The response of four ericaceous shrub species to multiple environmental resource variation

Natural environments are often limiting to plant growth in more than one resource due to the simultaneous fluctuations in resource supply and demand. The mechanisms a species uses to acclimate to simultaneous resource variation may not be uniform among species of the same growth form. Four evergreen ericaceous shrubs responded individualistically to fluctuations in light and water in an experimental garden study. Rhododendron maximum and Kalmia latifolia were able to acclimate photosynthetically to high and low irradiance under both high and low water availability. Rhododendron catawbiense and R. minus showed significantly higher acclimation to high light in high water treatments.

All four species were able to reduce their osmotic potential and water deficit at the turgor loss point seasonally, especially in low water treatments. Low soil water availability also reduced midday conductance and water potential in all four species. Rhododendron maximum and R. catawbiense were very conservative in their water use patterns. Rhododendron minus and K. latifolia exercised less stomatal control over water loss but did not appear to experience water stress under these treatment conditions. Rhododendron catawbiense was the most sensitive to low water availability and had the lowest turgor pressure of the four species.

Daily carbon dioxide assimilation was highest in high light, high water. treatments and lowest in low light, low water treatments for all four species. During the two years of this study, these species did not show any consistent pattern of increased growth in the high light, high water treatments where carbon dioxide assimilation was highest. Since these species are native to low resource habitats, their abilities to significantly increase growth during periods of high resource availability may be less than that of plants adapted to high resource availability.

The results of these experiments indicate that these four species of the same growth form respond differently to simultaneous fluctuations in light and water resources.