Nicolás Franck

Carbon allocation in fruit trees: from theory to modelling

Carbon allocation within a plant depends on complex rules linking source organs (mainly shoots) and sink organs (mainly roots and fruits). The complexity of these rules comes from both regulations and interactions between various plant processes involving carbon. This paper presents these regulations and interactions, and analyses how agricultural management can influence them. Ecophysiological models of carbon production and allocation are good tools for such analyses. The fundamental bases of these models are first presented, focusing on their underlying processes and concepts. Different approaches are used for modelling carbon economy. They are classified as empirical, teleonomic, driven by source–sink relationships, or based on transport and chemical/biochemical conversion concepts. These four approaches are presented with a particular emphasis on the regulations and interactions between organs and between processes. The role of plant architecture in carbon partitioning is also discussed and the interest of coupling plant architecture models with carbon allocation models is highlighted. As an illustration of carbon allocation models, a model developed for peach trees, describing carbon transfer within the plant, and based on source–sink and Münch transport theory is presented and used for analyzing the link between roots, shoots and reproductive compartments. On this basis, the consequences of fruit load or plant pruning on fruit and vegetative growth can be evaluated.

Limitation of coffee leaf photosynthesis by stomatal conductance and light availability under different shade levels

In agroforestry systems, the effect of shade trees on coffee net photosynthesis (An) has been the object of debates among coffee scientists. In this study, we undertook over 600 coffee An “spot” measurements under four different artificial shade levels (100, 72, 45 and 19% of full solar irradiance) and analyzed limitations to An by low light availability (photon flux density, PFD) and stomatal conductance (gs). These gas exchange measurements were carried out during two consecutive coffee growing seasons in a commercial plantation in the Orosi valley of Costa Rica. Levels of An were related to PFD and gs in order to calculate envelope functions which were used to establish PFD or gs limitations to An. Under the growing conditions of the present trial, mean leaf An remained stable for growth irradiance (GI) as low as 45% of full sun and decreased by ~20% at 19% GI. Limitation to An due to gs was strong in full sun and decreasing with increasing shade levels. On the other hand, limitation due to PFD remained at a similar level for all shade treatments. These different evolutions of limitations of An by PFD and gs in response to shade explain the absence of a decrease in coffee leaf An with a shade level up to 55%. Consequently, these results confirm that Arabica coffee is a shade-adapted plant with leaves that can maintain a high photosynthetic performance under low light availability.

Domestication of the Chilean guava (Ugni molinae Turcz.), a forest understorey shrub, must consider light intensity

A Chilean guava ecotype (Ugni molinae Turcz.) was cultivated in Santiago during the summer of 1999/2000 in order to assess the effect of shading on photosynthesis. Plants were grown under either 50% shading or full sunlight and chlorophyll fluorescence, net assimilation rates of CO2, photosynthetic pigment contents, were measured 2 months after planting, in each light regime, during the day. The capacity to recover the photochemical efficiency of photosystem II in light grown plants, measured as Fv/Fm after 30 min dark adaptation was markedly reduced, reaching values lower than 0.5 at midday, with a sunlight PPFD of 1600 mmol m � 2 s � 1 . On the other hand, the shaded plants showed a nearly complete recovery of the parameter. The photochemical quenching of chlorophyll fluorescence, reached a value of 0.47, also at midday, in full light grown plants, nearly half that observed in the shade, indicating a high PSII excitation pressure in the former. The light saturated net CO2 assimilation rates, measured in controlled conditions of temperature, were markedly lower in the full light plants compared to the shade ones. It is concluded that the Chilean guava is not able to cope with the light intensities characteristic of many Mediterranean climates, resulting in chronic photoinhibition.

Seasonal fluctuations in Vitis vinifera root respiration in the field

We studied the seasonal fluctuation of soil respiration (R(S)), and its root-dependent (R(R)) and basal (R(B)) components, in a Vitis vinifera (Chardonnay) vineyard. The R(S) components were estimated through independent field methods (y-intercept and trenching) and modeled on the basis of a Q(10) response to soil temperature, and fine and coarse root respiration coefficients. The effect of assimilate availability on R(R) was assessed through a trunk girdling treatment. The apparent Q(10) for R(R) was twice that of R(B) (3.5 vs 1.6) and increased linearly with increasing vine root biomass. The fastest R(R) of fine roots was during rapid fruit growth and the fastest R(R) of coarse roots was immediately following fruit development. R(S) was estimated at 32.6 kg ha(-1) d(-1) (69% as a result of R(R) ) for the hottest month and at 7.6 kg ha(-1) d(-1) (18% as a result of R(R)) during winter dormancy. Annual R(S) was low compared with other natural and cultivated ecosystems: 5.4 Mg ha(-1) (46% as a result of R(R)). Our estimates of annual vineyard R(S) are the first for any horticultural crop and suggest that the assumption that they are similar to those of annual crops or forest trees might lead to an overestimation.

Acclimation to sun and shade of three accessions of the Chilean native berry-crop murta

Murta (Ugni molinae Turcz.) is an evergreen shrub of the native forest understorey of southern Chile that produces berries which are consumed in the local markets. Because of the natural adaptation of murta to growing under the shade of trees, we propose that an adequate way of domesticating this species would be its cultivation in agroforestry systems. In order to assess the suitability of three murta accessions from different regions in southern Chile for their cultivation in such systems, we established a trial in which these accessions were submitted to six light transmittance levels (20%–100% of full solar irradiance) from planting in spring to the following autumn. Optimum growth, as assessed through dry mass accumulation and emission of branches and metamers, was achieved at moderate light transmittance levels (50%–65%). These growth traits showed stable positive responses to the relative amount of light intercepted by the plants (as estimated from plant structural traits) up to these optimum light transmittance levels and diverged to lower values thereafter. These stable relationships suggest that the differences in plant growth at low and moderate light transmittance levels can be attributed to restrictions of photosynthesis by light availability. The reduction in growth for higher light transmittance levels may be partly attributed to photoinhibition as suggested by reduced chlorophyll content and relatively low increments in carotenoid content in leaves at high light transmittance levels.

Simulation of Ecophysiological Processes on 3D Virtual Stands with the ARCHIMED Simulation Platform

Most classic ecophysiological models rely on crude representations of canopies as stacks of vegetation layers. Therefore, their use in complex canopies implies complicated adaptations as well as simplifying assumptions that are difficult to validate. Alternatively, the ARCHIMED simulation platform uses 3D virtual stands as a support for numerical simulations of biophysical processes such as leaf irradiation, transpiration and temperature and ultimately carbon assimilation. By doing so, detailed information can be integrated from the individual leaf scale up to the individual plant scale, even within complex stands such as agroforestry systems. Simple numerical methods are used for solving multiple feedbacks between light, energy, water and CO2 transfers at leaf, plant and plot scales. Numerical calculations applied at different scales allow simple implementation of complex models involving intricate processes.

Analysis of blueberry (Vaccinium corymbosum L.) fruit water dynamics during growth using an ecophysiological model

ABSTRACT Blueberry (Vaccinium corymbosum L.) fruits exhibit three growth stages associated with distinct biological processes. During these periods, water and carbon accumulate in the fruit, determining quality traits such as fruit size and sugar concentration. We adapted the Fishman-Génard model to blueberry and used it to analyse the effect of fruit load on fruit fresh mass and water dynamics, based on empirical observations of dry mass and sugar content performed throughout the fruit growth period. Different fruit load treatments were imposed during two seasons on ‘Brigitta’ blueberry plants growing under different culture systems. Increasing fruit load significantly reduced the fresh mass of the fruits at harvest, but did not affect sugar concentration, which was simulated and validated with a mean error of 7% for fresh mass and 15% for sugar concentration for the tested conditions. The most sensitive model parameters were those related to cell wall extensibility and sugar uptake. The simulations indicated that larger fresh mass of the fruit was mainly caused by increases in water fluxes rather than pressure differences. The model implementation provides the first estimates of a set of parameters which govern blueberry fruit water dynamics from fruit set to harvest.

Evaluación de la tolerancia a estrés por sequía en cuatro genotipos naturalizados de vid (Vitis vinifera) provenientes del norte de Chile

El cultivo de la vid (Vitis vinifera) se caracteriza por sufrir sequias estacionales en la mayoria de las regiones productoras, situacion que se incrementa en ambientes aridos y semiaridos de Chile, los cuales han sufrido disminuciones de precipitaciones y prolongados periodos de sequia, siendo una de las principales problematicas que afectan la productividad de las vides en el norte del pais. El objetivo planteado fue analizar las respuestas morfo-fisiologicas en genotipos naturalizados de vides expuestas a estres hidrico y determinar su nivel de tolerancia. Se evaluaron parametros fisiologicos y arquitecturales en cuatro genotipos de vides (10, 93, 134, 148), provenientes de un gradiente latitudinal en zonas aridas y semiaridas del norte de Chile (18°S a 32°S). Mediante el uso de un sistema de mini-rizotrones, material clonal de los cuatro genotipos fue sometido a tratamientos de estres hidrico leve y severo (60% y 40% de capacidad de campo, respectivamente), durante tres meses, bajo un diseno completamente aleatorio. Se obtuvieron diferencias significativas a nivel de tratamientos para la sobrevivencia y longitud de tallo, distancia entrenudos y todos los parametros de desempeno fisiologico evaluados. Asimismo, se obtuvieron diferencias significativas entre los genotipos en caracteres de longitud de raiz, distancia entrenudos, fotosintesis y potencial hidrico. Ello permitio identificar genotipos an-hisohidricos como 134 y 148, de genotipos isohidricos, como 10 y 93 en relacion al comportamiento de respuesta al estres. La determinacion de efectos tempranos de la sequia en desarrollo, sobrevivencia, y desempeno fisiologico, permitio diferenciar al genotipo 134 como el mas tolerante de los evaluados. La metodologia utilizada permitira seleccionar nuevos genotipos para uso potencial como portainjertos o injertos en zonas aridas y semiaridas, subrayando el rol fundamental de explorar la variabilidad genetica de vides y su uso como cultivo modelo

Evaluation of Morpho-Physiological Traits Adjustment of Prosopis tamarugo Under Long-Term Groundwater Depletion in the Hyper-Arid Atacama Desert

Water extraction from the underground aquifers of the Pampa del Tamarugal (Atacama Desert, Chile) reduced the growing area of Prosopis tamarugo, a strict phreatic species endemic to northern Chile. The objective of this work was to evaluate the effect of various architectural and morpho-physiological traits adjustment of P. tamarugo subjected to three groundwater depletion intervals (GWDr): <1 m (control), 1–4 m and 6–9 m. The traits were evaluated at three levels, plant [height, trunk cross-section area, leaf fraction (fGCC), and crown size], organ [length of internodes, leaf mass per unit area (LMA), leaflet mass and area], and tissue level [wood density (WD), leaf 13C, 18O isotope composition (δ), and intrinsic water use efficiency (iWUE)]. In addition, soil water content (VWC) to 1.3 m soil depth, pre-dawn and midday water potential difference (ΔΨ), and stomatal conductance (gs) were evaluated. At the deeper GWDr, P. tamarugo experienced significant growth restriction and reduced fGCC, the remaining canopy had a significantly higher LMA associated with smaller leaflets. No differences in internode length and WD were observed. Values for δ13C and δ18O indicated that as GWDr increased, iWUE increased as a result of partial stomata closure with no significant effect on net assimilation over time. The morpho-physiological changes experienced by P. tamarugo allowed it to acclimate and survive in a condition of groundwater depletion, keeping a functional but diminished canopy. These adjustments allowed maintenance of a relatively high gs; ΔΨ was not different among GWDrs despite smaller VWC at greater GWDr. Although current conservation initiatives of this species are promising, forest deterioration is expected continue as groundwater depth increases.