Olff H, Hoorens B, de Goede R G M, van der Putten W H, Gleichman J M
Nature Conservation and Plant Ecology Group, Wageningen Agricultural University, Bornsesteeg 69, 6708 PD Wageningen, The Netherlands, The Netherlands.
Soil Biology Group, Wageningen Agricultural University, P.O. Box 8005, 6700 EC Wageningen, The Netherlands, The Netherlands.
Oecologia. 2000 Oct;125(1):45-54. doi: 10.1007/PL00008890.
We analyzed the dynamics of dominant plant species in a grazed grassland over 17 years, and investigated whether local shifts in these dominant species, leading to vegetation mosaics, could be attributed to interactions between plants and soil-borne pathogens. We found that Festuca rubra and Carex arenaria locally alternated in abundance, with different sites close together behaving out of phase, resulting in a shifting mosaic. The net effect of killing all soil biota on the growth of these two species was investigated in a greenhouse experiment using gamma radiation, controlling for possible effects of sterilization on soil chemistry. Both plant species showed a strong net positive response to soil sterilization, indicating that pathogens (e.g., nematodes, pathogenic fungi) outweighed the effect of mutualists (e.g., mycorrhizae). This positive growth response towards soil sterilization appeared not be due to effects of sterilization on soil chemistry. Growth of Carex was strongly reduced by soil-borne pathogens (86% reduction relative to its growth on sterilized soil) on soil from a site where this species decreased during the last decade (and Festuca increased), while it was reduced much less (50%) on soil from a nearby site where it increased in abundance during the last decade. Similarly, Festuca was reduced more (67%) on soil from the site where it decreased (and Carex increased) than on soil from the site where it increased (55%, the site where Carex decreased). Plant-feeding nematodes showed high small-scale variation in densities, and we related this variation to the observed growth reductions in both plant species. Carex growth on unsterilized soil was significantly more reduced at higher densities of plant-feeding nematodes, while the growth reduction in Festuca was independent of plant-feeding nematode densities. At high plant-feeding nematode densities, growth of Carex was reduced more than Festuca, while at low nematode densities the opposite was found. Each plant species thus seems to be affected by different (groups of) soil-borne pathogens. The resulting interaction web of plants and soil-borne pathogens is discussed. We hypothesize that soil disturbances by digging ants and rabbits may explain the small-scale variation in nematode densities, by locally providing "fresh" sand. We conclude that soil-borne pathogens may contribute to plant diversity and spatial mosaics of plants in grasslands.
我们分析了一个放牧草原上优势植物物种长达17年的动态变化，并研究了这些优势物种在局部地区的更替，即导致植被镶嵌现象的原因，是否可归因于植物与土壤传播病原体之间的相互作用。我们发现，紫羊茅和砂苔草在局部地区的丰度交替变化，相邻的不同地点表现出不同步，从而形成了动态的镶嵌现象。在温室实验中，我们使用伽马射线辐射研究了杀死所有土壤生物群对这两个物种生长的净效应，并控制了灭菌对土壤化学性质可能产生的影响。两种植物对土壤灭菌均表现出强烈的净正向反应，这表明病原体（如线虫、致病真菌）的影响超过了共生生物（如菌根）的影响。这种对土壤灭菌的正向生长反应似乎并非由于灭菌对土壤化学性质的影响。在过去十年中该物种数量减少（而紫羊茅数量增加）的地点的土壤上，砂苔草的生长受到土壤传播病原体的强烈抑制（相对于在灭菌土壤上的生长减少了86%），而在过去十年中其数量增加的附近地点的土壤上，生长抑制程度要小得多（50%）。同样，在其数量减少（而砂苔草数量增加）的地点的土壤上，紫羊茅的生长减少幅度（67%）大于其数量增加的地点的土壤（55%，即砂苔草数量减少的地点）。以植物为食的线虫密度在小尺度上表现出高度变化，我们将这种变化与这两种植物观察到的生长减少联系起来。在未灭菌土壤上，砂苔草的生长在较高密度的以植物为食的线虫作用下显著降低，而紫羊茅的生长减少与以植物为食的线虫密度无关。在以植物为食的线虫高密度时，砂苔草的生长减少幅度大于紫羊茅，而在低密度时则相反。因此，每种植物似乎受到不同（组）土壤传播病原体的影响。我们讨论了由此产生的植物与土壤传播病原体的相互作用网络。我们推测，挖掘蚁和兔子造成的土壤扰动可能通过局部提供“新鲜”沙子来解释线虫密度的小尺度变化。我们得出结论，土壤传播病原体可能有助于草原植物的多样性和植物的空间镶嵌现象。
