High Frequency Minirhizotron Observations Reveal Diel Patterns of Root Growth Under Water Stress.

Automated minirhizotron imaging in a temperate grassland showed root growth occurred day-round except for about one month in spring, when growth was only in daytime.

• Why it matters: Belowground growth dynamics are rarely measured long-term, limiting understanding of how root growth patterns track fluctuating carbon and water availability across seasonal and diel scales.
• What they did: Roots were imaged automatically twice a day for nine months, quantifying root length density (RLD) to assess diel and seasonal changes under varying rainfall and soil moisture.
• The result: From winter to autumn, net RLD decreased as net turnover became predominant later in the season, and the spring daytime-only growth coincided with a roughly one-month rainless period with rapid soil moisture depletion.