Abstract
With the continuous increase in atmospheric carbon dioxide emissions, nitrogen (N) and phosphorus (P) as mineral elements increasingly restrict plant growth. To explore the effect of deficiency of P and N on growth and physiology, Fraxinus mandshurica (hereafter “F. mandshurica”) Rupr. annual seedlings of Wuchang (WC) provenance with fast growth and Dailing (DL) provenance with slow growth were treated with complete nutrition or starvation of N (N-), P (P-) or both elements (NP-). Although P- and N- increased the use efficiency of P (PUE) and N (NUE), respectively, they reduced the leaf area, chlorophyll content and activities of N assimilation enzymes (NR, GS, GOGAT), which decreased the dry weight and P or N amount. The free amino acid content and activities of Phosphoenolpyruvate carboxylase (PEPC) and acid phosphatase enzymes were reduced by N-. The transcript levels of NRT2.1, NRT2.4, NRT2.5, NRT2.7, AVT1, AAP3, NIA2, PHT1-3, PHT1-4 and PHT2-1 in roots were increased, but those of NRT2.1, NRT2.4, NRT2.5, PHT1-3, PHT1-4, PHT2-1 and AAP3 in leaves were reduced by P-. WC was significantly greater than DL under P- in dry weight, C amount, N amount, leaf area, PUE, NUE, which related to greater chlorophyll content, PEPC enzyme activity, N assimilation enzyme activities, and transcript levels of N and P transporter genes in roots and foliage, indicating a greater ability of WC to absorb, transport and utilize N and P under P-. WC was also greater than DL under N- in terms of the above indicators except the transcript levels of N and P assimilation genes, but most of the indicators did not reach a significant level, indicating that WC might be more tolerant to N- than DL, which requires further verification. In summary, WC was identified as a P-efficient provenance, as the growth rate was greater for the genetic type with high than low tolerance to P-.
Highlights
With the continuous increase in atmospheric carbon dioxide emissions, among the three major chemical elements—carbon (C), nitrogen (N) and phosphorus (P)—required for plant growth, N and P [1,2,3] as mineral elements increasingly restrict plant growth.N is the mineral element with the greatest demand for plant growth and development, and it is the basic component of macromolecules such as protein, nucleic acid and chlorophyll
Nitrate N is transported from the soil to the cells by root nitrate transporters (NRTs) and ammonium is carried out using ammonium transporters (AMTs) through active transport, respectively
The absorption of nitrate ions by roots is mainly performed by NRT2.1 [6], and AtNRT2.4, which is reduced by N starvation, will absorb some nitrate ions [7]
Summary
With the continuous increase in atmospheric carbon dioxide emissions, among the three major chemical elements—carbon (C), nitrogen (N) and phosphorus (P)—required for plant growth, N and P [1,2,3] as mineral elements increasingly restrict plant growth.N is the mineral element with the greatest demand for plant growth and development, and it is the basic component of macromolecules such as protein, nucleic acid and chlorophyll. In forests with short rotation period and rapid growth, the demand for N is large, and N deficiency is the main nutrient element that restricts plant growth [4]. There are two main forms of nitrogen absorption by plants: nitrate N and ammonium N. Nitrate N is transported from the soil to the cells by root nitrate transporters (NRTs) and ammonium is carried out using ammonium transporters (AMTs) through active transport, respectively. The absorption of nitrate ions by roots is mainly performed by NRT2.1 [6], and AtNRT2.4, which is reduced by N starvation, will absorb some nitrate ions [7]. The transcript levels of AtNRT2.7 are smaller in roots than in shoots [8]. High transcript levels of AtNRT2.7 have been detected in Arabidopsis seeds [9,10]. OsNRT2.4 is a dual-affinity nitrate transporter [13]
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