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- The effect of nitrogen source on photosynthesis of carob at high CO2 concentrationsPublication . Cruz, C.; Lips, S. H.; Martins-Loução, M. A.Carob seedlings (Ceratonia siliqua L. cv. Mulata), fed with nitrate or ammonium, were grown in growth chambers containing two levels of CO2 (360 or 800 μl l−1), three root temperatures (15, 20 or 25°C), and the same shoot temperature (20/24°C, night/day temperature). The response of the plants to CO2 enrichment was affected by environmental factors such as the type of inorganic nitrogen in the medium and root temperature. Increasing root temperature enhanced photosynthesis rate more in the presence of nitrate than in the presence of ammonium. Differences in photosynthetic products were also observed between nitrate- and ammonium-fed carob seedlings. Nitrate-grown plants showed an enhanced content of sucrose, while ammonium led to enhanced storage of starch. Increase in root temperature caused an increase in dry mass of the plants of similar proportions in both nitrogen sources. The enhancement of the rates of photosynthesis by CO2 enrichment was proportionally much larger than the resulting increases in dry mass production when nitrate was the nitrogen source. Ammonium was the preferred nitrogen source for carob at both ambient and high CO2 concentrations. The level of photosynthesis of a plant is limited not only by atmospheric CO2 concentration but also by the nutritional and environmental conditions of the root.
- The effect of NK fertilization on growth patterns and leaf nutrient concentration of carob-trees (Ceratonia siliqua L.)Publication . Correia, P. J.; Anastácio, L.; Martins-Loução, M. A.The purpose of this experiment was to analyse soil nutrient availability as factors controlling vegetative and reproductive growth in carob {Ceratonia siliqua) trees. The orchard with 10 year-old trees, was established on a calcareous soil (total calcium carbonate: 65.2 %; active lime: 17.5 %). Four fertilization levels were tested: no fertilizer (C); 0.8 kg N.tree-1 (N treatment); 1 kg K20.tree-1 (K treatment) and 0.8 kg N.tree-1 plus 1 kg K20.tree-1 (NK treatment). No irrigation was applied during the experimental period. Branch length increment, inflorescence number, leaf area index, fruit and leaf mineral content were registered. Correlations between growth patterns and climatic variables were evaluated in order to discriminate between fertilization effects and abiotic stress, typical of Mediterranean climate, such as drought. The preliminary results of a NK fertilization trial are here presented and tree responses to N and K application were discussed in terms of source-sink effects, namely vegetative versus reproductive growth. The knowledge of these growth patterns could be important for making decisions related to fertilization. Thus, modifying orchard fertilization regimes may be a helpful strategy to improve yield on these particular droughty sites.
- La fijacion biologica de nitrogeno atmosferico y la produccion vegetalPublication . Rodríguez-Barrueco, C.; Subramaniam, P.; Martins-Loução, M. A.Biological Nitrogen Fixation shows itself as a promising means to lower costs in plant protein production. It offers the scientist with a wide spectrum of possibilities to develop, by further research, what is already known on that process. Meanwhile, nitrogen fixation must be put to work and to that end a range of biological systems existing in Nature are outlined, though briefly, in the present article, mainly covering symbiotic, as well as free-living nitrogen-fixers. The use of synthetic nitrogen fertilizer is at stake due to increased fossil fuel prices, and trying to bring up new, not so costly alternatives, appears to be the point at issue. Suggestions on the use of the various systems, supported by experimental data, are given, and the attention of the reader called upon those points which should merit further research. La Fijación Biológica de Nitrógeno se muestra como un medio de reducir costes en la producción de proteína vegetal. El científico dispone de un amplio campo donde desarrolar unas investigaciones que se encuentran en constante dinâmica. Mientras tanto, la fijación de nitrógeno ha de utilizarse en la práctica al nivel que los conocimientos actuales nos lo permitan. Con este propósito se incluyen una serie de sistemas naturales capaces de ejercer aquella función, principalmente simbióticos y libres, respectivamente. El uso de fertilizantes nitrogenados de síntesis industrial se presenta cada día más problemático debido a los precios de los combustibles fósiles. Por ello han de desarrollarse nuevas alternativas, no tan costosas, sustitutivas, o en su caso complementarias. Se mencionan las posibilidades que los distintos sistemas nos ofrecen, apoyadas en resultados experimentales, así como aquellos aspectos del processo que merecen la atención del investigador.
- V.2 Carob (Ceratonia siliqua L.)Publication . Martins-Loução, M. A
- Effect of root temperature on carob growth: nitrate versus ammonium nutritionPublication . Cruz, Cristina; Lips, S. Herman; Martins-Loução, Maria AméliaThe response of carob (Ceratonia siliqua L.) seedlings grown at different root zone temperatures affected by nitrate and ammonium nutrition was studied. When root temperatures ranged from 10 to 35°C, ammonium‐fed plants were significantly larger than nitrate‐fed plants. Ammonium‐fed plants displayed toxicity symptoms and were much smaller at 40°C root temperature in comparison with the nitrate‐fed plants grown at the same root temperature. Root/shoot ratio slightly increase with root temperature in ammonium‐ and nitrate‐fed plants in a similar way, and shoot demand per root unit decreased with root temperature between 15 and 25°C. There was a general increase in net photosynthesis with root temperature, though nitrate‐fed plants were more sensitive to low and ammonium‐fed plants to high temperatures. Increasing the root temperature of ammonium fed plants from 10 to 40°C leads to a 30% increase in the amount of photosynthates sent to the roots. The presence of ammonium resulted in the distribution of newly fixed carbon away from carbohydrates and into nitrogen compounds. Potassium, calcium, and nitrogen content of the plants also increased with increasing root temperature.
- Seasonal variations of leaf water potential and growth in fertigated carob-trees (Ceratonia siliqua L.)Publication . Correia, P. J.; Martins-Loução, M. A.Variations of predawn and midday leaf water potential and relative growth rates were studied in mature carob trees (Ceratonia siliqua L. cv "Mulata") submitted to a fertigation experiment. Three levels of irrigation were tested: 0%, 50% and 100%, based on daily standard evaporation values. For each irrigation level two nitrogen amounts were applied - 21 and 63 kg N ha-1 year-l as ammonium nitrate. The experiment was run between July 91 and August 1993. Measurements of leaf water potential and absolute branch length increments were made at monthly intervals, during the entire experimental period or during seasonal growth, respectively. Leaf water potential was related to soil volumetric water content, maximum and minimum air temperature and daily evaporation. Predawn leaf water potentials were always higher than - 1.1 MPa. Midday leaf water potential values presented very large seasonal variations and very low values independent of treatments. The low leaf water potentials observed for the fertigated trees during summer, suggest that this parameter may be related not only to the evaporative demand but also to growth investment. The amount of fertigation was positively correlated with vegetative growth increment and fruit production. Practical implications for irrigation schedules of leaf water potential patterns together with drought adaptation mechanisms of carob tree are discussed.
- Nitrogen assimilation and transport in carob plantsPublication . Cruz, C.; Lips, S. H.; Martins-Loução, M. A.Most of the nitrate reductase activity (80%;) in carob (Ceratonia siliqua L. cv. Mulata) is localised in the roots. The nitrate concentration in the leaves is relatively low compared to that in the roots, suggesting that nitrate influx into the leaf may be a major factor limiting the levels of nitrate reductase in the shoot. Transport of nitrate from root to shoot appears limited by the entrance of nitrate into the xylem. In order to study this problem, we determined the nitrate concentrations and nitrate reductase activities along the roots of nitrate-grown plants, as well as the composition of the xylem sap and the nitrate levels in the leaves. Some of the the bypocotyl, in order to bypass the loading of nitrate into the xylem of the roots. The results show that the loading of nitrate into the xylem is a limiting step. The cation and anion concentrations of nitrate- and ammonium-fed plants were similar, showing almost no production of organic anions. In both nitrate- and ammonium-fed plants, the transport of nitrogen from root to shoot was in the form of organic nitrogen compounds. The nitrate reductase activity in the roots was more than sufficient to explain all the efflux of OH− into the root medium of nitrate-fed plants. In carob plants the K-shuttle may thus be operative to a limited extent only, corresponding to between 11 and 27%; of the nitrate taken up. Potassium seems to be the cation accompanying stored nitrate in the roots of carob seedlings, since they accumulate nearly stoichiometric amounts of K+ and NO−3.
- Effect of N-nutrition and irrigation on fruit production of carob (Ceratonia siliqua)Publication . Correia, P. J.; Martins-Loução, M. A.A combined fertilization and irrigation experiment was initiated in order to see whether such treatment could improve the productivity of carob (Ceratonia siliqua L. cv. Mulata) on Mediterranean marginal lands. Mature carob trees (20–30 years old) were submitted to 3 different irrigation levels (100%;, 50%; and 0%;) based on daily standard evaporation values, measured with a class A pan. For each water level either 21 or 63 kg N ha−1 was applied as ammonium nitrate. The results reported here refer to a two-year experiment, and show that the productivity of the trees could be improved due to a positive interaction between water and N application. In addition, they suggest that also under the normal dry conditions of these Mediterranean systems nitrogen application is effective, even without irrigation.
- Uptake of ammonium and nitrate by carob (Ceratonia siliqua) as affected by root temperature and inhibitorsPublication . Cruz, C.; Lips, S. H.; Martins-Loução, M. A.Seedlings of carob (Ceratonia siliqua L. cv. Mulata) were grown in nutrient solution culture for 5 weeks, with or without nitrogen at different root temperatures (10, 16, 22, 30, 35 or 40deg;C) and with the air temperature kept between 20 and 24°C. The nitrogen was given as either ammonium or nitrate. At all root temperatures studied, nitrogen-depleted plants developed higher net uptake rates for nitrogen than plants grown in the presence of nitrogen. Temperature affected the kinetic parameters of nitrate uptake more than those of ammonium uptake. With increasing root temperature, the Km of ammonium uptake decreased, but to a lesser extent than the Km for nitrate. The increase in Vmax of ammonium uptake with temperature was also less noticeable than that for nitrate uptake. Ammonium and nitrate uptakes were inhibited in a similar way by respiratory or protein synthesis inhibitors. It may be noted that ammonium uptake in the presence of inhibitors at 40°C was higher than uptake at 10°C without inhibitors. Some similarities between the transport mechanisms for nitrate and ammonium are underlined in the present work. Components of both transport systems displayed saturation kinetics and depended on protein synthesis and energy. The following components of nitrate uptake were distinguished: (a) a passive net influx into the apparent free space; (b) a constitutive active uptake and (c) active uptake dependent on protein synthesis. We may similarly define three ammonium uptake systems: (a) a passive influx into the apparent free space; (b) passive diffusion uptake at high temperature and (c) active uptake dependent on protein synthesis. The possible role of the ratio between mechanism (c) and mechanism (b) as determinant of ammonium sensitivity is discussed.
- Interations between nitrate and ammonium during uptake by carob seedlings and the effect of the form of earlier nitrogen nutritionPublication . Cruz, Cristina; Lips, S. Herman; Martins-Loução, Maria AméliaSeedlings of carob (Ceratonia siliqua L. cv. Mulata) were used in two sets of experiments in order to evaluate; (1) the reciprocal effects of each nitrogen form on net uptake of nitrate and ammonium, and (2) the effect of earlier nitrogen nutrition on ammonium versus nitrate uptake. In the former group of experiments we studied the kinetics of nitrate and ammonium uptake as well as the interference of each of the two forms with net uptake of ammonium and nitrate by both nitrogen depleted and nitrogen fed carob seedlings. On the whole, nitrogen depletion led to increase in both affinity and Vmax of the system for both forms of nitrogen, at the same time as the effects of nitrate on uptake of ammonium and vice versa were concentration dependent. In the second group of experiments the effects of earlier nitrogen nutrition on nitrate and ammonium uptake were characterized, and in this case we observed that: (a) if only one form of N was supplied, ammonium was taken up in greater amounts than nitrate; (b) the presence of ammonium enhanced nitrate uptake; (c) ammonium uptake was inhibited by nitrate; (d) there was a significant effect of the earlier nitrogen nutrition on the response of the plants to a different nitrogen source. The latter was evident mainly as regards ammonium uptake by plants grown in ammonium nitrate. The interactions between nitrate and ammonium uptake systems are discussed on the basis of the adaptation to the nitrogen source during early growth.