Light interception by the orange tree canopy during flower bud differentiation and subsequent

flowering and fruit setting has been monitored by continuous data recording from 48 silicon

cells distributed in different canopy zones. Two experimental conditions have been tested:

trees artificially shaded by a black nylon net cage, and non-shaded trees. Observations were

made on the total radiation accumulated in the different canopy zones, and they were related

to photosynthetic activity, stomatal conductance) flowering and fruiting pattern, and fruit

quality. The different light distribution affected both photosyntesis and stomatal conductance:

in fact, they were both drastically reduced in shaded trees, and a significant decrease was also

found in both shaded and unshaded trees in relation to different canopy zones. A significant

decrease of flowering and fruit setting was found from the top of the canopy to the bottom

and from outside to inside, in relation to the different amount of radiant energy availability.

Finally significant differences were found on fruit quality

Benincasa, Fabrizio

Canu, Annalisa

Deidda, Pietro

Farro, Laura

Filigheddu, Maria Rosaria

English

UnissResearch

ANNAbI 
DELLA FACOLTA' DI AGRARIA DELL' UNIVERSITA' 
SASSARI 
DIRETTORE: G. RIVOIRA 
COMITATO DI REDAZIONE: M. DATTILO - S. DE MONTIS - F. F;\TICHENTI 
C. GESSA - L. IDDA - F. MARRAS - P. MELIS - A. MILELLA - A. PIETRACAPRINA 
R.PROTA-A. VODRET 
studi s.ss.r.sl 
ORGANO UFFICIALE 
DELLA SOCIETÀ SASSARESE DI SCIENZE MEDICHE E NATURALI 
Ann. Fac. Agr. Univ. Sassari (I): 1988-1992,34: 115-122 
LIGHT DISTRIBUTION ON CITRUS CANOPY 
AFFECTS PHYSIOLOGICAL PARAMETERS 
AND FRUITING PATTERN (1) 
Piero DEIDDA (2) - Mafia Rosatio FILIGHEDDU (3) - Annalisa CANU (4) 
Laura FARRO (5) - Fabrizio BENINCASA (6) 
SUMMARY 
Light interception by the orange tree canopy during flower bud differentiation and subsequent 
flowering and fruit setting has been monitored by continuous data recording from 48 silicon 
cells distributed in different canopy zones. Two experimental conditions have been tested: 
trees artificially shaded by a black nylon net cage, and non-shaded trees. Observations were 
made on the total radiation accumulated in the different canopy zones, and they were related 
to photosynthetic activity, stomatal conductance) flowering and fruiting pattern, and fruit 
quality. The different light distribution affected both photosyntesis and stomatal conductance: 
in fact, they were both drastically reduced in shaded trees, and a significant decrease was also 
found in both shaded and unshaded trees in relation to different canopy zones. A significant 
decrease of flowering and fruit setting was found from the top of the canopy to the bottom 
and from outside to inside, in relation to the different amount of radiant energy availability. 
Finally significant differences were found on fruit quality. 
Keywords: Radiation distribution, Citrus sinensis L., Net photosinthesis, Stomatal conductance. 
RIASSUNTO 
Distribuzione della radiazione all'interno della chioma 
nell'arancio e sua influenza su alcuni parametri fisiologici e suUa fruttificazione 
La radiazione solare intercettata dalla chioma di piante di agrumi e stata nllsurata, nel periodo 
compreso tra l'induzione antogena e la fioritura, mediante l'impiego di 48 fotocellule al silicio 
colIegate ad un data-logger e distribuite nelle diverse zone del "globo". Sono state considerate 
m Lavoro eseguito con il contributo finanziario del C.N.R. (Contratto N. 90.01381.06; Titolare Dr.ssa 
Annalisa Canu). 
(2) Professore Ordinario presso l'Istituto di Coltivazioni arboree della Facolta di Agraria deU'Universita di 
Sassari. 
(3) Tecnico Laureato. Ibidem. 
(4) Ricercatore del Consorzio Ricerche Sardegna di Sassari. 11;;'-,_ 
(5) Tecnico. Ibidem. 
(6) Ricercatore del C.N.R. IATA di Firenze. 
116 
due condizioni sperimentaH: piante non ombreggiate e piante ombreggiate con una rete di 
nylon nera. I riHevi sperimentaH hanno riguardato la distribuzione dell' energia radiante nella 
struttura vegetale, l' attivita fotosintetica, la conduttanza stomatica, l' enita della fioritura 
nonche la distribuzione e le caratteristiche qualitative della produzione. Le osservazioni hanno 
messo in evidenza che la distribuzione della radiazione nelle diverse zone della chioma 
influisce sull' attivita fotosintetica e sulla conduttanza stomatica: infatti queste ultime hanno 
subito una drastica riduzione nelle piante ombreggiate ed e stata osservata una variazione 
significativa nelle diverse parti della chioma per entrambe le test Sono state riscontrate 
differenze significative sull' entita della fioritura, e dell' allegagione, nonche sulla distribuzione 
dei frutti, in relazione alla quantita di energia radiante disponibile nelle diverse zone della 
chioma. Infine, sono state riscontrate differenze significative sulla qualita dei frutti. 
Parole chiave: Distribuzione della radiazione, Citrus sinensis L., Fotosintesi netta, Conduttanza 
stomatica. 
INTRODUCTION 
Previous research has shown that the flowering and fruiting pattern in Citrus is 
greatly affected by the light distribution in the different canopy zones (1, 8, 9). In fact 
in the shaded zones inside the tree canopy low amounts of radiant energy should be 
assumed as responsible of the lower bearing ability of such zones (6, 7, 9). On the 
other hand, as stated elsewhere (2) it is difficult to explain this effect on the exclusive 
basis of the photosynthetic potential, since the wide range of responses due to 
phytochrome includes flower bud induction (13, 16), in addition to the complex 
light-gibberellins and light-auxins interactions. In this experiment further details on 
this topic are given, with particular reference to light distribution effects on 
photosynthesis, stomatal conductance and fruiting behaviour. 
MATERIALS AND METHODS 
The research has been made at the Institute Experimental Station, near Oristano 
(Sardinia), on a block of "Washington navel" orange trees, grafted on sour orange, 
planted in 1974 and spaced at 5.5 x 4 m. 
Two experimental conditions have been tested: trees artificially shaded by a black 
nylon net cage, and non-shaded trees. During flower bud differentiation and 
subsequent flowering and fruit setting (from November 1, 1987 to May 23, 1988) 
light interception by the tree canopy was monitored by continuous data recording 
from 48 silicon cells distributed for each tree in different canopy zones (fig. 1). The 
cells were connected to a data logger (previously described by Benincasa, 4) and the 
radiation data were recorded at hourly intervals. Normally each cell was placed in the 
vicinity of a leaf, in order to have similar conditions of light interception. Total 
117 
N 
t 
Fig. 1 - Cells location in different canopy zones. 
sunlight radiation was also monitored from 8 cells distributed above the canopy in 
all the directions. During the experiment several observations (normally once a 
month) were made on phosynthesis and stomatal conductance; such determinations 
were made during sunny days, using a CO2 analyser (LR.G.A.-ADC) and a Auto-
porometer Li 1600. Flowering rate, fruit setting and fruit quality were also recorded. 
All data were subjected to statistical analysis. 
RESULTS 
The total radiation accumulated in different canopy zones in relation to the 
treatments is shown in table 1. It is rather evident that artificial shading drastically 
reduced the total radiation available by the canopy. It is also evident that the light 
intercepted by the foliage decreased from the canopy top to the bottom, and from 
the external to the internal canopy zones. Furthermore the table 1 evidences that 
only a fraction of total available radiation reached the tree canopy. In fact in 
non-shaded tree the light intercepted by the canopy changed from 47% to 24% of 
total available radiation, depending on the different canopy zones, while in shaded 
trees this condition changed from 12% to only 3.8% (fig.2). This situation is also 
evidenced in figure 3 where are represented the diurnal changes of radiation in 
shaded and unshaded trees during two typically sunny days of December and May. 
Of course this different light distribution affected both photosynthesis and stomatal 
118 
Table 1 - Radiant energy accumulation in different canopy zones from flower bud differenti-
ation to fruit-setting, in shaded and unshaded trees (MJ m·2). 
11-01·1987 11·01·1987 
01·31·1988 05·23-1988 
TOTAL AV./DAY TOTAL AV.IDAY 
Top 129.6 c lA c 486A c 2A c 
Middle 101.0 b l.lb 368A b 1.8 b 
Bottom 74.0 a 0.8 a 304.8 a 1.5 a 
Sign. ** ** ** ** 
Extern. 114.0 1.2 473.8 2.3 
Intern. 89.0 0.9 299.3 1.5 
Sign. ** ** ** ** 
Shad. 32.6 OA 154.3 0.8 
Unsh. 171.0 1.9 618.8 3.0 
Sign. ** ** ** ** 
Tot. avail. 427.3 4.6 2224.0 10.8 
radiat. 
Table 2 - Net photosyntesis and stomatal conductance in relation to light distribution (as 
percentage of total available radiation) 
light distr. Stam. conduct. 
% cm 5-1 
CANOPY ZONE S NS S NS S NS 
Top 9.6 b 34.2 c 1.7 b 7.9 c 0.25 c 053 c 
Middle 5.9 a 27.2 b 1.4 a 6.1 b 0.20 b 0.39 b 
Bottom 5.3 a 22.0 a 1.3 a 2.8 a 0.15 a 0.29 a 
Sign. ** ** * ** ** ** 
Ext. 8.2 34A 1.7 7.1 0.23 OA7 
Int. 5.7 21.2 1.2 4.1 0.17 0.33 
Sign. ** ** * ** ** ** 
conductance (table 2). In fact, they were both drastically reduced in shaded trees and 
a significant decrease was also found in both shaded (S) and unshaded (NS) trees in 
relation to different canopy zones. The flowering rate and fruiting setting were also 
strongly influenced by the availability of solar radiation. In shaded trees (table 3) the 
flowering rate was about 25% of that of the control trees, while the amount of fruits 
119 
Fig. 2 - Intercepted radiant energy (as percentage of total available radiation) in different 
canopy zones of shaded and unshaded trees. 
Un shaded tree 
1. 2 1-., ..................... , ............•. , ................ , ..... .. 
0.8 
.... 
'1: 
I") 
I: 
e.4 
el-.'·~'~~· .. ·+·············;····· 
8 le 12 14 
Hours 
16 
- T.E 
-... T.:I 
• H.E 
-£)- H.:I 
18 
'I: 
I") 
I: 
e.l 
9 
Shaded tree 
11 13 15 17 
Hour .. 
Fig. 3 - Diurnal radiant energy interception by different canopy zones in December, 5, 1987. 
(T=Top; M=Middle; B=Bottom; E=Ext.; I=Int.) 
120 
Unshaded tree Shaded tree 
0.8 0.2 
"! "! 
E E 
"') "') 
1: 1: 
0.4 0.1 
6 9 12 15 18 21 6 9 12 16 18 21 
Hours Hours 
Fig. 4 - Diurnal radiant energy interception by different canopy zones in May, 30, 1988. 
(T=Top; M=Middle; B=Bottom; E==Ext.; I=Int.) 
Table 3 - Flowering and fruit setting in different canopy zones. 
FLOW. RATE () FRUIT NUMBER 
CANOPY ZONE S NS S NS 
Top 2.0 c 7.0 b 40 c 192 c 
Middle 1.5 b 6.2 b 24 b 126 b 
Bottom 1.0 a 3.5 a 14 a 108 a 
Sign. ** ** ** ** 
Ext. 2.6 6.3 44 262 
Int. 0.4 4.8 34 164 
Sign ** ** ** ** 
n Raring from 0 (no fl.) to 10 (max. fl.) 
harvested was about 18%. Moreover in both shaded and non-shaded trees there was 
a reduction of flowering and frnit setting from the canopy top to the bottom, and 
from the outside to the inside canopy. This decrease, which in unshaded trees 
averaged 47% in the bottom of the canopy and about 30% in the internal canopy 
zones, is clearly related to the reduction of light interception to a less than 30% of 
121 
Table 4 - Fruit quality in relation to different canopy zones in shaded and unshaded trees. 
FRUIT RIND RIND RIND JUICE TSS TA TSS/TA 
WEIGHT TEXTURE COLOR TICK. 
G (1) (2) mm % % % 
Top 301 a 7.2 b 10.3 b 5.9 47.1 b 10.7 b 1.04 10.3 
Middle 322 b 6.5 a 10.2 b 6.0 46.7 b 10.5ab 1.05 10.0 
Bottom 324 b 6.5 a 9.5 a 5.8 44.7 a 10.2 a 1.01 10.1 
Sign. * ** ** NS ** * NS NS 
Int. 320 6.7 9.7 5.4 46.9 10.3 1.08 9.5 
Ext. 312 6.8 10.3 6.4 45.3 10.7 0.98 10.9 
Sign. NS NS ** ** ** ** * ** 
Shad. 370 6.8 9.2 5.7 47.5 10.1 1.06 9.5 
Unsh. 262 6.7 10.8 6.1 44.7 10.9 1.00 10.9 
Sign. ** NS ** * ** ** NS ** 
(1) Visually determined on a scale ranking 1 to 8 
(2) Visually determined with the aid of a colour table on a scale ranking from 3 (dark green) to 13 (deep 
orange). 
the total available radiation (see also table 2). Significant differences were finally 
found on the fruit quality (table 4). Particularly the shaded trees produced bigger, 
paler fruit, with a thinner rind, more juice, and less TSS and TSS/TA ratio. Naturally 
similar differences were found between inside and outside fruit in both shaded and 
un shaded trees. On the other hand, fruit at the top of the canopy were smaller, with 
a finer and more brightly coloured rind and a higher juice and TSS content. 
CONCLUSIONS 
First of all this experiment confirmed that under normal cultural conditions the 
radiant energy intercepted by the Citrus canopy is progressively reduced from the 
canopy top to the bottom, and from outside to inside. This condition mostly when 
the reduction of light availability is less than 30% of total available radiation, may 
results in a significant decrease of flowering and fruit setting, so confirming previous 
experiments on Citrus (1, 5, 8, 9, 10, 11, 12, 15). Therefore all the cultural factors 
(Le. planting distances, row orientation and pruning) that induce ~bnormal shading, 
mainly during flower bud differentiation, negatively affect flowering and yield. Of 
course the different fruit distribution in the tree canopy in relation to the light 
availability implies also several differences in fruit quality, such as weight (due to 
different fruit number per unit of canopy volume), rind colour and thickness, juice 
and TSS content. Finally this research has evidenced that the shortage of radiant 
122 
energy negatively affects some physiological processes, like photosynthesis and 
stomatal conductance. Nevertheless, on the basis of the typical saturation curves of 
photosynthesis reported by Barden (3) and Proctor (14) it is difficult to explain the 
yield reduction on the exclusive basis of the photosynthetic potential. Therefore the 
shortage of light availability becomes critical mainly during flower bud induction and 
it is likely that other factors, such as light-photoreceptive pigments and light hormone 
relationship, could be involved. 
LITERATURE CITED 
1) AGABBIO M., FRAU A.M. (1976) - Il pompelmo "Marsh seedless" seL Frost. Osservazioni 
sull' attivita vegetativa e produttiva in rapporto alIa diversa intensita luminosa. L'Italia Agricola,l13 (7 1 
8): 100-115. 
2) BALDINI E., ROSSI F. (1987) - Radiant energy spectral distribution in fruit tree canopy. Int. Conf. 
on Agrometeorology, Cesena, 401-408. 
3) BARDEN J. (1977) - Net photosynthesis, dark respiration, specific leaf weight and growth of young 
apple trees as influenced by light regime. J. Am. Soc. Hort. Sd.99: 547-551. 
4) BENINCASA F., FASANO G., FRANCINI F., MATERASSIA. (1986) - Strumento per l'analisi della 
distribuzione della luce all'interno della vegetazione. Riv. di Ing. Agr.,4: 251-254. 
5) BOSWELL S.B., BURNS R.M. (1973) - Fruit bearing zones in California Citrus trees. Calif. Citrogr., 
58 (8),288: 311-312. 
6) CAIN J.C. (1971) - Effect of mechanical pruning of apple hedgerows with a slotting saw on light 
penetration and fruiting. J. Am. Soc. Hort. Sci.,96: 664-667. 
7) CAIN J.C. (1972) - Hedgerow orchard design for most efficient interception of solar radiation. Effects 
of tree size, shape, spacing, and row directions. Search Agriculture, 2, 7. 
8) DEIDDA P., AGABBIO M. (1977) Some factors influencing flowering and fruit-set of clementine 
mandarin. Proc. Int. Soc. Citriculture,2: 688-692. 
9) DEIDDA P., DETTORI S., PALA M. (1981) - Distribuzione della fruttificazione nell'arancio dolce 
e rapporti con la raccolta meccanizzata. Riv. Ortoflorofrutt. Italiana, 65,1: 35-58. 
10) IW AGAKI 1., ONO S., IDETA M. (1972) - Fruit distribution and relative light intensity in relation 
to tree shape of satsumas under different cultural conditions. Bull. of the Shik. Agric. Exp. Stat,25: 
71-81. 
11) IWAGAKI 1., ONO S., KUPO K., IDETA M. (1976) -Fruit distribution and light intensity in satsuma 
canopies. Bull. of the Shik. Agric. Exp. Stat.,29: 41-48. 
12) KUNTE Y.N., DESHPANDE V.B. (1970) - Quality of Santra fruit (Citrus reticulata BIanco) as 
affected by aspect (direction) and height on the tree. Nagpur Agric. ColI. Mag.,42: 33-39. 
13) MOHR H. (1972) - Lectures on photomorphogenesis. Berlin, Springer Verlag. 
14) PROCTORJ.T.A., WATSON R.L., LANDSBERG J.J. (1976) - The carbon budget of a young apple 
tree. Journ. Am. Soc. Hort. Sci.,101: 579-582. 
15) STEW ART 1. (1976) - Influence of tree position of Citrus fruit on the peel and juice color. Proc. Fla. 
St. Hort. Soc.,88: 312-314. 
16) VINCE-PRUE D., (1970) - The control of flowering and other responses to day lenght. Part. I, n. 
Royal Horticu1t. Soc.,45: 214-219. 
Lavoro pervenuto in redazione il 20-12-1'991. 
Gli estratti possono essere richiesti a: 
Prof. Piero Deidda, Istituto di Coltivazioni arboree - Facolta di Agraria dell'Universita di Sassari 
Via E. De Nicola - 07100 Sassari - Italy - TeI. 079/229234. 


Light distribution on <i>citrus canopy</i> affects physiological parameters and fruiting pattern

Abstract

Similar works

Full text

Available Versions

UnissResearch