Cedrus atlantica pollen morphology and investigation of grain size variability using laser diffraction granulometry

Figures & data

Figure 1. Map of the Middle Atlas and forest cover: dark green is predominately needleleaf evergreen, and light green is mixed broadleaf evergreen and needleleaf evergreen. Sample areas are shown in red and towns in black. Map created using Global Multi-resolution Terrain Elevation Data 2010 (GMTED2010) and forestry data extracted from Global Land Cover Characterization (GLCC) imagery. Data available from US Geological Survey (2017).

Table 1. Details of the sampling areas where pollen was collected.

Location^1	No. of samples	Longitude	Latitude	Altitude (m asl)^2	Mean annual precipitation (mm)^3	Temperature range (°C)^4
Ifrane	2	−5.11	33.43	1653	474 (836)	−1.8 to 28.0
Michliffen	15	−5.08	33.34	1940	516 (714)	−3.0 to 28.5
Ifrane National Park	6	−5.17	33.39	1723	516 (747)	−1.7 to 29.8
Col Du Zad	7	−5.07	33.07	2106	470 (515)	−3.8 to 29.6
Lake Sidi Ali	10	−4.99	33.08	2150	470 (408)	−3.3 to 29.2
Bikrit	9	−5.26	33.24	1611	516 (738)	−1.0 to 30.5
Kobbat	11	−5.21	33.19	2074	516 (667)	−3.8 to 27.7
Ain Kahla	6	−5.23	33.30	1939	516 (695)	−3.0 to 28.5
(near) Azrou	6	−5.24	33.35	1814	516 (696)	−2.2 to 29.3
Westonbirt, UK	5	−2.21	51.61	132	854	0.9 to 20.7
Manchester, UK	3	−2.21	53.41	43	890	1.4 to 19.6
Boston, USA	2	−71.12	42.30	45	1236	−9.2 to 27.1
Paris, France	4	2.36	48.84	35	618	1.8 to 24.8
Bordeaux, France	3	−0.60	44.85	23	958	2.4 to 25.2
Pyrenees, Spain	2	−0.55	42.57	820	753	−1.9 to 26.0

¹ Location within Morocco unless otherwise indicated.

² Average altitude (metres above sea level [asl]) of samples collected in the location.

³ CRU (East Anglia Climate Research Unit) data averaged over 30 years (1986–2015). Values in parentheses indicate interpolated precipitation values (Bell et al. 2017).

⁴ Mean annual minimums and maximums.

Figure 2. Schematic diagram of Cedrus atlantica pollen as it appears under light microscopy (LM), and the different measurements taken under LM.

Figure 3. Results from laser diffraction granulometry. Size data for each sample is presented as the particle size distribution of the sample.

Table 2. Grain size of each measured property (please refer to Figure 2) under light microscopy (LM; eight samples, 240 grains measured).

	1: TW (µm)	2: PA (µm)	3: TL (µm)	4: EX (µm)	5: LSL (µm)	6: LSW (µm)	7: RSL (µm)	8: RSW (µm)	9: CT (µm)	10: area (µm^2)	P/E ratio (EX/PA)
Mean	53.6	38.8	71.4	52.2	31.8	28.6	31.3	27.9	3.1	2774.9	1.4
Standard deviation	4.8	5.5	7.6	4.0	3.9	3.6	3.9	3.4	0.7	472.6	0.2
Minimum	35.5	25.5	49.8	43.8	19.1	20.1	21.5	19.7	1.4	1580.5	0.9
Maximum	68.0	54.0	89.1	63.8	42.5	39.7	43.0	37.3	5.2	4180.9	1.9

Table 3. Percentage change (%) in size for different properties (please refer to Figure 2) of the grain measured under light microscopy (LM) following chemical treatment with KOH.

1: TW	2: PA	3: TL	4: EX	5: LSL	6: LSW	7: RSL	8: RSW	9: CT	10: area	P/E ratio (EX/PA)
−2.8	8.5	9.3	−1.5	4.1	12.5	5.9	16.2	9.0	7.6	−7.1

Table 4. Correlation analysis between the laser diffraction granulometry D₅₀ grain size value, and light microscopy (LM) measurements.

Grain property	Pearson's r	p
Total width (TW)	0.68	0.062
Polar axis (PA)	0.39	0.345
Total length (TL)	0.66	0.076
Equatorial axis (EX)	0.91	0.002
Total area	0.67	0.069

Figure 4. Results of laser diffraction granulometry showing: (A) Dot plot of D₅₀ values for each sample by geographical sampling area, and (B) mean D₅₀ values for each area. Error bars show standard deviation, and dashed horizontal line represents the mean grain size of all samples.

Table 5. Results of regression analysis on pollen grain size. Analysis was tested using individual sample grain size values, and the average grain size for each geographical sampling area.

		Individual sample		Location average
Variable	Data source	r^2	p	r^2	p
Summer precipitation (2015)^1	CRU TS v3.24.01	0.00	0.812	0.03	0.515
Mean annual precipitation (2015)^2	CRU TS v3.24.01	0.00	0.441	0.10	0.246
Mean annual precipitation (30-year average)^3	CRU TS v3.24.01	0.00	0.509	0.07	0.331
Mean annual precipitation (interpolated values)	Bell et al. (2017)	0.00	0.890	0.00	0.789
Mean annual temperature (2015)	CRU TS v3.24.01	0.00	0.747	0.06	0.380
Mean summer temperature (2015)	CRU TS v3.24.01	0.00	0.598	0.07	0.319
Mean annual temperature (30-year average)	CRU TS v3.24.01	0.00	0.779	0.06	0.375
Mean summer temperature (30-year average)	CRU TS v3.24.01	0.00	0.628	0.06	0.352
Aridity (scPDSI)^4	Dai (2011)	0.00	0.586	0.07	0.324
Annual potential evapotranspiration (PET) (2015)	CRU TS v3.24.01	0.00	0.396	0.01	0.396
Summer PET (2015)	CRU TS v3.24.01	0.01	0.551	0.00	0.551
Carbon isotope discrimination (Δ^1^3C)^5	Bell et al. (2017)	0.05	0.029	0.10	0.234
Altitude	This study	0.00	0.439	0.07	0.316

¹ Summer corresponds to the development period for Cedrus atlantica pollen.

² Values for the year of pollen collection.

³ Values based on a 30-year average between 1986–2015.

⁴ Aridity values from self-calibrating Palmer Drought Severity Index (30-year average).

⁵ Carbon isotope discrimination calculated from δ¹³C values measured directly on the same pollen samples.

Figure 5. Biplots showing: (A) carbon isotope discrimination (Δ¹³C) (Bell et al. 2017) versus aridity (self-calibrating Palmer Drought Severity Index, scPDSI) (Dai 2011), and (B) pollen grain size versus aridity (scPDSI), with values averaged by each sampling area.

Plate 1. Photographs taken under light microscopy (LM) of Cedrus atlantica pollen grains. Scale indicated on each image. Figures 1–3. Equatorial view showing complete grain. Figures 4–5. Polar view of complete grain. Figures 7–8. Close-up of corpus surface. Figure 9. Corpus surface pattern (extracted using CorelDraw X8). Figures 10–11. Close-up of saccus surface. Figure 12. Saccus surface pattern.

Plate 2. Photographs taken under light microscopy (LM) of treated Cedrus atlantica pollen grains stained with Safranin. Scale indicated on each image. Figures 1–2. Equatorial view showing complete grain at different foci. Figures 3–4. Polar view of complete grain. Figure 5. Close-up of corpus surface. Figure 6. Close-up of saccus surface.

Plate 3. Scanning electron microscopy (SEM) images of Cedrus atlantica pollen grains. Scale indicated on each image. Figure 1. Polar view from the top. Figure 2. Close-up of corpus surface. Figure 3. Equatorial view. Figure 4. Close-up of saccus surface. Figure 5. Polar view from underneath the grain showing the leptoma. Figure 6. Close-up of leptoma, pollen wall visible to the left.

Plate 4. Scanning electron microscopy (SEM) images of treated Cedrus atlantica pollen grains. Scale indicated on each image. Figures 1–2. Polar view from the top and side. Figures 3–4. Equatorial view. Figure 5. Close-up of corpus surface. Figure 6. Close-up of leptoma.

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