Consistent spectral reflectance signatures of photosystem II thermal tolerance in contrasting foundation tree species

Photosystem II (PSII) is among the most thermally sensitive components of photosynthesis, and emerging evidence suggests that plants in diverse biomes face increasing risk of PSII damage under future climate change. However, uncertainties in the distribution and drivers of PSII thermal tolerance (Tcrit) limit our ability to predict thermal risk in plant communities across spatial scales. Here, we evaluate whether intraspecific variation in Tcrit corresponds to leaf reflectance spectra (400-2500nm) to identify mechanisms associated with Tcrit in field conditions and assess the potential of its remote estimation using remote sensing platforms. We measured Tcrit using temperature response curves of minimal fluorescence (Fo) along with corresponding leaf reflectance spectra in two foundation tree species: Populus fremontii (US Southwest) and Metrosideros polymorpha (Hawai‘i). P. fremontii was sampled under both moderate (<40ºC) and extreme (>45ºC) heat. Consistent spectral signatures ..., We used two established common gardens – one for P. fremontii near Yuma, Arizona (Cooper et al., 2018) and one for M. polymorpha near Volcano, Hawaii (Cordell et al., 1998) – to assess relationships between Tcrit and leaf reflectance (400-2500 nm). We sampled M. polymorpha in a single field campaign (February 2023), but sampled P. fremontii twice (May and August 2021) to compare spectral-Tcrit relationships in the same trees under moderate (<40ºC) and extreme (>45ºC) heat (Moran et al., 2023). For each dataset, we analyzed spectral trends and indices, compared how much variation in thermal tolerance each spectral region captured, and tested the ability of reflectance spectra to predict and classify Tcrit.
 Full methods can be found in the associated manuscript.
, # Consistent spectral reflectance signatures of photosystem II thermal tolerance in contrasting foundation tree species

Dataset DOI: [10.5061/dryad.h9w0vt4w3](10.5061/dryad.h9w0vt4w3)

## Description of the data and file structure

These data were collected to determine whether leaf thermal tolerance (Tcrit) can be detected with leaf reflectance spectra in two contrasting tree species, and if so, why. Numerous analyses were performed (see methods) to determine predictive accuracy of Tcrit using only leaf spectra as well as to determine the chemical, structural, and physiological basis for any relationship.

### Files and variables

#### File: Metrosideros_polymorpha_data.xlsx

**Description:** Combined leaf spectra and leaf thermal tolerance data from *Metrosideros polymorpha*, collected at a *M. polymorpha* common garden near Volcano, HI. Sheets include 'Spectra all scans' and 'Physiology data' 

##### Variables

* LeafID -- an ID that is specific to each leaf, in the format: Dx (Day ..., ,