Duration of growth is dependent on morphological events or changes in growth rate. It is the latter that is associated with phasic development. The most productive phase of plant growth is the linear or constant rate phase, primarily because it endures longer than the exponential phase. The purpose of our research was to objectively determine the true tree-height growth pattern, the linear and stationary phases of height growth, and to mathematically derive the maximum slope (maximum growth rate) of the growth curve, its location (inflection point), and the maximum slope of the logarithmic form (maximum relative growth rate) of the growth curve. The data were composed of 333 tree-height records covering 240 years from 200 beechwoods in the U.K. Height-age data were fitted using a splined function (S) and the Chapman-Richards function (CR). The growth curve and critical points on the curve were derived from the CR model. The linear phase began when trees were 9 and lasted 43 years. However, the stationary phase did not begin until age 162. Anecdotal evidence suggests that very little fruiting occurs before age 50. Based on derived critical points and anticipated source-sink dynamics, the reproductive stage should have taken place during the progressive “deceleration phase” when trees were between 31 (location of the maximum slope, also inflection point) and 162 (from quadratic root). The linear phase ended at 52 years, (coinciding with minimum acceleration) and may prove a more accurate estimate than 31. Maximum slope was 1.2 m per year occurring at age 31. Maximum slope of the log curve was 0.14 m·m–1 per year. The advantage of the CR function and the importance of the derived quantities and growth phases will be discussed.
F.D. Moore III, S.R. Nath, and Y-C Wang
K.G.V. Davidson, F.D. Moore III, E.E. Roos, S. Nath, and S. Sowa
Five seed-quality indices based on individual seed electrolyte leakage tests were evaluated. Zea mays L. seeds were soaked for 6 hours, and individual seed leachate conductivity values were obtained. A total of 100 cells were scanned, one seed per cell, at 5-minute intervals for the first 30 minutes, followed by 15-minute intervals for the remaining 330 minutes. Seeds were allowed to dry for 5 to 7 days at room temperature and then were tested for germinability at 25C for 7 days. Radicle lengths were measured after 72 hours. The Richards function was fitted to cumulative frequency distributions of μAmps to obtain internal slope (IS), mean μAmp, and median μAmp values for each scan. Initial leach rate (ILR) was estimated after fitting hyperbolic functions to μAmp vs. soak time data. Average leach rate (ALR) was also derived from fitting the Richards function to μAmp vs. soak time data. Linear regression of seed quality on IS, mean, and median μAmp values after 5 hours of imbibition yielded r2 values of 0.91, 0.81, and 0.86 for predicting viability and 0.56, 0.46, 0.52 for predicting radicle length. Thus, IS was the best seed quality predictor, followed closely by median and mean μAmp values. ILR and ALR were not correlated with seed quality.