Department of Natural Resources and Environmental Science, University of Nevada Reno, Reno, NV 89512, USA.
Oecologia. 2012 Jan;168(1):199-211. doi: 10.1007/s00442-011-2075-0. Epub 2011 Jul 21.
In semi-arid ecosystems, heterogeneous resources can lead to variable seedling recruitment. Existing vegetation can influence seedling establishment by modifying the resource and physical environment. We asked how a native legume, Lupinus argenteus, modifies microenvironments in unburned and burned sagebrush steppe, and if L. argenteus presence facilitates seedling establishment of native species and the non-native annual grass, Bromus tectorum. Field treatments examined mechanisms by which L. argenteus likely influences establishment: (1) live L. argenteus; (2) dead L. argenteus; (3) no L. argenteus; (4) no L. argenteus with L. argenteus litter; (5) no L. argenteus with inert litter; and (6) mock L. argenteus. Response variables included soil nitrogen, moisture, temperature, solar radiation, and seedling establishment of the natives Elymus multisetus and Eriogonum umbellatum, and non-native B. tectorum. In both unburned and burned communities, there was higher spring soil moisture, increased shade and reduced maximum temperatures under L. argenteus canopies. Adult L. argenteus resulted in greater amounts of soil nitrogen (N) only in burned sagebrush steppe, but L. argenteus litter increased soil N under both unburned and burned conditions. Although L. argenteus negatively affected emergence and survival of B. tectorum overall, its presence increased B. tectorum biomass and reproduction in unburned plots. However, L. argenteus had positive facilitative effects on size and survival of E. multisetus in both unburned and burned plots. Our study indicates that L. argenteus can facilitate seedling establishment in semi-arid systems, but net effects depend on the species examined, traits measured, and level of abiotic stress.
在半干旱生态系统中，不均匀的资源会导致幼苗的补充出现差异。现有的植被可以通过改变资源和物理环境来影响幼苗的建立。我们询问了一种本地豆科植物银叶 Lupinus argenteus 如何改变未燃烧和燃烧过的山艾灌木丛草原的微环境，以及 L. argenteus 的存在是否有助于本地物种和非本地一年生草本植物雀麦 Bromus tectorum 的幼苗建立。实地处理考察了 L. argenteus 可能影响建立的机制：(1)活的 L. argenteus；(2)死的 L. argenteus；(3)没有 L. argenteus；(4)没有 L. argenteus 但有 L. argenteus 凋落物；(5)没有 L. argenteus 但有惰性凋落物；(6)模拟 L. argenteus。响应变量包括土壤氮、水分、温度、太阳辐射和本地 Elymus multisetus 和 Eriogonum umbellatum 以及非本地 B. tectorum 的幼苗建立。在未燃烧和燃烧的群落中，L. argenteus 冠层下春季土壤水分较高，阴凉处较多，最高温度降低。只有在燃烧过的山艾灌木丛草原中，成年的 L. argenteus 才会导致更多的土壤氮（N），但 L. argenteus 凋落物会增加未燃烧和燃烧条件下的土壤 N。尽管 L. argenteus 总体上会对 B. tectorum 的出苗和存活产生负面影响，但它的存在会增加未燃烧的植物的生物量和繁殖。然而，L. argenteus 对未燃烧和燃烧的植物的 E. multisetus 的大小和存活有积极的促进作用。我们的研究表明，L. argenteus 可以促进半干旱系统中的幼苗建立，但净效应取决于所研究的物种、测量的特征和非生物胁迫的水平。
