Enhanced foliar ¹⁵N enrichment with increasing nitrogen addition rates: Role of plant species and nitrogen compounds

Abstract

Determining the abundance of N isotope (δ15N) in natural environments is a simple but powerful method for providing integrated information on the N cycling dynamics and status in an ecosystem under exogenous N inputs. However, whether the input of different N compounds could differently impact plant growth and their 15N signatures remains unclear. Here, the response of 15N signatures and growth of three dominant plants (Leymus chinensis, Carex duriuscula, and Thermopsis lanceolata) to the addition of three N compounds (NH4HCO3, urea, and NH4NO3) at multiple N addition rates were assessed in a meadow steppe in Inner Mongolia. The three plants showed different initial foliar δ15N values because of differences in their N acquisition strategies. Particularly, T. lanceolata (N2‐fixing species) showed significantly lower 15N signatures than L. chinensis (associated with arbuscular mycorrhizal fungi [AMF]) and C. duriuscula (associated with AMF). Moreover, the foliar δ15N of all three species increased with increasing N addition rates, with a sharp increase above an N addition rate of ~10 g N m−2 year−1. Foliar δ15N values were significantly higher when NH4HCO3 and urea were added than when NH4NO3 was added, suggesting that adding weakly acidifying N compounds could result in a more open N cycle. Overall, our results imply that assessing the N transformation processes in the context of increasing global N deposition necessitates the consideration of N deposition rates, forms of the deposited N compounds, and N utilization strategies of the co‐existing plant species in the ecosystem.

Aridity threshold for alpine soil nitrogen isotope signature and ecosystem nitrogen cycling

“…To the best of our knowledge, this is the first study revealing the quad- Furthermore, although we focused on the correspondence between soil δ 15 N and soil N cycling, foliage δ 15 N should also be included to explore the 15 N imprint between soils and plants. We only selected the two most widely distributed dominant species on the aridity gradient to explore foliage δ 15 N patterns, which may be insufficient to represent all the plant isotope signatures due to significant differences in foliage δ 15 N values among different functional types (Craine et al, 2009;Wang et al, 2023). Future studies should pay more attention to the diversification of plant isotopic niches along climatic gradients to better explore the coupling between leaf and soil δ 15 N under different drought conditions.…”

“…Understanding N cycle dynamics in ecosystems is crucial to investigate the effects of global change on vegetation and the carbon (C) cycle (Hungate et al, 2003;Kicklighter et al, 2019;Mason et al, 2022). The N isotope ratios (δ 15 N) of plants and soils provide insights into ecosystem N cycling and is frequently used to indicate terrestrial ecosystem N cycling and explore the response of N cycling to various drivers (Bai et al, 2012;Houlton et al, 2006Houlton et al, , 2015Wang et al, 2023;Xia et al, 2023). Specifically, high soil δ 15 N values generally indicate the "openness" of soil N cycling, characterized by high soil N availability and N losses (Bai & Houlton, 2009;Harris et al, 2022;Houlton & Bai, 2009).…”

Effects of nitrogen and phosphorus imbalance input on rhizosphere and bulk soil bacterial community of Suaeda salsa in the Yellow River Delta

“…The selection of the N-P addition ratio was referred to a previous study (Liu et al, 2019). Previous studies have found that urea addition has a stronger effect on soil N cycling than ammonia and nitrate N addition (Li et al, 2019a;Wang et al, 2022b). Therefore, urea was used as N fertilizer.…”

Nonlinear response of greenhouse gases emission to nitrogen addition in a meadow steppe

“…全球活性氮的固定和移动 (Niu et al, 2016), 导致大 量活性氮被广泛沉降到自然陆地生态系统中 。氮沉降改变了土壤理化性质、微生物群落 结构和植物生长过程 (Wang et al, 2023), 从而使3种 主要温室气体(CO 2 、CH 4 和N 2 O)的排放发生了变化 (Liu & Greaver, 2009), 进而影响大气化学组成, 加 剧全球增温的趋势。"截止到2019年, CO 2 、CH 4 和 N 2 O浓度分别达到了410 ppm、1 866 ppb和332 ppb 分别比工业化前(1750年)高了47%、 156%和23%, 并 且还有持续增加的趋势" (IPCC, 2021)。因此, 温室 气 体 排 放 也逐 渐 成 为 全球 变 化 研 究的 焦 点 (Lal, 2004;Yang et al, 2021), 特别是在大气氮沉降增加 的背景下。 草原是地球上分布最广的植被类型 (Scurlock et al, 2002), 也是温室气体排放的热点地区(IPCC, (Tang et al, 2019)。 刈割作为草原上广泛采用的草地 利用方式, 通过移走过度生长的植物生物量和其中 的氮, 被认为可以缓解氮沉降增加对温室气体排 放的影响。此外, 刈割还可以减少地表枯枝落叶的 积累 (Collins et al, 1998), 改变土壤表面温度、土壤 含水量和微生物活动等 (Bahn et al, 2006;Zhou et al, 2007) 态。放置暗箱前, 面向风口平稳晃动, 以使箱内气 体与大气平衡。 顶箱扣于基座后立即进行第一次取 样。利用三通阀和100 mL一次性注射器抽取100 mL 气体, 将取样气体注入100 mL铝箔气袋保存。此后…”