Diurnal Gas Exchange and Superior Resources Use Efficiency of Typical C4 Species in Hunshandak Sandland,China

Net photosynthetic rate (P _N), transpiration rate (E), stomatal conductance (g _s), leaf water potential (ψ_leaf), leaf nitrogen content, and photosynthetic nitrogen use efficiency (PNUE) were compared between a typical C₄ plant, Agriophyllum squarrosum and a C₃ plant, Leymus chinensis, in Hunshandak Sandland, China. The plant species showed different diurnal gas exchange patterns on June 12–14 when photosynthetic photon flux density (PPFD), air temperature (T _air), and water potential were moderate. P _N, E, and g _s of A. squarrosum showed distinct single peak while those of L. chinensis were depressed at noon and had two peaks in their diurnal courses. Gas exchange traits of both species showed midday depression under higher photosynthetic photon flux density (PPFD) and T _air when Ψ_leaf was significantly low down on August 6–8. However, those of A. squarrosum were depressed less seriously. Moreover, A. squarrosum had higher P _N, Ψ_leaf, water use efficiency (WUE), and PNUE than L. chinensis. Thus A. squarrosum was much more tolerant to heat and high irradiance and could utilise the resources on sand area more efficiently than L. chinensis. Hence species like A. squarrosum may be introduced and protected to reconstruct the degraded sand dunes because of their higher tolerance to stress and higher resource use efficiency. This revised version was published online in August 2006 with corrections to the Cover Date.     

Changes of leaf water potential and gas exchange during and after drought in triticale and maize genotypes differing in drought tolerance

Influence of drought (D) on changes of leaf water potential (Ψ) and parameters of gas exchange in D-resistant and D-sensitive genotypes of triticale and maize was compared. Soil D (from −0.01 to −2.45 MPa) was simulated by mannitol solutions. At −0.013 MPa significant differences in Ψ, net photosynthetic rate (P _N), transpiration rate (E), stomatal conductance (g _s), and internal CO₂ concentration (C _i) of D-resistant and D-sensitive triticale and maize genotypes were not found. Together with the increase in concentration of the mannitol solution the impact of D on E and g _s for D-sensitive genotypes (CHD-12, Ankora) became lower than for the D-resistant ones (CHD-247, Tina). Inversely, impact of D on Ψ was higher in D-sensitive than D-resistant genotypes. From 1 to 3 d of D, a higher decrease in P _N was observed in D-resistant genotypes than in the D-sensitive ones. Under prolonged D (5–14 d) and simultaneous more severe D the decrease in P _N was lower in D-resistant than in D-sensitive genotypes. Changes in Ψ, P _N, E, and g _s caused by D in genotypes differing in the drought susceptibility were similar for triticale and maize. Compared to control plants, increase of C _i was different for triticale and maize genotypes. Hence one of the physiological reasons of different susceptibility to D between sensitive and resistant genotypes is more efficient protection of tissue water status in resistant genotypes reflected in higher decrease in g _s and limiting E compared to the sensitive ones. Other reason, observed in D-resistant genotypes during the recovery from D-stress, was more efficient removal of detrimental effects of D.     

Effects of Drought Stress Induced by Polyethylene Glycol on Pigment Content and Photosynthetic Gas Exchange of Pistacia Khinjuk and P. Mutica

The effects of drought stress induced by polyethylene glycol, PEG (molecular mass 6000) on some ecophysiological characteristics of two wild pistachio species, Mastic and Khinjuk (P. mutica and P. khinjuk) selected as root stocks for production of edible pistachio trees (P. vera) in Iran and Turkey, were studied. Net photosynthetic rate (P _N), stomatal conductance (g _s), chlorophyll (Chl) fluorescence parameters, leaf water potential (Ψ₁), leaf osmotic potential (Ψ_π), leaf osmotic adjustment (ΔΨ_π), and Chl a and b were measured. All parameters were influenced by increase in concentra-tion of PEG in the nutrient solutions. P _N, g _s, and Chl a were significantly higher in P. mutica than in P. khinjuk but, compared to the control treatment, P. khinjuk showed a higher resistance to drought stress than P. mutica. This revised version was published online in August 2006 with corrections to the Cover Date.     

Diurnal and seasonal trends in photosynthetic performance of <Emphasis Type="Italic">Dalbergia sissoo</Emphasis> Roxb. and <Emphasis Type="Italic">Hardwickia binata</Emphasis> Roxb. from a semi-arid ecosystem

Diurnal and seasonal trends in net photosynthetic rate (P _N), stomatal conductance (g), transpiration rate (E), vapour pressure deficit, temperature, photosynthetic photon flux density, and water use efficiency (WUE) were compared in a two-year-old Dalbergia sissoo and Hardwickia binata plantation. Mean daily maximum P _N in D. sissoo ranged from 21.40±2.60 μmol m⁻² s⁻¹ in rainy season I to 13.21±2.64 μmol m⁻² s⁻¹ in summer whereas in H. binata it was 20.04±1.20 μmol m⁻² s⁻¹ in summer and 13.64±0.16 μmol m⁻² s⁻¹ in winter. There was a linear relationship between daily maximum P _N and g _s in D. sissoo but there was no strong linear relationship between P _N and g _s in H. binata. In D. sissoo, the reduction in g _s led to a reduction in both P _N and E enabling the maintenance of WUE during dry season thereby managing unfavourable environmental conditions efficiently whereas in H. binata, an increase in g _s causes an increase of P _N and E with a significant moderate WUE.     

Photosynthetic response to precipitation/rainfall in predominant tree (<Emphasis Type="Italic">Ulmus pumila</Emphasis>) seedlings in Hunshandak Sandland,China

The responses of gas exchange and chlorophyll fluorescence of field-growing Ulmus pumila seedlings to changes in simulated precipitation were studied in Hunshandak Sandland, China. Leaf water potential (Ψ_wp), net photosynthetic rate (P _N), stomatal conductance (g _s), and transpiration rate (E) were significantly increased with enhancement of precipitation from 0 to 20 mm (p<0.01), indicating stomatal limitation of U. pumila seedlings that could be avoided when soil water was abundant. However, P _N changed slightly when precipitation exceeded 20 mm (p>0.05), indicating more precipitation than 20 mm had no significant effects on photosynthesis. Maximum photochemical efficiency of photosystem 2, PS 2 (F_v/F_m) increased from 0.53 to 0.78 when rainfall increased from 0 to 10 mm, and F_v/F_m maintained a steady state level when rainfall was more than 10 mm. Water use efficiency (WUE) decreased significantly (from 78–95 to 23–27 μmol mol⁻¹) with enhancement of rainfalls. P _N showed significant linear correlations with both g _s and Ψ_wp (p<0.0001), which implied that leaf water status influenced gas exchange of U. pumila seedlings. The 20-mm precipitation (soil water content at about 15 %, v/v) might be enough for the growth of elm seedlings. When soil water content (SWC) reached 10 %, down regulation of PS2 photochemical efficiency could be avoided, but stomatal limitation to photosynthesis remained. When SWC exceeded 15 %, stomatal limitation to photosynthesis could be avoided, indicating elm seedlings might tolerate moderate drought.     

Critical responses of photosynthetic efficiency of goldspur apple tree to soil water variation in semiarid loess hilly area

Goldspur apple (Malus pumila cv. Goldspur) is one of the main fruit trees planted in semiarid loess hilly areas. The photosynthetic efficiency in leaves of eight-year-old trees were studied under different soil water conditions with a Li-6400 portable photosynthesis system and a Li-Cor1600 portable steady state porometer in order to explore the effects of soil water stress on photosynthesis and the suitable soil water content (SWC) for water-saving irrigation of apple orchards. The results showed that the leaf net photosynthetic rate (P _N), transpiration rate (E), water-use efficiency (WUE), stomatal conductance (g _s), intercellular CO₂ concentration (C _i), and stomatal limiting value (L _s) displayed different threshold responses to soil water variation. When SWC was within a range of about 60%–86% of field capacity (FC), P _N and E were maintained in a relative steady state. At an elevated level but below 60% of FC, both P _N and E decreased evidently with decreasing soil moisture. The SWC needed to support WUE in a relatively steady state and at a high level was in the range of about 50%–71% of FC. When SWC was less than 48% of FC, g _s and L _s declined with decreasing soil moisture, while C _i increased rapidly. Based on the analysis of the stomatal limitation of photosynthesis using two criteria (C _i and L _s) suggested by Farquhar and Sharkey, it was implied that the predominant cause of restricting P _N had changed from stomatal limitation to nonstomatal one under severe water stress. In terms of water-saving irrigation for enhancing water-use efficiency, it was concluded that in semiarid loess hilly areas, the suitable range of SWC for water-saving irrigation in goldspur apple orchards is in the range of about 50%–71% of FC, and the most severe degree of soil water stress tolerated for photosynthesis is about 48% of FC.     

Biomass Partitioning and Gas Exchange in Dalbergia sissoo seedlings under water stress

Biomass, leaf water potential (_l), net photosynthetic rate (P _N), transpiration rate (E), stomatal conductance (g _s), leaf to air temperature difference (T _diff), and instantaneous water use efficiency (WUE) were measured in the seedlings of Dalbergia sissoo Roxb. grown under irrigation of 20 (W₁), 14 (W₂), 10 (W₃), and 8 (W₄) mm. Treatments were maintained by re-irrigation when water content of the soil reached 7.4% in W₁, 5.6% in W₂, 4.3% in W₃, and 3.2% in W₄. Seedlings in a control (W₅) were left without irrigation after maintaining the soil field capacity (10.7%). Seedlings of W₁ had highest biomass that was one tenth in W₅. Biomass allocation was highest in leaf in W₂ and in root in W₄ and W₅ treatments. Difference between predawn leaf water potential (_Pd) and midday (_mid) increased with soil water stress and with vapour pressure deficit (VPD) in April and May slowing down the recovery in plant leaf water status after transpiration loss. P _N, E, and g _s declined and T _diff increased from W₁ to W₅. Their values were highly significant in April and May for the severely stressed seedlings of W₄ and W₅. P _N increased from 08:00 to 10:00 and E increased until 13:00 within the day for most of the seedlings whereas g _s decreased throughout the day from 08:00 to 17:00. P _N and E were highest in March but their values were low in January, February, April, and May. Large variations in physiological variables to air temperature, photosynthetically active radiation, and vapour pressure deficit (VPD) indicated greater sensitivity of the species to environmental factors. WUE increased from W₁ to W₂ but decreased drastically at high water stress particularly during hot summer showing a kind of adaptation in D. sissoo to water stress. However, low biomass and reduced physiological functions at <50% of soil field capacity suggest that this species does not produce significant biomass at severe soil water stress or drought of a prolonged period.     

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.     

Gas Exchange,Photochemical Efficiency,and Leaf Water Potential in Three Salix Species

Gas exchange, photochemical efficiency, and leaf water potential (_l) of Salix matsudana (non-indigenous species), S. microstachya and S. gordejevii (indigenous species) were studied in Hunshandak Sandland, China. _l of all the three species decreased from 06:00 to 12:00, and increased afterwards. S. matsudana showed higher values of _l than others. Net photosynthetic rate (P _N) and stomatal conductance (g _s) of S. matsudana were the lowest among all, with the maximum P _N at 10:00 being 75% of that of S. gordejevii. Compared with the indigenous species, the non-indigenous S. matsudana had also lower transpiration rate (E) and water use efficiency (WUE). The values of F_v/F_m in all the species were lower from 06:00 to 14:00 than those after 14:00, indicating an obvious depression in photochemical efficiency of photosystem 2 in both non-indigenous and native species. However, it was much more depressed in S. matsudana, the non-indigenous tree. P _N was positively correlated to g _s and negatively related to _l. The relationship between g _s and vapour pressure difference (VPD) was exponential, while negative linear correlation was found between g _s and _l.     

Effect of NaCl salinity on photosynthetic rate,transpiration rate,and oxidative stress tolerance in contrasting wheat genotypes

Wheat (Triticum aestivum L.) genotypes K-65 (salt tolerant) and HD 2329 (salt sensitive) were grown in pots under natural conditions and irrigated with NaCl solutions of electrical conductivity (ECe) 4.0, 6.0, and 8.0 dS m⁻¹. Control plants were irrigated without saline water. Observations were made on the top most fully expanded leaf at tillering, anthesis, and grain filling stages. The net photosynthetic rate (P _N), stomatal conductance (g _s), and transpiration rate (E) were reduced with the addition of NaCl. The reduction was higher in HD 2329 than in K-65. Salinity enhanced leaf to air temperature gradient (ΔT) in both the genotypes. NaCl increased the activities of superoxide dismutase (SOD) and peroxidase (POX); the percent increment was higher in K-65. The sodium and potassium contents were higher in the roots and leaves of K-65 over HD 2329. Thus at cellular level K-65 has imparted salt tolerance by manipulating P _N, E, g _s, and K accumulation in leaves along with overproduction of antioxidative enzyme activities (SOD and POX).     

Gas exchanges of an endangered species Syringa pinnatifolia and a widespread congener S. oblata

Net photosynthetic rate (P _N), transpiration rate (E), water use efficiency (WUE), stomatal conductance (g _s), and stomatal limitation (L_s) were investigated in two Syringa species. The saturation irradiance (SI) was 400 µmol m^-2s^-1 for S. pinnatifolia and 1 700 µmol m^-2s^-1 for S. oblata. Compared with S. oblata, S. pinnatifolia had extremely low g_s. Unlike S. oblata, the maximal photosynthetic rate (P _max) in S. pinnatifoliaoccurred around 08:00 and then fell down, indicating this species was sensitive to higher temperature and high photosynthetic photon flux density. However, such phenomenon was interrupted by the leaf development rhythms before summer. A relatively lower P _N together with a lower leaf area and shoot growth showed the capacity for carbon assimilation was poorer in S. pinnatifolia.This revised version was published online in March 2005 with corrections to the page numbers.     

Photosynthesis and the Enzymes of Photosynthetic Carbon Reduction Cycle in Mulberry During Water Stress and Recovery

Net photosynthetic rate (P _N), stomatal conductance (g _S), transpiration rate (E), intercellular CO₂ concentration (C _i), leaf water potential (_w), leaf area, chlorophyll (Chl) content, and the activities of photosynthetic carbon reduction cycle (PCR) enzymes in two mulberry (Morus alba L.) cultivars (drought tolerant Anantha and drought sensitive M-5) were studied during water stress and recovery. During water stress, P _N, g _S, and E declined whereas C _i increased. P _N, g _S, and E were less affected in Anantha than in M-5, which indicates tolerance nature of Anantha over M-5. Activities of ribulose-5-phosphate kinase, NAD- and NADP-glyceraldehyde-3-phosphate dehydrogenases, and 3-phosphoglycerate kinase decreased with increasing stress in both the cultivars. The enzyme activities less affected in tolerant (Anantha) than in sensitive cultivar (M-5) were restored after re-watering to almost initial values in both the cultivars. Re-watering of the plants led to an almost complete recovery of P _N, E, and g _S, indicating that a short-term stress brings about reversible effect in these two cultivars of mulberry.     

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.     

Determinant of photosynthetic capacity in rice leaves under ambient air conditions

At the grain-filling stage, net photosynthetic rate (P _N), stomatal conductance (g _s), and ribulose-1,5-bisphosphate carboxylation efficiency (CE) were correlated in order to find the determinant of photosynthetic capacity in rice leaves. For a flag leaf, P _N in leaf middle region was higher than in its upper region, and leaf basal region had the lowest P _N value. The differences in g _s and CE were similar. P _N, g _s, and CE gradually declined from upper to basal leaves, showing a leaf position gradient. The correlation coefficient between P _N and CE was much higher than that between P _N and g _s in both cases, and P _N was negatively correlated with intercellular CO₂ concentration (C _i). Hence the carboxylation activity or activated amount of ribulose-1,5-bisphosphate carboxylase/oxygenase rather than g_s was the determinant of the photosynthetic capacity in rice leaves. In addition, in flag leaves of different tillers P _N was positively correlated with g _s, but negatively correlated with C _i. Thus g _s is not the determinant of the photosynthetic capacity in rice leaves.The study was supported by the State Key Basic Research and Development Plan (No.G1998010100).     

Growth and Leaf Gas Exchange Characteristics in Dalbergia sissoo Roxb. and D. latifolia Roxb. Under Water Deficit

Forty two-month-old plants of Dalbergia sissoo and D. latifolia were subjected for 56 d to water deficit induced by withholding water. Drought stress caused a significant reduction in plant height, stem diameter, net photosynthetic rate (P _N), transpiration rate (E), and stomatal conductance (g _s) in both species, but the reduction was greater in D. sissoo than in D. latifolia. Water use efficiency (P _N/E) was adversely affected due to water stress only in D. latifolia, and intrinsic water use efficiency (P _N/g _s) was increased in both species. There was a slight effect of water stress on variable to maximum fluorescence (F_v/F_m) (quantum yield of photosystem 2) in both species, but the species did not differ significantly in this attribute.     

Leaf Gas Exchange and Water Relations of Grapevines Grown in Three Different Conditions

Diurnal and seasonal changes in the leaf water potential (), stomatal conductance (g _s), net CO₂ assimilation rate (P _N), transpiration rate (E), internal CO₂ concentration (C _i), and intrinsic water use efficiency (P _N/g _s) were studied in grapevines (Vitis vinifera L. cv. Touriga Nacional) growing in low, moderate, and severe summer stress at Vila Real (VR), Pinhão (PI), and Almendra (AL) experimental sites, respectively. In VR and PI site the limitation to photosynthesis was caused more by stomatal limitations, while in AL mesophyll limitations were also responsible for the summer decline in P _N.     

Tolerance to Water Stress in Tomato Cultivars

The effects of plant water stress imposed at vegetative, flowering, and fruiting stages of four cultivars of tomato (Lycopersicon esculentum Mill.) on net photosynthetic rate (P _N), stomatal conductance (g _s), transpiration rate (E), osmotic adjustment, and crop water stress index (CWSI) were investigated. Osmotic adjustment was the highest in cv. Arka Meghali, followed by cv. RFS-1. CWSI was lowest in cv. Arka Meghali and highest in cv. Pusa Ruby. Significant reduction in g _s, E, and P _N was observed in all the cultivars. The maximum reduction in E was observed in cv. Arka Saurabh during the fruiting stage (62.4 %) and maximum reduction in P _N at the flowering stage in Pusa Ruby (53.1 %). Maximum P _N was observed in Arka Meghali under water stress. The values of internal CO₂ concentration (C _i) did not follow the decrease in g _s which might be taken as an indication of mesophyll (non-stomatal) limitation to P _N. Magnitude of P _N decrease accompanying g _s reductions varied in the four cultivars. Arka Meghali which had highest rate of gas exchange efficiency (P _N/g _s) under water deficits can be recommended for rainfed cultivation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Photosynthesis and Growth Responses of Parthenocissus quinquefolia (L.) Planch to Soil Water Availability

Photosynthesis and growth characteristics of Parthenocissus quinquefolia were measured under differing soil water availability within a pot. Decreased soil moisture significantly reduced the leaf relative water content (RWC) and the above- and below-ground biomass. However, more biomass was allocated to the root than to the leaf. Net photosynthetic rate (P _N), stomatal conductance (g _s), and transpiration rate (E) were also significantly decreased but water use efficiency (WUE) was increased. Midday depressions in P _N and g _s were not evident for the well-irrigated plants. With the lower water availability, midday reductions in P _N and g _s were much more marked and the duration of the depression was longer. Additionally, the P _N-irradiance response curves also indicated that water supply affected photosynthesis capacity. The growth and photosynthetic response of P. quinquefolia to water supply indicated that this species could resilient to water availabilities and adapt to Hunshandak conditions very well.     

Biomass partition,leaf gas exchange and water relations of alfalfa and milkvetch seedlings in response to soil drying

This study compared physiological and growth responses to water stress of two legume species during the seedling stage. Potted alfalfa (Medicago sativa L. cv. Algonquin) and milkvetch (Astragalus adsurgens Pall. cv. Pengyang earlymaturing vetch) seedlings were grown under well-watered [soil water content (SWC) maintained at 14.92% daily] or water-stressed conditions (drying) for 15 days. Net photosynthetic rate (P _N), transpiration rate (E) and stomatal conductance (g _s) of both species decreased parabolically. When SWC decreased to 7.2% and 10.3%, g _s values for alfalfa and milkvetch were significantly different from those of the respective well-watered plants (p<0.05). When SWC decreased to 6.6% for alfalfa and 6.8% for milkvetch, leaf water potentials (ψ_L) were significantly different from those of the well-watered plants (p<0.05). Thus the difference between the SWC thresholds for a nonhydraulic root signal (nHRS) and a hydraulic root signal (HRS) were 0.6% and 3.5% for alfalfa and milkvetch, respectively. Milkvetch had a lower g _s than alfalfa for a given SWC (p<0.05). Although alfalfa seedlings had a higher dry mass (DM) and root:shoot ratio (R/S) than milkvetch in both treatments (p<0.05), we concluded that milkvetch seedlings had greater drought tolerance than alfalfa.     

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.