Department of Plant and Wildlife Sciences, Brigham Young University, Provo, UT, USA.
Department of Biological Sciences & the Environmental Change Initiative, University of Notre Dame, Notre Dame, IN, USA.
Glob Chang Biol. 2021 Apr;27(7):1408-1430. doi: 10.1111/gcb.15507. Epub 2021 Jan 27.
Climate change is creating widespread ecosystem disturbance across the permafrost zone, including a rapid increase in the extent and severity of tundra wildfire. The expansion of this previously rare disturbance has unknown consequences for lateral nutrient flux from terrestrial to aquatic environments. Lateral loss of nutrients could reduce carbon uptake and slow recovery of already nutrient-limited tundra ecosystems. To investigate the effects of tundra wildfire on lateral nutrient export, we analyzed water chemistry in and around the 10-year-old Anaktuvuk River fire scar in northern Alaska. We collected water samples from 21 burned and 21 unburned watersheds during snowmelt, at peak growing season, and after plant senescence in 2017 and 2018. After a decade of ecosystem recovery, aboveground biomass had recovered in burned watersheds, but overall carbon and nitrogen remained ~20% lower, and the active layer remained ~10% deeper. Despite lower organic matter stocks, dissolved organic nutrients were substantially elevated in burned watersheds, with higher flow-weighted concentrations of organic carbon (25% higher), organic nitrogen (59% higher), organic phosphorus (65% higher), and organic sulfur (47% higher). Geochemical proxies indicated greater interaction with mineral soils in watersheds with surface subsidence, but optical analysis and isotopes suggested that recent plant growth, not mineral soil, was the main source of organic nutrients in burned watersheds. Burned and unburned watersheds had similar δ N-NO , indicating that exported nitrogen was of preburn origin (i.e., not recently fixed). Lateral nitrogen flux from burned watersheds was 2- to 10-fold higher than rates of background nitrogen fixation and atmospheric deposition estimated in this area. These findings indicate that wildfire in Arctic tundra can destabilize nitrogen, phosphorus, and sulfur previously stored in permafrost via plant uptake and leaching. This plant-mediated nutrient loss could exacerbate terrestrial nutrient limitation after disturbance or serve as an important nutrient release mechanism during succession.
气候变化正在永久冻土带造成广泛的生态系统干扰，包括苔原野火的范围和严重程度迅速增加。这种以前罕见的干扰的扩大，对陆地向水生环境的侧向养分通量有未知的影响。侧向养分损失可能会减少碳吸收，并减缓已经受到养分限制的苔原生态系统的恢复。为了研究苔原野火对侧向养分输出的影响，我们分析了阿拉斯加北部 10 年前的阿纳克图夫克河火灾疤痕内及其周围的水化学。我们在 2017 年和 2018 年融雪期、生长高峰期和植物衰老后，从 21 个燃烧和 21 个未燃烧的流域收集水样。经过十年的生态系统恢复，燃烧流域的地上生物量已经恢复，但总体碳氮含量仍低 20%左右，活动层仍深 10%左右。尽管有机物质储量较低，但燃烧流域的溶解有机养分却大大增加，有机碳（高 25%）、有机氮（高 59%）、有机磷（高 65%）和有机硫（高 47%）的流量加权浓度更高。地球化学示踪剂表明，在地表沉降的流域中，与矿物土壤的相互作用更大，但光学分析和同位素表明，最近的植物生长而不是矿物土壤是燃烧流域有机养分的主要来源。燃烧和未燃烧流域的δ N-NO 相似，表明输出的氮来自燃烧前（即不是最近固定的）。与该地区估计的背景氮固定和大气沉积速率相比，来自燃烧流域的侧向氮通量高出 2 到 10 倍。这些发现表明，北极苔原的野火可以通过植物吸收和淋洗，使先前储存在永冻层中的氮、磷和硫失去稳定性。这种植物介导的养分损失可能会在干扰后加剧陆地养分限制，或在演替过程中成为重要的养分释放机制。
