Abstract：
Swiss needle cast (SNC), caused by a fungal pathogen, Nothophaeocryptopus gaeumannii, is a major forest disease of Douglas-fir (Pseudotsuga menziesii) stands of the Pacific Northwest (PNW). There is mounting concern that the current SNC epidemic occurring in Oregon and Washington will continue to increase in severity, frequency and spatial extent with future warming. Nothophaeocryptopus gaeumannii occurs wherever its host is found, but very little is known about the history and spatial distribution of SNC and its effects on growth and physiological processes of mature and old-growth forests within the Douglas-fir region of the PNW. Our findings show that stem growth and physiological responses of infected Douglas-fir to climate and SNC were different between sites, growth periods and disease severity based on cellulosic stable carbon and oxygen isotope ratios and ring width data in tree rings. At a coastal Oregon site within the SNC impact zone, variations in stem growth and Δ13C were primarily influenced by disproportional reductions in stomatal conductance (gs) and assimilation (A) caused by a loss of functioning stomates through early needle abscission and stomatal occlusion by pseudothecia of N. gaeumannii. At the less severely infected inland sites on the west slopes of Oregon\'s Cascade Range, stem growth correlated negatively with δ18O and positively with Δ13C, indicating that gs decreased in response to high evaporative demand with a concomitant reduction in A. Current- and previous-years summer vapor pressure deficit was the principal seasonal climatic variable affecting radial stem growth and the dual stable isotope ratios at all sites. Our results indicate that rising temperatures since the mid-1970s has strongly affected Douglas-fir growth in the PNW directly by a physiological response to higher evaporative demand during the annual summer drought and indirectly by a major SNC epidemic that is expanding regionally to higher latitudes and higher elevations.
摘要：
瑞士针铸造（SNC），由真菌病原体引起的，Nothophaeocryptopusgaeumannii，是西北太平洋（PNW）的道格拉斯冷杉（Pseudotsugamenziesii）林分的主要森林病害。人们越来越担心，目前在俄勒冈州和华盛顿州发生的SNC疫情将继续加剧，频率和空间范围与未来变暖。Nothophaeocryptopusgaeumannii发生在任何发现其宿主的地方，但是对SNC的历史和空间分布及其对PNW道格拉斯冷杉地区成熟和古老森林的生长和生理过程的影响知之甚少。我们的发现表明，受感染的道格拉斯冷杉对气候和SNC的茎生长和生理反应在不同地点之间是不同的，基于纤维素稳定的碳和氧同位素比率以及树木年轮中的年轮宽度数据的生长期和疾病严重程度。在SNC影响区内的俄勒冈州沿海站点，茎生长和Δ13C的变化主要受气孔导度（gs）和同化（A）不成比例的降低的影响，该降低是由于早期的针状脱落和假性气孔阻塞引起的气孔功能丧失。在俄勒冈州喀斯喀特山脉西坡上感染不太严重的内陆地点，茎生长与δ18O负相关，与Δ13C正相关，表明gs响应于高蒸发需求而减少，同时伴随着A的减少。当前和往年的夏季蒸气压不足是影响径向茎生长和所有地点双重稳定同位素比的主要季节性气候变量。我们的结果表明，自1970年代中期以来，气温上升直接影响了PNW中道格拉斯冷杉的生长，这直接是由于对年度夏季干旱期间较高蒸发需求的生理反应，间接影响了SNC的主要流行，该流行在区域范围内扩展到更高的纬度和更高的海拔。
