PEACH: A simulation model of reproductive and vegetative growth in peach trees

Abstract

The hypothesis that carbohydrate partitioning is driven by competition among individual plant organs, based on each organ's growth potential, was used to develop a simulation model of the carbon supply and demand for reproductive and vegetative growth in peach trees. In the model, photosynthetic carbon assimilation is simulated using daily minimum and maximum temperature and solar radiation as inputs. Carbohydrate is first partitioned to maintenance respiration, then to leaves, fruits, stems and branches, then to the trunk. Root activity is supported by residual carbohydrate after aboveground growth. Verification of the model was carried out with field data from trees that were thinned at different times. In general, the model predictions corresponded to field data for fruit and vegetative growth. The model predicted that resource availability limited fruit and stem growth during two periods of fruit growth, periods that had been identified in earlier experimental studies as resource-limited growth periods. The model also predicted that there were two periods of high carbohydrate availability for root activity. The fit between model predictions and field data supports the initial hypothesis that plants function as collections of semiautonomous, interacting organs that compete for resources based on their growth potentials.

Concepts of Modelling Carbon Allocation Among Plant Organs

“…In some models potential growth rates are used in combination with a priority sequence for (groups of) organs: First Eq. 2 is used to distribute dry matter among a group of organs, and only if supply exceeds demand of these organs (e.g., fruits, leaves and stems) assimilates are distributed to other organs (e.g., roots) (Wermelinger et al 1991;Grossman and DeJong 1994). These models, which are often used for trees, are also called hierarchical models (Lacointe 2000).…”

Integrating Photosynthesis, Respiration, Biomass Partitioning, and Plant Growth: Developing a Microsoft Excel®-based Simulation Model of Wisconsin Fast Plant (Brassica rapa, Brassicaceae) Growth with Undergraduate Students

“…In the laboratory portion of the course, groups of students conducted initial experiments to learn laboratory techniques and then completed the plant growth studies described in the next section. To learn about simulation modeling, the students engaged in activities that used two simulation modeling pro-grams, PEACH [14,15], and Environmental Decision Making (EDM; [30]), a model of the flow of energy and carbon in simulated pond, grassland, and forest ecosystems. After the end of the course, one student (AJS) who had not taken the plant ecophysiology course continued the modeling project during an eight-week summer research program and obtained the data used for the final version of the model.…”

“…Partitioning is the term applied to the set of processes that determine how much of the available dry matter each organ receives ( Figure 1). One partitioning hypothesis states that competition among organs determines the amount of dry matter that an organ receives, and that this competition is based upon each organ's "potential demand," the amount the organ is capable of growing on a given day [12,13,14,25,37]. For example, the maximum amount that the dry mass of a leaf can increase in one day is dictated by the number of cells present, the number added by cell division, and the maximum expansion rate for each cell [25].…”

“…Similarly, the amount of dry mass that a small, young pumpkin can incorporate on one day is much less than the amount that a nearly mature, large pumpkin can use. We may characterize the potential demand in terms using the potential relative growth rate (PotRGRX, g DM (g DM) −1 d −1 ), the maximum amount of dry mass that one gram of an organ can add in one day [12,13,14,24,25]. The potential RGR for each organ is analogous to its maximum possible interest rate.…”

“…We restricted the model to vegetative growth to keep the model simple. The Wisconsin Fast Plant Growth Model was developed as a highly simplified version of PEACH, a simulation model of the vegetative and reproductive growth of a peach (Prunus persica) tree [14,15]. We chose to implement the Wisconsin Fast Plant Growth Model in Microsoft Excel R (Microsoft Corporation, Redmond, Washington, USA) because this program is widely available and familiar to many students.…”