Akihiro Isoda

Adaptive Responses of Soybean and Cotton to Water Stress II. Changes in CO2 Assimilation Rate, Chlorophyll Fluorescence and Photochemical Reflectance Index in Relation to Leaf Temperature

Abstract Adaptive changes were studied comparatively in soybean and cotton grown in pots under four irrigation conditions i.e. normal irrigation (equal to the evapotranspiration of the crop), and 50%, 25% and 10% of the normal irrigation. In soybean, the maximum quantum yield of PSII (Fv/Fm) was generally higher while the actual quantum yield of PSII (∆F/Fm’) and CO2 assimilation rate (An) were lower than in cotton.The intensity of the decrease in Fv/Fm, ∆F/Fm’ and An by water-stress treatments was larger in soybean than in cotton. The decrease in ∆F/Fm’ in soybean under water stress was accompanied by a significant increase in non-photochemical quenching (NPQ) and significant decrease in photochemical reflectance index (PRI). Chlorophyll content decreased significantly under severe water stress only in soybean. The increase in leaf temperature (Tl) in response to water stress was significantly larger in soybean than in cotton. Tl was highly and negatively correlated with Fv/Fm, An, PRI and ∆F/Fm’ while it was highly and positively correlated with NPQ of both crops. Especially in soybean, the correlations of Tl with An, Fv/Fm and PRI were significant. It was concluded that soybean adapted to water stress by dissipating the excess excitation energy thermally with the down-regulation of PSII activity to protect its photosynthetic apparatus from the photodamaging effect of water stress and high Tl. This photoprotective mechanism might be supported by the paraheliotropic leaf movement of the crop. Cotton adapted to water stress by keeping Tl lower to protect the photosynthetic apparatus from photodamage. Probably higher transpiration kept Tl of the crop lower under drought stress.

Adaptive Responses of Soybean and Cotton to Water Stress: I. Transpiration Changes in Relation to Stomatal Area and Stomatal Conductance

Abstract The adaptive responses of soybean and cotton to various irrigation levels were explored in terms of transpiration, stomatal role in transpiration, leaf temperature (Tl) and CO2 assimilation rate (An). Compared with cotton, soybean showed a lower flow rate of stem sap (FRSS), transpiration rate (E), stomatal conductance (gs), stomatal density and An and had a smaller stomatal area but larger leaf area, heavier root dry matter and higher Tl at all irrigation levels. Under water stress conditions, FRSS, E, gs, and An decreased and Tl increased more in soybean than in cotton. Stomatal area decreased in response to water stress though nonsignificantly but stomatal density was not affected by water stress in soybean. Stomatal area decreased significantly in response to water stress in cotton. We concluded that soybean and cotton adapted to water stress differently. Soybean adapted to water stress by reducing transpiration while cotton adapted to water stress by maintaining higher transpiration as compared with soybean. Soybean reduced the transpiration rate by reducing gs. Reduction of gs in soybean was due to reduced FRSS, which might have resulted from the lower root moisture absorption efficiency. The higher transpiration in cotton was due to a higher gs, which was supported by a higher FRSS, larger stomatal area, and probably the diaheliotropism. The higher gs and transpiration rate suppressed the increase in Tl thus preventing the decrease of An in response to water stress.

Leaf Temperature and Transpiration of Field Grown Cotton and Soybean under Arid and Humid Conditions.

Abstract Abstract : Cotton (Gossypium hirsutum L.) and soybean (Glycine max (L.) Merr.) cultivars were grown under arid (Urumqi, Xinjiang, China) and humid (Matsudo, Chiba, Japan) conditions to analyze their abilities to adapt to arid conditions in terms of transpiration, leaf movement and leaf temperature. Under the arid condition, the leaf temperature of the cotton cultivars was higher than that of the soybean cultivar and the air temperature. There was no significant difference in leaf temperature among the cotton and soybean cultivars under the humid condition. The flow rate of stem sap in the cotton cultivars under the arid condition was always higher than that in the soybean cultivar, and was largely affected by vapor pressure deficit (VPD). Under the humid condition, however, the flow rates of stem sap were lower in the cotton cultivars than in the soybean cultivars. These results indicate that cotton can avoid heat stress by the high transpiring ability possibly supported by well-developed root systems, which leads to higher drought resistance under the arid condition. Soybean would adapt to arid conditions by the combination of paraheliotropic leaf movement and reduced transpiration.

Effects of Water Stress on Leaf Temperature and Chlorophyll Fluorescence Parameters in Cotton and Peanut

Abstract A greenhouse experiment was conducted to study the adaptive mechanism of cotton and peanut under water stress conditions. Five cultivars of cotton and six cultivars of peanut were grown in pots under two water levels; the control and water stress condition, where irrigation water equal to 100% and 50% of the daily transpiration, respectively, was daily applied. Peanut showed a greater increase than cotton in leaf temperature (Tl) and non-photochemical quenching (NPQ) and a greater decrease in water content per unit leaf area (WCLA), chlorophyll content and maximum quantum yield of photosystem II (PSII) (Fv/Fm) in the water stress condition. On the other hand, the water stress lowered the transpiration rate, actual quantum yield of PSII (ΔF/F’m) and leaf area (LA) more in cotton than in peanut. Cotton showed greater reduction in LA along with little reduction in the root dry weight (RDW) leading to high WCLA, while peanut showed increased RDW with little reduction in LA under the water stress condition. It was concluded that photodamage and down regulation in PSII were induced by water stress, coinciding with increases in leaf temperature regulated mainly by transpiration. Peanut showed more severe photodamage in PSII than cotton under the water stress condition.

High Yielding Performance of Soybean in Northern Xinjiang, China

Abstract The experimental site (Shihezi, Xinjiang, China) is located in an arid area of central Asia with abundant solar radiation of almost 10 daily sunshine hours from April to September. The yield potential in this area appears to be high if sufficient water is supplied. The yields of five soybean (Glycine max (L.) Merr.) cultivars including three semi-indeterminate Chinese cultivars (Shidadou 1, Xindadou 1 and Suinong 11) and two determinate Japanese cultivars (Toyomusume and Toyokomachi) were evaluated over three years. These cultivars were grown under drip irrigation, a high planting density (22.2 plants m-2) and heavy applications of farmyard manure (15 t ha-1). Each cultivar showed a high leaf area index (LAI). In particular, the maximum LAI was greater than 7 over the three years in Shidadou 1 and Toyokomachi. The three Chinese cultivars with a high plant height had a low LAI in the upper layers of the canopy, but the two Japanese cultivars with a short plant height had a higher LAI in the middle or upper layers. Toyokomachi and Shidadou 1 had the highest seed yield, followed by Toyomusume. In particular, the seed yield of Toyokomachi was as high as 8.67 t ha-1 on the average of the three years. These high-yielding cultivars had more than 60 pods per plant (1350 m-2). The high yields in this experiment could be due to the large amount of intercepted radiation owing to the high LAI and abundant solar radiation, frequent and sufficient irrigation by the drip irrigation, and large number of pods as a sink.

Growth of High-Yielding Soybeans and its Relation to Air Temperature in Xinjiang, China

Abstract The growth and seed yields of 2 Japanese and 3 Chinese cultivars of soybeans cultivated in 2002-2005 using a drip irrigation system in the arid area of Xinjiang, China, were analyzed with respect to growth parameters and air temperature. Seed yield was very high in 2002, 2003 and 2004, but relatively low in 2005. The variation among years in seed yield clearly depended on pod number. The mean leaf area index (LAI) and crop growth rate (CGR) in 2005 was lower than those in the other 3 years. CGR showed significant positive correlations with mean LAI at the early growing stages, and with net assimilation rate (NAR) at the later growing stages. The increasing rate of pod number (IRP) was positively correlated with the mean LAI and CGR at the pod setting period, suggesting that an adequate supply of photosynthates would be required for pod setting. It was concluded that excellent growth in the years with high yields was supported by the large LAI before the pod setting periods and by high NAR and vigorous pod growth at the latter half of the growing season.

Growth and Eco-Physiological Performance of Cotton under Water Stress Conditions

A cotton cultivar Xinluzao 8 was grown under four levels of water stress treatments (normal irrigation, slight, mild and severe water stress) from the initial reproductive growth stage in Shihezi, Xinjiang, China, in 2002, to evaluate the growth and eco-physiological performances. Under water stress conditions, the transpiration ability decreased while the leaf temperature increased. Although the relative leaf water content decreased as water stress increased, the differences among the treatments were small, indicating that cotton has high ability in maintaining water in leaf. The stomatal density increased as water stress increased, while the maximum stomatal aperture reduced only in the severest stressed plants. The time of the maximum stomatal aperture was delayed in the mild and severe stressed plants. When severe stress occurred, the stomata were kept open until the transpiration decreased to nearly zero, suggesting that the stomata might not be the main factor in adjusting transpiration in cotton. Cotton plant has high adaptation ability to water stress conditions because of decrease in both stomatal conductance and hydraulic conductance from soil-to-leaf pathway. The actual quantum yield of photosystem Ⅱ (PS Ⅱ) decreased under water stress conditions, while the maximum quantum yield of PS Ⅱ did not vary among treatments, suggesting that PS Ⅱ would not be damaged by water stress. The total dry weight reduced as water stress increased.

Transpiration and Leaf Movement of Cotton Cultivars Grown in the Field under Arid Conditions

Abstract Five cotton (Gossypium hirsutum L.) cultivars were grown in the field in Xinjiang, China to evaluate their adaptability to arid conditions in terms of leaf temperature, transpiration rate and leaf movement. Leaf temperature was higher in the morning and lower in the afternoon as compared with air temperature. There were large differences in the transpiration rate represented by the flow rates of stem sap per unit leaf area (FRSS) among the cotton cultivars. The transpiration rate in cotton generally depended on vapor pressure deficit (VPD). In the cultivars with a low transpiring ability, however, the influence of VPD was lower in the higher range of VPD. Cultivars with higher transpiring ability tended to have higher intercepted radiation per unit leaf area (IRL), i.e., to show active diaheliotropic leaf movement. The higher transpiring ability of cotton might be able to reduce heat stresses caused by diaheliotropic leaf movement and be profitable for yield under the arid conditions.

Effects of Paclobutrazol on Dry Matter Distribution and Yield in Peanut

Abstract Paclobutrazol (PB), an inhibitor of endogenous gibberellin synthesis, was applied to peanut plants altered dry-matter distribution and increased seed yield. PB solution at a concentration of 100, 200 or 400 ppm was sprayed on foliage at the beginning of the pod formation stage (BPFS), the early pod filling stage (EPFS) and the middle pod filling stage (MPFS) .The height of the plants treated with PB at BPFS and EPFS was shorter than that of the control plants by more than 10 and 5 cm, respectively. The pod number of the plants treated with 100 or 200 ppm PB at any developmental stage was higher than that of the plants treated with 0 or 400 ppm PB. The seed yield was increased by PB applied at any stage, and the yield after the treatment with 100 or 200 ppm PB at BPFS or EPFS was approximately 370 gm~2.

Soybean Cultivation on Desert Sand Using Drip Irrigation with Mulch

Abstract The growth and yield potential of soybean and the effects of mulching on desert sand were evaluated in relation to N accumulation in nodules. The experiment was conducted in concrete framed plots filled with sand obtained from the Dzungar desert or the normal field soil in Shihezi, Xinjiang, China. Drip irrigation with or without mulch was adopted for the experimental plots. The mean soil temperature in the sand plot with mulch was the highest among the plots during the early growth stages. The relative ureide-N content in the soil plots varied from 23.2% at the full flowering stage (R2) to 37.6% at the beginning of the maturity stage (R7). The sand plots showed higher values than the soil plots ranging from 48.7% at R2 to 80.5% at R7, indicating active N2 fixation by nodules. Seed yield did not show a significant difference between the soil and the sand plots. It ranged from 394 g m−2 in the soil plot without mulch to 472 g m−2 in the sand plots with mulch. The results suggested the possibility of extending soybean cultivation into marginal areas of deserts, provided that adequate water was available for drip irrigation and there was active nodulation.