van der Putten W H, Kowalchuk G A, Brinkman E P, Doodeman G T A, van der Kaaij R M, Kamp A F D, Menting F B J, Veenendaal E M
Netherlands Institute of Ecology, Centre for Terrestrial Ecology (NIOO-KNAW), P.O. Box 40, 6666 ZG Heteren, The Netherlands.
Ecology. 2007 Apr;88(4):978-88. doi: 10.1890/06-1051.
Enemy release of exotic plants from soil pathogens has been tested by examining plant-soil feedback effects in repetitive growth cycles. However, positive soil feedback may also be due to enhanced benefit from the local arbuscular mycorrhizal fungi (AMF). Few studies actually have tested pathogen effects, and none of them did so in arid savannas. In the Kalahari savanna in Botswana, we compared the soil feedback of the exotic grass Cenchrus biflorus with that of two dominant native grasses, Eragrostis lehmanniana and Aristida meridionalis. The exotic grass had neutral to positive soil feedback, whereas both native grasses showed neutral to negative feedback effects. Isolation and testing of root-inhabiting fungi of E. lehmanniana yielded two host-specific pathogens that did not influence the exotic C. biflorus or the other native grass, A. meridionalis. None of the grasses was affected by the fungi that were isolated from the roots of the exotic C. biflorus. We isolated and compared the AMF community of the native and exotic grasses by polymerase chain reaction-denaturing gradient gel elecrophoresis (PCR-DGGE), targeting AMF 18S rRNA. We used roots from monospecific field stands and from plants grown in pots with mixtures of soils from the monospecific field stands. Three-quarters of the root samples of the exotic grass had two nearly identical sequences, showing 99% similarity with Glomus versiforme. The two native grasses were also associated with distinct bands, but each of these bands occurred in only a fraction of the root samples. The native grasses contained a higher diversity of AMF bands than the exotic grass. Canonical correspondence analyses of the AMF band patterns revealed almost as much difference between the native and exotic grasses as between the native grasses. In conclusion, our results support the hypothesis that release from soil-borne enemies may facilitate local abundance of exotic plants, and we provide the first evidence that these processes may occur in arid savanna ecosystems. Pathogenicity tests implicated the involvement of soil pathogens in the soil feedback responses, and further studies should reveal the functional consequences of the observed high infection with a low diversity of AMF in the roots of exotic plants.
通过在重复生长周期中检验植物 - 土壤反馈效应，对外来植物从土壤病原体中“解脱”的情况进行了测试。然而，正向土壤反馈也可能是由于从当地丛枝菌根真菌（AMF）获得的益处增加所致。实际上很少有研究测试病原体的影响，而且没有一项研究是在干旱稀树草原上进行的。在博茨瓦纳的卡拉哈里稀树草原，我们比较了外来草双花蒺藜草与两种主要本地草——雷曼画眉草和南方三芒草的土壤反馈情况。外来草具有中性到正向的土壤反馈，而两种本地草均表现出中性到负向的反馈效应。对雷曼画眉草的根际真菌进行分离和测试，得到了两种寄主特异性病原体，它们对外来的双花蒺藜草或另一种本地草南方三芒草没有影响。没有一种草受到从外来双花蒺藜草根部分离出的真菌的影响。我们通过聚合酶链反应 - 变性梯度凝胶电泳（PCR - DGGE），以AMF的18S rRNA为目标，对外来草和本地草的AMF群落进行了分离和比较。我们使用了单一种植的田间植株的根以及种植在装有来自单一种植田间土壤混合物的花盆中的植株的根。外来草四分之三的根样本有两个几乎相同的序列，与多样硬囊霉的相似度达99%。两种本地草也与不同的条带相关，但这些条带中的每一个仅出现在一小部分根样本中。本地草所含的AMF条带多样性高于外来草。对AMF条带模式的典范对应分析表明，本地草和外来草之间的差异几乎与本地草之间的差异一样大。总之，我们的结果支持这样的假设，即从土壤传播的敌人中解脱出来可能有助于外来植物在当地的大量繁殖，并且我们提供了首个证据表明这些过程可能发生在干旱稀树草原生态系统中。致病性测试表明土壤病原体参与了土壤反馈反应，进一步的研究应该揭示在外来植物根系中观察到的高感染率和低AMF多样性的功能后果。
