Abstract
The coastal yucca species Hesperoyucca whipplei maintains specialized thickened contractile roots that function to pull the plant down further in the soil during periods of seasonal drought. Since H. whipplei is native to California and Baja California, it is important to understand how these specialized roots function during the high temperatures and limited precipitation associated with a seasonal drought. The first part of this research consisted of an eight-week quantitative measurement of root contraction both in normal and elevated temperatures. Six one-year-old H. whipplei plants and six H. whipplei seedlings were placed in a growth chamber maintaining a daytime temperature of 15?C and a nighttime temperature of 10?C. Another six one-year-old plants and seedlings were placed in a growth chamber where the temperature was 30?C during the day and 25?C at night. The second part of the research focused on transpiration and fluorescence measurements for 16 one-year-old H. whipplei , which were subjected to a one-week drought. Due to numerous problems with the growth chambers, the first experiment yielded no statistical difference between the H. whipplei grown in the hot growth chamber and those grown in the cold growth chamber. Preliminary data from the second part of the experiment revealed a highly significant decrease in transpiration during the drought period. The data collected from these experiments offers new insights into how increased temperatures associated with global warming may negatively impact even high temperature tolerant succulents.
