Small understorey trees have greater capacity than canopy trees to adjust hydraulic traits following prolonged experimental drought in a tropical forest.

Future climate change predictions for tropical forests highlight increased frequency and intensity of extreme drought events. However, it remains unclear whether large and small trees have differential strategies to tolerate drought due to the different niches they occupy. The future of tropical forests is ultimately dependent on the capacity of small trees (<10 cm in diameter) to adjust their hydraulic system to tolerate drought. To address this question, we evaluated whether the drought tolerance of neotropical small trees can adjust to experimental water stress and was different from tall trees. We measured multiple drought resistance-related hydraulic traits across nine common neotropical genera at the world's longest-running tropical forest throughfall-exclusion experiment and compared their responses with surviving large canopy trees. Small understorey trees in both the control and the throughfall-exclusion treatment had lower minimum stomatal conductance and maximum hydraulic leaf-specific conductivity relative to large trees of the same genera, as well as a greater hydraulic safety margin (HSM), percentage loss of conductivity and embolism resistance, demonstrating that they occupy a distinct hydraulic niche. Surprisingly, in response to the drought treatment, small trees increased specific hydraulic conductivity by 56.3% and leaf:sapwood area ratio by 45.6%. The greater HSM of small understorey trees relative to large canopy trees likely enabled them to adjust other aspects of their hydraulic systems to increase hydraulic conductivity and take advantage of increases in light availability in the understorey resulting from the drought-induced mortality of canopy trees. Our results demonstrate that differences in hydraulic strategies between small understorey and large canopy trees drive hydraulic niche segregation. Small understorey trees can adjust their hydraulic systems in response to changes in water and light availability, indicating that natural regeneration of tropical forests following long-term drought may be possible.

A comparative study of onychomycosis and traumatic toenail onychodystrophy dermoscopic patterns.

BACKGROUND: Onychomycosis (OM) and traumatic onychodystrophy (OD) are common causes of toenail changes. A clinical diagnosis is often impossible without mycology. Dermoscopy is helpful in this setting but yet underexplored. Prospective comparative studies between OM and OD onychoscopic findings have not been previously performed. OBJECTIVES: We sought to determine distinguishing dermoscopic presentations of OM and traumatic OD. METHODS: We performed a prospective, observational study including patients presenting with ≥1 toenail onychodystrophy. All underwent onychoscopy, clinical and mycological examination. Based on these results, patients received a final diagnosis of OM or OD. Dermoscopic presentations of OM and OD patients were classified in patterns and compared. RESULTS: In all, 110 cases of OM and 82 of traumatic OD were compared. Statistical analyses revealed that the distal pulverized and the irregular spiked macular dermoscopic patterns were predictors of an OM diagnosis. The regular macular, the non-classifiable, the total and partial homogeneous background dermoscopic patterns correlated with traumatic OD diagnosis. CONCLUSIONS: We demonstrated that OM and traumatic OD have distinctive onychoscopic presentations. Dermoscopy may be an important ancillary tool to guide their differential.