UNDERSTANDING STINKNET (ONCOSIPHON PILULIFER) RESPONSES TO DROUGHT IN POPULATIONS ACROSS THE SOUTHWEST USA

Abstract

Stinknet (Oncosiphon pilulifer) is a winter annual forb and an emerging invasive plant species in the American southwest. Over the past 50 years, populations have established in several counties of California and Arizona. Stinknet spreads rapidly, increasing the continuity of vegetation in arid landscapes, therefore increasing fire risk and emission of VOCs dangerous to human health. Despite its noxious weed status in multiple counties, little is known about the basic biology of stinknet. Here, we collected seeds from four populations of stinknet located in San Diego County, CA, Maricopa County, AZ and Pima County, AZ. We quantified germination rates under several conditions and examined the response of these four populations to experimental drought in a greenhouse experiment. Seeds from four populations of stinknet were exposed to three germination temperatures and two different burial treatments during germination trials. We found a significant difference in the time-to-event curves in the preliminary germination experiment (p=0.005) and recorded only a an average rate of 9.575% germination rate from both experiments The results of our germination experiment suggest that stinknet seeds have low germination rates across all populations, regardless of seed source location, and do not require cold stratification to germinate. The same four stinknet populations also underwent a six-week greenhouse-based experiment to understand drought tolerance and plant functional trait expression under a twice-a-week (full) water treatment and a control daily watering (even) treatment. Plants were grown under drought conditions, but received consistent or pulsed water. The results of the greenhouse experiment suggests that watering treatment, as well as the mean annual precipitation and mean annual temperature of the seed collection site, influence height and growth rate of greenhouse grown plants. However, mean annual precipitation and temperature are the only significant influences on mortality and root:shoot suggesting that some populations are more susceptible to drought conditions regardless of whether water is pulsed or consistent. Understanding how this species responds to various germination, drought, and precipitation conditions will help land managers understand which vegetation communities are at the greatest risk of invasion and how to control these populations based on certain external factors like precipitation amount and frequency.