherA than the unimproved stock. The lowest A of all vari-eties was in C2 and C3 may have been caused by low gsand limited supply of CO2 to the intercellular spaces, aswas also found by Riikonen et al. (2003) for B. pendulaclones. The C1–C3 came from the 1950s improvementprogramme when emphasis was on canker resistanceand not growth (Russell 2002); therefore it was notsurprising that C2 and C3 had low values of A. Thisimplies that the superior growth of the clones comparedto the unimproved stock, found by Kerr and Rose(2004) cannot be entirely related to differences in A and

Table 5 Rank of mean growth and physiological parameters of theseven varieties

Variety Heightincrement

RGR Aa Eb gsc Form

(mean value)

C1 2 3 1 1 1 2.6C2 4 5 6 6 7 2.9C3 5 2 7 7 6 2.4C4 3 4 2 3 4 1.9C5 1 1 3 4 3 1.4S1 7 7 5 5 5 2.2S2 6 6 4 2 2 2.0

aAssimilation rate, lmol m�2 s�1bEvapotranspiration rate, mmol m�2 s�1cStomatal conductance, mmol m�2 s�1

373

that the relationship between A and growth may not bevery strong.

Secondly, a significant difference between the twosources of unimproved stock was found in terms of gs(and borderline significant difference for E). This indi-cates that S1, the variety with the lower RGR and heightincrement according to Kerr and Rose (2004) may havea degree of stomatal limitation under conditions of highV. This is supported by the significant interaction ofWUE between the two unimproved stocks and day.However, the difference in growth rate between thesetwo treatments was quite small and the fact that anyphysiological differences were found at all is perhapssurprising. Again, the relationship between stomatalconductance and growth is weak and cannot be used topredict the growth potential of the varieties.

There were significant differences in A, E and gs be-tween the varieties. Other than clone 5, varieties wereranked in a similar order to the differences in growthfound by Kerr and Rose (2004) indicting that the cloneswith high A and high gs were the clones that grew best.Therefore there was a positive relationship between leaf-scale physiological parameters and growth for cherry, asfound by Ceulemans and Impens (1983) and Nelson andEhlers (1984) for Populus clones. However, the rela-tionship was confounded by other factors, resulting indiscrepancies, such as C5, which had the best growthdespite average assimilation rates. This suggests that thegood height growth of C5 was also influenced by theway in which the clone partitioned dry matter into itsmain stem and not ‘wasting’ it in the production ofexcessive side branches, rather than any measure of leafphysiology. Further evidence for this was the fact thatC5 had the best form of any of the seven varieties.Likewise, the high A of C1 may have been partially ‘lost’in poor form; this clone had the worst form of anyvariety.

Mebrahtu and Hanover (1991) found that weakcorrelations between A and growth parameters of Ro-binia pseudoacacia L. seedlings were improved byincluding the total plant leaf area. They conclude thatwhen using A as an indicator of yield, care must be takento define factors such as time of day, genetic variation inshoot structure and phenology, and environmentalconditions.

Conclusions

Although there was a positive relationship between Aand growth, the good growth of the clones compared tothe unimproved stock (Kerr and Rose 2004) was notentirely due to higher A. Likewise, although the varietieswith high A and gs tended to have the best growth, therewere exceptions, in particular C5.

Assimilation rates in C3 and S1 may have been lim-ited by stomatal closure to reduce water loss duringconditions of high V, perhaps contributing to their lowgrowth rates.

In conclusion, although a positive relationship wasfound between the quick and simple measurements ofassimilation rate and growth, the relationship was notstrong enough to assess growth potential of the cherryclones sufficiently accurately to be of use for breedingprogrammes. The influence of other factors, perhaps thegrowth form and allocation of dry matter within theplant, was large enough to confound the relationship.

Acknowledgment Many thanks to Jane Poole for advising on andcarrying out the statistical analyses.

References

Avery BW (1980) Soil classification for England and Wales (Highercategories). Soil survey technical monograph No.14. Soil Sur-vey of England and Wales, Harpenden

Centritto M, Loreto F, Massacci A, Pietrini F, Villani MC, Zac-chini M (2000) Improved growth and water use efficiency ofcherry saplings under reduced light intensity. Ecol Res 15:385–392

Ceulemans R, Impens I (1983) Net CO2 exchange and shootgrowth of young poplar Populus clones. J Exp Bot 34:866–870

Ceulemans R, Impens I, Steenackers V (1987) Variations in pho-tosynthetic, anatomical and enzymatic leaf traits and correla-tions with growth in recently selected Populus hybrids. Can JFor Res 17:273–283

ChunYing Y, XiAng W, BaoLi D, JianXun L, ChunYang L (2005)Early growth, dry matter allocation and water use efficiency oftwo sympatric Populus species as affected by water stress.Environ Exp Bot 53(3):315–322

Fasehun FE (1978) Effect of irradiance on growth and photosyn-thesis of Populus X. euramericana clones. Can J For Res8(1):94–99

GenStat (2003) The guide to GenStat release 7.1 Part 2: statistics.In: Payne RW (ed) Lawes agricultural trust (RothamsteadExperimental Station).VSN International, Oxford

Hunt R (1978) Plant growth analysis: studies in biology, vol 96.Edward Arnold, London

Kerr G, Evans J (1993) Growing broadleaves for timber. Forestrycommission handbook, vol 9. HMSO, London

Kerr G, Rose D (2004) An evaluation of Wildstar� clones ofPrunus avium L. Q J Forest 98(4):263–271

Lapido DO, Grace J, Sandford AP, Leakey RRB (1984) Clonalvariation in photosynthetic and respiration rates and diffusionresistances in the tropical hardwood Triplochiton scleroxylon K.Schum. Photosynthetica 18:20–27

Ledig FT (1976) Physiological genetics, photosynthesis and growthmodels. In: Cannell MGR, Last FT (eds) Tree physiology andyield improvement: carbon fixation efficiency. Academic Press,London

Long SP, Farage PK, Garcia RL (1996) Measurement of leaf andcanopy photosynthetic CO2 exchange in the field. J Exp Bot47:1629–1642

Mebrahtu T, Hanover JW (1991) Family variation in gas exchange,growth and leaf traits of black locust half-sib families. TreePhysiol 8:185–193

Nelson ND, Ehlers P (1984) Comparative carbon dioxide exchangefor two Populus clones grown in growth room, greenhouse andfield environments. Can J For Res 14:924–932

Niederleitner S, Knoppik D (1997) Effects of the cherry leaf spotpathogen Blumeriella jaapii on gas exchange before and afterexpression of symptoms on cherry leaves. Physiol Mol PlantPathol 51:145–153

Parsons R, Weyers JDB, Lawson T, Godber IM (1997) Rapid andstraightforward estimates of photosynthetic characteristicsusing a portable gas exchange system. Photosynthetica 34:265–279

374

Pearcy RW, Unstin SL (1984) Effects of salinity on growth andphotosynthesis of three California tidal marsh species. Oeco-logia 62:68–73

Postl WF, Bolhar-Nordenkampf HR (1993) GASEX: a program tostudy the influence of data variations on calculated rates ofphotosynthesis and transpiration. In: Hall DO, Scurlock JMO,Bolhar-Nordenkampf HR, Leegood RC, Long SP (eds) Pho-tosynthesis and production in a changing environment: a fieldand laboratory manual. Chapman and Hall, London

Quilot B, Genard M, Kervella J (2004) Leaf light-saturated pho-tosynthesis for wild and cultivated peach genotypes and theirhybrids: a simple mathematical modelling analysis. J Hortic SciBiotech 79(4):546–553

Riikonen J, Oksanen E, Peltonen P, Holopainen T, Vapaavuori E(2003) Seasonal variation in physiological characteristics of twosilver birch clones in the field. Can J For Res 33:2164–2176

Russell K (2002) Wild cherry program gets star rating. ForestTimber News (Woodland Owner Supplement) 1:4–6

Willoughby I, Dewar J (1995) The use of herbicides in the forest.Forestry commission handbook, vol 8. HMSO, London

375