Antonio L. García

Moderate water stress affects tomato leaf water relations in dependence on the nitrogen supply

The responses of water relations, stomatal conductance (gs) and growth parameters of tomato (Lycopersicon esculentum Mill. cv. Royesta) plants to nitrogen fertilisation and drought were studied. The plants were subjected to a long-term, moderate and progressive water stress by adding 80 % of the water evapotranspirated by the plant the preceding day. Well-watered plants received 100 % of the water evapotranspirated. Two weeks before starting the drought period, the plants were fertilised with Hoagland’s solution with 14, 60 and 110 mM NO3− (N14, N60 and N110, respectively). Plants of the N110 treatment had the highest leaf area. However, gs was higher for N60 plants and lower for N110 plants. At the end of the drought period, N60 plants showed the lowest values of water potential (Ψw) and osmotic potential (Ψs), and the highest values of pressure potential (Ψp). N60 plants showed the highest Ψs at maximum Ψp and the highest bulk modulus of elasticity.

Interactive Effect of Nitrogen and Long-term Moderate Water Stress on Water Relations in Tomato (Lycopersicon esculentum Mill.) Plants

Summary The influence of three levels of N ferdization on the water relations of tomato plants ( Lycopersicon esculentum Mill., cv. Royesta) grown on a sandy soil and subjected to long-term moderate water stress was established. In each treatment a volume representing 80% (stressed) or 100% (well-watered) of the water evapotranspired the day preceding supply of Hoagland’s solution (N0 treatment), Hoagland’s solution plus 60 mmol/L NO3 − (N 1 treatment) or Hoagland’s solution plus 110 mmol/L NO3 − (N2 treatment). The W Fft /W D ratio increased in stressed N0 and N2 plants, although no significant differences were observed between the values at either time considered. However, for the N1 dose a significant increase was observed in well-watered plants and no increase in stressed plants. The greatest decrease in LWP was observed in water-stressed N1 plants, while the LWP value of well-watered plants remained constant throughout the experiment. The smaller decrease in LOP tlp than LOP ft values in both stressed N1 and N2 plants suggests a mechanism of osmotic adjustment or an increase in cell wall elasticity. However, the significant increase in RWC tlp (3.5 %) and cell wall rigidity (130 % increase in E) and the drop in LOP tlp (16 %) indicate that there was a true osmotic adjustment of 0.10 MPa in stressed N1 plants.

Influence of amino acids in the hydroponic medium on the growth of tomato plants

ABSTRACT The effect on the growth of tomato plants (Lycopersicon esculentum Mill, cv Asun) of adding amino acids to Hoaglands nutritive solution, after ascertaining that a 50 mg L− 1 dose of three antibiotics was sufficient to limit micro-organism-plant competition for the nitrogen supplied, was studied. The experiment consisted of four treatments, T0 (control, Hoaglands solution), T1 (amino acids, Hoaglands solution plus a mixture of 0.2 mM each of serine, alanine, tyrosine, and phenylanine), T2 (antibiotics, Hoaglands solution plus a mixture of Ampicillinum trihydricum, Streptomycini sulfas, and Gentamicyni sulfas, 50 mg L− 1 of each antibiotic), and T3 (antibiotics and amino acids, Hoaglands solution plus a mixture of all antibiotics and amino acids). The relative growth rate (RGR) increased for the plants grown in T0 and T1, with the increase being significantly less in T1 compared with the control (T0), and was reduced for the plants grown in T3 and T2. The parameters absolute growth rate (AGR) and relative growth rate (RGR), demonstrated the negative effect of the antibiotics that cannot be mitigated by the presence of the amino acids (T3). Leaf stomatic conductance and transpiration values fell in all of the treatments. Daily water consumption increased in T0 and T1. At the end of the experiment, T2 and T3 plants consumed approximately 10% of the maximum value (93.8%).

Moderating water stress in tomato (Lycopersicon esculentum Mill.) plants by application of specific nitrogen doses

Summary The effect of different doses of nitrogen on water stress in tomato (Lycopersicon esculentum Mill. ‘Royesta’) plants grown in a sandy soil and exposed, or not, to long-term water stress was studied. Nitrogen dose treatments consisted of Hoagland’s solution (N1 treatment), Hoagland’s solution + 40 mM NO3– (N2 treatment), or Hoagland’s solution + 80 mM NO3– (N3 treatment) applied every 3 d, for a total of seven applications following plant establishment. Subsequently, daily application of 80% (stressed) or 100% (unstressed) of the water evapotranspired by control plants the previous day was combined, factorially, with the three nitrogen treatments, for a period of 2 weeks. The leaf fresh weight (FW) at full turgor:leaf dry weight (DW) ratio was high in plants under the N1 and N3 stress treatments, with no significant difference between them soon after the start and at the end of the water stress treatment. However, the N2 treatment produced a significant increase in the ratio in well-watered plants, but not in water-stressed plants at the end of the stress period. The surface area per leaf was greater in stressed than in control plants, except for N2. Leaf water potential was greatly reduced in stressed N2 and N3 plants, but was unaltered in their well-watered counterparts. The significant increases in relative water content at the turgor loss point (around 3%) and in cell membrane rigidity (an increase of more than 125% in the bulk modulus of elasticity) clearly indicate an osmotic adjustment in stressed N2 plants, confirming that this N dose moderated the effects of the water stress imposed on N2 plants.