Effects of three global climate change factors on soil water and sap flow of Larrea tridentata in the Mojave Desert
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Authors
Holmes, Christopher D.
Issue Date
2009
Type
Thesis
Language
Keywords
Larrea tridentata , Mojave Desert , Sap Flow , Soilwater
Alternative Title
Abstract
Water availability is the primary control of plant productivity and composition in
arid plant communities. Effects of simulated global changes on soil water and sap flow of
L. tridentata in a natural Mojave Desert ecosystem were measured over five years and
two years respectively. Global change treatments were summer irrigations that imitated a
northward shift of summer monsoons associated with global warming, nitrogen additions
that imitated increased nitrogen deposition from anthropogenic sources, and biological
crust disturbance that imitated disturbance from increased land use. Averaged over all
data, irrigated plots had 40% and 24% more soil water than non-irrigated plots at 0.2 m
and 0.4 m depths, respectively. Soil water from irrigation treatments consistently reached
0.6 m depth but only persisted in irrigated plots until October or November and hence is
unlikely to benefit deeper rooted C3 vegetation that is active during late winter and
spring. At no time during the study did soil water infiltrate beyond the rooting zone,
suggesting that deep percolation of soil water is very rare for this ecosystem. A
significant year-long effect of intact biological soil crusts was not found. However within
2-4 days following summer irrigation, plots with intact biological soil crusts were wetter
than plots with disturbed biological soil crusts to 0.6 m depths. No consistent effects of
nitrogen deposition on soil water content were found.
Larrea tridentata is one of the most abundant and widespread perennial plants in
deserts of southwestern North America. Averaged over all treatments, L. tridentata
exposed to summer irrigation treatments have significantly greater sap flow than plants in
non-irrigated plots. This irrigation effect lasts approximately seven weeks after the last
irrigation when a transition is made and plants in non-irrigated plots begin to have
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significantly greater sap flow until the irrigations of the following year. Not only is L.
tridentata able to respond to an increase in soil water during the hot summer months, but
evidence is also presented that suggests L. tridentata has an additional physiological
response to the increase in soil water within a two week period. L. tridentata plants
exposed to the highest nitrogen addition consistently had the greatest rates of sap flow.
The effect of the biological soil crust treatment on sap flow of L. tridentata was variable
and dependant on interactions with the irrigation and nitrogen treatments. These results
demonstrate that predicted impacts of global changes have the potential to have important
effects on the Mojave Desert by affecting the primary production of L. tridentata and the
ecohydrology of the ecosystem.
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