Spectral ecophysiology: hyperspectral pressure-volume curves to estimate leaf turgor loss.

Turgor loss point (TLP) is an important proxy for plant drought tolerance, species habitat suitability, and drought-induced plant mortality risk. Thus, TLP serves as a critical tool for evaluating climate change impacts on plants, making it imperative to develop high-throughput and in situ methods to measure TLP. We developed hyperspectral pressure-volume curves (PV curves) to estimate TLP using leaf spectral reflectance. We used partial least square regression models to estimate water potential (Ψ) and relative water content (RWC) for two species, Frangula caroliniana and Magnolia grandiflora. RWC and Ψ's model for each species had R2 ≥ 0.7 and %RMSE = 7-10. We constructed PV curves with model estimates and compared the accuracy of directly measured and spectra-predicted TLP. Our findings indicate that leaf spectral measurements are an alternative method for estimating TLP. F. caroliniana TLP's values were -1.62 ± 0.15 (means ± SD) and -1.62 ± 0.34 MPa for observed and reflectance predicted, respectively (P > 0.05), while M. grandiflora were -1.78 ± 0.34 and -1.66 ± 0.41 MPa (P > 0.05). The estimation of TLP through leaf reflectance-based PV curves opens a broad range of possibilities for future research aimed at understanding and monitoring plant water relations on a large scale with spectral ecophysiology.

Sap flow, xylem anatomy and photosynthetic variables of three Persea species in response to laurel wilt.

Laurel wilt, a lethal vascular wilt disease caused by the fungus Raffaelea lauricola, affects several tree species in the Lauraceae, including three Persea species. The susceptibility to laurel wilt of two forest tree species native to the southern USA, Persea borbonia and Persea palustris, [(Raf.) Sarg.] and avocado, Persea americana (Mill.) cv Waldin, was examined and related to tree physiology and xylem anatomy. Net CO2 assimilation (A), stomatal conductance (gs), leaf chlorophyll index (LCI), leaf chlorophyll fluorescence (Fv/Fm), xylem sap flow, theoretical stem hydraulic conductivity (Kh) and xylem vessel anatomy were assessed in trees of each species that were inoculated with R. lauricola and in control trees. Laurel wilt caused a reduction in A, gs, LCI, Fv/Fm and blockage of xylem vessels by tyloses formation that negatively impacted Kh and sap flow in all Persea species. However, disease susceptibility as indicated by canopy wilting and sapwood discoloration was less pronounced in P. americana cv Waldin than in the two forest species. Xylem vessel diameter was significantly smaller in P. borbonia and P. palustris than in P. americana cv Waldin. Differences in laurel wilt susceptibility among species appear to be influenced by physiological and anatomical tree responses.