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Tree-ring stable isotopes record the impact of a foliar fungal pathogen on CO2 assimilation and growth in Douglas-fir
Citation:
Saffell, B., F. Meinzer, S. Voelker, D. Shaw, J. Renee Brooks, B. Lachenbruch, AND J. McKay. Tree-ring stable isotopes record the impact of a foliar fungal pathogen on CO2 assimilation and growth in Douglas-fir. PLANT, CELL, AND ENVIRONMENT. Blackwell Publishing, Malden, MA, 37(7):1536-1547, (2014).
Impact/Purpose:
Climate change can have large impacts on the spread and severity of infectious diseases. Swiss needle cast (SNC) disease of Douglas-fir has important economical impacts on growth and productivity of this important commercial species, and has increased in severity over the past half century. Attempts to understand the potential influence of climate on the recent rise in disease severity have suggested that warm winter and spring temperatures and spring/summer leaf wetness may facilitate fungal growth and reproduction. The objectives of the present study were to determine: (1) whether analysis of tree-ring Δ13C and Δ18O can serve as a diagnostic tool for the detection of past SNC infection in Douglas-fir, and (2) which climate factors may modify the strength of the signal. Carbon stable isotope discrimination (∆13C) of treated Douglas-fir tree-rings was greater than that of untreated Douglas-fir tree-rings during the fungicide treatment period. Both annual growth and tree-ring ∆13C increased with treatment such that treated Douglas-fir had values similar to co-occurring western hemlock during the treatment period. Tree-ring ∆13C of diseased Douglas-fir was negatively correlated with relative humidity (RH) during the two previous summers, consistent with increased leaf colonization by SNC under high humidity conditions that leads to greater disease severity in following years. Differences in carbon stable isotope signatures of diseased Douglas-fir and a healthy reference species may eliminate noise contributed by other factors that affect needle retention and tree-ring width and provide another perspective of the relationship between climate and SNC disease severity.
Description:
Swiss needle cast (SNC) is a fungal disease of Douglas-fir (Pseudotsuga menziesii) that has recently become prevalent in coastal areas of the Pacific Northwest. We used growth measurements and stable isotopes of carbon and oxygen in tree-rings of Douglas-fir and a non-susceptible reference species (western hemlock, Tsuga heterophylla) to evaluate their use as proxies for variation in past SNC infection, particularly in relation to potential explanatory climate factors. We sampled trees from an Oregon site where a fungicide trial took place from 1996 to 2000, which enabled the comparison of stable isotope values between trees with and without disease. Carbon stable isotope discrimination (∆13C) of treated Douglas-fir tree-rings was greater than that of untreated Douglas-fir tree-rings during the fungicide treatment period. Both annual growth and tree-ring ∆13C increased with treatment such that treated Douglas-fir had values similar to co-occurring western hemlock during the treatment period. There was no difference in the tree-ring oxygen stable isotope ratio between treated and untreated Douglas-fir. Tree-ring ∆13C of diseased Douglas-fir was negatively correlated with relative humidity (RH) during the two previous summers, consistent with increased leaf colonization by SNC under high humidity conditions that leads to greater disease severity in following years.