Xylem Exudation Rate Research Articles

Differential Drought Responses of Soybean Genotypes in Relation to Photosynthesis and Growth-Yield Attributes.

Water scarcity leads to significant ecological challenges for global farming production. Sustainable agriculture depends on developing strategies to overcome the impacts of drought on important crops, including soybean. In this present study, seven promising soybean genotypes were evaluated for their drought tolerance potential by exposing them to water deficit conditions. The control group was maintained at 100% field capacity (FC), while the drought-treated group was maintained at 50% FC on a volume/weight basis. This treatment was applied at the second trifoliate leaf stage and continued until maturity. Our results demonstrated that water shortage exerted negative impacts on soybean phenotypic traits, physiological and biochemical mechanisms, and yield output in comparison with normal conditions. Our results showed that genotype G00001 exhibited the highest leaf area plant-1 (483.70 cm2), photosynthetic attributes like stomatal conductance (gs) (0.15 mol H2O m-2 s-1) and photosynthetic rate (Pn) (13.73 μmol CO2 m-2 s-1), and xylem exudation rate (0.25 g h-1) under drought conditions. The G00001 genotype showed greater leaf greenness by preserving photosynthetic pigments (total chlorophylls (Chls) and carotenoids; 4.23 and 7.34 mg g-1 FW, respectively) in response to drought conditions. Soybean plants accumulated high levels of stress indicators like proline and malondialdehyde when subjected to drought stress. However, genotype G00001 displayed lower levels of proline (4.49 μg g-1 FW) and malondialdehyde (3.70 μmol g-1 FW), indicating that this genotype suffered from less oxidative stress induced by drought stress compared to the other investigated soybean genotypes. Eventually, the G00001 genotype had a greater yield in terms of seeds pod-1 (SP) (1.90) and 100-seed weight (HSW) (14.60 g) under drought conditions. On the other hand, BD2333 exhibited the largest decrease in plant height (37.10%), pod number plant-1 (85.90%), SP (56.20%), HSW (54.20%), gs (90.50%), Pn (71.00%), transpiration rate (59.40%), relative water content (34.40%), Chl a (79.50%), total Chls (72.70%), and carotenoids (56.70%), along with the maximum increase in water saturation deficit (290.40%) and malondialdehyde content (280.30%) under drought compared to control conditions, indicating its higher sensitivity to drought stress. Our findings suggest that G00001 is a promising candidate to consider for field trials and further evaluation of its molecular signature may help breeding other elite cultivars to develop drought-tolerant, high-yielding soybean varieties.

Impact of crop and nutrient management on crop growth and yield, nutrient uptake and content in rice

System of rice intensification (SRI) together with appropriate nutrient management holds promise in increasing rice productivity with micronutrient enriched grains. Trials were conducted to investigate the performance of SRI vis-a-vis conventional management practices (CMP), both with either integrated nutrient management (INM) or organic sources of nutrients. Grain yields were consistently higher under SRI (34.6%) than with CMP under the same nutrient management system. At the same time, yields under INM were higher than for those with organic fertilization. There were significant differences among treatment combinations also; both SRI–INM and SRI–organic out-yielded CMP–INM and CMP–organic, respectively, by 43.8 and 24.8%. Further, SRI with organic sources produced 18.6% higher grain yield than CMP with INM, which showed a way to achieve higher output of rice grain grown organically. Significant improvements were observed with SRI in root growth, xylem exudation rate, LAI, canopy light interception, SPAD chlorophyll level, photosynthesis rate, and grain-filling rate. The improvements in physiological functioning evidently contributed to better grain formation and yield under SRI management. Both the rice grains and straw obtained with SRI methods contained more N, P, K, Fe, Mn, Cu, and Zn than grains and straw produced with CMP. SRI methods not only raised rice productivity, but also enhanced nutrient uptake due to greater root growth and activity, and improved the nutritional content and quality of produced grain.

The leaf-air temperature difference reflects the variation in water status and photosynthesis of sorghum under waterlogged conditions.

Waterlogging stress is one of the most important abiotic stresses limiting sorghum growth and development. Consequently, the responses of sorghum to waterlogging must be monitored and studied. This study investigated changes in the leaf water status, xylem exudation rate, leaf anatomical structure, leaf temperature and photosynthetic performance. Waterlogging-tolerant (Jinuoliang 01, abbreviated JN01) and waterlogging-sensitive (Jinza 31, abbreviated JZ31) sorghum cultivars were planted in pots. The experiment was carried out using a split block design with three replications. Waterlogging stress was imposed at the sorghum five-leaf stage. The leaf free water content (FWC) and relative water content (RWC) decreased under the waterlogged condition. The leaf thickness was thinner under the waterlogged condition, and the main changes occurred in the upper epidermal and mesophyll cells. Gas exchange parameters and the xylem exudation rate were also restrained by waterlogging; however, greater responses of these parameters were observed in JZ31. JZ31 had a higher leaf-air temperature difference (ΔT) than JN01. We found that changes in ΔT were always consistent with changes in the RWC and the gas exchange parameters. ΔT was significantly associated with the leaf RWC, photosynthetic rate (Pn) and transpiration rate (Tr). The results suggest that ΔT may be an indicator reflecting the water status in leaves and can be used to evaluate the tolerance of sorghum to waterlogging.

Insight into salt tolerance mechanisms of the halophyte Achras sapota: an important fruit tree for agriculture in coastal areas

Sapota (Achras sapota), a fruit tree with nutritional and medicinal properties, is known to thrive in salt-affected areas. However, the underlying mechanisms that allow sapota to adapt to saline environment are yet to be explored. Here, we examined various morphological, physiological, and biochemical features of sapota under a gradient of seawater (0, 4, 8, and 12 dS m-1) to study its adaptive responses against salinity. Our results showed that seawater-induced salinity negatively impacted on growth-related attributes, such as plant height, root length, leaf area, and dry biomass in a dose-dependent manner. This growth reduction was positively correlated with reductions in relative water content, stomatal conductance, xylem exudation rate, and chlorophyll, carbohydrate, and protein contents. However, the salt tolerance index did not decline in proportional to the increasing doses of seawater, indicating a salt tolerance capacity of sapota. Under salt stress, ion analysis revealed that Na+ mainly retained in roots, whereas K+ and Ca2+ were more highly accumulated in leaves than in roots, suggesting a potential mechanism in restricting transport of excessive Na+ to leaves to facilitate the uptake of other essential minerals. Sapota plants also maintained an improved leaf succulence with increasing levels of seawater. Furthermore, increased accumulations of proline, total amino acids, soluble sugars, and reducing sugars suggested an enhanced osmoprotective capacity of sapota to overcome salinity-induced osmotic stress. Our results demonstrate that the salt adaptation strategy of sapota is attributed to increased leaf succulence, selective transport of minerals, efficient Na+ retention in roots, and accumulation of compatible solutes.

Rice root growth, photosynthesis, yield and water productivity improvements through modifying cultivation practices and water management

Achieving higher productivity in irrigated rice production is becoming ever-more important. A modified rice-cultivation method, the System of Rice Intensification (SRI), recommends keeping rice fields moist but unflooded during the crop’s vegetative stage, usually with alternate-wetting-and-drying (AWD), then maintaining shallow flooding during the post-vegetative stage of crop growth. However, no evidence is available on how flooding paddy fields continuously vs. alternately during the post-vegetative stage under SRI might influence the crops’ physiology, root growth, grain yield, and water productivity.Field experiments were conducted to investigate the impacts of two alternative crop management systems, namely, SRI and conventional management practice (CMP) under different water management treatments during the vegetative stage [continuous flooding (CF) vs. AWD] and then during post-vegetative stage: CF vs. AWD @ 1-DAD (days after disappearance of ponded water), 3-DAD or 5-DAD.SRI practices, compared to CMP methods, significantly improved plants’ root growth and xylem exudation rate, leaf area index and light interception by the crop canopy, plus photosynthesis rate at the grain-filling stage, resulting in higher grain yield. Overall, this modified method of rice crop management produced 58% higher grain yield with 16% less water. Across all water management treatments, significantly more grain was produced per unit of water applied with SRI management (6.3 kg ha-mm−1) compared to CMP (3.3 kg grain ha-mm−1). The highest grain yield with SRI (6.2 t ha−1), and the greatest water productivity (6.7 kg ha-mm−1) were obtained with SRI and 3-DAD post-vegetative irrigation. With CMP, highest grain yield (4.1 t ha−1) and water productivity (3.5 kg ha-mm−1) were with 1-DAD irrigation.Differences measured in plants’ response to modified management practices and alternative irrigation schedules indicated how phenotypic and physiological performances can be improved for a given genotype. Combining changes in crop and water management can improve water productivity as well as grain yield.

Physiological Changes of Wheat Varieties Under Water Deficit Condition

The experiment was carried out at the research field of the Department of Agronomy of Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur during November 2014 to March 2015 to assess and evaluate the physiological derivations of wheat varieties under water deficit condition. The experiment was laid out in a split plot design comprising two water regimes (irrigated or control and water stress) in main plot and three wheat varieties (BARI Gom 25, BARI Gom 26 and Sourav) in sub-plot with four replications. Surface irrigation was applied into the irrigated plots in total growing season but it was applied in water stress plots up to 21 days after sowing after that irrigation was stopped in water stress plots. It was revealed that studied parameters were significantly influenced by water regimes, variety and their interaction. The xylem exudation rate, light interception, SPAD value, leaf water potential, relative water content, water retention capacity was higher in irrigated condition where canopy temperature, water uptake capacity, water saturation deficit higher in water stress condition.The wheat var. BARI Gom 26 showed the highest PAR, SPAD value, leaf water potential, relative water content, water retention capacity where BARI Gom 25 exhibit lowest under water deficit condition. On the other hand, BARI Gom 25 showd the highest canopy temperature, water uptake capacity and water saturation deficit in water deficit condition. Therefore, considering the physiological performance and other characters BARI Gom 26 could be considered preferably for water shortage condition followed by Sourav where BARI Gom 25 was susceptible one.Bangladesh Agron. J. 2016 19(2): 105-114

Plant water relations and canopy temperature depression for assessing water stress tolerance of potato

An experiment was conducted with five potato genotypes at Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur during 2010–2011 under control and water stress conditions to determine the effect of water stress on plant water relations and canopy temperature depression of potato. Of the five genotypes, CIP 393371.58 and CIP 396244.12 maintained higher relative water content (RWC) under both the conditions and showed comparatively less midday depression in RWC. The water stress condition significantly decreased water uptake capacity. Under water stress condition tolerant genotypes CIP 393371.58 and CIP 396244.12 showed highest xylem exudation rate of 0.26 and 0.18 g h−1, respectively and transpiration rate of 36 and 34 µg m−2 s−1, respectively at 50 days after planting, and both were positively and significantly correlated. Greater increases in canopy temperature were observed at noon in Asterix and CIP 391004.18 and lower in CIP 393371.58 and CIP 396244.12 and showed inverse relationship with transpiration rate. The genotypes CIP 393371.58 and CIP 396244.12 showed higher canopy temperature depression value and the genotypes CIP 391004.18 and Asterix showed lower canopy temperature depression value under water stress condition. Among the genotypes, CIP 393371.58 and CIP 396244.12 showed better tolerance to water stress condition.

Plant Water Relations and Proline Accumulations in Soybean Under Salt and Water Stress Environment

The study was carried out with three soybean genotypes viz. Galarsum, BD 2331 and BARI Soybean-6 in a vinyl house of Banghabandhu Sheikh Mujibur Rahman Agricultural University, Bangladesh during January to March, 2012 to analyze leaf water status, leaf temperature, xylem exudation and proline accumulation under salt and water stress environment. Treatments included control, water shortage, 50 mM NaCl irrigation, 50 mM NaCl irrigation with water shortage, 75 mM NaCl irrigation, and 75 mM NaCl irrigation with water shortage environments. The relative water content, xylem exudation, leaf water potential of soybean plants were sharply decreased at 75 mM NaCl salt combined with water stress environment. However, these changes were lower in Galarsum and recorded 74.28 % relative water content, 7 mg hr-1 xylem exudation rate and -1.03 MPa leaf water potential. Leaf temperature was more in BD 2331 and BARI Soybean-6 than Galarsum. Galarsum accumulated higher amount of proline in leaves under salt and water stress environment. At 75 mM NaCl salt combined with water stress treatment, the highest proline content was also recorded in Galarsum (2.34 µmoles g-1 fresh weight). Plant water status and biochemical changed sharply under combined salt and water stress condition. Among the soybean genotype, Galarsum was more capable than BD 2331 and BARI Soybean-6 to manage salt under water stress environment.

Enhancing water and cropping productivity through Integrated System of Rice Intensification (ISRI) with aquaculture and horticulture under rainfed conditions

The System of Rice Intensification (SRI), based on modifications in the management practices for rice cultivation, is being utilized in many countries, although not without some controversy. One reason cited for non-adoption or disadoption of SRI is difficulties with water management under rainfed conditions with unreliable or aberrant rainfall distribution, which causes either flooding or long dry spells, or both. These constraints could be dealt with by tapping groundwater resources or by capture and use of rainwater runoff and/or by diversification of the farming system.A 2-year field experiment was conducted in Odisha, India to evaluate SRI under rainfed conditions and also to explore options for enhancing the economic productivity of land and water under such conditions. Four rice cropping systems were evaluated: (i) conventional rice cultivation under rainfed conditions, (ii) SRI methods as adapted to rainfed cultivation, (iii) rainfed SRI methods with drainage facilities and supplementary pump-irrigation, and (iv) integrated SRI (ISRI) where rainwater runoff was harvested and stored for aquaculture and horticulture crops while also providing supplementary irrigation for the rice crop.The rice crop grown with adapted SRI practices under rainfed condition showed significant improvements in the plants’ morphology and physiology. Phenotypic changes included: greater plant height and tillering, more number of leaves, and expanded root systems. These changes were accompanied by changes in plants’ physiological functions like greater xylem exudation rate and more light interception by the canopy, increased chlorophyll content in the leaves, and higher light utilization and photosynthetic rates during flowering. These factors were responsible for improved yield-contributing characteristics and for higher grain yield (52%) as compared with crops grown by conventional production methods. Comparing yield from rainfed conventional vs. SRI methods between drought and normal-rainfall years indicated that the latter methods are more drought-tolerant and productive; greatly expanded and active root systems with SRI have been important contributing factors.Introducing drainage and supplementary irrigation improved both the grain yield (by 29%) and water productivity for rainfed SRI. Further, integrating aquaculture and horticulture with SRI management and rainwater harvesting increased the rice yield further (by 8%) and the net water productivity. This integrated system was found to raise the net income per unit of water by more than 60-fold compared to conventional rainfed rice cultivation. This option looks promising for improving food security for smallholders under erratic or diminished rainfall conditions.

Performance evaluation of rice varieties under the System of Rice Intensification compared with the conventional transplanting system

A field experiment was conducted at Deras Research Farm, Khurda district, Bhubaneswar, Orissa, India, to evaluate the performance of different rice varieties managed under System of Rice Intensification (SRI) compared with the current transplanting system (CTS). Five rice varieties were used for the study: (i) Khandagiri (early-duration, 90 days); (ii) Lalat (early-medium duration, 110 days); (iii) Surendra (late-medium duration, 130 days); (iv) Hybrid CRHR-7 (late-medium duration, 135 days); and (v) Savitri (long-duration, 145 days). It was seen that SRI practices significantly (p < 0.05) improved the harvest index, percentage of effective tillers, panicle length, and various yield components in all the varieties. SRI hills having an open-canopy structure with higher leaf area index (LAI) resulted in greater light interception than the conventional transplanting methods. At the ripening stage, SRI plants had better root growth and a higher xylem exudation rate than CTS plants. This was associated with higher levels of chlorophyll in the lower leaves and a higher photosynthesis rate. Delayed senescence with enhanced photosynthesis in the lower leaves was also responsible for supplying more assimilates toward the roots for maintaining their higher activity. These features might also contribute to the improvement of grain filling and grain weight in SRI-grown plants as all the varieties performed better in terms of grain yield (12–42% higher) with this alternative management.

Effects on rice plant morphology and physiology of water and associated management practices of the system of rice intensification and their implications for crop performance

Field experiments were conducted in Bhubaneswar, Orissa, India, during the dry season (January–May) in 2008 and 2009 to investigate whether practices of the System of Rice Intensification (SRI), including alternate wetting and drying (AWD) during the vegetative stage of plant growth, could improve rice plants’ morphology and physiology and what would be their impact on resulting crop performance, compared with currently recommended scientific management practices (SMP), including continuous flooding (CF) of paddies. With SRI practices, grain yield was increased by 48% in these trials at the same time, there was an average water saving of 22% compared with inundated SMP rice. Water productivity with AWD-SRI management practices was almost doubled (0.68 g l−1) compared to CF-SMP (0.36 g l−1). Significant improvements were observed in the morphology of SRI plants in terms of root growth, plant/culm height, tiller number per hill, tiller perimeter, leaf size and number, leaf area index (LAI), specific leaf weight (SLW), and open canopy structure. These phenotypic improvements of the AWD-SRI crop were accompanied by physiological changes: greater xylem exudation rate, crop growth rate, mean leaf elongation rate (LER), and higher light interception by the canopy compared to rice plants grown under CF-SMP. SRI plants showed delayed leaf senescence and greater light utilization, and they maintained higher photosynthetic rates during reproductive and grain-filling stages. This was responsible for improvement in yield-contributing characteristics and higher grain yield than from flooded rice with SMP. We conclude that SRI practices with AWD improve rice plants’ morphology, and this benefits physiological processes that result in higher grain yield and water productivity.

Effects of Soil Temperature on Growth and Root Function in Rice

The objective of this study was to clarify the effects of soil temperature in the stage from late tillering to panicle initiation (SI) and during the grain-filling stage (SII) on grain setting, dry matter production, photosynthesis, non-structural carbohydrate (NSC), xylem exudation and abscisic acid (ABA) levels in rice (Oryza sativa L. cv. Koshihikari). Rice plants were exposed to four different soil temperatures during SI or SII: 17.5, 25, 31.5 and 36.5°C (ST18, ST25, ST32 and ST37, respectively). The yield, yield components, grain filling and quality in SI were negatively influenced by high soil temperature of 37°C. On the other hand, there was no significant difference in those characters among temperature treatments in SII. The root/shoot ratio was smallest in the ST37 plants in both SI and SII, mainly due to their lighter root weight. At 7 days after initiation of treatment (DAT) in both SI and SII, the photosynthetic and xylem exudation rate tended to increase slightly as soil temperature increased up to 32°C. At 21 DAT, however, the photosynthetic rate was lowest in ST37, with concurrent decrease of diffusion conductance and SPAD value. In addition, decrease of NSC concentration in stem and xylem exudation rate, and increase of ABA level in leaves and xylem exudate were observed in ST37 plants at 21 DAT. These results suggested that high soil temperature before heading especially influenced yield, grain quality and plant growth. Possible mechanisms of the effect of soil temperature are discussed.

Biomass production, transpiration rate and endogenous abscisic acid levels in grafts of flacca and wild-type tomato (Lycopersicon esculentum).

ABA is a plant signalling-molecule that plays a key role in regulating stomatal response, stress-tolerance responses, and coordinated growth of roots and shoots. Knowledge of the relationship between endogenous ABA level and plant growth is essential for improving plant growth and productivity. The wild-type tomato Rheinlands Ruhm (RR) and its flacca mutant were grafted in order to determine the relationship between endogenous ABA levels and biomass production. The flacca genotype is an ABA-deficient mutant, characterized by high stomatal conductance during the day or the night, high transpiration rate, marked tendency to wilt, and smaller size. Flacca scions grafted on to wild-type rootstock (Fs/Wr) exhibited higher ABA levels, lower transpiration rate, and higher water content than those of a control graft of flacca scion on flacca rootstock (Fs/Fr). Fs/Wr exhibited a lower ABA concentration, xylem exudate rate, ABA xylem-loading rate, and dry weight biomass in wild-type rootstock than in control grafts of wild-type scion on wild-type rootstock (Ws/Wr). Flacca rootstock grafted to wild-type scion (Ws/Fr) showed a higher ABA level, xylem exudation rate, ABA xylem-loading rate, dry weight biomass and length than grafts to flacca scion (Fs/Fr). Ws/Fr did not induce significant changes in wild-type scion as compared with Ws/Wr. In double grafts, flacca shoot fresh weight was significantly increased in flacca scion and wild-type scion grafted on to flacca rootstock (Fs + Ws/Fr) or wild-type rootstock (Fs + Ws/Wr). There was a significant linear relationship between biomass and ABA in scions (r=0.997, P=0.001). These results support the notion that ABA increases growth of tomato seedlings via improved stomatal control.

Effect of Potassium, and Abscisic and Indole-3-Acetic Acids, on Maize Root Xylem Exudation and Potassium Efflux

The influence of potassium sulfate, abscisic acid (ABA) and indole-3-acetic acid (IAA) solutions on xylem exudation rate and potassium efflux from the apical cut end of root tips of intact maize (Zea mays L. cv. Dnepropetrovskaya) seedlings was studied. Foliar application of 5 mM K2SO4 considerably stimulated the exudation rate. The application of ABA and IAA (1 mM) also induced a high rate of xylem exudation, K+ efflux being simultaneously increased.

Xylem exudation is related to nitrate assimilation pathway in detopped maize seedlings: use of nitrate reductase and glutamine synthetase inhibitors as tools

The xylem exudation of detopped 7-d-old seedlings of Zea mays L. doubled when KCl was present in the root medium compared to seedlings maintained on water. It was further enhanced when KCl was replaced by nitrogen compounds such as nitrate, ammonium and glutamine. The role of the nitrate assimilation pathway on the enhancement of xylem exudation rate was investigated using tungstate, an inhibitor of nitrate reductase (NR) activity, and phosphinothricin or methionine sulphoximine, inhibitors of glutamine synthetase (GS) activity. The sap levels of NO 3 - , NH 4 + , glutamine, and asparagine was used to ascertain the in vivo inhibition of both enzymes. The tungstate effects were also checked by measuring leaf in vitro NR activity and NR protein content. Xylem exudation rate of detopped seedlings fed with KNO 3 decreased when the nitrate assimilation pathway was blocked either at the NR or at GS sites. This decrease was prevented when urea (acting as NH 4 + supply) was given simultaneously with tungstate. KNO 3 does not act directly on exudation, but through the involvement of NH 4 + . The involvement of glutamine was also shown since GS inhibition resulted in a cancellation of the enhancing effect of KNO 3 on exudation. As change of exudation rate was not linked to change in sap osmolarity, it is assumed that the assimilation chain could modify root water conductance. The role of glutamine was discussed.

ナスの収量並びに木部溢泌液中の無機成分及びホルモンレベルに及ぼす台木の影響

Eggplants, cv. Hayabusa, Kokuyou and Beikokudaimaru, grown either on their own roots or on the rootstocks, cv. VF, Akanasu and Torubamu, were used to study the effects of rootstock on the yield of eggplant in relation to the number of thick roots, mineral flux and hormone levels in xylem sap.1. All of three varieties grafted on VF showed the highest yield and the most vigorous growth, and more thick roots were found on those plants. Own-root plants produced lower yields with fewer thick roots than grants. There was a close positive correlation between the number of thick roots and yield.2. Xylem exudation rate and mineral flux in xylem sap were the highest in the plants grafted on VF. The mineral flux, especially nitrogen, was closely correlated with yield.3. Cytokinin, gibberellin-like substances and indole-acetic acid levels were the greatest in the xylem sap of plants grafted on VF rootstock, which produced the highest yield. The difference in yield between rootstocks was significantly attributed to difference in cytokinin production, depending on the number of thick roots.4. From these results, it may be concluded that the growth and yield of eggplant was affected by mineral absorption and hormones especially cytokinin production of rootstocks via many thick roots.

Influence of Nitrogen Form on Exudation Rate, and Ammonium, Amide, and Cation Composition of Xylem Exudate in Tomato1

Abstract A shift from NO3 to NH4-N nutrition for tomato (Lycopersicon esculentum Mill.) plants resulted in a significant decrease in xylem exudation rate within 15 minutes. Ammonium treatment also decreased Ca and Mg concentration in exudate in the 1.5 to 2.5 hour interval after the shift, whereas free NH4 and amides increased in the same period. Potassium ion concentration did not change in the time interval from 15 minutes to 7 days following the change of N form. Reduced exudate concentration or reduced exudation rate resulted in large decreases in the total amount of K, Ca, and Mg delivered in the presence of NH4 relative to that of NO3, and offers a possible explanation for the observed deficiencies of these cations in shoot tissues of plants under conditions of NH4 toxicity.