Spatiotemporal dynamics of nocturnal sap flow of Populus tomentosa and environmental impact factors

doi:10.17521/cjpe.2022.0162

Abstract

Abstract:

Aims In order to better understand the mechanisms of nocturnal water activity in tree stems, this paper explores the spatiotemporal dynamics of nocturnal sap flow and stem water filling in typical poplar plantations in the North China Plain and environmental influencing factors.

Methods Taking rainfed Populus tomentosa as the research object, the thermal diffusion method was used to continuously monitor the sap flow rate at different heights of stem in different growing periods. Soil water content and meteorological factors were measured simultaneously. Dynamics of nocturnal sap flow at different heights and its correlations with environmental factors were compared.

Important findings Before the rainy season, the ratio of nocturnal sap flow to daily sap flow at 0.35 and 1.30 m of the stem was significantly higher than that after the rainy season, while the ratio at 7.00 m increased by 49% after the rainy season. Nocturnal sap flow rate at different heights of the stem showed a high synchronization before the rainy season, and decreased with the increase of stem height. After the rainy season, the main water resource of nocturnal water use changed from root water uptake to stored water in stem base, which leading to 66% decrease of nocturnal sap flow at stem base. Meanwhile, the spatial characteristics of nocturnal sap flow at different heights also varied in different periods. After the rainy season, stem water refilling mainly occurred in 4.00-7.00 m stem segment with mean daily water refilling amount of 4.16 L, while the refilling amount in 1.30-4.00 m stem segment was much lower than others, possibly due to its primary function of water transport. Before the rainy season, vapor pressure deficit, air temperature and soil water content at 3 m depth were significantly correlated with nocturnal sap flow rate at different heights, but this relation was obviously weakened after the rainy season. And the correlations between the environmental impact factors and nocturnal sap flow were different at each height. This study finds the spatiotemporal variations of nocturnal sap flow and stem water refilling, which provide scientific support for optimizing diurnal water cycle and motion process simulation of poplar plantation in North China Plain.

Key words: poplar plantation, nocturnal sap flow, stem height, stem water refilling

FAN Yun-Xiang, DI Nan, LIU Yang, ZHANG Yu-Wen, DUAN Jie, LI Xin, WANG Hai-Hong, XI Ben-Ye. Spatiotemporal dynamics of nocturnal sap flow of Populus tomentosa and environmental impact factors[J]. Chin J Plant Ecol, 2023, 47(2): 262-274.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2022.0162

https://www.plant-ecology.com/EN/Y2023/V47/I2/262

Figures/Tables 10

Table 1 Growth information of sample trees of Populus tomentosa in Jiucheng Forest Farm

编号 Number	胸径 Diameter at breast height (cm)	树高 Height (m)	最低活枝高 Height of lowest living branch (m)
T1	14.21	17.10	9.79
T2	13.52	15.95	6.56
T3	13.60	16.96	9.81

Fig. 1 Variations in meteorological factors and soil water content (SWC) during the study period. ARH, air relative humidity; P, precipitation; T, air temperature; VPD, vapor pressure deficit; Ws, wind speed. Left figures show the variation before the rainy season (July), and right figures show the variation after the rainy season (September).

Table 2 Differences of diurnal and nocturnal meteorological factors before and after the rainy season

	空气相对湿度 Air relative humidity (%)		空气温度 Air temperature (℃)		水汽压亏缺 Vapor pressure deficit (kPa)		风速 Wind speed (m·s^-1)
	日间 Diurnal	夜间 Nocturnal	日间 Diurnal	夜间 Nocturnal	日间 Diurnal	夜间 Nocturnal	日间 Diurnal	夜间 Nocturnal
雨季前-雨季后 Before rainy season-after rainy season	0.511	-1.215	6.055^**	7.043^**	1.043	2.982^**	-3.059^**	-0.894
p	0.615	0.239	0.000	0.000	0.309	0.007	0.006	0.382

Fig. 2 Differences of soil water content in 0-6 m depth before and after the rainy season (mean ± SE). *, p < 0.05; **, p < 0.01.

Fig. 3 Ratio of nocturnal sap flow to total daily sap flow at different stem heights (mean ± SE). Different lowercase letters represent significant differences of the ratio between different heights in the same period (p < 0.05), * represent significant differences of the ratio before and after the rainy season at the same height (p < 0.05).

Fig. 4 Daily variations in momentary sap flow at different stem heights (mean ± SE of multi-day measurements of T1 sample tree). A, B show the variations before the rainy season, and C, D show the variations after the rainy season. B and D are the enlarge figures of nocturnal variations of momentary sap flow.

Fig. 5 Daily variations in stem water refilling at different heights. Positive values indicate stem water refilling, negative values indicate stem water loss. B is the enlarged figure of nocturnal variations of stem water refilling.

Table 3 Correlation coefficients between soil water content (SWC) and nocturnal sap flow rate

时期 Period	茎干高度 Stem height (m)	SWC_{0-1 m}	SWC_{1-2 m}	SWC_{2-3 m}	SWC_{3-4 m}	SWC_{4-5 m}	SWC_{5-6 m}
雨季前 Before rainy season	0.35	-0.757^**	-0.606^*	0.669^*	-0.827^**	-0.725^**	-0.610^*
	1.30	-0.437	-0.140	0.623^*	-0.510	-0.587^*	-0.590^*
	7.00	-0.769^**	-0.640^*	0.679^*	-0.833^**	-0.737^**	-0.630^*
雨季后 After rainy season	0.35	-0.084	-0.007	-0.030	-0.136	0.210	0.280
	1.30	-0.122	0.052	0.294	0.294	-0.154	-0.274
	7.00	-0.536^*	-0.306	0.267	-0.021	-0.162	-0.175

Fig. 6 Short term responses of nocturnal sap flow rate to nocturnal vapor pressure deficit and air temperature at different stem heights. *, p < 0.05; **, p < 0.01.

Fig. 7 Long term responses of nocturnal sap flow (rate) to wind speed and diurnal sap flow at different stem heights. *, p < 0.05; **, p < 0.01.

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