# A low‐cost protocol for the optical method of vulnerability curves to calculate P 50

## TL;DR

This paper introduces a low-cost method to measure plant drought resistance using affordable tools and automation.

## Contribution

A cost-effective protocol for measuring P50 using USB microscopes and Python automation is developed.

## Key findings

- The low-cost protocol successfully quantified P50 in two plant species.
- The method is replicable and uses widely available materials.
- Intra- and interspecific variation in stem P50 was observed.

## Abstract

The quantification of plant drought resistance, particularly embolism formation, within and across species, is critical for ecosystem management and agriculture. We developed a cost‐effective protocol to measure the water potential at which 50% of hydraulic conductivity (P
50) is lost in stems, using affordable and accessible materials in comparison to the traditional optical method.

Our protocol uses inexpensive USB microscopes, which are secured along with the plants to a pegboard base to avoid movement. A Python program automatized the image acquisition. This method was applied to quantify P
50 in an exotic species (Nicotiana glauca) and native species (Rhus integrifolia) of the Mediterranean vegetation in Baja California, Mexico.

The intra‐ and interspecific patterns of variation in stem P
50 of N. glauca and R. integrifolia were obtained using the low‐cost optical method with widely available and affordable materials that can be easily replicated for other species.