Source: UNIV OF IDAHO submitted to
RESOLVING THE STRATEGIES FOR MAINTAINING TREE HYDRAULIC FUNCTION DURING DROUGHT
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
TERMINATED
Funding Source
MCINTIRE-STENNIS
Reporting Frequency
Annual
Accession No.
1004149
Grant No.
(N/A)
Project No.
IDAZ-MS-0106
Proposal No.
(N/A)
Multistate No.
(N/A)
Program Code
(N/A)
Project Start Date
Sep 15, 2014
Project End Date
Oct 31, 2017
Grant Year
(N/A)
Project Director
Johnson, DA, .
Recipient Organization
UNIV OF IDAHO
875 PERIMETER DRIVE
MOSCOW,ID 83844-9803
Performing Department
Forest, Rangeland, and Fire Sciences
Non Technical Summary
Drought has been implicated in the recent large-scale decline in temperate forests (Allen 2009), and global climate change is predicted to increase the intensity and frequency of drought in many regions (IPCC 2007, 2013). Some mechanisms that limit water stress in trees can also limit photosynthesis and growth. For example, closure of stomata to prevent water loss also prevents CO2 from entering the leaf for photosynthesis. Also, in species that leave their stomata open during periods of drought stress, the tension (negative pressure) in their vascular systems can get so great that their vascular systems become filled with air (called xylem embolism) and are thus nonfunctional. Either of these situations, hydraulic dysfunction or reduction of photosynthesis, can result in slower growth, reduced vigor and tree mortality. To accurately predict the capacity for forests to grow and survive under current and future climate regimes, the mechanistic relationships between drought, tree growth and avoidance of hydraulic dysfunction must be more fully understood. We currently have very little ability to predict the outcome of drought on forest growth and survival. This project will measure hydraulic vulnerability to embolism in roots, leaves, branches and trunks in 20 ecologically- and commercially-important western US tree species. Stomatal sensitivity to drought will also be measured as will trunk and branch water storage (capacitance) which can buffer water stress in the vascular system. Previous research suggests a continuum exists across woody species in the relative reliance on these mechanisms: 1) stomatal sensitivity, 2) vulnerability to embolism and 3) capacitance, to tolerate drought. Current models predicting forest growth and survival have no capacitance or stomatal sensitivity functions and only use branch vulnerability to embolism as a predictor of performance during drought. This project will result in a transformative understanding of tree drought tolerance and will provide modelers with physiological parameters needed to accurately predict growth and survival in US western forests under scenarios of climate change.
Animal Health Component
0%
Research Effort Categories
Basic
80%
Applied
20%
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
1020610102033%
2060610102033%
2030610102034%
Knowledge Area
102 - Soil, Plant, Water, Nutrient Relationships; 203 - Plant Biological Efficiency and Abiotic Stresses Affecting Plants; 206 - Basic Plant Biology;

Subject Of Investigation
0610 - Conifer forests of the North;

Field Of Science
1020 - Physiology;
Goals / Objectives
The major goals of this proposal are 1) to understand the components of dramatically contrasting strategies for the maintenance of tree hydraulic function during daily and seasonal cycles of water stress across woody species, 2) to link the strategies employed during normal daily cycles of water stress with the mechanisms of coping with severe drought stress, and 3) to characterize the trade-offs implied in reliance on different suites of traits that maintain hydraulic function. There is emerging evidence that the contrasting strategies for maintaining hydraulic function (repair versus avoidance of embolism) and the highly disparate patterns of hydraulic safety margins (wide versus narrow) observed across species are directly related, and that their resolution would represent a significant advancement in understanding how trees cope with the range of water stress from daily cycles to severe drought.The overarching hypothesis for this project is that across species, there is a continuum of strategies to maintain hydraulic function in leaves, stems and roots ranging from daily or seasonal cycles of hydraulic loss and recovery to complete avoidance of hydraulic failure during daily or seasonal cycles of water stress. Each of these strategies has associated trade-offs: current theories on embolism refilling suggest it requires metabolic energy, and embolism avoidance necessitates either stomatal closure (resulting in reduced carbon gain), structural features in the xylem that enable the tree or organ to prevent air-seeding of embolisms, or sufficient hydraulic capacitance (C) to prevent daily maximum xylem tension from exceeding the embolism threshold.
Project Methods
Twenty commercially- and ecologically-important western US tree species having a wide range of xylem parenchyma abundance and wood densities, and likely associated sapwood capacitance, will be selected for this study. We will also select several species that are known to lose and recover leaf and stem hydraulic function daily and several species that do not. In addition, we will select species known to occupy different positions on the iso- vs. anisohydry (i.e. stomatal sensitivity to drought) spectrum and we will characterize this behavior for species we select based on other criteria.For each species, hydraulic vulnerability curves will be determined on leaves (Sack et al. 2002; Scoffoni et al. 2012), branches, trunks and roots (Sperry and Saliendra 1994) from adult trees. Following determination of vulnerability curves, well-watered plants (saplings; there is good correspondence between hydraulic parameters of saplings and adult trees of the same species) will be monitored as described below to determine organ-specific hydraulic safety margins. Water will then be withheld from groups of plants until they reach at least three species-dependent levels of stem percent loss of hydraulic conductivity (PLC) without causing mortality (e.g. 25, 50, 88%). Root and leaf PLCs corresponding to each level of stem PLC will also be determined. Following these measurements, plants will be re-watered to field capacity and recovery of hydraulic capacity will be evaluated after 12, 24 and 48 h. Loss and recovery of hydraulic capacity will be assessed with both non-invasive and invasive techniques to detect potential excision-induced artifacts. For non-invasive monitoring, sap flow and stem water potential (psychrometers, Scholz et al. 2007) will be measured continuously along with periodic measurements of water potential of transpiring and covered, non-transpiring leaves. These concurrent measurements of water flux and water potential at key points along the hydraulic continuum will allow us to partition loss and recovery of hydraulic conductance between roots, stems and leaves. For invasive monitoring, native PLC will be determined in excised roots, stems and leaves of subsets of plants using established techniques. Stem and root parenchyma volume fractions and diurnal fluctuations in root and stem non-structural carbohydrate content (Woodruff and Meinzer 2011) will also be measured. To determine whether stomatal control regulates stem water potentials over a range that maximizes the use of C, we will measure sapwood moisture release curves (Meinzer et al. 2003) to determine sapwood C over a range of water potentials. We will also measure leaf and stem water potentials using pressure chambers and stem psychrometry, whole-tree transpiration using sap flow probes, and stomatal conductance using a porometer.

Progress 09/15/14 to 10/31/17

Outputs
Target Audience:This research has reached scientists through peer-reviewed publications and talks at national meetings. The results of the research have also been presented at meetings for industry professionals. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Training has been provided for two graduate students and two undergraduate students. All of the students have been trained in physiological methods and the two graduate students have presented their work at the 2017 Ecological Society of America meeting. How have the results been disseminated to communities of interest?The results have been disseminated through peer-review published papers and through talks at the Ecological Society of America meetings. They have also been dessimanted to land managers through a series of workshops held at the Pitkin Nursery at the University of Idaho. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? We have determined, as hypothesized, that there is a continuum of hydraulic strategies in Northwestern conifers for dealing with drought stress. Some species are more conservative with their water use (e.g., Ponderosa pine) while other are less conservative (western larch). We have now observevd this continuum in both young seedling (Miller et al. 2017 Am. J. Bot) and young adult (Baker et al. Tree Phys. in review) life stages. We have also measured hydraulic capacitance(measurements ending October 2017; data currently being analyzed) in these trees and will be analyzing capacitance data and hydraulic data to test for tradeoffs among these strategies.

Publications

  • Type: Journal Articles Status: Published Year Published: 2017 Citation: Sparks, A.M., Smith, A.M., Talhelm, A.F., Kolden, C.A., Yedinak, K.M. and Johnson, D.M., 2017. Impacts of fire radiative flux on mature Pinus ponderosa growth and vulnerability to secondary mortality agents. International Journal of Wildland Fire, 26(1), pp.95-106.
  • Type: Journal Articles Status: Under Review Year Published: 2018 Citation: Baker KV, Miller ML, and Johnson DM. 2018


Progress 10/01/15 to 09/30/16

Outputs
Target Audience:The target audience for this work includes plant and forest scientists, land managers and policy makers. The data produced by this work will also be used by vegetation modelers to assess impacts of climate cheange on western US forests. We have engaged the plant and forest science community through presentations at the 2016 Ecological Society of America Annual Meeting. We have also intreracted with plant physiology faculty, postdocs and graduate students through a related NSF-funded project that brought international researchers together to work on methods development for measuring tree water stress and drought tolerance. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?This project has provided training for 2 graduate students and 10 undergraduate students, to date.The PI (Johnson) has trained these students directly and the entire group has met every 1-2 weeks to discuss research. At these meetings we also discuss "academic life skills" such as writing and presenting, scientific ethics, and work/life balance. How have the results been disseminated to communities of interest?We have published one manuscript and are preparing another based on the 2015 UIEF field work. Data from this project were also presentedat the 2016Ecological Society of America Meeting in Ft. Lauderdale, FL. What do you plan to do during the next reporting period to accomplish the goals?We will measure sap flow (upper canopy, basal, tap root, lateral root) and hydraulic capacitance in the replicated thinning experiment mentioned above. By combining sap flow and capacitance we will have a much more holistic understanding of the water realtions of these tree species. We will also be able to determine hydraulic tipping points where a small change in plant water status will result in a dramatic loss of plant water transport capacity. Using sap flow on canopy, trunk and roots will also allow us to determine whether or not nighttime transpiration and hydraulic redistribution compete for water for recharging capacitance and if these competing water sinks vary with different stand densities.

Impacts
What was accomplished under these goals? In addition to what has been accomplished as detailed in 2015 Progress Report, we have 1) developed a sap flow system for installation in Pinus ponderosa trees and we have 2) conducted a replicated thinning experiemnt in the University of Idaho Experimental Forest. This will be the basis of our 2017 field season (see below).

Publications

  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Johnson DM, Wortemann R, McCulloh KA, Jordan-Meille L, Ward E, Warren J, Palmroth S, Domec J-C A test of the hydraulic vulnerability segmentation hypothesis in angiosperm and conifer tree species. Tree Physiology 36:983-993


Progress 10/01/14 to 09/30/15

Outputs
Target Audience:The target audience for this work includes plant and forest scientists, land managers and policy makers. The data produced by this work will also be used by vegetation modelers to assess impacts of climate cheange on western US forests. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?This work has funded 2 graduate students and 7 undergraduates. These students have also worked directly with an NSF-funded postdoctoral researcher.The PI (Johnson) has trained these students directly and the entire group has met every 1-2 weeks to discuss research. At the se meetings we also discuss "academic life skills" such as writing and presenting, scientific ethics, and work/life balance. How have the results been disseminated to communities of interest?We have submitted one manuscript and are preparing another based on the 2015 UIEF field work. Data from this project were also presented at an organized session on tree mortality and drought at the 2015 Ecological Society of America Meeting in Baltimore MD. What do you plan to do during the next reporting period to accomplish the goals?We plan to measure sap flow (upper canopy and basal) andhydraulic capacitance in the same conifer species that we studied in 2015. By combining hydraulic conductance and capacitance we will have a much more holistic understanding of the water realtions of these tree species. We will also be able to determine hydraulic tipping points where a small change in plant water status will result in a dramatic loss of plant water transport capacity. In the same 5 conifer spcies as were measured in 2015, we plan to measure the degree of aniso/isohydry for each species. This is a key parameter that can help us understand what would happen under future drought scenarios. Species that fall on the more anisohydric part of the spectrum are hypothesized to be more susceptable to drought-induced mortality or attack by pathogens. Finally we plan to use our additive resistance model framework to determine the contribtion of leaf and root hydraulic failure to overall whole tree water transport in these conifer species.

Impacts
What was accomplished under these goals? We have measured water stress,gas exchange and hydraulic parameters (conductivity and vulnerability to cavitation in roots and branches)for 5 conifer species (Pinus ponderosa, Pinus monticola, Thuja plicata, Abies grandis and Pseudotsuga menziesii) for the 2015 growing season (May - October) all co-ocurring in the Univeristy of Idaho Experimental Forest (UIEF). The 2015 growing season alsojust happened to be the most severe drought ever recorded in northern Idaho. We also monitored soil water potentials and volumetric water content concurrently with measures of plantwater stress and gas exchange. We have measured hydraulic parameters (conductivity and vulnerability to cavitation) on roots, trunks, branches and leaves in 4 angiosperm and 4 conifer species and found that brancheswere consistently the most resistant organ to hydraulic dysfunction across all of the species measured. This has widespread implications since branch hydraulic parameters have long been used as proxy for the entire tree, even in global vegetation models.Usingan additive resistance model in this same study, we found that whole-tree hydraulic dysfunctionoccurs at water tentsions well belowwhat would induce branch dysfunction. This decrease in whole-treewater trasport with increased dryness is primarily driven leaf and root hydraulic failure.

Publications

  • Type: Journal Articles Status: Under Review Year Published: 2016 Citation: Johnson DM, Wortemann R, McCulloh KA, Jordan-Meille L, Ward E, Warren J, Palmroth S, Domec J-C A test of the hydraulic vulnerability segmentation hypothesis in angiosperm and conifer tree species (in review)


Progress 09/15/14 to 09/30/14

Outputs
Target Audience: Nothing Reported Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? Nothing Reported How have the results been disseminated to communities of interest? Nothing Reported What do you plan to do during the next reporting period to accomplish the goals? We plan to begin physiological measurements on plants collected from our field sites and to begin performing experiemntal manipulations in the greenhouse studies.

Impacts
What was accomplished under these goals? We have begun planning for field season of 2015 and have been outfitting the lab with equipment needed to carry out this research. @ graduate students have been recruited to work on this research.

Publications