title: Effects of mistletoe removal on growth, N and C reserves, and carbon and oxygen isotope composition in Scots pine hosts.
abstract: Most mistletoes are xylem-tapping hemiparasites, which derive their resources from the host's xylem solution. Thus, they affect the host's water relations and resource balance. To understand the physiological mechanisms underlying the mistletoe-host relationship, we experimentally removed Viscum album ssp. austriacum (Wiesb.) Vollmann from adult Pinus sylvestris L. host trees growing in a Swiss dry valley. We analyzed the effects of mistletoe removal over time on host tree growth and on concentrations of nonstructural carbohydrates (NSC) and nitrogen (N) in needles, fine roots and sapwood. In addition, we assessed the δ(13)C and δ(18)O in host tree rings. After mistletoe removal, δ(13)C did not change in newly produced tree rings compared with tree rings in control trees (still infected with mistletoe), but δ(18)O values increased. This pattern might be interpreted as a decrease in assimilation (A) and stomatal conductance (gs), but in our study, it most likely points to an inadequacy of the dual isotope approach. Instead, we interpret the unchanged δ(13)C in tree rings upon mistletoe removal as a balanced increase in A and gs that resulted in a constant intrinsic water use efficiency (defined as A/gs). Needle area-based concentrations of N, soluble sugars and NSC, as well as needle length, single needle area, tree ring width and shoot growth, were significantly higher in trees from which mistletoe was removed than in control trees. This finding suggests that mistletoe removal results in increased N availability and carbon gain, which in turn leads to increased growth rates of the hosts. Hence, in areas where mistletoe is common and the population is large, mistletoe management (e.g., removal) may be needed to improve the host vigor, growth rate and productivity, especially for relatively small trees and crop trees in xeric growth conditions.
authors.affiliation: State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China Swiss Federal Research Institute WSL, Zuercherstrasse 111, CH-8903 Birmensdorf, Switzerland State Key Laboratory of Forest and Soil Ecology, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110164, China.
authors.forename: Cai-Feng
authors.initials: CF
authors.lastname: Yan
authors.affiliation: Swiss Federal Research Institute WSL, Zuercherstrasse 111, CH-8903 Birmensdorf, Switzerland Leibniz Centre for Agricultural Landscape Research ZALF, Eberswalderstr. 84, 15374 Müncheberg, Germany Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), 14195 Berlin, Germany.
authors.forename: Arthur
authors.initials: A
authors.lastname: Gessler
authors.affiliation: Swiss Federal Research Institute WSL, Zuercherstrasse 111, CH-8903 Birmensdorf, Switzerland.
authors.forename: Andreas
authors.initials: A
authors.lastname: Rigling
authors.affiliation: Swiss Federal Research Institute WSL, Zuercherstrasse 111, CH-8903 Birmensdorf, Switzerland.
authors.forename: Matthias
authors.initials: M
authors.lastname: Dobbertin
authors.affiliation: State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China State Key Laboratory of Forest and Soil Ecology, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110164, China.
authors.forename: Xing-Guo
authors.initials: XG
authors.lastname: Han
authors.affiliation: Swiss Federal Research Institute WSL, Zuercherstrasse 111, CH-8903 Birmensdorf, Switzerland State Key Laboratory of Forest and Soil Ecology, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110164, China maihe.li@wsl.ch.
authors.forename: Mai-He
authors.initials: MH
authors.lastname: Li
mesh_terms: D050260:Carbohydrate Metabolism; D002244:Carbon / Q000378:metabolism*; D002247:Carbon Isotopes / Q000032:analysis; D006790:Host-Parasite Interactions; D009584:Nitrogen / Q000378:metabolism*; D010103:Oxygen Isotopes / Q000032:analysis; D041605:Pinus sylvestris / Q000254:growth & development / Q000378:metabolism / Q000469:parasitology*; D054046:Plant Stomata / Q000378:metabolism; D013557:Switzerland; D028182:Viscum album / Q000502:physiology*
chemical_list: D002247:Carbon Isotopes; D010103:Oxygen Isotopes; D002244:Carbon; D009584:Nitrogen
keywords: mistletoes; nitrogen; nonstructural carbohydrates; soluble sugars; stable carbon isotope; stable oxygen isotope; starch