Growth and Photosynthetic Activity of Selected Spelt Varieties (Triticum aestivum ssp. spelta L.) Cultivated under Drought Conditions with Different Endophytic Core Microbiomes

Abstract

The role of the microbiome in the root zone is critically important for plants. However, the mechanism by which plants can adapt to environmental constraints, especially water deficit, has not been fully investigated to date, while the endophytic core microbiome of the roots of spelt (Triticum aestivum ssp. spelta L.) grown under drought conditions has received little attention. In this study, we hypothesize that differences in the endophytic core of spelt and common wheat root microbiomes can explain the variations in the growth and photosynthetic activity of those plants, especially under drought conditions. Our greenhouse experimental design was completely randomized in a 2 × 4 × 3 factorial scheme: two water regime levels (well-watered and drought), three spelt varieties (T. aestivum ssp. spelta L.: 'Badenstern', 'Badenkrone' and 'Zollernspelz' and one wheat variety: T. aestivum ssp. vulgare L: 'Dakotana') and three mycorrhizal levels (autoclaved soil inoculation with Rhizophagus irregularis, control (autoclaved soil) and natural inoculation (non-autoclaved soil-microorganisms from the field). During the imposed stress period, relative water content (RWC), leaf chlorophyll fluorescence, gas exchange and water use efficiency (WUE) were measured. Microscopic observations of the root surface through fungi isolation and identification were conducted. Our results indicate that 'Badenstern' was the most drought tolerant variety, followed by 'Zollernspelz' and 'Badenkrone,' while the common wheat variety 'Dakotana' was the most drought sensitive. Inoculation of 'Badenstern' with the mycorrhizal fungi R. irregularis contributed to better growth performance as evidenced by increased whole plant and stalk dry matter accumulation, as well as greater root length and volume. Inoculation of 'Zollernspelz' with arbuscular mycorrhizal fungi (AMF) enhanced the photochemical efficiency of Photosystem II and significantly improved root growth under drought conditions, which was confirmed by enhanced aboveground biomass, root dry weight and length. This study provides evidence that AMF have the potential to be beneficial for plant growth and dry matter accumulation in spelt varieties grown under drought conditions.

Keywords: abiotic stress; arbuscular mycorrhizal (AM); chlorophyll fluorescence; fungal diversity; photosynthesis.

Figure 1

Comparable reaction between the physiological state of the plant, dry matter accumulation in the plant and root system in the common wheat variety ‘Dakotana’ (D), and spelt wheat varieties ‘Badenstern’ (B), ‘Badenkrone’ (BK) and ‘Zollernspelz’ (Z) under two water regimes (well-watered, drought). * Abbreviation as in Table 1: 1. Fv/Fm, 2. Y, 3. E., 4. A, 5. WUE, 6. Sk, 7. Sp, 8. l, 9. Ab, 10. v, 11. ETR, 12. R, 13. RWC, 14. rc. Scale represents high value (in yellow tint) to low value (in blue tint).

Figure 2

Comparable reaction between the physiological state of the plant, dry matter accumulation in the plant and root system in the common wheat variety ‘Dakotana’ (D), and spelt wheat varieties ‘Badenstern’ (B), ‘Badenkrone’ (BK) and ‘Zollernspelz’ (Z) in two water regimes (well-watered/drought) with different mycobiome composition in the roots (i—with G. irregulare inoculation, ni—natural inoculation in non-sterile soil, c—control, sterile soil). * Abbreviation as in Table 1: 1. Fv/Fm, 2. Y, 3. E., 4. A, 5. WUE, 6. Sk, 7. Sp, 8. l, 9. Ab, 10. v, 11. ETR, 12. R, 13. RWC, 14. rc. Scale represents high value (in yellow tint) to low value (in blue tint).

Figure 3

Root colonization by fungi (%) in wheat varieties with different mycobiome composition in roots (+i—with G. irregulare inoculation, +ni—natural inoculation) under well-watered and drought conditions. Variety without +i/ni—grown in sterile soil. Letters a–g indicate statistically different mean values at p < 0.05.

Figure 4

Effects of mycorrhizal inoculation (+i—with G. irregulare inoculation, +ni—natural inoculation) in wheat varieties under two water regimes (well-watered, drought) on: (a) photosynthesis rate (CO₂ assimilation)—A (µmol CO₂ m⁻² s⁻¹); (b) transpiration rate—E (mmol H₂O m⁻² s⁻¹). Variety without +i/ni—grown in sterile soil. Letters a–j indicate statistically different mean values at p < 0.05.

Figure 4

Effects of mycorrhizal inoculation (+i—with G. irregulare inoculation, +ni—natural inoculation) in wheat varieties under two water regimes (well-watered, drought) on: (a) photosynthesis rate (CO₂ assimilation)—A (µmol CO₂ m⁻² s⁻¹); (b) transpiration rate—E (mmol H₂O m⁻² s⁻¹). Variety without +i/ni—grown in sterile soil. Letters a–j indicate statistically different mean values at p < 0.05.

Figure 5

Effects of mycorrhizal inoculation (+i—with G. irregulare inoculation, +ni—natural inoculation) in wheat varieties under two water regimes (well-watered, drought) on the parameters of chlorophyll fluorescence (non-nominated units): (a) maximum photochemical efficiency of PSII (Fv/Fm), (b) quantum yield of photosystem II (Y) and (c) electron transport rate (ETR). Variety without +i/ni—grown in sterile soil. Letters a–h indicate statistically different mean values at p < 0.05.

Figure 5

Effects of mycorrhizal inoculation (+i—with G. irregulare inoculation, +ni—natural inoculation) in wheat varieties under two water regimes (well-watered, drought) on the parameters of chlorophyll fluorescence (non-nominated units): (a) maximum photochemical efficiency of PSII (Fv/Fm), (b) quantum yield of photosystem II (Y) and (c) electron transport rate (ETR). Variety without +i/ni—grown in sterile soil. Letters a–h indicate statistically different mean values at p < 0.05.

Figure 6

Relative water content (RWC: %) in leaves of wheat varieties inoculated with mycorrhiza (+i—with G. irregulare inoculation, +ni—natural inoculation) under well-watered and drought conditions. Variety without +i/ni—grown in sterile soil. Letters a–h indicate statistically different mean values at p < 0.05.

Figure 7

Effects of mycorrhizal inoculation (+i—with G. irregulare inoculation, +ni—natural inoculation) in wheat varieties on water use efficiency (WUE) (µmol CO₂/mmol H₂O). Control denotes variety without +i/ni—grown in sterile soil; letters a–d indicate statistically different mean values at p < 0.05.

Figure 8

Effects of mycorrhizal inoculation (+i—with G. irregulare inoculation, +ni—natural inoculation) in wheat varieties under two water regimes (well-watered, drought) on dry weight of: (a) aboveground part of plants (Ab), (b) stalk (Sk) and (c) spike (Sp) (g m⁻²). Variety without +i/ni—grown in sterile soil. Letters a–m indicate statistically different mean values at p < 0.05.

Figure 8

Effects of mycorrhizal inoculation (+i—with G. irregulare inoculation, +ni—natural inoculation) in wheat varieties under two water regimes (well-watered, drought) on dry weight of: (a) aboveground part of plants (Ab), (b) stalk (Sk) and (c) spike (Sp) (g m⁻²). Variety without +i/ni—grown in sterile soil. Letters a–m indicate statistically different mean values at p < 0.05.

Figure 9

Assessment of wheat variety root growth according to mycorrhizal inoculation (+i—with G. irregulare inoculation, +ni—natural inoculation) under well-watered and drought conditions: (a) root dry weight (g), (b) root length (cm) and (c) root volume (cm³). Variety without +i/ni—grown in sterile soil; Letters a–y indicate statistically different mean values p < 0.05.

Figure 10

Effect of common wheat and spelt wheat variety root growth according to mycorrhizal inoculation (1. with G. irregulare inoculation, 2. grown in sterile soil and 3. with natural inoculation) under well-watered and drought conditions.

Figure 11

Heat map based on the pairwise Pearson correlation coefficients between agronomic traits (1. dry weight of roots (R), 2. length (l), 3. root volume (v), 4. dry weight of aboveground part of plants (Ab), 5. spike (Sp), 6. stalk (Sk), 7. root colonization (rc)) and physiological parameters (8. maximum photochemical efficiency of PSII (Fv/Fm), 9. quantum yield of photosystem II (Y), 10. electron transport rate (ETR), 11. transpiration rate (E), 12. photosynthetic rate (A), 13. water use efficiency (WUE), 14. relative water content (RWC)) in different mycorrhizal inoculation (i) with G. irregulare inoculation, (c) grown in sterile soil, (ni) with natural inoculation under well-watered and drought conditions. A darker blue color indicates a stronger negative correlation, a darker yellow color indicates a stronger positive correlation (legend presents detailed correlation coefficient).

Figure 12

Heat map based on the pairwise Pearson correlation coefficients between agronomic traits (1. dry weight of roots (R), 2. length (l), 3. root volume (v), 4. dry weight of aboveground part of plants (Ab), 5. spike (Sp), 6. stalk (Sk), 7. root colonization (rc)) and physiological parameters (8. maximum photochemical efficiency of PSII (Fv/Fm), 9. quantum yield of photosystem II (Y), 10. electron transport rate (ETR), 11. transpiration rate (E), 12. photosynthetic rate (A), 13. water use efficiency (WUE), 14. relative water content (RWC)) in the common wheat variety ‘Dakotana’ (D), and spelt wheat varieties ‘Badenstern’ (B), ‘Badenkrone’ (BK) and ‘Zollernspelz’ (Z) under two water regimes (well-watered, drought). A darker blue color indicates a stronger negative correlation, a darker yellow color indicates a stronger positive correlation (legend presents detailed correlation coefficient).

Figure 13

Selected micrographs taken with light microscopy. Panel (A) shows variety ‘Zollernspellz’ with natural inoculation grown under drought conditions, (B–D): ‘Badenkrone’ with natural inoculation grown under drought conditions, (E,F): ‘Badenstern’ without inoculation grown under well-watered conditions, (G,H): ‘Badenstern’ with natural inoculation grown under well-watered conditions, (I): ‘Badenkrone’ with mycorrhizal inoculation grown under drought conditions. Abbreviations: (v) vesicle, (h) hyphae, (ms) microsclerotia and (ap) apresorium. Dotted lines marked magnifications locations.