The preference of nitrate uptake in Chinese prickly ash estimated by δ15N values and cation concentrations

et al. 2019

Preprint

Abstract. Metallic nutrients play a vital role in plant physiological and biochemical processes such as nitrogen uptake and assimilation, which cause isotopic fractionation against 15N. Thus, investigating the relationships between leaf nitrogen isotope ratio (&#948;15N) and leaf metallic nutrients could enhance our understanding of nitrogen (N) cycling. However, to our knowledge, these relationships have not been examined as yet. To fill in this research gap, we analyzed leaf &#948;15N and leaf potassium (K), Calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn) and zinc (Zn) contents of 624 non-N2-fixing plant samples and revealed the relationships between leaf &#948;15N and these metallic elements. Overall, leaf &#948;15N correlated positively with leaf K, Ca, Mg and Zn, and negatively with leaf Fe, whereas not with leaf Mn. The relationships of leaf &#948;15N with leaf K, Ca, Mg, Zn and Fe were not affected by both vegetation type and soil type, suggesting that the observed relationships could be universally valid. However, the relationship between leaf &#948;15N and leaf Mn depended on vegetation type and soil type, therefore, the observed relationship should not be considered to be universal. These metallic nutrients together accounted for 55.7&#8201;% of the variations in leaf &#948;15N; this emphasized the significance of metallic nutrients in determining leaf &#948;15N.

Section: Discussionmentioning

confidence: 93%

Relationships between leaf δ15N and leaf metallic nutrients

Chen

et al. 2019

Preprint

“…Xia et al (2021) found older stands accumulate N in biomass comparatively slowly than younger stands, resulting in a net gain of TON in topsoil and higher ION availability in the older stands. Higher NO 3 − ‐N content in Z. bungeanum stands was observed in the subsoil than topsoil because Z. bungeanum is an N demanding species and preferentially uptakes NO 3 − ‐N from shallow soil layers 0–40 cm (Zhou et al, 2020; Piao et al, 2017). While subsequent decline at 60–100 cm depth suggests lower risks of NO 3 − ‐N leaching to the groundwater (Figure 2).…”

Section: Discussionmentioning

confidence: 99%

“…-N content in Z. bungeanum stands was observed in the subsoil than topsoil because Z. bungeanum is an N demanding species and preferentially uptakes NO 3 À -N from shallow soil layers 0-40 cm (Zhou et al, 2020;Piao et al, 2017). While subsequent decline at 60-100 cm depth suggests lower risks of NO 3 À -N leaching to the groundwater (Figure 2).…”

mentioning

confidence: 98%

Post‐farmland conversion spatio‐temporal dynamics of net soil nitrogen mineralization and availability in a chronosequence of Zanthoxylum bungeanum plantations

Saba

et al. 2022

Land Degrad Dev

Afforestation on cultivated farmlands causes major shifts in the nitrogen (N) cycle. The consequences of large‐scale Zanthoxylum bungeanum afforestation on spatio‐temporal patterns of soil N mineralization and inorganic N (ION) availability have not been reported. Moreover, the regulatory roles of microbial biomass and soluble organic N (MBN and SON) in the N cycle are poorly characterized in soils below 20 cm. To investigate the long‐term effects of afforestation on the governing mechanism of vertical N dynamics, a 0–100 cm soil profile was collected from a chronosequence of Z. bungeanum plantations aged 8‐year (H8), 15‐year (H15), 20‐year (H20) and 28‐year (H28), as well as adjacent farmland and abandoned‐land (28‐year) as controls in an arid valley in Southwest China. With increasing stand age, conversion of farmland to Z. bungeanum plantations significantly improved soil organic carbon, available nutrients, and all N forms. These impacts were more evident in the topsoil (0–20 cm) than in the subsoil layers. MBN and SON contents improved by 1.42‐fold and 1.34‐fold in H28, respectively, compared to H8. Net N mineralization (1.31‐fold), net nitrification rates (1.30‐fold), and total ION (1.31‐fold) content followed similar trends of increase along with the stand age. Correlation and redundancy analysis also established a positive relationship and demonstrated that increased ION availability is due to improved MBN, SON, and urease activity with the plantations age. Although the nitrate‐N content was highest in abandoned‐land, its content also increased steadily in Z. bungeanum plantations with the stand age. A relatively low ammonium/nitrate ratio (0.331) in H28 advocated improved N supply via nitrification as well as low N leaching risks from plantations. The spatial investigation provided novel insights into controls of N cycle and suggested converting farmland to Z. bungeanum plantations is a suitable approach for restoring soil N.

“…Manganese (Mn) is a cofactor and activator of nitrite reductase, 24 while zinc (Zn) is involved in protein synthesis 25 . Thus, the levels of these metallic elements were found to correlate with the N content in plants 26,27 . Because the leaf N content is significantly correlated with leaf δ 15 N values, 9 we hypothesized that the levels of leaf metallic elements would correlate with leaf δ 15 N values.…”

Section: Introductionmentioning

confidence: 99%

Relationships between leaf δ¹⁵N and leaf metallic nutrients

Chen

Rapid Comm Mass Spectrometry

et al. 2020

Rationale Nitrogen (N) isotopic ratios (δ15N values) of plants are primarily determined by the δ15N values of their N sources. Metallic nutrients affect plant N uptake. However, there is little knowledge of the relationships between leaf δ15N values and leaf metallic nutrients. The δ15N values are often lower in soil nitrate (NO3−) than in ammonium (NH4+) due to large isotopic fractionation during nitrification. Plants acquire more NO3− than NH4+ when accumulating high potassium (K), calcium (Ca) and magnesium (Mg) to maintain charge balance. In addition, plants that absorb more NO3− than NH4+ increase the soil pH and decrease the availability of iron (Fe), manganese (Mn) and zinc (Zn). We therefore hypothesized that leaf δ15N values correlate negatively with K, Ca and Mg contents, while positively with Fe, Mn and Zn contents. Methods Leaves of non‐N‐fixing plants were sampled across an approx. 6000 km transect in China and their δ15N values and metallic nutrient content were determined using elemental analyzer/isotope ratio mass spectrometry. Results Inconsistent with the hypothesis, leaf δ15N values correlated positively with leaf K, Ca and Mg, indicating higher δ15N values of soil NO3− than NH4+. Higher δ15N values of soil NO3− revealed stronger denitrification than nitrification in the study regions because isotopic fractionation occurs during both processes. Leaf δ15N values correlated negatively with Fe, relating to decreases in soil Fe availability, which might be attributed to oxidation of Fe2+ to Fe3+ supplying electrons for denitrification, while greater uptake of NO3− than NH4+ of plants increases soil pH. Leaf δ15N values correlated positively with Zn and did not correlate with Mn. These observed relationships between leaf δ15N values and metallic nutrients, except Mn, were independent of vegetation or soil types. Conclusions This study has enriched our knowledge of associations between metallic nutrients and N cycling in plant–soil systems, especially for the roles of Fe in soil N transformations and K, Ca and Mg in plant N uptake.