Variation in Stomatal Characteristics of <i>Bursera simaruba</i> (L.) Sarg., a Dominant Tree Species of Tropical Hardwood Hammock Forest across a Habitat Gradient in the Florida Keys

Abstract

Tree species in coastal forests may exhibit specialization or plasticity in coping with drought through changes in their stomatal morphology or activity, allowing for a balance between gas exchange and water loss in a periodically stressful environment. To examine these responses, we sought to answer two primary research questions: a) how is variation in B. simaruba's stomatal traits partitioned across hierarchical levels, i.e., site, tree, and leaf; and b) is variation in stomatal traits an integrated response to physiological stress expressed across the habitat gradient of Florida Keys forests? At eight sites distributed throughout the Keys, five leaves were collected from three mature trees for stomatal analysis. Leaf carbon stable isotope ratio (δ 13 C) was determined to infer the changes in water use efficiency caused by physiological stress experienced by each tree. The results showed that substantial proportions of the total variance in three traits (stomatal density, stomatal size, and δ 13 C) were observed at all levels, suggesting that processes operating at each scale are important in determining trait values. A significant negative correlation between stomatal density and size across scales was observed. Path model analysis showed that environmental variables, distance to ground water and ground water salinity, affect leaf δ 13 C indirectly, via its effects on stomatal traits, not directly to leaf δ 13 C. Therefore, the combination of small and densely distributed stomata seems to represent a strategy that allows B. simaruba to conserve water under conditions of physiological drought induced by either higher ground water salinity or flooding stress at very low elevation.

Evidence for trait‐based community assembly patterns in hardwood hammock forests

“…The effect of salt stress is even more pronounced where water availability is limited such as in the Florida Keys forests (Ogurcak , Subedi et al. ). Therefore, the ability of trees to survive under salinity exposure, drought, and hurricanes clearly contributes to environmental filtering in the Florida Keys.…”

“…Trees are more susceptible to occasional salt water brought by storm, tide, and wave activities in coastal environments, and salt deposition in soil may occur in hurricane-prone areas such as the Florida Keys. The effect of salt stress is even more pronounced where water availability is limited such as in the Florida Keys forests (Ogurcak 2016, Subedi et al 2018. Therefore, the ability of trees to survive under salinity exposure, drought, and hurricanes clearly contributes to environmental filtering in the Florida Keys.…”

Coastal dry tropical forests in Florida and the Caribbean in peril: A review

“…In particular, the high energy reaching the coast during storms and hurricanes exposes coastal forests to damaging winds, and storm tides bring salt-water, sediments, and debris well inland. The impacts of stresses caused by salt spray or salt water flooding in coastal forests are similar to the ones faced by plants growing in dry environments (Subedi et al, 2018). Salt stress leads to cellular dehydration through xylem cavitation or through the toxicity imposed by salts on biochemical processes (Sternberg & Manganiello, 2014) which can limit vegetative growth (Fernandes et al, 2018) and alter biogeochemical cycles (Herbert et al, 2015;Hopfensperger et al, 2014).…”

“…Similarly, occasional airborne doses of salt spray brought by wind and wave activities in coastal environments, especially during storms and hurricanes, may cause physiological stress for CDTF plants (Subedi et al., 2018). During Hurricane Andrew, even forests in relatively low‐intensity wind fields at some distance from the eyewall experienced complete defoliation, allowing light to penetrate to a forest floor buried in dead vegetation (Armentano et al., 1995).…”

Adaptation strategies of leaf traits and leaf economic spectrum in urban garden plants

“…In the process of long evolution and adaptation to the environment, plants have formed a series of traits combinations which are the optimal to adapt the environment (Subedi et al 2016). LES provided a new theory and method for analyzing the adaptation mechanism of plants ).…”