How are anatomical and hydraulic features of the mangroves Avicennia marina and Rhizophora mucronata influenced by siltation?

Key message This article provides significant data in the debate on whether siltation might have a negative impact on the hydraulic functioning of two widespread mangrove tree species Avicennia marina and Rhizophora mucronata . Abstract Elevated sediment addition, or siltation, within mangrove ecosystems is considered as being negative for trees and saplings, resulting in stress and higher mortality rates. However, little is known about how siltation influences the hydraulic functioning of mangrove trees. Comparing two mangrove tree species ( Avicennia marina Vierh. Forsk. and Rhizophora mucronata Lam.) from low and high-siltation plots led to the detection of anatomical and morphological differences and tendencies. Adaptations to high siltation were found to be either mutual among both species, e.g., significant smaller single leaf area ( p A.marina = 0.058, F 1.38 = 3.8; p R.mucronata = 0.005, F 1.38 = 8.7; n = 20 × 20) and a tendency towards smaller stomatal areas ( p A.marina = 0.131, F 1.8 = 2.8; p R.mucronata = 0.185, F 1.8 = 2.1, n = 5 × 60), or species-specific trends for A. marina , such as higher phloem band/growth layer ratios ( p = 0.101, F 1.8 = 3.4, n = 5 × 3) and stomatal density ( p = 0.052, F 1.8 = 5.2, n = 5 × 4). All adaptations seemingly contributed to a comparable hydraulic conductivity independent of the degree of siltation. These findings indicate that silted trees level off fluctuations in their hydraulic performance as a survival mechanism to cope with this less favourable environment. Most of the trees’ structural adaptations to cope with siltation are similar to known drought stress-imposed adaptations.