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Suitability of Stem Diameter Variations as an Indicator of Water Stress of Cotton
Available online at www.sciencedirect.com Agricultural Sciences in China 2006, 5 ( 5 ) : 356-362
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May 2006
Suitability of Stem Diameter Variations as an indicator of Water Stress of Cotton ZHANG Ji-yang, DUAN Ai-wang, MENG Zhao-jiang and LIU Zu-guj Farmland Irrigation Research Institute, Chinese Academy of Agricultural Sciences, Xinxiang 453003, P.R. China
Abstract Water stress effects on stem diameter variations (SDV) were studied in a pot experiment on cotton (Gossypium hirustum L. Meimian99B). Water restriction was imposed at the flowering stage and were compared with a well-watered control treatment. The volumetric soil water content ((3,) and SDV were monitored continuously. The objective was to determine the feasibility of using the parameters derived from stem diameter measurements, including maximum daily stem shrinkage (MDS), maximum daily stem diameter (MXSD), and minimum daily stem diameter (MNSD) as indicators of plant water stress. The different behavior of SDV was founded at different growth stages. At stem-maturing stage, MDS increased and MNSD decreased in deficit-irrigated plants compared with the control plants, therefore, it appeared that MDS and MNSD ccould be used as available indicators of plant water status. At stem growth stage, there were no significant differences in MDS values between treatments but MXSD and MNSD responded sharply to soil water deficits. Thus, for rapidly growing cotton, the course of MXSD or MNSD with time offered a consistent stress indicator. SDV was also closely related to atmospheric factors, solar radiation (Rs) and vapor pressure deficit (VPD) were found to be the predominant factors affecting MDS, followed by the relative humidity (RH), while air temperature (Ta) and wind velocity had the least effect. A good linear relationship was founded (rz=O.921) between MDS and environmental variables (Rs, VPD, RH, and OV), which can be used to establish a reference value for detecting plant water stress based on the MDS patterns. Key words: stem diameter variations, water stress, atmospheric factors, cotton
INTRODUCTION Evidence of diurnal oscillations in the diameter of plant stem was identified long ago (Namken et al. 1969). Plant stems shnnk as the transpiration stream flows to replace the water lost when stomata open each morning, gas exchange between the leaves and the environment commences, and the leaves partially dehydrate. In the afternoon, as stomata close and transpiration rate decreases, root water uptake exceeds plant water loss and the stem starts to swell (Namken et al. 1969). Shortterm changes in stem diameter have been related to
concomitant changes in plant water status as transpiration loss draws water from the stem, primarily from phloem tissues (Klepper et al. 1971). Molz and Klepper (1973) found that stem diameter measurements could provide continuous records of plant water potential in cotton plants, and suggested that plant water status measurements could be automated and non-destructive. In recent years, renewed interest has arisen in continuous measurement of plant stem diameter as an indicator of plant water status and its application to irrigation scheduling (Nortes et al. 2005; Intrigliolo and Caste1 2004a; Fereres and Goldhamer 2003). Parameters derived from measurements of stem diameter variation
Received 20 December, 2005 Accepted 2 March, 2006 %HANG Ji-yang, MSc, Tel: +86-373-3393384, E-mail: [email protected]; Correspondence DUAN A]-wang, Professor, Ph D, Tel: +86-373-3393364, E-mail: duanaw @public.xxptt.ha.cn
Q2W,CAAS. All rightsresewed. Publishedby ElsevierLtd.
Suitability of Stem Diameter Variations as an Indicator of Water Stress of Cotton
(SDV) have demonstrated that they are very sensitive to changes in tree water supply in a number of fruit tree species, such.aspeach (Remorini and Massai 2003), lemon (Ortuiio et al. 2004a) and plum (Intrigliolo and Caste1 2004b). In all cases, good correlations were found between the degree of trunk shrinkage and swelling and the changes in tree water status. One of the most commonly used parameters is the maximum daily shrinkage (MDS) (Goldhamer and Fereres 2001). Goldhamer et al. (1999) demonstrated that the MDS of peach trunks was more sensitive than other established water status indicators, including stem water potential (SWP), in detecting tree water deficits. It is therefore possible to use MDS or related parameters as indicators of plant water stress. Besides its high sensitivity to plant water deficits, there are other operational and logistical advantages of the continuous records of SDV giving automatic measurements of MDS compared with SWP measurements taken manually at a single time during the day. Goldhamer and Fereres (2001) have proposed, on the basis of available information, general protocols for the use of measurements of SDV in irrigation scheduling of young and mature deciduous trees. Currently, there are very few data on the sensitivity of SDV measurements for detecting water deficit in field crops. The research reported here was conducted to quantify the influence of environmental conditions on SDVs to test whether the parameters derived from SDV measurements could be used as a sensitive indicator of plant water stress for cotton irrigation management by characterizing the behavior of both indicators at different growth stages under water deficits.
MATERIALS AND METHODS Plant material, experimental site and treatments This study was conducted at the Experimental Station with a rain shelter, Farmland Irrigation Research Institute of Chinese Academy of Agricultural Sciences, in Xinxiang City, Henan Province, China (35" 19' N, 113'53' E). Cotton (Gossypium hirustum cv. Meimian 99B) was grown in 12 iron cylinder pots (40 cm high and 30 cm diameter), and one plant per pot was cultivated. Each pot was filled with a sandy loam soil,
351
and the soil water content at field capacity and wilting point were 32 and 9.5% by volume, respectively. For each pot compound fertilizers (N:P:K= 15:15:15) 2.6 g were applied in order to ensure sufficient nutrition supply during the experimental period. Irrigation was carried out by daily drip irrigation using one emitter per plant, each delivering 2 L h-I, in order to maintain soil water content at around field capacity. On 1st July 2004, cotton plants were submitted to two different treatments for a period of 35 days in flowering stage: a well-watered treatment (TO), in which plants were irrigated daily with a volume of water equivalent to crop evapotranspiration of the previous day calculated from the data of reference evapotranspiration and a crop coefficient estimation based on the thermal time, and a deficit treatment (Tl), in which plants were irrigated for every 3 days using 50% of the water applied to TO plants. Design of the experiment was completely randomized with six replications, with one pot per replicate.
Meteorologicaldata Daily meteorological data, including air temperature (Ta), relative humidity (RH), wind speed and solar radiation were recorded in an automatic weather station located at the experimental site, and atmospheric vapor pressure deficit (VPD) was calculated from Ta and RH data.
Soil moisture Soil water status was measured every 1-3 days before application of irrigation water to plants. The volumetric soil water content (9,) was estimated in each pot using time domain reflectometry (TDR), installing a pair of TDR probes at a depth of 300 mm, midway between the plant and pot rim.
Stem diameter variations The micrometric SDVs were measured in six plants per treatment throughout the experimental period, using a set of linear variable displacement transducers (LVDT) (model DF 2 2.5 mm, accuracy k 10 ym, Solartron Metrology, Bognor Regis, UK) attached to the stem,
02M)6,CAAS All nghts resewed Publishedby ElsevierLtd
ZHANG Ji-yang et a1
358
with a special bracket made of Invar, an alloy of Ni and Fe with a thermal expansion coefficient close to zero (Katerji et al. 1994), and aluminum. Sensors were attached to the stem of selected cotton plants 10 cm above the ground (Klepper et al. 1971), and were covered with silver thermoprotected foil to prevent heating and wetting of the device. Measurements were taken for every 10 s and the datalogger (model CRlOX with AM 416 multiplexer, Campbell Scientific, Logan, UT, USA) was programmed to report 10 min means. The daily SDV cycle provided three different indices: maximum daily stem diameter (MXSD), minimum daily stem diameter (MNSD), and maximum daily stem shrinkage (MDS) which was calculated as the difference between MXSD and MNSD. Daily stem diameter growth rates were calculated by taking values of MXSD into account on two consecutive days (Goldhamer et al. 1999).
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Fig. 1 showed the diurnal course of SDVs, solar radiation (Rs) and vapor pressure deficit (VPD) for two successive days: clear day (1st July) and cloudy day (2nd July). Stem diameter decreased with high shortwave radiation and VPD in the morning both in wet and dry treatments, MNSD reached 14:OO and 16:OO h on 1st July and 2nd July respectively, and started to increase thereafter, with no pseudo-plateau. This very rapid response to changing environmental conditions has been described by Gamier and Berger (1986). The stem continued to swell until about 8:OO h next morning, and reached a maximum value (MXSD) not before sunrise, but 2-3 hours after dawn, even though dawn occurred at about 5:OO h. This phenomenon has been noticed on both treatments, particularly on the mornings with dew during the experimental period, and the amount of increase of stem diameter was greater on the wetter mornings. This increase appears to be related to the mount of dew. Presumably, leaf stomata open at dawn and water enters until the dew disappears. Evidence showing the responsiveness of the cotton
06
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E
Diurnal pattern of stem diameter variations: clear and cloudy
500 400 300 200 100
h
RESULTS
700
r
06 05040302 01
00: -0 1 ;j - 0 2 -0.3 I 00 .u
--c TO
TI
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Solar time (h)
Fig. 1 Diurnal course of solar radiation, vapor pressure deficit and stem diameter variations for 2 successive days: 1 July, clear day (left) and 2 July, cloudy day (right).
plant stem to contracting and expanding as caused by the changes in solar radiation and VPD is also shown in Fig.1. On 1st July (clear day), MDS was 0.102 and 0.199 mm in wet and dry treatments, respectively. On 2nd July (cloudy day), diurnal shrinkage was hardly apparent, and MDS was 0.025 and 0.053 mm, respectively, due to the very cloudy weather and low evaporative demand. This reflected the facts that stem shrinkage and expansion is very sensitive to the changes in the energy load at the evaporating surface of leaves.
Daily dynamics of stem diameter at different growth stages The evolution of MXSD also provides useful information. The difference between two consecutive
02006, CAAS.All rights reserved.Published by ElsevierLtd.
Suitability of Stem Diameter Variations as an Indicator of Water Stress of Cotton
359
* 0.8 21-Jul
6-Jul 11-Jul 16-Jul 21-Jul 26-Jul 31-Jul IS-Aug
Time (d-mon)
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I .2
I
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23-Jul
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+TO +T1
h
0.8 v
Fig. 2 Maximum daily stem diameter (MXSD) with time for cotton during the experimental period. Each point is the mean of six measurements.
0
(I)
P
0.6 0.4
MXSD values gives one measure of the stem growth rate while the trecd of MXSD establishes the cumulative growth. Daily MXSD for the experimental period from 3rd July to 4th August are presented in Fig.2. MXSD increased continuously until 17th July, after which the values of MXSD remained steady in both TO and T1 treatments in spite of somewhat of fluctuations. Based on the behavior of MXSD with time, we divided the whole experimental period into two stages: the stemgrowing stage and the stem-maturing stage. At the stemgrowing stage, the growth rate of control treatment (TO) was consistently higher than that of the deficitirrigated treatment (Tl), the cumulative growth was 1.738 and 1.26 mm by 17th July, respectively. Thus, for this sample of rapidly growing cotton, stem growth, as expressed by daily differences in MXSD, offers a consistent indicator of plant water status. Time-course patterns of the daily changes in MNSD were similar to that of MXSD and, thus, this growth record could also be used as a stress indicator (data not shown). At the stem-maturing stage, cotton stem growth followed by a stoppage or a shrinking trend even without water limitation. Thus, daily changes in MXSD have little significance when the stem is not growing, rendering this parameter less useful as a water deficit indicator in stem matured cotton. At stem-maturing stage, stem diameter growth rates of control plants were negligible (Fig.3) because vegetative growth had virtually ceased. According to MXSD values, the accumulated stem diameter growth during
0.2 I 21-Jul 1.2 -0-
I .o
*
* 23-Jul
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*T1
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'
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Fig. 3 Cotton stem diameter fluctuations at the stem mature stage from 22-30 July. Each point is the mean of six measurements and vertical bars are the standard error. Asterisks indicate statistically significant differences between treatments by LSD,,,,.
experimental period in control plants and deficit plants were approximately zero, positive and negative, respectively. There were no significant differences in MXSD values between treatments until on 27th July. However, statistically significant difference in MNSD and MSD between control and deficit-irrigated plants occurred from the first day onwards. Relative to control plants, MNSD decreased and MDS increased in deficit-irrigatedplants. It appears that MDS and MNSD can be used as available indicators of plant water status at stem-maturing stage, due to high sensitiveness to soil water deficits. At stem-growing stage, deficit irrigation had a clear influence on the evolution of stem diameter (Fig.4).
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360
among irrigation treatments. Such growth effects would be most important in the case of growing cotton for which parameters derived from MNSD or MXSD seem most valuable for detecting water stress.
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Influenceof the environmental conditionson stem shrinkage
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Fig. 4 Cotton stem diameter fluctuations at the stem growing stage from 3-10 July. Each point is the mean of six measurements and vertical bars are the standard error. Asterisks indicate statistically significant differences between treatments by LSD,,,.
Significant differences between treatments were found in MXSD and MNSD. Relative to control plants, accumulated stem diameter growth from 3rd to 10th July was 20% less in deficit plants when calculated from MXSD values. MNSD values presented a similar behavior to MXSD (Fig.4). However, there were no significant differences in MDS values between treatments; sometimes the control was greater than the deficit and sometimes the reverse. This was inconsistent with the behavior of MDS shown in Fig.3. What caused the MDS to be inconsistent at different growth stages? We believe it was stem growth rate. Higher growth rates can interact with measurements of trunk shrinkage masking the water-deficit-related differences in MDS
Stem shrinkage reflects the redistribution of water reserves due to the modification of both water potential gradients and the various resistances to water flow within the plant. Also, to a great extent, MSD appears to depend upon environmental factors, which affect plant transpiration (Gamier and Berger 1986). When using MDS as indicator of water stress it is important to know the action of environmental factors on the stem shrinkage. Correlations between MDS and Rs, VPD, Ta, RH, W, and Ov were given in Table. MDS correlated well with Rs, VPD and Oy (1.2=0.8504, 0.8391 and 0.8026, respectively). By contrast, the associations between MDS and Ta, RH and W were weak, as indicated by the smaller r2 ( r 2= 0.4246, 0.6179 and 0.4077, respectively). From the results of regression analysis it can be seen that Rs, VPD and Ov were the predominant factors affecting MDS, followed by the RH, while Ta and wind velocity had the least effect. Considering combined influence of the different factors, a multiple regression equation was established between MDS and environmental variables (Rs, VPD, RH, and Oy), which can be used to establish a reference value for detecting plant water stress based on MDS patterns. MDS =O.OOOO83Rs+0.4756VPD +O.WRH- 0.074030v - 2.5187 (n =48, 1-2= 0.921'7 (1)
Table Relationship between MDS and environmental factors in cotton Environmental variables
Regression eauation
r2
Rs (W m-*)
Y = 0.0003X-0.2407
0.8504"
48
VPD (kPa)
Y =0.4517X-0.0185
0.8391"
48
Ta ("C)
Y =0.0435X-0.8709
0.4246
48
RH (%) W (m s-I)
Y =-0.025X+2.4733
0.6179'
48
Y = 1.1 179X-0.0532
0.4077
48
(w
Y =-0.0584X+1.2426
0.8026"
48
8,
n refers to the number of observations used to compute each regression "Statistically significant at P<0.05; 'significant at P <0.10.
02006,CAAS. All nghts reserved. Published by Elsewer Ltd.
'
Suitability of Stem Diameter Variations as an Indicator of Water Stress of Cotton
DISCUSSION Deficit irrigation caused clear responses in the three SDV-derived parameters in cotton plants. Generally, the maximum daily stem diameter (MXSD) and the minimum daily stem diameter (MNSD) decreased in deficit-irrigated plants, and the maximum daily shrinkage (MDS) increased relative to well-watered plants (Figs. 3 and 4). These results are in general agreement with other studies conducted with crop species such as tomato (Gallardo et al. 2004) and pepper (Cohen et al. 1998). In tomato, deficit irrigation resulted in a considerable increase in MDS and reduced stem diameter growth-rate based on MXSD. In pepper grown in a growth chamber, both MDS and the daily difference in MXSD were affected shortly withholding irrigation particularly during the fruit-set and fruit-formation phases. Results from another species of maize are not consistent with the results reported here. Katerji et al. (1994) reported that in adult maize plants, while changes in MXSD were relative to other indicators of plant and soil water status such as leaf potential, stomata1 conductance and soil-water depletion, MDS was not. It appears that species-specific studies are required to assess the suitability of particular SDV-deriyed parameters as indicators of plant water status. Growth had a clear effect on parameters derived from SDV. In rapid growth stage, stem growth will be reflected in MXSD and MNSD records, making these parameters potentially useful water stress indicators (Fig.4). On the other hand, mature stem growth slows as the season progresses and may be followed by a stoppage or a shrinking trend. Thus, MNSD and MDS will generally be more applicable than MXSD. These results are in general agreement with other studies in various tree species (Ortuiioa et al. 2004b). In adult fruit trees with very low growth rates, MDS was identified as being the most sensitive indicator of plant water stress (Goldhamer et ul. 2000). In young trees, stem growth parameters such as trends in MXSD and MNSD over time or daily increments in MXSD and MNSD have been shown to be superior indicators of plant water status to MDS (Ortuiioa et al. 2004b). The overall results indicated that SDV, measured by linear variable displacement transducers, proved to be a sensitive method to analyze cotton water behavior
36 1
under water deficits. The comparison of stem diameter measurements and derived parameters, including MDS, MXSD and MNSD, at different growth stages to establish physiological indicators showed clearly the sensitivity of SDV for detecting water stress and changes in the environmental conditions. Pot cultural experiments against background of field environment are closer to practice and of significance bigger than those under complete control conditions. But the results are still different from that of field crops, for example, the water stress process is quicker and intensity is bigger in pots. Therefore, this method should be combined with field experiments.
Acknowledgements The research was funded by the National High Tech R&D Program (863 Program of China) (2001AA242081 and 2002AA2Z4071), and the National Food Fertility Project of China (2004BA520A06-W9).
References Cohen M, Save R, Biel C, Marfa 0. 1998. Simultaneous measurements of water stress with LVDT sensors and electrotensiometers: Application in pepper plants grown in two types of perlites. Acta Horticulturae, 421, 193-199. Fereres E, Goldhamer D A. 2003. Suitability of stem diameter variations and water potential as indicators for irrigation scheduling of almond trees. Journal of Horticultural Science & Biotechnology, 78, 139-144. Gallardo M, Thompson R B, Valdez L C. 2004. Response of stem diameter to water stress in greenhouse-grown vegetable crops. Acta Horticulturae, 644, 253-260. Gamier E, Berger A. 1986. Effect of water stress on stem diameter changes of peach trees growing in field. Journal of Applied Ecology, 23, 193-209. Goldhamer D A, Fereres E, Mata M, Girona J, Cohen M. 1999. Sensitivity of continuous and discrete plant and soil water status monitoring in peach trees subjected to geficit irrigation. Journal of the American Society for Horticultural Science, 124,437-444. Goldhamer D A, Fereres E, Cohen M, Girona J, Mata M. 2000. Comparison of continuous and discrete plant-based monitoring for detecting tree water deficits and bamers to grower adoption f o r irrigation management. Acta Horticulturae, 537,431-445. Goldhamer D A, Fereres E. 2001. Irrigation scheduling protocols using continuously recorded trunk diameter measurements. Irrigation Science, 20, 115-125.
02006, CAAS. All nghts reserved. Publishedby ElsevierLtd.
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Intrigliolo D S, Castel J R. 2004a. Feasibility of using LVDT and watermark sensor for irrigation scheduling. A c t a Horticulturae, 644, 317-323. Intrigliolo D S, Castel J R. 2004b. Continuous measurement of plant and'soil water status for imgation scheduling in plum. Irrigation Science, 23,93-102. Katerji N, Tardieu F, Bethenod 0, Quetin P. 1994. Behaviour of maize stem diameter during drying cycles: comparison of two methods for detecting water stress. Crop Science, 34, 165-169. Klepper B, Browning V D, Taylor H M. 1971. Stem diameter in relation to plant water status. Plant Physiology, 48, 683685. Molz F J, Klepper B. 1973. On the mechanism of water-stressinduced stem deformation. Agronomy Journal, 65,304-306. Namken L N, Bartholic J F, R u d e J R. 1969.Monitoring cotton
ZHANG Ji-yang et a1
plant stem radius as an indication of water stress. Agronomy Journal, 61, 891-893. Nortes P A, Pe'rez-Pastor A, Egea G, Conejero W, Doming0 R. 2005. Comparison of changes in stem diameter and water potential values for detecting water stress in young almond trees. Agricultural Water Management, 77, 296-307. OrtuAo M F, Alarc6n J J, Nicolhs E, Torrecillas A. 2004a. Comparison of continuously recorded plant-based water stress indicators for young lemon trees. Plant and Soil, 267, 263-270. Ortufio M F, Alarcdn J J, Nicolis E, Torrecillas A. 2004b. Interpreting trunk diameter changes in young lemon trees under deficit irrigation. Plant Science, 167,275-280. Remorini D, Massai R. 2003. Comparison of water status indicators for young peach trees. Irrigation Science, 22, 3946. (Edited by ZHANG Yi-min)
O Z W ,CAAS. All nghtsresewed. Publishea by Elsevier Ltd.
sCiENCe@DIRECT.
May 2006
Suitability of Stem Diameter Variations as an indicator of Water Stress of Cotton ZHANG Ji-yang, DUAN Ai-wang, MENG Zhao-jiang and LIU Zu-guj Farmland Irrigation Research Institute, Chinese Academy of Agricultural Sciences, Xinxiang 453003, P.R. China
Abstract Water stress effects on stem diameter variations (SDV) were studied in a pot experiment on cotton (Gossypium hirustum L. Meimian99B). Water restriction was imposed at the flowering stage and were compared with a well-watered control treatment. The volumetric soil water content ((3,) and SDV were monitored continuously. The objective was to determine the feasibility of using the parameters derived from stem diameter measurements, including maximum daily stem shrinkage (MDS), maximum daily stem diameter (MXSD), and minimum daily stem diameter (MNSD) as indicators of plant water stress. The different behavior of SDV was founded at different growth stages. At stem-maturing stage, MDS increased and MNSD decreased in deficit-irrigated plants compared with the control plants, therefore, it appeared that MDS and MNSD ccould be used as available indicators of plant water status. At stem growth stage, there were no significant differences in MDS values between treatments but MXSD and MNSD responded sharply to soil water deficits. Thus, for rapidly growing cotton, the course of MXSD or MNSD with time offered a consistent stress indicator. SDV was also closely related to atmospheric factors, solar radiation (Rs) and vapor pressure deficit (VPD) were found to be the predominant factors affecting MDS, followed by the relative humidity (RH), while air temperature (Ta) and wind velocity had the least effect. A good linear relationship was founded (rz=O.921) between MDS and environmental variables (Rs, VPD, RH, and OV), which can be used to establish a reference value for detecting plant water stress based on the MDS patterns. Key words: stem diameter variations, water stress, atmospheric factors, cotton
INTRODUCTION Evidence of diurnal oscillations in the diameter of plant stem was identified long ago (Namken et al. 1969). Plant stems shnnk as the transpiration stream flows to replace the water lost when stomata open each morning, gas exchange between the leaves and the environment commences, and the leaves partially dehydrate. In the afternoon, as stomata close and transpiration rate decreases, root water uptake exceeds plant water loss and the stem starts to swell (Namken et al. 1969). Shortterm changes in stem diameter have been related to
concomitant changes in plant water status as transpiration loss draws water from the stem, primarily from phloem tissues (Klepper et al. 1971). Molz and Klepper (1973) found that stem diameter measurements could provide continuous records of plant water potential in cotton plants, and suggested that plant water status measurements could be automated and non-destructive. In recent years, renewed interest has arisen in continuous measurement of plant stem diameter as an indicator of plant water status and its application to irrigation scheduling (Nortes et al. 2005; Intrigliolo and Caste1 2004a; Fereres and Goldhamer 2003). Parameters derived from measurements of stem diameter variation
Received 20 December, 2005 Accepted 2 March, 2006 %HANG Ji-yang, MSc, Tel: +86-373-3393384, E-mail: [email protected]; Correspondence DUAN A]-wang, Professor, Ph D, Tel: +86-373-3393364, E-mail: duanaw @public.xxptt.ha.cn
Q2W,CAAS. All rightsresewed. Publishedby ElsevierLtd.
Suitability of Stem Diameter Variations as an Indicator of Water Stress of Cotton
(SDV) have demonstrated that they are very sensitive to changes in tree water supply in a number of fruit tree species, such.aspeach (Remorini and Massai 2003), lemon (Ortuiio et al. 2004a) and plum (Intrigliolo and Caste1 2004b). In all cases, good correlations were found between the degree of trunk shrinkage and swelling and the changes in tree water status. One of the most commonly used parameters is the maximum daily shrinkage (MDS) (Goldhamer and Fereres 2001). Goldhamer et al. (1999) demonstrated that the MDS of peach trunks was more sensitive than other established water status indicators, including stem water potential (SWP), in detecting tree water deficits. It is therefore possible to use MDS or related parameters as indicators of plant water stress. Besides its high sensitivity to plant water deficits, there are other operational and logistical advantages of the continuous records of SDV giving automatic measurements of MDS compared with SWP measurements taken manually at a single time during the day. Goldhamer and Fereres (2001) have proposed, on the basis of available information, general protocols for the use of measurements of SDV in irrigation scheduling of young and mature deciduous trees. Currently, there are very few data on the sensitivity of SDV measurements for detecting water deficit in field crops. The research reported here was conducted to quantify the influence of environmental conditions on SDVs to test whether the parameters derived from SDV measurements could be used as a sensitive indicator of plant water stress for cotton irrigation management by characterizing the behavior of both indicators at different growth stages under water deficits.
MATERIALS AND METHODS Plant material, experimental site and treatments This study was conducted at the Experimental Station with a rain shelter, Farmland Irrigation Research Institute of Chinese Academy of Agricultural Sciences, in Xinxiang City, Henan Province, China (35" 19' N, 113'53' E). Cotton (Gossypium hirustum cv. Meimian 99B) was grown in 12 iron cylinder pots (40 cm high and 30 cm diameter), and one plant per pot was cultivated. Each pot was filled with a sandy loam soil,
351
and the soil water content at field capacity and wilting point were 32 and 9.5% by volume, respectively. For each pot compound fertilizers (N:P:K= 15:15:15) 2.6 g were applied in order to ensure sufficient nutrition supply during the experimental period. Irrigation was carried out by daily drip irrigation using one emitter per plant, each delivering 2 L h-I, in order to maintain soil water content at around field capacity. On 1st July 2004, cotton plants were submitted to two different treatments for a period of 35 days in flowering stage: a well-watered treatment (TO), in which plants were irrigated daily with a volume of water equivalent to crop evapotranspiration of the previous day calculated from the data of reference evapotranspiration and a crop coefficient estimation based on the thermal time, and a deficit treatment (Tl), in which plants were irrigated for every 3 days using 50% of the water applied to TO plants. Design of the experiment was completely randomized with six replications, with one pot per replicate.
Meteorologicaldata Daily meteorological data, including air temperature (Ta), relative humidity (RH), wind speed and solar radiation were recorded in an automatic weather station located at the experimental site, and atmospheric vapor pressure deficit (VPD) was calculated from Ta and RH data.
Soil moisture Soil water status was measured every 1-3 days before application of irrigation water to plants. The volumetric soil water content (9,) was estimated in each pot using time domain reflectometry (TDR), installing a pair of TDR probes at a depth of 300 mm, midway between the plant and pot rim.
Stem diameter variations The micrometric SDVs were measured in six plants per treatment throughout the experimental period, using a set of linear variable displacement transducers (LVDT) (model DF 2 2.5 mm, accuracy k 10 ym, Solartron Metrology, Bognor Regis, UK) attached to the stem,
02M)6,CAAS All nghts resewed Publishedby ElsevierLtd
ZHANG Ji-yang et a1
358
with a special bracket made of Invar, an alloy of Ni and Fe with a thermal expansion coefficient close to zero (Katerji et al. 1994), and aluminum. Sensors were attached to the stem of selected cotton plants 10 cm above the ground (Klepper et al. 1971), and were covered with silver thermoprotected foil to prevent heating and wetting of the device. Measurements were taken for every 10 s and the datalogger (model CRlOX with AM 416 multiplexer, Campbell Scientific, Logan, UT, USA) was programmed to report 10 min means. The daily SDV cycle provided three different indices: maximum daily stem diameter (MXSD), minimum daily stem diameter (MNSD), and maximum daily stem shrinkage (MDS) which was calculated as the difference between MXSD and MNSD. Daily stem diameter growth rates were calculated by taking values of MXSD into account on two consecutive days (Goldhamer et al. 1999).
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06
12
18
00
rI
1.2
-
1.0
-
0.8 0.6
-
0.4
-
01
00 0.7
5
-8 2 E
I!
ti
Fig. 1 showed the diurnal course of SDVs, solar radiation (Rs) and vapor pressure deficit (VPD) for two successive days: clear day (1st July) and cloudy day (2nd July). Stem diameter decreased with high shortwave radiation and VPD in the morning both in wet and dry treatments, MNSD reached 14:OO and 16:OO h on 1st July and 2nd July respectively, and started to increase thereafter, with no pseudo-plateau. This very rapid response to changing environmental conditions has been described by Gamier and Berger (1986). The stem continued to swell until about 8:OO h next morning, and reached a maximum value (MXSD) not before sunrise, but 2-3 hours after dawn, even though dawn occurred at about 5:OO h. This phenomenon has been noticed on both treatments, particularly on the mornings with dew during the experimental period, and the amount of increase of stem diameter was greater on the wetter mornings. This increase appears to be related to the mount of dew. Presumably, leaf stomata open at dawn and water enters until the dew disappears. Evidence showing the responsiveness of the cotton
06
0.2 -
E
Diurnal pattern of stem diameter variations: clear and cloudy
500 400 300 200 100
h
RESULTS
700
r
06 05040302 01
00: -0 1 ;j - 0 2 -0.3 I 00 .u
--c TO
TI
-
06
12
18
Solar time (h)
Fig. 1 Diurnal course of solar radiation, vapor pressure deficit and stem diameter variations for 2 successive days: 1 July, clear day (left) and 2 July, cloudy day (right).
plant stem to contracting and expanding as caused by the changes in solar radiation and VPD is also shown in Fig.1. On 1st July (clear day), MDS was 0.102 and 0.199 mm in wet and dry treatments, respectively. On 2nd July (cloudy day), diurnal shrinkage was hardly apparent, and MDS was 0.025 and 0.053 mm, respectively, due to the very cloudy weather and low evaporative demand. This reflected the facts that stem shrinkage and expansion is very sensitive to the changes in the energy load at the evaporating surface of leaves.
Daily dynamics of stem diameter at different growth stages The evolution of MXSD also provides useful information. The difference between two consecutive
02006, CAAS.All rights reserved.Published by ElsevierLtd.
Suitability of Stem Diameter Variations as an Indicator of Water Stress of Cotton
359
* 0.8 21-Jul
6-Jul 11-Jul 16-Jul 21-Jul 26-Jul 31-Jul IS-Aug
Time (d-mon)
25-Jul
27-Jul
29-Jul
25-Jul
27-Jul
29-Jul
25-Jul
27-Jul
29-Jul
I .2
I
I-Jul
23-Jul
1.o
+TO +T1
h
0.8 v
Fig. 2 Maximum daily stem diameter (MXSD) with time for cotton during the experimental period. Each point is the mean of six measurements.
0
(I)
P
0.6 0.4
MXSD values gives one measure of the stem growth rate while the trecd of MXSD establishes the cumulative growth. Daily MXSD for the experimental period from 3rd July to 4th August are presented in Fig.2. MXSD increased continuously until 17th July, after which the values of MXSD remained steady in both TO and T1 treatments in spite of somewhat of fluctuations. Based on the behavior of MXSD with time, we divided the whole experimental period into two stages: the stemgrowing stage and the stem-maturing stage. At the stemgrowing stage, the growth rate of control treatment (TO) was consistently higher than that of the deficitirrigated treatment (Tl), the cumulative growth was 1.738 and 1.26 mm by 17th July, respectively. Thus, for this sample of rapidly growing cotton, stem growth, as expressed by daily differences in MXSD, offers a consistent indicator of plant water status. Time-course patterns of the daily changes in MNSD were similar to that of MXSD and, thus, this growth record could also be used as a stress indicator (data not shown). At the stem-maturing stage, cotton stem growth followed by a stoppage or a shrinking trend even without water limitation. Thus, daily changes in MXSD have little significance when the stem is not growing, rendering this parameter less useful as a water deficit indicator in stem matured cotton. At stem-maturing stage, stem diameter growth rates of control plants were negligible (Fig.3) because vegetative growth had virtually ceased. According to MXSD values, the accumulated stem diameter growth during
0.2 I 21-Jul 1.2 -0-
I .o
*
* 23-Jul
TO
*T1
0.8
E E v
'
0.6 0.4 0.2 0 21-Jul
23-Jul
Time (d-mon)
Fig. 3 Cotton stem diameter fluctuations at the stem mature stage from 22-30 July. Each point is the mean of six measurements and vertical bars are the standard error. Asterisks indicate statistically significant differences between treatments by LSD,,,,.
experimental period in control plants and deficit plants were approximately zero, positive and negative, respectively. There were no significant differences in MXSD values between treatments until on 27th July. However, statistically significant difference in MNSD and MSD between control and deficit-irrigated plants occurred from the first day onwards. Relative to control plants, MNSD decreased and MDS increased in deficit-irrigatedplants. It appears that MDS and MNSD can be used as available indicators of plant water status at stem-maturing stage, due to high sensitiveness to soil water deficits. At stem-growing stage, deficit irrigation had a clear influence on the evolution of stem diameter (Fig.4).
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ZHANG Ji-yang et a1
360
among irrigation treatments. Such growth effects would be most important in the case of growing cotton for which parameters derived from MNSD or MXSD seem most valuable for detecting water stress.
0.5
1
Influenceof the environmental conditionson stem shrinkage
01
2-Jul
2.5
8
h
4-Jul
6-Jul
8-Jul
10-Jul
~
2.0
-
1.5
-
1.0
-
0.5
-
v
C
2 z
0L 2-Jul
4-Jul
6-Jul
-8-
8-Jul
10-Jul
8-Jul
1 0-Jul
TO
+TI
2-Jul
4-Jul
6-Jul
Time (d-mon)
Fig. 4 Cotton stem diameter fluctuations at the stem growing stage from 3-10 July. Each point is the mean of six measurements and vertical bars are the standard error. Asterisks indicate statistically significant differences between treatments by LSD,,,.
Significant differences between treatments were found in MXSD and MNSD. Relative to control plants, accumulated stem diameter growth from 3rd to 10th July was 20% less in deficit plants when calculated from MXSD values. MNSD values presented a similar behavior to MXSD (Fig.4). However, there were no significant differences in MDS values between treatments; sometimes the control was greater than the deficit and sometimes the reverse. This was inconsistent with the behavior of MDS shown in Fig.3. What caused the MDS to be inconsistent at different growth stages? We believe it was stem growth rate. Higher growth rates can interact with measurements of trunk shrinkage masking the water-deficit-related differences in MDS
Stem shrinkage reflects the redistribution of water reserves due to the modification of both water potential gradients and the various resistances to water flow within the plant. Also, to a great extent, MSD appears to depend upon environmental factors, which affect plant transpiration (Gamier and Berger 1986). When using MDS as indicator of water stress it is important to know the action of environmental factors on the stem shrinkage. Correlations between MDS and Rs, VPD, Ta, RH, W, and Ov were given in Table. MDS correlated well with Rs, VPD and Oy (1.2=0.8504, 0.8391 and 0.8026, respectively). By contrast, the associations between MDS and Ta, RH and W were weak, as indicated by the smaller r2 ( r 2= 0.4246, 0.6179 and 0.4077, respectively). From the results of regression analysis it can be seen that Rs, VPD and Ov were the predominant factors affecting MDS, followed by the RH, while Ta and wind velocity had the least effect. Considering combined influence of the different factors, a multiple regression equation was established between MDS and environmental variables (Rs, VPD, RH, and Oy), which can be used to establish a reference value for detecting plant water stress based on MDS patterns. MDS =O.OOOO83Rs+0.4756VPD +O.WRH- 0.074030v - 2.5187 (n =48, 1-2= 0.921'7 (1)
Table Relationship between MDS and environmental factors in cotton Environmental variables
Regression eauation
r2
Rs (W m-*)
Y = 0.0003X-0.2407
0.8504"
48
VPD (kPa)
Y =0.4517X-0.0185
0.8391"
48
Ta ("C)
Y =0.0435X-0.8709
0.4246
48
RH (%) W (m s-I)
Y =-0.025X+2.4733
0.6179'
48
Y = 1.1 179X-0.0532
0.4077
48
(w
Y =-0.0584X+1.2426
0.8026"
48
8,
n refers to the number of observations used to compute each regression "Statistically significant at P<0.05; 'significant at P <0.10.
02006,CAAS. All nghts reserved. Published by Elsewer Ltd.
'
Suitability of Stem Diameter Variations as an Indicator of Water Stress of Cotton
DISCUSSION Deficit irrigation caused clear responses in the three SDV-derived parameters in cotton plants. Generally, the maximum daily stem diameter (MXSD) and the minimum daily stem diameter (MNSD) decreased in deficit-irrigated plants, and the maximum daily shrinkage (MDS) increased relative to well-watered plants (Figs. 3 and 4). These results are in general agreement with other studies conducted with crop species such as tomato (Gallardo et al. 2004) and pepper (Cohen et al. 1998). In tomato, deficit irrigation resulted in a considerable increase in MDS and reduced stem diameter growth-rate based on MXSD. In pepper grown in a growth chamber, both MDS and the daily difference in MXSD were affected shortly withholding irrigation particularly during the fruit-set and fruit-formation phases. Results from another species of maize are not consistent with the results reported here. Katerji et al. (1994) reported that in adult maize plants, while changes in MXSD were relative to other indicators of plant and soil water status such as leaf potential, stomata1 conductance and soil-water depletion, MDS was not. It appears that species-specific studies are required to assess the suitability of particular SDV-deriyed parameters as indicators of plant water status. Growth had a clear effect on parameters derived from SDV. In rapid growth stage, stem growth will be reflected in MXSD and MNSD records, making these parameters potentially useful water stress indicators (Fig.4). On the other hand, mature stem growth slows as the season progresses and may be followed by a stoppage or a shrinking trend. Thus, MNSD and MDS will generally be more applicable than MXSD. These results are in general agreement with other studies in various tree species (Ortuiioa et al. 2004b). In adult fruit trees with very low growth rates, MDS was identified as being the most sensitive indicator of plant water stress (Goldhamer et ul. 2000). In young trees, stem growth parameters such as trends in MXSD and MNSD over time or daily increments in MXSD and MNSD have been shown to be superior indicators of plant water status to MDS (Ortuiioa et al. 2004b). The overall results indicated that SDV, measured by linear variable displacement transducers, proved to be a sensitive method to analyze cotton water behavior
36 1
under water deficits. The comparison of stem diameter measurements and derived parameters, including MDS, MXSD and MNSD, at different growth stages to establish physiological indicators showed clearly the sensitivity of SDV for detecting water stress and changes in the environmental conditions. Pot cultural experiments against background of field environment are closer to practice and of significance bigger than those under complete control conditions. But the results are still different from that of field crops, for example, the water stress process is quicker and intensity is bigger in pots. Therefore, this method should be combined with field experiments.
Acknowledgements The research was funded by the National High Tech R&D Program (863 Program of China) (2001AA242081 and 2002AA2Z4071), and the National Food Fertility Project of China (2004BA520A06-W9).
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Intrigliolo D S, Castel J R. 2004a. Feasibility of using LVDT and watermark sensor for irrigation scheduling. A c t a Horticulturae, 644, 317-323. Intrigliolo D S, Castel J R. 2004b. Continuous measurement of plant and'soil water status for imgation scheduling in plum. Irrigation Science, 23,93-102. Katerji N, Tardieu F, Bethenod 0, Quetin P. 1994. Behaviour of maize stem diameter during drying cycles: comparison of two methods for detecting water stress. Crop Science, 34, 165-169. Klepper B, Browning V D, Taylor H M. 1971. Stem diameter in relation to plant water status. Plant Physiology, 48, 683685. Molz F J, Klepper B. 1973. On the mechanism of water-stressinduced stem deformation. Agronomy Journal, 65,304-306. Namken L N, Bartholic J F, R u d e J R. 1969.Monitoring cotton
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O Z W ,CAAS. All nghtsresewed. Publishea by Elsevier Ltd.