Wed, Aug 17, 2022: 2:00 PM-2:15 PM
518B
Background/Question/MethodsPlant water potential is a key driver of water transport and carbon uptake, yet its response to environmental drivers remains poorly resolved. One limitation is the monthly to weekly temporal resolution of water potential necessitated by destructive sampling methods, which is generally insufficient to distinguish soil versus atmospheric moisture limitations. Furthermore, in water-limited ecosystems, vegetation responses can depend on past abiotic conditions at different strengths and temporal patterns. Here, we evaluated the effects of past environmental conditions on predawn water potential of Juniperus osteosperma. Seven mature trees were each instrumented with two automated stem psychrometers during the 2021 growing season in southeastern Utah. Using the stochastic antecedent model in a hierarchical Bayesian framework, we ask: 1) What is the relative sensitivity of predawn water potential (ΨPD) to atmospheric versus soil moisture? 2) On what timescales do the significant drivers operate? 3) What is the relative variability of environmental effects within versus among trees?
Results/ConclusionsAmong individual trees, ΨPD reached seasonal minima ranging between -3.7 and -8.5 MPa; distinct water potentials were also evident during routine instrument rotation among branches of the same tree. Therefore, we designed the hierarchical model to account for the nested effects of branches within trees and trees within population (R2 = 0.97). At the population level, shallow soil moisture (W10) positively correlated with ΨPD, while deep soil moisture (W50) primarily had a negative effect. Interestingly, maximum daily vapor pressure deficit (Dmax) was not significantly associated with ΨPD at the population or tree level, as individual branches exhibited a range of positive, negative, and neutral responses to Dmax. While both W10 and Dmax impacted ΨPD on relatively short time scales of 1-2 days prior, W50 from 5 weeks ago was also strongly influential. Low winter precipitation resulted in minimal recharge of deep soil in 2021, yet J. osteosperma were nevertheless sensitive to deep soil moisture. Overall, ΨPD responses to environmental drivers were non-stationary, as evidenced by highly variability within and among trees and dependence on antecedent conditions. We confirm previous research that J. osteosperma are physiologically responsive to summer precipitation and highly efficient at extracting transient shallow soil moisture.
Results/ConclusionsAmong individual trees, ΨPD reached seasonal minima ranging between -3.7 and -8.5 MPa; distinct water potentials were also evident during routine instrument rotation among branches of the same tree. Therefore, we designed the hierarchical model to account for the nested effects of branches within trees and trees within population (R2 = 0.97). At the population level, shallow soil moisture (W10) positively correlated with ΨPD, while deep soil moisture (W50) primarily had a negative effect. Interestingly, maximum daily vapor pressure deficit (Dmax) was not significantly associated with ΨPD at the population or tree level, as individual branches exhibited a range of positive, negative, and neutral responses to Dmax. While both W10 and Dmax impacted ΨPD on relatively short time scales of 1-2 days prior, W50 from 5 weeks ago was also strongly influential. Low winter precipitation resulted in minimal recharge of deep soil in 2021, yet J. osteosperma were nevertheless sensitive to deep soil moisture. Overall, ΨPD responses to environmental drivers were non-stationary, as evidenced by highly variability within and among trees and dependence on antecedent conditions. We confirm previous research that J. osteosperma are physiologically responsive to summer precipitation and highly efficient at extracting transient shallow soil moisture.