Data from: Uniform regulation of stomatal closure across temperate tree species to sustain nocturnal turgor and growth

Dataset Description

This dataset accompanies the manuscript "Uniform regulation of stomatal closure across temperate tree species to sustain nocturnal turgor and growth." The study investigates stomatal control in mature trees and their response to water availability by integrating leaf water potential (Ψleaf), stomatal conductance (gₛ), sap flow, and growth measurements across multiple sites in Europe and Australia. The dataset consists of six separate sheets, each providing detailed measurements from different locations and methodologies.

1. SCCII-gs-LWP: Swiss Canopy Crane II site – Leaf water potential and stomatal conductance

Measurements were conducted at the Swiss Canopy Crane II (SCCII) site in Hӧlstein, Switzerland (47.439°N, 7.776°E, 500 m a.s.l.). The site is equipped with a 50-meter-tall canopy crane with a 62.5-meter jib, which allowed access to the crowns of over 95 mature trees from 9 common European species. Over 35 sampling dates between 2020 and 2022, we measured concurrent midday (12:00–14:00 CET) stomatal conductance (gₛ) and leaf water potential (Ψleaf) in 95 individual trees, as well as pre-dawn (04:00–06:00 CET) Ψleaf to establish tree hydration status. Stomatal conductance was measured using the program provided on the LI-6800 Portable Photosynthesis System (LI-COR Biosciences GmbH, Bad Homburg, Germany).

Variables:

• tree_id – Unique tree identifier.
• species_id – Species identifier (first letter: genus, second letter: species).
• date – Measurement date.
• lwp_MPa_pd – Pre-dawn leaf water potential (Ψleaf) in MPa.
• lwp_MPa_md – Midday leaf water potential (Ψleaf) in MPa.
• gsw_molm.2s.1_leaf – Stomatal conductance (gₛ) in mol m⁻² s⁻¹.
• VPDleaf_kPa_leaf – Vapor pressure deficit at the leaf surface in kPa.

2. SCCII-growth_LWP: Swiss Canopy Crane II site – Dendrometer growth and leaf water potential

At the SCCII site, band dendrometers (D1 tree girth band, Meter GmbH, München, Germany) were mounted at breast height (1.3 m above ground) on the stems of all target trees. To ensure that drought-induced stem shrinkage was not included in the growth analysis, we applied the zero-growth concept before calculating growth rates. For analysis, we only considered data from June, July, and August to exclude growth cessation due to winter dormancy of the cambium. Measurements of Ψleaf were performed using a Scholander-type pressure chamber (PMS Instrument Company, Albany, Oregon, USA).

Variables:

• tree – Unique tree identifier.
• species – Species identifier (first letter: genus, second letter: species).
• date – Measurement date.
• doy – Day of the year.
• pdlwp – Pre-dawn leaf water potential (Ψleaf) in MPa.
• gs – Stomatal conductance (gₛ) in mol m⁻² s⁻¹.
• growth_micron – Stem radius growth rate derived from band dendrometers in microns per day.
• rel_growth – Growth rate relative to the 99th percentile of tree growth (unitless).
• prob_growth – Probability of growth occurrence (0 = no growth, 1 = growth) based on the zero-growth concept.

3. SCCII-growth-raw: Swiss Canopy Crane II site – Raw dendrometer measurements and leaf water potentials

This sheet contains the raw band dendrometer data before applying the zero-growth concept, complementing the processed data in SCCII-growth_LWP.

Variables:

• date – Measurement date.
• species – Full Latin name of the species.
• species_id – Species identifier (first letter: genus, second letter: species).
• tree_nr – Unique tree number.
• tree_id – Unique tree identifier.
• dbh_cm – Diameter at breast height (1.3 meters above ground) in cm.
• radius_mm – Stem radius at breast height (1.3 meters above ground) in mm.
• interval_day – Number of days between measurements.
• gr_mu_d1 – Stem radius growth rate in microns per day.

4. Europe-sapflow-LWP_mean: Sap flow and leaf water potential dynamics (site-averaged, Europe)

We tested whether pre-dawn Ψleaf is a stronger constraint on whole-tree transpiration across multiple monitoring sites in Europe. Measurements were compiled from published sources, including the Swiss Lötschental valley, Hofstetten (Switzerland), and the Tillar valley within the Poblet Nature Reserve (Prades Mountains, northeast Spain). Sap flow data were collected using thermal dissipation sap flow sensors, including either SFS2-M sensors (UP GmbH, Ibbenbüren, Germany) or self-made sensors. Pre-dawn and midday Ψleaf were matched with sap flow measurements. Data in this sheet are averaged across species and sites.

Variables:

• Site – Unique site identifier.
• Species – Unique European species identifier (first two letters: genus, last two letters: species).
• Tree_id – Unique identifier for the tree when relevant.
• Date – Measurement date.
• pd_LWP – Pre-dawn leaf water potential (Ψleaf) in MPa.
• md_LWP – Midday leaf water potential (Ψleaf) in MPa.
• max_sfd – Maximum daily sap flux density in cm³ cm⁻² h⁻¹.
• sc_sfd – Measurement of max_sfd relative to the maximum max_sfd for the tree (unitless).

5. Europe-sapflow-LWP_trees: Sap flow and leaf water potential dynamics (raw tree-level data, Europe)

This dataset provides raw sap flow and Ψleaf values at the individual tree level across European sites. It contains similar variables as Europe-sapflow-LWP_mean, but with values recorded for each tree separately.

Variables:

• Same as Europe-sapflow-LWP_mean, but applied at the individual tree level.

6. Australia-gs-LWP: Leaf water potential and stomatal conductance (Australia)

In Australia, stomatal conductance (gₛ) measurements were conducted using the LI-COR 1600 Steady-State Porometer (LiCor Inc., Lincoln, Nebraska, USA). Pre-dawn and midday Ψleaf were measured using a Scholander-type pressure chamber. Data were collected along a North Australian climate gradient from Darwin to Alice Springs.

Variables:

• Observation – Unique observation identifier.
• Time.hr – Hour of measurement.
• Time.min – Minute of measurement.
• Time.decimal – Time of measurement in decimal format.
• sample.id – Unique sample identifier.
• time.of.day.block – Unique identifier for the sampling time block.
• replicate – Indicates repeated measurements.
• month – Month of measurement.
• site – Site name.
• id_location – Unique location identifier.
• Mean.annual.precipitation.mm – Mean annual precipitation at the site (mm).
• species – Full Latin name of the species.
• id_species – Unique species identifier.
• family – Plant family classification.
• species.code – Species code (first two letters: genus, last three letters: species).
• Elevation.m.a.s.l. – Elevation above sea level (m).
• id_tree – Unique tree identifier.
• pdlwp – Pre-dawn leaf water potential (Ψleaf) in MPa.
• mdlwp – Midday leaf water potential (Ψleaf) in MPa.
• Conductance.mol.m2.s1 – Stomatal conductance (gₛ) in mol m⁻² s⁻¹.
• leaf.temp – Leaf temperature (°C).
• RH – Relative humidity at the leaf surface (%).
• Atmospheric.pressure.kPa – Vapor pressure deficit at the leaf surface (kPa).