Institute of Dendrology, Polish Academy of Sciences, Parkowa 5, 62-035 Kórnik, Poland.
Tree Physiol. 2010 Aug;30(8):969-78. doi: 10.1093/treephys/tpq060. Epub 2010 Jul 12.
Understory shrubs are frequently attacked by insect herbivores. However, very little is known regarding possible interactions between light condition, defoliation (D) and fine root vitality (% live roots) and metabolic activity, and whether different plant strategies (compensation, trade-off and equilibrium) to defoliation depend on individual species light requirements. To explore the response of roots to such conditions, an experiment was established in which we experimentally removed 50% of leaves in 1-year-old seedlings of Sambucus nigra, Cornus sanguinea, Prunus serotina, Frangula alnus and Corylus avellana grown in 15% and full sunlight. On average, defoliation leads to a 15% reduction in fine root (< 2 mm) vitality (% live roots). However, a statistically significant reduction in root vitality after defoliation was detected only in those species that are less herbivorized in nature (48% in S. nigra and 5% in C. sanguinea). On average, shade conditions (L) resulted in 18% decline in root vitality, and the effects of defoliation were also 22% higher than for plants grown in full light. Root vitality in both treatments (D and L) was significantly correlated with their dry mass, concentration of total phenol (TPh) and carbon to nitrogen ratio, and negatively correlated with nitrogen, soluble carbohydrates, starch and total non-structural carbohydrates (TNC). To a large extent, root vitality and chemistry varied by species. Higher root vitality was related to higher concentrations of phenolics, more than to N and TNC concentrations. Concentrations of phenolics also differed significantly between defoliated plants and controls. However, in defoliated plants, an increase in TPh was observed only in two species, which belong to two different groups in light requirements and susceptibility to insect grazing (C. sanguinea and P. serotina). This study indicated that higher vitality of roots occurred in species that are characterized by higher insect defoliation under natural conditions. It is likely that higher root vitality of these species was related to their high level of TPh and tannins. This was especially noticeable for the reduced light treatment, which represents natural conditions under which insect defoliation is highest. Our results suggest that varied strategies of resource allocation were used by the different species in response to variations in light and defoliation.
林下灌木经常受到昆虫食草动物的攻击。然而，对于光照条件、落叶（D）和细根活力（%活根）和代谢活性之间可能存在的相互作用，以及不同的植物策略（补偿、权衡和平衡）对落叶的依赖是否取决于个别物种的光照需求，人们知之甚少。为了探索根系对这些条件的反应，进行了一项实验，在这项实验中，我们对 15%和全光照下生长的 1 年生黑接骨木、红瑞木、欧洲甜樱桃、欧洲鹅耳枥和榛实的幼苗进行了实验性的 50%叶片去除。平均而言，落叶导致细根（<2 毫米）活力（%活根）降低 15%。然而，只有在那些在自然状态下受食草动物侵害较少的物种中（黑接骨木为 48%，红瑞木为 5%），才能检测到落叶后根系活力的统计学显著降低。平均而言，遮荫条件（L）导致根活力下降 18%，而与全光照下生长的植物相比，落叶的影响也高出 22%。在这两种处理（D 和 L）中，根活力与它们的干质量、总酚（TPh）浓度和碳氮比显著相关，与氮、可溶性碳水化合物、淀粉和总非结构性碳水化合物（TNC）呈负相关。在很大程度上，根活力和化学性质因物种而异。较高的根活力与较高的酚类浓度有关，而不是与 N 和 TNC 浓度有关。受食草动物侵害的植物与对照植物之间的酚类浓度也存在显著差异。然而，在受食草动物侵害的植物中，只有两种植物观察到 TPh 增加，它们属于对昆虫取食的光需求和敏感性不同的两个组（红瑞木和欧洲甜樱桃）。这项研究表明，在自然条件下受昆虫取食程度较高的物种中，根活力较高。这些物种较高的根活力可能与它们较高的 TPh 和单宁水平有关。在减少光照的处理中，这种情况更为明显，因为这种处理代表了昆虫取食率最高的自然条件。我们的研究结果表明，不同的物种对光照和落叶的变化使用了不同的资源分配策略。
