Maribela Pestana

Effectiveness of different foliar iron applications to control iron chlorosis in orange trees grown on a calcareous soil

The effectiveness on controlling Fe chlorosis in orange trees grown on calcareous soils was tested. The treatments were Fe(II) sulfate (500 mg Fe L−1), sulfuric acid (0.5 mM H2SO4), Fe(III)-chelate (Hampiron 654 GS, 120 mg Fe L−1) and distilled water as a control. A non-ionic wetting agent was used in all treatments. The use of frequent foliar sprays alleviated Fe chlorosis in orange trees. Sprays of Fe(II) sulfate increased the concentrations of chlorophyll, Fe and zinc in leaves and improved fruit size and quality compared to fruits of control trees. Sprays of Fe(III)-chelate also increased leaf chlorophyll and Fe concentrations and improved fruit quality, but did not increase fruit size. Sprays of sulfuric acid alone slightly increased leaf chlorophyll and Fe concentrations, without improving fruit size and quality. These results suggest that foliar sprays with Fe could help to avoid yield and quality losses caused by Fe chlorosis in citrus orchards. Furthermore, these treatments could be done with relatively cheap materials such as solutions containing Fe(II) sulfate.

RESPONSES OF “NEWHALL” ORANGE TREES TO IRON DEFICIENCY IN HYDROPONICS: EFFECTS ON LEAF CHLOROPHYLL, PHOTOSYNTHETIC EFFICIENCY, AND ROOT FERRIC CHELATE REDUCTASE ACTIVITY

Orange (Citrus sinensis L. Osb. cv. ‘Newhall’) plants grafted on Citrange troyer rootstock were grown in nutrient solution with 0, 5, 10, or 20 μM iron (Fe), with and without calcium carbonate. Calcium carbonate was added in order to mimic the natural conditions in calcareous soils. Leaf chlorophyll concentration was estimated every 3–4 days using the portable instrument SPAD-502 meter. Chlorophyll fluorescence parameters, photosynthetic capacity estimated from oxygen evolution, leaf Fe concentrations, and root tip ferric chelate reductase activity were measured at the end of the experiment. Plants from the 0 and 5 μM Fe treatments showed leaf chlorosis and had decreased leaf chlorophyll concentrations. Leaves of plants grown in the absence of Fe in the solution had smaller rates of oxygen evolution both in the presence and absence of calcium carbonate, compared with plants grown in the presence of 10 μM Fe. In the absence of calcium carbonate the photosystem II efficiency, estimated from fluorescence parameters, was similar in all treatments. A slight decrease in photosystem II efficiency was observed in plants grown without Fe and in the presence of calcium carbonate. A 2.5-fold increase in root tip ferric chelate reductase activity over the control values was found only when plants were grown with low levels of Fe and in the presence of calcium carbonate.

The use of floral analysis to diagnose the nutritional status of orange trees

A field experiment was conducted in a commercial orange orchard (Citrus sinensis L. cv. ‘Valencia late’), established on a calcareous soil in the south of Portugal, to investigate if flower analysis could be used to diagnose the nutritional status of the trees and predict fruit quality. In April 1996, during full bloom, flowers and leaves were collected from 20 trees. Leaf samples were again collected in June and August from the same trees. In February 1997 the fruits were harvested and their quality evaluated. The concentrations of phosporous (P) and magnesium (Mg) in flowers were correlated with those in leaves, and were also predictive of the chlorophyll content of leaves 60 days later. However, by 120 days after full bloom these effects were masked, possibly by a fertilizer application carried out by the farmer. The iron (Fe) concentration in flowers was correlated with chlorophyll measured either 60 or 120 days after full bloom. These parameters can therefore be used to predict the appearance of iron chlorosis. Fresh weight and diameter of fruit were related to flower P, Mg, and manganese (Mn) concentrations, while the percentage of citric acid in the fruit juice was inversely correlated with Fe flower concentrations.

Nutrient deficiencies in carob (Ceratonia siliqua L.) grown in solution culture

Summary The hypothesis was tested that carob (Ceratonia siliqua L.) is able to develop morphological and physiological adaptations to tolerate or at least mitigate soil nutrient deficiencies. In this work we studied the effects of N, P, Mg, Ca and Fe deficiencies on plant morphology, biomass partitioning, concentrations of chlorophyll, fluorescence and root tip ferric chelate-reductase in carob rootstocks grown in hydroponics. Young rootstock trees were grown in hydroponics with half-strength Hoagland’s solution (control) or without N, P, Mg, Ca and Fe (treatments N0,P0,Mg0, Ca0 and Fe0). Nitrogen, and P deficiency affected shoot and root growth but not biomass partitioning or photosynthetic efficiency. Plants without Mg had a few large non-ramificated roots and low photosynthetic efficiency, similar to the Fe-starved plants. Root ferric chelate-reductase activity (FC-R) expressed on a fresh weight basis was higher under P and Mg deficiencies compared with control plants, but Fe0 plants had lower FC-R activity if dry weights are used. The response of carob-tree to these particular nutrients depletion may support the ecological plasticity of this species. Under natural conditions, lack of Fe and Mg in the soil is not likely to occur, but if N and P are limiting, carob growth (shoot and root dry weights) may be negatively affected. Even so, photosynthetic efficiency is maintained, and under P stress FC-R activity may increase.

ROOT FERRIC CHELATE REDUCTASE IS REGULATED BY IRON AND COPPER IN STRAWBERRY PLANTS

In the present experiment, we studied the interaction between copper (Cu) and iron (Fe) in strawberry plants grown in nutrient solutions containing different concentrations of Fe. Plants grown in the absence of iron (Fe0) had the characteristic symptoms of Fe deficiency, with smaller chlorotic leaves, less biomass, acidification of the nutrient solution, and roots that were smaller and less ramified, while no symptoms of Fe deficiency were observed in plants grown with Fe. A greater amount of Cu was found in roots of chlorotic plants than in those grown with Fe, while plants grown with 20 μM of Fe (Fe20) in the nutrient solution had a greater amount of Fe compared with plants from the other treatments. Chlorotic plants (Fe0) and plants grown with the greatest level of Fe (Fe20) had a greater root ferric chelate reductase (FC-R; EC 1.16.1.17) activity compared with the other treatments with 5 or 10 μM Fe in the nutrient solution. The same pattern was obtained for relative FC-R mRNA concentration and for the sum of Fe and Cu contents in shoots (leaves plus crowns). The DNA obtained from amplification of the FC-R mRNA was cloned and several of the inserts analysed by single strand confirmation polymorphism (SSCP). Although there were different SSCP patterns in the Fe20 treatment, all the inserts that were sequenced were very similar, excluding the hypothesis of more than one FC-R mRNA species being present. The results suggest that Cu as well as Fe is involved in FC-R expression and activity, although the mechanism involved in this regulation is unknown so far. Both small contents of Fe and Cu in plants led to an over-expression of the FC-R gene and enhanced FC-R activity in strawberry roots.

The recovery of citrus from iron chlorosis using different foliar applications. Effects on fruit quality

The response of Encore trees grown on a calcareous soil to different foliar applications to offset iron deficiency. Four treatments were tested: distilled water (control); iron (II) sulphate (500 mg Fe.L−1); sulphuric acid (0.5 mM H2SO4) and Fe-EDDHA (120 mg Fe.L−1). The recovery from iron chlorosis was evaluated with the SPAD apparatus and the values converted to total chlorophyll density. We also evaluated effects of the treatments on some physical and chemical characteristics of the fruit. Chlorophyll density in the leaves, and the total sugar content of the fruits, were greater in all experimental treatments, compared with control, but with no significant differences between treatments. The concentration of citric acid decreased in the treated plants. The greatest diameter and fresh weight of fruits were obtained in the treatment with iron chelate. Foliar applications of iron sulphate or sulphuric acid led to values of these parameters that were intermediate between those of the control and the iron chelate treatments.

Changes in the concentration of organic acids in roots and leaves of carob-tree under Fe deficiency

Several fruit trees are able to cope with iron (Fe) deficiency when grown in calcareous soils in the Mediterranean region, although information regarding well adapted slow-growing species is scarce, and the mechanisms activated by these species are not described in the literature. A crucial issue related to tolerance is the need to transport Fe over relatively long distances inside the plant. To evaluate the possible role of organic acids in the movement of Fe in tolerant plants, we studied the concentration of low molecular weight organic acids in several organs of 1-year old carob plants grown for 55 days in nutrient solutions without Fe (0µM Fe) or with 1µM Fe and 10µM Fe. Roots, stems and leaves were harvested, and the biomass, Fe and organic acid contents quantified. Total leaf chlorophyll (Chl) was evaluated in young leaves over the experimental period and the activity of root ferric chelate-reductase (FC-R; EC 1.16.1.17) was determined after 35 days, when deficiency symptoms appeared. Iron chlorosis was observed only at the end of the experiment in plants grown in the absence of Fe, and these plants had a smaller DW of leaves and also significant greater activity of root FC-R. Iron deficiency (Fe0 and Fe1 treatments) induced significant changes in the concentrations of succinic, malic, citric and fumaric acids, which increased in roots, or in basal, middle and apical leaves. There were significant correlations between most organic acids (with the exceptions of 2-oxoglutaric and tartaric acids) and leaf Chl. Analysis of each type of leaf showed that more succinic and malic acids were present in young chlorotic leaves while the reverse was true for quinic acid. These changes in organic acids followed a root-to-foliage pathway that was similar in all leaf types and particularly evident in young chlorotic leaves. We hypothesised that it was associated with Fe transport from roots to aboveground tissues, as there were significant differences in Fe contents between treatments with and without Fe.

Nutritional Evaluation of Nitrogen and Potassium Fertilization of Carob Tree under Dry-Farming Conditions

Abstract The aim of this work was to assess how potassium (K) and nitrogen (N) fertilization might affect the variation of leaf and fruit nutrient concentrations in carob tree (Ceratonia siliqua L.) under low precipitation. A field study was conducted in 1997, 1998, and 1999 in a calcareous soil. Four fertilization treatments were tested: no fertilizer (C), 0.8 kg N tree−1 (N treatment), 0.83 kg K tree−1 (K treatment), and 0.80 kg N tree−1 plus 0.83 kg K tree−1 (NK treatment). During the hydrological cycle 1998/1999, only 250 mm of rain were recorded. Because of this, from 1998 to 1999 a decrease in the concentrations of mobile nutrients N, phosphorus (P), and K and an increase in calcium (Ca), iron (Fe), and manganese (Mn) were observed in leaves. The application of N led to higher leaf N concentration compared with other treatments. This response allowed the establishment of a linear model that relates soil plant analysis development (SPAD) readings with leaf N concentrations (r2=0.55; P<0.05). Compared with leaves, fruits showed similar amounts of N and P; less Ca, Mg, Fe, and Mn; and high concentrations of K. Fertilization did not change considerably the mineral composition of fruits, and because of large variation among trees, yield was similar for all treatments.

Nutritional and physiological responses of the dicotyledonous halophyte Sarcocornia fruticosa to salinity

Sarcocornia fruticosa (L.) A.J. Scott is a dicotyledonous halophyte that grows in areas with an arid climate such as the marshes of southern Spain. The species has potential uses for saline agriculture and biofuel production, but the effects of salt stress on its nutrition and physiology remain unclear. Plants of S. fruticosa were grown in pots with a mixture of sphagnum peat-moss and Perlite. In order to evaluate the effects of different levels of salinity, five treatments using different NaCl concentrations (10 (control), 60, 100, 200 and 300 mM NaCl) were applied over a period of 60 days. At the end of the experiment, the dry weight, the biomass allocation and the tissue water content were measured for each salinity treatment. The net uptake of various nutrients and their translocation rates were calculated for each salt treatment. Salt loss, shedding of plant parts and succulence in shoots were evaluated together with the K+/Na+ ratio, K-Na selectivity, concentrations of osmolytes and their estimated contributions to the osmotic potential. Our results showed that S. fruticosa can maintain its major physiological processes at 60 mM NaCl without significant dry weight reduction. Higher salinity resulted in negative values for net uptake and translocation rates from roots to shoots of N and P. As might be predicted from other dicotyledonous halophytes, S. fruticosa plants increased Cl– and Na+ uptake using both as osmotica instead of organic osmolytes. However, to survive salinity, this species has also evolved others mechanisms such as shedding old shoots, increased succulence in shoots at higher salt concentrations and the ability to maintain a lower K+/Na+ ratio and higher K-Na selectivity in all organs.

Nutrient Dynamics in Orange Trees: The Effect of Soil Fertility

Lime-induced iron (Fe) chlorosis is a nutritional disorder common in calcareous soils, which may result from a low level of Fe available or adverse factors that inhibit Fe mobilization and uptake by plants. Organic-matter amendments can prevent or correct Fe chlorosis in plants but the effect of endogenous soil organic matter (SOM) on this disorder is not known. The main subject of this work was to investigate the consequence of two contrasting levels of soil fertility on the nutritional status of an orange grove [Citrus sinensis (L.) Osb. cv. Valencia Late]. The field experiment was conducted in a commercial citrus grove using mature trees distributed in two plots with different values of SOM, phosphorus (P), and potassium (K), but with the same level of active lime. The concentration of nitrogen (N), P, K, magnesium (Mg), calcium (Ca), Fe, copper (Cu), zinc (Zn), and manganese (Mn) in young and mature leaves and flowers was evaluated. The level of Mg and the Mg/Zn ratio in flowers from both plots, although significantly different, only indicated moderate Fe chlorosis, as predicted by a previously developed model, and was consistent with the amount of chlorophyll present in the leaves. However, nutrient partitioning between leaves of contrasting age was very different. Mature leaves from trees grown in the high-fertility plot (HF) had larger concentrations of N, P, and K but lower concentrations of Ca, Fe, and Mn than did those from the low-fertility plot (LF). Young leaves from the LF had more N, P, Mg, Cu, and Mn and less Ca and Fe than did those from the HF. Flower analysis, although useful to predict Fe chlorosis, failed to detect differences in the nutritional status of plants resulting from contrasting levels of soil fertility. Furthermore, endogenous SOM had only a marginal effect on Fe chlorosis.