Investigating the effects of planting density and tree size on yield through functional-structural modeling

Reducing planting distances is one of the strategies to increase yield in fruit orchards. The yield of an orchard increases with tree density, especially in the case of small tree canopies. However, orchard yield can decrease when trees planted at high densities have a large canopy size. In trees growing in optimal conditions, i.e., without water or nutrient stress, this yield reduction is likely to be the result of competition for light as well as an imbalance between vegetative and fruit growth. Separating these factors and their interactions in the field is not straightforward. Models of carbon acquisition and distribution between organs have been used to simulate and understand some factors affecting yield tree or within the tree. Modeling might help to understand better the effects of tree density and size on orchard yield. We employed a functional-structural tree model to simulate individual organ growth within the canopy as well as tree and orchard yield with different planting distances and tree size. This virtual plant combined sub-models of light interception, photosynthesis, potential relative growth rates of individual organs and inter-organ competition for carbon. Tree canopy architecture measured in the field was used to create several virtual orchard canopies with a range of tree sizes and planting distances. The model simulated growth and yield of individual trees and orchards during one growing season. Virtual experiments showed how different tree densities and sizes affected yield. It increased our understanding of and supported our hypotheses about the effects of planting distances and tree size on orchard yields, which can be useful for designing future field experiments and orchards

Leaf area to fruit weight ratios for maximising grape berry weight, sugar concentration and anthocyanin content during ripening

Vineyard management requires the maintenance of the leaf area per unit weight of fruit necessary for growing grapes without detrimental effects on fruit composition. Leaf removal and bunch thinning experiments have previously shown some effects on berry composition. Several berry compositional parameters (e.g. berry weight, sugar concentration and colour) increase with leaf area to fruit weight ratio until reaching an optimum or saturation point. Further increases in the ratio do not have any significant effect. However, optimum ratios from previous experiments have been determined only at harvest and they are highly variable. Irrigated Merlot grapevines were used to study the relationship between leaf area to fruit weight ratio and mean berry weight, sugar concentration and anthocyanin content during ripening. Four defoliation treatments were applied to individual girdled shoots at berry pea size stage. After veraison, leaf and fruit samples were collected weekly until berry maturity and leaf area, fruit weight per shoot, berry weight, sugar concentration and anthocyanins were measured. Berry weight, sugar concentration and anthocyanin content were correlated with leaf area to fruit weight ratio from veraison through to maturity. The fitted regressions allowed us to determine the ratios that maximised the measured compositional parameters. Leaf area per fruit weight necessary for maximum berry weight was more variable than that for sugar concentration and anthocyanin content. Greater leaf area to fruit weight was required for maximising anthocyanin content than that for sugar concentration. We defined optimum leaf area to fruit weight ratios within certain ranges for the ripening period in our vineyard

Using functional-structural modeling of carbon acquisition and utilization to understand fruit size distribution in tree canopies

Fruit size is an important parameter affecting both yield and quality. Fruit of multiple sizes can be found within a tree canopy and this has been correlated with factors involving carbon availability, e.g., crop load, light and temperature. However, the underlying mechanisms determining fruit size distribution seem complex and not easy to identify. It is very difficult to carry out multi-factor field experiments to increase our understanding in this area due to time, economic and technical constraints. Functional-structural models of carbon acquisition and utilization have been previously employed to simulate and understand the effects of date of thinning and irrigation regime on size of individual fruits and fruit size distribution in the tree canopy. These models used concepts of potential relative growth rates of individual organs and inter-organ competition for carbon. We built a functional-structural model of canopy growth at the individual organ scale, and used this model to simulate and study patterns of fruit size distribution in tree canopies with different training systems, crop loads, light and temperature regimes. The functional-structural tree model combines models of light interception, photosynthesis, potential relative growth rates of individual organs and inter-organ competition for carbon within each shoot. Canopy architectural data were employed to reconstruct and visualize our trees in the modeling platform. These virtual canopies were selected as inputs for simulating the growth of individual shoots and fruits in the canopy during one growing season. Our model showed that we can simulate multi-factor experiments, allowing us to increase our understanding and test concepts about the effects of carbon availability on fruit size distribution in trees growing in orchard systems

Daily photosynthetic radiation use efficiency for apple and pear leaves: seasonal changes and estimation of canopy net carbon exchange rate

The estimation of whole canopy carbon assimilation rate using the relationship between daily net CO assimilation rate (A) and daily incident photosynthetically active radiation (PAR) for individual leaves within the canopy has been considered an alternative to whole canopy gas exchange measurements. This relationship has been reported as being linear, but it has been explored only between the end of active shoot growth and harvest and in few species. Apple (Malus domestica) trees were used to study the seasonal changes in the relationship between daily A and incident PAR in individual leaves during the growing season of 2007 and this was done for pear (Pyrus communis) trees in 2008. Fifty leaves exposed to different light environments within the canopy of a given tree were selected. For each leaf seven times a day incident PAR and A was measured. Daily incident PAR and A was estimated by integrating instantaneous values. The relationship between daily A and daily incident PAR within the canopy had different patterns depending on the time of the season. It was always curvilinear early and late in the season, but tended to be more linear between the end of active shoot and harvest (mid-season). The initial slope and curvature of the relationship changed during the season and both were significantly related to daily PAR above the canopy. Whole canopy net carbon exchange rate was estimated considering canopy intercepted PAR and the relationship between daily A and incident PAR in individual leaves. The values were similar to those reported in the literature during mid-season. Estimated whole canopy net carbon exchange rate varied substantially after harvest, depending on whether a linear or curvilinear response of daily A to PAR for individual leaves within the canopy was considered. We showed that apple and pear whole canopy net carbon exchange rate can be estimated during mid-season, which is the most relevant phase for tree fruit production, using the following parameters: photosynthetic rate of well exposed leaves, daily pattern of incident photosynthetically active radiation (PAR), daily integral of PAR intercepted by the canopy and leaf area

Intercepted radiation by apple canopy can be used as a basis for irrigation scheduling

Improved approaches for irrigation scheduling require specific protocols for adaptation to different growing conditions. We assessed crop intercepted radiation as the main factor for decision on irrigation scheduling. Over two growing seasons (2007-2008), apple trees growing in a large weighing lysimeter were used to measure daily canopy transpiration (Td). Seasonal patterns of daily canopy intercepted photosynthetically active radiation (IPARd) and midday stem water potential were also measured. In 2007, irrigation was withheld in two different times to study Td responses to midday stem water potential. Before harvest, under full irrigation, Td increased linearly with IPARd (R2=0.81 in 2007 and 0.84 in 2008). With the two year data combined, R2 increased from 0.74 to 0.80 when VPD was considered as a second variable. When irrigation was withheld in 2007 the ratio between Td and IPARd, which is defined here as transpiratory radiation use efficiency (TRUE), decreased linearly (R2=0.49) as midday stem water potential decreased. Due to the highly significant effect of IPARd and VPD on Td, TRUE showed potential applications in estimating the amount of irrigation water

Intercepted radiation by apple canopy can be used as a basis for irrigation scheduling

Improved approaches for irrigation scheduling require specific protocols for adaptation to different growing conditions. We assessed crop intercepted radiation as the main factor for decision on irrigation scheduling. Over two growing seasons (2007-2008), apple trees growing in a large weighing lysimeter were used to measure daily canopy transpiration (Td). Seasonal patterns of daily canopy intercepted photosynthetically active radiation (IPARd) and midday stem water potential were also measured. In 2007, irrigation was withheld in two different times to study Td responses to midday stem water potential. Before harvest, under full irrigation, Td increased linearly with IPARd (R2 = 0.81 in 2007 and 0.84 in 2008). With the two year data combined, R2 increased from 0.74 to 0.80 when VPD was considered as a second variable. When irrigation was withheld in 2007 the ratio between Td and IPARd, which is defined here as transpiratory radiation use efficiency (TRUE), decreased linearly (R2 = 0.49) as midday stem water potential decreased. Due to the highly significant effect of IPARd and VPD on Td, TRUE showed potential applications in estimating the amount of irrigation water.Light interception Malus domestica Water status Weighing lysimeter

Can greater understanding of macadamia canopy architecture lay the foundation for orchard productivity improvements?

Macadamia canopies tend to grow large and complex due to vigorous recurrent flushes of vegetative growth. New shoot growth can occur at any time of the year from apical and axillary buds, elongating existing axes and forming new axis orders, respectively. The macadamia canopy is relatively unmodified and low yielding, thus yield efficiency and management practices would benefit from an increased understanding of canopy growth dynamics and architecture. Here we detail a range of investigations into the architectural development of macadamia over different scales, and methods for modifying architecture with a view to this information being incorporated into the design of improved orchard systems. For isolated shoots we have documented the elongation of internodes and the whole growth unit (GU), and their relationship to thermal time. We have also undertaken a detailed architectural study on two cultivars of young trees leading up to their first flowering, in an attempt to compare and understand patterns of early vegetative development. At the tree scale there were no differences in canopy volume or tree height between cultivars, however, detailed scales revealed differences in canopy components such as GU number, GU length and branching patterns. Shoot bending can modify vegetative architecture and reproductive development in temperate crops, although responses in subtropical crops could be more complicated. Bending first-order shoots in macadamia reduced apical growth and induced axillary release. When shoots are bent at the time of floral initiation raceme number was increased on the first-order shoot axis, possibly due to a coincidence between bending-induced axillary bud release and time-dependent floral signals. Observing interactions between components at different scales aids understanding of the mechanisms and relationships controlling the structure and function of the growing macadamia canopy, thus providing opportunities to modify macadamia growth for the benefit of production efficiency

Demonstrative simulations of L-PEACH: a computer-based model to understand how peach trees grow

L-PEACH is a computer-based model that simulates the distribution of light in the peach canopy as the tree grows and carbohydrate assimilation of each leaf. The model integrates important concepts to simulate water and carbon transport within the tree with real environmental input data collected from weather stations. Tree architecture is based on developmental principles governing tree growth and detailed measurements of shoots of peach trees. While running L-PEACH, realistic three-dimensional depictions of simulated growing trees can be displayed on the computer screen for visualization of tree architecture. The L-PEACH model has been widely reported in the literature along with quantitative data generated during simulations. However, demonstrative simulations were never disseminated to the scientific community and they are an essential component for understanding the model and demonstrating principles of tree growth. Along with the modeling work several movies with demonstrative simulations of L-PEACH have been made public in a scientific repository to complement existing references. Demonstrative simulations are related with overall tree growth and the movement of carbon within the tree, detailed growth of leaves and fruit and responses of tree growth to pruning intensity, drought and size-controlling rootstocks. In this work each demonstrative simulation will be accompanied by a physiological and/or horticultural description to demonstrate the value of L-PEACH to study, understand and teach how trees grow