Forstbotanik und Baumphysiologie, Büsgen-Institut, Büsgenweg 2, 37077 Göttingen, Germany.
Tree Physiol. 2011 May;31(5):531-8. doi: 10.1093/treephys/tpr042.
Knowledge is limited about whether root nutrient concentrations are affected by mixtures of tree species and interspecific root competition. The goal of this field study was to investigate root nutrient element concentrations in relation to root and ectomycorrhizal (EM) diversity in six different mixtures of beech (Fagus sylvatica), ash (Fraxinus excelsior) and lime (Tilia sp.) in an old-growth, undisturbed forest ecosystem. Root biomass and nutrient concentrations per tree taxon as well as the abundance and identity of all EM fungi were determined in soil cores of a volume of 1 L (r=40 mm, depth=200 mm). Stand-level nutrient concentrations in overall root biomass and H' (Shannon-Wiener diversity) were obtained by pooling the data per stand. At stand level, Shannon H' for roots and aboveground tree species abundance were correlated. H' for roots and EM fungi were not correlated because of the contribution of ash roots that form only arbuscular mycorrhizal but no EM associations. Nutrient element concentrations in roots showed taxon-related differences and increased in the following order: beech ≤ lime < ash with the exception of calcium (Ca), which was lower in ash. Stand-level concentrations of Ca, magnesium, potassium and sulfur in roots increased with increasing tree diversity because of two effects: increasing contribution of ash roots to the mixture and increasing Ca accumulation in beech roots with increasing root diversity. On a small scale, increasing root diversity, but not EM diversity, was correlated with decreasing P concentrations in beech roots pointing to interspecific tree competition. Nitrogen (N) concentrations of beech roots were unaltered in relation to root and EM diversity. Opposing behavior was observed for lime and ash: the N concentrations in lime roots increased, whereas those in ash roots decreased with increasing EM diversity in a given soil volume. This suggests that EM diversity facilitates N acquisition of lime roots at the expense of non-EM ash.
关于树种混合和种间根系竞争是否会影响根系养分浓度，目前人们的了解还很有限。本野外研究的目的是调查与阔叶山毛榉（Fagus sylvatica）、白蜡树（Fraxinus excelsior）和椴树（Tilia sp.）6 种不同混交林中根系和外生菌根（EM）多样性相关的根养分元素浓度。在一个未受干扰的古老森林生态系统中，使用体积为 1 L（r=40 mm，深度=200 mm）的土壤芯来确定每棵树类群的根生物量和养分浓度以及所有 EM 真菌的丰度和身份。通过对每个林分的数据进行汇总，获得了总根生物量和 H'（香农-威纳多样性）的林分水平养分浓度。在林分水平上，根系和地上树种丰度的 Shannon H'呈正相关。由于只形成丛枝菌根而不形成 EM 共生体的白蜡树根系的贡献，根系和 EM 真菌的 H'没有相关性。根系养分浓度表现出与分类群相关的差异，并按以下顺序增加：山毛榉 ≤ 椴树 < 白蜡树，除了钙（Ca），白蜡树的 Ca 浓度较低。由于两个因素的影响，根中 Ca、镁、钾和硫的林分水平浓度随着树木多样性的增加而增加：白蜡树根系对混合物的贡献增加，以及随着根系多样性的增加，山毛榉根系中 Ca 的积累增加。在小尺度上，增加根多样性，而不是 EM 多样性，与山毛榉根系中 P 浓度的降低有关，这表明存在种间树木竞争。山毛榉根系的氮（N）浓度与根和 EM 多样性无关。椴树和白蜡树的行为则相反：在给定的土壤体积中，随着 EM 多样性的增加，椴树根系的 N 浓度增加，而白蜡树根系的 N 浓度降低。这表明，EM 多样性有利于椴树根系对 N 的获取，而牺牲了非 EM 白蜡树。
