Ultra-fine bubble irrigation promotes coffee (Coffea arabica) seedling growth under repeated drought stresses

Figures & data

Table 1. Details of treatments and environments in the six experiments.

	Year	Period	Drought period	Fertilizer date	Ave. Temp.	Rep.
Exp. 1	2019	23 Aug. − 18 Nov.	23 Aug. − 1 Sep, 10–15 Sep, 28 Sep. − 3 Oct, 14–30 Oct.	-	21.2	6
Exp. 2–1	2020	1 June − 7 July	1–9 June, 16–26 June	-	26.8	6
2–2	2021	24 May − 26 July	24 May − 1 June, 8–15 June, 23 June − 5 July, 10–20 July	-	26.4	6
Exp. 3–1	2020	3 Aug. − 19 Oct.	3–6, 14–17, 21–26 Aug, 2–8, 13–21 Sep. 30 Sep. − 11 Oct.	28 Aug.	25.8	20
3–2	2020	24 Aug. − 18 Nov.	24–28 Aug. 4–13, 21–29 Sep. 4–16, 22–31 Oct.	18 Sep.	22.8	20
Exp. 4	2021	17 Aug. − 4 Nov.	17–23 Aug. 1–7, 21–27 Sep. 6–10 Oct. 20 Oct. − 2 Nov.	-	24.7	20

Table 2. Plant height (cm) increase, and dry weight (DW; g plant⁻¹) of both shoot and root in experiment 1.

		Plant height increase	Shoot DW	Root DW
Environment	Treatment	(cm)	(g plant^−1)	(g plant^−1)
Control	non-UFB	8.7 ns	7.08 ns	2.47 ns
	UFB	8.0	6.66	2.17
	(UFB/non-UFB)	0.92	0.94	0.88
Drought	non-UFB	2.8*	4.08*	1.25***
	UFB	4.8	4.52	1.73
	(UFB/non-UFB)	1.70	1.11	1.38
ANOVA
	Environment	0.000***	0.000***	0.000***
	Treatment	0.394	0.981	0.241
	E*T	0.093	0.098	0.000***

* and *** indicate significance at 0.05 and 0.001 probability levels, respectively. ‘ns’ indicates non-significance. Student’s t-test was performed for the comparison between non-UFB and UFB. Two-way-ANOVA was performed using environment and treatment factors.

Table 3. Plant height (cm) increase, and dry weight (DW; g plant⁻¹) of shoot, leaf, and root in experiment 2.

		Plant height increase	Shoot DW	Leaf DW	Root DW
Environment	Treatment	(cm)	(g plant^−1)	(g plant^−1)	(g plant^−1)
(a) Experiment 2–1
Control	non-UFB	5.3 ns	0.52*	0.36*	0.18 ns
	UFB	6.0	0.74	0.51	0.25
	(UFB/non-UFB)	1.13	1.41	1.41	1.39
Drought	non-UFB	4.2*	0.50 ns	0.32 ns	0.12 ns
	UFB	5.9	0.67	0.49	0.17
	(UFB/non-UFB)	1.42	1.34	1.53	1.48
ANOVA
Environment		0.299	0.498	0.617	0.017*
Treatment		0.040*	0.010*	0.011*	0.032*
E*T		0.354	0.723	0.855	0.798
(b) Experiment 2–2
Control	non-UFB	9.0 ns	1.57 ns	1.06 ns	0.53 ns
	UFB	11.2	1.82	1.28	0.55
	(UFB/non-UFB)	1.24	1.16	1.22	1.04
Drought	non-UFB	8.1 ns	1.29 ns	0.88 ns	0.37 ns
	UFB	7.7	1.49	0.89	0.44
	(UFB/non-UFB)	0.95	1.15	1.01	1.17
ANOVA
Environment		0.005**	0.084	0.055	0.000***
Treatment		0.206	0.094	0.412	0.216
E*T		0.081	0.863	0.445	0.546

*, **, and *** indicate significance at 0.05, 0.01 and 0.001 probability levels, respectively. ‘ns’ indicates non-significance. Student’s t-test was performed for the comparison between non-UFB and UFB. Two-way-ANOVA was performed using environment and treatment factors.

Table 4. Plant height (cm) increase, and dry weights (DW; g plant⁻¹) of shoot, leaf, and root in experiment 3.

		Plant height increase	Shoot DW	Leaf DW	Root DW
Environment	Treatment	(cm)	(g plant^−1)	(g plant^−1)	(g plant^−1)
(a) Experiment 3–1
Control	non-UFB	8.2*	2.89 ns	1.89 ns	1.01 ns
	UFB	10.3	3.24	2.11	1.05
	(UFB/non-UFB)	1.25	1.12	1.12	1.04
Drought	non-UFB	8.0 ns	2.83 ns	1.92 ns	0.53 ns
	UFB	7.3	2.77	1.83	0.55
	(UFB/non-UFB)	0.91	0.98	0.95	1.04
ANOVA
Environment		0.005**	0.065	0.194	0.000***
Treatment		0.234	0.31	0.502	0.581
E*T		0.018*	0.161	0.108	0.852
(b) Experiment 3–2
Control	non-UFB	10.9 ns	3.53 ns	2.17 ns	1.35 ns
	UFB	10.2	3.43	2.24	1.31
	(UFB/non-UFB)	0.94	0.97	1.03	0.97
Drought	non-UFB	7.5 ns	3.17 ns	2.03 ns	0.91 ns
	UFB	8.3	3.4	2.21	0.93
	(UFB/non-UFB)	1.11	1.07	1.09	1.02
ANOVA
Environment		0.000***	0.043*	0.184	0.000***
Treatment		0.351	0.339	0.231	0.826
E*T		0.461	0.868	0.523	0.857

*, **, and *** indicate significance at 0.05, 0.01, and 0.001 probability levels. ‘ns’ indicates non-significance. Student’s t-test was performed for the comparison between non-UFB and UFB. Two-way-ANOVA was performed using environment and treatment factors.

Figure 1. Electrolyte leakage of coffee leaf disks in experiment 4. Data are means of four plant samples in each treatment. Vertical bars indicate standard errors (n = 4). Note:** indicates significance at 1% probability, ‘ns’ indicates non-significance. Student’s t-test was performed for the comparison between non-UFB and UFB.

Table 5. Plant height (cm) increase, and dry weight (DW; g plant⁻¹) of shoot, leaf, and root in experiment 4.

Environment	Treatment	Plant height increase	Shoot DW	Leaf DW	Root DW
		(cm)	(g plant^−1)	(g plant^−1)	(g plant^−1)
Control	non-UFB	12.4 ns	5.97 ns	3.44 ns	1.61 ns
	UFB	13.5	6.25	3.67	1.71
	(UFB/non-UFB)	1.09	1.05	1.07	1.07
Drought	non-UFB	9.6 ns	4.58*	1.86**	0.99**
	UFB	10.1	5.04	2.66	1.20
	(UFB/non-UFB)	1.05	1.10	1.43	1.22
ANOVA
	Environment	0.000***	0.000***	0.000***	0.000***
	Treatment	0.152	0.056	0.001**	0.012*
	E*T	0.592	0.644	0.064	0.377

*, **, and *** indicate significance at 0.05, 0.01, and 0.001 probability levels. ‘ns’ indicates non-significance. Student’s t-test was performed for the comparison between non-UFB and UFB. Two-way-ANOVA was performed using environment and treatment factors.

Table 6. Leaf number (LN; plant⁻¹), individual leaf area (ILA; cm²), total leaf area (TLA; cm²), specific leaf area (SLA; cm² g⁻¹), total root length (TRL; cm plant⁻¹), root surface area (RSA; cm² plant⁻¹), and specific root length (SRL; cm g⁻¹) in experiment 4.

Environment	Treatment	LN	ILA	TLA	SLA	TRL	RSA	SRL
		(plant^−1)	(cm^2)	(cm^2)	(cm^2 g^−1)	(cm)	(cm^2)	(cm^2 g^−1)
Control	non-UFB	24.2 ns	29.5 ns	707.3 ns	206.6 ns	3743 ns	582 ns	2397 ns
	UFB	25.6	30.2	766.5	209.4	4006	569	2371
	(UFB/non-UFB)	1.06	1.02	1.08	1.01	1.07	0.98	0.99
Drought	non-UFB	10.8***	33.3 ns	340.9***	179.8 ns	2444***	352**	2494 ns
	UFB	16.9	31.2	514.5	189.4	3097	440	2600
	(UFB/non-UFB)	1.57	0.94	1.51	1.05	1.27	1.25	1.04
ANOVA
	Environment	0.000***	0.050*	0.000***	0.000***	0.000***	0.000***	0.047*
	Treatment	0.000***	0.577	0.000***	0.205	0.000***	0.021*	0.062
	E*T	0.031*	0.263	0.076	0.487	0.099	0.002**	0.419

*, **, and *** indicate significance at 0.05, 0.01, and 0.001 probability levels, respectively. ‘ns’ indicates non-significance. Student’s t-test was performed for the comparison between non-UFB and UFB. Two-way-ANOVA was performed using environment and treatment factors.