Responses of short-term water use efficiency to environmental factors in typical trees and shrubs of the loess area in West Shanxi, China

doi:10.17521/cjpe.2021.0220

Abstract

Abstract:

Aims We studied changes in the short-term water use efficiency with environmental factors in typical trees and shrubs of the loess area in West Shanxi. Our objective was to determine the patterns of water use and adaptive strategies in plants of this region, aiming for improving the efficiency of vegetation establishment in the loess area.

Methods Two typical trees, Pinus tabuliformis and Robinia pseudoacacia, and two typical understory shrubs, Rosa xanthina and Periploca sepium, were investigated in this study. Measurements were made on the stable carbon isotope of soluble sugars in leaves (δ¹³C_leaf) and phloem in branches (δ¹³C_branch). δ¹³C_leaf was used to calculated the trend of short-term water use efficiency (WUE_leaf) at the leaf level. δ¹³C_branch was used to determine the carbon fractionation from photosynthesis. We compared the difference in WUE_leaf between species and determined the responses of WUE_leaf to changes in environmental factors.

Important findings From July through to October in the year of investigation, the δ¹³C_leafshowed an overall decreasing trend in the four species, whilst δ¹³C_branch displayed a temporal pattern of “up and down”. δ¹³C_leaf differed among the species and between life forms, in the order of shrubs > trees, and Pinus tabuliformis (an evergreen tree) > Robinia pseudoacacia (a deciduous tree). The WUE_leaf values remained stable from July to August in the four species, and then gradually increased from September to October. Abrupt changes in the WUE_leafvalue occurred at 21.5 °C with temperature (T_a), 0.9 kPa with vapor pressure deficit (VPD), and 52.4% with relative humidity (RH), respectively. Following the abrupt changes, the WUE_leaf value remained steady with further increases in T_a, VPD,and RH in the four species. There were significantly negative correlations between the WUE_leaf value and T_a, RH, and VPD. T_a altered the photosynthetic rate by non-stomatal factors, specifically through the effects on enzymes, causing changes in the WUE_leaf value. The water factor affects transpiration by controlling stomatal opening, and then changes the WUE_leaf value. With increases in soil water content (SWC), the value of WUE_leaf showed a trend of an initial increase and then decreases. The WUE_leaf reached peak value at 15%-18% of SWC in the Pinus tabuliformis stands and 13%-14% in the Robinia pseudoacacia stands. The dominant environmental factors influencing WUE_leaf also differed among species. Linear mixed model (LMM) analysis identified RH as the dominant environmental factor on Pinus tabuliformis, and VPD on Robinia pseudoacacia, respectively; T_a was identified as the dominant environmental factor on both Periploca sepium and Rosa xanthina. This study provides quantitative analysis of water use ability of typical trees and shrubs in the loess area, the internal water consumption mechanism in the growing season, and the major controlling environmental factors, which provides a theoretical basis for the vegetation configuration in this region.

Key words: water use efficiency, stable carbon isotope, soluble sugar, the loess area, linear mixed model

HAN Lu, YANG Fei, WU Ying-Ming, NIU Yun-Ming, ZENG Yi-Ming, CHEN Li-Xin. Responses of short-term water use efficiency to environmental factors in typical trees and shrubs of the loess area in West Shanxi, China[J]. Chin J Plant Ecol, 2021, 45(12): 1350-1364.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2021.0220

https://www.plant-ecology.com/EN/Y2021/V45/I12/1350

Figures/Tables 12

Table 1 Basic information of sampling plots for typical trees and shrubs in the loess area of West Shanxi (mean ± SD)

样地编号 Plot No.	胸径 Diameter at breast height (cm)	树高 Tree height (m)	海拔 Altitude (m)	林分密度 Stand density (tree·hm^-2)	坡度 Slope gradient (°)
PTF 1	12.38 ± 3.49	7.04 ± 1.04	1 140	1 050	32
PTF 2	13.38 ± 2.13	7.29 ± 0.96	1 130	1 325	27
PTF 3	13.88 ± 2.47	7.94 ± 1.03	1 120	1 100	29
RPF 1	10.08 ± 4.33	8.29 ± 1.89	1 120	1 675	20
RPF 2	10.68 ± 2.56	9.28 ± 1.20	1 120	1 425	20
RPF 3	9.41 ± 2.71	8.20 ± 2.23	1 130	1 475	21

Table 2 Basic information of shrubs in the loess area of West Shanxi (mean ± SD)

种名 Species	株高 Shrub height (m)	基径 Shrub diameter (cm)	盖度 Coverage (%)	冠幅长度 Crown length (m)	冠幅宽度 Crown width (m)
黄刺玫 Rosa xanthina	1.05 ± 0.19	0.51 ± 0.08	26.60 ± 0.07	2.43 ± 0.13	2.30 ± 0.16
杠柳 Periploca sepium	0.53 ± 0.09	0.35 ± 0.10	16.81 ± 0.04	1.30 ± 0.07	1.23 ± 0.06

Fig. 1 Variations of environmental factors during the observation period in the study area in the loess area of West Shanxi. Since the weather station for measuring solar radiation was repaired in September, the net solar radiation in B missed part of the data for September and all the data for October. PTF, Pinus tabuliformis forest; RPF, Robinia pseudoacacia forest.

Table 3 One way ANOVA of meteorological factors in different months in the loess area of West Shanxi (mean ± SD)

月份 Month	温度 Temperature (℃)	n	太阳净辐射 Solar radiation (μmol·m^-2·s^-1)	n	相对湿度 Relative humidity (%)	n	饱和水汽压差 Vapor pressure difference (kPa)	n
7	24.66 ± 2.84^a	22	304.45 ± 117.92^a	22	69.38 ± 7.25^a	22	0.97 ± 0.32^a	22
8	23.14 ± 2.71^b	31	331.81 ± 114.69^a	31	72.37 ± 9.57^a	31	0.81 ± 0.33^ab	31
9	17.37 ± 2.14^c	30	345.06 ± 39.74^a	9	59.19 ± 8.86^b	30	0.82 ± 0.21^b	30
10	13.12 ± 3.10^d	6	-	0	55.94 ± 10.70^b	6	0.65 ± 0.10^b	6

Fig. 2 Changes in intercellular CO2 concentration (Ci) of different plant species in different months in typical trees and shrubs in the loess area of West Shanxi. Ps, Periploca sepium; Pt, Pinus tabuliformis; Rp, Robinia pseudoacacia; Rx, Rosa xanthina.

Fig. 3 Changes in the stable carbon isotope of soluble sugars in leaves (δ13Cleaf) and phloem in branches (δ13Cbranch) of different plants during the observation period in the loess area of West Shanxi (mean ± SD).

Fig. 4 Box plots of the stable carbon isotope ratios (δ13C) of leaves and branches for different tree species in the loess area of West Shanxi from July to October. *, p < 0.05; **, p < 0.01.

Fig. 5 Changes in the short-term water use efficiency (WUEleaf) and stomatal limit values (Ls) of different plant species during the observation period in the loess area of West Shanxi (mean ± SD).

Fig. 6 Box plots of the short-term water use efficiency (WUEleaf) for different tree species in the loess area of West Shanxi from July to October. Ps, Periploca sepium; Pt, Pinus tabuliformis; Rp, Robinia pseudoacacia; Rx, Rosa xanthina. *, p < 0.05; **, p < 0.01; ***, p < 0.001.

Fig. 7 Trends of changes in the short-term water use efficiency (WUEleaf) with temperature (Ta)(A), relative humidity (RH)(B), vapor pressure deficit (VPD)(C) and soil water content (SWC)(D) in the loess area of West Shanxi (mean ± SD). Ps, Periploca sepium; Pt, Pinus tabuliformis; Rp, Robinia pseudoacacia; Rx, Rosa xanthina.

Table 4 Difference in Akaike information criterion (AIC)(difference between AIC of the calculated model and the lowest AIC) in different mixed linear models for short-term water use efficiency (WUEleaf) of four plant species in the loess area of West Shanxi

模型固定因子 Model fixed factors	油松 Pinus tabuliformis	黄刺玫 Rosa xanthina	刺槐 Robinia pseudoacacia	杠柳 Periploca sepium
T_a + RH	-	0.19	7.99	5.24
P + VPD	-	4.38	3.83	2.34
R_n + VPD	5.51	-	9.75	16.07
P + R_n + VPD	-	5.03	4.13	2.98
T_a + P + SWC	9.83	2.22	-	0.00
T_a + R_n + SWC	2.38	6.11	7.50	5.01
P + RH + SWC	0.00	-	433.28	-
T_a + RH + SWC	-	0.00	8.89	6.80
T_a + VPD + SWC	-	3.16	8.84	4.45
P + VPD + SWC	-	2.73	0.00	2.15
R_n + VPD + SWC	5.43	-	11.74	16.01
RH + VPD + SWC	12.76	12.84	28.29	19.72

Table 5 Comparision of contributions by different linear mixed models for short-term water use efficiency (WUEleaf) of the four plant species in the loess area of West Shanxi

树种 Species	固定因子 Fixed factor	R²	方差解释量占比 Percentage of variance explained (%)	p
黄刺玫 Rosa xanthina	T_a	0.497	54.33	0.000^***
	RH	0.447	48.84	0.837
	SWC	0.005	0.57	0.352
杠柳 Periploca sepium	T_a	0.851	88.74	0.000 ^***
	SWC	0.006	0.57	0.946
	P	0.120	12.50	0.249
油松 Pinus tabuliformis	RH	0.769	84.12	0.000^***
	SWC	0.019	2.06	0.167
	P	0.145	15.91	0.078
刺槐 Robinia pseudoacacia	VPD	0.637	68.91	0.000^***
	SWC	0.044	4.71	0.032^*
	P	0.276	29.78	0.000^***

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