J.L. Araus

Mineral accumulation, carbon isotope discrimination and indirect selection for grain yield in two-rowed barley grown under semiarid conditions

Mineral accumulation in vegetative plant parts and in mature kernels has been proposed as an indirect selection criterion, either in addition to, or in substitution of, carbon isotope discrimination (Δ), to assess grain yield of temperate cereals in Mediterranean areas. However, the association between mineral concentration, in different plant parts, and grain yield is not yet fully understood. In order to study these relationships, four rain-fed trials were established in northeastern Spain involving 10 two-rowed barley (Hordeum vulgare L.) cultivars. Carbon isotope discrimination and total ash concentration were measured at maturity in kernels and straw. As expected, the Δ values of kernels (Δ-K) and straw (Δ-S) were positively correlated within environments. By contrast, Δ-K and ash concentration in kernels were often negatively related within environments, which suggests that mineral accumulation in kernels is not associated with the transpiration efficiency of the plants during grain filling. The lack of a positive relationship between ash concentration in the straw and either Δ-K or Δ-S indicates that ash concentration in vegetative tissues sampled at maturity may be of limited value as a surrogate of Δ. Grain yield correlated positively with either Δ-K or Δ-S, and negatively with ash concentration in kernels, especially in the poorest rain-fed environments. However, the ash concentration in the straw was not consistently associated with grain yield. While our results confirm that Δ traits are valid indicators of grain yield under Mediterranean conditions, the use of ash concentration in kernels for screening purposes is not warranted at this time due to the lack of a more accurate understanding of the physiological mechanisms underlying mineral accumulation in kernels. Prediction of grain yield through multiple linear regression has shown, however, that ash concentration in kernels could be used as a complementary criterion to Δ in poor rain-fed environments.

Stable carbon isotopes in archaeobotanical remains and palaeoclimate

Es descriu una metodologia recent per a inferir la precipitacio en nel passat basada en lanalisi de la composicio isotopica del carboni n(δ13C) en restes arqueobotaniques. Un cop descrita la base nfisiologica de la tecnica, sil·lustra laplicabilitat de δ13C mitjancant nun exemple referent al NE peninsular. Hom preten proporcionar nuna estimacio quantitativa de levolucio de la precipitacio nestacional (primavera) i anual al llarg dels darrers quatre mil anys nbasada en δ13C. Les mostres analitzades comprenen carbons n(pi blanc) i llavors carbonitzades (blat i ordi), i sobtenen estimes npluviometriques superiors en el passat que actualment, amb una ntendencia gradual cap a condicions progressivament mes arides. nNo obstant aixo, aquesta tendencia no esdeve uniforme, ni es detecten dues fases de major precipitacio (1800-900 aC; n300 aC - 300 dC) alternadament amb periodes relativament nsecs (900-300 aC; 900 dC - present). Dels resultats presentats ntambe es despren que la importancia relativa de la pluja primaveral nen el passat fou variable. Des daproximadament el 300 aC nen endavant, el periode primaveral subministra una major proporcio nde pluja anual que actualment. Contrariament, durant el nperiode 1800-800 dC la seva contribucio va esdevenir inferior, i nva apareixer una fase transitoria (800-300 aC) que mostra una nrecuperacio sobtada en aportacio primaveral. Posteriorment a naquesta fase la sincronia de canvis en δ13C en granes i carbons nsuggereix larribada del clima mediterrani a la regio.

Ontogenetic changes in photosynthetic capacity and dry matter production of flag wheat leaves during the grain filling period

The relationships between photosynthetic capacity and dry matter accumulation during the grain filling period have been studied in flag leaves of Triticum aestivum L., cv. Kolibri grown in Mediterranean field conditions. Particular importance has been given to assimilate accumulation in relation to the onset of senescence. During grain filling, the time course of specific dry weight (SDW) was similar in the blade and in the sheath. Variations in SDW were about six times larger in the sheath than in the blade. Minimum blade SDW values occurred during heading and at anthesis. Maximum blade SDW values were observed two weeks after anthesis. After this, SDW values decreased sharply. The dry matter increase per grain in the period from two weeks after anthesis to the end, was only about 25% of final grain dry weight. The importance of environmental constraints on maximum SDW values are discussed. Maximum SDW values occurred at the beginning of the period of rapid decline in blade net CO2 assimilation rate and leaf nitrogen content, that is, at the beginning of senescence. On the other hand, the stomatal resistance to CO2 and the development of senescence are not apparently related. The maximum blade dry weight increase (considering a value of zero at heading) was about 60 mg dry weight per g fresh weight. The possible relationships between dry matter accumulation and senescence onset are discussed.

Isótopos estables aplicados al estudio de los sistemas paleoagrícolas mediterráneos

En diferentes foros y medios de comunicación han aparecido recientemente quejas diversas acerca de una aparente redución del dinero para la investigación, que parece haberse traducido en un menor número de proyectos de investigación financiados por el Gobierno, una menor dotación por proyecto y una disminución del número de becas y contratos concedidos (por ejemplo, contratos Ramón y Cajal). Los análisis hechos públicos por la Fundació per la Pau y la Campaña Por la Paz: ¡No a la investigación militar! sobre los presupuestos de I+D y, especialmente, el último informe sobre los presupuestos de I+D para el próximo año 2006, pueden ayudar a explicar esta reducción o, cuanto menos, ponen en evidencia las tendencias actuales de la inversión del estado para la investigación en España. Creo que la comunidad científica debe conocer esta información, y por este motivo resumo aquí algunos de los puntos clave de la misma: