The characteristics of soil N transformations regulate the composition of hydrologic N export from terrestrial ecosystem

Abstract

It is important to clarify the quantity and composition of hydrologic N export from terrestrial ecosystem and its primary controlling factors, because it affected N availability, productivity, and C storage in natural ecosystems. The most previous investigations were focused on the effects of N deposition and human disturbance on the composition of hydrologic N export. However, few studies were aware of whether there were significant differences in the concentrations and composition of hydrologic N export from natural ecosystems in different climate zones and what is the primary controlling factor. In the present study, three natural forest ecosystems and one natural grassland ecosystem that were located in different climate zones and with different soil pH range were selected. The concentrations of total dissolved N, dissolved organic nitrogen (DON), NH4+, NO3− in soil solution and stream water, soil properties, and soil gross N transformation rates were measured to answer above questions. Our results showed that NO3− concentrations and the composition pattern of hydrologic N export from natural ecosystems varied greatly in the different climate zones. The NO3− concentrations in stream water varied largely, ranging from 0.1 mg N L−1 to 1.6 mg N L−1, while DON concentration in stream water, ranging from 0.1 to 0.9 mg N L−1, did not differ significantly, and the concentrations of NH4+ were uniformly low (average 0.1 mg N L−1) in all studied sites. There was a trade‐off relationship between the proportions of NO3− and DON to total dissolved N in stream water. In subtropical strongly acidic forests soil site, DON was the dominance in total dissolved N in stream water, while NO3−‐N became dominance in temperate acidic forests soil site, subtropical alkaline forests soil region, and the alpine meadow sites on the Tibetan Plateau. The proportions of NO3− to total dissolved N in both soil solution and stream water significantly increased with the increasing of the gross autotrophic nitrification rates (p < 0.01). Our results indicated that the characteristics of soil N transformations were the most primary factor regulating the composition of hydrologic N losses from ecosystems. The nitrification was the central soil N transformation processes regulating N composition in soil solution and hydrologic N losses. These results provided important information on understanding easily the composition of hydrologic N export from terrestrial ecosystem.

Terrestrial N cycling associated with climate and plant‐specific N preferences: a review

“…Furthermore, the nitrification process plays a central role in regulating the composition of mineral N (e.g. the ratio of NO 3 − to NH 4 + ) in soil (Zhang et al ., ). For O NH4 /M > 0.5, NO 3 − ‐N is the dominant inorganic N form, whereas with O NH4 /M < 0.5, NH 4 + ‐N is generally the more abundant (Schimel & Bennett, ; Zhang et al ., ).…”

“…The medians of gross rates of soil N transformations in different wet and dry climate zones: rates of (a) mineralization, (b) immobilization of NH 4 + , (c) heterotrophic nitrification, (d) oxidation of NH 4 + to NO 3 − and (e) immobilization of NO 3 − , and (f) ratio of rates of oxidation of NH 4 + to NO 3 − to gross rate of N mineralization. Data are cited from 16 publications (Zhang et al , 2013a; Zhang et al , ; Wang et al , ; Zhang et al , ; Gao et al , ; Huygens et al , ; Huygens et al , ; Rütting et al , ; Staelens et al , ; Zhang et al , ; Müller et al , ; Rütting & Müller, 2008; Müller et al , ; Müller et al , ; Gao et al , ; Wang et al , a) (Table S1, Supporting Information). Most data were obtained within China, but other data were measured in Germany, Chile, Belgium and Northern Ireland.…”

“…Numerous investigations and reviews have focused on controlling soil gross N transformations (Booth et al ., ; Zhang et al ., 2013a; Cheng et al ., ; Wang et al ., ); therefore, we do not address this in the present review. We focus on the connection between soil N transformations and N fate, specifically N‐use efficiency (NUE), N leaching and soil N retention (Zhang et al ., ). We discuss the inherent connections between soil gross N transformations, species‐specific N preferences and climate, and emphasize the role of these three aspects in enhancing NUE and minimizing environmental impacts.…”

“…Thus, we need to maximize the benefits of Nr while minimizing the negative effects on the environment (Galloway et al ., ). The fate of soil N often depends on N status and flux, and its chemical forms, which are primarily regulated by the rate of soil N biogeochemical processes (Houlton et al ., ; Galloway et al ., ; Rennenberg et al ., ; Zhang et al ., ,b). The interplay of simultaneous rates of N transformation regulates the availability and dynamics of Nr in the soil.…”

Nitrogen leaching from natural ecosystems under global change: a modelling study

“…Ammonium is much less susceptible to leaching since soils generally have a much higher capacity for retaining cations than anions. As a result, inorganic N losses occur mainly in the form of nitrate and its formation by nitrification is an important control for leaching losses (Zhang et al, 2016). Since plants and microbes preferentially take up ammonium over nitrate, nitrification rates are usually low in N-limited ecosystems.…”