Our research centers around the physiology and ecology of trees and other woody species. We are particularly interested in water transport in plants, which is essential for plant survival. Plant water transport properties are directly related to plant distributions and plant carbon capture (and many other things). Research Leaf Hydraulics Research We are interested in the pathway of water movement inside leaves. The bottlenecks for water flow through leaves has only recently been explored and there is a lot left to figure out! Since the leaf is the organ that is primarily responsible for controlling the water balance of the plant, this is a critical area of research. Check back soon for some very cool images..... Ponderosa pine needles. Upper left, cryoSEM of fully hydrated needle. Upper right, fluorescence image of vascular bundle of fully hydrated needle. Lower left, cryoSEM of vascular bundle of mildly dehydrated needle (-1.4 MPa) and lower right cryoSEM of vascular bundle of severely dehydrated needle (-3.2 MPa), from Johnson et al. 2009. Whole Plant Hydraulics We are interested in the water transport properties of entire plants - leaves, branches, roots, trunks. Sometimes this means sampling destructively, but hey, it's for science. The vast majority of our understanding of plant hydraulics is based on studies of terminal branches. This offers us a very limited understanding of how water moves through whole plants and how drought might affect whole plants. The above image shows one way of measuring embolism (air bubble formation) in leaf xylem - this method is acoustic emission (super-sensitive microphones). Below is a set of tropical liana stems being prepared for hydraulic measurements. Seedlings In nature, most newly-germinated seedlings die. Mortality in young seedlings is typically >99%! In order for species to migrate with climate change, seedlings have to establish beyond the current species boundary. Yet, the newly germinated seedling stage is the life stage of trees that we know least about. We are currently studying the physiology and anatomy of newly-germinated seedlings as they develop during their first year of life. Drought Severe droughts are predicted to become more frequent with climate change. Northern Idaho experienced its worst drought on record in 2015 (record keeping began in 1895) and central TX experienced its worst drought in over 1200 years in 2011-2015. We are trying to understand what this might mean for different tree species in different habitats. Above is an image showing the impact of the 2011-2015 Texas drought. This picture was taken in July of 2013 - everything in grey is dead. We are also working on what happens after drought when precipitation returns. For example, is there a physiological legacy of drought or do plants just go back to business as usual? We are using field- and greenhouse-based studies, along with process-based models, to try to understand the mechanisms of drought induced mortality and plant responses to drought alleviation. Select Publications Visit my Google Scholar page 2022 Johnson DM, Katul G, Domec JC. 2022. Catastrophic hydraulic failure and tipping points in plants. Plant, Cell and Environment (accepted, in press) Benson MC, Miniat CF, Oishi AC, Denham SO, Domec JC, Johnson DM, Missik JE, Phillips RP, Wood JD, Novick KA. 2022. The xylem of anisohydric Quercus alba L. is more vulnerable to embolism than isohydric co-dominants . Plant, Cell and Environment (accepted, in press) Trueba S, Theroux-Rancourt G, Earles JM, Buckley TN, Love DM, Johnson DM, Brodersen C. 2022.The 3d construction of leaves is coordinated with water use efficiency in conifers. New Phytologist 233:851-861. 2021 Mrad A, Johnson DM, Love DM, Domec JC. 2021. The roles of conduit redundancy and connectivity in xylem hydraulic functions. New Phytologist 231:996-1007. Domec JC, King JS, Carmichael MJ, Overby AT, Wortemann R, Smith WK, Maio G, Noormets A, Johnson DM. 2021. Root water gates and not changes in root structure provide new insights into plant physiological responses to drought, flooding and salinity. Journal of Experimental Botany 72:4489-4501. Sonawane BV, Koteyeva N, Johnson DM, Cousins A. 2021. Differences in leaf anatomy determines temperature response of leaf hydraulic and mesophyll CO2 conductance in phylogenetically related C4 and C3 grass species. New Phytologist 230:1802-1814. Hammond WM, Johnson DM, Meinzer FC. 2021. A thin line between life and death: radial sap flux failure signals trajectory to tree mortality. Plant, Cell and Environment 44:1311-1314. Feltrin RP, Smith AMS, Adams HD, Kolden CA, Johnson DM. 2021. Short- and long-term effects of fire on stem hydraulics in Pinus ponderosa saplings. Plant, Cell and Environment 44:696-705. 2020 Feltrin RP, Johnson DM, Sparks AM, Adams HD, Kolden CA, Nelson AS, Smith AMS. 2020. Drought increases vulnerability of Pinus ponderosa saplings to fire-induced mortality. Fire 3:56. Miller ML, Roddy AB, Brodersen CR, McElrone AJ, Johnson DM. 2020. Anatomical and hydraulic responses to desiccation in emergent conifer seedlings. American Journal of Botany 107:1177-1188. Halbritter AH, De Boeck HJ, plus 113 co-authors (including DMJ). 2019. The handbook for standardized field and laboratory measurements in terrestrial climate-change experiments and observational studies (ClimEx). Methods in Ecology and Evolution 11:22-37. Research Areas: Forestry Forest Biology
