A semi-automated method for measuring xylem vessel length distribution

Knowledge about the length of xylem vessels is essential to understand water transport in plants because these multicellular units show a 100-fold variation, from less than a centimeter to many meters. However, the available methods to estimate vessel length (VL) distribution are excessively time consuming and do not allow large and in-depth surveys. Here, we describe a semi-automated method to measure hydraulically-weighted VL (VLH) using an automated Pneumatron device. Gas conductivity of a xylem tissue with a certain length is estimated with the Pneumatron in a straightforward and precise way, theoretically similar to the air-injection method. Besides giving results similar to the silicone-injection method, the pneumatic-based method enables faster and easier measurements of more than 50 samples per day, which is a significant advantage. Herein, a detailed description of the methodology is presented as well as the software and an R-script for data analysis. The method described represents an important contribution to studies on plant hydraulic architecture and can improve our understanding about the role of VL(H)in plant performance under varying water availability.