High levels of atmospheric nitrogen (N) deposition to southern California chaparral shrublands may interact with fire to affect biomass production and plant species composition during secondary succession. To determine the potential interactions between post fire recovery and N deposition we compared rates of aboveground net primary production (ANPP), shrub growth, and the relative abundance of Adenostoma fasciculatum, other sub-dominant shrubs, and herbaceous species of three chaparral stands exposed to different levels of atmospheric N deposition over the first 3 years of post-fire succession. Our data suggest that rates of ANPP (gdw m(-2) month(-1)) and aboveground N storage (gN m(-2) month(-1)) for these chaparral stands were not related to N deposition even though sites exposed to high levels of N deposition had significantly higher rates of shrub growth (gdw plant(-1) month(-1)) and N uptake (gN plant(-1) month(-1)). However, high-N stands were composed of larger shrubs with a lower density, and this trade-off between shrub size and density may explain the low correlation between N deposition and post-fire ANPP. Differences in relative plant species abundance between sites were significantly correlated with N deposition exposure, where stands exposed to high N deposition had a lower relative abundance of A. fasciculatum and a higher relative abundance of other shrub and herbaceous species. While many factors can affect rates and patterns of post-fire recovery, these results suggest that chronic exposure to N deposition may significantly alter plant growth and species composition in successional chaparral stands.

中文翻译：

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暴露于不同水平氮沉降的丛林林地火灾后初级生产和植物群落动态


南加州灌木丛中高水平的大气氮（N）沉降可能与火灾相互作用，影响次生演替过程中的生物量生产和植物物种组成。为了确定火后恢复和氮沉降之间的潜在相互作用，我们比较了暴露于以下环境的三个丛林林地的地上净初级生产力（ANPP）、灌木生长以及束状腺孔藻、其他次优势灌木和草本物种的相对丰度。火后连续的前三年内不同水平的大气氮沉降。我们的数据表明，这些丛林林分的ANPP率（gdw·m（-2）月（-1））和地上氮储存率（gN·m（-2）月（-1））与氮沉降无关，即使地点暴露于高水平的氮沉降下，灌木生长率（gdw植物（-1）月（-1））和氮吸收率（gN植物（-1）月（-1））显着更高。然而，高氮林分由密度较低的较大灌木组成，灌木大小和密度之间的这种权衡可以解释氮沉降与火后ANPP之间的低相关性。不同地点之间相对植物物种丰度的差异与氮沉降暴露显着相关，暴露于高氮沉降的林分中束状花的相对丰度较低，而其他灌木和草本物种的相对丰度较高。虽然许多因素会影响火灾后恢复的速度和模式，但这些结果表明，长期暴露于氮沉降可能会显着改变连续灌木丛中的植物生长和物种组成。