Dynamics of mangrove functional traits under osmotic and oxidative stresses

Abstract

Mangroves inhabit coastal areas, estuaries and river mouths experiencing extreme abiotic stress conditions, which severely impact their growth and survival. They are constantly exposed to abiotic stresses such as salinity, drought, temperature, UV radiations, flood, and heavy metal toxicity, biotic stresses such as herbivory, pest infestation, and pathogenic attack, and anthropogenic disturbances such as land clearing, pollution and aquaculture. Though mangroves are well recognized as potent halophytes and stress-tolerant species, they also get disturbed by very high salinities and other stress extremities. To combat osmotic and oxidative stresses, mangroves exhibit many remarkable functional modifications such as ultrafiltration, salt secretion, altered xylem, modified wood anatomy and crown displacement. By differentially regulating antioxidant enzymes, transcription factors, metabolic pathways, and accumulating osmolytes/soluble sugars, mangroves survive to some extent under highly stressful conditions. In this review, we analyzed the existing evidence on the effects of osmotic (salinity, salinity-induced drought and freezing) and oxidative (flood and flood-induced anoxia and hypoxia) stresses on mangrove functional traits and their habitat adaptations. As plant functional traits are the characteristic determinants of plant-environmental interactions, this review discusses the dynamics of mangrove functional traits at the whole plant, morpho-anatomical, physiological, biochemical, reproductive and phenological levels. The proposed perspectives could be beneficial for gaining in-depth understanding of the effects of stresses on mangrove functional traits that are important for the conservation and management of mangroves.