No evidence of a trade‐off between drought and shade tolerance in seedlings of six coastal desert shrub species in north‐central Chile

Abstract

AbstractQuestionIs there evidence of a trade‐off between drought and shade tolerance in coastal desert shrubs?LocationArid scrubland, Atacama desert, north‐central Chile.MethodsOne‐week‐old seedlings of six coastal desert shrub species (Centaurea chilensis, Encelia canescens, Flourensia thurifera, Pleocarphus revolutus, Senna cumingii and Haplopappus parvifolius) were planted in the field under six treatment combinations: three light environments (low, intermediate and high radiation) and two water levels (natural rainfall (55.4 mm) and natural rainfall plus 100 mm irrigation). We quantified seedling survival for each species during 22 weeks, estimated relative growth rate, and examined how light and water affect whole‐plant responses, particularly specific leaf area, leaf mass ratio and root–shoot ratio.ResultsWe found species‐specific differences in the temporal pattern of mortality. Water and/or light levels affected seedling survival of all species, excluding C. chilensis. Relative growth rate (RGR) increased in low‐light conditions in C. chilensis and P. revolutus, but otherwise did not vary in response to differences in either light or water, independently or to their interaction. Across species, the effect of water on specific leaf area (SLA) was inconsistent, increasing both in drought conditions (C. chilensis) and in treatments with supplemental water (S. cumingii). Additionally, SLA tended to increase with decreasing light levels for most species (F. thurifera, H. parvifolius, C. chilensis). In our study, only F. thrurifera and C. chilensis showed changes in leaf mass ratio (LMR) and only with respect to light levels; specifically, LMR tended to increase with decreasing light level. Biomass allocation was independent of light and water for all species except F. thurifera, which showed an increase in root biomass in drought conditions.ConclusionsOverall, we did not find evidence to support a trade‐off between drought and shade tolerance during early plant establishment. Our results suggest that water is the most important resource that limits recruitment in the coastal desert. Therefore, increased aridity in this system is likely to severely hinder seedling recruitment of the native coastal desert shrubs.