Hydraulic conductance, resistance, and resilience: how leaves of a tropical epiphyte respond to drought

• Published in: American journal of botany Vol. 106; no. 7; pp. 943 - 957
• Main Authors: North, Gretchen B., Brinton, Erin K., Browne, Marvin G., Gillman, Madeline G., Roddy, Adam B., Kho, Tiffany L., Wang, Emily, Fung, Vitor A., Brodersen, Craig R.
• Format: Journal Article
• Language: English
• Published: United States Botanical Society of America, Inc 01-07-2019; Wiley Blackwell (John Wiley & Sons); John Wiley and Sons Inc
• Subjects: aerenchyma; aquaporins; Aquaporins - metabolism; Bromeliaceae; Bromeliaceae - anatomy & histology; Bromeliaceae - physiology; Conductance; cuticular conductance; Drought; Droughts; Drying; Embolism; Gene expression; Greenhouses; Guzmania monostachia; Hydraulics; intercellular air space; leaf anatomy; Leaves; Measurement methods; Modelling; Plant Leaves - anatomy & histology; Plant Leaves - physiology; Rainforests; Refilling; Resilience; Resistance; tank bromeliad; Tolerances; Water - physiology; Xylem; leaf anatomy; aquaporins; aerenchyma; Bromeliaceae; embolism; intercellular air space; tank bromeliad; cuticular conductance; Guzmania monostachia
• ISSN: 0002-9122; 1537-2197
• DOI: 10.1002/ajb2.1323

Premise
Because of its broad range in the neotropical rainforest and within tree canopies, the tank bromeliad Guzmania monostachia was investigated as a model of how varying leaf hydraulic conductance (Kleaf) could help plants resist and recover from episodic drought. The two pathways of Kleaf, inside and outside the xylem, were also examined to determine the sites and causes of major hydraulic resistances within the leaf.
Methods
We measured leaf hydraulic conductance for plants in the field and laboratory under wet, dry, and rewetted conditions and applied physiological, anatomical, and gene expression analysis with modeling to investigate changes in Kleaf.
Results
After 7 d with no rain in the field or 14 days with no water in the glasshouse, Kleaf decreased by 50% yet increased to hydrated values within 4 d of tank refilling. Staining to detect embolism combined with modeling indicated that changes outside the xylem were of greater importance to Kleaf than were changes inside the xylem and were associated with changes in intercellular air spaces (aerenchyma), aquaporin expression and inhibition, and cuticular conductance.
Conclusions
Low values for all conductances during drying, particularly in pathways outside the xylem, lead to hydraulic resilience for this species and may also contribute to its broad environmental tolerances.