NOAA/WDS Paleoclimatology - Bert - Biscarosse B1 Pontenx P8 Landes de Gascogne - QURO - ITRDB FRAN048

Quercus robur and Q. petraea are major European forest tree species. They have been affected by powdery mildew caused by Erysiphe alphitoides for more than a century. This fungus is a biotrophic foliar pathogen that diverts photosynthetate from the plant for its own nutrition. We used a dendrochronological approach to investigate the effects of different levels of infection severity on the radial growth of young oak trees. Oak infection was monitored at individual tree level, at two sites in southwestern France, over a five-year period (2001–2005). Mean infection severity was almost 75% (infected leaf area) at the end of the 2001 growing season, at both sites, but only about 40% in 2002, and 8%, 5% and 2% in 2003, 2004 and 2005, respectively. Infection levels varied considerably between trees and were positively related between 2001 and 2002. Increment cores were taken from each tree to assess annual ring widths and increases in basal area. Annual radial growth was standardised to take the effect of tree size into account. Annual standardised radial growth was significantly and negatively correlated with infection severity in the same year, for both 2001 and 2002, and at both sites. The decrease in growth reached 70–90% for highly infected trees. The earlywood width was poorly correlated with infection severity, but the proportion of latewood in tree rings was lower in highly infected trees (60%) than in less heavily infected trees (85%). Infection in 2001 and 2002 was found to have a cumulative effect on radial growth in these years, together with a delayed effect detectable in 2003. Thus, even non-lethal pathogens like powdery mildew can have a significant impact on tree functioning. This impact should be taken into account in growth and yield models, to improve predictions of forest net primary production.

夏栎(Quercus robur)与无梗花栎(Quercus petraea)是欧洲主要的森林树种。一个多世纪以来，它们持续受栎白粉菌(Erysiphe alphitoides)引发的白粉病侵害。该真菌为活体营养型叶部病原菌，会从宿主植物夺取光合产物以满足自身营养需求。
本研究采用树木年轮学方法，探究了不同病害严重度水平对幼栎径向生长的影响。研究在法国西南部两个样地开展，以单株林木为监测单元，在2001至2005年的五年周期内，对栎树的感染情况进行了系统性跟踪调查。
2001年生长季结束时，两个样地的平均病害严重度（感病叶面积占比）均接近75%；2002年该比例仅约40%，2003、2004、2005年则分别降至8%、5%与2%。单株间的感病水平差异显著，且2001年与2002年的感病程度呈显著正相关。
研究人员从每株树木钻取生长芯(increment cores)，用以测定年轮宽度与胸高断面积增量。为消除林木初始大小对径向生长的干扰，对年度径向生长数据进行了标准化校正。标准化后的年度径向生长量与当年的病害严重度呈显著负相关，该结果在2001、2002年以及两个样地中均成立。高度感病林木的生长量降幅可达70%–90%。早材宽度与病害严重度的相关性较弱，但高度感病林木的年轮晚材占比（60%）显著低于轻度感病林木（85%）。
研究发现，2001年与2002年的感染不仅对这两年的径向生长存在累积效应，还能在2003年检测到延迟效应。由此可见，即便像白粉病这类非致死性病原菌，也会对林木的生理功能产生显著影响。在构建林木生长与产量模型时，应纳入该类影响因素，以提升森林净初级生产力的预测精度。