Islands of fertility induce co-occurring negative and positive plant-soil feedbacks promoting coexistence
Islands of fertility induce co-occurring negative and positive plant-soil feedbacks promoting coexistence
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DOI：
10.1007/s11258-007-9371-0
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发表时间：
2008-08-01
期刊：
影响因子：
1.7
通讯作者：
Mazzoleni, Stefano
中科院分区：
文献类型：
--
作者：
Bonanomi, Giuliano;Rietkerk, Max;Mazzoleni, Stefano
“生态系统工程师”的积极植物-土壤反馈是资源有限的生态系统构建和组织的重要驱动力。尽管大量证据表明植物-土壤反馈的范围可以从积极到强烈消极，但它们在植物群落中的共现尚未得到调查。我们检验了这样的假设：沙丘群落的初级演替过程中，固氮灌木紫花苜蓿码头产生的植物-土壤反馈对共存的草 Lophochloa pubescens 产生积极影响，而对灌木物种本身产生负面影响。我们进行了实地测量和实验室生物测定，以评估（1）肥力岛对其生态系统工程师的招募和生长以及共存物种的表现的影响，以及（2）可以解释肥力岛对共存物种的相反影响的机制。紫花苜蓿冠下存在肥力岛，这通过较高的有效氮、可提取的磷和钾、有机质、微生物活性、持水能力、土壤湿度和较低的盐浓度来证明。这些生育岛的影响显然是物种特异性的，对 Lophochloa 有促进作用，对苜蓿补充有负面影响。与灌木树冠区域外相比，当根在内部时， Lophochloa 更密集并且产生更多的生物量。相反，与基于随机分布的预测相比，尽管种子丰度较高，但紫花苜蓿的幼苗数量在内部较低，而在成年灌木冠区外部的幼苗数量较高，因此显示出 Janzen-Connell 分布。实验室实验证明了苜蓿植物-土壤负反馈的发生，并且地上衰老植物材料的自毒性是解释这种负反馈以及由此产生的田间 Janzen-Connell 分布的潜在重要机制。
Positive plant-soil feedback by "ecosystem engineers" is an important driver for the structuring and organization of resource-limited ecosystems. Although ample evidence demonstrates that plant-soil feedbacks can range from positive to strongly negative, their co-occurrence in plant communities have not yet been investigated. We test the hypothesis that the plant-soil feedback generated by the nitrogen-fixer shrub Medicago marina during primary succession in a sand dune community has a positive effect on the coexisting grass Lophochloa pubescens and a negative effect on the shrub species itself. We conducted field measurements and laboratory bioassays to evaluate (1) the effects of islands of fertility on the recruitment and growth of its ecosystem engineer and on the performance of a coexisting species and (2) the mechanisms involved that can explain the opposite effects of islands of fertility on coexisting species. Islands of fertility were present under Medicago crowns evidenced by higher available nitrogen, extractable phosphorus and potassium, organic matter, microbial activity, water holding capacity, soil humidity, and lower salt concentrations. The effects of these islands of fertility were clearly species-specific, with a facilitative impact on Lophochloa and a negative effect on Medicago recruitment. Lophochloa was denser and produced more biomass when rooted inside as compared to outside the crown area of the shrub. Contrarily, the number of seedlings of Medicago was lower inside, despite the higher seed abundance, and higher outside the crown area of adult shrubs as compared to predictions based on random distribution, thus showing a Janzen-Connell distribution. Laboratory experiments demonstrate the occurrence of Medicago negative plant-soil feedback, and that the auto-toxicity of the aboveground senescent plant material is a potentially important underlying mechanism explaining this negative feedback and the resulting Janzen-Connell distribution in the field.