Manuel Nieves

Effect of salinity on the growth and nitrogen uptake by wheat seedlings

Abstract Saline conditions affect nitrogen (N) assimilation of higher plants. To study the effect of salinity and N source on growth and N uptake in wheat (Triticum aestivum L.), plants were grown in a growth chamber under controlled conditions. The nutrient solution contained 4 mM N, applied as either calcium nitrate [Ca(NO3)2] or ammonium sulfate [(NH4)2SO4], or a mixture of both, and the salinity treatments consisted in two levels of sodium chloride (NaCl) (1 and 60 mM). Salinity significantly reduced shoot and root growth and the effect of the N source was dependent on which salinity treatment was applied. Salinity decreased the net uptake rate of nitrate (NO3) and NO3+ammonium (NH4), but had little effect on NH4 uptake when this nutrient was applied alone. Dark conditions affected NO3 uptake to a greater extent than NH4 uptake. The best N source for wheat growth was a mixture of NO3 and NH4, especially under saline conditions or periods of low irradiance.

Salt tolerance of two lemon scions measured by leaf chloride and sodium accumulation

Abstract Effects of salinity on growth, ion content, water relationships, and chlorophyll and proline levels were measured on one‐year‐old ‘Verna’ and ‘Fino’ lemon (Citrus limon [L] Burm. F.) scions budded to either Sour orange (C. aurantium L.) or macrophylla (C. macrophylla Wester) rootstock. Trees were grown in nutrient solutions containing 2 (control), 40, or 80 mol m‐3 NaCl for 75 days. Growth of all combinations was reduced by salinity, but this effect was greater for both scions budded on macrophylla. Leaf chloride and sodium concentrations were lower in both scions budded on Sour orange. Leaf salt concentration was scion dependent. Leaves of ‘Fino’ lemon had higher levels of both chloride and sodium than did leaves of ‘Verna’ lemon, regardless of the rootstock considered. Despite an accumulation of chloride and sodium in the leaves of salinized trees, leaf water potential and leaf water content increased above the control level. However, stomatal conductance declined in all rootstock/scion combina...

Leaf nitrogen productivity is the major factor behind the growth reduction induced by long-term salt stress

Plant growth response to salinity on a scale of years has not been studied in terms of growth analysis. To gain insights into this topic, 2-year-old Mediterranean Fan Palm (Chamaerops humilis L.) and Mexican Fan Palm (Washingtonia robusta H. Wendl) seedlings, each with its own distinct plant morphology, were grown for 2 years in a peat soil and irrigated with water of 2 dS m(-1) (control) or 8 dS m(-1) (saline). Plants were harvested on seven occasions and the time trends in relative growth rate (RGR, the rate of increase of biomass per unit of biomass already existing) and its components were analysed. In the long term, salinity produced a slight reduction in the mean RGR, values in both species. In the short term, salinity caused a reduction in RGR. However, during the second year, plants irrigated with 8 dS m(-1) grew somewhat more quickly than the control plants, probably as a result of delay in the growth kinetics due to salinity. Regarding RGR components, leaf nitrogen productivity (the rate of biomass gain per unit leaf N and time) was the major factor causing the differences in RGR resulting from salinity. Washingtonia robusta showed a relatively high plasticity in plant morphology by increasing root and decreasing stem biomass allocation in the presence of salinity. However, the long-term response of W. robusta to salinity, based to a great extent, on this morphological plasticity, was less effective than that of C. humilis, which is based mainly on the contribution of leaf N to RGR values.

Effect of interstock (‘Salustiano’ orange) on growth, leaf mineral composition and water relations of one year old citrus under saline conditions

Summary We investigated the effects of salinity on the growth, mineral composition (leaf, stem and root) and water relations in one year old plants of ‘Cleopatra’ mandarin ( Citrus reticulata Blanco) (CM), ‘Salustiano’ orange ( Citrus sinensis (L.) Osbeck) grafted on ‘Cleopatra’ mandarin (CM/SAO), ‘Valencia Late’ orange ( Citrus sinensis (L) Osbeck) on ‘Cleopatra’ mandarin (CM/VLO) and ‘Valencia Late’ grafted on CM/SO (CM/SAO/VLO). Plants were grown in sand culture under greenhouse conditions and supplied with nutrient solution containing either 5 (control) or 50.mM NaCl. After ten weeks of salt treatment, the CM/SAO/VLO leaf growth was not affected, while CM/SAO showed the greatest leaf growth reduction. Root growth was less affected than leaf growth by salt treatment, and was similar for all four combinations. In the salt treatment, the leaf chloride concentration of CM/SAO/VLO was the lowest compared with the other plants and leaf Na concentration of CM/SAO/VLO was lower than CM/VLO, suggesting that the interstock limited Cl and Na uptake and/or transport from roots to leaves. The high leaf growth reduction observed in CM/SAO could be related to a decrease in turgor, due to a decrease in leaf water potential caused by salt treatment not being compensated by a reduction in leaf osmotic potential.

Differences in growth and ornamental parameters between young Chamaerops humilis L. and Washingtonia robusta H. Wendl palm trees in response to salinity.

Summary Chamaerops humilis L. and Washingtonia robusta H. Wendl trees represent two ornamental palms which differ in size and water use, the result of which may confer contrasting responses to salinity. Two-year-old plants (112 per species) were grown over two additional years with irrigation water having an electrical conductivity (ECw) of 2, 4, 6, or 8 dS m–1, and were harvested in seven successive harvests. The saline treatments had a statistically significant linear effect upon the reduction in relative biomass yield. The threshold and slope values were: 2.7 dS m–1 and 7.0% dS–1 m for C. humilis; and 3.3 dS m–1 and 9.5% dS–1 m for W. robusta. There were no significant differences in the levels of toxic ions in the leaves of W. robusta between the 2 – 8 dS m–1 treatments. In contrast, the levels of toxic ions increased significantly in the leaves of C. humilis. The results suggest that W. robusta is more sensitive to osmotic stress than C. humilis. This may be the cause of the steeper slope of the salt-tolerance equation for W. robusta. There were significant reductions in plant height and in leaf area at an EC of 8 dS m–1, but these effects were more marked in W. robusta. This species also suffered significantly reduced numbers of leaves in saline treatments at 6 or 8 dS m–1.We conclude that both young palm tree species can be classified as moderately tolerant to salinity. However, at high saline levels, a drought-tolerant palm such as C. humilis is more salt-tolerant than W. robusta. It would be appropriate to water 3-year-old palms with water having an ECw of 2 dS m–1, and with water at 4 dS m–1 in the following year.

Orange varieties as interstocks increase the salt tolerance of lemon trees

Summary We investigated the ability of interstocks to increase salt tolerance in lemon trees. We compared 2-year-old ‘Verna’ lemon trees [Citrus limon (L.) Burm.; VL] grafted on Sour Orange (C. aurantium L.; SO) rootstock either without an interstock (VL/SO), or interstocked with ‘Valencia’ orange (C. sinensis Osbeck; VL/V/SO), or with ‘Castellano’ orange (C. sinensis Osbeck; VL/C/SO). Trees were grown under greenhouse conditions and supplied with nutrient solutions containing 0, 30, or 60 mM NaCl. Reductions in leaf growth caused by salt treatment were greatest in non-interstocked (VL/SO) trees, followed by VL/C/SO trees, and were the least in VL/V/SO trees. Although the levels of Cl− and Na+ ions in the roots and stems were not affected by either interstock, leaf concentrations of Cl− and Na+ were higher in VL/SO trees than in VL/C/SO or VL/V/SO trees, suggesting that an interstock in Citrus trees could limit the uptake and transport of such ions to the shoots. Saline-treated VL/SO trees also tended to have the lowest shoot:root (S:R) ratios; so, overall, there was a negative relationship between S:R ratio and leaf Cl- ion concentration. Leaf transpiration (Eleaf) may also be involved in the reduction in leaf Cl− concentration, as interstocked trees had lower Eleaf values at mid-day than non-interstocked trees. Salinity increased leaf concentrations of Ca2+ in VL/C/SO trees and increased both leaf K+ and N concentrations in all trees, regardless of interstock. Salinity reduced leaf water potentials and osmotic potentials, such that leaf turgor was increased in all trees.

Rapid estimation of nutritional elements on citrus leaves by near infrared reflectance spectroscopy

Sufficient nutrient application is one of the most important factors in producing quality citrus fruits. One of the main guides in planning citrus fertilizer programs is by directly monitoring the plant nutrient content. However, this requires analysis of a large number of leaf samples using expensive and time-consuming chemical techniques. Over the last 5 years, it has been demonstrated that it is possible to quantitatively estimate certain nutritional elements in citrus leaves by using the spectral reflectance values, obtained by using near infrared reflectance spectroscopy (NIRS). This technique is rapid, non-destructive, cost-effective and environmentally friendly. Therefore, the estimation of macro and micronutrients in citrus leaves by this method would be beneficial in identifying the mineral status of the trees. However, to be used effectively NIRS must be evaluated against the standard techniques across different cultivars. In this study, NIRS spectral analysis, and subsequent nutrient estimations for N, K, Ca, Mg, B, Fe, Cu, Mn, and Zn concentration, were performed using 217 leaf samples from different citrus trees species. Partial least square regression and different pre-processing signal treatments were used to generate the best estimation against the current best practice techniques. It was verified a high proficiency in the estimation of N (Rv = 0.99) and Ca (Rv = 0.98) as well as achieving acceptable estimation for K, Mg, Fe, and Zn. However, no successful calibrations were obtained for the estimation of B, Cu, and Mn.

Response of three citrus genotypes used as rootstocks grown under boron excess conditions

In citrus, the effects of an excess of boron (B) are conditioned by the type of rootstock. In the present work, the morphological, physiological and biochemical responses of seedlings from three citrus genotypes, commonly used as rootstocks in citriculture. In particular, Citrange Carrizo (CC), Citrus macrophylla (CM) and sour orange (SO) seedlings were treated with an excess of B (10 mg L-1) in the nutrient solution in order to determine the relative tolerance and to understand the possible mechanisms that make a rootstock more tolerant than the others. To assess these responses, different parameters were measured in plants, such as vegetative growth, B concentration in leaves, stems and roots, gas exchange and chlorophyll fluorescence, the concentration of osmolytes and the activity of enzymes related to the antioxidant system. The results showed, according to the growth parameters, that the SO rootstock was the most tolerant to an excess of B; while CC was the most sensitive. This result was due to the fact that SO plants accumulated less B in leaves, as its roots have a great capacity of restricting the uptake and transport of B towards the aerial part. Moreover, SO is suggested to diminish B toxicity risk through its antioxidant system, since it presented high activity of ascorbate peroxidase (APX) and superoxide dismutase (SOD), as well as high accumulation of quaternary ammonium compounds (QACs).

NUTRIENT REQUIREMENTS OF CHAMAEROPS HUMILIS L. AND WASHINGTONIA ROBUSTA H. WENDL PALM TREES AND THEIR LONG-TERM NUTRITIONAL RESPONSES TO SALINITY

The ornamental value of plants used in semiarid areas can be improved by knowledge of their required nutrients and of their nutritional responses under saline conditions. We present a long-term study concerning the nutritional status in Chamaerops humilis and Washingtonia robusta. Two-year-old plants were grown for two years outdoors in pots using water with electrical conductivity values of 2 (control) or 8 dS m−1 (saline conditions). Nutrient specific absorption rates and leaf nutrient transport rates were estimated by fitting a Richards function regression. We suggest fertilizing C. humilis and W. robusta plants with nitrogen (N): phosphorus pentoxide (P2O5): dipotassium oxide (K2O) ratios of 4:1:5 and 5:1:3, respectively. Diagnosis and Recommendation Integrated System (DRIS) and Plant Analysis with Standardized Scores (PASS) norms were also evaluated. PASS norms provided better nutritional diagnosis than DRIS norms. In saline conditions, PASS-INI (Independent nutrient index) pointed to a deficiency (<−10) of phosphorus in C. humilis and of nitrogen in W. robusta.