Full-strength Nutrient Solution Research Articles

Evaluating the Aqueous Phase From Hydrothermal Carbonization of Cow Manure Digestate as Possible Fertilizer Solution for Plant Growth.

Improving the agronomic use of recycled nutrients derived from organic waste is one of the priorities within the measures adopted by the European community to reduce environmental issues but remains an unexplored area of research. This study focused on investigating the possibility of using innovative fertilizer solutions in hydroponic systems for the growth of agricultural plants. To this purpose, a liquid fraction [aqueous hydrothermal carbonization (HTC) liquid (AHL)] derived from HTC of cow manure digestate was chemically characterized (pH, electrical conductivity, mineral elements, and organic compounds such as phytotoxins), diluted with distilled water (1:30, 1:60, and 1:90, v/v) to reduce its potential phytotoxicity, and used to grow hydroponic maize (Zea mays L.) plants instead of the classical full-strength nutrient solution. The results indicated that the dilution ratio 1:30 of the AHL solution maintained a high level of toxicity for the plants (phytotoxic substances, especially Na and alkalinity), inducing the arrest of their growth. Differently, the two other dilution ratios (i.e., 1:60 and 1:90) seemed to considerably limit the levels of toxicity, since they allowed the plants to develop. However, these dilution ratios were poor in nutrient elements, inducing alteration in photosynthesis and an onset of deficiency symptoms such as pronounced leaf chlorosis. In view of an eco-friendly approach, future studies are, therefore, needed to identify the correct species-specific dilution ratio to supply both low levels of phytotoxins and adequate content of essential nutrients for appropriate plant growth and development. Furthermore, in order to lower specific Na phytotoxicity, treatments are of utmost importance before using AHL as a fertilizer solution.

Photosynthesis and morphological responses of rice cultivars to seedling stage soil N stress

Continuous cultivation of dry seeded rice in addition to adverse environmental factors make the rice soils deficient of nitrogen more than any other essential nutrient. The study was conducted under greenhouse conditions in pots by varying soil N during seedling growth. Six cultivars with diverse genetic background, CL152, R4100412, Antonio, Bowman, Nipponbare, and Rex, were seeded in 6 × 12 inch PVC pots filled with 3:1 (sand: soil) as the rooting medium. All plants were irrigated with full-strength Hoagland nutrient solution, delivered three times for 28 days after sowing. Then, half the plants in each cultivar were supplied with 100% of control nutrient solution minus N for another 4 weeks. Agronomic, physiological and root parameters measurements recorded at optimum interval. Cumulative indices were calculated by summing each response index value as a ratio of treatment by control values. Cultivars were classified based on total cumulative N stress response index (TCNSRI), the sum of all the traits measured, into different groups based on mean and standard error. The reductions in most of the measured traits were less in CL152 and R4100412 than other rice cultivars to soil N stress. Based on total cumulative N stress response indices, the cultivars were classified. The cultivar R41004122 was identified as tolerant, CL152 as intermediate, and Antonio, Bowman, Nipponbare and Rex were sensitive to soil N stress. The identified soil N stress tolerant and intermediately tolerant cultivars will be useful to breeders to develop new genotypes and farmers to select cultivars best suited for dry seeded rice.

Macronutrient deprivation eustress elicits differential secondary metabolites in red and green-pigmented butterhead lettuce grown in a closed soilless system.

Through precise control of the nutrient solution (NS), closed soilless systems enable targeted manipulation of plant secondary metabolites, which constitute health-promoting components of the human daily diet. A nutrient film technique (NFT) system was employed to assess the effect of NS macronutrient-based concentration (full, half-, and quarter-strength corresponding to electrical conductivity (EC) of 1.5, 0.75, and 0.5 dS m-1 ) on the bioactive profile of red and green-pigmented Salanova® butterhead lettuce. Half-strength NS reduced fresh biomass of both cultivars by 14%, whereas quarter-strength NS reduced the fresh biomass of green and red Salanova by 24% and 38%, respectively. However, moderate nutrient stress (half-strength NS) boosted red Salanova total ascorbic acid, chlorogenic, chicoric, caffeoyl-meso-tartaric, total phenolic acids, and anthocyanins concentrations by 266%, 199%, 124%, 251%, 162%, and 380%, respectively compared with the control, full-strength NS. Nutritional eustress and appropriate cultivar selection are effective means to increase phytochemical content and optimize year-round production of lettuce in closed soilless systems. © 2019 Society of Chemical Industry.

Biostimulant Application with a Tropical Plant Extract Enhances Corchorus olitorius Adaptation to Sub-Optimal Nutrient Regimens by Improving Physiological Parameters

The emerging role of plant biostimulants in enhancing nutrient efficiency is important for maintaining soil fertility under sub-optimal nutrient regimens. We aimed to elucidate the morpho-physiological and biochemical effects as well as mineral composition changes of greenhouse jute (Corchorus olitorius L.) treated with a commercial vegetal-derived biostimulant from a tropical plant extract (PE; Auxym®, Italpollina, Rivoli Veronese, Italy). Plants were sprayed in weekly intervals with a solution containing 2 mL·L−1 PE. Jute plants were supplied with three nutrient solution concentrations: full-, half-, and quarter-strength. Decreasing macronutrient concentrations in the nutrient solution (NS), especially at quarter-strength, triggered a decrease in several morphological (plant height, leaf number, and dry biomass) and physiological (net CO2 assimilation rate (ACO2) and SPAD (Soil Plant Analysis Development) index) parameters. PE application triggered specific ameliorative effects in terms of fresh yield at both half- and quarter-strength nutrient solution (15.5% and 29.5%, respectively). This was associated with an enhancement in ACO2, SPAD index, and especially the nutritional status (high nitrate, K, and Mg contents, and low Na content). The foliar application of PE, strongly increased chlorophyll b content, enhancing jute plant adaptation to fluctuating light and therefore the efficiency of photosynthesis, positively affecting starch, soluble proteins, and total amino acids content but only when jute plants were irrigated with full-strength NS, compared to the respective control treatment. At lower nutrient strength, PE reprogrammed the nitrogen distribution, allowing its remobilization from glutamate, which was quantitatively the major amino acid under lower nutrient strength, but not from chlorophylls, thus maintaining efficient photosynthesis. We confirmed that PE Auxym® acts in a balanced manner on the main metabolic pathways of the plant, regulating the uptake and transport of mineral nutrients and protein synthesis, increasing the accumulation of essential amino acids under full nutritive solutions, and re-distributing nitrogen from amino acids to allow leaf growth and expansion even under sub-optimal nutrient conditions. Overall, the use of natural plant biostimulants may be a potential solution in low-input conditions, where environmental constraints and restricted use of fertilizers may affect potential crop productivity.

Effect of Silicon on the Tolerance of Wheat (Triticum aestivum L.) to Salt Stress at Different Growth Stages: Case Study for the Management of Irrigation Water.

This paper aims to determine the most tolerant growth stage(s) of wheat to salinity stress with the addition of silicon. The aim was to investigate whether saline water could be used instead of good quality water for irrigation without implicating a greater risk to crop production. Local wheat cv. Gimmiza 11 was germinated and grown in sand cultures. Four different NaCl salinity levels were used as treatments: 0, 60, 90 and 120 mM. This was in the presence of 0 and 0.78 mM Si which added as sodium meta- silicate (Na2SiO3·9H2O). Both the NaCl and Si treatments were carried out using a full strength nutrient solution that was adjusted at pH 6.0 and used for irrigation in four replications. The application of Si with the saline nutrient media significantly enhanced superoxide dismutase (SOD) and catalase (CAT) activities in plant leaves at the booting stage compared to the other stages. This was associated with a marked decline in the H2O2 content. At the booting stage, the Si treatment promoted CAT activity in 120 mM NaCl-stressed leaves compared to the leaves treated with only 120 mM NaCl solution. SOD showed greater prevalence at the booting stage when Si was added into the saline media, and it also revealed maximum activity at the milky stage with salinity stress. This was associated with a smaller reduction in shoot fresh and dry weights, greater reduction in the leaf Na+ content and an increase in the K+ content, which ultimately increased the cytosolic K+/Na+ ratio. Chlorophyll a and b and carotenoid (total photosynthetic pigments) were also higher at the booting stage of salt-stressed plants treated with Si compared to other stages. Accordingly, Si application enhanced the salt tolerance of wheat and reduced the inhibitory effect of Na+ and oxidative stress damage as growth proceeded towards maturity, particularly at the booting stage. This shows that saline water can be used for wheat irrigation at the booting stage (much water is consumed) when good quality water is not available for supplemental irrigation. A field study is needed to confirm the greenhouse results.

NaCl alleviates iron deficiency through facilitating root cell wall iron reutilization and its translocation to the shoot in Arabidopsis thaliana

The present study was undertaken to investigate the mechanism underlying NaCl-alleviated Fe (iron) deficiency in Arabidopsis thaliana Col-0 (Columbia ecotype). Six-week-old Col-0 with rosettes of similar diameters was grown in full-strength nutrient solution lacking Fe (Fe-deficient) or full-strength nutrient solution (Fe-sufficient) with or without 10 mM NaCl for 7 days. Roots were then harvested for analysis of total Fe content, soluble Fe concentration, and abscisic acid (ABA) content as well as for cell wall and RNA extraction, while shoots were harvested for total Fe content and soluble Fe concentration measurements. The total Fe content and the soluble Fe concentration were higher in roots and shoots of −Fe + NaCl-treated plants than −Fe-treated plants, whereas Fe retention in the cell wall was reduced, suggesting the presence of a cell wall Fe-reutilization mechanism. This conclusion was confirmed by the observation that less hemicelluloses Fe was found in plants under −Fe + NaCl treatment. In addition, associated to the upregulation of genes related to the long-distance transport of Fe, such as FRD3 (FERRIC REDUCTASE DEFECTIVE3), YSL2 (YELLOW STRIPE-LIKE), and NAS1 (NICOTIANAMINE SYNTHASE1) under −Fe + NaCl treatment, more Fe was available in shoots. Furthermore, endogenous ABA is involved in NaCl-alleviated Fe deficiency, as the addition of Flu (fluridone), an inhibitor of ABA biosynthesis, abolished the positive effect of NaCl on Fe deficiency. Under −Fe condition, NaCl not only is involved in the reutilization of cell wall Fe but also participates in the translocation of Fe from root to shoot in Arabidopsis, partially through its effect on ABA contents.

Implication of Antioxidant Defence in Tolerance to Fe Deficiency of Pisum Sativum Leaves

The intend of this work was to investigate whether some leaf parameters involved in the antioxidant mechanisms were differently expressed in two pea (Pisum sativum L.) cultivars characterized by different tolerance to Fe deficiency: cv. Kelvedon, tolerant and cv. Lincoln, susceptible. Both cultivars were grown in a full strength nutrient solution (C), in the absence of Fe (direct deficiency, DD) or in the presence of Fe and bicarbonate (induced deficiency, ID) for 12 days. Our results show that peroxidase activity and isoform expression increased in Kelvedon in both treatments, while it decreased in Lincoln plants grown in the presence of bicarbonate, suggesting the involvement of this activity improvement in Fe deficiency tolerance of pea plants. Interestingly, while only slight differences were reported between both cultivars under DD, the adaptation of Kelvedon under ID seems to be related, at least in part, to its greater ability to enhance the antioxidant defense at leaf level.

Influence of Humic Acid in Diluted Nutrient Solution on Growth, Nutrient Efficiency, and Postharvest Attributes of Gerbera

A hydroponics experiment was conducted to study the effect of humic acid (HA) on gerbera (Gerbera jamesonii L.) cv. Malibu in different diluted nutrient solutions. The HA (500 mgL−1) was added to a nutrient solution (NS) of gerbera with two dilution levels of NS, ½ NS and ¼ NS, and full-strength nutrient solution (NSc). The HA application compensated for nitrogen, magnesium, and iron deficiency in the ½ NS. Nutrient utilization efficiency (NUTE) of nitrogen in shoot decreased and that of Fe increased in the ½ NS compared with the ¼ NS when HA was applied. The number of harvested flowers per plant was the greatest in the NSc and the ½ NS with incorporating HA. Flower vase life improved by increasing NS level (9.33 days). It seems HA could be successfully considered as a compound to decrease nutrients input in gerbera hydroponics production.

Ultrastructural damage in tomato plants exposed to chromium III

The study aimed to investigate the short-term effects of Cr on the ultrastructure of root, stem and leaf cells of tomato plants (Solanum lycopersicum L.), and to verify the compartmentalization of the transition metal. Tomato seedlings were grown in an environmental chamber maintained at 25 ±1°C, with relative humidity of 70% and a 12 h photoperiod, in full-strength nutrient solution containing 25 or 50 mg L -1 of Cr(III), while control plants were cultured in the absence of Cr. An electron probe X-ray microanalyzer equipped with a wavelength dispersive spectrometer was used in association with transmission electron microscopy in order to localize Cr deposits. In tomato roots Cr deposits were concentrated mainly in the cell walls, while in stems and leaves the deposits could be observed in the cells walls as well as in vacuoles, suggesting that these compartments act as barriers against metal phytotoxicity. Plants exposed to Cr presented leaves containing abnormally shaped chloroplasts, with reduced numbers of grana and atypical thylakoids, whereas the mitochondria presented reduced numbers of cristae. These Cr-induced alterations result in the diminution of photosynthetic and respiratory activities with harmful consequences to plant health. The microanalytical methods employed in this study have shed new light onto the possible causes of Cr phytotoxicity. Such knowledge is valuable in understanding the mechanisms employed by plants to circumvent the uptake and transport of potentially toxic metals.

FERTILIZER CONCENTRATION AND IRRIGATION METHOD AFFECTS GROWTH AND FLOWERING OF TWO BEDDING PLANTS

Zonal geranium (Pelargonium × hortorum ‘Real Mintaka’) and petunias (Petunia × hybrid Hort. Vilm.-Andr. ‘Giove’) were grown in closed soilless systems to evaluate the effects of irrigation system (drip and subirrigation) and nutrient solution concentration (half and full) during spring growing season in terms of substrate electrical conductivity (EC(s)), growth, quality, crop evapotranspiration, and growth index water use efficiency (WUE(GI)). For both crops, at the end of the cultural cycle the highest EC(s) in the upper and lower layers were recorded in plants fertilized with the full strength solution, whereas the effect of irrigation system was less pronounced where the highest EC(s) was recorded in subirrigation but only in the upper layer. The highest EC(s) recorded with subirrigation under full strength nutrient solution on geranium had a negative effect on plant growth parameters (shoot dry weight, root-to-shoot ratio, final leaf area, and growth index) and on number of flowers, while no significant effects were observed for petunia, indicating that this bedding plant can be considered more tolerant to salinity. No significant differences among treatments were recorded for the petunia WUE(GI), whereas for geranium the lowest value of WUE(GI) was observed in the subirrigation treatment using half strength nutrient solution.

Nutrient solution concentration on pepper grown in a soilless closed system: yield, fruit quality, water and nutrient efficiency

The aim of the experiment was to verify how the adoption of a reduced strength nutrient solution in a soilless closed system could influence the production and quality of pepper and improve the use efficiency of water and minerals. Two nutrient solutions characterized by the same ion ratio but macronutrient concentration equal to 100% or 60% were adopted. The total yield did not differ between the treatments; however the lower concentration of nutrients determined a significant reduction of incidence of unmarketable fruits (blossom-end rot) and thus a higher marketable production (+15%). Within the fruit quality characteristics the dry matter content and the titratable acidity were significantly higher adopting the full strength nutrient solution. Important differences were found when the agronomic water use efficiency was considered: the weight of marketable pepper produced per m3 of water input was about 32% higher using the reduced concentration treatment according to the lower volume of water released in the environment due to the lower renewal of recirculated nutrient solution. A similar pattern was observed for the use efficiency of the main nutrients. With reduced strength nutrient solution the amounts of nitrogen, phosphorus and potassium released per ton of marketable tomatoes were respectively 83%, 80% and 81% lower than the control. The use of a reduced strength nutrient solution in soilless closed system for pepper cultivation did not influence the total yield and improved the use efficiency of water and minerals. Moreover, the environmental impact of the system was drastically reduced.

Simulation of crop water and mineral relations in greenhouse soilless culture

A composite model was developed for water and mineral relations of greenhouse tomato ( Solanum lycopersicum L.) cultivated in semi-closed or open soilless (rockwool) culture. The model simulated on a daily basis: (i) the evolution of crop leaf area index and water uptake using empirical equations; and (ii) the variations of ion concentrations and electrical conductivity (EC) in the recirculating or drainage nutrient solution using a mass balance equation based on the concept of ion uptake concentration. The model was calibrated using measured data collected in previous works and validated in two independent experiments carried out in 2005 and 2007. In these experiments, different fertigation strategies were tested using nutrient solutions prepared with saline (9.5 mol m −3 NaCl) water. In semi-closed systems, the recirculating nutrient solution was discharged whenever EC exceeded a pre-defined threshold (4.5, 6.5 or 7.5 dS m −1, depending on the experiment) and/or nitrate (NO 3 −) concentration was lower than 1.0 mol m −3. This value was selected because 20 mg L −1 (1.43 mol m −3) is the limit imposed to NO 3 − concentration of wastewater discharged into surface water by the current Italian legislation. In open system, the crop was irrigated with full-strength nutrient solution without recirculation of drainage water. In both years, fertigation strategy did not affect significantly crop growth, fruit yield and water uptake. In most cases, simulations of seasonal crop water uptake were within the confidence interval of the measurements with a maximum deviation of −6%. The model predicted acceptably the time course of EC and ion concentration in recirculating (semi-closed systems) or drainage (open system) nutrient solution. A moderate discrepancy between observations and simulations was found for NO 3 − concentration, especially during the first weeks after planting. In general, there was a good agreement between simulated and measured values of total water and nitrogen (N) use. In 2005, simulated values of N uptake in semi-closed systems were −11% to +5% of measured values. Prediction of N uptake was less accurate in 2007, when simulated values were +17% of measured values. In open system, the model underestimated N uptake (−17%) mainly due to overestimation of N leaching (+6%). Applications of the composite model for operative management of soilless culture and for scenario analysis are discussed.

Strategies to decrease water drainage and nitrate emission from soilless cultures of greenhouse tomato

In the spring-summer season of 2005 and 2006, we explored the influence of three fertigation strategies (A–C) on the water and nitrogen use efficiency of semi-closed rockwool culture of greenhouse tomato conducted using saline water (NaCl concentration of 9.5 mol m−3). The strategies under comparison were the following: (A) crop water uptake was compensated by refilling the mixing tank with nutrient solution at full strength (with the concentrations of macronutrients equal or close to the corresponding mean uptake concentrations as determined in previous studies) and the recirculating nutrient solution was flushed out whenever its electrical conductivity (EC) surpassed 4.5 dS m−1 due to the accumulation of NaCl; (B) the refill nutrient solution had a variable EC in order to maintain a target value of 3.0 dS m−1; due to the progressive accumulation of NaCl, the EC and macronutrient concentrations of the refill nutrient solution tended to decrease with time, thus resulting in a progressive nutrient depletion in the recycling water till N–NO3− content dropped below 1.0 mol m−3, when the nutrient solution was replaced; (C) likewise Strategy A, but when EC reached 4.5 dS m−1, crop water uptake was compensated with fresh water only in order to reduce N–NO3− concentration below 1.0 mol m−3 before discharge. In 2005 an open (free-drain) system (Strategy D), where the plants were irrigated with full-strength nutrient solution without drainage water recycling, was also tested in order to verify the possible influence of NaCl accumulation and/or nutrient depletion in the root zone on crop performance. In the semi-closed systems conducted following strategies A, B or C, the nutrient solution was replaced, respectively, 10, 14 and 7 times in 2005, and in 19, 24 and 14 times in 2006, when the cultivation lasted 167 days instead of 84 days in 2005. In both years, there were no important differences in fruit yield and quality among the strategies under investigation. Strategy C produced the best results in terms of water use and drainage, while Strategy B was the most efficient procedure with regard to nitrogen use. In contrast to strategies A and D, the application of strategies B and C minimized nitrogen emissions and also resulted in N–NO3− concentrations in the effluents that were invariably lower than the limit (approximately 1.42 mol m−3) imposed to the N–NO3− concentration of wastewater discharged into surface water by the current legislation associated to the implementation of European Nitrate Directive in Italy.

The influence of irrigation system and nutrient solution concentration on potted geranium production under various conditions of radiation and temperature

Zonal geranium ( Pelargonium × hortorum ‘Real Mintaka’) were grown in closed soilless systems to evaluate the effects of irrigation system (drip and subirrigation) and nutrient solution concentration (half and full) under various conditions of radiation and temperature (winter and summer) in terms of substrate electrical conductivity (EC s), growth, quality, crop evapotranspiration (ET c) and growth index water use efficiency (WUE GI) and nutrient uptake. At he end of the cultural cycle the highest EC s in the upper and lower layers were recorded in the spring season on plants grown in subirrigation using a full nutrient solution concentration. The highest shoot biomass, leaf area, plant growth index, and quality index were recorded in the winter season on plants grown in both drip-irrigation and subirrigation using half and full nutrient solution concentration, whereas the lowest value was observed in the spring season on plants grown with subirrigation using the full nutrient solution concentration. The highest maximum air temperature recorded during the first 20 days after transplanting in the spring growing season was presumably responsible for the reduction in shoot biomass production, growth and quality index, and in time of geranium flowering compared to the plants grown in the winter season. The ET c was 44% higher in spring than in winter season treatment, while the effect of the irrigation system was less pronounced with an increase in 11% in the subirrigation treatment compared with the drip-irrigation system. WUE GI was not stable and showed a seasonal variability. Solar radiaton ( R s), air temperature ( T a) and vapour pressure deficit (VPD) were greatly higher in the spring season, which influenced WUE GI negatively. The WUE GI improved especially when R s, T a and VPD were below 12 MJ m 2, 20 °C and 0.6 kPa, respectively. The highest N, and Mg uptake were recorded in the winter season, especially on plants grown with subirrigation at 2 dS m −1. The highest P, K, and Ca uptake values were measured during winter season using subirrigation system, and on plants grown under full strength nutrient solution. The variation of the nitrate concentration and EC in the nutrient solution during the spring growing cycle was less pronounced in the subirrigation than with a drip-irrigation system which represents an important aspect for the simplification of the closed loop management of the nutrient solution.

Reduction of mineral nutrient availability accelerates flowering of Arabidopsis thaliana

The time of flowering is regulated by various environmental cues, and in some plant species, it is known to be affected by abiotic stresses. We investigated the effect of nutrient stress caused by an abrupt reduction of mineral nutrition on flowering of Arabidopsis thaliana. We used a hydroponic culture system that enabled us to precisely control nutrient levels. When plants were grown in full-strength nutrient solution for several weeks and then transferred to a diluted medium, the time from sowing to bud appearance was significantly shortened. This acceleration of flowering was more pronounced in short days than in long days, and stronger in the ecotype Landsberg erecta than in Columbia and San Feliu-2. The response was also affected by the age of plants at the beginning of nutrient stress and by the concentration of the diluted medium: earlier treatment and more diluted solutions strengthened the effect. Flowering was affected by nutrient stress, not by a change in the osmotic potential of the medium: addition of mannitol to a 1000-fold diluted solution had no effect on the promotion of flowering. When 3-week-old Landsberg erecta plants were exposed to 1000-fold diluted nutrient solution in an 8-h day length, flower bud appearance was strongly and reproducibly advanced by 10.8-12.8d compared with control plants (which developed buds 41.1-46.2d after sowing). This treatment can serve as an optimized protocol for future studies concerning physiological, molecular and ecological aspects of flower induction by nutrient stress in A. thaliana.

Regulation of K uptake, water uptake, and growth of tomato during K starvation and recovery

In order to analyze the dynamics of growth, water and K uptake, the effects of 1, 3 and 7 days of potassium starvation and the recovery capability during 7 days afterwards were investigated in vegetative tomato plants. After 7 days of K starvation, plant dry matter was reduced by 36% compared to control plants. After 3 days of starvation plants showed a 15% reduction in dry matter and a 25% reduction in growth rate (not statistically significant). K starvation reduced leaf area and specific leaf area (SLA) and it increased leaf dry matter percentage. K starvation enhanced dry matter partitioning into the roots at the expense of the stem. Plant K concentration was reduced by K starvation with the strongest effect in the leaves and roots. When a 3-day K starvation period was followed by 7 days of recovery with full strength nutrient solution, growth and plant K concentration completely recovered, but not after 7 days of K starvation. Xylem sap flow was reduced by K starvation and after 7 days of starvation the K concentration in the sap was reduced by 60%. During the starvation period, the reduction in relative growth rate was linearly related to the plant K concentration. The critical potassium concentration in the plant (the K concentration at which relative growth rate was reduced by 10%) was determined according to the nutrient interruption technique. The critical concentration was 4.3% K which was reached after 2.5 days of K starvation while the potassium concentration of control plants was 6.3%. During recovery the dry matter growth rate seemed to be the most important factor determining K uptake.

A gnotobiotic system for studying root carbon release using lettuce ( Lactuca sativa L.)

A cultivation system was developed for studies of root exudation and plant–microbial interactions under gnotobiotic, hydroponic conditions. The system was tested by determining root carbon release from lettuce ( Lactuca sativa L. cv. Grand Rapids) grown axenically at different ionic strengths for 3 weeks. Growth of the axenic plants was similar at 25, 50 or 100% of the full strength nutrient solution (NS) during the first 2 weeks. After 3 weeks, however, plant dry weights and total uptake of K, Ca, P, S, Mn, Fe, Zn and Cu were highest when the full strength NS was supplied. Also, the concentration of dissolved organic carbon (DOC) in the NS was higher in the 100% compared with the more dilute NSs. Estimated net root release of DOC after 3 weeks varied from 6 to 14 mg g −1 root dry weight. The DOC relative release rate (RRR) was lower than the relative plant growth rate (RGR), indicating a reduction of the amount of DOC released per gram root dry weight with increasing plant growth. We conclude that the cultivation system allows axenic studies of root carbon release during 3 weeks with a high number of experimental units and a low incidence of contamination.

Regulation of nutrient uptake, water uptake and growth under calcium starvation and recovery

SummaryTo analyze the dynamics of growth, water and nutrient uptake, the effects of 1, 3 and 7 d of calcium starvation and the recovery capability during 7 d afterwards were investigated in vegetative tomato plants. Results showed that after only 1.d of Ca-starvation, leaf photosynthesis, leaf expansion and leaf transpiration were already reduced and root growth had stopped completely. Leaf Ca concentration was reduced by a Ca-starvation with the strongest effect in the youngest leaves. When 1 d Ca-starvation period was followed by 7 d of recovery with full-strength nutrient solution, leaf photosynthesis and growth completely recovered. During the recovery period, Ca concentrations in the young leaves increased to higher values than these concentrations in the control plants. During the recovery period calcium uptake showed positive linear relationships with dry-matter increase of the plant as well as with water uptake. Most of the measured growth parameters showed a strong correlation with the plant Ca concentration, but the relations were not always identical during starvation and recovery. We discuss the role different forms and functions of Ca may play in regulating growth and developmental processes.

Interactions between phosphorus supply and total nutrient availability on mycorrhizal colonization, growth and photosynthesis of cucumber

The effects of arbuscular mycorrhizal (AM) infection by Glomus mosseae (Nicolson & Gerdemann) Gerdemann & Trappe on growth, photosynthesis and nutrient concentration of cucumber ( Cucumis sativus L. var. Telegraph Improved) were studied in sand culture with three different nutrient solutions based on the Long Ashton formula. These were high P+high concentrations of the other essential nutrients (full-strength solution containing 1.3 mM P), low P (0.13 mM)+ high concentrations of the other nutrients and low P+low concentrations of the other nutrients (10% of the full-strength nutrient solution). AM infection was found to depend on both P supply and the availability of other nutrients. Plants grown at low P with high concentrations of other nutrients had the highest AM infection, and a higher biomass due to an enhanced maximum net photosynthetic rate ( P m). Although this was unrelated to the N concentration of leaves, there was evidence that the higher P m was associated with a low leaf P concentration and the significance of these results is discussed. With high P and high concentrations of the other nutrients, a growth depression was found with +AM plants, although this was not due to a reduction in photosynthesis or an increase in leaf dark respiration rate. It was, however, associated with a reduction in photosynthetic nitrogen use efficiency. Overall, the present study indicates that any advantages or disadvantages associated with AM infection in cucumber are a result of complex interactions between P supply and the availability of other essential nutrients.

Seed Treatment and Cultural Practices Influence Seedling Growth of Hydroponic Lettuce

Raw, pelleted or germinated seeds of `Cortina' lettuce (Lactuca sativa L.) were sown in phenolic foam cubes preplant soaked in water or fullstrength nutrient solution (2 mmho·cm−1, 2 dS·m−1). The seeds were left uncovered or covered with fine vermiculite (grade 5), and seedling emergence characteristics were subsequently determined. Shoot fresh masses and their coefficients of variation (cv) by 9 days after planting (1 or 2 true leaves) and by 31 days after planting (4 or 5 true leaves) also were determined. Soaking the cubes in nutrient solution rather than water increased seedling emergence percentage and rate, and increased shoot fresh masses by 9 or 31 days after planting. This increased shoot fresh mass was accompanied by lower cv of shoot fresh mass by 9 days after planting, but not by 31 days after planting. Covering seeds with vermiculite decreased emergence from 99% to 93%, but increased shoot fresh mass by 9 and 31 days after planting when cubes were soaked in water, but not in nutrient solution. Seed treatments influenced shoot fresh mass at 9 and 31 days after planting in the order germinated > pelleted > raw. Germinated seeds resulted in lower cv of shoot fresh mass (24%) than raw or pelleted seeds (29%) by 31 days after planting. Thus, sowing germinated seeds into foam cubes soaked in full-strength nutrient solution, with or without covering the seeds with vermiculite, produced the heaviest and most uniform seedlings.