Thorpe Andrea S, Perakis Steven, Catricala Christina, Kaye Thomas N
Institute for Applied Ecology, Corvallis, Oregon, United States of America.
United States Geological Survey, Forest and Rangeland Ecosystem Science Center, Corvallis, Oregon, United States of America.
PLoS One. 2013 Dec 27;8(12):e84593. doi: 10.1371/journal.pone.0084593. eCollection 2013.
Nutrient rich conditions often promote plant invasions, yet additions of non-nitrogen (N) nutrients may provide a novel approach for conserving native symbiotic N-fixing plants in otherwise N-limited ecosystems. Lupinus oreganus is a threatened N-fixing plant endemic to prairies in western Oregon and southwest Washington (USA). We tested the effect of non-N fertilizers on the growth, reproduction, tissue N content, and stable isotope δ(15)N composition of Lupinus at three sites that differed in soil phosphorus (P) and N availability. We also examined changes in other Fabaceae (primarily Vicia sativa and V. hirsuta) and cover of all plant species. Variation in background soil P and N availability shaped patterns of nutrient limitation across sites. Where soil P and N were low, P additions increased Lupinus tissue N and altered foliar δ(15)N, suggesting P limitation of N fixation. Where soil P was low but N was high, P addition stimulated growth and reproduction in Lupinus. At a third site, with higher soil P, only micro- and macronutrient fertilization without N and P increased Lupinus growth and tissue N. Lupinus foliar δ(15)N averaged -0.010‰ across all treatments and varied little with tissue N, suggesting consistent use of fixed N. In contrast, foliar δ(15)N of Vicia spp. shifted towards 0‰ as tissue N increased, suggesting that conditions fostering N fixation may benefit these exotic species. Fertilization increased cover, N fixation, and tissue N of non-target, exotic Fabaceae, but overall plant community structure shifted at only one site, and only after the dominant Lupinus was excluded from analyses. Our finding that non-N fertilization increased the performance of Lupinus with few community effects suggests a potential strategy to aid populations of threatened legume species. The increase in exotic Fabaceae species that occurred with fertilization further suggests that monitoring and adaptive management should accompany any large scale applications.
营养丰富的条件通常会促进植物入侵，然而添加非氮（N）养分可能为在其他方面受氮限制的生态系统中保护本地共生固氮植物提供一种新方法。俄勒冈羽扇豆是一种濒危的固氮植物，原产于美国俄勒冈州西部和华盛顿州西南部的草原。我们在三个土壤磷（P）和氮有效性不同的地点，测试了非氮肥料对俄勒冈羽扇豆的生长、繁殖、组织氮含量和稳定同位素δ(15)N组成的影响。我们还研究了其他豆科植物（主要是野豌豆和硬毛野豌豆）的变化以及所有植物物种的覆盖度。背景土壤磷和氮有效性的变化塑造了不同地点的养分限制模式。在土壤磷和氮含量低的地方，添加磷增加了俄勒冈羽扇豆组织中的氮，并改变了叶片的δ(15)N，表明固氮受磷限制。在土壤磷含量低但氮含量高的地方，添加磷刺激了俄勒冈羽扇豆的生长和繁殖。在第三个土壤磷含量较高的地点，只有不添加氮和磷的微量和大量养分施肥增加了俄勒冈羽扇豆的生长和组织氮。在所有处理中，俄勒冈羽扇豆叶片的δ(15)N平均为 -0.010‰，并且随组织氮的变化很小，表明对固定氮的持续利用。相比之下，随着组织氮的增加，野豌豆属植物的叶片δ(15)N向0‰偏移，这表明促进固氮的条件可能有利于这些外来物种。施肥增加了非目标外来豆科植物的覆盖度、固氮量和组织氮，但仅在一个地点总体植物群落结构发生了变化，并且只有在将优势种俄勒冈羽扇豆排除在分析之外之后才发生变化。我们的发现，即非氮施肥提高了俄勒冈羽扇豆的性能且对群落影响较小，这表明了一种帮助濒危豆科植物种群的潜在策略。施肥导致外来豆科植物物种增加，这进一步表明在任何大规模应用中都应进行监测和适应性管理。
