BUSCADOR RECOLECTA

The widespread use of NO3− fertilization has had a major ecological impact. NH4+ nutrition may help to reduce this impact, although high NH4+ concentrations are toxic for most plants. The underlying tolerance mechanisms are not yet fully understood, although they are thought to include the limitation of C, the disruption of ion homeostasis, and a wasteful NH4+ influx/efflux cycle that carries an extra energetic cost for root cells.
In this study, high irradiance (HI) was found to induce a notable tolerance to NH4+ in the range 2.5–10 mM in pea plants by inducing higher C availability, as shown by carbohydrate content. This capacity was accompanied by a general lower relative N content, indicating that tolerance is not achieved through higher net N assimilation on C-skeletons, and it was also not attributable to increased GS content or activity in roots or leaves. Moreover, HI plants showed higher ATP content and respiration rates. This extra energy availability is related to the internal NH4+ content regulation (probably NH4+ influx/efflux) and to an improvement of the cell ionic balance.
The limited C availability at lower irradiance (LI) and high NH4+ resulted in a series of metabolic imbalances, as reflected in a much higher organic acid content, thereby suggesting that the origin of the toxicity in plants cultured at high NH4+ and LI is related to their inability to avoid large-scale accumulation of the NH4+ ion., This work was supported by the Spanish MICIIN (grant nos. AGL2006-12792-CO2-01 and AGL2009-13339-CO2-02 [to P.A.-T.] and AGL2007-64432/AGR [to J.F.M.]). IA was supported by a doctoral Fellowship from the Public University of Navarre.

The use of urea as an N fertilizer has increased to such an extent that it is now the most widely used fertilizer in the world. However, N losses as a result of ammonia volatilization lead to a decrease in its efficiency, therefore different methods have been developed over the years to reduce these losses. One of the most recent involves the use of urea combined with urease inhibitors, such as N-(n-butyl) thiophosphoric triamide (NBPT), in an attempt to delay the hydrolysis of urea in the soil. The aim of this study is to perform an in-depth analysis of the effects that NBPT use has on plant growth and N metabolism. Wheat plants were cultivated in a greenhouse experiment lasting four weeks and fertilized with urea and NBPT at different concentrations (0, 0.012, 0.062, 0.125%). Each treatment was replicated six times. A non-fertilized control was also cultivated. Several parameters related with N metabolism were analysed at harvest.
NBPT use was found to have visible effects, such as a transitory yellowing of the leaf tips, at the end of the first week of treatment. At a metabolic level, plants treated with the inhibitor were found to have more urea in their tissues and a lower amino acid content, lower glutamine synthetase activity, and lower urease and glutamine synthetase content at the end of the study period, whereas their urease activity seemed to have recovered by this stage., This work was supported by the Spanish MICIIN (grant no. AGL2009-13339-CO2-02 [to P.A.T.]). S.C was supported by a doctoral fellowship from the Public University of Navarre.

The development of new nitrogen fertilizers is necessary to optimize crop production whilst improving the environmental aspects arising from the use of nitrogenous fertilization as a cultural practice. The use of urease inhibitors aims to improve the efficiency of urea as a nitrogen fertilizer by preventing its loss from the soil as ammonia. However, although the action of urease inhibitors is aimed at the urease activity in soil, their availability for the plant may affect its urease activity. The aim of this work was therefore to evaluate the effect of two urease inhibitors, namely acetohydroxamic acid (AHA) and N-(n-butyl) thiophosphoric triamide (NBPT), on the germination of pea and spinach seeds. The results obtained show that urease inhibitors do not affect the germination process to any significant degree, with the only process affected being imbibition in spinach, thus also suggesting different urease activities for both plants. Our findings therefore suggest an activity other than the previously reported urolytic activity for urease in spinach. Furthermore, of the two inhibitors tested, NBPT was found to be the most effective at inhibiting urease activity, especially in pea seedlings., This work was supported by the Spanish MICIIN (Grant No. AGL2009-13339-CO2-02 [to P.A.T.]).

The amount of carbon dioxide (CO2) in Earth's atmosphere has exceeded 400 parts per million
(ppm) during three continuous months of observations in 2014, which is an absolute record for
the last 800,000 years. As a consequence, plants, as photosynthetic organisms, will inevitably be
influenced by the changed growing conditions that result from the increased [CO2]. The effect
of increased [CO2] on plants has been widely studied and goes far beyond favouring
carboxylation of Rubisco and generating higher growth rates. The present thesis aims to
highlight the relevance of different nitrogen sources in the response of Arabidopsis thaliana, a C3
model plant, to elevated [CO2]. For this purpose, this has been an integrated study of leaf and
root organs combining techniques that range from plant physiology to molecular biology. Under
nitrate nutrition and elevated [CO2] conditions, Arabidopsis thaliana plants increase their biomass
and maximum photosynthetic rates; nevertheless, the total soluble protein, Rubisco content and
leaf N content reveal a general decrease in leaf N availability (chapter I). Although the expression
of nitrate transporters was substantially upregulated in roots, plants did not efficiently transport
nitrate and other minerals from roots to leaves, which compromised leaf N and mineral status.
Therefore, our results suggest that the diminution of transpiration rates causes a reduction in the
xylem flux, which inexorably generates an imbalance in the transport of nitrate and mineral
elements between organs under elevated [CO2]. Moreover, root nitrate assimilation (based on
the amino acid content) is favoured in order to overcome N limitations due to the reduction in
leaf nitrate assimilation. In chapter II plant performance under elevated [CO2] and ammonium
nitrate conditions was characterized and it was found that biomass doubled due to substantially
increased photosynthetic rates. Gas exchange characterization revealed that these plants
overcame photosynthetic acclimation. Plants maintained Rubisco concentrations at control
levels alongside enhanced energy efficiency. The increments found in leaf carbohydrates and
organic acid content linked to enhanced respiration rates supported the fact that the plants under
elevated [CO2] maintained their energy status. The transcriptomic analysis enabled the
identification of photoassimilate allocation and remobilization as fundamental processes used by the plants to avoid photosynthetic acclimatization. Moreover, based on the relationship between
plant carbon status and hormone functioning, the transcriptomic analyses provided an
explanation of why phenology accelerates under elevated [CO2]. Finally, in chapter III the
relevance of ammonium nutrition under elevated [CO2] was analysed; for this purpose a double
nitrate reductase mutant (NR mutant, nia1-1/chl3-5 defective) was used. These results highlight
that plants under elevated [CO2] which preferentially assimilate ammonium as their only N
source maintain leaf growth and photosynthetic rates similar to plants receiving ammonium
nitrate. However, under ambient [CO2] concentrations, ammonium toxicity symptoms emerge
and development is extremely constrained. In elevated [CO2] conditions, an NR mutant
maintained the energy supply for the Calvin cycle pathway and managed efficient
photoassimilate transport between plant tissues. Furthermore, the data suggest active ammonium
assimilation in leaves due to the exceptional conditions (C skeletons, ATP, adequate pH
homeostasis and no photoinhibition) of these plants under elevated [CO2]. Hence, the results
obtained in the present doctoral thesis aim towards the incorporation of the source of nitrogen as
key in the response at the elevated [CO2] of Arabidopsis thaliana plants. Consequently, the
present doctoral thesis aims to determine whether the incorporation of the correct source of
nitrogen is the key component in how Arabidopsis thaliana plants respond to elevated [CO2]., This work was funded by the project: AGL2009-13339-C02-02 and AGL2012-37815-C05-5, Programa Oficial de Doctorado en Agrobiología Ambiental (RD 1393/2007), Ingurumen Agrobiologiako Doktoretza Programa Ofiziala (ED 1393/2007)

El crecimiento de la población y sus necesidades de alimentación en las últimas décadas han sido mayoritariamente sustentados por un modelo productivo lineal a escala global basado en consumir recursos y generar residuos. Este modelo en muchas ocasiones ha contribuido de manera crucial al deterioro de agrosistemas y al cambio climático global.
Para mejorar la sostenibilidad de los agrosistemas y mitigar el cambio climático es fundamental potenciar modelos productivos circulares locales basados en aprovechar residuos del entorno como recursos que permitan mejorar la fertilidad y resiliencia de los agrosistemas y desarrollar una agricultura más sostenible.
Es por esto, que esta tesis tiene por objetivo general el estudio del uso continuado de residuos orgánicos en suelos agrícolas como enmiendas.
Esta investigación se ha desarrollado en dos ensayos de larga duración ubicados en Navarra (España) donde se realizan distintos manejos de fertilización con residuos orgánicos. El primero de ellos es una viña de DOC Rioja (Bargota) en la que desde 1998 se aplican anualmente 3 compost diferentes. El segundo ensayo es una rotación cerealista (Arazuri) que desde 1992 recibe anualmente lodos de EDAR a distintas dosis.
Los resultados de estos ensayos muestran un claro efecto beneficioso de la aplicación de distintos residuos orgánicos como fertilizantes en ambos agrosistemas., Azken hamarkadetan biztanleriak eta beren janari beharrak hazkunde ikaragarria jasan dute. Hazkunde hori gehienetan ekoizpen eredu global eta lineal batez asetua izan da. Eredu honetan baliabideak kontsumitzen eta hondakinak sortzen dira neurri gabean. Honen ondorioz, askotan nekazaritza sistemen hondamena eta klima-aldaketa globala eragin ditu.
Nekazaritza sistemen iraunkortasuna hobetzeko eta klima-aldaketan eraginak arintzeko ezinbestekoa da tokiz-tokiko ekonomia zirkularrean oinarritutako ekoizpen ereduak indartzea. Hondakin organikoak ongarri bezala erabiltzea aukera ona da, bai nekazaritza sistemen emankortasuna, eta bai bere erresilientzia handitzeko. Baina epe luzera izan ahal dituen zenbait alde negatibo ebaluatu behar dira.
Hori dela eta, tesi honen helburu orokorra lurzoruan epe luzera hondakin organikoen aplikazio jarraiaren zenbait ingurugiro alde aztertzea da.
Ikerketa hau Nafarroan (Espainian) kokatzen diren epe luzerako ongarri organikoen bi entsaioetan burutua izan da. Lehenengoa Bargotako DOC Errioxako mahatsean, zeinetan 1998az geroztik 3 konpost diferente aplikatzen diren. Bigarrena, Arazuriko zereal errotazio batean zeinean 1992az geroztik urtero EDAR-lohi dosi ezberdin aplikatzen diren.
Entsaio hauetan lortutako emaitzek gai organiko hauek epe luzera erabiltzearen abantailak agerian utzi dituzte., The population growth rate and their diet and the land required to meet this demand has been largely supported by a global model based on a linear economy that consumes resources and generates wastes. This model has often contributed to the deterioration of agricultural systems and global climate change.
The sustainability of agricultural systems can be improved, on one hand, and climate change can be mitigated, on the other, by empowering circular productive models based on local resources and their rational exploitation. If soil fertility is regarded as an important feature of food production, then an important occasion for the contribution of agricultural practices is set to achieve food sustainability.
This research was conducted in two sites in Navarra (Spain) where long-term trials have been established with different fertilization management and by the use of organic wastes, either composted or treated. The first trial was a vineyard situated in the P.D.O. La Rioja, Navarra, in which three different compost have been applied annually since 1992. The second trial is on cereal crops in rotation in Arazuri, Navarra, that have been receiving Treated Sewage Sludge annually since 1992.
The results of this thesis show a clear beneficial effect after organic wastes have been applied to soil as organic amendments in both agricultural systems., Esta tesis doctoral ha sido financiada con una Beca de formación de personal investigador de la Universidad Pública de Navarra (2011- 2015) y ha recibido financiación del Ministerio de Economía y Competitividad (Proyectos: AGL2009-13339-C02-02; AGL2012-37815-C05-05)., Programa Oficial de Doctorado en Agrobiología Ambiental (RD 1393/2007), Ingurumen Agrobiologiako Doktoretza Programa Ofiziala (ED 1393/2007)