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 arboretums 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 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 Masters 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), Masters student(2012 to present)).
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 Arboretums Valencia orange trees before
installing them on Navel orange trees at UC Riversides Citrus Experiment Station for her Masters thesis project.
Sarah Taylor-Laine (biology undergraduate (2011-12) and Masters 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 Masters 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!
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