Distinct effect of pH on N uptake and assimilation in two conifer species

Abstract

Key message Prince Rupprecht's Larch from the Loess Plateau takes up and assimilates a greater proportion of N as NO 3 2 , particularly at neutral pH, whereas Chinese Fir assimilates a greater proportion of N as NH 4 1 , particularly at low pH levels.Abstract The effects of pH on nitrate and ammonium uptake and assimilation in two coniferous species were compared. Prince Rupprecht's Larch (Larix principis-rupprechtii Mayr) grows on the loess plateau in alkaline soils with low available nitrogen (N), whereas Chinese Fir (Cunninghamia lanceolata) grows in acidic soils. In the present study, the net fluxes in ammonium (NH 4 ? ) and nitrate (NO 3 2 ) were measured using a non-invasive microelectrode ion flux measurement system, and the expression of NH 4 ? and NO 3 2 transporters (AMTs and NRTs, respectively) as well as H ? -ATPase was examined to provide insights into the N uptake mechanisms in Prince Rupprecht's Larch and Chinese Fir. The enzyme assays involved in N assimilation were also determined. For Prince Rupprecht's Larch, low pH (pH 4) resulted in a decrease in net ammonium uptake, which remained unchanged in Chinese Fir. Net nitrate uptake in Prince Rupprecht's Larch and Chinese Fir was much lower in soils with pH 4 relative to those with pH 7. Low pH significantly decreased the H ? -ATPase activity and the expression level of NRTs in roots of Prince Rupprecht's Larch. However, the expression level of AMTs in Prince Rupprecht's Larch was significantly higher at pH 7 than at pH 4. The H ? -ATPase activity in roots of Chinese Fir remained unaltered in response to changes in pH, and the transcript abundances of AMTs and NRTs were down-regulated by low pH. Low pH decreased N assimilation in both conifer species with the exception of NH 4 ? assimilation in Chinese Fir, which displayed higher glutamine synthetase (GS) and glutamate synthetase (GOGAT activities) at low pH. Prince Rupprecht's Larch from the Loess Plateau takes up and assimilates a greater proportion of N as NO 3 2 , particularly at neutral pH, whereas Chinese Fir assimilates a greater proportion of N as NH 4 ? , particularly at low pH levels. This study contributes to our understanding of nitrogen metabolism mechanisms in response to pH changes.

Soil Type Influences Rhizosphere Bacterial Community Assemblies of Pecan Plantations, a Case Study of Eastern China

“…This result was different from the results reported by Huang et al [34]. Different forms of nitrogen have significant impacts on the pH of the plant root environment [35]; alkaline medium is conducive to the absorption of NH4 + by plant roots and reduces the content of NH4 + -N in soil [36]. Therefore, the high concentration of NH4 + -N in the rhizosphere soil reduced the pH, and some microbiomes could not adapt to the acidic environment, resulting in a decrease in diversity.…”

Morphological and physiological responses of Picea asperata to different nitrogen availability and pH

“…This was also found for other plants such as Picea abies (Peuke and Tischner, 1991), wheat (Zsoldos et al, 1999), Chinese fir (Meng et al, 2016), Douglas fir, Pinus contorta and soybean (Hawkins and Robbins, 2010). Furthermore, P. asperata, regardless of N availability and pH, always exhibited a greater uptake of NH þ 4 in compare to that of NO À 3 , which is in line with previous results that the preference of conifers would be NH þ 4 (Lucash et al, 2005;Meng et al, 2016). This result might be partly explained by the fact that the NH þ 4 preference of P. asperata may be an adaptive strategy to the greater availability of NH þ 4 in forest soils.…”

“…5a, d), because NO À 3 uptake is directly associated with the reduction rate of NO À 3 to nitrite (Calatayud et al, 2008). This was also found for other plants such as Picea abies (Peuke and Tischner, 1991), wheat (Zsoldos et al, 1999), Chinese fir (Meng et al, 2016), Douglas fir, Pinus contorta and soybean (Hawkins and Robbins, 2010). Furthermore, P. asperata, regardless of N availability and pH, always exhibited a greater uptake of NH þ 4 in compare to that of NO À 3 , which is in line with previous results that the preference of conifers would be NH þ 4 (Lucash et al, 2005;Meng et al, 2016).…”

Distinct Carbon and Nitrogen Metabolism of Two Contrasting Poplar Species in Response to Different N Supply Levels

“…A non-invasive micro-test technique (NMT), a powerful tool in the investigation of in situ ion fluxes, has been widely used to explore the electrophysiological processes of nitrogen acquisition at the root surface [ 16 ]. Spatial and temporal dynamics of net ion fluxes and influences of environmental factors such as pH in the media on net ion fluxes have been reported for roots of maize, barley, rice, poplar, and species of eucalyptus and coniferous [ 3 , 17 , 18 , 19 ]. Additionally, many studies assume that 15 N at natural abundance levels acts as a tracer, and significant discrimination has been observed for plants [ 20 ].…”