Response Of Leaf Photosynthesis Research Articles

Response of leaf photosynthesis, chlorophyll content and yield of hydroponic tomatoes to different water salinity levels.

Tomato (Solanum lycopersicum L.) is an important vegetable crop that grows easily under controlled conditions, such as in greenhouses and hydroponics. To overcome freshwater scarcity, researchers are searching for alternatives to groundwater sources such as desalinated water (saline water) for irrigation. High salinity in irrigation water alters physiological functions and crop development, thereby reducing the yield. Best management practices and the use of grafted tomato plants on salt-tolerant rootstocks can alleviate salinity stress. The present study was conducted to address the impact of salinity stress on leaf transpiration (Tr), stomatal conductance (gs), photosynthesis (Pn), leaf chlorophyll content, proline content, and yield of hydroponically cultivated tomato plants. Saline (NaCl) water was used for the preparation of nutrient solution with three salinity levels, electrical conductivity (EC, dS m-1) of 2.5 (control), 6.0, and 9.5. Three commercial tomato cultivars (Valouro-RZ, Ghandora-F1, and Feisty-Red) were used. Both self-rooted plants and plants grafted onto Maxifort rootstocks were transplanted onto a perlite substrate. The recorded data revealed that all studied cultivars were critically affected by higher salinity (≈ 9.5 dS m-1) compared to low (≈ 2.5 dS m-1) and medium (≈ 6.0 dS m-1) salinity levels. The Variations in Tr, Pn, gs, chlorophyll content of leaf, and yield between medium and high salinity trials were reported at 3%, 5%, 9%, 5%, and 7.1%, respectively, whereas no significant differences were observed between low and medium salinities. However, at medium salinity levels, grafted plants performed better in photosynthesis than non-grafted plants. This is due to the accumulation of leaf proline, which maintains osmotic regulation and photosynthetic activity by preventing cell damage at medium salinities. Hence, this study confirmed the use of saline water for growing tomatoes under hydroponic conditions up to an EC of 6.0 dS m-1 including the EC of nutrient fertilizers.

Transcriptome analysis on responses of leaf photosynthesis and nitrogen metabolism of Larix gmelinii to environmental change

To reveal molecular mechanisms underlying photosynthesis responses of Dahurian larch (Larix gmelinii) to environmental changes, we used the high-throughput sequencing technology to sequence the transcriptome of larch leaves from four latitudinal sites with different environmental conditions, and compared differential expression genes (DEGs). The four sites from high- to low-latitude were Tahe (52°52' N), Songling (50°72' N), Heihe (49°22' N), and Dailing (47°08' N). A total of 282428811 clean reads were sequenced out, among which the abundace of DEGs were 16915, 18812, 28536, 20635, 29957 and 23617 for the Tahe-Songling, Tahe-Heihe, Tahe-Dailing, Songling-Heihe, Songling-Dailing, and Heihe-Dailing comparisons, respectively. The expression of nine Psb genes family (i.e., PsbB, PsbK, PsbO, PsbP, PsbQ, PsbS, PsbW, Psb27, and Psb28) encoding Photosystem Ⅱ and that of three genes (ATPF1A,atpA, ATPF1G, atpG, and ATPF1D, atpH) encoding F-type ATPase, which were involved in photosynthesis pathway, were significantly up-regulated with increasing environmental differences among the sites. A similar up-regulation pattern occurred for the expression of genes encoding glutamine synthetase (glnA, GLUL), nitrate reductase (NR), and carbonic anhydrase (cynT, can) that were involved in nitrogen metabolism pathway. The numbers of DEGs and up-regulated genes increased with the increases in environmental changes among the sites, resulting in inter-site divergence of photosynthetic capacity of larch trees.

土壌水分条件に対するダイズ品種‘美里在来’の個葉光合成速度と水分パラメータの応答．

土壌水分条件に対するダイズ品種‘美里在来’の個葉光合成速度と水分パラメータの応答．

Photosynthesis in Ranunculus asiaticus L.: The Influence of the Hybrid and the Preparation Procedure of Tuberous Roots.

Ranunculus asiaticus L. is a quantitative long-day geophyte, grown in a cold greenhouse for cut flowers and potted plants. Flowering in ranunculus is a complex process, strongly steered by temperature and photoperiodism. Vernalization of rehydrated tuberous roots anticipate sprouting and leaf rosette formation and flowering. It is known that the time for flowering and the sensitivity to cold treatment, in terms of flowering anticipation, varies in numerous hybrids, while no information seems to be available on the influence of hybrids and on the vernalization on the photosynthetic process and primary metabolite profiling. We investigated the influence of two ranunculus hybrids, MDR and MBO, and two preparation procedures of tuberous roots, only rehydration (Control, C) and rehydration followed by vernalization (V), on the photosynthesis and photochemistry of plants grown in a climatic chamber, under a controlled environment. In addition, in MBO plants, in which the vernalization showed the main effects, carbohydrate, amino acid and protein levels were also investigated. In control plants, the response of leaf photosynthesis, to increasing white light, revealed higher photosynthetic activity in MDR than in MBO. The quantum yield of PSII (ϕPSII), electron transport rate (ETR) and non-photochemical quenching (NPQ) did not differ between the two hybrids. The maximal photochemical efficiency (Fv/Fm) was higher in MBO than in MDR and showed a decrease in both hybrids after vernalization. The preparation treatment of propagation material affected the light response of photosynthesis in the two hybrids differently, which increased in plants from vernalized tuberous roots, compared to those from only rehydrated in MBO and decreased in MDR, in accordance to the effects of vernalization observed in leaf photosynthetic pigments. In MBO vernalized tuberous roots, starch was rapidly degraded, and the carbon skeletons used to synthesize amino acids. Control plants of MBO, developed more leaves than those of MDR and a consequent larger plant leaf area. Compared to only rehydration, vernalization of rehydrated tuberous roots increased the plant leaf area in both the hybrids. Compared to the control, vernalized tuberous roots of MBO showed higher concentrations of sucrose and free amino acids, which could act as a long-distance signal promoting floral transition in young leaf primordia.

Physiological and Dry Matter Characteristics of Spring Maize in Northeast China under Drought Stress

This paper examined impacts of drought on both physiological and dry matter characteristics of spring maize grown in Liaoning, China in 2016. We compared responses of dry matters of various parts, yield components, leaf photosynthesis, and transpiration to four drought levels: RD (no drought treatment), D1 (drought treatment between the 38th and 65th day after sowing), D2 (drought treatment between the 38th and 79th day after sowing), and D3 (drought treatment between the 53rd and 93rd day after sowing). Results indicate that the long-term drought in either jointing period or tasseling period had a severer impact on the dry matters and yield components than the short-term drought in jointing period. Moreover, the dry matters and the corresponding partitioning coefficients of different parts were distinct. The yield reduction was caused by the decreases of ear length and bald tip ratio during the short-term drought at jointing period, while it was caused by the reductions of ear length, ear diameter, and grain number per spike during the long-term drought in jointing and tasseling periods. Responses of leaf photosynthesis and transpiration to drought were lagging, but reactions of tasseling drought were faster. Leaf photosynthesis and transpiration after a short-term drought in jointing period could recover to an average level but that after the long-term drought in either jointing or tasseling period could not, after irrigation.

Differential responses of Picea asperata and Betula albosinensis to nitrogen supply imposed by water availability.

A pot experiment was conducted to investigate the effects of nitrogen (N) addition (0, 20, 40 g N m-2 year-1, N0, N20, N40, respectively) on the growth, and biomass accumulation and allocation of coniferous and deciduous (Picea asperata Mast. and Betula albosinensis Burk.) seedlings under a range of soil moisture limitation (40%, 50%, 60%, 80% and 100% of field capacity, FC). At 100% FC, growth of shade-tolerant P. asperata increased with N supply, while that of shade-intolerant B. albosinensis reached a maximum at N20, declining somewhat thereafter. At 60% FC and lower moisture content, water availability limited the growth of P. asperata seedlings, while N availability became progressively limiting to growth with moisture increasing above 60% FC. The transition from principally water-limited response to N-limited response in B. albosinensis occurred at lower moisture content. For P. asperata, these patterns reflected the responses of roots, consistent with changes in root/shoot biomass. For B. albosinensis the response reflected changes in shoot dimensions and root biomass fraction, the latter decreasing with size and foliar [N]. We are not aware of another study demonstrating such differences in the shape of the growth responses of seedlings of differing potential growth rate, across a range in belowground resource supply. The responses of leaf photosynthesis (as well as photosynthetic water and N-use efficiencies) were consistent with the observed growth response of P. asperata to water and N availability, but not of B. albosinensis, suggesting that leaf area dynamics (not measured) dominated the response of this species. Betula albosinensis, a fast-growing species, has a relative narrow range of soil water and N availability for maximum growth, achieved by preferential allocation to the shoot as resources meet the requirements at moderate N and water supply. In contrast, P. asperata increases shoot biomass progressively with increasing resources up to moderate water supply, preferentially growing more roots when resources are not limiting, suggesting that its capacity to produce shoot biomass may reach a biological limit at moderate levels of resource supply.

Responses of Leaf Photosynthesis, Plant Growth and Fruit Production to Periodic Alteration of Plant Density in Winter Produced Single-truss Tomatoes

Responses of Leaf Photosynthesis, Plant Growth and Fruit Production to Periodic Alteration of Plant Density in Winter Produced Single-truss Tomatoes

Effects of Diffuse Light on Radiation Use Efficiency of Two Anthurium Cultivars Depend on the Response of Stomatal Conductance to Dynamic Light Intensity.

The stimulating effect of diffuse light on radiation use efficiency (RUE) of crops is often explained by the more homogeneous spatial light distribution, while rarely considering differences in temporal light distribution at leaf level. This study investigated whether diffuse light effects on crop RUE can be explained by dynamic responses of leaf photosynthesis to temporal changes of photosynthetic photon flux density (PPFD). Two Anthurium andreanum cultivars (‘Pink Champion’ and ‘Royal Champion’) were grown in two glasshouses covered by clear (control) and diffuse glass, with similar light transmission. On clear days, diffusing the light resulted in less temporal fluctuations of PPFD. Stomatal conductance (gs) varied strongly in response to transient PPFD in ‘Royal Champion,’ whereas it remained relatively constant in ‘Pink Champion.’ Instantaneous net leaf photosynthesis (Pn) in both cultivars approached steady state Pn in diffuse light treatment. In control treatment this only occurred in ‘Pink Champion.’ These cultivar differences were reflected by a higher RUE (8%) in ‘Royal Champion’ in diffuse light treatment compared with control, whereas no effect on RUE was observed in ‘Pink Champion.’ We conclude that the stimulating effect of diffuse light on RUE depends on the stomatal response to temporal PPFD fluctuations, which response is cultivar dependent.

Impacts of rising tropospheric ozone on photosynthesis and metabolite levels on field grown soybean

The response of leaf photosynthesis and metabolite profiles to ozone (O3) exposure ranging from 37 to 116ppb was investigated in two soybean cultivars Dwight and IA3010 in the field under fully open-air conditions. Leaf photosynthesis, total non-structural carbohydrates (TNC) and total free amino acids (TAA) decreased linearly with increasing O3 levels in both cultivars with average decrease of 7% for an increase in O3 levels by 10ppb. Ozone interacted with developmental stages and leaf ages, and caused higher damage at later reproductive stages and in older leaves. Ozone affected yield mainly via reduction of maximum rate of Rubisco carboxylation (Vcmax) and maximum rates of electron transport (Jmax) as well as a shorter growing season due to earlier onset of canopy senescence. For all parameters investigated the critical O3 levels (∼50ppb) for detectable damage fell within O3 levels that occur routinely in soybean fields across the US and elsewhere in the world. Strong correlations were observed in O3-induced changes among yield, photosynthesis, TNC, TAA and many metabolites. The broad range of metabolites that showed O3 dose dependent effect is consistent with multiple interaction loci and thus multiple targets for improving the tolerance of soybean to O3.

Responses of leaf photosynthesis, pigments and chlorophyll fluorescence within canopy position in a boreal grass (Phalaris arundinacea L.) to elevated temperature and CO<sub>2</sub> under varying water regimes

The effects of elevated growth temperature (ambient + 3.5°C) and CO2 (700 μmol mol-1) on leaf photosynthesis, pigments and chlorophyll fluorescence of a boreal perennial grass (Phalaris arundinacea L.) under different water regimes (well watered to water shortage) were investigated. Layer-specific measurements were conducted on the top (younger leaf) and low (older leaf) canopy positions of the plants after anthesis. During the early development stages, elevated temperature enhanced the maximum rate of photosynthesis (P max) of the top layer leaves and the aboveground biomass, which resulted in earlier senescence and lower photosynthesis and biomass at the later periods. At the stage of plant maturity, the content of chlorophyll (Chl), leaf nitrogen (NL), and light response of effective photochemical efficiency (ΦPSII) and electron transport rate (ETR) was significantly lower under elevated temperature than ambient temperature in leaves at both layers. CO2 enrichment enhanced the photosynthesis but led to a decline of NL and Chl content, as well as lower fluorescence parameters of ΦPSII and ETR in leaves at both layers. In addition, the down-regulation by CO2 elevation was significant at the low canopy position. Regardless of climate treatment, the water shortage had a strongly negative effect on the photosynthesis, biomass growth, and fluorescence parameters, particularly in the leaves from the low canopy position. Elevated temperature exacerbated the impact of water shortage, while CO2 enrichment slightly alleviated the drought-induced adverse effects on P max. We suggest that the light response of ΦPSII and ETR, being more sensitive to leaf-age classes, reflect the photosynthetic responses to climatic treatments and drought stress better than the fluorescence parameters under dark adaptation.

Responses of leaf photosynthesis and plant growth to altered source–sink balance in a Japanese and a Dutch tomato cultivar

We investigated the effects of altered source/sink ratio by leaf or fruit pruning on leaf photosynthetic characteristics and whole-plant growth of ‘Momotaro York’, a Japanese cultivar, and ‘Dundee’, a Dutch cultivar and verified a hypothesis for sink-limitation of plant growth proposed by Tanaka and Fujita (1974). Plants were grown hydroponically with a high-wire system in a greenhouse for 11 weeks. Light-saturated photosynthesis of young, fully expanded leaves measured at atmospheric CO 2 partial pressure of 37 Pa and at an intercellular CO 2 partial pressure of 20 Pa was not influenced by alteration of source/sink ratio for either cultivar. Although soluble sugars were accumulated in leaves under high source/sink conditions, the amount of ribulose-1,5-bisphosphate carboxylase/oxygenase, a rate-limiting factor for CO 2-limited photosynthesis, was not affected by the altered source–sink balance. Net assimilation rate of a whole plant increased with decreasing source/sink ratio, but this can be accounted for by the changes in light interception per unit leaf area, without taking the source–sink relationship into consideration. It was concluded that the altered source/sink ratio did not change leaf photosynthetic capacity and the sink-limitation hypothesis cannot be applied to either cultivar under the conditions of the present study.

The Response of Leaf Photosynthesis and Dry Matter Accumulation to Nitrogen Supply in an Older and a Newer Maize Hybrid

Nitrogen use efficiency is higher in newer than in older maize (Zea mays L.) hybrids, but the physiological mechanisms underlying differences in N‐use efficiency are unknown. The objective of this study was to quantify differences between an older and a newer maize hybrid in their response to N availability throughout the life cycle at both the leaf and the whole‐plant level. An older and a newer maize hybrid were grown in a field hydroponic system located near Guelph, ON, in 2005 at a high and a low N level. Leaf carbon exchange rate (CER), chlorophyll index, and the thylakoid electron transport rate (ETR) were measured weekly from 2 wk presilking to 8 wk postsilking. Plant‐component dry matter and N content were determined from 1 wk presilking to maturity. At the leaf level, leaf CER declined during the grain‐filling period, and the decline was greater under low than high N availability. The decline in leaf CER during the grain‐filling period was less in the newer than in the older hybrid under both high and low N availability, and differences in leaf CER were associated most strongly with a reduction in leaf CER per unit absorbed photosynthetic photon flux density. At the whole‐plant level, reduction in grain yield in low vs. high N was greater in the older than in the newer hybrid. The hybrid × N interaction for grain yield was attributable predominantly to a greater decline in the proportion of dry matter allocated to the grain in the older hybrid.

Responses of leaf photosynthesis and plant water status in rice to low water temperature at different growth stages

Effects of low water temperature ( T w) on the rate of light-saturated leaf photosynthesis ( P max), plant water content and sap bleeding rate of rice ( Oryza sativa L.) were examined from field trials for 4 years. Cool irrigation water was applied at three temperature levels (16–25 °C in daily average and 20–30 °C in daily maximum) for 20–34 days firstly during the vegetative and secondly during the reproductive growth periods. P max during the reproductive growth period had a significant positive correlation with T w at the time of measurements in 3 of 4 years, where a 1 °C decrease of T w from 25 °C decreased P max by 1.8–2.4%. On the other hand, no significant relation between P max and T w was observed during the vegetative growth period. Stomatal conductance ( g s) followed a similar trend to that of P max. Plant water content and sap bleeding rate were reduced by low T w for the first 5–12 days after start of treatment, but the effects of low T w became progressively smaller. Chlorophyll meter values (SPAD values) taken with the Minolta SPAD-502 chlorophyll meter, were significantly higher under low T w than those under high T w in the second half of each treatment period. Multiple regression analysis revealed that the negative effect of decreased g s on P max caused by low T w was alleviated by factors associated with increased SPAD values. These results supported our previous finding that radiation use efficiency was less affected by low T w than canopy radiation capture [Field Crops Res. 73 (2002) 67]. Although complex interactions are involved, the limited responses of P max to the long-term exposure to low T w also suggest that detailed physiological mechanisms that determine P max can be simplified in a crop growth model that evaluates the effects of T w on rice growth and yield under cool climates.

Response of Leaf Photosynthesis during the Grain‐Filling Period of Maize to Duration of Cold Exposure, Acclimation, and Incident PPFD

Maize (Zea mays L.) leaf photosynthesis during the grain-filling period is affected by low (≈4°C) night temperatures. Three factors that are potentially involved in this phenomenon were examined: (i) duration of cold exposure, (ii) acclimation prior to exposure to light, and (iii) level of incident photosynthetic photon flux density (PPFD) following cold exposure. Studies were carried out with plants grown hydroponically under both field and controlled-environment conditions. Three hybrids (‘Pride 5’, ‘Pioneer 3902’, and ‘Cargill 1877’) were used in the field experiments and Pioneer 3902 was used in controlled-environment experiments. Plants were exposed to 4°C in the dark for either 2 or 16 h and, subsequently, acclimated for either 0 or 1 h in the dark before exposure to high PPFD. Four incident PPFD levels (400, 650, 1200, and 2000 μmol m−2 s−1) after cold exposure were examined. Both duration of cold exposure and acclimation after cold exposure affected the reduction in leaf carbon exchange rate (CER). Leaf CER was reduced by 18.0% after a 2-h exposure and by 30.4% after a 16-h exposure to 4°C, and leaf CER was reduced by 20.4 and 28.0% for 1- and 0-h acclimation, respectively. Dark-adapted Fv/Fm (Fv = variable fluorescence; Fm = maximum chlorophyll fluorescence), that is, maximum quantum efficiency of Photosystem II, was 0.71 after cold exposure during the night compared with 0.81 for the control. The Fv/Fm was affected by duration of cold exposure (0.74 and 0.68 for 2- and 16-h exposure, respectively) but not by acclimation. Reduction in leaf photosynthesis after cold exposure was linearly related to the incident PPFD level. Results support the contention that the reduction in CER due to low night temperature is not associated with photoinhibition.

Improved temperature response functions for models of Rubisco-limited photosynthesis

Predicting the environmental responses of leaf photosynthesis is central to many models of changes in the future global carbon cycle and terrestrial biosphere. The steadystate biochemical model of C3 photosynthesis of Farquhar et al .( Planta 149, 78‐90, 1980) provides a basis for these larger scale predictions; but a weakness in the application of the model as currently parameterized is the inability to accurately predict carbon assimilation at the range of temperatures over which significant photosynthesis occurs in the natural environment. The temperature functions used in this model have been based on in vitro measurements made over a limited temperature range and require several assumptions of in vivo conditions. Since photosynthetic rates are often Rubisco-limited (ribulose, 1-5 bisphosphate carboxylase/oxygenase) under natural steady-state conditions, inaccuracies in the functions predicting Rubisco kinetic properties at different temperatures may cause significant error. In this study, transgenic tobacco containing only 10% normal levels of Rubisco were used to measure Rubisco-limited photosynthesis over a large range of CO2 concentrations. From the responses of the rate of CO2 assimilation at a wide range of temperatures, and CO2 and O2 concentrations, the temperature functions of Rubisco kinetic properties were estimated in vivo. These differed substantially from previously published functions. These new functions were then used to predict photosynthesis in lemon and found to faithfully mimic the observed pattern of temperature response. There was also a close correspondence with published C3 photosynthesis temperature responses. The results represent an improved ability to model leaf photosynthesis over a wide range of temperatures (10‐40 °C) necessary for predicting carbon uptake by terrestrial C3 systems.

Ozone effects on wheat in relation to CO2: modelling short‐term and long‐term responses of leaf photosynthesis and leaf duration

SummaryA combined stomatal–photosynthesis model was extended to simulate the effects of ozone exposure on leaf photosynthesis and leaf duration in relation to CO2. We assume that ozone has a short‐term and a long‐term effect on the Rubisco‐limited rate of photosynthesis, Ac. Elevated CO2 counteracts ozone damage via stomatal closure. Ozone is detoxified at uptake rates below a threshold value above which Ac decreases linearly with the rate of ozone uptake. Reduction in Ac is transient and depends on leaf age. Leaf duration decreases depending on accumulated ozone uptake. This approach is introduced into the mechanistic crop simulation model AFRCWHEAT2. The derived model, AFRCWHEAT2‐O3, is used to test the capability of these assumptions to explain responses at the plant and crop level.Simulations of short‐term and long‐term responses of leaf photosynthesis, leaf duration and plant and crop growth to ozone exposure in response to CO2 are analysed and compared with experimental data derived from the literature. The model successfully reproduced published responses of leaf photosynthesis, leaf duration, radiation use efficiency and final biomass of wheat to elevated ozone and CO2. However, simulations were unsatisfactory for cumulative radiation interception which had some impact on the accuracy of predictions of final biomass. There were responses of leaf‐area index to CO2 and ozone as a result of effects on tillering which were not accounted for in the present model. We suggest that some model assumptions need to be tested, or analysed further to improve the mechanistic understanding of the combined effects of changes in ozone and CO2 concentrations on leaf photosynthesis and senescence. We conclude that research is particularly needed to improve the understanding of leaf‐area dynamics in response to ozone exposure and elevated CO2.

The relations of stomatal closure and reopening to xylem ABA concentration and leaf water potential during soil drying and rewatering

Two tropical tree species, Acacia confusa and Leucaena leucocephala, were used to study the relationships among stomatal conductance, xylem ABA concentration and leaf water potential during a soil drying and rewatering cycle. Stomatal conductance of both A. confusa and L. leucocephala steadily decreased with the decreases in soil water content and pre-dawn leaf water potential. Upon rewatering, soil water content and pre-dawn leaf water potential rapidly returned to the control levels, whereas the reopening of stomata showed an obvious lag time. The length of this lag time was highly dependent not only upon the degree of water stress but also on plant species. The more severe the water stress, the longer the lag time. When A. confusa and L. leucocephala plants were exposed to the same degree of water stress (around −2.0 MPa in pre-dawn leaf water potential), the stomata of A. confusa reopened to the control level 6 days after rewatering. However, it took L. leucocephala about 14 days to reopen fully. A very similar response of leaf photosynthesis to soil water deficit was also observed for both species. Soil drying resulted in a significant increase in leaf and xylem ABA concentrations in both species. The more severe the water stress, the higher the leaf and xylem ABA concentrations. Both leaf ABA and xylem ABA returned to the control level following relief from water deficit and preceded the full recovery of stomata, suggesting that the lag phase of stomatal reopening was not controlled by leaf and/or xylem ABA. In contrast to drying the whole root system, drying half of the root system did not change the leaf water relations, but caused a significant increase in xylem ABA concentration, which could fully explain the decrease of stomatal conductance. After rewatering, the stomatal conductance of plants in which half of the roots were dried recovered more rapidly than those of whole-root dried plants, indicating that the leaf water deficit that occurred during the drying period was related to the post-stress stomatal inhibition. These results indicated that the decrease in stomatal conductance caused by water deficit was closely related to the increase in xylem ABA, but xylem ABA could not fully explain the reopening of stomata after relief of water stress, neither did the leaf ABA. Some unknown physiological and/or morphological processes in the guard cells may be related to the recovery process.

Mechanisms of Different Responses of Leaf Photosynthesis in African Rice(Oryza glaberrima Steud.) and Rice(Oryza sativa L.) to Low Leaf Water Potential.

This research was conducted to elucidate the mechanisms in water stress tolerance of Oryza glaberrima Steud. with special reference to stomatal conductance. Leaf photosynthesis (LPS) of O. glaberrima Steud. with developing soil water deficiency, was still maintained above zero when the leaf water potential decreased to as low as -2.0 MPa, while in O. sativa L. LPS became zero at -1.6 MPa. Stomatal conductances also changed in parallel with LPS in both species, suggesting that the different response of LPS to reduced leaf water potential is due to the different stomatal response between two species. In the relationship between the stomatal conductance and abscisic acid (ABA) content in the leaves, Saka, a line of O. glaberrima Steud., showed a slower decrease of stomatal conductance with increase of ABA than Nipponbare, a cultivar of O. sativa L. This attenuated response of stomatal conductance to leaf ABA content in O. glaberrima Steud. was supposed to be the cause of maintenance of higher LPS than in O. sativa L. under low leaf water potential conditions. The Rubisco content showed no significant difference in the response to developing low leaf water potential between the two species.

Leaf thickness and response of leaf photosynthesis to water stress in soybean varieties

A comparative study of photosynthetic response to soil moisture was conducted with soybean varieties (Harosoy, Norin No. 1 and Hogyoku). When the plants were grown in May before the rainy season under a high radiation level, per unit leaf area the photosynthetic rate of Harosoy leaves was significantly higher throughout the entire range of soil water potentials and leaf water potentials than that of Norin No. 1 leaves. The high photosynthetic rate of Harosoy under non-stress conditionsaand mild water stress was associated with both the high specific leaf weight and the high leaf areal nitrogen content. The photosynthetic response of the Harosoy leaves developed during rainy season under a low radiation level, however, was similar to that of Norin No. 1; no significant difference was observed between these two varieties in the specific leaf weight and in the leaf areal nitrogen content.