Growth attributes,xylem sap composition,and photosynthesis in common bean as affected by nitrogen and phosphorus deficiency

The effects of nitrogen (N‐) and phosphorus (P‐) deficiency, isolatedly or in combination, on growth, nitrogenous fraction, and inorganic phosphate in xylem exudade, and photosynthesis of common bean (Phaseolus vulgaris L. cv. Negrito) were investigated. Plants were grown in nutrient solution adjusted daily to pH 5.5 and aerated continuously. Ten days after emergence mineral deficiency was imposed. Plants were then supplied with high N (7.5 mol m^‐3) or low N (0.5 mol m^‐3), and also with high P (0.5 mol m^‐3) or low P (0.005 mol m^‐3). All sampling and measurements were made 28 days after emergence. N‐ or P‐deprivation brought about large decreases in total leaf area by inhibiting the emergence of new leaves and primarily the expansion of the leaves. The specific leaf area did not change under N‐ but decreased under P‐limitation. The decreased shoot to root ratio in all deficiency treatments was a consequence of a lowering mass of above‐ground organs, especially of leaves.

The content of chlorophylls declined significantly only under N‐deficiency alone; carotenoids declined under both N‐ and combined N‐ and P‐limitation. No alteration in amino acid concentration in xylem exudate occurred in plants experiencing N‐starvation, while ureides increased by 79%, and nitrate and inorganic phosphate decreased greatly. Under P‐deprivation, amino acids and nitrate in xylem sap dropped by about half; ureides were held relatively constant, and phosphate was severely depressed. Total upward translocation of N through xylem was estimated to be about 16% higher in N‐deficient plants than in plants without mineral limitation, but leaf N levels in the former were lower as compared to control plants. The net carbon (C) assimilation decreased similarly regardless of the imposed deficiency treatment. Such a decrease was mainly determined by non‐stomatal factors. In general, no additive effect between N‐ and P‐limitation on any of measured parameters was observed.     

Interactive effects of salinity and iron deficiency on different rice genotypes

Salinity adversely affects plant growth, photosynthesis, and availability of nutrients including iron. Rice (Oryza sativa L.) is susceptible to soil salinity and highly prone to iron (Fe) deficiency due to lower release of Fe‐chelating compounds under saline conditions. In order to investigate the effects of salinity and low iron supply on growth, photosynthesis, and ionic composition of five rice genotypes (KS‐282, Basmati Pak, Shaheen Basmati, KSK‐434 and 99417), a solution culture experiment was conducted with four treatments (control, 50 mM NaCl, Fe‐deficient, and 50 mM NaCl + Fe‐deficient). Salinity and Fe deficiency reduced shoot and root growth, photosynthetic and transpiration rates, chlorophyll concentration, and stomatal conductance. The reduction in all these parameters was more in the interactive treatment of salinity and low Fe supply. Moreover, a significant increase in shoot and root Na⁺ with corresponding decrease in K⁺ and Fe concentrations was also observed in the combined salinity and Fe‐deficiency treatment. Among the tested genotypes, Basmati Pak was the most sensitive genotype both under salt stress and Fe deficiency. The genotype KS‐282 performed better than other genotypes under salinity stress alone, whereas Shaheen Basmati was the best genotype under Fe deficiency in terms of all the studied parameters.     

Growth and chloride accumulation in soybean cultivars treated with excess KCl in solution culture

Abstract

Sensitivity to chloride was measured in soybean [Glycine max (L.) Merr.] cultivars Rinjani, Lokon, and Merbabu from Indonesia, and Lee from the United States. Plants were grown in solution culture to which KCl (0, 50, or 100 mol m^‐3) was added gradually during days 7–14 after emergence. Excess KCl reduced growth, measured as leaf area, shoot and root biomasses, total biomass, and root/shoot ratio in 24‐day‐old plants of all cultivars. The cultivar x KCl treatment interaction was significant for all growth parameters. The order of chloride tolerance at 50 mol m^‐3 Cl^‐, based on the mean of all growth parameters relative to the control, was Lee>Rinjani>Lokon=Merbabu. In the 50 mol m^‐3 Cl^‐ treatment Lee excluded Cl^‐ from the leaves, and accumulated Cl^‐ in the roots; Lokon, Rinjani, and Merbabu excluded less Cl^‐ from the leaves. At 100 mol m^‐3 KCl, cultivar Lee lost its capacity to exclude Cl^‐ from the leaves and its growth was poor. Chloride exclusion from the leaves at 100 mol m^‐3 KCl was most effective in Lokon, which corresponded to the relatively good growth of this cultivar in the high KCl treatment.     

Phosphorus affects storage root yield of cassava through root numbers

Abstract

The objective of this study was to determine the effect of phosphorus applied through fertigation on growth and root yield of cassava. This was achieved through a greenhouse pot-experiment consisting of 1, 4, 7, 10, 20 and 30?mg?P?L^?1. Increasing P from 1 to 30?mg?P?L^?1 realized a 57.1 and 150.0% increase in leaf blade P in 2014 and 2015, respectively. Similarly, chlorophyll content and shoot growth increased as P concentration in solution increased. However, leaf stomatal conductance and net photosynthesis reached a maximum in 7 and 20?mg?P?L^?1 in 2014 and 2015, respectively. This trend of stomatal conductance and net photosynthesis was consistent with that of dry root yield and storage roots numbers. Regressing dry root yield against storage root numbers showed that R² = 0.80. Phosphorus encourages formation of storage roots and the duration of cassava’s growth affects the amount of P required for maximum root yield.     

EFFECT OF NITROGEN APPLICATION ON GROWTH PARAMETERS,YIELD AND LEAF NITRATE CONTENT OF GREENHOUSE LETTUCE CULTIVATED DURING THREE SEASONS

Lettuce (Lactuca sativa L., cv. ‘Parris Island’) was grown hydroponically in autumn, winter and spring under five levels of nitrogen (N) fertilization. Plant biomass was highest in spring and lowest in autumn at N rates of 200 and 260 mg L^?1, respectively. Increasing N application correlated positively with rates of photosynthesis, transpiration, stomatal carbon dioxide (CO₂) conductance and leaf chlorophyll concentration. Photosynthetic rate, stomatal CO₂ conductance, and chlorophyll a/b ratio were higher in spring than in autumn or winter. Nitrate concentrations within the leaves increased with increasing N application in all seasons. It is concluded that lettuce growth and yield is higher in spring than in winter or autumn due to enhanced photosynthesis thanks to increasingly favorable photoperiod. Regardless of season, high N rates promote yield but increase leaf nitrate concentrations. Therefore, for the production of healthy produce the recommended N rate should be based not just on yield but also on the nitrate content.     

Physiological changes in soybean treated with ozone and molybdenum

Abstract

An open‐top field chamber experiment was conducted to evaluate the impact of Molybdenum (Mo) addition to soil on the physiological changes in soybean (Glycine max L. Merrill) exposed to ozone (O₃). Plants grown with Mo (0, 1.0, or 2.0 mg kg"¹ soil dry weight) were exposed to O₃ (O, 0.06, or 0.12 μmol mol^‐1) in open‐top field chambers for 12 h d^‐1 for 21 d with a N‐free fertilizer, during the sensitive growth stage (R2). The rate of photosynthesis (PN), specific root nodule nitrogenase activity (SNA), leaf nitrogen (N), chlorophyll (chl‐a, chl‐b) and biomass of soybean were measured. The increase in O₃ levels significantly reduced PN, SNA, leaf‐N, chl‐a, chl‐b, and biomass. Addition of Mo increased leaf‐N, shoot, root, and nodule dry weights but did not change PN, SNA, or chlorophyll. The addition of Mo (2 mg kg ^‐1) helped in significantly increasing PN and chlorophyll in the presence of 0.06 umol mol^‐1 O₃ but no change was observed in the presence of 0.12 μmol mol^‐1 O₃.     

Genotypic Difference in Nitrogen Acquisition Ability in Maize Plants Is Related to the Coordination of Leaf and Root Growth

ABSTRACT

The capacity of a plant to take up nitrate is a function of the activity of its nitrate-transporter systems and the size and architecture of its root system. It is unclear which of the two components, root system or nitrate-uptake system, is more important in nitrogen (N) acquisition under nitrogen-sufficiency conditions. Two maize (Zea mays L.) inbred lines (478 and Wu312) grown in nutrient solution in a controlled environment were compared for their N acquisition at 0.1, 0.5, 2.5, 5, and 10 mmol L^?1 nitrate supply. Genotype 478 could take up more N than Wu312 at all nitrate concentrations, though the shoot biomass of the two genotypes was similar. Genotype 478 had a larger leaf area and longer root length. The specific N uptake rate of 478 (μmol N g^?1 root. d^?1) was lower than that of Wu312. In an independent nitrate-depletion experiment, the potential nitrate uptake rate of 478 was also lower than that of Wu312. No genotypic difference was found in photosynthesis rate. It was concluded that the greater N acquisition ability in 478 involves the coordination of leaf and root growth. Vigorous leaf growth caused a large demand for N. This demand was met by the genotype's large root system. Besides providing a strong sink for N uptake, the larger leaf area of 478 might also guarantee the carbohydrate supply necessary for its greater root growth.     

Path and Correlation Analyses of the Factors affecting Biomass Production of Brassica Cultivars under Phosphorus‐Deficiency Stress Environment

Abstract

Path analysis is a statistical technique that partitions correlations into direct and indirect effects and distinguishes between correlation and causation, whereas correlation in general measures the extent and direction (positive or negative) of a relationship occurring between two or more variables. The estimates of correlation and path coefficients can help us to understand the role and relative contribution of various plant traits in establishing growth behavior of crop cultivars under given environmental conditions. Dependence of shoot dry‐matter (SDM) production of six hydroponically grown Brassica cultivars on various growth parameters and characteristics of P metabolism was investigated using the modified Johnson's nutrient solution to maintain deficient (10 µM) and adequate (200 µM) P levels. Root dry‐matter (RDM), total dry‐matter, P content in shoot, and P‐utilization efficiency (PUE) had significant and positive effects on production of SDM in a P‐deficient environment. Root–shoot ratio (RSR), however, negatively affected SDM of cultivars exposed to P‐deficient conditions and did not show any impact on SDM production in either of the two treatments. In a pot study, six Brassica cultivars were grown in a sandy loam soil that was deficient in NaHCO₃‐extractable P (3.9 mg P kg^?1 soil) for 49 days. Significant positive correlations were observed between SDM and some other plant traits such as RDM, leaf area per plant, P uptake, and PUE, at both genotypic and phenotypic levels. The correlations of SDM with RSR, however, were not observed, implying that relative partitioning of biomass into roots or shoots had little role to play in SDM production by Brassica cultivars under P‐deficiency stress. Path analysis revealed that favorable impact of RDM and leaf area on SDM production was indirect through positive effect of these parameters on P uptake and PUE. Thus, under P‐deficiency stress, better P acquisition and efficient P utilization by the cultivars for biomass synthesis collectively formed the basis of higher SDM production by the cultivars, evidencing that P uptake and utilization efficiency are two important plant traits for selecting P‐deficiency‐stress‐tolerant Brassica cultivars.     

Insensitivity of soybean photosynthesis to ultraviolet‐b radiation under phosphorus deficiency

Soybean [Glycine max (L.) Merr. cv Essex] was grown in sand in a greenhouse under 2 levels of biologically effective ultraviolet‐B radiation (effective daily dose: 0 and 11.5 kJ/m² UV‐BBE and 2 levels of P (6.5 and 52 μM). Plants were grown in each treatment combination up to the fifth trifoliolate stage. UV‐B radiation had no affect on plant growth and net photosynthesis at 6.5 μM P supply but decreased both these parameters when grown in the higher P concentration. Reductions in net photosynthesis were apparently due to direct effects on the photosynthetic machinery, since chlorophyll concentration and stanatal conductance were unaffected by UV‐B radiation. Both UV‐B radiation and reduced P supply increased the level of UV‐B absorbing compounds in leaf tissues and their effects were additive. The reduced sensitivity of P deficient plants to UV‐B radiation may be the result of this increase in UV absorbing compounds and possibly uv protective mechanisms associated with growth inhibition.     

Osmotic potentials and solute concentrations in sugar beet plants cultivated with varying potassium/sodium ratios

Cell saps from leaves, petioles and storage root of sugar beet plants were analysed to indicate the possible specific and/or non-specific (osmotic) function of K and Na ions for the regulation of assimilate partitioning in sugar beet. Plants were cultivated up to 94 days in nutrient solutions containing either 4.5 mol m^?3 K + 0.5 mol m^?3 Na (K plants) or 0.5 mol m^?3 K + 4.5 mol m^?3 Na (Na plants) or 0.5 mol m^?3 K + 0.5 mol m^?3 Na (control). Osmotic potentials of the cell sap of leaf blades (?1.4 to ?1.6 MPa) and petioles (?1.6 to ?2.0 MPa), respectively, were rather low and similar. It was concluded that in these organs Na may replace K in its osmoregulatory functions. While shoot growth was favoured by Na, a principally improved translocation of K into the taproot was noted. This was - especially in the K-treatment - associated with increased growth of the storage root and a simultaneously stimulated sucrose accumulation. The results are discussed in terms of a different compartmentation of K, Na and Cl within the cell and within the whole plant and of a specific role of potassium in the process of assimilate translocation and storage.     

Impact of sulfate nutrition on the utilization of atmospheric SO2 as sulfur source for Chinese cabbage

The ability of Chinese cabbage (Brassica pekinensis) to utilize atmospheric sulfur dioxide (SO₂) as sulfur (S) source for growth was investigated in relation to root sulfate (SO ) nutrition. If seedlings of Chinese cabbage were transferred to a sulfate‐deprived nutrient solution directly after germination, plants became rapidly S‐deficient. Plant‐biomass production was decreased and the shoot‐to‐root ratio decreased. Sulfate deprivation resulted in a substantial decrease in total S, sulfate, organic‐S, and water‐soluble nonprotein thiol contents and in an increase in amino‐acid content of both shoot and root. The sulfate‐uptake rate of the root was strongly increased, whereas nitrate‐uptake rate was decreased. Upon resupply of sulfate, the onset of S‐deficiency symptoms was prevented, and growth was restored, whereas sulfate and nitrate‐uptake rates were quite similar to those of the sulfate‐sufficient plants. A 6‐day exposure to 0.12 µL L^–1 SO₂ of sulfate‐sufficient plants did not affect plant‐biomass production, shoot‐to‐root ratio, S and nitrogen (N) compounds of shoot and root, or sulfate and nitrate uptake by the root. Exposure of sulfate‐deprived plants to SO₂ resulted in enhanced total S, organic‐S, and water‐soluble nonprotein thiol contents of the shoot. The contribution of SO₂ as S source for biomass production depended on the duration of the sulfate deprivation. If Chinese cabbage was transferred to a sulfate‐deprived nutrient solution and simultaneously exposed to SO₂, then plants benefited optimally from the foliarly absorbed S. The development of S‐deficiency symptoms was prevented, and shoot‐biomass production was quite similar to that of sulfate‐sufficient plants. However, upon SO₂ exposure root‐biomass production was even higher than that of sulfate‐sufficient plants, whereas sulfate uptake was still enhanced. Evidently, upon SO₂ exposure there was no strict and direct shoot‐to‐root signaling in tuning sulfate uptake by the root and its transport to the shoot to the need for growth, via down‐regulation of sulfate uptake and normalizing shoot–to–root biomass partitioning.     

Effect of nutrient solution concentration on photosynthesis,growth, and content of the active substances of passionfruit 1

The objective of this study was to investigate the effects of exposure of passionfruit plants (Passiflora edulis Sims. var edulis) to five different electrical conductivity (EC) levels (1.2, 2.3, 4.5, 6.8, and 9.0 mS/cm) of the nutrient solution on net gas exchange (Pn), content of chlorophyll, the biologically active substances, vitexin and orientin, total biomass production, and morphological traits using plants grown in a greenhouse. Important traits, such as plant height, number of internodes, and leaf number per plant were significantly influenced and showed a linear relation to the increased EC levels of the solution. The highest biomass production, chlorophyll concentration, net carbon dioxide (CO₂) assimilation and leaf area were obtained at an EC of 6.8 mS/cm. At an EC level of 9.0 mS/cm, the growth of the plants was depressed and photosynthetic rate sharply declined. The highest photosynthetic rate (8.45 μmol/m²/s) was measured at an EC of 6.8 mS/cm and a photosynthetic photon flux of 1600 μmol/m²/s. The trend of photosynthesis was closely related to those of chlorophyll content, transpiration and mesophyll conductance. There was significant regression relating the shoot yield to increasing EC of the nutrient solution. The leaf chlorophyll content increased from 0.70 mg/g (75 mg/m²) at an EC of 0 to 1.74 mg/g at an EC of 6.8 mS/cm. The leaf water potential sharply declined with the increasing EC levels. The specific leaf area was high at EC of 2.3,4.5, and 6.8 mS/cm. The mean ratio of the root to the shoots decreased as EC was increased up to 6.8 mS/cm. Orientin content was the highest (168 mg %) at an EC of 9.0 mS/cm, having a linear effect, while the lowest vitexin content (36 mg %) was achieved at an EC of 6.8 mS/cm. The results suggest a positive role of increasing nutrient solution EC for orientin accumulation than to vitexin.     

Phosphorus Influx and Root‐Shoot Relations as Indicators of Phosphorus Efficiency of Different Crops

Abstract

The large variation in phosphorus acquisition efficiency of different crops provides opportunities for screening crop species that perform well on low phosphorus (P) soil. To explain the differences in P efficiency of winter maize (Zea mays L.), wheat (Triticum aestivum L.), and chickpea (Cicer arietinum L.), a green house pot experiment was conducted by using P‐deficient Typic ustochrept loamy sand soil (0.5 M NaHCO₃‐extractable P 4.9 mg kg^?1, pH 7.5, and organic carbon 2.7 g kg^?1) treated with 0, 30, and 60 mg P kg^?1 soil. Under P deficiency conditions, winter maize produced 76% of its maximum shoot dry weight (SDW) with 0.2% P in shoot, whereas chickpea and wheat produced about 30% of their maximum SDW with more than 0.25% P in shoot. Root length (RL) of winter maize, wheat, and chickpea were 83, 48, and 19% of their maximum RL, respectively. Considering relative shoot yield as a measure of efficiency, winter maize was more P efficient than wheat and chickpea. Winter maize had lower RL/SDW ratio than that of wheat, but it was more P efficient because it could maintain 2.2 times higher P influx even under P deficiency conditions. In addition, winter maize had low internal P requirement and 3.3 times higher shoot demand (i.e., higher amount of shoot produced per cm of root per second). Even though chickpea had 1.2 times higher P influx than winter maize, it was less P efficient because of few roots (i.e., less RL per unit SDW). Nutrient uptake model (NST 3.0) calculations satisfactorily predicted P influxes by all the three crops under sufficient P supply conditions (C_Li 48 µM), and the calculated values of P influx were 81–99% of the measured values. However, in no‐P treatment (C_Li 3.9 µM), under prediction of measured P influx indicated the importance of root exudates and/or mycorrhizae that increase P solubility in the rhizosphere. Sensitivity analysis showed that in low P soils, the initial soil solution P concentration (C_Li) was the most sensitive factor controlling P influx in all the three crops.     

Combined effects of phosphorus nutrition and elevated carbon dioxide concentration on chlorophyll fluorescence,photosynthesis, and nutrient efficiency of cotton

To examine the combined effects of phosphorus (P) nutrition and CO₂ on photosynthesis, chlorophyll fluorescence (CF), and nutrient utilization and uptake, two controlled‐environment experiments were conducted using 0.01, 0.05 and 0.20 mM external phosphate each at ambient and elevated CO₂ (aCO₂: 400 and eCO₂: 800 µmol mol^?1, respectively). The CF parameters were affected more by P nutrition than by CO₂ treatment. Photoinhibition of photosystem II (PSII) was due to increased minimal CF (Fo′) and decreased maximal CF (Fm′), and efficiency of energy harvesting (Fv′/Fm′). In addition, reduced electron transport rate (ETR), the quantum yield of PSII (Φ_PSII) and CO₂ assimilation ( ), and overall photochemical quenching in the P‐deficient leaves led to reduction in the efficiency of energy transfer to the PSII reaction center. Stimulation in the Φ_PSII/ and photorespiration (ETR/P_net) was found under P deficiency, whereas the opposite was the case under CO₂ enrichment. On average, photosynthetic rate (P_net) and stomatal conductance declined by 50–53% at 0.05 mM P and by 70–72% at 0.01 mM P as compared to the 0.20 mM P treatment. However, P deficiency, especially at eCO₂, tended to increase the intrinsic water‐use efficiency. In the P‐deficient plants, the decline in the P and N utilization efficiency (up to 91%) of biomass production was mainly associated with greater reduction in the biomass relative to the tissue P concentration as the P supply was reduced. However, it was significantly stimulated by eCO₂ especially at higher P supply. The CO₂ × P interaction was observed for some parameters such as Fo′, Fm′, P utilization efficiencies of photosynthesis and biomass production that might be attributed to the irresponsiveness of these parameters to eCO₂ under low P treatment. Thus, P deficiency limited the beneficial effect of eCO₂. A close relationship between total biomass and photosynthesis with the P and N utilization or uptake efficiencies was found. The P utilization efficiency of P_net appeared to be stable across a range of leaf P concentrations, whereas the N‐utilization efficiency markedly increased with leaf P and differed between CO₂ levels. An apparent effect of both the treatments (P and CO₂) on N‐uptake and utilization efficiency also indicated the alteration in N acquisition and assimilation in cotton plants.     

Partitioning of biomass in water‐ and nitrogen‐stressed cotton during pre‐bloom stage

The partitioning of biomass between aboveground parts and roots, and between vegetative and reproductive plant parts plays a major role in determining the ability of cotton (Gossypium hirsutum L.) to produce a crop in a given environment. We evaluated the single and combined effects of water and N supply on the partitioning of biomass in cotton plants exposed to two N supply levels, 0 and 12 mM of N, and two water regimes, well irrigated and water‐stressed at an early reproductive stage. The N treatments began when the third true leaf was visible, while water deficit treatments were imposed over the N treatments when the plants were transferred into controlled‐environment chambers at a leaf area near 0.05 m². Both water deficits and N deficits inhibited total biomass accumulation and its partitioning in cotton. Water deficit alone and N deficit alone inhibited the growth of leaves, petioles, and branches, but did not inhibit growth of the stem and enhanced the accumulation of biomass in squares. When water deficit was superimposed on N deficit, leaf growth was inhibited, although to a lesser extent than when it was the sole stress factor, and the accumulation of biomass in squares was also inhibited. Yet, the dry weight of squares in plants exposed to water and N deficits was greater than that of non‐stressed plants. Water and N deficits, either alone or in combination, did not inhibit the growth of the tap root. Growth of lateral roots was not inhibited either by water deficit alone or in combination with N deficit, but was enhanced when plants were exposed to N deficit alone. Exposure to water deficit alone or in combination with N deficit decreased the shoot:root ratio through the inhibition of shoot growth. Exposure to N deficit alone decreased the shoot:root ratio through the combination of shoot growth inhibition and root growth enhancement.     

Photosynthesis and Leaf Area of Brachiaria brizantha in Response to Phosphorus and Zinc Nutrition

Phosphorus (P) and zinc (Zn) are important determinants of plant productivity, particularly in the tropical grasslands of Brazil. Nutrient deficiency is one of the most important factors limiting plant productivity, decreasing photosynthesis efficiency and plant development. The present study investigates in Brachiaria brizantha (Hochst. ex A. Rich.) Stapf. cv. ‘Marandu’: 1) the gas exchange measurements; 2) the total leaf area development; and 3) the dry matter production due to P and Zn nutrition. Plants of B. brizantha cv. ‘Marandu’ were grown in nutrient solution under five rates of P (0.1, 0.6, 1.1, 1.6, and 2.1 mmol L^?1) and five rates of Zn (0.00, 0.75, 1.5, 2.25, and 3.00 μmol L^?1), in a fractioned factorial. Plants were harvested two times. Phosphorus supply increased carbon dioxide (CO₂) assimilation and stomatal conductance, and decreased intercellular CO₂. The interaction P rates x Zn rates were significant for the total leaf area variables and shoot dry matter in the second growth period. The nutrition of P and Zn interfered in the B. brizantha productivity by changing the grass photosynthesis and leaf area.     

Upland rice genotypes evaluation for phosphorus use efficiency

Phosphorus (P) deficiency is one of the most important yield‐limiting factors in acid soils in various parts of the world. The objective of this study was to evaluate the growth and P‐use efficiency of 20 upland rice (Oryza sativa L.) genotypes at low (0 mg P kg^‐1), medium (75 mg P kg^‐1), and high (150 mg P kg^‐1) levels of applied P on an Oxisol. Plant height, tillers, shoot and root dry weight, shoot‐root ratio, P concentration in root and shoot, P uptake in root and shoot, and P‐use efficiency were significantly (P<0.01) affected by level of soil P as well as genotype. Shoot weight and P uptake in shoot were found to be the plant parameters most sensitive to P deficiency, suggesting that these two parameters may be most suitable for screening rice genotypes for P‐use efficiency under greenhouse conditions.     

Foliar Applied Phosphorous Enhanced Growth,Chlorophyll Contents,Gas Exchange Attributes and PUE in Wheat (Triticum aestivum L.)

A pot experiment was conducted to evaluate the foliar applied phosphorous with and without pre-plant dose (50 kg hac.^?1) of phosphorous on growth, chlorophyll contents, gas exchange parameters and phosphorous use efficiency (PUE) of wheat. The experiment was conducted in net house at Department of Crop Physiology, University of Agriculture Faisalabad, Pakistan. Two promising wheat cultivar AARI 2011 and FSD 2008 were used as a test crop with 5 foliar phosphorus (P) rates (0, 2, 4, 6, 8 kg ha^?1). The foliar applied P with pre-plant performed better than without pre-plant and control treatments. Foliar treatment of phosphorus at 6 kg ha^?1 P proved to be the best among other foliar treatments followed by 8 kg ha^?1 P. The foliar application of phosphorous at 6 kg hac.^?1 with pre-plant soil applied P increased the shoot length, root length, shoot fresh weight, root fresh weight, shoot dry weight and root dry weight. The chlorophyll contents (Chl. a and b) were increased with the foliar application of phosphorous. The gas exchange parameters (net carbon dioxide (CO₂) assimilation rate, transpiration rate, stomatal conductance and sub-stomatal CO₂ rate) were significantly improved by foliar applied P. The maximum values of net CO₂ assimilation rate (5.27 μ mol m^?2 sec.^?1), transpiration rate (3.44 μ mol m^?2 sec.^?1), stomatal conductance (0.81 μ mol m^?2 sec.^?1) and sub-stomatal CO₂ (271.67 μ mol m^?2 sec.^?1), were recorded in the treatment where P was foliar applied at 6 kg hac.^?1 with pre-plant soil applied Phosphorous. The foliar application of phosphorous with pre-plant soil applied P enhanced Phosphorous use efficiency (PUE) in both varieties. The maximum value of PUE (15.42%) was recorded in the treatment where foliar feeding of P was done at 6 kg hac.^?1 with pre-plant soil applied P in both genotypes.     

氯对白菜幼苗的生长及养分吸收的影响

采用土培实验,研究了外源氯（CK,低氯,中氯,高氯）对大白菜 [Brassica campestris L. ssp. Pekinesis (Lour)Olsson]幼苗叶绿素含量、根系活力以及对N、P、K养分吸收、累积的影响。结果表明:低浓度氯处理对大白菜幼苗没有明显的影响。中氯和高氯处理,都显著降低了白菜幼苗生物量、叶绿素含量和根系活力。随着氯浓度的升高,白菜幼苗叶片和根Cl-含量显著升高,中氯处理Cl-累积量最高,过量的氯降低了N、P、K养分在白菜幼苗体内的累积。氯胁迫抑制作物根系活力和光合作用从而减少主动养分的有效供应是造成生物量降低的主要原因。     

Root renewal of sugar beet as a mechanism of P uptake efficiency

Sugar beet (Beta vulgaris L.) was grown in two different long‐term P fertilization experiments on a sandy and a loamy soil. The P supply levels of the soils were ”︁low”, ”︁sufficient”, and ”︁high”, according to the German recommendation scheme. The low P level decreased shoot and storage root yield only on the loam soil, where the recovery of the P‐deficient plants after a drought period was slower than at a sufficient P supply. The size of the living root system, as determined by a conventional auger sampling method, peaked at early July and decreased until harvest on the sandy soil without any influence of the P level. On loam, the living root systems were more constant and larger at P shortage. Total root production, as determined by the ingrowth core method, was about 120 km m^—2 in the well P supplied loam treatments and 200 km m^—2 at P deficiency, which was 3—4 times and 5 times higher than the average size of the living root systems, respectively. Hence, a rapid root renewal took place. On sand, where no P deficiency occurred, total root production was not different between the P supply levels but higher than in the well‐supplied loam treatments. Modelling P uptake revealed that this root turnover and the concomitant better exploitation of the soil facilitates P uptake at a low P level in soil, but is of no advantage at a sufficient P supply. The increase of root production at P shortage increased calculated P uptake by 25% compared to a calculation with the ”︁usual” root production at a sufficient supply.