Comparison of transpiration of differently aged apple orchards on the Loess Plateau of China at multiple temporal scales

Figures & data

Figure 1. Location of the 8- and 18-year-old apple orchards in the Wangdonggou watershed on the Loess Plateau of China

Figure 2. Variation of precipitation (P), solar radiation (Rs), air temperature (AT), wind speed (Ws), relative humidity (RH), vapour pressure deficit (VPD) and daily reference evapotranspiration (ET₀) in 2013, 2014, 2015 and 2016

Table 1. Numbers of sample trees and frequencies of trees in four diameter classes in the 8- and 18-year-old orchards

Diameter class	8-year-old				18-year-old
	Diameter (mm)	Number of trees	Frequency (%)	Sample trees	Diameter (mm)	Number of trees	Frequency (%)	Sample trees
1	<90	11	13.8	1	<130	24	30	2
2	90–100	17	21.3	2	130–140	17	21.3	2
3	100–110	17	21.3	2	140–150	16	20	2
4	>110	35	43.8	3	>150	23	28.7	2
Total		80	100	8		80	100	8

Figure 3. Variation of monthly leaf area index (LAI) of the 8- and 18-year-old apple orchards in 2013, 2014, 2015 and 2016

Figure 4. Relative extractable water (REW) at 0–600 cm in the 8-year-old and 18-year-old apple orchards in 2013, 2014, 2015 and 2016. The dot line indicates the threshold of soil water deficits

Figure 5. Daily transpiration in the 8- and 18-year-old apple orchards and differences (18 years minus 8 years) between the two orchards in 2013, 2014, 2015 and 2016

Figure 6. Daily mean transpiration in the 8- and 18-year-old apple orchards in 2013, 2014, 2015 and 2016. The same capital letters indicate no significant difference according to the least significant difference (LSD_0.05) test. The error bars indicate the coefficient of variation of daily mean transpiration in each year

Table 2. Pearson correlation and partial correlation coefficients between daily sap flow velocity, meteorological factors and ET₀ for the 8- and 18-year-old apple orchards for 2013, 2014, 2015 and 2016

Tree age	Year	ET0		Rs		AT		RH		Ws		VPD
		N	R	N	R	N	R	N	R	N	R	N	R
8-year-old	2013	0.854**	0.305**	0.810**	0.220**	0.509**	0.115	−0.624**	0.050	0.059	−0.209*	0.730**	0.042
	2014	0.824**	0.237**	0.763**	0.138	0.514**	0.036	−0.633**	0.039	0.042	−0.211*	0.745**	0.048
	2015	0.926**	0.805**	0.641**	0.076	0.338**	0.012	−0.623**	−0.071	0.247**	−0.007	0.572**	0.001
	2016	0.813**	0.517**	0.502**	−0.070	0.518**	−0.027	−0.591**	−0.042	0.332**	−0.210*	0.743**	0.066
	2013–2016	0.871**	0.544**	0.714**	0.082	0.638**	−0.087	−0.478**	0.188*	0.239**	−0.146	0.741**	0.129
18-year-old	2013	0.857**	0.278**	0.824**	0.258**	0.512**	0.163*	−0.643**	−0.001	0.019	−0.290**	0.743**	0.030
	2014	0.784**	0.221*	0.737**	0.118	0.489**	0.093	−0.600**	−0.026	0.035	−0.179*	0.698**	−0.030
	2015	0.889**	0.728**	0.648**	0.107	0.335**	−0.023	−0.626**	0.061	0.197*	−0.061	0.581**	0.030
	2016	0.805**	0.477**	0.519**	0.009	0.551**	0.007	−0.558**	−0.007	0.316**	−0.180*	0.731**	0.073
	2013–2016	0.848**	0.503**	0.689**	0.073	0.651**	−0.001	−0.447**	0.124	0.200*	−0.175*	0.715**	0.062

*, **significance at p < 0.05, <0.01, respectively; N: Pearson correlation; R: partial correlation; Js: sap flow velocity; ET₀: Reference evapotranspiration; Rs: solar radiation; AT: air temperature; RH: relative humidity; Ws: wind speed; VPD: Vapour pressure deficit.

Figure 7. Daily sap flow velocity of the 8- and 18-year-old apple orchards and differences (8 years minus 18 years) between the two orchards in 2013, 2014, 2015 and 2016

Table 3. Multivariate regression models for daily sap flow velocity in the 8- and 18-year-old apple orchards during the growing season of 2013–2016

Tree age	Year	Multivariate stepwise linear regression	Coefficient of determination
8-year-old	2013	Js = 0.242ET0 + 0.031Rs+0.027AT-0.704	0.789
	2014	Js = 0.214ET0 + 0.020Rs+0.021AT-0.399	0.699
	2015	Js = 0.356ET0 + 0.005	0.857
	2016	Js = 0.299ET0 + 0.213VPD-0.102Ws+0.059	0.676
	2013–2016	Js = 0.351ET0 + 0.006Rs+0.008AT-0.081Ws-0.165	0.854
18-year-old	2013	Js = 0.13ET0 + 0.021Rs+0.019AT-0.394	0.800
	2014	Js = 0.125ET0 + 0.014Rs+0.013AT-0.196	0.638
	2015	Js = 0.217ET0 + 0.004Rs+0.031	0.797
	2016	Js = 0.245ET0 + 0.023	0.646
	2013–2016	Js = 0.216ET0 + 0.005Rs+0.007AT-0.062Ws-0.065	0.846

Js: sap flow velocity; ET₀: Reference evapotranspiration; Rs: solar radiation; AT: air temperature; RH: relative humidity; Ws: wind speed; VPD: Vapour pressure deficit.

Table 4. Characteristics of monthly transpiration for the 8- and 18-year-old apple orchards in 2013, 2014, 2015 and 2016

Year	Month	T 8-year-old (mm)					T 18-year-old (mm)
		Max	Min	Mean	Total	CV (%)	Max	Min	Mean	Total	CV (%)
2013	May	1.5	0.1	0.9	26.4	48.9	1.9	0.1	1.1	35.0	44.3
	June	1.9	0.1	1.0	30.8	47.1	2.4	0.1	1.4	41.1	40.7
	July	2.1	0.1	0.8	23.4	76.1	2.4	0.1	1.0	31.5	62.2
	August	1.8	0.1	1.2	35.6	42.0	2.0	0.1	1.5	45.3	36.5
	September	1.1	0.0	0.5	14.1	67.8	1.4	0.0	0.7	21.8	54.8
	Total	2.1	0.0	0.9	130.3	60.3	2.4	0.0	1.1	174.6	51.3
2014	May	1.9	0.1	0.8	25.9	42.4	2.2	0.2	1.1	34.0	36.9
	June	1.6	0.1	1.0	30.0	43.4	2.0	0.3	1.3	39.5	38.4
	July	1.5	0.2	1.3	39.0	23.7	2.0	0.3	1.6	49.5	22.6
	August	1.4	0.1	0.8	24.0	55.8	1.9	0.1	1.0	32.1	51.4
	September	1.0	0.0	1.0	5.2	78.5	1.4	0.1	1.4	7.5	70.0
	Total	1.9	0.0	0.9	124.0	46.8	2.2	0.1	1.2	162.5	42.5
2015	May	1.5	0.3	0.8	23.9	40.3	1.7	0.4	1.0	31.2	36.1
	June	1.1	0.1	0.6	18.0	52.2	1.6	0.2	0.9	25.8	47.4
	July	1.5	0.5	0.9	28.7	29.6	2.0	0.6	1.2	37.8	28.4
	August	1.4	0.1	0.8	26.0	41.3	1.9	0.2	1.2	36.8	37.2
	September	1.3	0.2	0.7	21.3	42.1	1.6	0.3	1.0	28.8	40.7
	Total	1.5	0.1	0.8	118.0	42.2	2.0	0.2	1.1	160.3	39.1
2016	May	1.2	0.1	0.6	19.0	49.1	1.4	0.3	0.8	25.5	42.2
	June	1.7	0.2	0.9	26.3	47.8	2.0	0.4	1.1	33.5	43.5
	July	1.8	0.2	0.9	26.3	52.5	2.2	0.5	1.1	35.2	49.4
	August	1.7	0.4	1.0	31.0	35.0	2.0	0.5	1.3	40.7	32.0
	September	1.3	0.2	0.6	18.9	47.7	1.5	0.3	0.8	25.2	44.3
	Total	1.8	0.1	0.8	121.4	49.5	2.2	0.3	1.1	160.1	45.6

CV: Coefficient of variation; T: transpiration.

Figure 8. Monthly total precipitation (P), transpiration (T) and differences (P minus T) for the 8- and 18-year-old apple orchards in 2013, 2014, 2015 and 2016

Table 5. Annual precipitation, transpiration and the ratio of transpiration to precipitation for the 8- and 18-year-old apple orchards in 2013, 2014, 2015 and 2016

		2013	2014	2015	2016	Mean	CV (%)
	P (mm)	388.7	383.3	264.6	274.0	327.6	20.6
8-year-old	T (mm)	130.3	124.0	118.0	121.4	123.4	4.2
	T/P (%)	33.5	32.4	44.6	44.3	37.7	20.5
18-year-old	T (mm)	174.6	162.5	160.3	160.1	164.4	4.2
	T/P (%)	44.9	42.4	60.6	58.4	50.2	20.3

P: annual precipitation; T: transpiration; T/P: the ratio of transpiration to precipitation; CV: Coefficient of variation.