Nano-Scale Zero Valent Iron (nZVI) Priming Enhances Yield, Alters Mineral Distribution and Grain Nutrient Content of Oryza sativa L. cv. Gobindobhog: A Field Study

Abstract

In recent decades, nano-scale zero valent iron is reported to have plant growth enhancement capacity under laboratory conditions, but till date, there is no report to highlight its effect on the growth and yield of field-grown plants. In this study, we have evaluated the potential of nZVI priming on rice yield. A two-year field study has been conducted with different concentrations (10, 20, 40, and 80 mg l^-1) of nZVI for seed priming. The efficacy of nanopriming was compared with the hydroprimed control set. Seeds were treated for 72 h and sown in nursery beds and after 30 days seedlings were transplanted in the field. Root anatomy and morphology were studied in 7 days old seedlings where no changes were found. RAPD analysis also confirmed that low doses of nZVI were not genotoxic. Nanoprimed plants also had broader leaves, higher growth, biomass, and tiller number than control plants. Maximum yield was obtained from the 20 mg l^-1 nZVI primed set (3.8 fold higher than untreated control) which is achieved primarily because of the increase in fertile tiller numbers (two fold higher than untreated control). Higher values of other agronomic parameters like growth rate, net assimilation rate proved that nZVI priming enhanced photosynthetic efficiency and helped in the proper storage of photo-assimilates. All these attributed to increased accumulation of phytochemicals like starch, soluble sugar, protein, lipid, phenol, riboflavin, thiamine, and ascorbic acid in the grains. The elemental analysis confirmed that nZVI priming also promoted higher accumulations of macro and micronutrients in grains. Thus, nanoprimed seeds showed better crop performance compared to the traditional hydropimed seeds. Hence, nZVI can be considered as 'pro-fertilizer' and can be used commercially as a seed treatment agent which is capable of boosting plant growth and yield along with minimum interference to the soil ecosystem.

Supplementary information: The online version contains supplementary material available at 10.1007/s00344-021-10335-0.

Keywords: Agronomic traits; Grain nutrient; Nano-scale zero valent iron; Rice; Seed priming; Yield.

Fig. 1

a Localization of iron in the embryonic region of nZVI primed seeds after Perl’s Prussian blue staining. (EM embryo, End endosperm). b EDX data of root tip surface of 7 days old seedlings treated with 0–80 mg l⁻¹nZVI

Fig. 2

Scanning electron micrograph of 7 days old rice seedlings A, B, C, D, and E represents control, 10, 20, 40, and 80 mg l⁻¹nZVI primed seedling root vascular tissue after transverse sections (EN endodermis, PR pericycle, PH phloem, MX metaxylem, CMX central metaxylem)

Fig. 3

Influence of nZVI treatment on RAPD profiles of 7 days old rice root tissue (► indicates the disappearance of the band)

Fig. 4

Photographic images of a 60 days old rice seedlings and b panicles of 0–80 mg l⁻¹ nZVI primed sets

Fig. 5

Influence of seed priming with different concentrations of nZVI on a plant height, b leaf area, c effective tiller number, d biomass. of rice plants after maturity. Data represent the mean of five replicates and error bars represent standard error. Means with the same letters are not significantly different (Tukey’s HSD multiple comparisons at p ≤ 0.05). Significant differences between session 2018 and 2019 plants are indicated by symbol ‘*’ as obtained from unpaired t test analysis

Fig. 6

Influence of seed priming with different concentrations of nZVI on a AGR, b CGR, c NAR of rice plants after maturity (1st harvest—on 30 DAS, 2nd harvest—on 60 DAS, 3rd harvest—at maturity). Data represent the means of five replicates and error bars represent standard error. Means with the same letters are not significantly different (Tukey’s HSD multiple comparisons at p ≤ 0.05). Significant differences between session 2018 and 2019 plants are indicated by symbol ‘*’ as obtained from unpaired t test analysis

Fig. 7

Influence of seed priming with different concentrations of nZVI on panicle characters like a Panicle number per m², b panicle length, c panicle weight, d total seed per panicle. Data represent the mean of five replicates and error bars represent standard error. Means with the same letters are not significantly different (Tukey’s HSD multiple comparisons at p ≤ 0.05). Significant differences between session 2018 and 2019 plants are indicated by symbol ‘*’ as obtained from unpaired t test analysis

Fig. 8

Influence of seed priming with different concentrations of nZVI on yield-related traits; a percentage of hollow grains, b grain density, c seed weight per 100 seeds, d.Yield (kg m⁻²). Data represent the mean of five replicates and error bars represent standard error. Means with the same letters are not significantly different (Tukey’s HSD multiple comparisons at p ≤ 0.05). Significant differences between session 2018 and 2019 plants are indicated by symbol ‘*’ as obtained from unpaired t test analysis

Fig. 9

Influence of seed priming with different concentrations of nZVI on primary metabolite levels in rice grains a starch, b soluble sugar, c protein, d lipid. Data represents data of 3 replicates. Data with the same letters are not significantly different (Tukey’s HSD multiple comparisons at p ≤ 0.05). Significant differences between session 2018 and 2019 plants are indicated by symbol ‘*’ as obtained from unpaired t test analysis

Fig. 10

Influence of seed priming with different concentrations of nZVI on secondary metabolite levels in rice grains a phenol, b riboflavin, c thiamine, d Ascorbic acid. Data represents data of 3 replicates. Data with the same letters are not significantly different (Tukey’s HSD multiple comparisons at p ≤ 0.05). Significant differences between session 2018 and 2019 plants are indicated by symbol ‘*’ as obtained from unpaired t test analysis

Fig. 11

Influence of seed priming with different concentrations of nZVI on macronutrient levels in rice grains a S, b Ca, c Mg, d P and e K. Data represent data of 3 replicates. Data with the same letters are not significantly different (Tukey’s HSD multiple comparisons at p ≤ 0.05). Significant differences between session 2018 and 2019 plants are indicated by symbol ‘*’ as obtained from unpaired t test analysis

Fig. 12

Influence of seed priming with different concentrations of nZVI on macronutrient levels in rice grains a Mn, b Zn, and c Fe. Data represents data of 3 replicates. Data with the same letters are not significantly different (Tukey’s HSD multiple comparisons at p ≤ 0.05). Significant differences between session 2018 and 2019 plants are indicated by symbol ‘*’ as obtained from unpaired t test analysis

Fig. 13

Agronomic traits correlation analyses. a, b Pearson’s correlation analysis of 12 agronomic characters obtained after maturity for session 2018 and 2019 respectively. C-D. Pearson’s correlation analysis of 7 agronomic characters obtained from seedlings for session 2018 and 2019 respectively for rice plants cultivated after nanopriming seeds with different concentrations of nZVI. Solid lines represent a significant positive correlation and dashed lines represent a significant negative correlation. Thinner lines indicate significance at the 0.05 level and thicker lines indicate significance at the 0.01 level (Ht: Plant height, Bm: biomass, LA: leaf area, Et: effective tiller number, Pn: total panicle number per m⁻², PL: panicle length, Pw: panicle weight, Gd: grain density, Sp: number of seed per panicle, Sw: seed weight, FEP: final emergence percentage, RL: root length, SL: shoot length. MET: mean emergence time, FL: flowering time, Mt: maturity time, and Yd: total yield)

Fig. 14

Pearson’s correlation analysis of 8 mineral concentrations in grains (a i–ii), shoot (b i–ii), and root (c i–ii), of rice plants grown for session 2018 and 2019 respectively after nanopriming seeds with different concentrations of nZVI. Solid lines represent a significant positive correlation and dashed lines represent a significant negative correlation. Thinner lines indicate significance at the 0.05 level and thicker lines indicate significance at the 0.01 level