Transpiration of spring barley under nitrogen and phosphorus deficiency during leaf wilting

In an open gas exchange system with a thermocouple psychrometer the transpiration rate of the first leaf in 8-day plants of spring barley was measured in dependence on the water saturation deficit (ΔW _sat). The plants were cultivated in Richter’s nutrient solution, either complete, or deficient in nitrogen or phosphorus. The cuticular transpiration (as measured in the dark) was unaffected by N and P deficiency. The N deficiency reduced the transpiration rate by increasing stomatal resistance since full water saturation of the leaf (67% rate of the control variant) up to stomatal closing at Δ W_sat = 14%. The P deficiency does not affect the transpiration rate at initial phases of wilting, but the stomata close only at a higher Δ W_sat (25%) than those in the control.     

Dry matter production and partitioning in potato plants subjected to combined deficiencies of nitrogen, phosphorus and potassium

Three experiments examined effects on growth, dry matter partitioning and nutrient uptake in potato plants grown in large pots under different combinations of adequate and deficient levels of nitrogen, phosphorus and potassium. N supply affected the growth of all leaves, with low N reducing both the size of individual leaves and the extent of branch growth. P and K availability affected the growth of later formed leaves and only when both were deficient was branch growth substantially reduced. At later stages of growth, total green leaf area was significantly reduced by deficiency of each of the nutrients. Partitioning of dry matter to tubers was markedly reduced by K deficiency and increased in one experiment by P deficiency. When both P and K were deficient, partitioning approximated that under non‐limiting conditions. Leaf weight ratio (LWR) was higher under K deficiency, but not when P was also deficient, and was consistently higher when the ratio of K : P in dry matter was less than approximately five. In these experiments, LWR was not consistently related to shoot N% and N supply had relatively little effect on partitioning. There were large treatment effects on tuber dry matter percentage, characterised by significant interactions especially between N and K. Deficiency of one nutrient increased the concentration of others but uptake was highly regulated as crop content of all three nutrients was reduced when the supply of any one was deficient. The results show that the response of potatoes to single deficiencies may be influenced greatly by the levels of other nutrients.     

Phosphorus nutrition of jarrah (Eucalyptus marginata) seedlings

Summary Effects of calcium phosphate supply on plant dry matter and phosphorus concentrations of parts of jarrah (Eucalyptus marginata) seedlings grown in a lateritic topsoil from the jarrah forest were examined in two glasshouse trials. Phosphorus deficiency depressed root and shoot dry weights and severely deficient leaves were smal and purple with prominent red major veins. Phosphorus deficiency severely reduced stem phosphorus levels (0.5% to 0.02%, experiment 1). Phosphorus concentrations were higher in bark than wood and the amount of phosphorus in the bark was sensitive to stem age and phosphate supply. Phosphorus adequate plants had bark phosphorus concentrations in the range 0.2–0.9% compared to <0.1% in deficient plants (experiment 2). Jarrah leaves accumulated dry matter up to 80 days after expansion and some leaves exported phosphorus during this period. Bark analysis may therefore be preferable to leaf analysis for detecting phosphorus deficiency in this species.     

Effect of Phosphorus Deficiency and Water Deficit on Phosphatase Activities from Wheat Leaves

Wheat was sown in a phosphorus (P) deficient soil. Plants atlow levels of applied P had lower growth rates and lower concentrationsof phosphate in the shoots than plants grown with ‘highP’. Activities of both insoluble and soluble phosphataseincreased with P deficiency in the mature leaves. Soluble phosphataseactivities increased 2.5–3.0 fold as the concentrationof phosphate in the leaves fell from 0.4% to 0.1% dry weightThis increase was not a consequence of reduced growth, as severenitrogen deficiency had no effect on phosphatase activity. Soluble phosphatase activities were higher in young than inmature leaves, and also increased 3–4 fold with severewater deficit. However these increases in activity were notaccompanied by low concentrations of phosphate. Moreover, solublephosphatase activities in mature leaves of plants grown underconditions of water deficit rapidly decreased after rewatering.In contrast, the high soluble phosphatase activities in matureleaves of P deficient wheat persisted for up to 12 d after theresupply of P to adequate levels.     

Alteration of nutrient allocation and transporter genes expression in rice under N,P, K,and Mg deficiencies

Nitrogen (N), phosphorus (P), potassium (K), and magnesium (Mg) have essential physiological functions in plants. Their interactions in plants are not fully understood especially at the molecular level. In this study, we detected the physiological and molecular responses of rice plants at the vegetative growth phase to N, P, K, and Mg starvations. Deficiencies of N and P resulted in accumulation of soluble sugar and starch in the leaves. The root to shoot ratio increased under N and P deficiencies, but decreased under K and Mg deficiencies. In addition, deficiency of either K or Mg resulted in accumulation of the other cation in shoots. Moreover, K starvation decreased both K and soluble sugar contents in the roots pronouncedly. RT-PCR analysis showed that several sugar transporter genes in the leaves orchestrated with sugar accumulation induced by the nutrient shortages. Expression of a high affinity K transporter gene (OsHAK1) and a putative Mg transporter gene (OsMGT) showed opposite down- and up-regulation in the roots by K starvation. These findings suggest that deficiencies of the major nutrients suppressed the export of carbohydrates from source leaves. The regulated sugar and nutrient transporter genes investigated in this study could be used for elucidating the molecular mechanism of plants in their adaptation to varied nutrient supply.     

Latent manganese deficiency increases transpiration in barley (Hordeum vulgare)

To investigate if latent manganese (Mn) deficiency leads to increased transpiration, barley plants were grown for 10 weeks in hydroponics with daily additions of Mn in the low n M range. The Mn-starved plants did not exhibit visual leaf symptoms of Mn deficiency, but Chl a fluorescence measurements revealed that the quantum yield efficiency of PSII (F_v/F_m) was reduced from 0.83 in Mn-sufficient control plants to below 0.5 in Mn-starved plants. Leaf Mn concentrations declined from 30 to 7 μg Mn g⁻¹ dry weight in control and Mn-starved plants, respectively. Mn-starved plants had up to four-fold higher transpiration than control plants. Stomatal closure and opening upon light/dark transitions took place at the same rate in both Mn treatments, but the nocturnal leaf conductance for water vapour was still twice as high in Mn-starved plants compared with the control. The observed increase in transpiration was substantiated by ¹³C-isotope discrimination analysis and gravimetric measurement of the water consumption, showing significantly lower water use efficiency in Mn-starved plants. The extractable wax content of leaves of Mn-starved plants was approximately 40% lower than that in control plants, and it is concluded that the increased leaf conductance and higher transpirational water loss are correlated with a reduction in the epicuticular wax layer under Mn deficiency.     

Effects of potassium deficiency on water relations and photosynthesis of the tomato plant

Potassium deficient (−K) and potassium sufficient (+K) plants were exposed to four days of water stress. Well watered −K and +K plants had comparable rates of transpiration. But +K plants had a larger leaf area and depleted the soil moisture to a greater extent on day 1 of stress. For days 2 and 3 their transpiration rate, leaf water potential and relative water content fell below those of −K plants. Well watered −K plants had a significantly lower rate of photosynthesis than +K plants. Photosynthesis of −K plants was more sensitive to reduction in plant water potential than that of +K plants. Reduction of photosythesis in −K leaves was due to impairment of photosynthetic capacity and not to stomatal closure. Growth was significantly reduced in −K plants.     

The Influence of Potassium on the Transpiration Rate and Stomatal Opening in Triticum aestivum andPisum sativum

The investigation concerns the influence of potassium on the transpiration rate of Triticum aestivum and Pisum sativum grown in nutrient solutions. Plants with high amounts of potassium were found to have the lowest transpiration rates. Shoot/root ratio, stomatal frequency, and stomatal aperture were correlated with the potassium concentration in the leaves. In Triticum no correlations with leaf concentration of Na were evident. Short term experiments were carried out in order to investigate the effects on the transpiration rate of a sudden increase in potassium concentration in the nutrient solution. An addition of potassium chloride to potassium deficient wheat plants resulted in a decrease in the transpiration rate of up to 50% within two hours. Comparative tests with sodium chloride resulted in a decrease in transpiration rate of the same magnitude, indicating that the short-time reaction is not specific to potassium. The experiments show that the transpiration rate can be regulated by varied potassium and sodium concentrations. The observed effect is supposed to be due to changes in the stomatal aperture.     

Micro-Nutrient Deficiency and Transpiration in Tropaeolum majus L.

The transpiration of Tropaeolum plants, grown in water culture,on full nutrient solutions and on solutions deficient in oneof the following, i.e. boron, copper, manganese, and zinc, wasstudied. The transpiration rate of the control plants grownon the full nutrient solution was significantly higher thanthat of the deficient ones. The more acute the deficiency, thegreater was the disparity. Under the condition of the experiment, the control plants weresmaller in size, having fewer and smaller leaves than the deficientones, but the foliage was much greener and healthier in appearance.     

Effects of Kinetin on Transpiration Rate and Abscisic Acid Content of Water Stressed Young Wheat Plants

Effects of kinetin on transpiration rate and abscisic acid content were determined. Leaves from 9-day-old wheat plants (Triticum aestivum L. cv. Weibull's Starke II) were used. —Transpiration rate decreased in excised leaves put in water, but it was maintained at a higher rate when kinetin was supplied. When excised leaves were water stressed by air-drying for 1 h, addition of kinetin resulted in a considerable stimulation of transpiration rate. The effect reached its maximum after 15 h and this level remained relatively unchanged for at least 10 h. Intact seedlings which were stressed before leaf excision, showed only a slight stimulation of kinetin on transpiration rate. — Abscisic acid content slowly increased up to three-fold in 2 days in excised leaves put in water. In excised and water-stressed leaves the abscisic acid content was reduced during the first 24 h and then increased. As the leaves were fully turgid, the increase could not have been caused by water stress. However, both in stressed and unstressed leaves kinetin addition reduced the increase in abscisic acid content. — It is suggested that the stimulation by kinetin on transpiration rate in excised and water stressed leaves was mainly due to the combined effect of (1) a reduction in the activity of endogenous cytokinins, (2) kinetin acting as a ‘substitute’ for the inactivated cytokinins but exerting a stronger effect on transpiration than the endogenous cytokinins, and (3) the ‘extra’ reduction in abscisic acid content caused by the kinetin treatment. Furthermore, the results indicate that changes in cytokinins might be partly responsible for the aftereffect on transpiration.     

Plant morphology and root hydraulics are altered by nutrient deficiency in Pistacia lentiscus (L.)

The plants in arid and semiarid areas are often limited by water and nutrients. Morpho-functional adjustments to improve nutrient capture may have important implications on plant water balance, and on plant capacity to withstand drought. Several studies have shown that N and P deficiencies may decrease plant hydraulic conductance. Surprisingly, studies on the implications of nutrient limitations on water use in xerophytes are scarce. We have evaluated the effects of strong reductions in nitrogen and phosphorus availability on morphological traits and hydraulic conductance in seedlings of a common Mediterranean shrub, Pistacia lentiscus L.. Nitrogen deficiency resulted in a decrease in aboveground biomass accumulation, but it did not affect belowground biomass accumulation or root morphology. Phosphorus-deficient plants showed a decrease in leaf area, but no changes in aboveground biomass. Root length, root surface area, and specific root length were higher in phosphorus-deficient plants than in control plants. Nitrogen and phosphorus deficiency reduced both root hydraulic conductance and root hydraulic conductance scaled by total root surface area. On the other hand, nutrient limitations did not significantly affect root conductance per unit of foliar surface area. Thus, adaptation to low nutrient availability did not affect seedling capacity for maintaining water supply to leaves. The implications for drought resistance and survival during seedling establishment in semi-arid environments are discussed.     

The Effect of Potassium Deficiency on Stomatal and Cuticular Resistance in Tea (Camellia sinensis)

The effect of potassium deficiency on cuticular resistance and diurnal variation in stomatal diffusive resistance was studied in tea (Camellia sinensis). The plants were grown in sand and potassium deficiency induced by withholding the supply of potassium. The results showed that during the day potassium-deficient leaves had a higher stomatal diffusive resistance than control leaves. However when solar radiation was reduced by clouds the stomatal diffusive resistance in both control and potassium-deficient leaves was not significantly different. Night opening of stomata was observed in both control and potassium-deficient leaves, but noticeably lower in the latter. Potassium-deficient leaves had a lower cuticular resistance than control leaves.     

Phosphorus concentrations in the leaves of defoliated white clover affect abscisic acid formation and transpiration in drying soil

Increased leaf phosphorus (P) concentration improved the water-use efficiency (WUE) and drought tolerance of regularly defoliated white clover plants by decreasing the rate of daily transpiration per unit leaf area in dry soil. Night transpiration was around 17% of the total daily transpiration. The improved control of transpiration in the high-P plants was associated with an increased individual leaf area and WUE that apparently resulted from net photosynthetic assimilation rate being reduced less than the reductions in the transpiration (27% vs 58%). On the other hand, greater transpiration from low-P plants was associated with poor stomatal control of transpirational loss of water, less ABA in the leaves when exposed to dry soil, and thicker and smaller leaf size compared with high-P leaves. The leaf P concentration was positively related with leaf ABA, and negatively with transpiration rates, under dry conditions ( P < 0.001). However, leaf ABA was not closely related to the transpiration rate, suggesting that leaf P concentration has a greater influence than ABA on the transpiration rates.     

Transpiration in potato plants infected with Verticillium spp

Potato plants (cv. King Edward) infected with Verticillium albo-atrum and with V. dahliae transpired more slowly than healthy plants; this difference increased as the disease progressed. Diurnal fluctuations in transpiration were smaller in infected plants than in controls because infection markedly reduced water loss during the normal daytime peak period. Transpiration at night was unaffected by infection.
Both stomatal and cuticular transpiration of single, detached leaves were reduced by infection. A linear correlation was obtained between 'water saturation deficit' and transpiration rate in both diseased and healthy plants until the leaves wilted, suggesting that reductions in the stomatal rate are a consequence of the greater water deficits found in diseased plants, the differences in cuticular rates probably being due to anatomical differences between healthy and diseased leaves.
Close parallels between transpiration and water deficit indicate that in diseased plants water loss is largely determined by leaf water content. Thus wilting, commonly seen as a symptom of infection, is not the result of excessive water loss but follows a reduction in the supply of water to the leaves.
The author thanks Professor I. Isaac of this department and Dr G. C. Evans of the Botany School, Cambridge for their advice. The research was sponsored by the Potato Marketing Board.     

Balance between Potassium and Phosphorus in the Nutrition of Barley: I. The Influence on Amine Content

Potassium-deficient barley accumulates the amines agmatine andputrescine, the latter of which is known to produce necroticspots on the leaves in some seasons. The severity of potassiumdeficiency symptoms is strongly influenced by the external levelof phosphorus. An experiment was conducted in water culture,using two-week-old barley to discover whether amine accumulationwas similarly affected. Four levels of potassium —1/64,1/6, 1/4, and 1/1 of full supply—were combined factoriallywith the same levels of phosphorus, the diagonal in this designbeing a series of ‘balanced’ solutions in whichpotassium and phosphorus were present in the same ratio as inthe full nutrient. The plants were sampled three times duringthe ten-week period of growth, and the form of the results wassimilar each time. Whenever potassium was reduced, putrescinecontent rose above normal, but for large amounts of putrescineto be accumulated, phosphorus supply had to be in excess ofpotassium. The highest levels of agmatine were also found wherepotassium was low and phosphorus in excess, but significantaccumulations also developed whenever phosphorus was low relativeto potassium, that is, where high levels of potassium were observedin the plants. Since agmatine and putrescine are very closely related biochemicallyand together make up 90 per cent of the amine content of barley,the influence of potassium and phosphorus on their summed contentwas considered. Potassium was found to have the dominant effect:at any one level of phosphorus supply, the summed content wasminimal at the highest level of potassium, and reduction inpotassium always increased it. The effect of phosphorus dependedon the degree of imbalance between potassium and phosphorusin the nutrient. High summed contents were found where eitherpotassium or phosphorus was present in excess, and minimum contentwas found where the levels were balanced. There were significantpartial correlations between summed amine content and the potassiumand phosphorus contents of the plants. The high significanceof correlations between amine content and the proportion ofdead and moribund shoot material suggested that amine accumulationmight be partly responsible for the rapid death of the leavesof the deficient plants as well as for the production of necroses,which are only limited in area.     

Diurnal courses and factorial dependencies of leaf conductance and transpiration of differently potassium fertilized and watered field grown barley plants

During the grain filling period we followed diurnal courses in leaf water potential (ψ₁), leaf osmotic potential (ψ_π), transpiration (E), leaf conductance to water vapour transfer (g) and microclimatic parameters in field-grown spring barley (Hordeum distichum L. cv. Gunnar). The barley crop was grown on a coarse textured sandy soil at low (50 kg ha⁻¹) or high (200 kg ha⁻¹) levels of potassium applied as KCl. The investigation was undertaken at full irrigation or under drought. Drought was imposed at the beginning of the grain filling period. Leaf conductance and rate of transpiration were higher in the flag leaf than in the leaves of lower insertion. The rate of transpiration of the awns on a dry weight basis was of similar magnitude to that of the flag leaves. On clear days the rate of transpiration of fully watered barley plants was at a high level during most part of the day. The transpiration only decreased at low light intensities. The rate of transpiration was high despite leaf water potentials falling to rather low values due to high evaporative demands. In water stressed plants transpiration decreased and midday depression of transpiration occurred. Normally, daily accumulated transpirational water loss was lower in high K leaves than in low K leaves and generally the bulk water relations of the leaves were more favourable in high K plants than in low K plants. The factorial dependency of the flag leaf conductances on leaf water potential, light intensity, leaf temperature, and leaf-to-air water vapour concentration difference (ΔW) was analysed from a set of field data. From these data, similar sets of microclimatic conditions were classified, and dependencies of leaf conductance on the various environmental parameters were ascertained. The resulting mathematical functions were combined in an empirical simulation model. The results of the model were tested against other sets of measured data. Deviations between measured and predicted leaf conductance occurred at low light intensities. In the flag leaf, water potentials below-1.6 MPa reduced the stomatal apertures and determined the upper limit of leaf conductance. In leaves of lower insertion level conductances were reduced already at higher leaf water potentials. Leaf conductance was increased hyperbolically as photosynthetic active radiation (PAR) increased from darkness to full light. Leaf conductance as a function of leaf temperature followed an optimum curve which in the model was replaced by two linear regression lines intersecting at the optimum temperature of 23.4°C. Increasing leaf-to-air water vapour concentration difference caused a linear decrease in leaf conductance. Leaf conductances became slightly more reduced by lowered water potentials in the low K plants. Stomatal closure in response to a temperature change away from the optimum was more sensitive in high K plants, and also the decrease in leaf conductance under the influence of lowered ambient humidity proceeded with a higher sensitivity in high K plants. Thus, under conditions which favoured high conductances increase of evaporative demand caused an about 10% larger decrease in leaf conductance in the high K plants than in the low K plants. Stomatal sizes and density in the flag leaves differed between low and high K plants. In plants with partially open stomata, leaf conductance, calculated from stomatal pore dimensions, was up to 10% lower in the high K plants than in the low K plants. A similar reduction in leaf conductance in high K plants was measured porometrically. It was concluded that the beneficial effect of K supply on water use efficiency reported in former studies primarily resulted from altered stomatal sizes and densities.     

Mineral nutrition of cacao (Theobroma cacao L.)

Summary Two experiments on cacao seedlings grown in sand culture are described, the first of which was concerned with variations in the levels of nitrogen, phosphorus, potassium, calcium, magnesium and sulfur (the macronutrient experiment) and the second dealing with variations in the levels of iron, copper, zinc, boron, manganese, and molybdenum (the micronutrient experiment).Many of the deficiency symptoms obtained were similar to those reported in the literature and they have not been described again. However, additional information is provided for symptoms of phosphorus, potassium, calcium, iron, manganese, copper, boron, and molybdenum deficiencies.The effects of all treatments on the dry weights of leaves, stems, and roots are presented. The effects of the macronutrient treatments on the levels of nitrogen, phosphorus, potassium, calcium, and magnesium in the leaves of eight month old plants and the effects of micronutrient treatments on the levels of nitrogen, phosphorus, potassium, calcium, magnesium, iron, manganese, copper, zinc, boron, molybdenum, sodium, and aluminium in the leaves of eleven-month-old plants are presented and discussed.     

Does water and phosphorus uptake limit leaf growth of Rhizoctonia-infected wheat seedlings?

Wheat seedlings infected with a pure inoculum of the root-rotting fungus Rhizoctonia solani were grown in pots designed to fit in pressure chambers, to allow the effects of the Rhizoctonia infection on leaf growth to be studied while maintaining the leaves at elevated water status. Wheat was grown to the third leaf stage in soil inoculated with three different levels of Rhizoctonia, and the pots were then pressurised for seven days to maintain the leaf xylem at the point of bleeding (ie. the leaves were at full turgor). The reduction in leaf expansion caused by Rhizoctonia was not overcome by pressurisation, indicating that a reduced supply of water to the leaves was not responsible for reduced leaf growth. The addition of phosphorus to pots marginally deficient in P did not increase the leaf growth of Rhizoctonia-infected plants, despite increased P uptake to the leaves. These results indicate that a reduced supply of water to the leaves and a supply of phosphorus that was bordering on deficient was not the cause of the growth reduction in seedlings with Rhizoctonia infection. The nature of this reduced growth remains uncertain but may involve growth regulators produced by the fungus, or by the plant as a result of the infection process. The mechanism of these growth reductions is of interest as it may provide a key to the development of plant resistance mechanisms. This revised version was published online in June 2006 with corrections to the Cover Date.     

Magnesium deficiency in expanding leaves of Phaseolus vulgaris-gas exchange and nutrient concentrations

Phaseolus vulgaris was cultured either with or without magnesium in an aerated nutrient solution in growth chambers from 21 days after germination. Five days after transfer to Mg-deficient nutrient solution, terminal leaflets of first trifoliate leaves stopped expansion. From the fifth day after transfer, the net assimilation rate, the transpiration rate and the leaf water vapour conductance of first trifoliate leaves of the deficient plants declined. Following resupply of Mg on the seventh day after transfer to the Mg-deficient solution, the assimilation rate increased to 93% by the 12th day, the transpiration rate to 76% and the leaf water vapour conductance to 50% of the control plants.     

The Ultrastructure of Chloroplasts in Mineral-deficient Maize Leaves

The ultrastructure of mesophyll chloroplasts in full-nutrient and mineral-deficient maize (Zea mays) leaves was examined by electron microscopy after glutaraldehyde-osmium tetroxide fixation. Nitrogen, calcium, magnesium, phosphorus, potassium, and sulfur deficiencies were induced by growing the plants in nutrient culture. Distinctive chloroplast types were observed with each deficiency. Chloroplasts from nitrogen-deficient plants were reduced in size and had prominent osmiophilic globules and large grana stacks. Magnesium deficiency was characterized by the accumulation of osmiophilic globules and the progressive disruption of the chloroplast membranes. In calcium deficiency, the chloroplast envelope was often ruptured. Chloroplasts from potassium- or phosphorus-deficient plants possessed an extensive system of stroma lamellae. Sulfur deficiency resulted in a pronounced decrease of stroma lamellae, an increase in grana stacking, and the frequent occurrence of long projections extending from the body of the chloroplast. These morphological changes were correlated with functional alterations in the chloroplasts as measured by photosystem I and II activities. In chloroplasts of the nitrogen- and sulfur-deficient plants an increase in grana stacking was associated with an increase in photosystem II activity.