Observations of night-time water use in kiwifruit vines and apple trees

Agricultural and Forest Meteorology, 48 ( 1989 ) 251-261

251

Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

O B S E R V A T I O N S OF N I G H T - T I M E WATER U S E IN K I W I F R U I T VINES AND APPLE TREES

S.R. GREEN, K.G. MCNAUGHTON and B.E. CLOTHIER

Plant Physiology Division, DSIR, Palmerston North (New Zealand) (Received June 6, 1988; revision accepted February 4, 1989)

ABSTRACT Green, S.R., McNaughton, K.G. and Clothier, B.E., 1989. Observations of night-time water use in kiwifruit vines and apple trees. Agric. For. Meteorol., 48:251-261. Transpiration rates of two 7-year-old kiwifruit vines (Actinidia deliciosa) and a 10-year-old apple tree (Malus sylvestris X Red delicious) were measured for 15 days in summer using the heatpulse technique. Environmentaldata were collected at the same time, every half-hour. Significant transpiration rates were observed at night, in both kiwifruit and apple, whenever the saturation deficit remained elevated. Night-time water use in kiwifruit plants ranged from 1.4 to 19.2 l, for saturation deficits of between 0.44 and 3.1 g kg- 1. Nocturnal transpiration of the apple tree ranged from 0.3 to 5.3 1for saturation deficits between 0.2 and 3.3 g kg ~. Mean night-time water use for kiwifruit and apple was 19% (n= 15 nights) and 6% (n= 15), respectively of the total daily transpiration. Nocturnal transpiration increased linearly with mean saturation deficit and saturation deficit increased with mean wind speed. Nocturnal transpiration was therefore greater on windy nights. The directly measured nocturnal transpiration rates in kiwifruit were compared with rates of water use calculated using the Penman-Monteith combination equation with stomatal resistance data obtained by porometry on one night. There was satisfactory agreement between the two results.

INTRODUCTION

For plants to transpire at night the stomata of the leaves must remain open. Also the saturation deficit of the air around the leaves must remain elevated. Usually stomata are closed during the night and they open in response to light after sunrise (Jarvis and Mansfield, 1981), so night time water use will be negligible. However the stomata of some dicotyledons can remain open in the dark (Meidner and Mansfield, 1965; Muchow et al., 1980). Open stomata have also been observed at night in cotton (Sharpe, 1973), soya beans (Turner et al., 1980), and kiwifruit (Judd and McAneney, 1986). Thus there may sometimes be an opportunity for significant transpiration at night if the saturation deficit can remain elevated through the night. Several observations of night-time water use have been reported. Muchow 0168-1923/89/$03.50

© 1989 Elsevier Science Publishers B.V.

252 et al. (1980) estimated that up to 20% of the total diurnal transpiration in kenaf occurred on nights of high advection. Similarly, Rosenberg ( 1969 ) found nocturnal water use from alfalfa growing in lysimeters (including both soil evaporation and plant transpiration) to account for up to 20% of the daily total. J u d d and McAneney (1986) observed that night-time transpiration in two excised kiwifruit vines contributed up to 26% of daily water uptake. The nocturnal transpiration ratio from roses in a greenhouse was found by Seginer (1984) to be about 10%, and Kozai et al. (1982) found between 10 and 20% of the daily water use from cucumbers grown in a glasshouse occurred at night. Thus significant nocturnal transpiration is not uncommon. In this paper we present our observations of night-time water use in kiwifruit vines and apple trees. MATERIALS AND METHODS

Experimental procedure Measurements were made of sap flux in one apple tree at Hawkes Bay (latitude 39.3 ° S, longitude 176.6 ° E) during the period 17 February to 3 March 1987. Solar radiation (Rs), air temperature, humidity and wind speed were logged by an automatic weather station. Similar measurements were made for a kiwifruit vine at Palmerston North (latitude 40.2 ° S, longitude 175.4 ° E) during 10-16 March 1987, and for a second kiwifruit vine in the same orchard during the period 17-26 April 1987. These measurements showed significant nocturnal transpiration on some occasions, for both the apple and kiwifruit plants. Following this discovery, the leaf area of the second kiwifruit vine was measured and a diurnal set of observations of stomatal resistance was made to assist in the interpretation of this night-time sap flow. In the analysis, night-time was assumed as being whenever solar radiation (averaged for 30 min) was less than 1 W m -2

Plant material The apple tree was 10 years old and of the Red delicious cultivar grafted onto MM105 root stock. The tree was pruned and trained as a centre leader, about 3.5 m tall, and the canopy was about 2.5 m wide at the base, with three main levels of branches. The trunk diameter was about 82 mm. Leaf area and stomatal resistance were not measured. The two kiwifruit vines were similar, each a 7-year-old female H a y w a r d cultivar grafted onto Bruno root stock. The vines were planted at a spacing of 5 X 5 m with a vertically projected canopy area of about 10 m 2 supported on a T-bar trellis. This is typical of many kiwifruit orchards in New Zealand. The

253 canopy was approximately horizontal, supported on wires at a height of 1.8 m above ground. The stem diameters were approximately 60 mm. Meteorological measurements Environmental measurements were made every 15 s using a Campbell CR21X data logging system. Averages were recorded every 30 min. Solar radiation (Rs) was measured above the canopy using an Eppley pyranometer. Air temperature (Ta) and relative humidity were measured using a Campbell 207 temperature and humidity probe placed just within the upper levels of the canopy. Values of saturation deficit (Da) were later calculated from these measurements. Wind speed was measured between the rows of plants at a height of 2 m using a Casella three-cup anemometer. The anemometer was positioned at mid-canopy height in the apple tree and immediately above the canopy of the kiwifruit vine. Transpiration measurement Transpiration measurements were made on plants located in the centre of an orchard block. Transpiration rates were measured from the rate of sap movement upwards through the plant stem using the compensation heat-pulse technique (Swanson and Whitfield, 1981). Three sets of probes, each comprising a heater and two temperature probes, each containing four sensors, were installed into holes drilled radially into the tree stem. The temperature probes were positioned at a vertical distance of 20 mm above and 5 mm below the heater, and sap velocity measured as described by Green and Clothier (1988). The three probe sets were spaced equally around the stem circumference; all sets were placed at about the same height in the stem. Sap velocity was measured at four depths below the cambium and at three positions around the stem. Volume flow rates were calculated from the integral, over the sapwood cross-section, of a second-order least squares regression equation fitted to the sap velocity profiles. Transpiration was calculated as the average of the three sap-flow measurements. The heat-pulse equipment was connected to the CR21X data logger which controlled the operation of the heater circuit and measured sap flow and environmental data automatically every 30 min. Technical details of the system are described by Green and Nicholson (1987). Measurements of stomatal resistance and leaf areas A diurnal set of observations of stomatal resistance were made on the second kiwifruit plant at Palmerston North, on 26 April 1987, using a Delta-T Mk3 diffusion porometer. The porometer was calibrated before and after each set

254 of m e a s u r e m e n t s using t h e s t a n d a r d c a l i b r a t i o n plate. K i w i f r u i t leaves are hyp o s t o m a t o u s , so m e a s u r e m e n t s were m a d e o n l y o n t h e leaf underside. M e a n r e s i s t a n c e s were c a l c u l a t e d for leaves on t h e u p p e r ( d a y l i g h t sunlit) a n d lower (daylight full s h a d e d ) p a r t s of t h e c a n o p y using m e a s u r e m e n t s f r o m 10 sunlit a n d 10 s h a d e d leaves. T h e leaves were c h o s e n r a n d o m l y f r o m t h e u p p e r a n d lower p a r t s of t h e c a n o p y , respectively. T h e t o t a l leaf area (one side) of t h e kiwifruit p l a n t was f o u n d by c o u n t i n g all the leaves on t h e vine a n d m e a s u r i n g t h e w i d t h s of a s u b s a m p l e of leaves (20%) c h o s e n f r o m all p a r t s of t h e canopy. A linear regression b e t w e e n leaf width a n d leaf area for individual leaves (E.R. M o r g a n , p e r s o n a l c o m m u n i c a tion, 1987 ) was used to calculate the t o t a l leaf area o f t h e kiwifruit plant. RESULTS AND DISCUSSION

Experimental observations M e a n values of n i g h t - t i m e sap flow in t h e apple t r e e t o g e t h e r with e n v i r o n m e n t a l d a t a for the p e r i o d 17 F e b r u a r y to 5 M a r c h 1987 are p r e s e n t e d in T a b l e 1. On average a b o u t 6% of t h e day's (24 h) t r a n s p i r a t i o n o c c u r r e d at night. T h e t i m e course o f t r a n s p i r a t i o n f r o m the apple tree for t h e p e r i o d 21-27 FebTABLE1 Transpiration and mean environmental data during the night for a 10-year-old apple tree in Hawkes Bay during 17 February to 3 March 1987 Day February 17 18 19 20 21

22 23 24 25 26 27 28 March 1 2 3

Ta (°C)

u (m s -1)

Da (g kg -1)

E (1 night -1)

E (1 day -1)

15.59 14.47 10.61 10.45 12.26 15.14 15.66 19.41 13.48 11.16 14.98 15.53

0.58 0.33 0.62 0.29 0.28 0.32 0.36 0.61 0.29 0.28 0.29 0.34

0.76 0.52 0.44 0.12 0.20 0.40 0.55 3.27 0.39 0.16 0.23 0.22

2.87 1.50 1.56 0.41 0.57 0.81 0.98 5.32 1.03 0.79 0.14 0.39

26.97 10.85 30.07 29.27 29.43 33.66 36.30 31.15 24.02 23.69 23.05 15.03

12.38 14.16 18.20

0.33 0.31 0.65

0.16 0.13 0.50

0.44 0.67 1.05

24.24 21.46 20.11

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Fig. 1. Daily pattern of water use (21-27 February 1987) in a 10-year-old Red delicious apple tree at Hawkes Bay. Half-hourly means of environmental data were collected; solar radiation (Rs) was measured above the canopy, saturation deficit (D~) was measured within the tree canopy, and wind speed at a height of 2 m. TABLE 2 Transpiration and mean environmental data during the night for two 7-year-old kiwifruit vines near Palmerston North during 11-16 March and 17-26 April 1987 Day March 11 12 13 14 15 April 17 18 19 20 21 22 23 24 25 26

Ta (°C)

u (m s - ' )

D. (g k g - ' )

E (1 n i g h t - ' )

E (1 day -1)

11.58 13.54 15.57 15.71 14.67

0.34 0.76 0.32 0.28 1.13

0.16 1.18 0.59 0.58 2.53

2.15 5.86 3.15 3.91 16.38

59.48 36.22 38.04 50.24 51.19

15.31 13.19 12.67 15.11 15.50 14.48 13.31 8.58 4.44 13.78

0.89 0.60 0.75 1.17 0.41 0.83 0.53 0.81 0.35 0.72

2.71 3.13 2.17 1.24 0.44 0.65 0.44 0.41 0.17 0.50

13.02 19.77 12.65 9.38 1.43 6.75 4.90 3.02 0.68 6.03

65.12 57.23 45.28 31.43 17.46 17.55 22.73 25.96 24.52 43.91

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Fig. 2. Daily pattern of water use ( 16-22 April 1987) in a 7-year-old kiwifruit vine near Palmerston North. 8

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Fig. 3. Diurnal pattern of stomatal resistance (26 April 1987) of kiwifruit leaves from a 7-yearold vine near Palmerston North. The lower-canopy leaves are shown by the pecked line, the uppercanopy leaves by the solid line. Error bars are _+1 SD about the mean of 10 leaves.

ruary is shown in Fig. 1. Also shown are measurements of solar radiation, wind speed at mid-canopy level, and saturation deficit within the canopy. A prominent feature in the diurnal pattern of transpiration is the significant water use during the night of 23 February with transpiration rates up to 25% of peak

257

daytime rates. On this night 5.3 1 was transpired. This corresponds to about 15% of the water use for the entire day. Similar patterns of transpiration during the night were measured in kiwifruit. Values of night-time transpiration and environmental data for the period 11-15 March for one vine, and for the period 17-26 April for a second, similar vine nearby are presented in Table 2. The time course of sap flux from the second kiwifruit vine for the period 17-22 April is shown in Fig. 2. The kiwifruit plants transpired at significant rates during some nights, with transpiration rates up to 25% of the daytime peak. On the night of 17-18 April some 19.8 1 were transpired, which was about 30% of the water use from dawn to dusk on the preceding day. On average about one-fifth of the day's transpiration occurred at night, during the period shown in Fig. 2. Stomatal resistance was measured on the second kiwifruit plant on 26 April, the day after the last set of transpiration measurements were made. The diurnal pattern of stomatal resistance of both upper-canopy and lower-canopy leaves is shown in Fig. 3. The stomata remained partially open at night with a resistance of between two and three times the day time minimum values. The resistance of leaves of the lower canopy was always greater than leaves in the upper canopy, somewhat surprisingly even at night.

Analysis Inspection of the environmental data shows that the saturation deficit within the canopy was higher on nights when the apple tree and the kiwifruit vines had elevated rates of sap flow. A plot of nocturnal sap flow in the kiwifruit vines against the mean saturation deficit at night shows a clear linear relation20

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Fig. 4. The relationship between mean saturation deficit at night (17 February-3 March 1987 ) and nocturnal transpiration in a 7-year-old kiwifruit vine near Palmerston North. Average air temperatures and wind speeds for these nights are given in Table 1.

258 ship (Fig. 4 ). The observations of partly open stomata and elevated saturation deficit confirm qualitatively the observed significant rates of night-time sap flow. A more "quantitative" comparison can be made by using the P e n m a n - M o n teith model to calculate transpiration. The equation for transpiration of a symmetrical, hypostomatous leaf is given by Jarvis and M c N a u g h t o n ( 1986 ) as L E = eRn +pCpDa/rb (W m -2)

e+2+rs/rb where e =s2l/Cp, s is the slope of the saturation vapour pressure curve (mb C - 1), 2 is the latent heat of vapourization (J k g - 1 C - 1), C, is the specific heat capacity of air at constant pressure (J k g - 1 ), p is the density of air (kg m - "~), R n is the net radiation (W m - e ) , rs is the stomatal resistance (s m -~) and rb is the leaf boundary layer resistance (s m - ~ ) . This expression differs from Jarvis and M c N a u g h t o n (1986) in the factor 2 which arises because rb is calculated as the parallel sum over both sides of a leaf. Canopy transpiration rates are calculated by summing over all leaves. Measurements had not been made either concurrently or in sufficient detail to calculate canopy transpiration with any great accuracy, so the following approximations were adopted. For the purpose of calculation the horizontal kiwifruit canopy was divided into an upper layer with a total projection area of 10 m e and a lower layer of the remaining 32 m 2 (a leaf area index of 4.2). The time course of stomatal resistance of the leaves in the upper layer was taken from the solid curve of Fig. 3 while that of the leaves in the lower layer was taken from the pecked curve in Fig. 3. The curves were chosen as a simple fit, by eye, to the data. Net radiation was assumed to be zero at all times in the lower layer. For the upper layer, net radiation was calculated by assuming an albedo of 0.2 and a net longwave balance of - 4 0 W m -e. This is a value midway between the extremes for a clear sky and a complete overcast. Thus the net radiation throughout the day was calculated using Rn = 0 . 8 R s - 4 0 ( W m -2) Leaf aerodynamic resistance was assumed equal in the two layers and was calculated according to the expression for clustered leaves developed by Landsberg and Powell (1973)

r=135(D/u) 1/2 (s m -1) where D is the characteristic leaf dimension (taken as 0.2 m for a kiwifruit leaf) and u is the wind speed (m s - ~) across the leaf surface. Since the kiwifruit canopy was approximately horizontal with a vertical thickness of less than 0.5 m, variations in wind speed through the canopy were assumed negligible. Val-

259

ues of wind speed immediately above the canopy were used to calculate leaf aerodynamic resistance. Evaporation rates were calculated from a measured leaf area and are presented in 1 h - 1 to match volume flow rates measured with the heat-pulse technique (Fig. 5). The calculated evaporation rates agree closely with the measured fluxes, albeit perhaps fortuitously. This agreement increases our confidence that the observed nocturnal sap fluxes are real and represent transpiration at night rather than rehydration of leaf and twig tissue. The heatpulse measurements were later confirmed by an excision experiment on the kiwifruit vine (data not presented) in a manner similar to that described by Green and Clothier (1988). There remains the question of how common are the conditions of elevated saturation deficit that promote high nocturnal transpiration? Our results suggest that high nocturnal D a w a s associated with higher wind speeds (Fig. 6). This correlation probably reflects the common observation, that nocturnal ground-based inversions which usually form as the surface cools at night by radiation loss are weak when winds are strong, and the saturation deficit near the ground does not then fall to near zero; rather the wind speed generates turbulence in the lower atmosphere and this promotes the transport of air from aloft down to the surface. This air usually has a larger saturation deficit, reflecting conditions in the mixed layer which has formed during the preceding day (McNaughton, 1988). The moderate scatter in the relationship shown between mean nocturnal saturation deficit and wind speed reflects fairly consistent weather conditions at the site at Palmerston North, with wind mostly from the southeasterly i

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Fig. 5. Daily pattern of sap flow in a 7-year-old kiwifruit vine (solid line) and transpiration rate calculated with the Penman-Monteith combination equation (pecked line) using half-hourly mean environmental data and stomatal resistance measurements of Fig. 4.

260

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Fig. 6. The relationship between mean wind speed and saturation deficit at night ( 17 February-3 March 1987) in an orchard near Palmerston North (from Table 2 ).

quarter. The outlying point on the plot (Fig. 6), for 18 April, is for a night when there was a sudden change in wind direction. It is possible that some larger scale weather disturbance passed over the site during the night and that this was responsible for overturning the lower layers of the atmosphere. The observed association between elevated nocturnal saturation deficit and higher wind speeds can be interpreted in terms of larger scale processes in the atmosphere, and this gives cause to expect that similar relationships will apply in other local sites. CONCLUSION

Nocturnal transpiration for most plants is commonly assumed to be negligible. Our observations show that sometimes at least 30% of the total 24-h water use of kiwifruit may occur during the night. Elevated rates of sap flow at night were also observed in apple trees. Conditions conducive to such high rates may be common in windy weather which prevents the formation of an intense nocturnal inversion above orchards. Nocturnal transpiration is thus probably a significant component of the water economy of orchards in windy climates. ACKNOWLEDGEMENTS

We acknowledge the New Zealand Kiwifruit Authority and the New Zealand Apple and Pear Marketing Board for their financial support of this project. We are grateful to Mr. E. Cameron for allowing us to use the kiwifruit vines at the

261

Massey University orchard. Thanks are also due to Mr. Van Howard for allowing us to work in his apple orchard in Hawkes Bay.

REFERENCES Green, S.R. and Clothier, B.E., 1988. Water use of kiwifruit vines and apple trees by the heatpulse technique. J. Exp. Bot., 39: 115-123. Green, S.R. and Nicholson, H.F., 1987. Use of a Campbell CR21X data logger to measure sap flow in plants by the heat-pulse technique. Technical Report No. 29, Plant Physiology Division, DSIR, Palmerston North, 29 pp. Jarvis, P.G. and Mansfield, T.A., 1981. Stomatal Physiology. Cambridge University Press, Cambridge, 295 pp. Jarvis, P.G. and McNaughton, K.G., 1986. Stomatal control of transpiration: Scaling up from leaf to region. In: Advances in Ecological Research. Academic Press, London, Vol. 15, pp. 1-49. Judd, M.J. and McAneney, K.J., 1986. Water use by sheltered kiwifruit under advective conditions. N.Z.J. Agric. Res., 29: 83-92. Kozai, T., Hayashi, M., Suzuki, H. and Watanabe, I., 1982. Effects of environmental factors on evapotranspiration of greenhouse cucumber crops in hydroponic culture. J. Agric. Meteorol., 38: 153-159. Landsberg, J.J. and Powell, D.B.B., 1973. Surface exchange characteristics of leaves subject to mutual interference. Agric. Meteorol., 12: 169-184. McNaughton, K.G., 1988. Regional interactions between canopies and the atmosphere. In: B. Marshall, P.G. Jarvis and G. Russel (Editors), Plant Canopies: Their Growth, Form and Function. SEB Seminar Series, 31: 63-81. Meidner, H. and Mansfield, T.A., 1965. Stomatal responses to illumination. Biol. Rev., 40:483 509. Muchow, R.C., Ludlow, M.M., Fisher, M.J. and Meyers, R.J.K., 1980. Stomatal behaviour of kenaf and sorgham in a semiarid tropical environment. I. During the night. Aust. J. Plant Physiol., 7: 609-619. Rosenberg, N.J., 1969. Seasonal patterns of evapotranspiration by irrigated alfalfa in the central Great Plains. Agron. J., 61: 879-886. Seginer, I., 1984. On the night transpiration of greenhouse roses under glass or plastic cover. Agric. Meteorol., 30: 257-268. Sharpe, P.J.H., 1973. Adaxial and abaxial stomatal resistance of cotton in the field. Agron. J., 65: 570-574. Swanson, R.H. and Whitfield, D.W.A., 1981. A numerical analysis of heat-pulse velocity theory and practice. J. Exp. Bot., 32: 221-239. Turner, N.C., Begg, J.E., Rawson, H.M., English, S.D. and Hearn, A.B., 1980. Agronomic and physiological responses of soyabean and sorgham crops to water deficits. III. Components of leaf water potential, leaf conductance, C02 photosynthesis, and adaption to water deficits. Aust. J. Plant Physiol., 1978: 179-194.