Nighttime stomatal conductance differs with nutrient availability in two temperate floodplain tree species.

Area of Science:

• Plant physiology
• Forest ecology
• Environmental science

Background:

• Nighttime stomatal opening in plants is a debated phenomenon.
• Transpiration during the night may enhance nutrient uptake via mass flow of soil water.
• Plant species exhibit distinct responses to nutrient availability and water stress.

Purpose of the Study:

• To investigate the effects of nitrogen (N) and phosphorus (P) fertilization, and drought on daytime (gs) and nighttime (gn) stomatal conductance in Fraxinus excelsior and Ulmus laevis.
• To determine how these factors influence plant growth over an 18-week period.
• To understand species-specific strategies for nutrient and water uptake.

Main Methods:

• Controlled experiments with Fraxinus excelsior and Ulmus laevis.
• Application of varying levels of nitrogen and phosphorus fertilization.
• Simulated short-term drought conditions.
• Measurement of stomatal conductance (gs and gn) and pre-dawn leaf water potential (Ψpd).
• Assessment of plant growth and biomass allocation.

Main Results:

• Both F. excelsior and U. laevis exhibited nighttime stomatal opening (gn), with responses differing from daytime stomatal conductance (gs).
• N-deficiency increased gn in F. excelsior, particularly with sufficient P, indicating enhanced nighttime water uptake.
• U. laevis showed higher gn under high nutrient conditions (especially N) and adjusted its root:shoot ratio differently than F. excelsior.
• Drought reduced gn and Ψpd in F. excelsior but had minimal impact on U. laevis's growth parameters.
• Nutrient and water stress responses were species-specific and influenced by measurement timing.

Conclusions:

• Nighttime transpiration rates are significantly influenced by nutrient status and water availability, with species-specific variations.
• Eutrophication and predicted increases in drought frequency may alter plant-water dynamics in floodplain forests.
• These changes can have substantial ecosystem-level consequences, especially in forests dominated by F. excelsior and U. laevis.