Best Selling Books by Margaret Davidson

Much attention is devoted to understanding whole plant physiology and the architectural manipulation of fruit tree canopies to optimize yield, minimize excessive vegetative growth and to understand developmental responses to the environment. One method to visualize and understand plant physiological responses is to synthesize field data sets into mechanistically based computer simulation models. The L-PEACH model is a functional-structural interactive plant model that simulates 3D peach tree architecture, carbohydrate flow and dry matter distribution. The construction of a virtual tree is based on phytomers, repetitive subunits defined as node+leaf+axillary meristem+internodal segments. The time elapsing between the additions of phytomers can be represented by the appearance of leaves at every node known as the leaf appearance rate (LAR). The inverse of LAR is the phyllochron, the time or thermal time elapsing between the appearances of successive leaves along a stem. Plant genotype interactions with environment are responsible for the timing of the phyllochron. Temperature is thought to be most responsible for regulating the phyllochron. Therefore the first objective of this study was to observe the effects of temperature on the phyllochron and to determine the cardinal minimum, optimum and maximum values of a growing-degree-hour model for measuring the phyllochron of Prunus persica of proleptic shoots of field-grown trees. The cardinal temperatures were as follows: minimum (4°C), the optimal range (18-32°C) and the maximum temperature (40°C). Using the GDH or time scale, the phyllochron of proleptic shoots fluctuated and generally increased over the season. This slowing of the phyllochron over the season is likely due to an endogenous rank effect.Previous studies in peach reported shorter shoots under water deficit treatments. In annual crops, studies show that irrigation affects the phyllochron, but we were uncertain of how water deficit affects incremental growth (i.e., the phyllochron) in peach. For this reason, we observed the phyllochron for both proleptic and epicormic shoots in well-watered and water deficit treatments. The phyllochron of epicormic shoots in 2010 had significant differences between water treatments while phyllochrons for epicormic shoots in 2011 remained unaffected. Likewise the phyllochron for proleptic shoots also remained unaffected.The L-PEACH is a carbon balance model; therefore, we were interested in seeing how carbon availability affected the phyllochron. Carbohydrate availability for vegetative growth is influenced by crop load, as fruits compete as strong sinks for photosynthate. Crop load is known to have significant effects on shoot growth rates, but we did not know how it would affect the tree on a phytomer scale. To answer this question, 100% of the fruit were removed from trees in an un-cropped treatment, while other trees were left un-thinned. The phyllochron of epicormic and proleptic shoots was significantly greater on trees with heavy crop loads. These findings indicate that the phyllochron of field-grown peach trees is apparently sensitive to carbohydrate availability. This led us to our final hypothesis, that excess carbon availability would therefore decrease the phyllochron.To test this hypothesis, a 38-day growth chamber study was conducted to determine if elevated CO2 decreased the phyllochron. Young Prunus persica plants were grown in concentrations of either ambient (~400 ppmv) or elevated (~800 ppmv) CO2. Doubling ambient CO2 concentration had no effect on the phyllochron even though leaf CO2 assimilation rates, leaf starch and total non-structural carbohydrate concentrations were greater in trees grown in elevated CO2. Additionally there were no significant treatment differences in incremental shoot growth or number of lateral syleptic shoots.These studies allowed us to address the fundamental biological question of what regulates the phyllochron in a perennial fruit tree. The findings in the aforementioned studies will be incorporated into the L-PEACH model to allow for more accurate simulations and predictions of physiological growth in response to environmental and cultural factors.

Presents the piratical adventures of Pierre le Grand, Bartholemy Portuguez, Captain Flood, Red Legs Greaves, and Blackbeard.