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University Stem Initiative

Monitoring Air Bubbles in Plants

Plants that develop air bubbles in their hydraulic system don’t get enough water. Severe cases can lead to the death of roots, branches or the whole plant, explains Dr. Schenk, a plant biologist and CSUF faculty member since 2002.


Research in the Plants & H2O Lab at Cal State Fullerton, conducted at the Fullerton Arboretum

H. Jochen Schenk (Professor of Biological Science) & Susana Espino (Research Scientist).

Research in the Plants & H2O Lab addresses many aspects of the interactions between plants and water and ranges in scope from plant physiology to the role of plants in the global water cycle. The current focus is on plant hydraulics, the structure and function of plant hydraulic systems, and specifically on how plants deal with air bubbles (embolisms) that can form in their water-conducting systems during drought stress or frost. Our research explores basic physiological mechanisms of plant water transport and drought tolerance, as well as the implications for water conservation and irrigation needs of horticultural plants. Most of the research involves undergraduate and graduate students, and much of the research since the year 2006 has been conducted at the Fullerton Arboretum, mainly on plants in the desert collection, on chaparral hill, the subtropical woodland collection, and the cultivated orchard collection.

Alex (Gloria) Gallardo (biology undergraduate student; project from 2013-14).
Xylem sap proteins in Phymosia umbellata

Alex studied the plant Phymosia umbellata (Fa. Malvaceae), a large forest shrub native to Mexico grown in the arboretum’s subtropical woodlands collection. The goal of this project was to analyze the sap for proteins that may play a role as surfactants and coat bubbles that from in the plants’ hydraulic system under drought conditions.

Velia Villarreal (biology undergraduate student; project from 2012-14).
Ultrasonic emissions from drying woody plant stems.
Velia Villareal
Velia conducted research on ultrasonic acoustic emissions associated with bubble (embolism) formation in the shrub species Echium candicans (Fam. Boraginaceae) and Malosma laurina (Fam. Anacardiaceae). The cohesion-tension theory states that water within a plant moves under negative pressure (i.e., tension). As a plant is subjected to drought, tension increases, which can cause water to rapidly convert from the liquid into the gas phase, forming embolisms. This event, called cavitation, produces ultrasonic acoustic emissions. It is hypothesized that as a plant dries and loses hydraulic conductivity the amount of embolisms increases, and as a result more acoustic emissions are produced. Velia successfully tested this hypothesis for the two species she studied, including Malosma laurina on chaparral hill in the Fullerton Arboretum.

Miriam Morua (biology undergraduate student, 2012-13)
Effects of surface drip irrigation compared to sub surface irrigation on the yield of peppers

Conservation of irrigation water is a major concern for urban agriculture in semi-arid regions such as southern California. Miriam carried out a field experiment in the Fullerton Arboretum in 2013 in order to compare the efficiency of different drip irrigation systems for growing arbol and poblano peppers. The two systems that were compared were surface irrigation and subsurface irrigation. The highest productivity of peppers was seen for plants under subsurface irrigation and soil moisture contents for subsurface irrigation varied less over time than those for surface irrigation. This suggests that there was less evaporation and more water retention in the soil. Thus, it is concluded that (at about the same price) subsurface irrigation is a better system for conserving water and maintaining high pepper yields.

Donald D. Quick (biology Master’s student, 2012 to present).
Correcting temperature effects for stem-psychrometry on deeply-rooted plants.

Stem psychrometer measurements allow continuous measurements of plant water status and water stress by measuring sapwood water potentials. Stem psychrometer measurements of water potentials for plants in the field often vary strikingly from those made for the same plants using a pressure chamber, which is the standard method, but is destructive and labor-intensive. Psychrometers measure water potential as the relative humidity in a small, air-tight chamber attached to a section of exposed sapwood. Psychrometric measurements are highly temperature-dependent. Deeply-rooted plants, such as the chaparral shrubs Malosma laurina (Fam. Anacardiaceae). Heteromeles arbutifolia (Fam. Rosaceae), and the Mediterranean tree Quercus suber (Fam. Fagaceae), all on chaparral hill in the arboretum, tap cool water deep in the soil, which may create temperature gradients within the plant that can affect psychrometric readings. The goal of this research project is to correct pyschrometric measurements for temperature gradients in the wood, which would make it possible to use stem psychrometers on many more plants in the field.

Emily Wieber (biology undergraduate (2010-12), Master’s student(2012 to present)). Research
Drought tolerance and xylem vulnerability of citrus trees

Emily studied the drought tolerance of three citrus varieties in the cultivated orchard collection of the Fullerton Arboretum: Valencia orange, Star Ruby red grapefruit, and tangerine. To investigate physiological mechanism of drought tolerance, she measured the formation of xylem embolisms in stems, which are air bubbles that prevent water flow through vascular tissues. She also tested sap flow sensors on the Arboretum’s Valencia orange trees before installing them on Navel orange trees at UC Riverside’s Citrus Experiment Station for her Master’s thesis project.

Sarah Taylor-Laine (biology undergraduate (2011-12) and Master’s student (2011 to present)).
Hydraulic conductance and xylem osmoregulation in Laurel Sumac (Malosma laurina)

As an undergraduate, Sarah used Laurel Sumac to test a new method to measure the movement of water through plants in real-time. This method has advantages over previous methods because it can be used on living plants in the field, allowing quantification of plant physiological parameters in real-time and under natural conditions. As a graduate student, Sarah is studying how living cells embedded within the wood of plants are related to hydraulic functioning, especially under drought stress. Specifically, these cells are thought to use sugars to aid in the repair of air-filled xylem conduits. She is still working with her favorite plant, Laurel Sumac, on chaparral hill of the arboretum.

Miriam Morua (biology Master’s student, 2014-present)
Investigating continuous measures of water stress for avocado trees to guide irrigation decisions

California is currently suffering from persistent drought, which has spurred new interest in developing ways of irrigation that minimizes water use. One way to do this is to irrigate only when plants truly need additional water. Trees continuously adjust their own water balance, and measuring these physiological variables can be useful for irrigation scheduling of orchards. The purpose of this study is to investigate plant-based measures of water stress in avocado trees that can be continuously monitored to be used for irrigation decisions. The level of water stress in the trees will be determined directly using destructive measurements of leaf water potential. Other responses to water stress that will be continuously measured will include stem diameter variations, branch sap flow, trunk sap flow, trunk water potential, and wood water content. Leaf water potential, a direct, destructive water stress measure, will be compared to the continuous measurements to determine the best continuous plant-based measures for irrigation scheduling.

Read the CSUF article!


2014, Elizaveta Litvak, Neeta Bijoor, Diane Pataki, assessed the contribution of turfgrass and the role of tree shading in evapotranspiration of irrigated landscapes in the Los Angeles region. The Fullerton Arboretum managed lawn was one of the eight chosen lawns for this study. They used portable chamber measurements and empirical modelling to estimate irrigated turfgrass evapotraspiration and analyze its variability and environmental control. It was concluded that reductions in turgrass evapotranspiration caused by shading effects of open-grown trees were more important in influencing total landscape evapotranspiration than the addition of tree transpiration. This suggests that low-density planting of trees that partially shade irrigated urban lawns may be a water-saving measure in semi-arid irrigated environments.

Litvak E, Bijoor NS, Pataki DE. 2014. Adding trees to irrigated turfgrass lawns may be a water-saving measure in semi-arid environments. Ecohydrology, In press (DOI: 10.1002/eco.1458)

2012, Elizaveta Litvak, Heatehr McCarthy, Diane Pataki, studied stomatal responses to pressure deficit in irrigated trees in the urban landscape of Los Angeles, California. In 2008, sap flux data from the grove of irrigated coast redwood (Sequoia sempervirens) from the Fullerton Arboretum was collected and compared to seven other sites. The study confirms systematic differences in water relations in ring-versus diffuse-porous species, but these differences appear to be more strongly related to the relationship between stomatal sensitivity to pressure deficit and vulnerability to cavitation rather than to stomatal sensitivity per se.

Litvak E, McCarthy HR, Pataki DE. 2012. Transpiration from urban trees in a semi-arid climate is constrained by xylem vulnerability to cavitation. Tree Physiology 32: 373-388.

2011, Elizaveta Litvak, Heatehr McCarthy, Diane Pataki, investigated the water relations of coast redwood (Sequoia Sempervirens) planted in the urbanized semi-arid Los Angeles Basin, where it often experiences leaf chlorosis and senescence. Coast redwoods from the Fullerton Arboretum represented one of the three sites of the irrigated, urban trees that were used for this experiment. It was concluded that water stress was not a direct factor in causing leaf chlorosis and senescence as has been proposed. Instead, the relatively strong stomatal control that is adaptive in the native habitat of coast redwood may lead to carbon limitation and other stresses in semi-arid, irrigated habitats.

Litvak E, McCarthy HR, Pataki DE. 2011. Water relations of coast redwood planted in the semi-arid climate of Southern California. Plant, Cell and Environment, 34(8): 1384-1400.

Visit the Urban Ecology Research Lab

Road Disturbances in the Mojave Desert


In 2013, Miguel Macias, Darren Sandquist (CSUF), David Bedford, and David Miller (USGS), conducted an experiment to quantify road disturbances in the Mojave Desert. Sap-flow gauges were used on Creosote Bush (Larrea tridentate) to provide automated and efficient long-term measurements after simulating rain events at three sites on the foot of the Providence Mountains in the Mojave Desert. Miguel Macias is currently collecting stem samples from the Fullerton Arboretum to calibrate the sap-flow gauges and determine the accuracy of the home-made device.

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Research on Experiences in Nature

Research on the effects from nature finds that environments with more natural features (e.g., vegetation and plants) as compared to manmade characteristics (e.g., buildings and concrete) are associated with a range of positive influences, such as coping better with stress (Parsons, 1991) and greater positive affect (Berman et al., 2012). Matthew Ballew, a Doctoral Student in Applied Social Psychology at Claremont Graduate University, is currently studying the psychological effects of experiences in nature at the Fullerton Arboretum. He hopes to contribute to literature on the causal positive effects from nature and will communicate his findings upon completion of the study.


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Recent Research from the Fullerton Arboretum

Below is an article from the CSUF UEE

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The U-ACRE program at CSUF, in connection with Monkey Business Cafe, recognized in the Fullerton Observer.

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