LeonidAsipovVsOscillations5.pdf the whyners thought they had protection

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LeonidAsipovVsOscillations5.pdf the whyners thought they had protection

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Title: There are No Short-Term Oscillations in Plant Transpiration. 1
The Observed Weight Scale Signal Oscillations Were an Artifact. 2
Author: Leonid Asipov 3
E-Mail Address: [email protected] 4
Telephone: [phone]
Institution: The Hebrew University of Jerusalem, faculty of food and agricultural sciences, 6
Rehovot. 7
Words: 1165 8
Number of Figures: 6 (all black and white). 9
Date of submission: 16.5.2014 10
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There are No Short-Term Oscillations in Plant Transpiration. 39
The Observed Weight Scale Signal Oscillations Were an Artifact. 40
Leonid Asipov 41
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Abstract 43
In order to avoid artifacts of measurement, control should be introduced. The study 44
"Development of synchronized, autonomous, and self-regulated oscillations in transpiration rate 45
of a whole tomato plant under water stress", which measured plant transpiration by weight loss 46
using an electronic weight scale, has focused on short-period fluctuations in the measured 47
weight loss rate. No control was introduced for case that the fluctuations are result of weight 48
scale measurement system noise. In the current study, a control is introduced. The control is 49
simultaneous measurement of transpiration by leaf gas-exchange. The results show lack of 50
short-term oscillations in the transpiration rate. Longer oscillations correlate with irradiation 51
levels in the greenhouse. The conclusion is that short-term fluctuations in the transpiration rate 52
seen in the weight scale signal are an artifact of the weight scale. A theoretic consequence of 53
this finding is that no central transpiration control mechanisms exist in plants. Plant cells 54
respond independently to changing environment. 55
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Keywords: Oscillations, plant, transpiration, weight scale, weight loss, gas exchange 57
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Introduction 77
The authors of an article (Wallach et al. 2010) have measured plant transpiration by weight loss, 78
using an electronic weight scale and paid attention to short-term (3 minutes) fluctuations of the 79
transpiration rate. The weight scale measurement system, however, has its precision limitation 80
and substantial noise is abundant. The data, which is sampled every 10 seconds, has a large 81
random noise, resulting from analog to digital conversion and the transducer itself. To reduce 82
the noises, the data was averaged for a period of 3 minutes (18 points). After the averaging, the 83
noises were still about +- 1.6 grams. It is impossible to relate to a biological phenomenon 84
happening on short time periods of few minutes due to the large weight scale noise. The 85
significance of the data rises as we average it for longer time period. The writers of the article 86
(Wallach et. al 2010) have presented the short-term oscillations seen in the weight scale signal 87
as biological phenomena of short-term changes in stomata apertures. Since the oscillations are 88
seen on basis of a whole plant, the stomata change of aperture has to be centrally synchronized. 89
However, there was no control for case that the short-term oscillations are an artifact of the 90
weight scale. In the next section, a proper control is introduced: simultaneous measurement of 91
transpiration with leaf gas-exchange method. 92
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Materials and Methods 94
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Weight scale measurement: Tedea-Vishay 1040 transducer connected to an analog to digital 96
converter. The data was logged every 10 seconds and averaged every 2.5 minutes. 97
Gas-exchange measurement: LICOR LI6400 portable photosynthesis system. Clear-Top chamber 98
was used so the illumination in the chamber was the same as in the greenhouse. The H2O and 99
CO2 scrubbers were turned off, so the CO2 and humidity was the same as in the surroundings. 100
The data was logged every 2 minutes. No averaging was applied. 101
Plants: wt Solanum lycopersicum from Ailsa Claig strain of approximately 3 month old. 102
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Results 115
Simultaneous measurement from electronic scales and gas-exchange 116
To prove that short-term oscillations result from measurement noise, an additional transpiration 117
measurement method (leaf gas-exchange) was used simultaneously with the weight scale 118
(Fig.1). Short term oscillations were seen only at the electronic scales measurement. During the 119
day, there were fluctuations in irradiation levels and transpiration was well correlated to them 120
(Fig. 1). These oscillations are longer-term (12-30 minutes) and seen on the gas-exchange and 121
the smoothed weight-scale measurement (Fig. 2). In the transpiration measured with the 122
weight scale (Fig. 1) there were short-term (3 minutes) oscillations during the day and the night. 123
We would expect the daily oscillations to be larger since transpiration is larger. However, they 124
were not different. The short-term oscillations exist only in weight scale measurement and they 125
are day/night unspecific. No nocturnal oscillations (short or long term) were seen in gas-126
exchange. 127
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Comparison of weight scale signals from a plant and from a bowl of water. 129
For control purposes, during weight-scale measurement of plants, a simple bowl of water, 130
exposed to air, was measured (Fig. 3). The short-term oscillations exist as well in the bowl of 131
water signal. The noise from the plant and from the bowl of water was similar by its pattern. 132
The amplitude of the oscillations seen in the bowl of water signal is slightly less, possibly due to 133
the smaller weight of the bowl of water. 134
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Measurement of transpiration by weight-scale and gas-exchange in controlled environment. 136
In controlled environment, the light is constant and no longer-term (related to light) oscillations 137
are expected. Plant transpiration was measured by weight-scale and by gas-exchange to explain 138
the nature of the short-term oscillations seen in the weight scale signal. 139
Large short-term oscillations in the weight-scale signal were seen (Fig. 4). 140
The transpiration signal measured by gas-exchange is stable (Fig. 5). No oscillations seen, short 141
or long term. 142
The response speed of LI-6400 to changes in humidity of the air. 143
To make sure that the LI-6400 Portable Photosynthesis System responds quickly enough to 144
changes in humidity to potentially track the short-term oscillations seen in the weight-scale 145
measurement, humidity was suddenly changed during continuous measurement. The built-in 146
H2O absorber absorbs humidity from the air. Turing it on or off, changes the humidity suddenly. 147
It is possible to see that the response time of LI-6400 to sudden changes in humidity is about 10-148
15 seconds (Fig. 6). If short-term oscillations were really happening they would have been 149
tracked by the gas-exchange measurement. 150
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Discussion 153
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No short-term oscillations were seen in gas exchange measurement (Fig. 1, 5). Therefore, the 155
short term oscillations of the weight scale are an artifact resulting from measurement noise of 156
the weight scale. The observed short-term oscillations are similar during the day and the night, 157
without relation to the extent of the transpiration rate (Fig. 1). If they were a real phenomenon, 158
we would have seen differences in the extent of the oscillations between the day and the night 159
and also they would have appeared on the gas-exchange measurement. 160
Longer oscillations result from irradiation changes. They are synchronized by abiotic factors. The 161
plant cells respond to environment independently and stomata aperture is changed according to 162
the turgor pressure of the guard cells. There is no point in speculating an existence of a "central 163
control" to transpiration while the normal explanation of "no central control" is sufficient. 164
Short-term oscillations are observed in the bowl of water evaporation (Fig. 3). This is the reason 165
why the plant transpiration's short-term oscillations are not a result of biological phenomenon. 166
The controlled room results support the finding that the short-term oscillations are an artifact. 167
No oscillations were found in the gas-exchange signal (Fig. 5). 168
The response time of LI-6400 to changes in humidity is quick (Fig. 6) and the short-term 169
oscillations would have been tracked by the gas-exchange if they were really happening. 170
The reported short-term oscillations (Wallach et. al 2010) seen in weight scale measurement of 171
transpiration are an artifact of the weight scale and not a result of biological phenomena. 172
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References
(1)
Wallach R, Da-Costa N, Raviv M, Moshelion M. 2010. Development of synchronized,
autonomous, and self-regulated oscillations in transpiration rate of a whole tomato plant under
water stress. Journal of Experimental Botany 61, 3439-3449 .

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Figure Legends

Fig. 1
Simultaneous measurement of transpiration by gas-exchange and weight scale. Irradiation (first),
transpiration measured by gas-exchange (second) and transpiration measured by weight scale
(third) is plotted relative to time

Fig. 2
Smoothing of the transpiration measured by weight scale. Moving average of two points at each
side, twice. The initial data is the same as in Fig. 1. Irradiation (first) and smoothed transpiration
measured with a weight scale (second) is plotted relative to time

Fig. 3
Weight loss signal of a plant vs bowl of water. The weight data is unscaled (the units are
change of volts in three minutes). Gray is plant and black is bowl of water relative to time

Fig. 4
Measurement of transpiration by weight-scale in controlled environment. Light sensor (first),
raw weight (second), weight loss rate (third) is plotted relative to time

Fig. 5
Measurement of transpiration by gas-exchange in controlled environment. Illumination (first)
and transpiration (second) is plotted relative to time

Fig. 6
LI-6400 response time to sudden changes in humidity. Arrows indicate changes in the mode
of the H2O absorber. When it is turned on, water is absorbed from the air. Relative
humidity of the chamber is plotted vs time

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Figures


Fig. 1

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Fig. 2

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Fig. 3

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Fig. 5

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