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.

Responses of the structure and function of the understory plant communities to precipitation reduction across forest ecosystems in Germany

“…This is in agreement with previous observations in various understory species (Hommel et al 2014;Yan et al 2016). Moreover, Hommel et al (2014) also observed that drought could have stronger effects on assimilation rate than on stomatal conductance, thus potentially explaining the increase in Δ 13 C upon drought in grasses in late summer 2013 (Fig.…”

Evergreen Quercus aquifolioides remobilizes more soluble carbon components but less N and P from leaves to shoots than deciduous Betula ermanii at the end-season

“…Leaf carbon components decreased at the end of growing season in order to maximize resource allocation, i.e., during leaf senescence, recycling nutrients from assimilating leaves back to storage organs (Chapin et al 1990). Stored resources may support new leaf and shoot growth after dormancy (Yan et al 2016), as well as defense and reproduction (Chapin et al 1990). Many studies have shown that leaves play a major role in resources remobilization (Millard 1996, Eckstein et al 1998, Cherbuy et al 2001.…”

Mistletoe, friend and foe: synthesizing ecosystem implications of mistletoe infection

“…While mistletoe leaves are capable of photosynthesizing and producing basic sugars, they typically have lower photosynthesis rates than their hosts, and many mistletoe species acquire large amounts of heterotrophic carbon from the host phloem sap to allow expansion of the mistletoe leaf area ( This reduces carbon availability for the host tree, which leads to reduced growth rates and reductions in host leaf biomass (Meinzer et al 2004, Rigling et al 2010, Agne et al 2014, Raftoyannis et al 2015. Such degradations of the host canopy will further reduce carbon assimilation rates and deplete the non-structural carbohydrate reserves of the host tree (Rigling et al 2010, Yan et al 2016).…”