Differential responses of leaf water-use efficiency and photosynthetic nitrogen-use efficiency to fertilization in Bt-introduced and conventional rice lines

Leaf stomatal conductance (g _s), transpiration rate (E), and light-saturated net photosynthetic rate (P _Nmax) at three developmental stages (tillering stage, jointing-booting stage, and milking stage) and leaf total nitrogen concentration (LTNC) and δ¹³C value at milking stage were measured for a conventional rice line (Minghui 63) and its corresponding Bacillus thuringiensis (Bt)-gene [cry1A (b and c)] introduced line (Bt line) under three fertilizer levels. Compared to conventional line, Bt line showed lower g _s, which was associated with lower P _Nmax and E, but instantaneous water-use efficiency (WUE), measured as the ratio of P _Nmax to E, was higher in the Bt line than in the conventional line, particularly in the jointing-booting stage. However, δ¹³C values were not significantly different across treatments, suggesting that intrinsic water-use efficiency (WUE_in) might be indistinguishable between Bt and conventional lines. LTNC was higher but P _Nmax was lower in Bt line compared to conventional line, resulting in significantly lower photosynthetic nitrogen-use efficiency (PNUE). This might result from the additional cost of producing Bt protein in the Bt line due to the effect of competing nitrogen with photosynthetic machinery. Bt-gene introduction and expression does not significantly change WUE_in but may significantly decrease leaf PNUE. Thus we suggest that Bt rice should be carefully examined in relation to environmental risks (e.g. water-body pollution) before planting commercially.     

Variations of leaf morphology,photosynthetic traits and water-use efficiency in Western-Mediterranean tomato landraces

Modern tomato (Solanum lycopersicum L.) breeding has mainly focused on increasing productivity under unlimited watering. In contrast, some Mediterranean accessions have been traditionally cultivated under water shortage and selected on the basis of their water-use efficiency (WUE). Ramellet and Penjar landraces were planted with other traditional, old and modern inbreeds, under full irrigation. In order to found differences between the tomato accessions, gas-exchange and leaf morphology measurements were performed. Despite high variability, Ramellet and Penjar presented clear differences compared to modern cultivars, mostly related to leaf morphology and photosynthetic traits, while no differences were found in WUE. Results highlighted that better leaf CO₂ conductance might be a main factor determining the improvement of net CO₂ assimilation and WUE.     

Population differences in water-use efficiency of Eucalyptus microtheca seedlings under different watering regimes

Gas exchange, water-use efficiency (WUE), carbon isotope composition ( Δ ¹³C) and growth traits were compared among 5 populations of Eucalyptus microtheca F. Muell. Seedlings grown from seed collected across the natural distribution of the species were maintained under water-stressed and well-watered conditions. Gas exchange was measured in terms of net photosynthesis (A) and transpiration (E); WUE was measured in terms of instantaneous water-use efficiency (WUE_i) and transpiration efficiency (WUE_T); growth traits were measured in terms of total biomass (TB), root/shoot ratio (RS), and specific leaf area density (DEN). Significant differences in all traits were detected among the populations. Overall population variation was 1.68–2.50 and 1.48–2.26 μmol CO₂ uptake per mmol H₂O transpired (WUE_i), 1.97–3.04 and 1.64–2.36 g dry matter accumulation per kg water transpired (WUE_T), and Δ ¹³C was −28.81 to −26.75‰ and −30.56 to −30.04‰ under the water-stressed and well-watered conditions, respectively. In addition, WUE_i, WUE_T and Δ ¹³C were significantly correlated with A, E, RS, DEN and TB. The study indicated that measurement of WUE may be a useful trait for selecting genotypes with improved drought adaptation and biomass productivity under different environmental conditions.     

Divergent patterns of photosynthetic phosphorus-use efficiency versus nitrogen-use efficiency of tree leaves along nutrient-availability gradients

1.  Nitrogen (N) and phosphorus (P) are essential nutrients for photosynthetic carbon assimilation and most frequently limit primary productivity in terrestrial ecosystems. Efficient use of those nutrients is important for plants growing in nutrient-poor environments.
2.  We investigated the pattern of photosynthetic phosphorus-use efficiency (PPUE) in comparison with photosynthetic nitrogen-use efficiency (PNUE) along gradients of P and N availability across biomes with 340 tree and shrub species. We used both total soil N and P concentration and foliar N/P ratios for indicating nutrient-availability gradients.
3.  Photosynthetic phosphorus-use efficiency increased with greater leaf mass per area (LMA) toward decreasing P availability. By contrast, PNUE decreased with greater LMA towards decreasing N and P availability.
4.  The increase in PPUE with decreasing P availability was caused by the net effects of a relatively greater reduction in foliar P concentration and a relatively constant photosynthetic carbon assimilation rate. The decrease in PNUE with decreasing N availability was caused by the effects of a reduction in photosynthetic carbon assimilation rate with greater LMA.
5. Synthesis . Our results suggest that higher PPUE may be an effective leaf-level adaptation to P-poor soils, especially in tropical tree species. Future research should focus on the difference between PPUE and PNUE in relation to leaf economics, physiology and strategy.     

Significance of mesophyll conductance for photosynthetic capacity and water-use efficiency in response to alkaline stress in Populus cathayana seedlings

Cuttings of Populus cathayana were exposed to three different alkaline regimes (0, 75, and 150 mM Na₂CO₃) in a semicontrolled environment. The net photosynthesis rate (P _N), mesophyll conductance (g _m), the relative limitations posed by stomatal conductance (L _s) and by mesophyll conductance (L _m), photosynthetic nitrogen-use efficiency (PNUE), carbon isotope composition (δ¹³C), as well as specific leaf area (SLA) were measured. P _N decreased due to alkaline stress by an average of 25% and g _m decreased by an average of 57%. Alkaline stress caused an increase of L _m but not L _s, with average L _s of 26%, and L _m average of 38% under stress conditions. Our results suggested reduced assimilation rate under alkaline stress through decreased mesophyll conductance in P. cathayana. Moreover, alkaline stress increased significantly δ¹³C and it drew down CO₂ concentration from the substomatal cavities to the sites of carboxylation (C _i-C _c), but decreased PNUE. Furthermore, a relationship was found between PNUE and C _i-C _c. Meanwhile, no correlation was found between δ¹³C and C _i/C _a, but a strong correlation was proved between δ¹³C and C _c/C _a, indicating that mesophyll conductance was also influencing the ¹³C/¹²C ratio of leaf under alkaline stress.     

Quantitative trait loci for water-use efficiency in barley (Hordeum vulgare L.) measured by carbon isotope discrimination under rain-fed conditions on the Canadian Prairies

Barley (Hordeum vulgare L.) yield is commonly limited by low rainfall and high temperature during the growing season on the Canadian Prairies. Empirical knowledge suggests that carbon isotope discrimination (Δ(13)C), through its negative relationship with water-use efficiency (WUE), is a good index for selecting stable yielding crops in some rain-fed environments. Identification of quantitative trait loci (QTL) and linked markers for Δ(13)C will enhance its use efficiency in breeding programs. In the present study, two barley populations (W89001002003?×?I60049 or W?×?I, six-row type, and Merit?×?H93174006 or M?×?H, two-row type), containing 200 and 127 recombinant inbred lines (RILs), were phenotyped for leaf Δ(13)C and agronomic traits under rain-fed environments in Alberta, Canada. A transgressive segregation pattern for leaf Δ(13)C was observed among RILs. The broad-sense heritability (H (2)) of leaf Δ(13)C was 0.8, and there was no significant interaction between genotype and environment for leaf Δ(13)C in the W?×?I RILs. A total of 12 QTL for leaf Δ(13)C were detected in the W?×?I RILs and 5 QTL in the M?×?H RILs. For the W?×?I RILs, a major QTL located on chromosome 3H near marker Bmag606 (9.3, 9.4 and 10.7?cM interval) was identified. This major QTL overlapped with several agronomic traits, with W89001002003 alleles favoring lower leaf Δ(13)C, increased plant height, and reduced leaf area index, grain yield, harvest index and days to maturity at this locus or loci. This major QTL and its associated marker, when validated, maybe useful in breeding programs aimed at improving WUE and yield stability of barley on the Canadian Prairies.     

Carbon isotope discrimination and water-use efficiency of six crops grown under wet and dryland conditions

Mustard (Sinapis alba L.), Argentine canola (Brassica napus L. cv. Westar), Polish canola (Brassica campestris L. cv. Tobin), pea (Pisum sativum L.), durum wheat (Triticum durum L. cv. Kyle) and soft wheat (Triticum aestivum L. cv. Fielder) were grown at Outlook, Saskatchewan, Canada, under irrigated and dryland conditions. Carbon isotope discrimination (Δ) and water-use efficiency (W), defined as grams of above ground dry matter produced per kilogram water used, were negatively correlated in the six field-grown crops. In irrigated plants Δ remained relatively constant (20–21‰) throughout the growing season. However, in dryland plants, Δ declined in response to the progressive depletion of stored soil water (Polish canola, 20-2-18-8‰; mustard, 19.9–18 5‰; pea, 19.9–17 2‰ durum wheat, 19.7–16.4‰; Argentine canola, 19.4–17.6‰; soft wheat, 19.0–17.4‰). Although there were genetic differences in Δ among the species, water availability was the major factor controlling Δ.     

Benefit, cost and water-use efficiency of arbuscular mycorrhizal durum wheat grown under drought stress

 Arbuscular mycorrhizal fungi (AMF) living symbiotically with host plants enhance plant growth by improving the acquisition of mineral nutrients and water relations. This study determined the effects of AMF inoculation on growth, benefit/cost and water-use efficiency (grams dry matter produced per kilogram water evapotranspired) in two durum wheat genotypes (drought sensitive and drought tolerant) under water-stressed and well-watered conditions. Plants were grown in a low-P silty clay (Typic Xerochrept) soil mix in a greenhouse. Shoot and root dry matter (DM) and root AMF colonization were higher for well-watered than for water-stressed plants. The mycorrhizal plants were more water-use efficient than nonmycorrhizal plants. Shoot DM differences between mycorrhizal and nonmycorrhizal plants represent the benefit derived by plants from AMF-root associations. Shoot DM differences between mycorrhizal and nonmycorrhizal plants under similar conditions of water treatment represent the cost to the plant of AMF-root associations. Values of benefit/cost for AMF-root associations were highest when plants were water-stressed and decreased under well-watered conditions. Genotypic differences in calculated costs and benefits were pronounced. Benefit/cost analysis may be helpful in evaluating host plant genotypes in order to optimize efficiencies of AMF symbiosis under different environmental conditions. Accepted: 4 April 1998     

Carbon isotope composition,water-use efficiency and biomass productivity of Eucalyptus microtheca populations under different water supplies

Variation in carbon isotope composition (δ¹³C), water-use efficiency (WUE) and biomass productivity were compared among three populations of Eucalyptus microtheca F. Muell. in a greenhouse. Seedlings were maintained under one well-watered (Control, keeping the soil at field capacity) and two different water deficit conditions (Drought stress I, keeping the same soil water content; Drought stress II, keeping the same soil water supply). In each treatment, significant population differences in δ¹³C, WUE, and dry matter accumulation and allocation were detected. A negative correlation between WUE and biomass productivity was detected under control and drought stress I, but a positive correlation under drought stress II. The results suggested that there were different water-use strategies among the populations, the southeastern population with lower WUE may employ a prodigal water-use strategy, whereas the northwestern and central populations with higher WUE may employ a conservative water-use strategy. This knowledge may be useful as criteria for genotype selection within a breeding program for this species. This revised version was published online in June 2006 with corrections to the Cover Date.     

Types of photosynthetic gas exchange of leaves of beet and maize in relation to the CO2 regimes in their crop stands

A close correlation has been established between peculiar features of carbon dioxide exchange of leaves of maize (C₄-plant) and beet (C₃-plant), the types of phytocenoses formed by these plants, and the CO₂ regimes in these phytocenoses.     

Comparative water-use efficiency of Sporobolus arabicus and Leptochloa fusca and its relation with carbon-isotope discrimination under semi-arid conditions

Water-use efficiency (WUE) of Leptochloa fusca (L.) Kunth (Kallar grass) and Sporobolus arabicus Boiss. was determined under different soil moisture regimes. Plants grown in lysimeters were subjected to three soil moisture regimes, viz. well-watered (100%), medium-watered (75%), and low-watered (50%) of total available water (TAW). The soil moisture was restored on alternate days by adding the required volume of water on the basis of neutron moisture meter readings taken from neutron access tubes installed in each lysimeter. The grasses were harvested after suitable intervals (4 months) to obtain maximum biomass. Leaf samples collected at each harvest were analyzed for carbon-isotope discrimination (¹³C) with an isotope ratio (¹³C/¹²C) mass spectrometer. Results indicated significant differences in WUE of both grasses subjected to different water regimes. Sporobolus arabicus showed higher WUE than Kallar grass. However, Kallar grass showed better value of yield response factor (k _y = 0.649) compared with Sporobolus (k _y = 1.06) over the entire season. The data confirm that these grasses can be grown successfully in water-limited environments by selecting an optimum soil moisture level for maximum biomass production. The mean carbon-isotope discrimination (¹³C) of Kallar grass (–14.4) and Sporobolus (–12.8) confirm that both are C₄ plants. The carbon-isotope discrimination () was significantly and negatively correlated with WUE of the two species studied. The results of the present study confirm that ¹³C or of leaves can be used as good predictor of WUE in some C₄ plants.     

Species diversity improves the efficiency of mercury-reducing biofilms under changing environmental conditions

Six mercury-resistant environmental proteobacterial isolates and one genetically modified mercury-resistant Pseudomonas putida strain were analyzed for physiological traits of adaptive relevance in an environment of packed-bed bioreactors designed for the decontamination of mercury-polluted chlor-alkali wastewater. The strains displayed characteristic differences in each trait (i.e., biofilm formation capability, growth rate in mercury contaminated wastewaters, and mercury reduction efficiency). Subsequently, they were immobilized either as a monoculture or as a mixed culture on porous carrier material in packed-bed bioreactors through which different batches of filter-sterilized industrial chlor-alkali wastewater were pumped. In monospecies bioreactors, the mercury retention efficiency was sensitive to rapidly increasing mercury concentrations in the wastewater. Mixed culture biofilms displayed a high mercury retention efficiency that was not affected by rapid increases in mercury or continuously high mercury concentrations. The dynamic in the community composition of the mixed culture bioreactors was determined by ribosomal intergenic spacer polymorphism analysis. Mercury-mediated selective pressure decreased the number of prevalent strains. Microbial diversity was completely restored after easing of the selective pressure. Microbial diversity provides a reservoir of strains with complementary ecological niches that results in a superior bioreactor performance under changing environmental conditions.     

Inhibition of photosynthetic activities under slow water stress measured in vivo by the photoacoustic method

A slow water stress over several days was imposed on tobacco plants (Nicotiana tabacum L. var. Xanthi) by withholding water from the soil. Photosynthesis was measured in leaves from those water-stressed plants by the photoacoustic method. Slow drought induced marked changes in the photoacoustic signals, which were largely similar to those observed previously in leaves subjected to rapid desiccation in air (over 3–4 h), reflecting two simultaneous changes: 1) Modification of the heat and oxygen diffusion characteristics of the leaves due to changes in their anatomical structure [shown by the change in the slope of the plot of the oxygen (A_OX) to photothermal signal (A_PT) ratio vs the square root of the modulation frequency]; 2) Inhibition of gross photosynthesis measured by the extrapolation of the A_OX/A_PT ratio to zero frequency. However, in contrast to rapid water stress in detached leaves, where it was shown that mainly the oxidizing side of photosystem II (PS II) was damaged, we found a slower and more complex phenomenology having largely biphasic kinetics. During the first 6 days, there was a strong reduction in the photochemical energy storage, but the inhibition of oxygen evolution was relatively mild. The Emerson enhancement in state 1 dropped considerably, indicating lowering of the apparent absorption cross-section of PS II. Fluorescence measurements suggest that PS II reaction center itseIf may be the primary site of the damage. PS I activity, judged by cytochrome f photooxidation, remained largely intact. The subsequent days were associated with a further spectacular decrease in the oxygen evolution quantum yield with both photosystems damaged. The photochemical energy storage continued to decrease further. The Emerson enhancement ratio of the remaining activities in both State 1 and 2 showed a marked increase, indicating the reestablishment of a strong imbalance in the distribution of excitation energy within the photochemical apparatus in favor of PS II. All the photoacoustic changes observed in response to drought were completely reversible within 2–3 days upon rewatering of the soil.     

Canopy and leaf photosynthetic characteristics and water use efficiency of sweet sorghum under drought stress

The objective of this paper was to examine the relationship between Water Use Efficiency (WUE) at the canopy and leaf levels, to determine soil moisture conditions, which can optimize yield, and WUE of sweet sorghum (Sorghum bicolor (Linn.) Moench), thus providing some theoretical foundation for using marginal land effectively and developing production of sweet sorghum. Three levels of soil moisture conditions were established, and photosynthetic characteristics and yield were measured. The canopy apparent photo-synthetic rate (CAP) and leaf photosynthetic rate (P _N) were reduced gradually with increased drought stress, and the CAP was lower than the P _N under every soil moisture conditions. The P _N had a midday depression phenomenon, but the CAP did not exhibit this midday depression phenomenon under severe drought stress. The linear regression relationship of CAP and P _N was CAP = 1.5945 + 0.1496 P _N. The canopy apparent WUE_C and leaf WUE_L were the highest under moderate drought stress. The first was 5.3 and 5.8 times higher than the WUE_L in mid-July and late August, respectively. The stem fresh biomass yield was 77 tons/ha under moderate drought stress and WUE of aboveground biomass yield (WUE_B) was also the highest. Our results showed that moderate drought stress did not result in a significant reduction in biomass yield but increased WUE significantly.     

Relationship of photosynthetic efficiency and seed-setting rate in two contrasting rice cultivars under chilling stress

Low temperature during the vegetative stage affects rice (Oryza sativa L.) seed-setting rate in Heilongjiang province at Northeast China. However, little is known about changes of the photosynthetic rate and physiological response in contrasting rice cultivars during chilling periods. In this study, two rice cultivars with different chilling tolerance were treated with 15°C from June 27 to July 7. The chilling-susceptive cultivar, Longjing11 (LJ11), showed a significant decrease in a ripening rate and seed-setting rate after being treated for four days, whilst chilling-tolerant cultivar, Kongyu131 (KY131), was only slightly affected after 4-d treatment. The photosynthetic activities, chlorophyll contents, and antioxidative enzyme activities in LJ11 decreased significantly along with the chilling treatment. The decrease in ß-carotene contents might play a role as it could cause direct photooxidation of chlorophylls and lead to the inhibition of the photosynthetic apparatus. In the meantime, no significant damage was found in leaves of KY131 from June 27 to July 11. In conclusion, the chilling-tolerance mechanism of rice is tightly related to the photosynthetic rate, metabolism of reactive oxygen species, and scavenging system in the vegetative stage.     

Chilling and photosynthetic productivity of field grown maize (Zea mays); changes in the parameters of the light-response curve,canopy leaf CO2 assimilation rate and crop radiation-use efficiency

The effect of growth temperatures on the photosynthetic performance of field grown maize (Zea mays cv. LG11) was examined for crops sown on 1 May and 28 June 1991. During the period of growth, 2 May to 10 August, the early-sown crop experienced temperatures below 10 °C on 33 occasions compared with only one for the crop sown on 28 June. The prolonged period of low temperatures throughout May and beginning of June were associated with a marked depression in CO₂ assimilation rates at all light levels in the early-sown treatment. Chill-induced depression of the photosynthetic light-response curve reflected a sustained reduction in canopy leaf photosynthesis and crop radiation-use efficiency (RUE). During the early stages of growth, RUE was 65% lower in the early- than late-sown treatment, with no marked recovery observed in the former treatment until approximately three weeks after chilling conditions had ceased. Data show a close correlation between chill-induced depression of quantum yield () and RUE, with corresponding reductions in the light-saturated rates of CO₂ assimilation (P_max). The convexity of the light-response curve recovered most rapidly from chilling temperatures, and at least three weeks before any improvement in RUE. It is concluded that photosynthetic productivity of immature maize stands is less sensitive to changes in the convexity of the light response, than to changes in either or P_max.     

The role of mycorrhizae and plant growth promoting rhizobacteria (PGPR) in improving crop productivity under stressful environments

Both biotic and abiotic stresses are major constrains to agricultural production. Under stress conditions, plant growth is affected by a number of factors such as hormonal and nutritional imbalance, ion toxicity, physiological disorders, susceptibility to diseases, etc. Plant growth under stress conditions may be enhanced by the application of microbial inoculation including plant growth promoting rhizobacteria (PGPR) and mycorrhizal fungi. These microbes can promote plant growth by regulating nutritional and hormonal balance, producing plant growth regulators, solubilizing nutrients and inducing resistance against plant pathogens. In addition to their interactions with plants, these microbes also show synergistic as well as antagonistic interactions with other microbes in the soil environment. These interactions may be vital for sustainable agriculture because they mainly depend on biological processes rather than on agrochemicals to maintain plant growth and development as well as proper soil health under stress conditions. A number of research articles can be deciphered from the literature, which shows the role of rhizobacteria and mycorrhizae alone and/or in combination in enhancing plant growth under stress conditions. However, in contrast, a few review papers are available which discuss the synergistic interactions between rhizobacteria and mycorrhizae for enhancing plant growth under normal (non-stress) or stressful environments. Biological interactions between PGPR and mycorrhizal fungi are believed to cause a cumulative effect on all rhizosphere components, and these interactions are also affected by environmental factors such as soil type, nutrition, moisture and temperature. The present review comprehensively discusses recent developments on the effectiveness of PGPR and mycorrhizal fungi for enhancing plant growth under stressful environments. The key mechanisms involved in plant stress tolerance and the effectiveness of microbial inoculation for enhancing plant growth under stress conditions have been discussed at length in this review. Growth promotion by single and dual inoculation of PGPR and mycorrhizal fungi under stress conditions have also been discussed and reviewed comprehensively.     

The influence of phosphate and crop species on endogone spores and vesicular-arbuscular mycorrhiza under field conditions

Summary The numbers of Endogone spores (mainly of the laminate type) and the amount of vesicular-arbuscular (VA) mycorrhiza were examined in field soil given different phosphate treatments and planted with a rotation of potatoes, barley and swedes. Most spores usually occurred in barley and potato plots given intermediate amounts of phosphate, and there was most VA infection in barely and potato roots from plots given least phosphate. The effects of phosphate were much less marked than those reported for nitrogen under field conditions. Swede roots were not infected. In pot experiments swede seedlings inoculated with Endogone did not become mycorrhizal and they inhibited mycorrhizal development in seedlings of onion, which is normally a strongly mycorrhizal plant.