城市残余草地中增加和减少的本地物种对氮添加和干扰的反应不同。
Increasing and declining native species in urban remnant grasslands respond differently to nitrogen addition and disturbance.
机构信息
Department of Ecology, Environment and Evolution, La Trobe University, Bundoora, Victoria, Australia.
出版信息
Ann Bot. 2018 Mar 14;121(4):691-697. doi: 10.1093/aob/mcx200.
BACKGROUND AND AIMS
Atmospheric nitrogen deposition and natural fire regime suppression are key drivers of vegetation change in urbanizing grasslands. Some species thrive under these conditions, while others face local extinction. In the natural grasslands that surround Melbourne, Australia, biotic homogenization has occurred with intensifying urbanization. Some native species have become rarer (decreaser species) across the landscape, while others have become more widespread (increaser species). This study experimentally examined the response of increaser and decreaser plant species to nitrogen addition/depletion, and examined the presence/absence of annual disturbance to the vegetation.
METHODS
Decreaser and increaser species were planted into 60 field plots established in an urban Melbourne grassland and examined over 2 years. Annual removal of above-ground biomass occurred in half the plots to simulate biomass removal via fire, with the remaining plots undisturbed. Soil nitrogen was depleted in one-third of plots, one-third received no nitrogen treatment and one-third were fertilized with nitrogen. Increaser plant species were predicted to persist in the absence of disturbance, and thrive when fertilized. In contrast, high mortality was predicted for decreaser species in the absence of disturbance, with fertilization providing no advantage.
KEY RESULTS
Seedling mortality for increaser and decreaser species was unrelated to the treatments. The mortality of decreaser species was high (69 %), and the mortality of increaser species low (20 %). However, seedling growth was related to the treatments. The total biomass of decreaser species was highest in annually disturbed plots, with growth suppressed in undisturbed plots. In contrast, the total biomass of increaser species was unrelated to the disturbance regime, but responded positively to nitrogen enrichment.
CONCLUSIONS
The results provide evidence that by affecting plant growth, declines in biomass removal and atmospheric nitrogen deposition could be key drivers of biotic homogenization in urban grasslands.
背景与目的
大气氮沉降和自然火灾抑制是城市化草原植被变化的关键驱动因素。一些物种在这些条件下茁壮成长，而另一些则面临局部灭绝。在澳大利亚墨尔本周围的自然草原中，随着城市化的加剧，生物同质化已经发生。一些本地物种在整个景观中变得更加稀少（减少物种），而另一些则变得更加普遍（增加物种）。本研究通过实验检验了增加和减少植物物种对氮添加/耗尽的反应，并检查了植被是否存在/不存在年度干扰。
方法
将减少和增加的物种种植到在城市墨尔本草原中建立的 60 个野外样地中，并在 2 年内进行了检查。一半的样地每年都会去除地上生物量，以模拟火灾引起的生物量去除，而另一半样地则不受干扰。三分之一的样地土壤氮被耗尽，三分之一的样地没有接受氮处理，三分之一的样地接受氮施肥。预计增加的植物物种在没有干扰的情况下会持续存在，并在施肥时茁壮成长。相比之下，在没有干扰的情况下，减少物种的死亡率很高，施肥没有优势。
主要结果
增加和减少物种的幼苗死亡率与处理无关。减少物种的死亡率很高（69%），而增加物种的死亡率很低（20%）。然而，幼苗生长与处理有关。减少物种的总生物量在每年受干扰的样地中最高，在不受干扰的样地中生长受到抑制。相比之下，增加物种的总生物量与干扰制度无关，但对氮富集反应积极。
结论
结果表明，通过影响植物生长，生物量去除和大气氮沉降的下降可能是城市草原生物同质化的关键驱动因素。
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