title: Impacts of dwarf mistletoe on the physiology of host Tsuga heterophylla trees as recorded in tree-ring C and O stable isotopes.
abstract: Dwarf mistletoes, obligate, parasitic plants with diminutive aerial shoots, have long-term effects on host tree water relations, hydraulic architecture and photosynthetic gas exchange and can eventually induce tree death. To investigate the long-term (1886-2010) impacts of dwarf mistletoe on the growth and gas exchange characteristics of host western hemlock, we compared the diameter growth and tree-ring cellulose stable carbon (C) and oxygen (O) isotope ratios (δ(13)Ccell, δ(18)Ocell) of heavily infected and uninfected trees. The relative basal area growth of infected trees was significantly greater than that of uninfected trees in 1886-90, but declined more rapidly in infected than uninfected trees through time and became significantly lower in infected than uninfected trees in 2006-10. Infected trees had significantly lower δ(13)Ccell and δ(18)Ocell than uninfected trees. Differences in δ(18)Ocell between infected and uninfected trees were unexpected given that stomatal conductance and environmental variables that were expected to influence the δ(18)O values of leaf water were similar for both groups. However, estimates of mesophyll conductance (gm) were significantly lower and estimates of effective path length for water movement (L) were significantly higher in leaves of infected trees, consistent with their lower values of δ(18)Ocell. This study reconstructs the long-term physiological responses of western hemlock to dwarf mistletoe infection. The long-term diameter growth and δ(13)Ccell trajectories suggested that infected trees were growing faster than uninfected trees prior to becoming infected and subsequently declined in growth and leaf-level photosynthetic capacity compared with uninfected trees as the dwarf mistletoe infection became severe. This study further points to limitations of the dual-isotope approach for identifying sources of variation in δ(13)Ccell and indicates that changes in leaf internal properties such as gm and L that affect δ(18)Ocell must be considered.
authors: Forest Ecosystems and Society, Oregon State University, 321 Richardson Hall, Corvallis, OR 97331, USA danielle.marias@oregonstate.edu.
authors: Danielle E
authors: DE
authors: Marias
authors: Pacific Northwest Research Station, USDA Forest Service, Corvallis, OR 97331, USA.
authors: Frederick C
authors: FC
authors: Meinzer
authors: Pacific Northwest Research Station, USDA Forest Service, Corvallis, OR 97331, USA.
authors: David R
authors: DR
authors: Woodruff
authors: Forest Engineering, Resources and Management, Oregon State University, 280 Peavy Hall, Corvallis, OR 97331, USA.
authors: David C
authors: DC
authors: Shaw
authors: Biology Department, Southern Oregon University, 1250 Siskiyou Blvd, Ashland, OR 97520, USA.
authors: Steven L
authors: SL
authors: Voelker
authors: Western Ecology Division, US EPANHEERL, Corvallis, OR 97331, USA.
authors: J Renée
authors: JR
authors: Brooks
authors: Forest Ecosystems and Society, Oregon State University, 321 Richardson Hall, Corvallis, OR 97331, USA.
authors: Barbara
authors: B
authors: Lachenbruch
authors: Forest Engineering, Resources and Management, Oregon State University, 280 Peavy Hall, Corvallis, OR 97331, USA.
authors: Kristen
authors: K
authors: Falk
authors: College of Earth, Oceanic, and Atmospheric Sciences, Oregon State University, 104 CEOAS Administration Building, Corvallis, OR 97331, USA.
authors: Jennifer
authors: J
authors: McKay
mesh_terms: D002244:Carbon / Q000378:metabolism*; D002247:Carbon Isotopes / Q000032:analysis; D006790:Host-Parasite Interactions; D058503:Mesophyll Cells; D010100:Oxygen / Q000378:metabolism*; D010103:Oxygen Isotopes / Q000032:analysis; D010788:Photosynthesis / Q000502:physiology; D010935:Plant Diseases / Q000469:parasitology*; D018515:Plant Leaves / Q000254:growth & development / Q000469:parasitology / Q000502:physiology; D018547:Plant Stems / Q000254:growth & development / Q000469:parasitology / Q000502:physiology; D018526:Plant Transpiration / Q000502:physiology; D014197:Trees; D028225:Tsuga / Q000254:growth & development / Q000469:parasitology / Q000502:physiology*; D028163:Viscaceae / Q000502:physiology*; D014861:Washington; D014867:Water / Q000378:metabolism
chemical_list: D002247:Carbon Isotopes; D010103:Oxygen Isotopes; D014867:Water; D002244:Carbon; D010100:Oxygen
keywords: effective path length; mesophyll conductance