To develop reliable revegetation protocols for arid regions subject to fugitive dust, environmental conditions and the microenvironmental impacts of, and plant physiological responses to, site modification techniques were measured. Temperature, humidity, photosynthetically active radiation, and wind speed measured at two meters above ground level were typical for this location over the evaluation period. Rainfall was observed only between February and April. Clear skies led to high levels of incident radiation, but this was reduced by half in winter. The temperature regime was similar in summer and early fall, and in winter and early spring. Wind speeds were considerably greater in summer than in winter, but maximum wind gusts in the year 2000 were near 15 ms-1 in all months except May, 2000.
Effects on microenvironment were investigated for herbivory protection (with and without plastic shelters) and surface applied soil amendments (with and without a compost mulch). Within canopy temperatures, relative humidity, leaf surface wetness, and soil temperatures were all affected by growth within protection. Plants grown inside protective shelters had higher within canopy air and soil temperatures, particularly during the day and during the summer, with much smaller effects at night and during the cool season. Shelters similarly increased relative humidity and dew formation and persistence inside the shelters during active growth periods, ie. the winter, and both day and night. Compost mulch in a thin layer applied to the surface did little to alleviate soil heating during summer, bu resulted in warmer soil temperatures in cooler months, both day and night.
Plant physiological responses to modifications were assayed in these treatments and in two irrigation treatments (surface and deep pipe injection) and two windbreaks (with and without berms of soil). Modifications were compared using diagnostic gas exchange responses to intercellular carbon dioxide concentration, manipulated only during the measurements and not throughout te growth period. Photosynthetically active radiation, humidity and temperature were held constant during measurements. Photosynthetic rates were greater in May than in September, and overall in Atriplex canescens than in A. polycarpa. Significant treatment differences in maximal photosynthetic rate were observed in the Fall. No differences were observed in carboxylation efficiencies, CO2 compensation points, and stomatal limitations. Plants grown on open sites exhibited greater maximal photosynthesis than those grown with wind protecting soil berms. Similarly plants watered by surface irrigation surpassed those watered with deep pipe injection. This may have reflected different root placement, and the occurrence of rainfall prior to measurements. The transplanted shrubs at this site exhibited much greater photosynthetic rates than those previously established by direct seeding in the Emergency Watershed Protection program. This probably reflects irrigation and younger plant age, as well as residual soil nitrogen. Further physiological measurements are required to fully characterize the behavior of these species in revegation programs.
These physiological investigations suggest that A. canescens is the best species for revegetating abandoned and eroding lands in this environment.
For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753
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