Does drought limit resprouter recruitment in Erica? A test using seeder and resprouter seedlings of Erica coccinea

Abstract

Context It has been proposed that the distribution of resprouter and seeder Erica in the Cape Floristic Region (CFR) of South Africa is determined by drought rather than by fire frequency. Seedlings of Erica seeders are predicted to withstand the mild droughts of the southwest CFR better than those of Erica resprouters, which would account for the abundance of seeders in this region. Aims This study aimed to test this hypothesis using Erica coccinea (L.), which contains both a resprouter and a seeder form. Methods One-year-old seedlings of both forms were subjected to a progressively severe 50-day drought in the greenhouse. Key results Contrary to expectations, seeder seedlings had 67% higher mortality than resprouters during the initial phase of drought (30% vs 18% after 32days). However, both forms were unable to survive as the drought progressed, resulting in 95% mortality by Day50. There were limited differences between the forms in gas exchange and water potential, and no difference in root:shoot ratios. However, resprouters had significantly higher soluble carbohydrates than did seeders, which may have aided in delaying mortality. Conclusions Our results showed no evidence of resprouter seedlings being more vulnerable to mild drought than seeders in E. coccinea. Implications Our findings challenge the hypothesis that the distribution of this species can be explained by the vulnerability of resprouter seedlings to mild drought.