Xylem resistance to cavitation increases during summer in Pinus halepensis

Cavitation resistance has often been viewed as a relatively static trait, especially for stems of forest trees. Meanwhile, other hydraulic traits, such as turgor loss point (psi(tlp)) and xylem anatomy, change during the season. In this study, we hypothesized that cavitation resistance is also dynamic, changing in coordination with psi(tlp). We began with a comparison of optical vulnerability (OV), microcomputed tomography (mu CT) and cavitron methods. All three methods significantly differed in the slope of the curve,psi(12) and psi(88), but not in psi(50) (xylem pressures that cause 12%, 88%, 50% cavitation, respectively). Thus, we followed the seasonal dynamics (across 2 years) of psi(50) in Pinus halepensis under Mediterranean climate using the OV method. We found that psi(50) is a plastic trait with a reduction of approximately 1 MPa from the end of the wet season to the end of the dry season, in coordination with the dynamics of the midday xylem water potential (psi(midday)) and the psi(tlp). The observed plasticity enabled the trees to maintain a stable positive hydraulic safety margin and avoid cavitation during the long dry season. Seasonal plasticity is vital for understanding the actual risk of cavitation to plants and for modeling species' ability to tolerate harsh environments.

Automated summary

The study found that cavitation resistance is a dynamic trait that changes in coordination with turgor loss point. Comparisons of different methods showed differences in the results. Through a two-year observation in a Mediterranean climate, it was found that the cavitation pressure (psi(50)) of pine trees had plasticity, decreasing by approximately 1 MPa from the end of the wet season to the end of the dry season, in coordination with the dynamics of midday xylem water potential (psi(midday)) and turgor loss point (psi(tlp)). Seasonal plasticity is crucial for understanding the risk of cavitation and modeling species' ability to tolerate harsh environments.