Fitodesalinización asistida por microorganismos para la recuperación de suelos agrícolas

El planeta Tierra está sufriendo graves alteraciones debido a la actividad del ser humano, entre las que cabe destacar el crecimiento exponencial de la población mundial. Dicho aumento conlleva la necesidad de producir más alimentos básicos. Consecuentemente, se están sobreexplotando las zonas agrícolas, lo que aumenta la demanda tanto de abono como de agua, que en ocasiones, hace que se utilice para el riego agua de baja calidad. Esto produce una salinización del suelo agrícola que se empobrece y deja de ser útil. Se hace por tanto necesaria la recuperación de zonas de cultivo salinizadas, para atender la creciente demanda de alimentos. Entre las soluciones que se plantean para recuperar dichos suelos está la fitodesalinización, es decir, el uso de plantas para corregir el exceso de sal. En concreto, existe un grupo de plantas denominadas halófitas (requieren sal para desarrollarse de forma óptima) que poseen un alto potencial para ser usadas en la desalinización. A su vez, diversos estudios han mostrado que el empleo de bacterias promotoras del crecimiento de las plantas (PGPB) mejora la capacidad remediadora de las especies vegetales. Con dichas ideas, el objetivo de esta Tesis Doctoral fue estudiar la capacidad de la halófita Arthrocnemum macrostachyum (Morric.) Moris para fitodesalinizar suelos contaminados por exceso de sal y determinar la influencia en este proceso de bacterias con propiedades PGP. Tras estudiar la rizosfera (suelo alrededor de las raíces) de A. macrostachyum, se aislaron 182 cepas bacterianas que se caracterizaron por su tolerancia a la salinidad y a altas temperaturas, por la producción de auxinas (AIA) y acil-homoserina lactona (AHL), así como por la capacidad para solubilizar hierro y fosfato. Una vez analizadas todas las propiedades, se concluyó que las más comunes en la colección bacteriana, fueron la producción de auxinas y la solubilización de hierro. Respecto a la interacción que se establece entre A. macrostachyum y las bacterias seleccionadas hay diferentes aspectos a destacar. Por un lado, las cepas bacterianas Hv16, RTE9 y OR133 inhibieron el efecto negativo que la sal ejerce sobre la germinación de la halófita, mejorándola al menos un 20 %. Además, se determinó que la sal es un factor que modula dicha interacción, de manera que se promueve más el crecimiento de la planta en ausencia de sal o en una concentración por debajo del óptimo de la halófita. Se observó que, gracias a los inoculantes Hv16 y C58, enraizaron mejor las estaquillas de A. macrostachyum, produciendo un 20 % más de raíces. También se comprobó que la mayor interacción entre A. macrostachyum-bacteria, se produce cuando la planta es inoculada a nivel de semilla. En un experimento de fitodesalinización de suelos agrícolas se consiguió disminuir la salinidad de los suelos entre un 31-80 %, independientemente de la inoculación realizada en la halófita, permitiendo que se desarrollaran, a posteriori, diversos cultivos en el suelo remediado. Se observó que la coinoculación con las cepas bacterianas Hv16 y RTE9 permitió mejorar la gestión de los recursos hídricos de A. macrostachyum, sin mermar por ello su capacidad fitodesalinizadora. En conclusión, la halófita A. macrostachyum inoculada con las cepas bacterianas Hv16 (Kocuria polaris) y RTE9 (Rahnela aquatilis) se propone como una bioherramienta para la recuperación de suelos agrícolas en desuso debido a la contaminación por sales

Impact of short-term extreme temperature events on physiological performance of Salicornia ramosissima J. Woods under optimal and sub-optimal saline conditions

Increasing extreme temperature climatic events could exert an important effect on plant photosynthetic performance, which could be modulated by the co-occurrence with other environmental factors, such as salinity, in estuarine ecosystems. Therefore, a mesocosm experiment was designed to assess the impact of temperature events for three days (13/5 °C, 25/13 °C and 40/28 °C) in combination with two NaCl concentrations (171 and 1050 mM NaCl) on the physiological performance of Salicornia ramosissima. Extreme temperature events had a negative impact on S. ramosissima photosynthetic efficiency, this effect being more marked with cold wave at both salinities, compared with heat wave, even in presence of NaCl excess. This differential thermotolerance in the photosynthetic apparatus was ascribed to the greater integrity and functioning of its photosynthetic pathway at high temperature, as indicated by constant gs, Vc,max values at optimal salinity and the higher values of those parameters and gm recorded in combination with NaCl excess. Moreover, S. ramosissima was able to upregulate the energy sink capacity of its photochemical apparatus at elevated temperature and salinity by a greater energy excess dissipation capacity. This could have contributed to reducing the risk of oxidative stress, along with the recorded higher capacity for antioxidant enzyme activity modulation under these conditions.España, MINECO Project CGL2016– 75550-

Sarcocornia fruticosa recovery capacity after exposure to co-existed water and salinity stress

The capacity of halophytes species to resist abiotic stress has been tested on multiple occasions. The ability of these species such as Sarcocornia fruticosa to cope with severe stress conditions has been shown, as well as their utility as a phytoremediation tool or even as potential crop species. However, there is a lack of literature on the effect that these abiotic factors have on their physiological response after a recovery period. In a greenhouse experiment, S. fruticosa plants were subjected to a combination of water regimen (water stress/field capacity) and salinity concentration (171/510 mM NaCl) grown conditions for 30 days. After these stress periods, plants were left 15 days in recovery conditions (field capacity and 171 mM NaCl). To study the effect of stress during both periods, osmotic potential, net photosynthetic rate, stomatal conductance, intercellular CO2 concentration, quantum efficiency of PS II, OJIP-derived parameters and photosynthetic pigment concentrations were measured. Our results show the already known resistance of this species to drought and salinity stress. However, the combination of both factors did affect the ability of S. fruticosa to maintain its level of carbon assimilation due to a decrease in stomatal conductance. In addition, the recovery period helped us to describe a synergic effect of both abiotic factors showing that plants subjected to both stresses received a better response during the recovery period than those only affected by salinity stress.8 página

Salinity Modulates Juncus acutus L. Tolerance to Diesel Fuel Pollution

Soil contamination with petroleum-derived substances such as diesel fuel has become a major environmental threat. Phytoremediation is one of the most studied ecofriendly low-cost solutions nowadays and halophytes species has been proved to have potential as bio-tools for this purpose. The extent to which salinity influences diesel tolerance in halophytes requires investigation. A greenhouse experiment was designed to assess the effect of NaCl supply (0 and 85 mM NaCl) on the growth and photosynthetic physiology of Juncus acutus plants exposed to 0, 1 and 2.5% diesel fuel. Relative growth rate, water content and chlorophyll a derived parameters were measured in plants exposed to the different NaCl and diesel fuel combinations. Our results indicated that NaCl supplementation worsened the effects of diesel toxicity on growth, as diesel fuel at 2.5% reduced relative growth rate by 25% in the absence of NaCl but 80% in plants treated with NaCl. Nevertheless, this species grown at 0 mM NaCl showed a high tolerance to diesel fuel soil presence in RGR but also in chlorophyll fluorescence parameters that did not significantly decrease at 1% diesel fuel concentration in absence of NaCl. Therefore, this study remarked on the importance of knowing the tolerance threshold to abiotic factors in order to determine the bioremediation capacity of a species for a specific soil or area. In addition, it showed that NaCl presence even in halophytes does not always have a positive effect on plant physiology and it depends on the pollutant nature

Stimulation of PGP Bacteria on the Development of Seeds, Plants and Cuttings of the Obligate Halophyte <i>Arthrocaulon (Arthrocnemum) macrostachyum</i> (Moric.) Piirainen & G. Kadereit

The Earth is undergoing alterations at a high speed, which causes problems such as environmental pollution and difficulty in food production. This is where halophytes are interesting, due to their high potential in different fields, such as remediation of the environment and agriculture. For this reason, it is necessary to deepen the knowledge of the development of halophytes and how plant growth-promoting bacteria (PGP) can play a fundamental role in this process. Therefore, in this work were tested the effects of five PGP bacteria on its rhizosphere and other endophytic bacteria at different concentrations of NaCl on seed germination, plant growth (0 and 171 mM) and cutting growth (0 mM) of Arthrocaulon macrostachyum. The growth promotion in this strict halophyte is highlighted due to the presence of PGP bacteria and the fact that no salt is needed. Thus, without salt, the bacterial strains Kocuria polaris Hv16, Pseudarthrobacter psychrotolerans C58, and Rahnella aceris RTE9 enhanced the biomass production by more than 60% in both stems and roots. Furthermore, germination was encouraged by more than 30% in the presence of both R. aceris RTE9 and K. polaris Hv16 at 171 mM NaCl; the latter also had a biocontrol effect on the fungi that grew on the seeds. Additionally, for the first time in cuttings of this perennial species, the root biomass was improved thanks to the consortium of K. polaris Hv16 and P. psychrotolerans C58. Finally, this study demonstrates the potential of PGPs for optimising the development of halophytes, either for environmental or agronomic purposes

Soil phenanthrene phytoremediation capacity in bacteria-assisted Spartina densiflora

Polycyclic aromatic hydrocarbons (PAH) have become a threat for the conservation of wetlands worldwide. The halophyte Spartina densiflora has shown to be potentially useful for soil phenanthrene phytoremediation, but no studies on bacteria-assisted hydrocarbon phytoremediation have been carried out with this halophyte. In this work, three phenanthrene-degrading endophytic bacteria were isolated from S. densiflora tissues and used for plant inoculation. Bacterial bioaugmentation treatments slightly improved S. densiflora growth, photosynthetic and fluorescence parameters. But endophyte-inoculated S. densiflora showed lower soil phenanthrene dissipation rates than non-inoculated S. densiflora (30% below) or even bulk soil (23% less). Our work demonstrates that endophytic inoculation on S. densiflora under greenhouse conditions with the selected PAH-degrading strains did not significantly increase inherent phenanthrene soil dissipation capacity of the halophyte. It would therefore be advisable to provide effective follow-up of bacterial colonization, survival and metabolic activity during phenanthrene soil phytoremediation.Ministerio de Economía y Competitividad CGL2016-75550-RMinisterio de Educación, Cultura y Deporte FPU014/0398