RESUMEN
The effects of varying intensities of light on plants depend on when they occur, even if the total amount of light received is kept constant. We designed an experiment using two clones of robusta coffee (Coffea canephora) intercropped with shelter trees in such a way that allowed us to compare coffee bushes shaded in the morning (SM) with those shaded in the afternoon (SA), and then confronting both with bushes receiving full sunlight over the course of the day (FS). The SM bushes displayed better gas-exchange performance than their SA and FS counterparts, in which the capacity for CO2 fixation was mainly constrained by stomatal (SA bushes) and biochemical (FS bushes) factors. Physiological traits associated with light capture were more responsive to temporal fluctuations of light rather than to the amount of light received, although this behavior could be a clone-specific response. The activity of key antioxidant enzymes differed minimally when comparing the SM and SA clones, but was much larger in FS clones. No signs of photoinhibition or cell damage were found regardless of the light treatments. Acclimations to varying light supplies had no apparent additional cost for constructing and maintaining the leaves regardless of the light supply. Both the SM and SA individuals displayed higher return in terms of revenue streams (e.g. higher mass-based light-saturated photosynthetic rates, photosynthetic nitrogen use efficiencies and long-term water use efficiencies) than their FS counterparts. In conclusion, shading may improve the physiological performance of coffee bushes growing in harsh, tropical environments.
Asunto(s)
Coffea/fisiología , Hojas de la Planta/fisiología , Aclimatación , Antioxidantes/metabolismo , Brasil , Dióxido de Carbono/metabolismo , Clorofila/metabolismo , Enzimas/metabolismo , Luz , Fotosíntesis/fisiología , Estomas de Plantas/metabolismo , Luz SolarRESUMEN
In this study, the combined effects of light and water availability on the functional relationships of the relative growth rate (RGR), leaf chemical composition, construction and maintenance costs, and benefits in terms of payback time for Coffea arabica are presented. Coffee plants were grown for 8 months in 100% or 15% full sunlight and then a four-month water shortage was implemented. Plants grown under full sunlight were also transferred to shade and vice versa. Overall, most of the traits assessed were much more responsive to the availability of light than to the water supply. Larger construction costs (12%), primarily associated with elevated phenol and alkaloid pools, were found under full sunlight. There was a positive correlation between these compounds and the RGR, the mass-based net carbon assimilation rate and the carbon isotope composition ratio, which, in turn, correlated negatively with the specific leaf area. The payback time was remarkably lower in the sun than in shade leaves and increased greatly in water-deprived plants. The differences in maintenance costs among the treatments were narrow, with no significant impact on the RGR, and there was no apparent trade-off in resource allocation between growth and defence. The current irradiance during leaf bud formation affected both the specific leaf area and leaf physiology upon transferring the plants from low to high light and vice versa. In summary, sun-grown plants fixed more carbon for growth and secondary metabolism, with the net effect of an increased RGR.
Asunto(s)
Coffea/crecimiento & desarrollo , Coffea/efectos de la radiación , Luz , Hojas de la Planta/química , Hojas de la Planta/crecimiento & desarrollo , Agua/fisiología , Análisis de Varianza , Biomasa , Carbono/metabolismo , Coffea/metabolismo , Hojas de la Planta/efectos de la radiación , Análisis de Componente PrincipalRESUMEN
Los hongos micorrízicos arbusculares (HMA) facilitan la absorción de nutrientes a las plantas hospederas, por esta razón estos microorganismos cumplen un rol fundamental en el funcionamiento de los agroecosistemas. El objetivo de este trabajo fue evaluar el efecto de la asociación simbiótica entre HMA nativos y comerciales y plántulas de Elaeis guineensis en condiciones de vivero con un nivel alto de fósforo (P) en el suelo. Plantas de tres meses de edad fueron sometidas a cuatro tratamientos: Inóculo Nativo (IN), Inóculo Comercial (IC), Mixto (M) y Testigo absoluto (TA). Se evaluaron los parámetros: peso seco total de la planta, peso seco raíz, peso seco parte aérea de la planta, altura de la planta, tasa de crecimiento relativo, colonización micorrízica y número de esporas en el suelo. Se realizaron tres muestreos, uno inicial (día 0), uno a los 45 y a los 90 días después del trasplante de las plántulas (ddt). Los datos fueron analizados mediante un ANOVA o Kruskall-Wallis según el comportamiento de los datos, seguido de un test de Duncan para comparar las medias o un test modificado de Tuckey para datos no paramétricos. Se observaron diferencias significativas en el número de esporas entre los tratamientos IN, M y TA, a los 45 ddt. Para la variable colonización micorrízica se observaron diferencias significativas a los 45 ddt entre los tratamientos IC y TA, mientras que a los 90 ddt se presentaron diferencias entre los tratamientos IN, IC y M, con respecto al TA. A pesar de que el nivel de P en el suelo fue alto, el porcentaje de colonización micorrízica estuvo por encima del 50% en los muestreos realizados a los 45 y 90 días. El tratamiento IN funcionó mejor que los tratamientos IC y M, para las condiciones edáficas de este experimento.
The arbuscular mycorrhizal fungi (AMF) facilitate the absorption of nutrients to the host plants. These microorganisms therefore, fulfill a fundamental roll in the operation of agroecosytems. The aim of this work was to evaluate the effect between native and commercial arbuscular mycorrhizal fungi and Elaeis guineensis seedlings in greenhouse conditions with high P level. Plants of three months of the age were put under four treatments: Native inoculate (NI), Foreign inoculate (FI), Mixture (M) and control (TA). It was evaluated total dry weight of the plant, root and aerial part dry weight, height of the plant, relative growth rate (RGR), mycorrhizal colonization and spores number. At 45 and 90 days after the transplant these variable were evaluated. An initial sampling dry mass was taking by to determine RGR. The data were analyzed through the ANOVA or Kruskall-Wallis according to the behavior of the data, followed of a test of averages of Duncan or a modified test of Tuckey for nonparametric data. Significant differences in the spores number between the treatments NI, FI, M and TA and between NI and M to the 45 days appeared. In the colonization mycorrhizal differences between the treatments FA and TA were observed the 45 days. To the 90 days between all the treatments with respect to the TA. Although the P level in the soil was high, also it was it the mycorrhizal colonization at the two evaluated times. Through time the treatment NI worked better in the soil edaphic conditions used in this experiment.