Picture (above): Sedona, US. Credit: Pixabay (Pexels).

The degree to which plants regulate the openness of their stomatal pores as soil water availability changes varies markedly. In plant hydraulics, this behaviour has been characterised using an isohydric (strong regulation) / anisohydric (weak regulation) concept.

Understanding how iso/anisohydricity changes over time in response to year‐to‐year variations in environmental dryness and how such responses vary across different regions remains poorly understood.

In this paper, the researchers investigated how dryness, represented by the aridity index, affects the inter-annual variability of ecosystem iso/anisohydricity at the regional scale, estimated using satellite microwave vegetation optical depth observations. This ecosystem‐level analysis was further complemented with published field observations of species‐level observations.

The researchers found different behaviours in the directionality and sensitivity of isohydricity (σ) with respect to the inter-annual variation of dryness in different ecosystems. These behaviours can largely be differentiated by the average dryness of the ecosystem itself. In mesic ecosystems –  a type of habitat with a moderate or well-balanced supply of moisture like a temperate forest – isohydricity decreases in drier years with a higher sensitivity to dryness. In xeric ecosystems – deserts or dry shrublands that include springs and experience occasional extreme rain events – isohydricity increases in drier years with a lower sensitivity to dryness. These results were supported by the species‐level synthesis.

Overall, the study provides new insights into how plants adjust their water use across years and will help advance our understanding of plant respond to drought at regional scales.

  • Paper: Wu, G., Guan, K., Li, Y., Novick, K.A., Feng, X., McDowell, N.G., Konings, A.G., Thompson, S.E., Kimball, J.S., De Kauwe, M.G., Ainsworth, E.A. and Jiang, C. (2020), Interannual variability of ecosystem iso/anisohydry is regulated by environmental dryness. New Phytologist, DOI:10.1111/nph.17040