Mediterranean annual grasses in western North America: kids in a candy store
Mediterranean annual grasses in western North America: kids in a candy store
复制标题
北美西部的地中海一年生草：糖果店里的孩子
作者：
J. Norton;T. Monaco;U. Norton
在本期《植物与土壤》中，Blank和Sforza（2007）对外来一年生草如何入侵美国西部生态系统的理解做出了贡献。他们的研究发现，medusahead野生水母（Taeniatherum caput-medusae） [L。[Nevski])在未被入侵的美国土壤上的生产力最高，来自美国种子的植物可能已经进化到利用更高的营养浓度，平行的其他结果表明，美国西部脆弱生态系统的土壤与这些杂草原生和非侵入性的土壤在功能上不同（即，更有效的营养丰富）（Blumenthal 2005; Davis et al. 2000）。虽然已经确定外来的一年生草可以通过促进增加的有效养分来维持自己的环境（例如，Ehrenfeld和Scott 2001； Norton et al. 2003），但我们必须记住，为了生态恢复，最初的入侵是由慢性干扰引起的，这些干扰破坏了本地的养分和有机物循环，增加了养分的可用性。美国西部生态系统与本土入侵的一年生草生态系统之间的主要区别在于慢性干扰发生的时间长短。在地中海地区，对草和灌木生态系统的集约化管理很久以前就耗尽了养分，因此本地植被适应了“今天在这里，明天就消失”的战略。在干旱和半干旱的美国西部生态系统中，多年生植物主导的原生营养循环最近被集约化土地利用所破坏。大规模放牧和改变的火灾制度等形式的慢性干扰开始释放储存在土壤有机质（SOM）中数千年的营养物质。当外来的一年生草的种子到达时，他们发现糖果店还开着。在这篇评论中，我们回顾了美国西部半干旱地区生态系统过程发生重大变化的证据，并呼吁开展更多的研究，将生态恢复工作的结果与侵入性一年生植物与被入侵环境之间相互作用的知识体系联系起来。在美国西部易受杂草入侵的生态系统中，几乎任何类型的生态系统破坏的后果都是从固定化的转变，Plant Soil (2007) 298:1-5 DOI 10.1007/s11104-007-9364-8
In this issue of Plant and Soil, Blank and Sforza (2007) contribute to understanding of how exotic annual grasses invade ecosystems in the western United States. Their findings, that medusahead wildrye (Taeniatherum caput-medusae [L.] Nevski) was most productive on non-invaded US soil and that plants from US-derived seeds may have evolved to utilize higher nutrient concentrations, parallel other results that suggest soils of vulnerable western US ecosystems are functionally different (i.e., more available-nutrient rich) than soils where these weeds are native and noninvasive (Blumenthal 2005; Davis et al. 2000). While it has been well established that exotic annual grasses can perpetuate their own environment by fostering increased available nutrients (e.g., Ehrenfeld and Scott 2001; Norton et al. 2003), we must remember, for the sake of ecological restoration, that initial invasiveness is caused by chronic disturbances that disrupt native nutrient and organic matter cycles and increase nutrient availability. The principal difference between western US ecosystems and those where invasive annual grasses are native is the amount of time during which chronic disturbances have occurred. In the Mediterranean region, intensive management of grass and shrubland ecosystems depleted nutrients long ago, so that native vegetation is adapted to a “here today, gone tomorrow” strategy. In ecosystems of the arid and semiarid western USA, perennial-plantdominated native nutrient cycles were disrupted by intensive land use much more recently. Chronic disturbances in the form of extensive grazing and altered fire regimes began to unlock nutrients stored in soil organic matter (SOM) for millennia. When seeds of exotic annual grasses arrived they found that the candy store was open. In this commentary, we review evidence for major shifts in ecosystem processes across the semiarid western USA and we call for more research that links results of ecological restoration efforts to the growing body of knowledge about interactions between invasive annuals and invaded environments. In western US ecosystems vulnerable to weed invasion, the consequence of almost any type of ecosystem disruption is a shift from immobilizing, Plant Soil (2007) 298:1–5 DOI 10.1007/s11104-007-9364-8