Crassulacean Acid Metabolism Photosynthesis in Pineapple (Ananas comosus (L.) Merr.) Grown under Hydroponic Culture

In order to shorten the cultivation period of pineapple, a crassulacean acid metabolism (CAM) plant, it is important to increase the rate of CO2 exchange rate and improve dry matter production, especially at the early growth stage. When plants are grown under hydroponic conditions, absorption of nutrients and plant water availability are generally increased, and in the case of CAM plants, hydroponics could be expected to improve growth rate through promoting stomatal open during daytime. The objective of this study was to examine the effect of culture method (hydroponic and soil culture) on diurnal changes in gas exchange rate and CO2 balance in pineapple. The daily CO2 balance under hydroponics tended to be higher than under soil culture, especially in Phase-4. This was due to a shortened Phase-3 and a prolonged Phase-4 under hydroponics compared to soil culture. In Phase-4, the CO2 exchange rate was significantly correlated with stomatal conductance, indicating CO2 balance was affected by stomatal activity. Rubisco consumption activated under hydroponic culture may have shortened the duration of Phase-3 when stomatal opening was suppressed. The CO2 balance tended to be increased because of the shortening of Phase-3, resulting in higher dry matter productivity. From these results, it is suggested that hydroponic culture could promote growth in pineapple. However, net assimilation rate under soil culture was equivalent to that under hydroponics. Further study is needed to reveal the relationship between hydroponic cultivation and whole-plant photosynthetic ability

Rapid Evaluation of Leaf Photosynthesis using a Closed-chamber System in a C4 Plant, Sugarcane

ABSTRACTTo accelerate research on improving sugarcane biomass production, a rapid phenotyping method for individual leaf photosynthetic rates is required. Recently, a closed-type measurement system, which is faster, lighter, and less expensive than conventional open-type systems, has been developed and utilized for C3 crops. For future utilization of the system in phenotyping photosynthetic rates in sugarcane which exhibits higher photosynthetic rate than C3 crops, diurnal changes and genotypic differences were measured simultaneously using an open-type and a closed-type system to verify the accuracy of the measurements in assessing environmental responses and genetic variation. As the relative root-mean-square error, a regression accuracy between the measurements with two systems, was < 20% when evaluating diurnal changes and genotypic differences, closed system accurately evaluated photosynthetic rates in multiple samples. Overall, the measured values with the closed system tended to be higher than those with the open system, especially in high values above 30 µmol m−2 s−1. The reason for this was presumably not leaf morphology, such as stomatal distribution, but a fundamental difference in the measurement systems (steady-state values for the open system and instantaneous values for the closed system). The open system required 5–7 min to measure a single record, whereas the closed system could measure at < 40 s per record. Although it would be desirable to develop a regression equation using measurements involving the open system for each cultivar to examine physiological response in detail, we conclude that the closed system has greater potential for use in phenotyping sugarcane photosynthesis

Nitrogen use efficiency and drought tolerant ability of various sugarcane varieties under drought stress at early growth stage

The experiment was conducted under glasshouse conditions to evaluate nitrogen use efficiency and drought tolerant ability of the five different sugarcane varieties (including NiF3, Ni9, Ni17, Ni21 and Ni22) under early growth stage from 60 to 120 days after transplanting. The results showed drought stress reduced the photosynthetic rate, growth parameters including plant height, leaf area; partial and total dry weights; and nitrogen use efficiency (NUE) traits including photosynthetic NUE, nitrogen utilization efficiency and biomass NUE of measured sugarcane varieties. The significant differences were found among varieties in growth parameters, dry weights, NUE traits and drought tolerant index (DTI). The significant positive correlations among NUE traits and DTI suggested higher NUEs could support better a tolerant ability to drought stress at the early growth stage. Because of larger contributions, DTIs for aboveground and stalk dry weight could be used as the important DTIs to evaluate drought tolerant ability in sugarcane varieties. Abbreviations Amax: potential photosynthetic rate; DAT: days after transplanting; DTI: drought tolerant index; NL: specific leaf nitrogen content; NUE: nitrogen use efficiency; NUEb: biomass nitrogen use efficiency; NUEt: nitrogen utilization efficiency; PNUE: photosynthetic nitrogen use efficiency; TN: total nitrogen content; TNU: total nitrogen uptake; WW: well-watered; DS: water stress

Changes in Agronomic and Physiological Traits of Sugarcane Grown with Saline Irrigation Water

In Japan, the highest salt concentration in irrigation water for sugarcane cultivation has been reported to be above 2500 mg L&minus;1, which may cause harmful effects to the crops; however, little information is available on the relationship between the salinity of irrigation water and sugarcane. To investigate its effects on agronomic and physiological traits, a Japanese cultivar, Saccharum spp cv. NiF8, was grown with 0, 200, 500, 1000, 2000, and 3000 mg NaCl L&minus;1 under pot conditions. The treatments significantly lowered leaf area; however, NaCl levels up to 500 mg L&minus;1 did not greatly reduce culm weight and juice sugar concentration. These traits were impaired when the tested cultivar was grown with 1000 mg NaCl L&minus;1 or higher, indicating that salt concentration is desired to be lower than 1000 mg L&minus;1. CO2 assimilation rate was inhibited mainly due to stomatal closure caused by salt stress. The treatments significantly altered Na+, Cl&minus;, and K+ concentrations in juice but not those in leaf, suggesting that juice analysis is an effective method to estimate its salinization status. Culm weight and juice sugar concentration were severely affected as juice conductivity exceeded 900 mS m&minus;1; thereby, sugarcane plants of NiF8 possessing conductivity above this level could be considered salt-stressed where water salinity is a concern

Photosynthetic response and nitrogen use efficiency of sugarcane under drought stress conditions with different nitrogen application levels

Drought stress which often occurs during early growth stage is one constraint in sugarcane production. In this study, the response of sugarcane to drought and nitrogen application for physiological and agronomical characteristics was investigated. Two water regimes (well-watered and drought stress from 60 to 120 day after transplanting) and four nitrogen levels (0, 4.4, 8.8 and 13.2 g pot−1 equivalent to 0, 90, 180 and 270 kg ha−1, respectively) were assigned in a Split-plot design with three replications. The results showed that photosynthetic responses to light intensity and intercellular CO2 concentrations of sugarcane were different between fertilized and non-fertilized treatments. Photosynthetic rates of 180 and 270 N treatments, normally, were significantly higher than that of 90 N, but not significant at drought conditions. Photosynthetic rates of 0 N treatment were the lowest under both conditions. Higher nitrogen application supported higher photosynthetic rate, stomatal conductance, and chlorophyll content because of higher nitrogen concentration accumulated into the leaf. Drought significantly reduced the potential photosynthetic rate, stomatal conductance, SPAD, leaf area, and biomass production. Higher nitrogen applications with larger root system could support higher photosynthetic activities to accumulate more dry mass. Strong positive coefficient between photosynthetic and biomass nitrogen use efficiency and drought tolerance index may suggest that higher nitrogen use efficiency could help plants have higher ability to tolerate drought stress

Effects of duration and combination of drought and flood conditions on leaf photosynthesis, growth and sugar content in sugarcane

Global climate change will result in extreme environments, such as droughts and floods. We investigated the individual and combined effects of droughts and floods of varying duration on sugarcane (Saccharum spp.) growth using a pot experiment under glasshouse conditions with the following six treatments: drought for 15 d, prolonged drought for 30 d, flood for 15 d, prolonged flood for 30 d, short flood followed by prolonged drought, and prolonged flood followed by prolonged drought. Plants that were subjected to drought conditions, including drought after a flood, had reduced CO2 assimilation (through stomatal closure) and leaf areas, whereas flood conditions showed no effect. During flooding, some roots died, and adventitious roots with well-developed aerenchyma appeared from the submerged nodes. At the time of harvest, there were no significant differences in stem fresh weight, sucrose content, or sugar yield between the treatments. However, ion content analysis revealed that flood conditions caused an accumulation of sodium in the bottom of stems and adventitious roots. Therefore, under flood conditions, plants may develop adventitious roots, which may offset the negative effects of root death, helping them to maintain their growth and yield