Impaired Water Relations in Carbon-Limited Ponderosa Pines: Implications for Belowground Interactions
Authors
Anna Sala1* (anna.sala@umontana.edu), Alex Goke1, Jacob Kleimann1, Jazmine Raymond1, Ella Keefer1, Ylva Lekberg1,2, Roger Koide3, Gerard Sapés4
Institutions
1University of Montana, Missoula, MT; 2MPH Ranch, Missoula, MT; 3Brigham Young University, Provo, UT; 4University of Florida, Gainesville, FL
Abstract
How drought kills trees is not fully understood. Drought reduces carbon (C) assimilation, but C demand for energy continues, and plants eventually use their stored nonstructural carbohydrate (NSC) reserves to meet demand. Whether depletion of stored NSC impairs turgor maintenance in the field is not known, but it is critical for models to predict vegetation responses to drought. Researchers tested whether depletion of stored NSC impairs water relations in ponderosa pine in the field, and whether common mycorrhizal networks (CMN) could mediate these effects on surviving trees when connected trees die and cease to supply C below ground.
In the summer of 2022, researchers subjected trees under ambient precipitation and experimental drought to either full sun or to 8 weeks of shade. The team measured NSC content in needles, pre-dawn needle water potential, osmotic potential, and turgor pressure prior to shading and at weekly intervals for 8 weeks. In the summer of 2023, researchers girdled trees under ambient precipitation and under drought, and tested whether connected neighbor trees became NSC depleted and the consequences on drought tolerance.
In 2022, shade depleted stored NSC in ambient trees but not under drought. NSC depletion impaired osmoregulation capacity in shaded trees but not in nonshaded trees, suggesting that negative effects of NSC depletion on drought tolerance occur only when trees are C limited. In 2023, girdling reduced C supply underground, and tentative results indicate that neighbor trees connected through CMN became NSC depleted, and their turgor maintenance was compromised. Researchers demonstrate that stored NSC depletion can impair water relations in ponderosa pine in the field, and tentatively suggest that when some trees die, CMN could mediate C limitation and impair drought tolerance in connected surviving neighbors.