Low-Temperature Plasma-Assisted Nitrogen Fixation for Corn Plant Growth and Development

Abstract

Nitrogen fixation is crucial for plants as it is utilized for the biosynthesis of almost all biomolecules. Most of our atmosphere consists of nitrogen, but plants cannot straightforwardly assimilate this from the air, and natural nitrogen fixation is inadequate to meet the extreme necessities of global nutrition. In this study, nitrogen fixation in water was achieved by an AC-driven non-thermal atmospheric pressure nitrogen plasma jet. In addition, Mg, Al, or Zn was immersed in the water, which neutralized the plasma-treated water and increased the rate of nitrogen reduction to ammonia due to the additional hydrogen generated by the reaction between the plasma-generated acid and metal. The effect of the plasma-activated water, with and without metal ions, on germination and growth in corn plants (Zea Mays) was investigated. The germination rate was found to be higher with plasma-treated water and more efficient in the presence of metal ions. Stem lengths and germination rates were significantly increased with respect to those produced by DI water irrigation. The plants responded to the abundance of nitrogen by producing intensely green leaves because of their increased chlorophyll and protein contents. Based on this report, non-thermal plasma reactors could be used to substantially enhance seed germination and seedling growth.

Keywords: chlorophyll; germination rate; non-thermal atmospheric pressure nitrogen plasma; plasma-activated water; plasma-assisted nitrogen fixation; proteins; seedling growth.

Figure 1

Schematic representation of the experiment design.

Figure 2

(a) Typical current and voltage waveforms of the plasma discharge. (b) Corresponding Q–V Lissajous figure. (c) The energy consumption for ammonia synthesis with various metal immersed in water. (d) Optical emission spectroscopy (OES) results for the nitrogen plasma measured at a position 3 mm downstream of the nozzle of the quartz tube. Applied voltage, 10 kV; Frequency, 33 kHz; Working gas, nitrogen.

Figure 3

Germination of corn seeds watered with DI water, PAW, PAW with Zn (Zn-PAW), PAW with Al (Al-PAW), or PAW with Mg (Mg-PAW) after sowing on cotton. (a) Photograph of Seedling growth on the 4th day after sowing. (b) Average germination rate at the end of the 2nd, 3rd, 4th, and 5th days after sowing.

Figure 4

The effect of watering corn plants with DI water, PAW, PAW with Zn (Zn-PAW), PAW with Al (Al-PAW), and PAW with Mg (Mg-PAW). (a) Photograph of sample plants watered with various activated waters and the control treatment (DI water) depicting growth on the 9th day. (b) Average stem length (including leaf) on days 6, 7, 8, and 9.

Figure 5

(a) Photograph of corn plants and (b) average shoot (including leaf) and root lengths on the 10th day after sowing on vermiculite, and after soaking in DI water, only PAW, PAW with Zn (Zn-PAW), PAW with Al (Al-PAW), or PAW with Mg (Mg-PAW). The symbol * is for t-test result which rejects the null hypothesis at the 5% significance level.

Figure 6

Average dry weight of shoot and roots after the 10th day of soaking in DI water, PAW, PAW with Zn (Zn-PAW), PAW with Al (Al-PAW), or PAW with Mg (Mg-PAW). The symbol * is for t-test result above the 5% significance level.

Figure 7

(a) Chlorophyll content in leaves and (b) total soluble protein content in leaves and roots of fresh corn plants after the 10th day of soaking in DI water, PAW, PAW with Zn (Zn-PAW), PAW with Al (Al-PAW), or PAW with Mg (Mg-PAW). The symbol * represents a t-test result with a significance level greater than 5%.

Figure 8

(a) NO${}_3$-N (b) NH${}_3$ or NH${}_4^{+}$ present in the root and shoot tissues of dry corn plants after the 10th day of soaking in DI water, PAW, PAW with Zn (Zn-PAW), PAW with Al (Al-PAW), or PAW with Mg (Mg-PAW). The symbol * is for t-test result above the 5% significance level.

Figure 9

Spatial distribution of NO below the nozzle of the quartz tube.

Figure 10

Chemical pathways of plasma-assisted nitrogen fixation and acid neutralization.

Figure 11

Schematics showing general nitrogen assimilation in the roots and leaves of plants and the chemical structures of chlorophyll and amino acids.

Figure 12

(a) Schematic of the atmospheric-pressure nitrogen plasma jet. (b) Photograph of the plasma source.