Agriculture and Science 2022/6

Nutrient water absorption and its transfer during day and night in tomato

Former Graduate School of Natural Science and Technology, Okayama University
Masaharu Masuda

Introduction

　Living organisms on the earth live in a natural day-night cycle. The earth rotates around the sun once a year, but because the axis of rotation around the south and north poles is tilted 23.5 degrees from the so-called orbital plane, the length of day and night and temperature change in mid-latitude regions such as Japan, resulting in four seasons. Many plants flower and bear fruit in response to these day lengths and temperatures. In low-latitude regions near the equator, where the earth's rotation and revolution are on the same orbit, the four seasons do not occur, and day and night repeat at approximately 12-12 hours per day. In this region, there are wet and dry seasons, and many plants flower in response to the rain. The desert is home to many succulent plants, some of which store water like cacti, while others, like the baobab, store water in their trunks, shedding their leaves during the dry season and growing more leaves during the rainy season. Thus, it can be said that plants on earth have evolved by adapting to their natural environment, including light, temperature, and water.

　The various forms found in the above-ground part of the plant are only possible through the maintenance of the individual organism, and its survival would not be possible without the presence of roots. Roots receive photosynthetic products from the above-ground parts, and they also transfer water and nutrients to the above-ground parts. The flow of water is shown in Figure 1. Roots absorb water attracted to the soil (called water potential, the value of which is always negative) and raise the water from the stem to the leaves, where the water potential is lower. Rather than being lifted, the water is pulled up by the transpiration force generated by the water potential of the leaves. The water evaporates from the leaf and cools the leaf surface as heat of vaporization. At this time, the various nutrients dissolved in water in the form of ions are distributed to the various parts of the plant. The water flow in the plant differs greatly from day to night.

　This paper is a review of how root nutrient uptake and translocation changes in response to the day-night environment of the above-ground zone, mainly based on the author's previous research, citing the literature.

2. daytime and nighttime stem and root elongation and fruit enlargement

　Stem elongation in tomato is greater at night than during the day, with 70-801 TP3T taking place during the night25) , and stem diameter shrinks during the day (Figure 2). This phenomenon of daytime shrinkage has been clearly demonstrated in grapes4) . This is due to a decrease in water potential in the stem tissue during the daytime, resulting in a decrease in cell swelling pressure. Tomato fruit diameter has also been shown to decrease during the daytime and reach a minimum around 13:00 (Figure 3).

　The author placed tomato seedlings on a sloping tin plate, continuously poured nutrient solution at 24°C, and measured the roots growing under the black sheet at 6:00 am and 6:00 pm.

　As cited in the previous report on the National Center Test for University Entrance Examinations12) , roots respond to the absorption of water and nutrients by signals sent from the above-ground part of the plant. For example, when large tomatoes were harvested when they had reached the third fruit cluster, the dry matter weight of the roots increased by 30% of the control plants after 12 days, and the concentrations of NO3-N, Ca, and Mg in the culture medium plummeted. This means that the absorbed concentrations (n/w, see below) of these 5) components increase rapidly with fruit picking. However, no change was observed in the concentrations of P and K13) . The reason why the rate of absorption differs among the components is still unknown.

　Recently, Tsukamoto et al.23) used the Positronemitting Tracer Imaging System (PETIS), which can visualize the dynamics of substances in plant organisms nondestructively, to determine the contribution rate of 11CO2 to the fruit of lateral leaves of tomato plants based on the migration images of 11CO2 treated on the leaves of lateral branches. This method is expected to be applicable to the analysis of nutrient dynamics in roots associated with leaf removal and fruit picking, and will be very useful in the future.
The company is expected to

3. leaf and fruit water potentials during day and night

-The appearance of the fruit...

　As mentioned earlier, transpiration from plant leaves decreases the water potential in the body. This creates water absorption, and water is drawn up through conduits as mass flow. Normal water potential decreases during the day and increases at night. However, even at night, the water potential is always negative and never positive. As shown in Figure 5, the water potential of tomato leaves reaches a minimum around 14:00 at -1.0 MPa and a maximum at midnight, regardless of the irrigation rate. It is widely known that fruit breakage occurs frequently, especially when rainfall occurs after drought, and techniques such as rain-fed cultivation have been widely used to prevent fruit breakage.

　(Ota 17) investigated mini-tomato fruiting, and found that fruit breakage was related to fruit expansion due to increased pressure potential, since fruit breakage occurred more frequently in the early morning from 5 to 7 am and the lateral diameter of the fruit increased at this time. Furthermore, he thought that the promotion of transpiration by leaves at night would reduce the inflow of water into the fruit, so he used 6000 lux lighting at night, which reduced the number of fruit breakage to 401 TP3 T or less than that in the control. Even taking into account the differences between soil and hydroponic conditions, and between regular and mini-tomatoes, there is still a time lag of about 6 hours between the midnight period when the leaf water potential is at its highest and the morning period when fruit breakage occurs, as shown in Figure 5. If the dynamics of water inflow into the fruit pulp and peel tissue during this 6-hour period can be clarified using a heavy water tracer, it is expected that further control techniques for fruit breakage will be developed.

4. day/night nutrient absorption concentrations (n/w) and nutrient transfer

　The author and his colleagues reported at the 1984 Horticultural Society of Japan Spring Meeting that the concentration of nutrients absorbed (n/w) by tomato plants during the daytime was close to that of the culture medium, but during the nighttime it was 2.2 to 3.7 times higher than that during the daytime. At the same meeting, Terabayashi et al. also reported similar results. The absorbed concentration is a concept proposed by Yamazaki et al. 24) in the 1970s and has been widely used as a guideline for vegetable culture medium management. It is a value obtained by dividing the amount of components absorbed by the crop (n) by the amount of water (w), and is usually expressed in me/ℓ. The absorption concentration is calculated by dividing the amount of n by the amount of water (w), and is usually expressed in me/ℓ. The n/w values of this nutrient water content are shown in Figure 6 for 5 days during the spring season, when the same plants were transferred from one pot for daytime (6:00-18:00) and another pot for nighttime (18:00-6:00). The daytime n/w values were close to the initial culture medium concentration, but the nighttime n/w values were 2 to 3 times the culture medium concentration for all components, especially P, which was nearly 6 times higher. (Terabayashi et al. 22) also studied P in the summer season by transferring plants for four days from 7:00-19:00 during the day and from 19:00-7:00 during the night, and found that the nighttime n/w of P
The inter-absorption rate is admittedly very high compared to other components.

　Assuming Xℓ of initial culture, Yℓ of liquid at the end, Zℓ of water surface evaporation during this period (blank area), a concentration before treatment, and b concentration after treatment, n/w is expressed as (aX-bY) / (X-Y-Z). The fact that n/w is higher at night strongly suggests that the concentration of xylem liquid transferred to the ground is also higher. Therefore, we cut stems of 1.5-month-old tomato plants at 10 cm from the ground and collected and analyzed the xylem secretions, and found that the amount of secretions at night was half that of daytime, the concentrations of NO3-N and K were higher during the daytime, and P, Ca, and Mg were higher during the nighttime. P, Ca, and Mg were found to be higher at night. In particular, K was 1.4 times higher in the daytime than in the nighttime, and P was 2.5 times higher in the nighttime than in the daytime (Table 1).

　Furthermore, analysis of the juice collected from tomato plants grown in the same culture medium for 15 minutes by cutting one stem every hour for 24 hours revealed that K increased from morning to noon and P increased from evening to 10 pm in the regression curves for the concentration of components14) .

　To what extent does stem excision reduce the velocity of xylem fluid? A heat-pulse thermistor was inserted a few centimeters below the site of planned stem excision to measure the xylem flow velocity of 2-month-old tomato plants. After the stem was cut, the flow velocity decreased rapidly, reaching 18 cm/h for the former and 6 cm/h for the latter after 10 minutes, showing a gradual decrease with time (Figure 7).

　In general, the rate of water movement from the roots to the surface is determined by the intensity of transpiration and root pressure. In transpiring plants, the effect of root pressure is extremely small and almost negligible, and the root pressure decreases as the transpiration rate increases away from the roots, and finally is not observed at all18) . Therefore, this result can be understood as indicating the ratio of the effects of transpiration and root pressure at 10 cm above the ground. When the stem is cut, the transpiration power is lost and the flow velocity drops drastically, reaching about one-fourth of its value before cutting during the daytime. From this, it can be inferred that transpiration force and root pressure work at this site in the ratio of about 751 TP3T and 251 TP3T, respectively, for water movement during the day.

　The concentration of components in the ileocortical fluid should reflect the concentration of components in the xylem fluid of the intact plant.
This point has been discussed by many researchers, and Armstrong and Kirkby1) found that the concentrations at 15 to 60 minutes after stem excision were stable and best representative of those of intact individuals. The authors also collected and analyzed secretions every 15 minutes for one hour after stem cutting, and found little change in the concentration of components within one hour after cutting, suggesting that this value reflects the concentration of xylem fluid in intact individuals9) . However, the development of a microsensor that can be inserted into the growing tomato stem to detect the concentration of xylem fluid components is still needed to dynamically monitor the transfer of nutrients.

5. daytime and nighttime xylem secretion and culture medium concentrations

　Assuming that water and nutrients are moving from the roots to the ground without retention, the concentration of secretion is equal to the concentration of absorption (n/w). Of course, if we look at these over time, the former is a point analysis and the latter is a linear analysis, so the numerical values rarely coincide, but it is thought that the analytical values of secretion at midnight and noon will not be far from approximating the n/w values at night or in the daytime. It is also a well-known fact that root nutrient water absorption varies with seedling age.

　Therefore, tomatoes were sown in January, February, and March, grown in 1/2 culture medium, and stem cut in May (12:00 and 0:00), and the XylemSapConcentration Factor (XSCF) was determined from the analysis of the 1-hour collection of the seminal fluid and culture medium (Table 2). XSCF is the value obtained by dividing the concentration of secretion fluid by the concentration of culture medium, which is the name given by the author according to the transpiration stream concentration factor (TSCF) of Russel and Shorrocks20) .)
The larger the age of the tree, the greater the amount of fluid produced, with 12:00 being 3 to 5 times greater than 0:00 at any age. The XSCF of nutrients NO3-N, Ca, and Mg decreased with age. Especially in 4-month-old tomatoes, Ca was 0.7 in the daytime and Mg was 0.5 in the daytime and 0.6 in the nighttime, which were less than 1, indicating that the concentration of secretion solution was lower than that of culture solution.

　In contrast, the XSCF of P was as high as 2.1 during the day and 7.0 at night, even at 4 months of age, and was much higher at night. Conversely, the XSCF of K was 8.1 during the day and 5.6 at night, with daytime values much higher. The extremely high XSCF of K for both day and night may be due to the fact that the concentration of the culture medium at the time of analysis (2.5 me/ℓ) had decreased to 1/3 of the original concentration, as noted at the bottom of Table 2.

　As discussed above, the n/w of each component is higher at night when water absorption is low and lower during the day when water absorption is high. In particular, the n/w of P at night is 4 to 5 times higher than that in the daytime, much higher than the values of other components. Why is P absorbed more than other components even at night when water transfer is low? Among the multifaceted physiological functions of P, it may be because P is involved in cell division and proliferation, the formation of nucleic acids and cell membranes, and the production of ATP necessary for respiration, all of which take place constantly during the night, and are required to the same extent as during the day.

　On the other hand, XSCF is higher during the daytime even though K n/w is higher at night. Ben Zioni et al.2) proposed a feedback mechanism of K from aboveground to roots in plants, in which K acts as a counter ion to NO3-N N. In tomatoes, K is also transferred from aboveground to roots. In tomato, it has been confirmed that K transferred from the aboveground to the roots is transferred back to the aboveground, and although it varies depending on the growth conditions, it is estimated to account for 20% of the transport concentration at the highest level1, 7) . The author has also shown that K concentration in xylem secretion increases from dawn14) , and this is likely to be related to the re-translocation of K that has been translocated to the roots. As mentioned above, if we can visualize the movement of P during the night and the movement of K during the day using 32P and 40K (which are considered extremely difficult to produce), it will provide extremely useful information for crop management.

6. last but not least - future prospects

　When the me sum of cation absorption by plants (NH4++K++Ca2++Mg2++Na+) exceeds the sum of anion absorption (NO3-+SO42-+H2PO4-+Cl-), plants must discharge cations (H+) into the rhizosphere.
The excess cations taken up are said to increase the synthesis of organic acids to regulate the increase in intracellular pH in order to maintain homeostasis16) . This physiological function of living organisms can be understood as an example of "dynamic equilibrium" 3). The cation-anion balance must be maintained in xylem fluids as well, and it is a matter of great interest to know what counter ions are associated with the XSCF of night P and day K, and whether they play a part in each other by retrotranslocating to the roots.

　On the other hand, root water permeability shows diurnal variation, with high water permeability during the day and low permeability at night, which is closely related to the level of aquaporin expression. Since aquaporin expression is at its lowest a few hours after the onset of the dark period and then gradually increases toward the onset of the light period, the daily variation in aquaporin expression is thought to be controlled by circadian rhythms8) . The rapid induction of root-specific aquaporin gene expression after the onset of light, but no induction of aquaporin gene expression was observed when the aboveground humidity was kept near 100%, suggesting that the rapid induction of aquaporin expression in roots is largely related to transpiration demand from the aboveground area in addition to circadian rhythm21) . 21).

　The authors analyzed the amount of xylem secretion and inorganic components of grafted and self-rooted cucumbers using an hourly fraction collector for 48 hours, and found that the amount of secretion in both pumpkin and cucumber roots showed a clear circadian rhythm. It rose sharply from around 8:00 a.m. and peaked at 2:00 p.m., followed by a gradual curve. Thereafter, it gradually curved gently and reached its lowest around sunrise (Figure 8). At this time, the concentration of inorganic component NO3-N rapidly decreased and was approximately one-half of that immediately after 6 hours, while the concentration of P rapidly increased and was nearly twice that immediately after 6 hours11) . In this experiment, the effect of transpiration can be disregarded because the above-ground portion was removed, and it is understood to be a reaction of the roots themselves (root pressure).

　How are aquaporin genes involved in this circadian rhythm? In rice roots, many aquaporin molecular species show diurnal variation with a peak in gene expression a few hours after the start of the light period, and another peak in protein levels two to three hours later21) . Recently, Ayaka Maeda of Notre Dame Girls' High School in Okayama, Japan, examined in detail the diurnal variation of water uptake in Asian rice plants under constant temperature and light/dark conditions and found that increased water uptake is evident before the onset of the light period and that aquaporin transcript levels increase around the start of the light period, indicating that water uptake is likely to be triggered before transpiration This was presented at JSEC-2019 (the Science and Technology Challenge for High School and College of Technology Students, an academic award for students sponsored by the Asahi Shimbun and others).

　Although it is well known that water transport in the xylem is mediated by transpiration and root pressure, there have been no reports on the relationship between root pressure-induced water absorption and aquaporin gene expression. Since root water uptake is related to solution osmotic pressure, which in turn promotes or inhibits nutrient absorption, water and nutrients must be considered as polar opposites in the analysis of root function. Considering that roots respond to signals from the above-ground part, it is important to utilize the above-mentioned heavy water tracer and PETIS technology as a means of analyzing the dynamics in individuals and to apply the results to higher-level integrated science6) , especially in the field of crop cultivation and production science.

References

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8. Lopez, F., Bousser, A., Sissoëff, I., Gaspa M., Lachaise, B., Hoarau, J. and A. Mahé. Diurnal regulation of water transport and aquaporin gene expression in maize roots: contribution of PIP2 proteins. Diurnal regulation of water transport and aquaporin gene expression in maize roots: contribution of PIP2 proteins.
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mineral concentration in xylem sap after decapitation of grafted and non-grafted
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　Matsumoto, T. and Y. Kitagawa. 2011. Transpiration from shoots triggers diurnal
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Soil and flower - 12th
　　Manure Effectiveness and Soil Conditions
　　-The blackness of the soil is the deciding factor.

Hokkaido Branch Office, JCM Agri Co.
　Teruo Matsunaka Technical Advisor

　In the previous issue, I reviewed the history of how, in the days before the advent of chemical fertilizers, farmers overcame the difficult problem of supplying nutrients to farmland by devising a material called compost. I also mentioned the difference in the way of farming between the fields in Europe and the rice paddies in Japan, which led to a difference in the way of thinking about compost. Even after the advent of chemical fertilizers, compost is expected to have various effects. However, these various effects do not occur in all soil types without exception. Let us consider what are the conditions of soil that cause differences in the manifestation of these effects.

1. expected effects of compost

　Compost is expected to have three major effects (Table 1). (1) as a nutrient, (2) as a stable organic matter that is relatively resistant to decomposition, and (3) as a source of living organisms. It is often said that composting will automatically produce all three effects at the same time. This is probably the reason why people think that compost improves the soil. However, these three effects are "expected effects" and do not always appear.

　(1) Effect as a nutrient

　The first is its effect as a nutrient. This is the effect that can be expected directly from the application of compost. Specifically, it is (1) a source of multiple elements, especially the three elements (nitrogen, phosphorus, and potassium), (2) a source of trace elements, (3) an effect as a slow-release fertilizer, and (4) a source of plant hormones. Among these effects, the following effects can be expected regardless of soil conditions
is the effect of (1) as a three-factor fertilizer. This is because it is difficult to imagine a normal field or paddy soil in which nitrogen, phosphorus, and potassium are not limiting factors for crop production. In addition, (iii) as a slow-release fertilizer, it can be expected to work regardless of the soil conditions. This is because after compost is fed to the soil, animals (e.g., stoneflies, borers, earthworms) and microorganisms (e.g., bacteria, actinomycetes, filamentous fungi) in the soil cooperate to decompose the compost, and nutrients are gradually released from the compost as a result of this decomposition. If compost is used continuously, a cumulative and continuous effect of nutrients can be expected.

　However, the effect of (2) as a trace element fertilizer cannot be expected in paddy fields. This is because trace elements are dissolved in irrigation water in rice paddies, and the amount of trace elements supplied by irrigation water, which is taken up in large quantities during rice cultivation, is large. Even if the compost contains trace elements, the limited amount of trace elements supplied by the compost will not be equal to the natural supply from the irrigation water.

　It is not yet well known how effective the plant hormones (4) can actually be in fields and rice paddies with a history of cultivation. However, it is likely to be effective when the surface soil containing organic matter is completely removed and the subsoil containing little organic matter is used as the cropping soil, as is the case in cultivated land.

(2) Effect as stable organic matter

　The second expected effect is as stable organic matter. Stable organic matter is organic matter that remains in the soil after being decomposed to some extent by animals and microorganisms, and is relatively difficult to decompose. This becomes the substance known as soil organic matter (humus), which gives the soil its black color.

　When compost is incorporated into the soil, the easily decomposable organic matter in the compost is decomposed to produce a nutrient effect. On the other hand, the organic matter that remains in the soil because it is relatively difficult to decompose, together with the organic matter that was already in the soil, will show effects as stable organic matter. These effects include (1) improvement of physical properties of the soil, such as the size and proportion of gaps in the soil (pore distribution), ease of drainage (permeability), water retention (water holding capacity), air permeability (aeration), and ease of cultivation (tillability), (2) increase in nutrient holding capacity, and (3) suppression of toxic substances, for example, when organic matter binds with aluminum When organic matter combines with aluminum, it suppresses the toxic effects of aluminum (chelating action), making it difficult for aluminum to combine with phosphorus.

　As a result, the effect of phosphorus nutrients becomes easier to produce, (4) trace elements are often in a form that is difficult to dissolve in water, and (5) organic matter has the ability to stop environmental changes. However, as organic matter is decomposed, carbon dioxide (CO2) is released, which dissolves in water to form carbonated water, making trace elements easier to dissolve, and (5) organic matter has the ability to soften environmental changes (buffering capacity).

　However, these various expected effects of compost as stable organic matter appear only when the organic matter content of a given soil is less than a certain criterion (ranging from 2 to 5%, depending on the soil), and no effect can be expected if it is higher (Yamane, 1981). This is because in soils with high organic matter content, the physical properties of the soil are less likely to be a limiting factor in crop production, since the soil originally contains more stable organic matter (humus).

　(3) Effect as a source of living organisms

　The third effect is as a source of biological supply. Many organisms (worms and other small animals, microorganisms, etc.) live in compost. Feeding compost is expected to be effective as a source of these organisms because it supplies them to the soil. However, if the soil to which compost is applied is normal soil, the number of organisms living in the soil is overwhelmingly larger than the number of organisms in the compost, and it is difficult to expect a direct effect of compost as a source of soil organisms. This effect is also unlikely to occur if the soil is extremely low in organic matter, such as in built-up areas.
It should be limited to cases where the soil

　The effect of compost application on soil organisms is more likely to be cumulative than a one-year effect. However, even in this case, the direct effect of the diversification and increase in the number of organisms on crop growth may vary depending on other soil conditions.

2. the less organic matter in the soil, the more effective compost is.

　When we give compost to the soil nowadays, are we just giving it to the soil without any particular reason, just because it is for "soil building"? We need to think carefully about why we are giving compost to the soil and what effect we expect it to have. Depending on soil conditions, compost may or may not have the desired effect. As shown in Table 1, the criterion is whether the soil has more or less organic matter.

　The amount of organic matter in the soil can only be determined by strictly analyzing it. To determine the amount of organic matter without analyzing the soil, look at the color of the soil. If the color of the soil is black to dark brown with a black tint, you can judge that there is a lot of organic matter in the soil.

　Soils with low organic matter (light black color) can expect diverse effects from compost feeding. For soils with high organic matter (dark black color), we should expect mainly nutrient effects as a slow-release three-element fertilizer.