A comparative study on physiological responses to drought in walnut genotypes (RX1, Vlach, VX211) commercially available as rootstocks

Predicting Stomatal Closure and Turgor Loss in Woody Plants Using Predawn and Midday Water Potential

“…days versus weeks) can result in a more or less severe stress response for a given level of soil moisture. A slow drydown (weeks) would provide time for stress adaptions linked to plant anatomical changes, for example, root suberization to minimize water loss back to the soil and reductions in vessel diameters to secure long-distance transport capacity (Barrios-Masias et al, 2015;Knipfer et al , 2020. Here, we conducted a slow and fast drydown experiment for walnut trees to test if the WP curve (i) remains triphasic and (ii) predicts stomatal closure in both types of experiments.…”

“…earlier stomatal closure, because the time period for anatomical adaptations -which would aid to maintain plant performance for the imposed level of stress -was too short. Data by Knipfer et al (2020) show that walnut fine roots develop a multi-seriate endodermis in response to a slow drydown, and data by Meyer et al (2009) indicate that the development of a multiseriate exodermis in Iris germanica requires approximately days. However, and especially for the purpose of using the WP curve method to select for genotypes with improved drought resistance, future work is required to exactly determine the effect experimental time period, soil medium, irrigation frequency and pot characteristics on the shape of the WP curve (Turner, 2019).…”

“…This example demonstrates that our WP method can be used to categorize the sequence of physiological and anatomical events that occur under progressive drought stress into three distinct phases. Moreover, we propose that the WP curve method can assist in the determination of -thresholds that mark the breakdown of the soil-to-root hydraulic continuum (Rodrigues-Dominguez and Brodribb 2020; Carminati et al, 2020) and xylem hydraulic failure by embolism (Cuneo et al, 2016;Knipfer et al, 2019;), and facilitate the selection for woody perennial genotypes with improved drought-resistance (Knipfer et al, 2020).…”

“…days, no supplemental irrigation): The slow drydown experiment was performed on n=65 trees. Irrigation was adjusted based on estimates of bulk soil moisture (SM, = weight H2O / weight H2O-pot-capacity x 100%) as calculated from pot weights (for details see Knipfer et al, 2020). A subset of n=27 plants was located on mini-weighing lysimeters to continuously monitor pot weight and SM (see Supplemental Figure S6 for representative data of two individuals); to account for temporal effects, trees were either maintained well-watered or subjected to a drydown.…”

Tomato Rootstocks Mediate Plant-Water Relations and Leaf Nutrient Profiles of a Common Scion Under Suboptimal Soil Temperatures

“…Samples were kept at 4 • C until processed. Primary roots were free-hand sectioned at 1 and 3 cm from the root apex and staining was conducted according to Knipfer et al (2020) using Toluidine Blue-O (Acros Organics, NJ, United States). Images of cross sections were taken using a Leica DFC-295 digital camera for bright field images as well as with a LEICA thunder imager with a DAPI filter for fluorescence images (Leica, Hesse, Germany).…”