Systems Ecology, Department of Ecological Science, VU University Amsterdam, Amsterdam, The Netherlands.
Department of Ecology and Environmental Science, Climate Impacts Research Centre, Umeå University, Abisko, Sweden.
Glob Chang Biol. 2017 Oct;23(10):4257-4266. doi: 10.1111/gcb.13804. Epub 2017 Jul 25.
Climate warming increases nitrogen (N) mineralization in superficial soil layers (the dominant rooting zone) of subarctic peatlands. Thawing and subsequent mineralization of permafrost increases plant-available N around the thaw-front. Because plant production in these peatlands is N-limited, such changes may substantially affect net primary production and species composition. We aimed to identify the potential impact of increased N-availability due to permafrost thawing on subarctic peatland plant production and species performance, relative to the impact of increased N-availability in superficial organic layers. Therefore, we investigated whether plant roots are present at the thaw-front (45 cm depth) and whether N-uptake ( N-tracer) at the thaw-front occurs during maximum thaw-depth, coinciding with the end of the growing season. Moreover, we performed a unique 3-year belowground fertilization experiment with fully factorial combinations of deep- (thaw-front) and shallow-fertilization (10 cm depth) and controls. We found that certain species are present with roots at the thaw-front (Rubus chamaemorus) and have the capacity (R. chamaemorus, Eriophorum vaginatum) for N-uptake from the thaw-front between autumn and spring when aboveground tissue is largely senescent. In response to 3-year shallow-belowground fertilization (S) both shallow- (Empetrum hermaphroditum) and deep-rooting species increased aboveground biomass and N-content, but only deep-rooting species responded positively to enhanced nutrient supply at the thaw-front (D). Moreover, the effects of shallow-fertilization and thaw-front fertilization on aboveground biomass production of the deep-rooting species were similar in magnitude (S: 71%; D: 111% increase compared to control) and additive (S + D: 181% increase). Our results show that plant-available N released from thawing permafrost can form a thus far overlooked additional N-source for deep-rooting subarctic plant species and increase their biomass production beyond the already established impact of warming-driven enhanced shallow N-mineralization. This may result in shifts in plant community composition and may partially counteract the increased carbon losses from thawing permafrost.
气候变暖会增加亚北极泥炭地表层土壤（主要根系区）中氮的矿化作用。永冻层解冻和随后的矿化作用会增加解冻前沿周围可被植物利用的氮。由于这些泥炭地的植物生产受到氮的限制，因此这些变化可能会极大地影响净初级生产力和物种组成。我们的目的是确定由于永冻层解冻导致的氮可利用性增加对亚北极泥炭地植物生产和物种表现的潜在影响，与表层有机层氮可利用性增加的影响相比。因此，我们调查了在最大解冻深度期间（与生长季节结束时间一致），植物根系是否存在于解冻前沿（45 厘米深度），以及氮是否在解冻前沿被吸收（氮示踪剂）。此外，我们进行了一项独特的为期 3 年的地下施肥实验，对深层（解冻前沿）和浅层施肥（10 厘米深度）以及对照进行了完全因子组合。我们发现某些物种的根系存在于解冻前沿（Rubus chamaemorus），并且在秋季和春季地上组织大部分衰老时，它们具有从解冻前沿吸收氮的能力（R. chamaemorus，Eriophorum vaginatum）。对 3 年浅层地下施肥（S）的响应，浅层（Empetrum hermaphroditum）和深根系物种都增加了地上生物量和氮含量，但只有深根系物种对解冻前沿增强的养分供应做出了积极响应（D）。此外，浅层施肥和解冻前沿施肥对深根系物种地上生物量生产的影响在数量上相似（S：增加 71%；与对照相比，D：增加 111%），且具有累加性（S+D：增加 181%）。我们的研究结果表明，从永冻层解冻中释放的可被植物利用的氮可能成为深根系亚北极植物物种迄今为止被忽视的额外氮源，并增加其生物量生产，超过了由变暖驱动的增强的浅层氮矿化作用所建立的影响。这可能导致植物群落组成的变化，并可能部分抵消永冻层解冻导致的碳损失增加。
