Combination of factors rather than single disturbance drives perturbation of the nitrogen cycle in a temperate forest

IF 3.9 3区 环境科学与生态学 Q2 ENVIRONMENTAL SCIENCES Biogeochemistry Pub Date : 2023-12-03 DOI:10.1007/s10533-023-01105-z
Mark B. Green, Linda H. Pardo, John L. Campbell, Emma Rosi, Emily S. Bernhardt, Charles T. Driscoll, Timothy J. Fahey, Nicholas LoRusso, Jackie Matthes, Pamela H. Templer
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Abstract

Nitrogen (N) is a critical element in many ecological and biogeochemical processes in forest ecosystems. Cycling of N is sensitive to changes in climate, atmospheric carbon dioxide (CO2) concentrations, and air pollution. Streamwater nitrate draining a forested ecosystem can indicate how an ecosystem is responding to these changes. We observed a pulse in streamwater nitrate concentration and export at a long-term forest research site in eastern North America that resulted in a 10-fold increase in nitrate export compared to observations over the prior decade. The pulse in streamwater nitrate occurred in a reference catchment in the 2013 water year, but was not associated with a distinct disturbance event. We analyzed a suite of environmental variables to explore possible causes. The correlation between each environmental variable and streamwater nitrate concentration was consistently higher when we accounted for the antecedent conditions of the variable prior to a given streamwater observation. In most cases, the optimal antecedent period exceeded two years. We assessed the most important variables for predicting streamwater nitrate concentration by training a machine learning model to predict streamwater nitrate concentration in the years preceding and during the streamwater nitrate pulse. The results of the correlation and machine learning analyses suggest that the pulsed increase in streamwater nitrate resulted from both (1) decreased plant uptake due to lower terrestrial gross primary production, possibly due to increased soil frost or reduced solar radiation or both; and (2) increased net N mineralization and nitrification due to warm temperatures from 2010 to 2013. Additionally, variables associated with hydrological transport of nitrate, such as maximum stream discharge, emerged as important, suggesting that hydrology played a role in the pulse. Overall, our analyses indicate that the streamwater nitrate pulse was caused by a combination of factors that occurred in the years prior to the pulse, not a single disturbance event.

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因子的组合而不是单一的扰动驱动了温带森林氮循环的扰动
氮(N)是森林生态系统中许多生态和生物地球化学过程的关键元素。氮的循环对气候、大气二氧化碳(CO2)浓度和空气污染的变化非常敏感。流经森林生态系统的水流硝酸盐可以表明生态系统如何对这些变化作出反应。我们在北美东部的一个长期森林研究地点观察到水流硝酸盐浓度和出口的脉冲,导致硝酸盐出口与前十年的观测结果相比增加了10倍。2013水年某参考流域出现了径流硝酸盐的脉动,但与明显的扰动事件无关。我们分析了一系列环境变量来探索可能的原因。当我们在给定的河流观测之前考虑变量的先决条件时,每个环境变量与河流硝酸盐浓度之间的相关性始终较高。在大多数情况下,最佳的前期期超过两年。我们通过训练机器学习模型来预测河流硝酸盐脉冲前几年和期间的河流硝酸盐浓度,评估了预测河流硝酸盐浓度的最重要变量。相关分析和机器学习分析的结果表明,径流硝酸盐的脉冲增加是由以下两方面造成的:(1)由于陆地初级生产总量降低,植物吸收减少,可能是由于土壤霜冻增加或太阳辐射减少,或两者兼而有之;(2) 2010 ~ 2013年暖化导致净氮矿化和硝化作用增加。此外,与硝酸盐水文运输相关的变量,如最大水流流量,也变得很重要,这表明水文在脉冲中发挥了作用。总的来说,我们的分析表明,水流硝酸盐脉冲是由脉冲前几年发生的各种因素的组合引起的,而不是单一的干扰事件。
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来源期刊
Biogeochemistry
Biogeochemistry 环境科学-地球科学综合
CiteScore
7.10
自引率
5.00%
发文量
112
审稿时长
3.2 months
期刊介绍: Biogeochemistry publishes original and synthetic papers dealing with biotic controls on the chemistry of the environment, or with the geochemical control of the structure and function of ecosystems. Cycles are considered, either of individual elements or of specific classes of natural or anthropogenic compounds in ecosystems. Particular emphasis is given to coupled interactions of element cycles. The journal spans from the molecular to global scales to elucidate the mechanisms driving patterns in biogeochemical cycles through space and time. Studies on both natural and artificial ecosystems are published when they contribute to a general understanding of biogeochemistry.
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