Maximum Growth Potential and Periods of Resource Limitation in Apple Tree

Abstract

Knowledge of seasonal maximum potential growth rates are important for assessing periods of resource limitations in fruit tree species. In this study we assessed the periods of resource limitation for vegetative (current year stems, and woody biomass) and reproductive (fruit) organs of a major agricultural crop: the apple tree. This was done by comparing relative growth rates (RGRs) of individual organs in trees with reduced competition for resources to trees grown under standard field conditions. Special attention was dedicated to disentangling patterns and values of maximum potential growth for each organ type. The period of resource limitation for vegetative growth was much longer than in another fruit tree species (peach): from late May until harvest. Two periods of resource limitation were highlighted for fruit: from the beginning of the season until mid-June, and about 1 month prior to harvest. By investigating the variability in individual organs growth we identified substantial differences in RGRs among different shoot categories (proleptic and epicormic) and within each group of monitored organs. Qualitatively different and more accurate values of growth rates for vegetative organs, compared to the use of the simple compartmental means, were estimated. Detailed, source-sink based tree growth models, commonly in need of fine parameter tuning, are expected to benefit from the results produced by these analyses.

MuSCA: a multi-scale model to explore carbon allocation in plants

“…Growth at compartment level was in the range of field observations (Fig.4). Relative growth rates obtained at M scale (Table 3) were comprised between normal growth observed in the field and maximum potential growth data used for calibration of sink demands, but were closer to the latter (Reyes et al 2016) between 5.3*10 −3 and 3.1 *10 −2 mg/g for the old wood, between 0.4 and 1.2 mg/g for shoots and between 1.9 and 2.8 mg/g for fruits).…”

“…The three simulated trees represented tree structures in late June (day of the year = 182), namely after the end of shoot elongation. On them, initial individual fruit dry weight was set identical for all fruits and equal to 8 g (Reyes et al 2016).…”

“…In particular, volumes of internodes are first computed as truncated cones, summed up to provide the volume of individual shoots and stored at a “current year shoot” coarse scale. The length of current year shoots is then obtained by summing the lengths of their internodes, and used to estimate shoot biomass by means of a thermal-time dependent allometric relationship (Table 1) (Reyes et al 2016). Finally, the dry biomass of individual internodes is calculated as their individual volumetric fraction in the shoot to which they belong, multiplied by the shoot dry biomass.…”

“…Sink strength were estimated based on the analysis of maximum potential growth of the different organs of apple trees of the same cultivar (Table 2). Maximum potential growth curves were obtained by fitting thermal-time-dependent gompertz functions to organ-type-specific maximum dry weights (Grossman and DeJong 1995) of proleptic and epicormic shoots, and fruits of apple Fuji trees growing in conditions where competition for carbohydrates was minimized (Reyes et al 2016). Their normalized derivatives (Hunt 1982; Grossman and DeJong 1995) represents the seasonal patterns of organ type specific activities (or maximum potential relative growth rates).…”

“…Their normalized derivatives (Hunt 1982; Grossman and DeJong 1995) represents the seasonal patterns of organ type specific activities (or maximum potential relative growth rates). Regarding the old wood, the slope of a linear relationship fitted through the logarithm of the relative growth rate of the old wood biomass vs growing degree days (GDD) obtained by Reyes et al (2016) was used.…”