Physiological performance of sugarcane genotypes under different irrigation levels

Aims: This study aimed to investigate the effects of different irrigation water levels on evapotranspiration, water use efficiency, stomatal conductance, photosynthesis rates and yields in 14 drought-sensitive and resistant cotton varieties.Methods and Results: The trial was carried out according to the random blocks experimental design pattern. The experimental study was conducted on ST 506, ST468, BA525, BA119, FLASH, SIOKRA L-22, TAM SPHINX, TAM 94L-25, PIMA S-7, TAMCOT-22, TAMCOT SP 21 S, TAMCOT SP 23, TAMCOT CAMD-ES and AKSEL cultivars. Evapotranspiration, water use efficiency, stomatal conductance, transpiration and photosynthesis rates and yields of the mentioned cultivars were determined. Photosynthesis rate, transpiration rate and stomatal conductance were measured only at the levels of full irrigation (I100) and 25% of the full irrigation (I25).Conclusions: The total numbers of irrigation done in the first and second years were four and six, respectively. The amount of irrigation water applied varied between 270 and 480 mm in the first year, and 298 and 520 mm in the second year. Yield and evapotranspiration increased depending on the amount of irrigation water applied. The highest and lowest yields were determined as 358 kg da-1 in Aksel cultivar and 555 kg da-1 in BA525 variety, respectively. On average, the photosynthesis rate was measured as 12,616 µmol m-2 s-1 for I100, and 7.549 µmol m-2 s-1 for I25. As the stomatal conductance increased, the yield also increased (0.093 mol m-2 s-1 for I25 and 0.182 mol m-2 s-1 for I100). Transpiration rate was determined as 2.947 mmol m-2 s-1 for I25 and 3.919 mmol m-2 s-1 for I100. The varieties did not significantly differ in terms of water stress. Aksel cultivar is drought-sensitive, whereas the others are drought-resistant varieties.Significance and Impact of the Study: The research revealed the physiological characteristics, plant water consumption and water use efficiency of 14 different cotton varieties widely grown in eastern Mediterranean conditions. And also, when the relationship of the mentioned parameters with yield was examined, the relationship between stomatal conductance and yield was found lower than the one between transpiration and photosynthesis rates.

The instability between water demand and availability is making it challenging to cultivate viable, sustainable crops. To address this, improved irrigation scheduling regimes need to be adopted, focusing on full crop water requirements to determine optimal water allocation. This study aimed to identify suitable intercropping combinations of leguminous dry bean plants with indigenous African leafy vegetables (specifically cleome gynandra and cucumis myriocarpus) that could enhance interactions with regulated deficit irrigation. The experiment was designed in 3 (irrigation levels: 100%, 75%, and 50%) × 5 (three monocrops and two intercrops) split plot arrangement within a randomized complete block design (RCBD), replicated three times across four growth stages. The study was designed to rigorously assess the effectiveness of two intercrops compared to three monocrops, each cultivated under varying irrigation levels of 100%, 75%, and 50%. There was an increase in selected gaseous parameters, such as stomatal conductance and photosynthesis rates when dry beans were intercropped with cucumis myriocarpus and subjected to 75% deficit irrigation during the mid-pod stage of the dry bean. In contrast, decreased gaseous parameters were noted under a 50% deficit irrigation across all dry bean growth stages, which also negatively affected the growth of African leafy crops. Regarding yield, an inverse relationship was observed between the crops. The yield of dry beans significantly increased under 75% irrigation during the mid-pod stage. Meanwhile, yields of cucumis myriocarpus increased under both 75% and 100% irrigation levels during the early-pod stage of the dry beans, which corresponded to the vegetative stage of the two African leafy crops. In conclusion, regulating irrigation under 75% deficit irrigation during the mid-growth stage is recommended as an ideal irrigation level for intercropping dry beans with cucumis myriocarpus, and this can potentially save 25% of water.

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.

This study was conducted to clarify the genotypic differences in diurnal variations in leaf gas exchange characteristics and the effect of irrigation levels, growth stages and cultivars on leaf water status, gas exchange characteristics and seed yields. Associations of leaf water status with photosynthetic rate in five cultivars of snap bean were also determined. Diurnally, leaf gas exchange was highest at 9:30 h, decreased but remained constant between 11:30 to 14:15 h and then decreased up to 16:15 h. Cultivars Haibushi and Ishigaki-2 displayed higher photosynthetic activity throughout the day. The cultivars having higher seed yield showed higher leaf conductance, transpiration rate and leaf vapor pressure deficit at floral bud initiation stage and higher leaf water potential and relative water content in the irrigated plot at flowering stage. The cultivars with slow development of leaf water deficit displayed higher rates of photosynthesis and vice versa. The results showed that midday hours showed large genotypic differences in leaf gas exchange characteristics with constancy of photosynthetically active radiation. Therefore, screening of snap bean cultivars can be made during midday hours for gas exchange characteristics irrespective of growth stages and irrigation levels. Cultivars maintaining higher leaf water content with increasing water deficit can be selected for higher rates of photosynthesis.

Abstract. Farmers are encouraged to shift conventional surface irrigation to sprinkler irrigation in semi-arid regions of China to cope with the decreasing availability of water for agricultural irrigation and frequent occurrence of droughts. This study was aimed at providing an optimal management practice of irrigation and fertilization for sprinkler irrigation of maize. The experiments were conducted on a 14.8 ha field with sandy soil irrigated by a one-span (85.5 m) lateral move sprinkler system in Inner Mongolia Autonomous Region. Three irrigation levels of 40, 70, and 100% of full irrigation (referred to as I1, I2, and I3, respectively) and four nitrogen rate of 80, 160, 240, and 320 kg ha -1 (referred to as N1, N2, N3, and N4, respectively) were tested using a randomized complete block design (RCBD) with three replications. Irrigation level demonstrated a substantially more important influence on plant height, leaf area index (LAI), dry matter above ground, and yield than nitrogen applied. A higher irrigation level produced a significantly greater plant height, LAI, dry matter above ground, and yield. The yield averaged over the four nitrogen rates for the full irrigation (100%) level was 19.3% and 5.3% greater than the 40% irrigation level and the 70% irrigation level, respectively. For a given irrigation level, the nitrogen rate of 160 kg ha -1 (N2) usually gave a slightly higher yield than the other three nitrogen levels. A management practice of nitrogen rate of 160 kg ha -1 and 100% full irrigation was recommended by the current study to obtain a high production at a relatively low fertilizer input.

The production of drought-tolerant rice varieties in Malaysia and the information regarding the response of local varieties to water stress are still lacking. Therefore, this experiment was conducted to determine the growth, physiological performance, molecular response, and yield of ten available rice varieties, namely MR 219, MR 220-CL2, MR 297, MRQ 76, Vietnam Hybrid, UKM RC2, UKM RC8, Putra 1, MR 303, and MR 307, under ten days of cyclic water stress. The experiment was arranged in a Randomized Complete Block Design (RCBD) with three replications. Plant height, tiller number, photosynthesis rate, stomatal conductance, transpiration rate, chlorophyll content, biomass partitioning, genotyping of SSR markers, days of harvest, and yield component were measured. Results showed that water limitations reduced tiller number per hill, while plant height, leaf dry matter, and panicle length were enhanced. It was found that MR 297 had the shortest plant height, while MR 220-CL2 had a short maturity period, a shorter panicle length, and an enhanced filled grain percentage. Putra 1 and UKM RC8 showed a higher photosynthesis rate, stomatal conductance, and transpiration rate under water limitation at 99 days after sowing (DAS). Under well-watered conditions, the total grain weight per pot of Putra 1 and MR 307 was enhanced compared to MR 219. Meanwhile, under water limitation, the total grain weight per pot of UKM RC2, MR 220-CL2, MR 307, MR 297, and Vietnam Hybrid was comparable to MR 219 and slightly enhanced in UKM RC8, Putra 1, and MR 303. Among the tested varieties, MR 220-CL2 can be selected based on early maturity criteria for the potential development of drought-tolerant varieties.

Regulated deficit irrigation (RDI) is a common and useful practice for water conservation and improving grape quality. To attain better grape characteristics and wine quality, a substantial degree of irrigation stress is intentionally allowed to occur during the first part of berry formation and can continue until later into veraison. Understanding the effects of deficit irrigation on photosynthetic rates could be helpful in determining at what degree and duration a grower should perform this irrigation practice. The focus of this study was to determine the effects of using differing degrees of RDI in a vineyard located in Paso Robles, California (central coast region) on gas exchange of the Syrah variety. The target irrigation levels were set for each season at 75, 60, 45, and 30% ETc of a fully irrigated vine (100% ET). The 60% replication was considered as the control for this study, as it is the standard target ET rate for the vineyard where this study was conducted. A gas analyzer (LICOR 6200) was used to measure the overall rate of photosynthesis during two successive growing seasons (2004 & 2005). Measurements were taken from bloom through harvest and were compared among the four different irrigation levels. Along with overall photosynthetic rate, the leaf temperature, stomatal conductance, light level, and relative humidity were also measured. The results of the two year study were statistically compared through an analysis of variance (ANOVA) and analyzed for their significance. The results of the study showed that minor differences in the mean photosynthetic rates were found to occur during brief periods of the growing season. These differences ranged from 1-4 weeks and did not occur at similar times of the growing season. However, no statistical significant differences were found to exist when compared among the four irrigation levels for the entire growing season. Observed differences in canopy sizes indicated that irrigation amounts had affected the overall growth to some degree during this two year study. Several plant physiological measurements showed a significant difference in the measured gas exchange rates between sun exposed leaves and the shade leaves within the treatment area. A significant correlation of the effect of leaf temperature on stomatal conductance was observed to exist in one of the irrigation treatments (45% ET) during this study. Other plant physiological measurements indicated that highly significant differences existed between the photosynthesis rate and leaf temperature. Photosynthetic rates were highly significantly correlated to leaf

Influence of deficit irrigation and warming on plant water status during the late winter and spring in young olive trees

SummaryAn experimental procedure is described by which contemporaneous assessments of leaf resistance, rates of transpiration and of carbon dioxide exchange can be made on attached leaves. The relative humidity and carbon dioxide concentration of an air stream flowing into a leaf chamber are controlled, and of the outflowing stream monitored. The effects of light intensity and of water relations of the leaf were investigated with reference to leaf resistance and rates of transpiration and photosynthesis. In Pelargonium × hortorum quick stomatal opening in response to illuminatioxi was observed in plants which were not under water stress. On illumination of darkened leaves the rates of transpiration and photosynthesis were shown to rise rapidly, bearing a relation to leaf resistance, and indicating stomatal control of these processes. Over long periods of illumination water deficits develop, leaf resistance increases and rates of transpiration and photosynthesis decline. Typical findings of the levels of leaf resistance at a range of light intensities, and the corresponding values of transpiration rate and photosynthetic rate, are given.The overriding importance of water deficit in influencing stomatal behaviour in leaves under substantial water stress is shown in a series of experiments. When water deficits are fairly small, the stomata of leaves open in response to illumination, but more slowly than those of leaves of well‐watered plants; in leaves under water stress stomatal closure is also much accelerated on darkening. Under moderate water deficits, the stomata of leaves may open in response to light, but close again fairly quickly as the stress increases. Changes in rates of transpiration and photosynthesis parallel closely those of leaf resistance under these conditions. The effect of watering plants under water stress on leaf resistance and rates of gaseous exchange is shown in two experiments. The results indicate that watering leads to stomatal closure at first, with decreased rates of photosynthesis and transpiration, but subsequently leaf resistance diminishes and the rates increase as normal turgor relations in the leaf re‐establish. Stomatal behaviour and control of rates of transpiration and photosynthesis are discussed, and the water relations of the leaf shown to be of critical importance in this connection.

Plant response to drought may be altered by the variation in air temperature and humidity and these interactions may be more frequent and intense with expected climate changes. The study examines impact of temporal changes in air temperature and air humidity on spring barley grown in dry and wet soil.The impact of two hours long changes in air temperature and relative humidity (RH) was evaluated on spring barley grown in soil of optimum and limited soil water availability. The alterations in stomatal conductance, transpiration photosynthesis, leaf temperature in response of air humidity and air temperature were analyzed.Air RH strongly differentiated leaf stomatal conductance in plants grown in well-watered soil. Despite the low impact of air RH on leaf conductance in plants grown in dry soil, a significant decline in transpiration with an increase in air RH occurred. The increase in air RH induced significant increase in leaf temperature in well-watered plants. Changes in leaf vapor pressure deficit (LVPD) differently affected stomatal conductance (gH2O) in plants grown in soil with optimum and limited water availability.Temporal changes in air humidity and temperature differently affected barley grown under optimum and limited water availability.

Tea (Camellia sinensis L.) is one of the most popular beverages consumed in the world and Kenya is the leading exporter in Africa and only 3rd worldwide after China and India. Nutrient deficiency in soils and poor fertilization are possibly two reasons for low yields and quality of tea. The use of organic matter and mineral fertilizers has been proved to be a sound soil amendment and fertility management strategy. Therefore, this study was conducted to evaluate the possibility of using readily available organic manures in combination of inorganic fertilizers on the physiological processes of tea clones in Kenya. The study was conducted within Timbilil estate, KALRO- Tea Research Institute in Kericho County on variety clone TRFK31/8. It was laid out in a Randomized Complete Block Design (RCBD) and replicated three times. There were 14 treatments that randomly assigned in each block. Data on tea response was determined from photosynthesis rate, transpiration rate and stomatal conductance then recorded and analyzed using GenStat Version 15.1. There were significant differences between the treatments on the transpiration rate, stomatal conductance and the photosynthetic rate in both seasons for all the months recorded. The transpiration rate was highest during the wet season in the months of June, July and August while lower transpiration rates were recorded during the dry season in the months of December, January and February with 0.1 g m−2 s−1 transpiration rates recorded in several treatments in the month of February. Stomatal conductance, photosynthetic rate and transpiration rate were higher where NH4+ was introduced through the organic manure in all the seasons and therefore confirms that it is highly important to incorporate soil amendments with higher organic matter in tea production in Kenya.

To explore the effects of triacontanol (TR) on drought tolerance of strawberry plants (cv Fertona), two field experiments were carried out to study the effects of three supplementary foliar TR rates (0, 0.5, and 1 ppm) under the following three levels of water irrigation: 11 m3/hectare (40% of water holding capacity (WHC) severe as a drought treatment, 22 m3/hectare (80% of WHC) as moderate drought stress, and normal irrigation with 27 m3/hectare (100% of WHC) server as a control treatment. TR treatments were applied five times after 30 days from transplanting and with 15-day intervals. The results showed that drought stress (40% and 80%) markedly decreased the growth, fruit yield, and chlorophyll reading, as well as the gas exchange parameters (net photosynthetic rate, stomatal conductance, and transpiration rate). Meanwhile, drought stress at a high rate obviously increased antioxidant enzyme activities such as superoxide dismutase (SOD), peroxidase (POX), and catalase (CAT) contents in the leaves of the strawberry plants. The moderate and high drought stress rates enhanced some strawberry fruit quality parameters such as total soluble solids (TSS), vitamin C, and anthocyanin content compared to the control. Additionally, TR increased the activities of SOD, POX, and CAT. TR treatment significantly increased the chlorophyll contents, gas exchange parameters (photosynthetic rate and stomatal conductance), and water use efficiency (WUE). Plant height, fruit weight, and total biomass were increased also via TR application. Total yield per plant was increased 12.7% using 1 ppm of TR compared with the control. In conclusion, our results suggested that TR application could relieve the adverse effects of drought stress on the growth of strawberry plants by enhancing the antioxidant enzymes, photosynthesis rate, and WUE of the leaves.

The socio-economic development of a country is highly dependent on water availability. Nowadays, increasing water scarcity is a major global challenge. Continuing improvements in water-use efficiency are essential for cotton production sustainability. Reduced irrigation in cotton could be a solution to water shortage in the arid climate without compromising the cotton yield. Therefore, a two-year field study was conducted to assess the effect of two levels of irrigation i.e., 50% and 100% of available water content (AWC) on the yield of four cotton genotypes (CIM-678, CIM-343, CRIS-613, and CYTO-510). The maximum seed cotton yield was observed in CIM-678, which was 2.31 and 2.46 Mg ha−1 under 100% AWC during 2018 and 2019, respectively, and was non-significantly reduced by 7.7 and 8.94%, owing to deficit irrigation. The maximum water use efficiency (WUE) of 0.55 and 0.64 Kg ha−1 mm−1 was observed under 50% AWC in CIM-678, which was significantly higher than WUE at 100% AWC during both years. Leaf area index and physiological parameters such as photosynthesis rate, transpiration rate, and stomatal conductance were not significantly affected by deficit irrigation. So, it was concluded that the reduced irrigation technique performed well without significant yield loss, improve WUE, and saved 37 cm of water that could be used for other crops or to increase the area of the cotton crop.

Agriophyllum squarrosum is an annual psammophyte species and wildly distributed in all deserts and sand lands in China. Changes of plant height,survival rate,photosynthetic rate( Pn),transpiration rate( Tr),stomatal conductance( Gs) and water use efficiency( WUE) of A. squarrosum seedlings was measured in a sand burial experiment during 2010—2011 in Horqin Sand Land of Inner Mongolia to understand effect of sand burial on the growth,photosynthesis and transpiration of annual psammophyte seedlings. The experiment included ten burial treatments: buried to 0%( CK,no burial),25%( A),50%( B),75%( C),100%( D),133%( E),166%( F),200%( G),233%( H) and 266%( I) of seedling height. The results showed that A. squarrosum had a strong ability to withstand sand burial. The survival rate and the plant height of A. squarrosum seedlings increased significantly at 25% burial depth of the seedling height.When subjected to sand burial at 50% —100%,the difference was not significant between the sand-buried treatments and the none-sand buried CK although the plant height and the survival rate decreased. The survival rate and the plant height decreased significantly only when the burial depth exceeded the height of the seedlings,but some individuals still kept survived when the burial depth was 266% of the seedling height. Buried by sand to the fifth day,the photosynthesis rate of A. squarrosum seedlings decreased slowly,the transpiration rate and the stomatal conductance and the water use efficiency fluctuated greatly with the increase of sand burial depth. The photosynthesis rate and the water use efficiency decreased by14. 6% and 19. 2%,and the transpiration rate,the stomatal conductance increased by 3. 0% and 3. 7% in the I treatment than that in the CK,respectively. With the prolongation of sand burial time,the photosynthesis rate,the transpiration rate and the stomatal conductance decreased significantly,but the water use efficiency was still fluctuated with increase of sand burial depth. Buried in sand to the tenth day,the photosynthesis rate,the transpiration rate,the stomatal conductance and the water use efficiency decreased by 89. 7%,84. 4%,85. 7% and 54. 0% in the I treatment than that in the CK,respectively. Buried in sand to the fifteenth day,the photosynthesis rate,the transpiration rate,the stomatal conductance and the water use efficiency decreased by 86. 7%,90. 0%,89. 0% and 4. 2% in the I treatment than that in the CK,respectively. Correlation analysis suggested that the survival rate and the seedling height had significant and positive correlations with the photosynthesis rate,the transpiration rate,the stomatal conductance and the water use efficiency.There were significant positive correlations among the photosynthesis rate, the transpiration rate and the stomatal conductance,but the correlation was not significant between them and the water use efficiency. It was concluded that sustained severe burial by sand had a significant damage to survival and growth of A. squarrosum seedlings. The decrease of the survival rate and the plant height in A. squarrosum seedlings were resulted not only from emergence difficult and decrease of photosynthetic area under sand burial stress,but also from decrease of the photosynthetic rate,the transpiration rate and the stomatal conductance.

Increased water scarcity necessitates the implementation of water-conserving irrigation management practices to sustain crop production,especially in water-limited areas. A two-year field study was conducted during 2019 and 2020 to evaluate the effect of deficit irrigation on physiology, plant growth, and yield of cucumber cultivars. The experiment was conducted in a split-plot design with four irrigation levels (100% ETc (crop evapotranspiration), 80% ETc, 60% ETc, and 40% ETc) as main plot factor and two cultivars (Poinsett 76 and Marketmore 76) as subplot factor with three replications. Results showed that stomatal conductance (gs), transpiration rate (E), photosynthesis rate (Pn), intercellular CO2 concentration (Ci), and leaf area were significantly lower in 60% ETc and 40% ETc compared to 100% ETc while stomatal limitations, intrinsic water use efficiency (WUEi), and relative leaf temperature were significantly higher in 60% ETc and 40% ETc compared to 100% ETc. The observed values of these aforementioned parameters were comparable between 100% ETc and 80% ETc. A decrease in leaf area, as well as a decrease in Pn, resulted in a decline in overall photosynthesis per plant in 60% ETc and 40% ETc compared to 100% ETc. As a consequence of this, plant dry biomass and total fruit yield were significantly lower in 60% ETc and 40% ETc compared to 100% ETc. However, photosynthesis per plant was comparable between 100% ETc and 80% ETc due to comparable Pn and leaf area between them. Because of comparable photosynthesis per plant, plant dry biomass and fruit yield were comparable between 100% ETc and 80% ETc. Marketmore 76 had significantly higher gs, E, Pn, Ci, and leaf area and it had significantly lower stomatal limitations, WUEi, and relative leaf temperature than Poinsett 76. Vegetative dry biomass and total above-ground dry biomass were higher in Marketmore 76 but fruit yield was higher in Poinsett 76. These results suggest that 80% ETc irrigation level and Poinsett 76 cultivar can be recommended for successful cucumber production without causing a significant decline in fruit yield in water-limited Southern High Plains of United States.