Call Anson C, St Clair Samuel B
Department of Plant and Wildlife Sciences, Brigham Young University, Provo, UT 84602, USA.
Tree Physiol. 2017 Sep 1;37(9):1198-1207. doi: 10.1093/treephys/tpx088.
In the spring of 2015, a severe outbreak of the necrotrophic pathogen Drepanopeziza (also known as Marssonina) spread across large portions of aspen (Populus tremuloides Michx.) forests in the western United States. Among adjacent stands, some were diseased and others were not. Drepanopeziza infection in diseased aspen stands stimulated compensatory growth of second-flush leaves at the top of the canopy. These patterns of infection provided an opportunity to characterize associations of pathogen infection and leaf functional traits. Eight pairs of adjacent healthy and diseased aspen stands were identified across a forest landscape in northern Utah. Average leaf surface area, specific leaf area (SLA), photosynthesis, starch concentration and defense chemistry expression (phenolic glycosides and condensed tannins) were measured on original, first-flush leaves in the lower portion of the tree canopy of healthy and diseased stands and compensatory, second-flush leaves produced in the canopy top of diseased stands. Only first-flush leaves of diseased stands showed high levels of Drepanopeziza infection. Leaf area of second-flush leaves of diseased stands was threefold larger than all other leaf types in healthy or diseased stands. Lower canopy leaves of healthy stands had the highest SLA. Photosynthesis was lowest in infected first-flush leaves, highest in second-flush leaves of diseased stands and intermediate in leaves of healthy stands. Foliar starch concentrations were lower in leaves of diseased stands than leaves from healthy stands. Condensed tannins were greater in second-flush leaves than first-flush leaves in both healthy and diseased stands. Phenolic glycoside concentrations were lowest in infected leaves of diseased stands. Diseased stands leafed out a week earlier in the spring than healthy stands, which may have exposed their emerging leaves to rainy conditions that promote Drepanopeziza infection. Compensatory leaf regrowth of diseased stands appears to offset some of the functional loss (i.e., photosynthetic capacity) of infected leaves.
2015年春天，坏死营养型病原菌盘多毛孢属（也称为盘二孢属）在美国西部的大片山杨（颤杨）林中严重爆发。在相邻的林分中，有些患病，有些未患病。患病山杨林分中的盘多毛孢属感染刺激了树冠顶部二次抽生叶片的补偿性生长。这些感染模式为表征病原菌感染与叶片功能性状之间的关联提供了契机。在犹他州北部的一片森林景观中，确定了八对相邻的健康和患病山杨林分。在健康和患病林分树冠下部的原始初生叶片以及患病林分树冠顶部产生的补偿性次生叶片上，测量了平均叶面积、比叶面积（SLA）、光合作用、淀粉浓度和防御化学物质表达（酚糖苷和缩合单宁）。只有患病林分的初生叶片显示出高水平的盘多毛孢属感染。患病林分次生叶片的叶面积比健康或患病林分中的所有其他叶片类型大三倍。健康林分树冠下部的叶片具有最高的比叶面积。光合作用在受感染的初生叶片中最低，在患病林分的次生叶片中最高，在健康林分的叶片中居中。患病林分叶片中的叶淀粉浓度低于健康林分的叶片。在健康和患病林分中，次生叶片中的缩合单宁都比初生叶片中的多。患病林分受感染叶片中的酚糖苷浓度最低。患病林分在春季比健康林分提前一周长出叶子，这可能使它们新长出的叶子暴露在促进盘多毛孢属感染的多雨条件下。患病林分的补偿性叶片再生似乎抵消了受感染叶片的一些功能损失（即光合能力）。
