Global patterns of soil gross immobilization of ammonium and nitrate in terrestrial ecosystems

Abstract

Microbial nitrogen (N) immobilization, which typically results in soil N retention but based on the balance of gross N immobilization over gross N production, affects the fate of the anthropogenic reactive N. However, global patterns and drivers of soil gross immobilization of ammonium (INH4) and nitrate (INO3) are still only tentatively known. Here, we provide a comprehensive analysis considering gross N production rates, soil properties, and climate and their interactions for a deeper understanding of the patterns and drivers of INH4 and INO3. By compiling and analyzing 1966 observations from 274 15N‐labelled studies, we found a global average of INH4 and INO3 of 7.41 ± 0.72 and 2.03 ± 0.30 mg N kg−1 day−1 with a ratio of INO3 to INH4 (INO3:INH4) of 0.79 ± 0.11. Soil INH4 and INO3 increased with increasing soil gross N mineralization (GNM) and nitrification (GN), microbial biomass, organic carbon, and total N and decreasing soil bulk density. Our analysis revealed that GNM and GN were the main stimulators for INH4 and INO3, respectively. The structural equation modeling showed that higher soil microbial biomass, total N, pH, and precipitation stimulate INH4 and INO3 through enhancing GNM and GN. However, higher temperature and soil bulk density suppress INH4 and INO3 by reducing microbial biomass and total N. Soil INH4 varied with terrestrial ecosystems, being greater in grasslands and forests, which have higher rates of GNM, than in croplands. The highest INO3:INH4 was observed in croplands, which had higher rates of GN. The global average of GN to INH4 was 2.86 ± 0.31, manifesting a high potential risk of N loss. We highlight that anthropogenic activities that influence soil properties and gross N production rates likely interact with future climate changes and land uses to affect soil N immobilization and, eventually, the fate of the anthropogenic reactive N.

Nitrogen fertilization weakens the linkage between soil carbon and microbial diversity: A global meta‐analysis

“…In managed ecosystems, available N for plants and microbes mainly comes from N fertilization (Carrara et al, 2018; Li et al, 2019; Louca et al, 2018). Nitrogen deposition and fertilization are important sources of N that alleviate N limitations in terrestrial ecosystems on a global scale (Elrys, Ali, et al, 2021; Elrys et al, 2022; Yu et al, 2019). The rate of atmospheric N deposition has been predicted to increase by 2.5 times worldwide in the next century (IPCC, 2014).…”

“…Increased N deposition and N fertilization increase N losses to the environment. For example, recent meta‐analysis studies showed that increased N input increases the potential risk of N loss in different ecosystems (Chen et al, 2019; Elrys et al, 2022; Yu et al, 2019), and the N imbalance will become worse in the future.…”

Inhibition of Elevated Atmospheric Carbon Dioxide to Soil Gross Nitrogen Mineralization Aggravated by Warming in an Agroecosystem

“…For instance, elevated CO 2 may increase soil total N (TN) 17 and thus likely promote gross N mineralization, 18 but soil organic carbon (SOC) 19 increases simultaneously, which could enhance ammonium (NH 4 + ) immobilization into microbial biomass. 20 Therefore, the net NH 4 + production rate may not be affected while the rate of overall NH 4 + turnover may increase, resulting in a more active and dynamic system. 21 As a result, it is important to quantify soil gross N transformation rates in response to elevated CO 2 and temperature.…”

“…Although net N transformation rates can provide the proxy of N availability, they only represent the outcome of multiple simultaneously occurring gross N transformation rates and thus fail to offer a mechanistic understanding of how climate change factors affect specific N transformation pathways in soils. For instance, elevated CO 2 may increase soil total N (TN) and thus likely promote gross N mineralization, but soil organic carbon (SOC) increases simultaneously, which could enhance ammonium (NH 4 + ) immobilization into microbial biomass . Therefore, the net NH 4 + production rate may not be affected while the rate of overall NH 4 + turnover may increase, resulting in a more active and dynamic system .…”

Reduced nitrogen losses from drained temperate agricultural peatland after mineral soil coverage

“…Higher soil 15 N recovery at Cov might be due to a higher microbial 15 N uptake. Microbial N use is positively correlated with soil substrate availability and soil pH (Elrys et al 2022). Compared with Ref, the SOM pool from Cov is small (Table 1), but relatively young and labile as previous shown from a 14 CO 2 measurement on the same site (Wang et al 2021).…”