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

Abstract

Question Is there evidence of a trade‐off between drought and shade tolerance in coastal desert shrubs? Location Arid scrubland, Atacama desert, north‐central Chile. Methods One‐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. Results We 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. Conclusions Overall, 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.

Growth and early seedling survival of four Atacama Desert shrub species under experimental light and water availability regimes

“…Finally, the positive effects of shade under dry conditions as well as with increased irrigation were even more evident when considering the trajectory of the survival curve with the Cox's proportional hazards model, which showed a positive effect in all four species. Our results are in agreement with those of other studies that show that a facilitative effect of shade under dry conditions is a key driver for seedling establishment not only in Mediterranean (Maestre et al 2003b, Sánchez-Gómez et al 2006) and desert ecosystems (Martínez-Tillería et al 2012) but also in a wet tropical environment (Holmgren et al 2012).…”

“…These results are consistent with other studies examining shrub seedling establishment in arid and semiarid ecosystems (Maestre et al 2003a;León et al 2011;Martínez-Tillería et al 2012). For example, León et al (2011) showed that seedling establishment in the Atacama Desert was possible only when rainfall levels were above 206 mm, which is similar to an El Niño event (Montecinos and Aceituno 2003).…”

“…Similar results were found by Martínez-Tillería et al (2012) for six Coastal Atacama Desert shrubs. These positive effects of intermediate shade on seedling survival suggest first that, compared with low shade, artificial shelters could promote stress amelioration of the environmental conditions by reducing PAR levels (83% reduction compared with low shade).…”

“…For example, León et al (2011) showed that seedling establishment in the Atacama Desert was possible only when rainfall levels were above 206 mm, which is similar to an El Niño event (Montecinos and Aceituno 2003). Similarly, Martínez-Tillería et al (2012) found that the addition of water enhanced seedling survival of native Atacama shrubs. In summary, because seedlings are very sensitive to dehydration (Evans and Etherington 1991), an additional water input can have a large impact on the regeneration dynamics of Atacama Desert shrubs, which corroborates the relevance of El Niño years for plant regeneration in this region.…”

“…One week before plants were transplanted to the field, we manually removed all weeds present in the experimental setting. Because experiments were initiated during the drought period, 1 day prior to transplanting, we applied 15 mm of water to emulate conditions that would typically follow emergence in these species (Pacheco 2000, Martínez-Tillería 2012. Moreover, 2 weeks after seedlings were transplanted, we applied 35 mm of irrigation to all plots to ensure seedling establishment prior to the start of the experimental treatments.…”