Drought causes widespread global impacts on ecological patterns and processes. Rainfall interception shelters (“rain-out shelters”) are frequently used to study the ecological consequences of drought. One commonly-used shelter design employs V-shaped clear plastic troughs spaced on a supporting frame to achieve a desired amount of rainfall interception. Shading by the frame, reflection from the plastic, and infrared radiation from the structure materials may alter the radiative environment under shelters in ways independent of their intended effect on soil moisture. Moreover, cost sometimes precludes use of inverted troughs as controls. We measured microclimate and several photosynthetic variables for fertigated potted plants under shelters and in unsheltered control plots. We tested whether shading, reflection, infrared, or other unintended effects of shelter infrastructure altered aboveground micrometeorology and photosynthesis. We quantified effects on photosynthesis in terms of traits associated with light harvesting by Photosystem II (PSII) and leaf-level gas exchange on control and shelter plots under ambient irradiation, as well as the quantum yield of PSII for darkened leaves, dark respiration, and nocturnal stomatal conductance. We compared five native Californian species that are commonly used in ecological restoration: Elymus glaucus, E. triticoides, Eriogonum latifolium, Mimulus aurantiacus, and Morella californica.
The rain shelter infrastructure briefly reduced PAR by as much as 70% at certain times of the day. Air temperature (Tair), leaf temperature, and leaf-to-air VPD were not different under shelters compared to controls during the day. Photosynthesis varied widely among species. There were no effects of shelters on net CO2 assimilation, stomatal conductance to water vapor (gs), internal leaf [CO2], the apparent quantum yield of PSII in light (ΦPSII), quenching coefficients (qN, qP), or electron transport during the daytime for any of the species. The one exception was that gs was higher under shelters for Morella during the day. At night Tair was 0.6°C higher under shelters, and leaf temperature, internal leaf [CO2], and dark adapted quantum yield (FV/FM) were higher under shelters for Eriogonum. There were no effects of shelters on dark respiration or nocturnal stomatal conductance for any of the species. Results suggest that despite some differences in micrometeorology under shelters compared to control plots, there are minimal unintended, non-drought effects of the shelters on photosynthesis for fertigated, potted plants of five California native plant species. Thus, rain-out shelters are robust for testing drought effects on plant and ecosystem productivity in this ecosystem.