Suding Katharine N, LeJeune Katherine D, Seastedt Timothy R
Department of Ecology and Evolutionary Biology, University of California at Irvine, Irvine, CA, USA.
Oecologia. 2004 Nov;141(3):526-35. doi: 10.1007/s00442-004-1678-0. Epub 2004 Aug 3.
Changes in competitive interactions under conditions of enhanced resource availability could explain the invasion success of some problematic plant species. For one invader of North American grasslands, Centaurea diffusa (diffuse knapweed), we test three hypotheses: (1) under ambient (high resource) conditions, C. diffusa is better able to tolerate competition from the resident community (competitive response), (2) under ambient conditions, C. diffusa strong impacts the competitive environment (competitive effect), and (3) reductions in nitrogen and/or phosphorus availability diminish these advantages. In support of our first hypothesis, C. diffusa was the most tolerant to neighbor competition of the four focal species under current resource conditions. In opposition to our second hypothesis, however, neighborhoods that contained C. diffusa and those where C. diffusa had been selectively removed did not differ in their impact on the performance of target transplant individuals or on resource conditions. Reduction in resource availability influenced competitive tolerance but not competitive impact, in partial support of our last hypothesis. Reduction in soil nitrogen (via sucrose carbon addition) enhanced the degree of neighbor competition experienced by all species but did not change their relative rankings; C. diffusa remained the best competitor under low nitrogen conditions. Reduction of soil phosphorus (via gypsum addition) weakened the ability of C. diffusa to tolerate neighbor competition proportionately more than the other focal species. Consequently, under low phosphorus conditions, C. diffusa lost its competitive advantage and tolerated neighbor competition similarly to the other focal species. We conclude that C. diffusa invasion may be double-edged: C. diffusa is less limited by nitrogen than the other focal species and is better able to utilize phosphorus to its competitive advantage.
在资源可利用性增强的条件下，竞争相互作用的变化可以解释一些有问题的植物物种的入侵成功。对于北美草原的一种入侵植物——白花矢车菊（diffuse knapweed），我们测试了三个假设：（1）在环境（高资源）条件下，白花矢车菊更能耐受来自本地群落的竞争（竞争响应）；（2）在环境条件下，白花矢车菊对竞争环境有强烈影响（竞争效应）；（3）氮和/或磷可利用性的降低会削弱这些优势。支持我们的第一个假设的是，在当前资源条件下，白花矢车菊是四种重点研究物种中对邻体竞争耐受性最强的。然而，与我们的第二个假设相反，包含白花矢车菊的邻体和白花矢车菊被选择性移除的邻体对目标移植个体的表现或资源条件的影响并无差异。资源可利用性的降低影响了竞争耐受性，但没有影响竞争效应，部分支持了我们的最后一个假设。土壤氮的减少（通过添加蔗糖碳）增强了所有物种所经历的邻体竞争程度，但没有改变它们的相对排名；在低氮条件下，白花矢车菊仍然是最佳竞争者。土壤磷的减少（通过添加石膏）比其他重点研究物种更能削弱白花矢车菊耐受邻体竞争的能力。因此，在低磷条件下，白花矢车菊失去了其竞争优势，对邻体竞争的耐受性与其他重点研究物种相似。我们得出结论，白花矢车菊的入侵可能具有双重性：白花矢车菊比其他重点研究物种受氮的限制更小，并且更能利用磷来获得竞争优势。
