# Hydraulic Traits Constrain Salinity-Dependent Niche Segregation in Mangroves

## TL;DR

This study shows how different mangrove species adapt to varying salinity levels through their hydraulic traits, influencing their distribution in intertidal zones.

## Contribution

The study reveals how hydraulic traits drive salinity-dependent niche segregation in mangroves, offering new insights into their salt adaptation strategies.

## Key findings

- A. marina and B. gymnorhiza showed the highest resistance to xylem embolism with the most negative P50 values.
- P50 and P88 values decreased with increasing salinity, reflecting a shift from isohydric to anisohydric water regulation strategies.
- B. gymnorhiza had a larger hydraulic safety margin and smaller SLA, suggesting better water retention and lower hydraulic failure risk.

## Abstract

To understand the mechanisms underlying species assemblage along salt gradients in intertidal zones, we measured the xylem hydraulic vulnerability curves (HVCs), leaf water potential (ψ), stomatal conductance (gs), specific leaf area (SLA), and wood density (WD) for six mangrove species of Avicennia marina, Bruguiera gymnorrhiza, Aegiceras corniculatum, Kandelia obovata, Sonneratia apetala, and Sonneratia caseolaris. We found the following: (1) A. marina and B. gymnorhiza had the most negative P50 (water potential at which 50% of hydraulic conductivity was lost), while S. caseolaris and S. apetala had the least negative P50, indicating different resistance to embolism in xylem; (2) P50 and P88 (water potential at which 88% of hydraulic conductivity was lost) declined with increasing salinity from the onshore to offshore species, as their water regulation strategy meanwhile transitioned from isohydry to anisohydry; (3) B. gymnorhiza had smaller SLA but larger hydraulic safety margin (HSM), implying potentially higher capacity of water retention in leaves and lower risk of hydraulic failure in xylem. These results suggest that hydraulic traits play an important role in shaping the salt-driven niche segregation of mangroves along intertidal zones. Our research contributes to a more comprehensive understanding of the hydraulic physiology of mangroves in salt adaption and may facilitate a general modeling framework for examining and predicting mangrove resilience to a changing climate.