Water use and stomatal behavior of sweetgum (Liquidambar styraciflua L.) relative to reference evaporation in three contrasting regions

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ISHS Acta Horticulturae




International Society for Horticultural Science

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We investigated water use and a water needs index multiplier relative to reference evapotranspiration (ETo) for a sweetgum cultivar (Liquidambar styraciflua L. ‘Moraine’) in three different regions of the US: semi-arid (Logan, Utah), semi-humid (Lubbock, Texas), and humid (Orlando, Florida). Three individual field-grown trees, approximately 80 mm trunk diameter, were potted in to large containers with organic media at each location. Sweetgum water use (Tsw) was then measured over the season at each location with load cells connected to data-loggers, concurrent with measurement of ETo from adjacent weather stations. Dawn-to-dusk stomatal conductance (Gs) was measured several times during the season at all locations. Trees were watered daily, and in Utah were subjected to deficit irrigation where midday and morning conductance, as well as predawn water potential, were measured. At the end of the season total tree leaf area was collected and used to normalize volumetric water use data to depth units. Tsw was highest in Florida, up to 4 mm day-1, as was maximum daily Gs. Tsw only reached 2.5 mm day-1 in Texas and Utah due in part to stomatal sensitivity to high vapor pressure deficits that moderated transpiration. There was no relationship between Tsw and ETo at ETo levels above 4 mm day-1 in Texas and Utah, resulting in substantial scatter in the water needs index multiplier relative to ETo that centered on 0.3 in Texas and 0.4 in Utah. Tsw in Florida showed an upper boundary relationship with ETo, under which it varied considerably, with the water needs index multiplier centered on 0.6. During deficit irrigation in Utah, morning Gs was unaffected while afternoon Gs declined progressively under mild water stress, resulting multiplier values of 0.15-2. The study shows that regional climate affects tree water use differently than ETo, increasing the uncertainty estimating sweetgum water use as a fraction of ETo.