Effects of foliar application of nitrogen on the photosynthetic performance and growth of two fescue cultivars under heat stress

The effects of nitrogen fertilization on the growth, photosynthetic pigment contents, gas exchange, and chlorophyll (Chl) fluorescence parameters in two tall fescue cultivars (Festuca arundinacea cv. Barlexas and Crossfire II) were investigated under heat stress at 38/30 °C (day/night) for two weeks. Shoot growth rate of two tall fescue cultivars declined significantly under heat stress, and N supply can improved the growth rates, especially for the Barlexas. Chl content, leaf net photosynthetic rate, stomatal conductance, water use efficiency, and the maximal efficiency of photosystem 2 photochemistry (F_v/F_m) also decreased less under heat stress by N supply, especially in Crossfire II. Moreover, cultivar variations in photosynthetic performance were associated with their different response to heat stress and nitrogen fertilization, which were evidenced by shoot growth rate and photosynthetic pigment contents.     

Leaf appearance, tillering and their coordination in response to NxP fertilization in barley

The aim of this work was to study the effects of nitrogen (N) and phosphorus (P) deficiencies and their interaction on the appearance of leaves and tillers of barley (Hordeum vulgare spp. distichum L.) by analyzing the rate and duration of the appearance period. Three microcrops experiments were carried out in 200 L containers using malting barley cv. Quilmes Palomar. Treatments were a factorial combination of two levels on N and two or three levels of P fertilization. Both N and P deficiencies delayed leaf and tiller appearance rates but leaf appearance was less susceptible to nutrient deficiencies than tiller appearance. P deficiency effects on leaf emergence differed from N effects. While N deficiency diminished the rate of leaf appearance (RLA), it has no significant effect on the duration of leaf appearance or on the duration of the period from emergence to flowering. On the other hand, P deficiency diminished RLA, and increased both the duration of leaf appearance and the duration of the period from emergence to flowering.     

Effects of rhizobia inoculation and nitrogen fertilization on photosynthetic physiology of soybean

Plant growth, contents of photosynthetic pigments, photosynthetic gas exchange, and chlorophyll (Chl) fluorescence in soybean [Glycine max (L.) Merr. cv. Heinong37] were investigated after it was inoculated with Sinorhizobium fredii USDA191 or treated with 5 mM (NH₄)₂SO₄ (N5) and 30 mM (NH₄)₂SO₄ (N30), respectively. In the plants following N5 fertilization, not only plant biomass, leaf area, and Chl content, but also net photosynthetic rate (P _N), stomatal conductance (g _s), carboxylation efficiency (CE), maximum photochemical efficiency (F_v/F_m) of photosystem 2 (PS2), and quantum yield of PS2 (Φ_PS2) were markedly improved as compared with the control plants. There were also positive effects on plant growth and plant photosynthesis after rhizobia inoculation, but the effects were much less than those of N5 fertilization. For N30 plants there were no significant positive effects on plant growth and photosynthetic capacity. Plant biomass, P _N, and g _s were similar to those of N-limited (control) plants. Φ_PS2 and photochemical quenching (q_P) were obviously declined while content of carotenoids and non-photochemical quenching (q_N) were significantly enhanced in N30 treated plants. This indicated that excess N supply may cause some negative effects on soybean plants.     

Grain yield, symbiotic N2 fixation and interspecific competition for inorganic N in pea-barley intercrops

The effect of mixed intercropping of field pea (Pisum sativum L.) and spring barley (Hordeum vulgare L.), compared to monocrop cultivation, on the yield and crop-N dynamics was studied in a 4-yr field experiment using ¹⁵N-isotope dilution technique. Crops were grown with or without the supply of 5 g ¹⁵N-labeled N m^-2. The effect of intercropping on the dry matter and N yields, competition for inorganic N among the intercrop components, symbiotic fixation in pea and N transfer from pea to barley were determined. As an average of four years the grain yields were similar in monocropped pea, monocropped and fertilized barley and the intercrop without N fertilizer supply. Nitrogen fertilization did not influence the intercrop yield, but decreased the proportion of pea in the yield. Relative yield totals (RYT) showed that the environmental sources for plant growth were used from 12 to 31% more efficiently by the intercrop than by the monocrops, and N fertilization decreased RYT-values. Intercrop yields were less stable than monocrop barley yields, but more stable than the yield of monocropped pea. Barley competed strongly for soil and fertilizer N in the intercrop, and was up to 30 times more competitive than pea for inorganic N. Consequently, barley obtained a more than proportionate share of the inorganic N in the intercrop. At maturity the total recovery of fertilizer N was not significantly different between crops, averaging 65% of the supplied N. The fertilizer N recovered in pea constituted only 9% of total fertilizer-N recovery in the intercrop. The amount of symbiotic N₂ fixation in the intercrop was less than expected from its composition and the fixation in monocrop. This indicates that the competition from barley had a negative effect on the fixation, perhaps via shading. At maturity, the average amount of N₂ fixation was 17.7 g N m^-2 in the monocrop and 5.1 g N m^-2 in the intercropped pea. A higher proportion of total N in pea was derived from N₂ fixation in the intercrop than in the monocrop, on average 82% and 62%, respectively. The ¹⁵N enrichment of intercropped barley tended to be slightly lower than of monocropped barley, although not significantly. Consequently, there was no evidence for pea N being transferred to barley. The intercropping advantage in the pea-barley intercrop is mainly due to the complimentary use of soil inorganic and atmospheric N sources by the intercrop components, resulting in reduced competition for inorganic N, rather than a facilitative effect, in which symbiotically fixed N₂ is made available to barley.Abbreviations MC monocrop - IC intercrop - PMC pea monocrop - BMC barley monocrop - PIC pea in intercrop - BIC barley in intercrop     

Effects of fertilization on the growth,photosynthesis, and biomass accumulation in juvenile plants of three coffee (<Emphasis Type="Italic">Coffea arabica</Emphasis> L.) cultivars

We carried out a field experiment in order to study effects of fertilization in juvenile plants of three coffee (Coffea arabica) cultivars in Yunnan, SW China. Fertilization treatments included a control without fertilizer (CK), combinations of three NPK fertilization rates [high fertilization (F_H), medium fertilization (F_M), and low fertilization (F_L) with 135, 90, and 45 g per plant per year, respectively], and at two N:P₂O₅:K₂O ratios (R₁, 1:0.5:0.8; R₂, 1:0.8:0.5). The growth in juvenile plants was not altered by fertilization, with two clear growth peaks being observed in both the height and stem growth rates (RGRs) throughout a year. Both F_M and F_H resulted in significantly higher RGRs in both height and stem diameter compared to F_L and CK in all three cultivars. At the same fertilization rate, the leaf area, branch number, longest branch length, internode number, and biomass of R₂ were higher than those of R₁, and P significantly affected the root biomass and root to shoot ratio. Compared to the F_L treatment, both F_M and F_H treatments resulted in higher net photosynthetic rates and stomatal conductance across seasons, and in higher intrinsic water-use efficiency during the dry season and at the middle of the wet season. Photosynthetic nitrogen-use efficiency at R₂ was higher than that at R₁, but no significant differences were observed between the different fertilization rates. Among the three coffee cultivars, Caturra exhibited the highest height, stem diameter, longest branch length, and internode number. Our results indicated that the optimal N:P₂O₅:K₂O ratio was 1:0.8:0.5 for the juvenile growth of coffee plants. Both F_M and F_H could help optimize the growth and photosynthetic rate of coffee plants, but F_M is suitable for the ecological friendly agriculture and economic sustainability at coffee plantations.     

The influence of salinity on cell ultrastructures and photosynthetic apparatus of barley genotypes differing in salt stress tolerance

A hydroponic experiment was conducted to elucidate the difference in growth and cell ultrastructure between Tibetan wild and cultivated barley genotypes under moderate (150 mM NaCl) and high (300 mM NaCl) salt stress. The growth of three barley genotypes was reduced significantly under salt stress, but the wild barley XZ16 (tolerant) was less affected relative to cultivated barley Yerong (moderate tolerant) and Gairdner (sensitive). Meanwhile, XZ16 had lower Na⁺ and higher K⁺ concentrations in leaves than other two genotypes. In terms of photosynthetic and chlorophyll fluorescence parameters, salt stress reduced maximal photochemical efficiency (F _v/F _m), net photosynthetic rate (Pn), stomatal conductance (Gs), and intracellular CO₂ concentration (Ci). XZ16 showed relatively smaller reduction in comparison with the two cultivated barley genotypes. The observation of transmission electron microscopy found that fundamental cell ultrastructure changes happened in both leaves and roots of all barley genotypes under salt NaCl stress, with chloroplasts being most changed. Moreover, obvious difference could be detected among the three genotypes in the damage of cell ultrastructure under salt stress, with XZ16 and Gairdner being least and most affected, respectively. It may be concluded that high salt tolerance in XZ16 is attributed to less Na⁺ accumulation and K⁺ reduction in leaves, more slight damage in cell ultrastructure, which in turn caused less influence on chloroplast function and photosynthesis.     

Patterns of genetic and eco-geographical diversity in Spanish barleys

The pool of Western Mediterranean landraces has been under-utilised for barley breeding so far. The objectives of this study were to assess genetic diversity in a core collection of inbred lines derived from Spanish barley landraces to establish its relationship to barleys from other origins, and to correlate the distribution of diversity with geographical and climatic factors. To this end, 64 SSR were used to evaluate the polymorphism among 225 barley (Hordeum vulgare ssp. vulgare) genotypes, comprising two-row and six-row types. These included 159 landraces from the Spanish barley core collection (SBCC) plus 66 cultivars, mainly from European countries, as a reference set. Out of the 669 alleles generated, a large proportion of them were unique to the six-row Spanish barleys. An analysis of molecular variance revealed a clear genetic divergence between the six-row Spanish barleys and the reference cultivars, whereas this was not evident for the two-row barleys. A model-based clustering analysis identified an underlying population structure, consisting of four main populations for the whole genotype set, and suggested further possible subdivision within two of these populations. Most of the six-row Spanish landraces clustered into two groups that corresponded to geographic regions with contrasting environmental conditions. The existence of wide genetic diversity in Spanish germplasm, possibly related to adaptation to a broad range of environmental conditions, and its divergence from current European cultivars confirm its potential as a new resource for barley breeders, and make the SBCC a valuable tool for the study of adaptation in barley. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Pathogenicity of three RPV isolates of Barley Yellow Dwarf Virus on barley, wheat and wheat alien addition lines

Barleys with and without the Yd₂ resistance factor, wheat alien addition stocks with other barley yellow dwarf virus (BYDV) resistance factors and true wheats were challenged with three Australian isolates of BYDV-RPV. Yd₂ resistance was effective against two of the BYDV-RPV isolates and inoculated barleys which carry Yd₂ did not develop BYD symptoms and shoot growth was not affected. However, barleys with Yd₂ were susceptible to the third BYDV-RPV isolate. All barley lines inoculated with the third virus isolate developed typical BYD symptoms (yellowing), shoot growth was reduced compared to uninfected controls and virus titres determined by ELISA were high and similar in barleys with and without Yd₂. In contrast, resistances from Thinopyrum intermedium and Agropyron pulcherrimum in wheat backgrounds were effective against all three BYDV-RPV isolates. Shoot growth of inoculated plants with either of these resistance factors did not differ from uninfected controls and virus titres determined by ELISA were very low.     

Relationship between quantum efficiency of PSII and cold-induced plant resistance to fungal pathogens

The aim of the presented work was to study whether the efficiency of photosynthesis may influence resistance of hardened plants to disease. Seedlings of spring barley, meadow fescue and winter oilseed rape were chilled at 5 °C for 2, 4 or 6 weeks and at these deadlines the changes in cell membrane permeability (expressed as electrolyte leakage), chlorophyll fluorescence (initial fluorescence - F₀, maximal fluorescence - F_m, quantum yield of PSII - F_v/F_m) and net photosynthesis rate (F_N) were measured. Also, the influence of cold on the degree of plant resistance to economically important pathogens -Bipolaris sorokiniana or Phoma lingam was estimated. Two, four or six week-hardened plants were artificially infected: barley and fescue by B. sorokiniana, and oilseed rape by P. lingam. Hardening at 5 °C stimulated resistance of barley, fecue and rape to their specific pathogens. Six-week long acclimation was the most effective for plant resistance. Cold significantly changed cell membrane permeability and decreased chlorophyll fluorescence (F₀, F_m and F_v/F_m) of all studied plant species, while net photosynthesis rate was found to decrease only in barley. The results indicate that cold-induced resistance of plants to pathogens was correlated with a decrease in cell membrane permeability. In the case of fescue and barley a significant connection between the quantum yield of PSII and their resistance to B. sorokiniana was shown. Additionally, the resistance of barley to fungus was depended on net photosynthesis rate. In general this research shows that the efficiency of photosynthesis may be used as an indicator of plant resistance to disease.     

Impact of phosphorus application on drought resistant responses of Eucalyptus grandis seedlings

Eucalyptus grandis is the most widely planted tree species worldwide and can face severe drought during the initial months after planting because the root system is developing. A complete randomized design was used to study the effects of two water regimes (well‐watered and water‐stressed) and phosphorus (P) applications (with and without P) on the morphological and physio‐biochemical responses of E. grandis. Drought had negative effects on the growth and metabolism of E. grandis, as indicated by changes in morphological traits, decreased net photosynthetic rates (P_n), pigment concentrations, leaf relative water contents (LRWCs), nitrogenous compounds, over‐production of reactive oxygen species (ROS) and higher lipid peroxidation. However, E. grandis showed effective drought tolerance strategies, such as reduced leaf area and transpiration rate (E), higher accumulation of soluble sugars and proline and a strong antioxidative enzyme system. P fertilization had positive effects on well‐watered seedlings due to improved growth and photosynthesis, which indicated the high P requirements during the initial E. grandis growth stage. In drought‐stressed seedlings, P application had no effects on the morphological traits, but it significantly improved the LRWC, P_n, quantum efficiency of photosystem II (F_v/F_m), chlorophyll pigments, nitrogenous compounds and reduced lipid peroxidation. P fertilization improved E. grandis seedling growth under well‐watered conditions but also ameliorated some leaf physiological traits under drought conditions. The effects of P fertilization are mainly due to the enhancement of plant N nutrition. Therefore, P can be used as a fertilizer to improve growth and production in the face of future climate change.     

Resistance to Rhynchosporium secalis in the winter barley cultivar Vulcan

The six-rowed winter barley cultivar Vulcan was found to be highly resistant to Rhynchosporium secalis in the field, although this resistance was not apparent in routine screening tests of barley genotypes carried out at the seedling stage. More precise seedling tests, using graded inoculum levels to derive dose-response curves, showed that cv. Vulcan had an ED₅₀ which was 4.8 times that of the susceptible, two-rowed cv. Maris Otter, and 4.1 times that of cv. Maris Puma. The inheritance of resistance was investigated at the adult plant stage in a cross with cv. Maris Otter. Although a clear-cut segregation of the F₃ progeny into resistant, segregating and susceptible phenotypes was not observed, the genetic variance of the F₃ family means was compatible with the hypothesis of monogenic control of resistance. Resistance was inherited independently of the factor for six-rowed head type.     

Promotion of AM utilization through reduced P fertilization 2. Field studies

The hypothesis of this study was that cumulative P fertilization decreases the contribution of arbuscular mycorrhiza (AM) to crop growth and nutrient uptake in Northern European field conditions. The modes of action of P fertilization were evaluated through effects on mycorrhization, crop dependence on AM, and AM fungal (AMF) community. Field studies were carried out within long-term experiments on soils with low and intermediate initial content of extractable P, where no P fertilization and 45 kg ha^–1 a^–1 P were applied for 20 years. AM effectiveness in terms of growth and nutrient uptake of flax, red clover and barley, percentage root length colonized by AMF, P response of flax, and spore densities and species composition of the AMF communities, were assessed. In the soil with low initial P supply, cumulative P fertilization decreased AM contribution to crop growth and nutrient uptake. The higher AM effectiveness in soil with no added P compensated the cumulative P fertilization (soil P_H2O 2.5 v. 9.5 mg kg^–1) for flax, but not completely for clover. In contrast, barley obtained no benefit from AM at harvest and only a slight benefit from cumulated P. In the soil with intermediate initial P supply, AM reduced growth of flax and barley, especially with no added P, and no response to AM was obtained on clover due to retarded mycorrhization. Cumulative P fertilization reduced yield losses of flax by AM (P_H2O 18.8 v. 5.4 mg kg^–1), because fertilization inhibited mycorrhization. In both soils, root colonization and spore density were decreased by cumulative P fertilization, but no changes in AMF species composition were observed.     

Low nitrogen stress regulates chlorophyll fluorescence in coordination with photosynthesis and Rubisco efficiency of rice

Nitrogen (N) is the basis of plant growth and development and, is considered as one of the priming agents to elevate a range of stresses. Plants use solar radiations through photosynthesis, which amasses the assimilatory components of crop yield to meet the global demand for food. Nitrogen is the main regulator in the allocation of photosynthetic apparatus which changes of the photosynthesis (P_n) and quantum yield (F_v/F_m) of the plant. In the present study, dynamics of the photosynthetic establishment, N-dependent relation with chlorophyll fluorescence attributes and Rubisco efficacy was evaluated in low-N tolerant (cv. CR Dhan 311) and low-N sensitive (cv. Rasi) rice cultivars under low-N and optimum-N conditions. There was a decrease in the stored leaf N under low-N condition, resulting in the decreased P_n and F_v/F_m efficiency of the plants through depletion in the activity and content of Rubisco. The P_n and F_v/F_m followed the parallel trend of leaf N content during low-N condition along with depletion of intercellular CO₂ concentration and overall conductance under low-N condition. Photosynthetic saturation curve cleared abrupt decrease of effective quantum yield in the low-N sensitive rice cultivar than the low-N tolerant rice. Also, the rapid light curve highlighted the unacclimated regulation of photochemical and non-photochemical quenching in the low-N condition. The low-N sensitive rice cultivar triumphed non-photochemical quenching, whereas the low-N tolerant rice cultivar rose gradually during the light curve. Our study suggested that the quantum yield is the key limitation for photosynthesis in low-N condition. Regulation of Rubisco, photochemical and non-photochemical quenching may help plants to grow under low-N level.

     

Leaf Gas Exchange and Chlorophyll Fluorescence Parameters in Phaseolus Vulgaris as Affected by Nitrogen and Phosphorus Deficiency

The effects of N and P deficiency, isolated or in combination, on leaf gas exchange and fast chlorophyll (Chl) fluorescence emission were studied in common bean cv. Negrito. 10-d-old plants grown in aerated nutrient solution were supplied with high N (HN, 7.5 mol m⁻³) or low N (LN, 0.5 mol m⁻³), and also with high P (HP, 0.5 mol m⁻³) or low P (LP, 0.005 mol m⁻³). Regardless of the external P supply, in LN plants the initial fluorescence (F₀) increased 12 % in parallel to a quenching of about 14 % in maximum fluorescence (F_m). As a consequence, the variable to maximum fluorescence ratio (F_v/F_m) decreased by about 7 %, and the variable to initial fluorescence ratio (F_v/F₀) was lowered by 25 % in relation to control plants. In LP plants, F_v/F_m remained unchanged whilst F_v/F₀ decreased slightly as a result of 5 % decline in F_m. Under N deficiency, the net photosynthetic rate (P _N) halved at 6 d after imposition of treatment and so remained afterwards. As compared to LN plants, P _N declined in LP plants latter and to a less extent. From 12 d of P deprivation onwards. P _N fell down progressively to display rates similar to those of LN plants only at the end of the experiment. The greater P _N in LP plants was not reflected in larger biomass accumulation in relation to LN beans. In general, P and N limitation affected photosynthesis parameters and growth without showing any synergistic or additive effect between deficiency of both nutrients. This revised version was published online in June 2006 with corrections to the Cover Date.     

Photosynthesis and PSII functionality of drought-resistant and drought-sensitive weeping lovegrass plants

World areas subject to drought are expected to increase under conditions of climate change. The purpose of this study is to clarify the response of grass species that can grow and produce under water stress. Therefore leaf photosynthesis, chlorophyll fluorescence and pigment content response to water stress were studied in two varieties of the C₄ grass Eragrostis curvula. Two-year-old plants of cv Ermelo and Consol were grown in plastic pots. Drought stress was imposed by withholding irrigation for 15 days and then rewatering for 5 days. During drought relative water content (RWC) decreased 65% in cv Ermelo, while lower reductions of RWC were observed in cv Consol. During the experiment in cv Ermelo increasing drought stress severity caused large decreases in photosynthetic rates, maximal PSII photochemical efficiency (F_V/F_M) and leaf pigment content. Cv Consol showed small variations in these parameters. Compared to cv Consol, after 15 days of drought, effective PSII quantum yield (Φ_II) was significantly lower in cv Ermelo. Reductions of Φ_II were related to significant reductions of open PSII energy capture efficiency (F′_V/F′_M). Photosynthetic response to increasing PPFD levels and to internal CO₂ concentration (C_i) were reduced by drought in cv Ermelo. Compared to well-watered control plants and to cv Consol, drought stressed plants of cv Ermelo showed also reductions of the initial slope of photosynthetic response to C_i and in the photosynthetic rate measured at saturating C_i. Moreover stomatal conductance (g) of both cvs decreased during drought. However, g was lower in drought stressed plants of cv Consol than in cv Ermelo. Water stress caused large reductions in leaf chlorophyll and carotenoid content in cv Ermelo, and small reductions in cv Consol. In drought-sensitive cv Ermelo water stress reduced the capabilities to down regulate PSII functionality through thermal energy dissipation. Results suggest that drought resistance of cv Consol, can be attributed to a higher water use efficiency.     

Identification and mapping of a new leaf stripe resistance gene in barley (Hordeum vulgare L.)

Pyrenophora graminea is the seed-borne pathogen causal agent of barley leaf stripe disease. Near-isogenic lines (NILs) carrying resistance of the cv ”Thibaut” against the highly virulent isolate Dg2 were obtained by introgressing the resistance into the genetic background of the susceptible cv ”Mirco”. The segregation of the resistance gene was followed in a F₂ population of 128 plants as well as on the F₃ lines derived from the F₂ plants; the segregation fitted the 1:2:1 ratio for a single gene. By using NILs, a RAPD marker associated with the resistance gene was identified; sequence-specific (STS) primers were designed on the basis of the amplicon sequence and a RILs mapping population with an AFLP-based map were used to position this molecular marker to barley chromosome 1 S (7HS). STS and CAPS markers were developed from RFLPs mapped to the telomeric region of barley chromosome 7HS and three polymorphic PCR-based markers were developed. The segregation of these markers was followed in the F₂ population and their map position with respect to the resistance gene was determined. Our results indicate that the Thibaut resistance gene, which we designated as Rdg2a, maps to the telomeric region of barley chromosome 7HS and is flanked by the markers OPQ-9₇₀₀ and MWG 2018 at distances of 3.1 and 2.5 cM respectively. The suitability of the PCR-based marker MWG2018 in selection- assisted barley breeding programs is discussed. Received: 22 June 2000 / Accepted: 16 October 2000     

Polymorphism of the cultivated barley (<Emphasis Type="Italic">Hordeum vulgare</Emphasis> L.) of South Arabia at hordein-coding loci

Electrophoresis in starch gel was used to study the polymorphism of hordeins controlled by loci Hrd A, Hrd B, and Hrd F in 89 accessions of the local barleys from South Arabia (Yemen). Overall, 36 alleles were detected for locus Hrd A; 48 alleles, for Hrd B; and 5 alleles, for Hrd F. The existence of the blocks of hordein components controlled by loci Hrd A and Hrd B was demonstrated. Calculation of genetic distances allows us to conclude that the barley populations from Yemen and Ethiopia are more similar compared with the populations from Egypt. This confirms the hypothesis of Bakhteev on the origin of Ethiopian barleys.     

Effects of Long-Term Fertilization on Leaf Photosynthetic Characteristics and Grain Yield in Winter Wheat

Based on a 20-year fertilization experiment with wheat-maize double cropping system, the effects of different long-term fertilization treatments on leaf photosynthetic characteristics and grain yield in different winter wheat (Triticum aestivum L.) cultivars were studied in the growing seasons of 2000–2001 and 2001–2002. A total of nine fertilization treatments were implemented, i.e. no fertilizer (CK), N fertilizer (N), N and P fertilizers (NP), N and K fertilizers (NK), N, P, and K fertilizers (NPK), only organic manure (M), organic manure and N fertilizer (MN), organic manure and N and P fertilizers (MNP), and organic manure and N, P, and K fertilizers (MNPK). With the treatments of combined organic manure and inorganic fertilizers (TMI), net photosynthetic rate (P _N), maximal activity of photosystem 2, PS2 (F_v/F_m), and chlorophyll content (SPAD value) of flag leaves and leaf area index (LAI) were much higher at the mid grain filling stage (20 or 23 d post anthesis, DPA), and exhibited slower declines at the late grain filling stage (30 DPA), compared with the treatments of only inorganic fertilizers (TI). The maximal canopy photosynthetic traits expressed as P _N×LAI and SPAD×LAI at the mid grain filling stage were also higher in TMI than those in TI, which resulted in different grain yields in TMI and TI. Among the treatments of TMI or among the treatments of TI, both flag leaf and canopy photosynthetic abilities and yield levels increased with the supplement of inorganic nutrients (N, P, and K fertilizers), except for the treatment of NK. Under NK, soil contents of N and K increased while that of P decreased. Hence the unbalanced nutrients in soil from the improper input of nutrients in NK treatment were probably responsible for the reduced flag leaf and canopy photosynthetic characteristics and LAI, and for the fast declining of flag leaf photosynthetic traits during grain filling, resulting in the reduced yield of NK similar to the level of CK.     

Field assessment of the effectiveness of a barley yellow dwarf virus resistance gene following its transference from spring to winter barley

Resistance to infection by barley yellow dwarf virus (BYDV) has been transferred to the winter-hardy barley cv. Vixen. The effects of various sowing and inoculation dates on this resistance have been studied at two levels of BYDV infection. At levels most likely to be encountered in the field cv. Vixen suffered only slight yield losses and even under the most extreme conditions consistently yielded more than the susceptible cv. Igri. Comparison of the range of measurements used to determine the effects of BYDV infection showed that assessment of resistance to BYDV in field-grown winter barleys is most reliably based on yield measurements.     

Sustained effects of atmospheric [CO2] and nitrogen availability on forest soil CO2 efflux

Soil CO₂ efflux (F_soil) is the largest source of carbon from forests and reflects primary productivity as well as how carbon is allocated within forest ecosystems. Through early stages of stand development, both elevated [CO₂] and availability of soil nitrogen (N; sum of mineralization, deposition, and fixation) have been shown to increase gross primary productivity, but the long‐term effects of these factors on F_soil are less clear. Expanding on previous studies at the Duke Free‐Air CO₂ Enrichment (FACE) site, we quantified the effects of elevated [CO₂] and N fertilization on F_soil using daily measurements from automated chambers over 10 years. Consistent with previous results, compared to ambient unfertilized plots, annual F_soil increased under elevated [CO₂] (ca. 17%) and decreased with N (ca. 21%). N fertilization under elevated [CO₂] reduced F_soil to values similar to untreated plots. Over the study period, base respiration rates increased with leaf productivity, but declined after productivity saturated. Despite treatment‐induced differences in aboveground biomass, soil temperature and water content were similar among treatments. Interannually, low soil water content decreased annual F_soil from potential values – estimated based on temperature alone assuming nonlimiting soil water content – by ca. 0.7% per 1.0% reduction in relative extractable water. This effect was only slightly ameliorated by elevated [CO₂]. Variability in soil N availability among plots accounted for the spatial variability in F_soil, showing a decrease of ca. 114 g C m^?2 yr^?1 per 1 g m^?2 increase in soil N availability, with consistently higher F_soil in elevated [CO₂] plots ca. 127 g C per 100 ppm [CO₂] over the +200 ppm enrichment. Altogether, reflecting increased belowground carbon partitioning in response to greater plant nutritional needs, the effects of elevated [CO₂] and N fertilization on F_soil in this stand are sustained beyond the early stages of stand development and through stabilization of annual foliage production.