FC - Artigos em Revistas Internacionais
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- 51 effect of ammonium and nitrate nutrition on the growth of Carob (Ceratonia siliqua L.) plantsPublication . Martins-Loução, M. A.; Duarte, P.
- Arbuscular mycorrhizal fungal propagules in a salt marshPublication . Carvalho, Luís M.; Correia, Patrícia M.; Martins-Loução, M. AméliaThe tolerance of indigenous arbuscular mycorrhizal fungi (AMF) to stressful soil conditions and the relative contribution of spores of these fungi to plant colonization were examined in a Portuguese salt marsh. Glomus geosporum is dominant in this salt marsh. Using tetrazolium as a vital stain, a high proportion of fieldcollected spores were found to be metabolically active at all sampling dates. Spore germination tests showed that salt marsh spores were not affected by increasing levels of salinity, in contrast to two non-marsh spore isolates, and had a significantly higher ability to germinate under increased levels of salinity (20‰) than in the absence of or at low salinity (10‰). Germination of salt marsh spores was not affected by soil water levels above field capacity, in contrast to one of the two non-marsh spore isolates. For the evaluation of infectivity, a bioassay was established with undisturbed soil cores (containing all types of AM fungal propagules) and soil cores containing only spores as AM fungal propagules. Different types of propagules were able to initiate and to expand the root colonization of a native plant species, but spores were slower than mycelium and/or root fragments in colonizing host roots. The AM fungal adaptation shown by this study may explain the maintenance of AMF in salt marshes.
- Arbuscular mycorrhizal fungi enhance root cadmium and copper accumulation in the roots of the salt marsh plant Aster tripolium L.Publication . Carvalho, Luís M.; Caçador, Isabel; Martins-Loução, M. AméliaIt is known that vegetation plays an important role in the retention of heavy metals in salt marshes by taking up and accumulating the metals. In this study, we investigated whether arbuscular mycorrhizal fungi (AMF) increase Cd and Cu uptake and accumulation in the root system of the salt marsh species Aster tripolium L., and whether indigenous AMF isolated from polluted salt marshes have higher capacity to resist and alleviate metal stress in A. tripolium than isolates of the same species originated from nonpolluted sites. Plants inoculated with Glomus geosporum, either isolated from a polluted salt marsh site (PL isolate) or from a non-polluted site (NP isolate), and non-mycorrhizal (NM) plants were compared in a pot experiment at four different Cd and Cu concentrations. Cd had no effect in root colonization, whereas high concentrations of Cu decreased colonization level in plants inoculated with the NP isolate. AM colonization did not increase plant dry weight or P concentration but influenced root Cd and Cu concentrations. Inoculation with PL and NP isolates enhanced root Cd and Cu concentrations, especially at highest metal addition levels, as compared to NM plants, without increasing shoot Cd and Cu concentrations. There was no evidence of intraspecific variation in the effects between AMF isolated from polluted and non-polluted sites, since there were no differences between plants inoculated with PL or NP isolate in any of the tested plant variables. The results of this study showed that AMF enhance metal accumulation in the root system of A. tripolium, suggesting a contribution of AMF to the sink of metals within vegetation in the salt marshes.
- Are mycorrhiza always beneficial?Publication . Corrêa, A.; Strasser, R.J.; Martins-Loução, M. A.In this work we evaluate whether the effect of ectomycorrhiza in the early developmental stages of symbiosis establishment is detrimental or beneficial to plant productivity and whether this effect is dependent on either N nutrition or plant age. Groups of Pinus pinaster L. plants with different ages and nutritional status were inoculated with alive or dead Pisolithus tinctorius. The plants were fed with either 1.9 mM or 3.8 mM ammonium as N source. Ectomycorrhiza establishment was monitored until 1 month after the inoculation through daily chlorophyll a fluorescence measurements and the analysis of fast fluorescence kinetics O-J-I-P, biomass increment and photosynthesis. Our results show that plants react differently to ectomycorrhiza formation depending on their age (stage of development, leaf area), their initial nutritional status, and the amount of nitrogen supplied. Mycorrhiza formation was found to constitute a stress depending on the plants’ age. Increased availability of N softened or eliminated the negative impact of mycorrhiza formation. Only younger plants eventually developed a higher net photosynthesis rate when mycorrhizal. It is concluded that ectomycorrhiza formation may have a detrimental rather than a beneficial effect on plants’ productivity during their establishment and early developmental stages, and that this depends on the amount of N available to the plant, on the nutritional status and on the age of the plant. Chlorophyll a fluorescence measurements proved to be a non-destructive, non-invasive and reliable tool able to identify the first signals of plant-mycorrhiza fungi interactions.
- Belowground traits of mediterranean woody plants in a portuguese shrublandPublication . Silva, Joaquim S.; Rego, Francisco C.; Martins-Loução, Maria A.Below ground traits vary widely. Apart from the influence of the environment both genetic and ontogenic factors are responsible for this variation. For mediterranean woody plants there is also evidence of a relationship between regenerative strategies and root system characteristics. With the general aim of studying these different aspects, the root systems of seventeen obligate seeders and sixteen re s p routers from ten different species and different deve l o pmental stages we re exc a vated at Tapada Nacional de Ma f ra in Central West Portugal. Root systems were photographed, weighted and measured. Root length and the ave rage root diameter we re determined using digital image software. Root-to-shoot ratio (R/S) and the specific root length (SRL) we re computed for all plants. Basal section was used as an indicator of plant development. A principal component analysis (PCA) was perf o rmed in order to study the relationships between variables and between plants. The analysis showed a clear distinction of plants according to the respective developmental stage but also according to the regenerative characteristics of the different species. Allometric relationships were found between root biomass, shoot biomass and basal section. Statistical tests showed that resprouters had higher maximum rooting depth, average root diameter and R/S and lower SRL, than obligate seeders. A decrease of R/S and SRL with basal section was verified for a sub-sample of four species.
- C allocation to the fungus is not a cost to the plant in ectomycorrhizaePublication . Corrêa, A.; Gurevitch, J.; Martins-Loução, M. A.; Cruz, C.Mycorrhizal benefit to plants is most frequently evaluated through growth differences between mycorrhizal (M) and non-mycorrhizal (NM) plants. These growth differences are often considered to be due to differences in belowground C expenditure, or in cost efficiency, i.e. amount of nutrients acquired per C expended. We searched published reports for relations between plant growth and belowground C allocation, C use efficiency, or nutrient uptake, in ectomycorrhizal (ECM) versus non-mycorrhizal plants. We found a similar number of cases of negative, null or positive effects of ECM on plant growth. These effects were not correlated with differences on belowground C allocation or C use efficiency between M and NM plants. In contrast, they were very strongly correlated with mycorrhizal effects on plant N gain. A comprehensive analysis of the published data therefore provided evidence that C is an excess, rather than a costly, resource, and that the outcome of the symbiosis depends only on whether mycorrhizae result in increased or decreased nutrient acquisition compared with NM plants, and not on cost efficiency differences between M and NM plants. Consequences of this finding for the regulation of resource exchange between symbionts and the nature of the symbiosis are discussed.
- Causes of change in nitrophytic and oligotrophic lichen species in a Mediterranean climate: impact of land cover and atmospheric pollutantsPublication . Pinho, P.; Augusto, S.; Martins-Loução, M. A.; Pereira, M. J.; Soares, A.; Máguas, C.; Branquinho, C.With the aim of determining the main drivers of changes in nitrophytic and oligotrophic macro-lichen communities in an industrial region with a Mediterranean climate, we considered both land-cover types and atmospheric pollutants. We determined the relation between the abundance of nitrophytic and oligotrophic species with environmental factors considering the distance of influence of land-cover types. The results showed that oligotrophic species decreased in the proximity of artificial areas, barren land and agricultural areas, associated with higher concentrations of NO2 and Zn, and Ti, probably dust of industrial and agricultural origin. Nitrophytic species were positively related to all the mentioned land-cover types, and with higher concentrations of Fe and N. Magnesium, probably from ocean aerosols, was negatively related to oligotrophic species and positively to nitrophytic.
- Depletion of the heaviest stable N isotope is associated with NH4 plantsPublication . Ariz, Idoia; Cruz, Cristina; Moran, Jose F.; González-Moro, María B.; García-Olaverri, Carmen; González-Murua, Carmen; Martins-Loução, Maria A.; Aparicio-Tejo, Pedro MBackground: In plants, nitrate (NO3 -) nutrition gives rise to a natural N isotopic signature (δ15N), which correlates with the δ15N of the N source. However, little is known about the relationship between the δ15N of the N source and the 14N/15N fractionation in plants under ammonium (NH4 +) nutrition. When NH4 + is the major N source, the two forms, NH4 + and NH3, are present in the nutrient solution. There is a 1.025 thermodynamic isotope effect between NH3 (g) and NH4 + (aq) which drives to a different δ15N. Nine plant species with different NH4 +-sensitivities were cultured hydroponically with NO3 - or NH4 + as the sole N sources, and plant growth and δ15N were determined. Short-term NH4 +/NH3 uptake experiments at pH 6.0 and 9.0 (which favours NH3 form) were carried out in order to support and substantiate our hypothesis. N source fractionation throughout the whole plant was interpreted on the basis of the relative transport of NH4 + and NH3. Results: Several NO3 --fed plants were consistently enriched in 15N, whereas plants under NH4 + nutrition were depleted of 15N. It was shown that more sensitive plants to NH4 + toxicity were the most depleted in 15N. In parallel, N-deficient pea and spinach plants fed with 15NH4 + showed an increased level of NH3 uptake at alkaline pH that was related to the 15N depletion of the plant. Tolerant to NH4 + pea plants or sensitive spinach plants showed similar trend on 15N depletion while slight differences in the time kinetics were observed during the initial stages. The use of RbNO3 as control discarded that the differences observed arise from pH detrimental effects. Conclusions: This article proposes that the negative values of δ15N in NH4 +-fed plants are originated from NH3 uptake by plants. Moreover, this depletion of the heavier N isotope is proportional to the NH4 +/NH3 toxicity in plants species. Therefore, we hypothesise that the low affinity transport system for NH4 + may have two components: one that transports N in the molecular form and is associated with fractionation and another that transports N in the ionic form and is not associated with fractionation
- Disturbance influences the outcome of plant–soil biota interactions in the invasive Acacia longifolia and in native speciesPublication . Carvalho, Luís M.; Antunes, Pedro M.; Martins-Loução, M. Amélia; Klironomos, John N.Interrelated causes of plant invasion have been gaining increasing recognition. However, research on this subject has mainly focused around conceptual models. Here we explore whether plant–soil biota feedbacks and disturbance, two major factors capable of facilitating invasive plants in introduced ranges, interact to preferentially benefit exotics compared to native plants. We investigated the influence of fire disturbance on plant–soil biota interactions for the invasive Acacia longifolia and two dominant natives (Cytisus striatus and Pinus pinaster) in Portuguese dune systems. In the first experiment, we grew exotic and native plants in soil inoculated with soil biota from unburned or recently burned soils collected in an area with small invasion intensity by A. longifolia. Soil biota effects on the exotic legume A. longifolia changed from neutral to positive after fire, whereas the opposite outcome was observed in the native legume C. striatus, and a change from negative to neutral effects after fire occurred in the native P. pinaster. Fire reduced mycorrhizal colonization in all species and rhizobial colonization in C. striatus but not in A. longifolia. In the second experiment, we grew the exotic and native plants with conspecific and heterospecific soil biota from undisturbed soils (area with low invasion intensity by A. longifolia), and from post-fire soils (area affected by a fire ~12 years ago and currently heavily invaded by A. longifolia). The exotic benefited more from post-fire than from undisturbed soil biota, particularly from those associated with natives. Natives did not experience detrimental effects with invasive-associated soil biota. Our results show that fire disturbance affected the functional interactions between soil biota and plants that may benefit more the exotic than some native species. Disturbance may open a window of opportunity that promotes invader success by altering soil enemy and mutualistic impacts.
- 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.