Genotypic and within canopy variation in leaf carbon isotope discrimination and its relation to short-term leaf gas exchange characteristics in cassava grown under rain-fed conditions in the tropics

In a field rain-fed trial with 15 cassava cultivars, leaf gas exchanges and carbon isotope discrimination (Δ) of the same leaves were determined to evaluate genotypic and within-canopy variations in these parameters. From 3 to 7 months after planting leaf gas exchange was measured on attached leaves from upper, middle, and lower canopy layers. All gas exchange parameters varied significantly among cultivars as well as canopy layers. Net photosynthetic rate (P _N) decreased from top canopy to bottom indicating both shade and leaf age effects. The same trend, but in reverse, was found with respect to Δ, with the highest values in low canopy level and the lowest in upper canopy. There were very significant correlations, with moderate and low values, among almost all these parameters, with P _N negatively associated with intercellular CO₂ concentration (C _i), ratio of C _i to ambient CO₂ concentration C _i/C _a, and Δ. Across all measured leaves, Δ correlated negatively with leaf water use efficiency (WUE = photosynthesis/stomatal conductance, g _s) and with g _s, but positively with C _i and C _i/C _a. The later parameters negatively correlated with leaf WUE. Across cultivars, both P _N and correlated positively with storage root yield. These results are in agreement with trends predicted by the carbon isotope discrimination model.     

Photosynthesis,Transpiration, and Water Use Efficiency of Vegetative and Reproductive Shoots of Grassland Species from North-Eastern China

The differences in net photosynthetic rate (P _N), transpiration rate (E), and water use efficiency (WUE) between the vegetative and reproductive shoots of three native grass species from the grassland of northeastern China [grey-green and yellow green populations of Leymus chinensis (Trin.) Tzvel., Puccinellia tenuiflora (Griseb) Scrib & Merr, Puccinellia chinampoensis Ohwi] were compared. The two type shoots experienced similar habitats, but differed in leaf life-span and leaf area. The leaf P _N and WUE for the vegetative shoots were significantly higher than those for the reproductive shoots in the grasses, while their E were remarked lower in the dry season. Relative lower leaf P _N and WUE for the reproductive shoots of grassland grasses may explain the facts of lower seed production and the subordinate role of seed in the grassland renewal in north-eastern China.     

Diurnal and Seasonal Patterns of Water Potential,Photosynthesis, Evapotranspiration and Water Use Efficiency of Clusterbean

Diurnal patterns of leaf water potential (_W), canopy net photosynthetic rate (P _N), evapotranspiration rate (E), canopy temperature (T_c), and water use efficiency (WUE) of clusterbean [Cyamopsis tetragonoloba (L.) Taub., cv. Desi] were studied at six phenological stages of plant development under field conditions at CCS Haryana Agricultural University, Hisar. The highest P _N, E, and WUE were observed at pod initiation stage (61 DAS). Daily maxima of P _N were usually between 11:00 to 14:00 h while those of E and WUE between 12:30 and 16:00 h. P _N was mainly dependent on photosynthetically active radiation and E on air temperature (T_a) but the relationships varied at different growth stages. WUE declined with the increase in T _a. At mid-day, _W was highest during pod initiation.     

Compensatory effects of elevated CO<Subscript>2</Subscript> concentration on the inhibitory effects of high temperature and irradiance on photosynthetic gas exchange in carrots

We determined the interactive effects of irradiance, elevated CO₂ concentration (EC), and temperature in carrot (Daucus carota var. sativus). Plants of the cv. Red Core Chantenay (RCC) were grown in a controlled environmental plant growth room and exposed to 3 levels of photosynthetically active radiation (PAR) (400, 800, 1 200 μmol m⁻² s⁻¹), 3 leaf chamber temperatures (15, 20, 30 °C), and 2 external CO₂ concentrations (C _a), AC and EC (350 and 750 μmol mol⁻¹, respectively). Rates of net photosynthesis (P _N) and transpiration (E) and stomatal conductance (g _s ) were measured, along with water use efficiency (WUE) and ratio of internal and external CO₂ concentrations (C _i/C _a). P _N revealed an interactive effect between PAR and C _a. As PAR increased so did P _N under both C _a regimes. The g _s showed no interactive effects between the three parameters but had singular effects of temperature and PAR. E was strongly influenced by the combination of PAR and temperature. WUE was interactively affected by all three parameters. Maximum WUE occurred at 15 °C and 1 200 μmol m⁻² s^{− 1} PAR under EC. The C _i /C _a was influenced independently by temperature and C _a. Hence photosynthetic responses are interactively affected by changes in irradiance, external CO₂ concentration, and temperature. EC significantly compensates the inhibitory effects of high temperature and irradiance on P _N and WUE.     

Photosynthesis,Transpiration, and Water Use Efficiency of Two Puccinellia Species on the Songnen Grassland,Northeastern China

The intra- and inter-specific variations in net photosynthetic (P _N) and transpiration (E) rates and water use efficiency (WUE) of Puccinellia tenuiflora and Puccinellia chinampoensis leaves were compared. The two species experienced a similar habitat, but differed in leaf area, leaf colour, and nitrogen contents. Leaf P _N and E for both reproductive and vegetative shoots of the two species declined with leaf age. P _N for reproductive shoots was less than for vegetative shoots, but their E was greater than that of vegetative shoots in the dry season. The average P _N and E for reproductive shoots of P. tenuiflora were lower than those of P. chinampoensis, but higher for vegetative shoots.     

Physiological divergences between two rhizomatous grasses from a desertification steppe,North China

The inter-and intra-specific physiological differences, e.g. rates of net photosynthesis (P _N) and transpiration (E), stomatal conductance (g _s), and water use efficiency (WUE), were compared between two grasses, Calamagrostis epigeios (L.) Roth. and Psammochloa villosa (Trin.) Bor., and between their leaf types in a desertification steppe in North China. The two species had a similar habitat, but differed in leaf area and rhizome depth. Leaf P _N, E, and g _s for P. villosa were significantly greater than those for C. epigeios in the growing season, but WUE for the former species was only 50 and 80 % of that for the latter one in dry and rainy seasons, respectively. In general, leaf P _N, E, g _s, and WUE for both vegetative and reproductive shoots of the two species exhibited little variations between leaf types or with leaf age, even though there were some remarkable differences between dry and rainy seasons. The mean leaf P _N and E in reproductive shoots of P. villosa were significantly lower than those in its vegetative shoots in rainy season, while these differences were much smaller for those of C. epigeios. P. villosa with deeper rhizome roots has relative higher leaf P _N, E, and g _s, but a smaller WUE in the arid desertification steppe region.     

Comparison of Photosynthetic Traits Between Two Typical Shrubs: Legume and Non-Legume in Hunshandak Sandland

In Huanshandak Sandland, China, net photosynthetic rate (P _N), transpiration rate (E), stomatal conductance (g _s), intercellular CO₂ concentration (C _i), water use efficiency (WUE), photochemical efficiency of photosystem 2 (F_v/F_m), and leaf nitrogen content were compared for Hedysarum fruticosum var. mongolicum (H.f.m.), a nitrogen fixing shrub, and Salix gordejevii (S.g.), a nitrogen non-fixing shrub. P _N, E, and g _s of the two shrubs were similar in trends, i.e. two peaks were observed in diurnal courses. However, except C _i, other parameters of H.f.m. were higher during the measured days than those of S.g. The midday depression of P _N was mainly due to decrease in stomata conductance and to reduction of F_v/F_m at midday. The higher P _N of H.f.m. was consistent with the higher leaf N content and there was a positive relation between them. In addition, several C₄ traits were found in H.f.m., i.e. high saturation irradiance and WUE, low dark respiration rate, and C _i, which partly resulted in higher P _N. This seems to indicate that the C₃ plant H.f.m. may have C₄ photosynthesis pathway or C₄ enzymes.     

Limitation of transpiration by hydraulic conductance and xylem cavitation in Betula occidentalis

The extent to which stomatal conductance (g_s) was capable of responding to reduced hydraulic conductance (k)and preventing cavitation-inducing xylem pressures was evaluated in the small riparian tree, Betula occidentalis Hook. We decreased k by inducing xylem cavitation in shoots using an air-injection technique. From 1 to 18 d after shoot injection we measured midday transpiration rate (E), g_s, and xylem pressure (Ψ_p-xylem) on individual leaves of the crown. We then harvested the shoot and made direct measurements of k from the trunk (2–3 cm diameter) to the distal tip of the petioles of the same leaves measured for E and g_s. The k measurement was expressed per unit leaf area (k_l, leaf-specific conductance). Leaves measured within 2 d of shoot injection showed reduced g_s and E relative to non-injected controls, and both parameters were strongly correlated with k_l At this time, there was no difference in leaf Ψ_p-xylem between injected shoots and controls, and leaf Ψ_p-xylem was not significantly different from the highest cavitation-inducing pressure (Ψ_p-cav) in the branch xylem (-1.43 ± 0.029 MPa, n=8). Leaves measured 7–18 d after shoots were injected exhibited a partial return of g_s and E values to the control range. This was associated with a decrease in leaf Ψ_p-xylem below Ψ_p-cav and loss of foliage. The results suggest the stomata were incapable of long-term regulation of E below control values and that reversion to higher E caused dieback via cavitation.     

Gas Exchange Responses to CO2 Concentration Instantaneously Elevated in Flag Leaves of Winter Wheat Cultivars Released in Different Years

Three winter wheat (Triticum aestivum L.) cultivars, representatives of those widely cultivated in Beijing over the past six decades, were grown in the same environmental conditions. Net photosynthetic rate (P _N) per unit leaf area and instantaneous water use efficiency (WUE) of flag leaves increased with elevated CO₂ concentration. With an increase in CO₂ concentration from 360 to 720 µmol mol^–1, P _N and WUE of Jingdong 8 (released in 1990s and having the highest yield) increased by 173 and 81 %, while those of Nongda 139 (released in 1970s) increased by 88 and 66 %, and Yanda 1817 (released in 1945, with lowest yield) by 76 and 65 %. Jingdong 8 had the highest P _N and WUE values under high CO₂ concentration, but Yanda 1817 showed the lowest P _N. Stomatal conductance (g _s) of Nongda 139 and Yanda 1817 declined with increasing CO₂ concentration, but g _s of Jingdong 8 firstly went down and then up as the CO₂ concentration further increased. Intercellular CO₂ concentration (C _i) of Jingdong 8 and Nongda 139 increased when CO₂ concentration elevated, while that of Yanda 139 increased at the first stage and then declined. Jingdong 8 had the lowest C _i of the three wheat cultivars, and Yanda 1817 had the highest C _i value under lower CO₂ concentrations. However, Jingdong 8 had the highest P _N and lowest C _i at the highest CO₂ concentration which indicates that its photosynthetic potential may be high.     

Carbon Dioxide Assimilation,Transpiration, and Leaf Conductance of Bean (Phaseolus Vulgaris L.) Under Blue and Red Radiation

In bean (Phaseolus vulgaris L.) seedlings well supplied with water, rates of transpiration (E) and CO₂ assimilation (P _N) of the primary leaves were measured under blue (BR) or red (RR) irradiance of 150 µmol(photon) m^–2 s^–1. The leaf conductance to H₂O vapour transfer (g _H2O), as well as the intercellular concentrations of H₂O vapour (e _i) and of CO₂ (C _i) were calculated. Under BR, g _H2O was significantly greater, but P _N was lower, and E similar as compared with corresponding values found under RR. The increase of stomata aperture under BR was evident although C _i was higher and e _i was lower than under RR. Results agree with the suggestion that BR directly activates guard cell metabolism and in well watered plants determines mainly the stomata aperture.     

Photosynthetic photon flux density,carbon dioxide concentration,and vapor pressure deficit effects on photosynthesis in cacao seedlings

Independent short-term effects of photosynthetic photon flux density (PPFD) of 50–400 μmol m⁻² s⁻¹, external CO₂ concentration (C _a) of 85–850 cm³ m⁻³, and vapor pressure deficit (VPD) of 0.9–2.2 kPa on net photosynthetic rate (P _N), stomatal conductance (g _s), leaf internal CO₂ concentration (C _i), and transpiration rates (E) were investigated in three cacao genotypes. In all these genotypes, increasing PPFD from 50 to 400 μmol m⁻² s⁻¹ increased P _N by about 50 %, but further increases in PPFD up to 1 500 μmol m⁻² s⁻¹ had no effect on P _N. Increasing C _a significantly increased P _N and C _i while g _s and E decreased more strongly than in most trees that have been studied. In all genotypes, increasing VPD reduced P _N, but the slight decrease in g _s and the slight increase in C _i with increasing VPD were non-significant. Increasing VPD significantly increased E and this may have caused the reduction in P _N. The unusually small response of g _s to VPD could limit the ability of cacao to grow where VPD is high. There were no significant differences in gas exchange characteristics (g _s, C _i, E) among the three cacao genotypes under any measurement conditions.     

Effect of Foliar Application of Chitin and Chitosan Oligosaccharides on Photosynthesis of Maize and Soybean

On the first day after foliar application, chitosan pentamer (CH5) and chitin pentamer (CHIT5) decreased net photosynthetic rate (P _N) of soybean and maize, however, on subsequent days there was an increase in P _N in some treatments. CH5 caused an increase in maize P _N on day 3 at 10^–5 and 10^–7 M; the increases were 18 and 10 % over the control plants. This increase was correlated with increases in stomatal conductance (g _s) and transpiration rate (E), while the intercellular CO₂ concentration (C _i) was not different from the control plants. P _N of soybean plants did not differ from the control plants except for treatment CH5 (10^–7 M) which caused an 8 % increase on day 2, along with increased g _s, E, and C _i. On days 5 and 6 the CHIT5 treatment caused a 6–8 % increase in P _N of maize, which was accompanied by increases in g _s, E, and C _i. However, there was no such increase for soybean plants treated with CHIT5. In general, foliar application of high molecular mass chitin (CHH) resulted in decreased P _N, particularly for 0.010 % treated plants, both in maize and soybean. Foliar applications of chitosan and chitin oligomers did not affect (p > 0.05) maize or soybean height, root length, leaf area, shoot or root or total dry mass.     

Influence of irradiance on photosynthesis and PSII photochemical efficiency in maize during short-term exposure at high CO<Subscript>2</Subscript> concentration

This work aimed to evaluate if gas exchange and PSII photochemical activity in maize are affected by different irradiance levels during short-term exposure to elevated CO₂. For this purpose gas exchange and chlorophyll a fluorescence were measured on maize plants grown at ambient CO₂ concentration (control CO₂) and exposed for 4 h to short-term treatments at 800 μmol(CO₂) mol⁻¹ (high CO₂) at a photosynthetic photon flux density (PPFD) of either 1,000 μmol m⁻² s⁻¹ (control light) or 1,900 μmol m⁻² s⁻¹ (high light). At control light, high-CO₂ leaves showed a significant decrease of net photosynthetic rate (P _N) and a rise in the ratio of intercellular to ambient CO₂ concentration (C _i/C _a) and water-use efficiency (WUE) compared to control CO₂ leaves. No difference between CO₂ concentrations for PSII effective photochemistry (Φ_PSII), photochemical quenching (q_p) and nonphotochemical quenching (NPQ) was detected. Under high light, high-CO₂ leaves did not differ in P _N, C _i/C _a, Φ_PSII and NPQ, but showed an increase of WUE. These results suggest that at control light photosynthetic apparatus is negatively affected by high CO₂ concentration in terms of carbon gain by limitations in photosynthetic dark reaction rather than in photochemistry. At high light, the elevated CO₂ concentration did not promote an increase of photosynthesis and photochemistry but only an improvement of water balance due to increased WUE.     

Intrinsic changes in photosynthetic parameters of carrot leaves under increasing CO<Subscript>2</Subscript> concentrations and soil moisture regimes

A controlled growth chamber experiment was conducted to investigate the short-term water use and photosynthetic responses of 30-d-old carrot seedlings to the combined effects of CO₂ concentration (50–1 050 μmol mol⁻¹) and moisture deficits (−5, −30, −55, and −70 kPa). The photosynthetic response data was fitted to a non-rectangular hyperbola model. The estimated parameters were compared for effects of moisture deficit and elevated CO₂ concentration (EC). The carboxylation efficiency (α) increased in response to mild moisture stress (−30 kPa) under EC when compared to the unstressed control. However, moderate (−55 kPa) and extreme (−70 kPa) moisture deficits reduced α under EC. Maximum net photosynthetic rate (P _Nmax) did not differ between mild water deficit and unstressed controls under EC. Moderate and extreme moisture deficits reduced P _Nmax by nearly 85 % compared to controls. Dark respiration rate (R _D) showed no consistent response to moisture deficit. The CO₂ compensation concentration (Γ) was 324 μmol mol⁻¹ for −75 kPa and ranged 63–93 μmol mol⁻¹ for other moisture regimes. Interaction between moisture deficit and EC was noticed for P _N, ratio of intercellular and ambient CO₂ concentration (C _i/C _a), stomatal conductance (g _s ), and transpiration rate (E). P _N was maximum and C _i/C _a was minimum at −30 kPa moisture deficit and at C _a of 350 μmol mol⁻¹. The g _s and E showed an inverse relationship at all moisture deficit regimes and EC. Water use efficiency (WUE) increased with moisture deficit up to −55 kPa and declined thereafter. EC showed a positive influence towards sustaining P _N and increasing WUE only under mild moisture stress, and no beneficial effects of EC were noticed at moderate or extreme moisture deficits.     

The effects of nitrogen stress on the stable carbon isotope composition, productivity and water use efficiency of white spruce (Picea glauca (Moench) Voss) seedlings

A, assimilation rate
a, fractionation against ¹³C for CO₂ diffusion through air
b, net fractionation against ¹³C during CO₂ fixation
C_a, ambient CO₂ concentration
C_c, CO₂ concentration at the chloroplast
C_i, intercellular CO₂ concentration
D, vapour pressure deficit
E_n, needle transpiration rate
E_p, whole plant water use
g_w, leaf internal transfer conductance to CO₂
g_s, stomatal conductance to water vapour
L, projected leaf area
NUE, nitrogen use efficiency
PEP, phosphoenolpyruvate
Rubisco, ribulose-1,5-biphosphate carboxylase
TDR, time domain reflectometry
WUE, water use efficiency
Δ, carbon isotope discrimination
δ¹³C, carbon isotope abundance parameter
δ¹³C_a, carbon isotopic composition of atmospheric CO₂
θ, volumetric soil water content

The effect of nitrogen stress on needle δ¹³C, water-use efficiency (WUE) and biomass production in irrigated and dry land white spruce (Picea glauca (Moench) Voss) seedlings was investigated. Sixteen hundred seedlings, representing 10 controlled crosses, were planted in the field in individual buried sand-filled cylinders. Two nitrogen treatments were imposed, nitrogen stressed and fertilized. The ranking of δ¹³C of the crosses was maintained across all combinations of water and nitrogen treatments and there was not a significant genetic versus environmental interaction. The positive relationships between needle δ¹³C, WUE and dry matter production demonstrate that it should be possible to use δ¹³C as a surrogate for WUE, and to select for increased WUE without compromising yield, even in nitrogen deficient environments. Nitrogen stressed seedlings had the lowest needle δ¹³C in both irrigated and dry land conditions. There was a positive correlation between needle nitrogen content and δ¹³C that was likely associated with increased photosynthetic capacity. There was some indication that decreased nitrogen supply led to increased stomatal conductance and hence lower WUE. There was a negative correlation between intrinsic water use efficiency and photosynthetic nitrogen use efficiency (NUE). This suggests that white spruce seedlings have the ability to maximize NUE when water becomes limited. There was significant genetic variation in NUE that was maintained across treatments. Our results suggest that in white spruce, there is no detectable effect of anaplerotic carbon fixation and that it is more appropriate to use a value of 29‰ (‘Rubisco only’) for the net discrimination against ¹³C during CO₂ fixation. This leads to excellent correspondence between values of C_i/C_a derived from gas exchange measurements or from δ¹³C.     

Gas Exchange Characteristics and Water Relations in Some Elite Okra Cultivars Under Water Deficit

Thirty-days-old plants of two cultivars of okra (Hibiscus esculentus L.), Sabzpari and Chinese-red, were subjected for 30 d to two water regimes (100 and 60 % field capacity). Leaf water potential and osmotic potential of both lines decreased significantly with the imposition of drought. Both the leaf pressure potential and osmotic adjustment were much lower in Chinese-red than those in Sabzpari. Chlorophyll (Chl) b content increased, whereas Chl a content remained unchanged and thus Chl a/b ratios were reduced in both lines. Drought stress also caused a significant reduction in net photosynthetic rate (P _N), transpiration rate (E), stomatal conductance (g _s), and water use efficiency (WUE) especially in cv. Sabzpari. The lines did not differ in intrinsic WUE (P _Ng_s) or intercellular/ambient CO₂ ratio. Overall, the growth of two okra cultivars was positively correlated with P _N, but not with g _s or P _N/E, and negatively correlated with osmotic adjustment.     

Photosynthesis Parameters in Two Cultivars of Mulberry Differing in Salt Tolerance

Three-month-old mulberry (Morus alba L.) cultivars (salt tolerant cv. S1 and salt sensitive cv. ATP) were subjected to different concentrations of NaCl for 12 d. Leaf area, dry mass accumulation, total chlorophyll (Chl) content, net CO₂ assimilation rate (P _N), stomatal conductance (g _s), and transpiration rate (E) declined, and intercellular CO₂ concentration (C _i) increased. The changes in these parameters were dependent on stress severity and duration, and differed between the two cultivars. The tolerant cultivar showed a lesser reduction in P _N and g _s coupled with a better C _i and water use efficiency (WUE) than the sensitive cultivar. This revised version was published online in June 2006 with corrections to the Cover Date.     

Triadimefon enhances growth and net photosynthetic rate in NaCl stressed plants of Raphanus sativus L.

The effect of sodium chloride and triadimefon (TDM) on the chlorophyll (Chl) content, net photosynthetic rates (P_N), rate of transpiration (E), and intercellular CO₂ concentration (C_i) in Raphanus sativus was studied. The effect of NaCl salinity was partially ameliorated by TDM which caused increase in Chl content, P_N, and C_i. TDM also increased root dry matter production, decreased E, and increased the water use efficiency. This revised version was published online in June 2006 with corrections to the Cover Date.     

Comparison of water-use efficiency and internal leaf carbon dioxide concentration in juvenile leaves and phyllodes of Acacia koa (leguminosae) from Hawaii,estimated by two methods

To gain further insight into comparative ecophysiology of different leaf types, water-use efficiency (WUE) and internal leaf carbon dioxide concentration (C_i) were estimated in the field for juvenile leaves and phyllodes of Acacia koa by carbon dioxide and water vapor exchange using a closed system infrared gas analyzer and humidity sensor, and by δ¹³C measurements. Both methods indicate that phyllodes possessed higher WUE and lower C_i than juvenile leaves. However, C_i predicted by δ¹³C for juvenile leaves and phyllodes was lower than the average gas exchange estimated values of C_i and closer to minimal gas exchange estimated values of C_i. It is suggested that δ¹³C may be influenced more during times of maximal assimilation and leaf expansion than during maintenance.     

Effect of Fruiting on Leaf Gas Exchange in Olive (Olea Europaea L.)

The effect on traits of photosynthesis and water relations of assimilate demand was studied in olive tree that has strong alternate bearing. The diurnal and seasonal leaf gas exchanges, area dry mass, and saccharide and chlorophyll (Chl) contents were measured by comparing shoots with fruit of "on-trees" (heavy fruit load) with shoots without fruit on both "on-trees" and "off-trees" (light fruit load). In spite of large seasonal and diurnal differences, leaf net photosynthetic rate (P _N), stomatal conductance (g _s), sub-stomatal CO₂ concentration (C ₁), transpiration rate (E), and respiration rate (R _D) were not significantly influenced by fruit load or by the presence or absence of fruit on the shoot. An only exception was at the beginning of July when the one-year-old leaves on shoots with fruit had slightly higher P _N and E than leaves on shoots without fruit. Water content, Chl and saccharide contents, and area dry mass of the leaf were not substantially influenced by the presence/absence of fruit on the shoot or fruit load. Hence the sink demand, associated with fruit growth, did not improve leaf photosynthetic efficiency in olive. This revised version was published online in August 2006 with corrections to the Cover Date.