Melgoza Graciela, Nowak Robert S, Tausch Robin J
Department of Range Wildlife and Forestry, University of Nevada Reno, 1000 Valley Road, 89512, Reno, NV, USA.
Oecologia. 1990 May;83(1):7-13. doi: 10.1007/BF00324626.
Causes for the widespread abundance of the alien grass Bromus tectorum (cheatgrass) after fire in semiarid areas of western North America may include: (1) utilization of resources freed by the removal of fireintolerant plants; and (2) successful competition between B. tectorum and individual plants that survive fire. On a site in northwestern Nevada (USA), measurements of soil water content, plant water potential, aboveground biomass production, water use efficiency, and B. tectorum tiller density were used to determine if B. tectorum competes with either of two native species (Stipa comata and Chrysothamnus viscidiflorus) or simply uses unclaimed resources. Soil water content around native species occurring with B. tectorum was significantly lower (P<0.05) than around individuals without B. tectorum nearby. Native species had significantly more negative plant water potential when they occurred with B. tectorum. Aboveground biomass was significantly higher for native species without B. tectorum. However, the carbon isotope ratio of leaves for native species with B. tectorum was not significantly different from individuals without B. tectorum. Thus, B. tectorum competes with native species for soil water and negatively affects their wate status and productivity, but the competition for water does not affect water use efficiency of the native species. These adverse effects of B. tectorum competition on the productivity and water status of native species are also evident at 12 years after a fire. This competitive ability of B. tectorum greatly enhances its capability to exploit soil resources after fire and to enhance its status in the community.
北美西部半干旱地区火灾后外来草本植物野燕麦（ cheatgrass）广泛大量生长的原因可能包括：（1）利用因不耐火植物被清除而释放的资源；以及（2）野燕麦与火灾后存活的单株植物之间的成功竞争。在美国内华达州西北部的一个地点，通过测量土壤含水量、植物水势、地上生物量生产、水分利用效率和野燕麦分蘖密度，来确定野燕麦是与两种本地物种（针茅和粘叶金盏花）中的某一种竞争，还是仅仅利用未被占用的资源。与野燕麦伴生的本地物种周围的土壤含水量显著低于（P<0.05）附近没有野燕麦的单株植物周围的土壤含水量。当本地物种与野燕麦伴生时，其植物水势明显更负。没有野燕麦的本地物种地上生物量显著更高。然而，与野燕麦伴生的本地物种叶片的碳同位素比率与没有野燕麦的单株植物没有显著差异。因此，野燕麦与本地物种竞争土壤水分，并对它们的水分状况和生产力产生负面影响，但对水分的竞争并不影响本地物种的水分利用效率。野燕麦竞争对本地物种生产力和水分状况的这些不利影响在火灾后12年也很明显。野燕麦的这种竞争能力极大地增强了其在火灾后利用土壤资源并提升其在群落中地位的能力。
