Water 2009, 1, 32-42; doi:10.3390/w1010032
Daily Variations of Water Use with Vapor Pressure Deficit in a
Plantation of I214 Poplars
Etienne Muller 1,2,* and Luc Lambs 1,2
1 Université de Toulouse, UPS, INP, EcoLab (Laboratoire d’écologie fonctionnelle), 29 rue Jeanne
Marvig, F-31055 Toulouse, France
2 CNRS, EcoLab, 29 rue Jeanne Marvig, F-31055 Toulouse, France
* Author to whom correspondence should be addressed; Tel.: +33-562269981; Fax: +33-562269999;
Received: 22 September 2009; in revised form: 26 October 2009 / Accepted: 5 November 2009 /
Published: 6 November 2009
Abstract: Daily rates of whole tree water use were measured in a homogeneous 7-year-old
plantation over 84 days. Two trees were selected in the two most contrasting ends, i.e., with
mean water table at -1.5 m and -3.5 m. Results showed that the mean tree water use was
close to 80 dm3 day–1 with a small mean difference between the two sites (5.4 dm3 day–1,
about 7%). Higher daily variations were observed on a single tree over the season (from 17
to 138 dm3 day–1). These fluctuations could be modeled using linear regressions on the
vapor pressure deficit (VPD). Results also indicated decreasing sap flux densities with
radial sapwood depth and that the whole tree water use could be estimated from the sap flux
densities measured at the 0–2 cm depth.
Keywords: Populus; I214; sap flux; water use; water table
In the plant kingdom, the largest biomass for a single genome has probably been reached with the
poplar I214. This poplar was first identified and tested in Italy around 1929 as a natural hybrid from a
female American eastern cottonwood, Populus deltoides ssp. angulata or ssp. monilifera and a male
European black poplar, P. nigra L. Both species belong to the Aigeros section of the Populus genus,
Water 2009, 1
which is characterized by phreatophytic and riparian obligate trees . The I214 poplar was
intensively multiplied by cuttings and became the most cultivated poplar clone in the world, especially
in floodplains . Although new poplar clones have been selected and tested over the last few decades,
I214 still remains one of the most popular and widespread clones.
Surprisingly, nothing is known of the daily water uptake of I214 trees and of the range of changes
in water use that may occur throughout a vegetative season. In the literature, indications exist for other
poplar clones, e.g., the euramerican hybrid ‘Flevo’ or the inter-american hybrids ‘50–194’ and
‘Beaupré’ [3-5]. However, comparison between trees is not easy because factors such as clone, age or
size of the tree, the local climate, the soil type and time of the estimates within the vegetative season
are generally not the same.
In addition, the diffuse-porous xylem of Populus sp. and of the Salicaceae in general is
characterized by a conductivity and sap-movement within several peripheral annual rings [3,6-9].
Consequently, measurements have to be taken at several radial depths in the trunk to calculate the total
water uptake by a tree. Multiple probes have already been used in diffuse-porous trees for
characterizing the radial pattern of sap flow and its change over time [7,10-12]. However, few studies
have considered Populus sp. and measurements were made over only a short period [8,13].
The objective of this study was to better understand the variation of the radial sap flux profiles in
the poplar I214 and the variation in daily whole tree water use during a growing season at the scale of
a small plantation plot. It could be hypothesized that water use would remain rather similar from one
side to the other, as trees were the same age, from the same genetic stock (clone I214) and had the
same life history (same farm practices) since they were planted. However, such poplars are generally
grown in floodplains and the proximity of the water table is a determinant factor to take into
consideration as it may modify the water use by trees. 15 to 60% of the water transpired by the hybrid
clone TT32 (P. trichocarpa Torr & A. Gray x P. tacamahaca L.) was taken from groundwater, with the
proportion increasing as the soil dried out in the unsaturated zone . Moreover, during low water
flows and droughts, poplar trees may drastically reduce water uptake if they are disconnected from the
water table . Therefore, sap flow patterns were measured in the two contrasting ends of an
apparently homogeneous plantation plot, but with a high water table gradient. Another issue was to try
regression methods to predict the whole tree water use from measurements made with a single probe
instead of several, and from environmental parameters such as the vapor pressure deficit.
2. Results and Discussion
2.1. Variation in sap flow
Following electronic problems with the probes some data were missing in the first poplar tree (P1)
between mid-August and mid-September. However, results were comparable between the two poplar
trees P1 and P2 over 84 days, i.e., almost three months (Figure 1). Measurements in P1 showed a
steady decrease in the mean daily Qsi from the outer to inner depth; i.e., from 24.9 dm3 dm–2 day–1 at
0–2 cm to 13.5 dm3 dm–2 day–1 at 6–8 cm (Table 1). In P2, sap flows were more homogeneous and
slightly lower, except in the inner 6–8 cm. From one day to another, very high daily variations in Qsi
could be observed, with possible sharp drops or increases from one day to another. Maximum Qsi
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15. McQueen, I.S.; Miller, R.P. Soil moisture and energy relationships associated with riparian
vegetation near San Carlos, Arizona, Gila River phreatophyte project; Geological Survey
professional paper 655-E. USGS, Washington DC, USA, 1972; pp. 5-15.
16. Lambs, L.; Loudes, J.P.; Berthelot, M. The use of the stable oxygen isotope (18O) to trace the
distribution and uptake of water in riparian woodlands. Nukleonika 2002, 47, 71–74.
17. Lambs, L.; Loubiat, M.; Girel, J.; Tissier, J.; Peltier, J-P.; Marigo, G. Survival and adaptation of
Populus nigra to drier conditions after damming of an alpine river, southeast France. Ann. For.
Sci. 2006, 63, 377-385.
18. Hogg, E.H.; Hurdle, P.A. Sap flow in trembling aspen: implication for stomatal responses to
vapor pressure deficit. Tree Physiol. 1997, 17, 501–509.
19. Granier, A. A new method to measure the raw sap flux in the trunk of trees. Ann. For. Sci. 1985,
© 2009 by the authors; licensee Molecular Diversity Preservation International, Basel, Switzerland.
This article is an open-access article distributed under the terms and conditions of the Creative
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