There are many studies examining species' responses to changes in average conditions but few studies examine species responses to extreme events (e.g. heatwaves). Extreme events typically are short events that challenge species beyond their ability to acclimate. In California the heatwave season is expected to increase by up to thirteen weeks, yet it remains unclear whether it will start earlier or end later. These two possibilities will have different effects on plants because sudden heat in the cool, wet spring should affect plants differently than extreme heat at the end of the dry summer, when plants have acclimated to high temperatures but soil water availability is low. Moreover, the responses of species may be different across their ranges because of climatic differences across California, where coastal sites are buffered from high temperatures and their annual climate is more stable than inland sites. If plants found in climatically stable sites are adapted to stable climates, they may be disproportionately harmed by increases in climatic extremes. We will determine if variation in response to heatwaves is greater within a population, between inland and coastal populations, or between distant populations. We will create artificial heatwaves and measure performance and stress in seedlings before and after these events and we will study the effect of naturally occurring heatwaves on adult plants.
Heatwaves pose a grave threat to biodiversity. To determine the magnitude of threats, and to provide a strong scientific basis for conservation and management strategies, we must forecast responses to climate change. The proposed research is some of the first to examine the influence of local genetic pools on responses to heatwaves. One proposed human adaptation to climate change is assisted migration. Our data will provide valuable insight into the consequences of moving native seed out of its home climate. This project will directly involve undergraduates from the diverse population at UC Berkeley and the scientific process from this project will be disseminated to the public through the Flat Stanley @ Cal Project which pairs a paper doll sent in by a student with a scientist who writes about the "adventure" online.
Project Outcomes Plant and animal species are already responding to climate change and in the next hundred years they will face rising temperatures, more heatwaves, and a longer heatwave season. Heatwaves are expected to increase dramatically in California in the future and pose a grave threat to biodiversity and to human welfare. The goal of this research was to determine (1) how plants respond to naturally occurring spring versus fall heatwaves (2) if the ability to tolerate heatwaves varied among different populations of a widespread California native plant. We measured adult plants of the California native shrub Heteromeles arbutifolia before, during and after a naturally occurring fall heatwave and compared the results to the same plants measured during a spring heatwave. During the spring heatwave, when water availability was high, plants kept pores in their leaves (i.e. stomata) open, which allowed water loss from the leaves. This resulted in lower leaf temperatures, similar to how humans sweat to cool off. This strategy was an effective way for the plants to deal with sudden high temperature days. However, this cooling effect was not present in the fall heatwave, when water was scarce due the long summer drought of California’s Mediterranean-type climate. During the fall heatwave plants shut down their activity during the high temperature days (i.e. closed their stomatal pores). To determine if the ability to tolerate heatwaves varied among different populations of Heteromeles arbutifolia we performed a greenhouse experiment where we exposed plants to artificial heatwaves. We compared plants grown from northern, southern, coastal, and inland populations. In California, coastal populations experience a much more mild climate than inland populations and northern populations experience cooler temperatures than southern populations. We predicted that the sudden temperature variation from a heatwave would be less detrimental in southern and inland populations because southern and inland populations experience more temperature variation on a seasonal basis. One measure of plant stress is respiration rate and we found in our greenhouse experiment that during the heatwave respiration rates were higher in northern populations but not in southern populations. We also found that photosynthetic rates were lower during the heatwave in the northern populations but not in the southern populations. Photosynthesis is the process plants use to gain food, so lower rates indicate the plants were less active. Both of these metrics suggest that the heatwave was more detrimental to the northern populations. Our research is some of the first to show that plants respond differently depending on the seasonality of the heatwave and some of the first to show that there is within species variation in response to heatwaves. Along with its success in advancing our understanding of how plants respond to heatwaves our project also advanced education, outreach, and training. During this project we worked with 15 undergraduate students, many of them from under-represented groups, first generation Americans, or the first in their family to go to college. These students assisted with field work and greenhouse studies. Two students received academic credit for their work and one student presented the results of her work at the 2012 Ecological Society of America Annual Meeting. Co-PI Shuldman was an active participant in Botanical Society of America's PlantingScience program. She mentored middle and high school students, from rural and urban areas across the country, performing plant based research. Student projects focused primarily on questions related to photosynthesis and seed germination. Co-PI Shuldman also participated in Community Resources for Science, which bring scientists into local middle school classrooms for hand-on science activities. In addition co-PI Shuldman was a committee chair for the UC Berkeley Expanding Your Horizons Conference. This conference brings local middle school girls to UC Berkeley for a day of hands on workshops in science, technology, engineering and math (STEM) fields led by female role models. The primary goal is to introduce young girls to a variety of career options in the STEM fields and encourage them to take full advantage of the math and science classes their high schools offer. All of these education, outreach, and training activities advanced discovery and understanding, broadened participation of under-represented groups, and broadened dissemination of scientific understanding.
