Characteristics of canopy stomatal conductance of Populus simonii stands with different degradation degrees and its responses to environmental factors

doi:10.17521/cjpe.2023.0106

Abstract

Abstract:

Aims Canopy stomatal conductance (g_s) is an important indicator for measuring canopy atmospheric water vapor exchange. Studying its characteristics and responses to environmental factors could enhance the understanding of canopy water vapor exchange process and the comprehensive mechanism of environmental factors controlling forest canopy. Currently, differences in canopy stomatal conductance characteristics and its responses to environmental factors of the same tree species with different degradation degrees are still unclear.

Methods In the growing-season of 2019 (May-September), four types of Populus simonii stands with different degrees of degradation (non-degraded, mildly degraded, moderately degraded and severely degraded) in Zhangbei County of Bashang Plateau were selected, and thermal diffusion technology (TDP) probes were set to monitor trunk sap flow continuously. Environmental factors such as photosynthetically active radiation (PAR), vapor pressure deficit (VPD), air temperature (T), relative air humidity (RH) and soil water content (SWC) were monitored synchronously to analyze the sap flow rate and canopy stomatal conductance characteristics of P. simonii and their responses to environmental factors.

Important findings (1) The daily variation of sap flow rate in P. simonii showed a single-peak curve, while the g_s showed a double-peak curve. On the monthly scale, both sap flow rate and g_s showed a trend of increasing at first and declining subsequently, and then reaching the highest values in July. The differences in sap flow rate and g_s of P. simonii among the four stands of degradation degrees were significant in May and September. (2) The g_s was all affected by T, VPD and SWC. However, due to the differences in degradation, g_s in the non-degraded stands was mainly affected by T, VPD and 80-160 cm SWC. In the mildly degraded stands g_s was mainly affected by T, 0-80 cm SWC and VPD, and that in the moderately degraded was mainly affected by 0-80 cm SWC, T, VPD, while it in the severely degraded was mainly affected by T, PAR and VPD. (3) For the all P. simonii of different degradation degrees, the g_s above 18 °C was positively correlated with T. At 0.6-2.2 kPa, it was positively correlated with VPD, while negatively correlated with SWC. The g_s of the severely degraded P. simonii was positively correlated PAR when it was below 250 μmol·m^-2·s^-1. (4) Compared to the other three types of P. simonii, the severely degraded one had a more positive response to T changes and a lower sensitivity to other environmental factors. Due to morphological degradation, control of canopy transpiration of the severely degraded P. simonii will be even stricter to avoid further degradation or dieback.

Key words: canopy stomatal conductance, Populus simonii, degradation, environmental response, sap flow

ZHANG Xiao-Yu, JIA Guo-Dong, YU Xin-Xiao, SUN Li-Bo, JIANG Tao. Characteristics of canopy stomatal conductance of Populus simonii stands with different degradation degrees and its responses to environmental factors[J]. Chin J Plant Ecol, 2024, 48(9): 1143-1156.

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Figures/Tables 13

References 54

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编号Number	人工林退化程度 Degradation degree of stand	树高 Tree height (m)	胸径 Diameter at breast height (cm)	冠幅 Crown diameter (m)
编号Number	人工林退化程度 Degradation degree of stand	树高 Tree height (m)	胸径 Diameter at breast height (cm)	东西 East-west	南北 South-north
1	无退化 Non-degradation	14.3	32.0	6.7	5.3
2	无退化 Non-degradation	14.2	23.5	4.1	2.1
3	无退化 Non-degradation	13.5	24.2	6.5	5.2
4	轻度退化 Mild degradation	14.2	23.5	2.8	3.5
5	轻度退化 Mild degradation	13.7	26.0	3.5	2.5
6	轻度退化 Mild degradation	13.4	24.2	2.8	3.5
7	中度退化 Moderate degradation	12.6	21.8	2.8	3.1
8	中度退化 Moderate degradation	11.1	16.2	2.2	3.5
9	中度退化 Moderate degradation	12.9	23.7	2.2	3.5
10	重度退化 Severe degradation	13.7	41.0	6.7	5.3
11	重度退化 Severe degradation	10.6	18.5	6.5	5.1
12	重度退化 Severe degradation	12.9	23.7	6.4	5.3

编号Number	人工林退化程度 Degradation degree of stand	树高 Tree height (m)	胸径 Diameter at breast height (cm)	冠幅 Crown diameter (m)
编号Number	人工林退化程度 Degradation degree of stand	树高 Tree height (m)	胸径 Diameter at breast height (cm)	东西 East-west	南北 South-north
1	无退化 Non-degradation	14.3	32.0	6.7	5.3
2	无退化 Non-degradation	14.2	23.5	4.1	2.1
3	无退化 Non-degradation	13.5	24.2	6.5	5.2
4	轻度退化 Mild degradation	14.2	23.5	2.8	3.5
5	轻度退化 Mild degradation	13.7	26.0	3.5	2.5
6	轻度退化 Mild degradation	13.4	24.2	2.8	3.5
7	中度退化 Moderate degradation	12.6	21.8	2.8	3.1
8	中度退化 Moderate degradation	11.1	16.2	2.2	3.5
9	中度退化 Moderate degradation	12.9	23.7	2.2	3.5
10	重度退化 Severe degradation	13.7	41.0	6.7	5.3
11	重度退化 Severe degradation	10.6	18.5	6.5	5.1
12	重度退化 Severe degradation	12.9	23.7	6.4	5.3

月份 Month	无退化 Non-degradation	轻度退化 Mild degradation	中度退化 Moderate degradation	重度退化 Severe degradation
5月 May	43.54 ± 3.90^b	31.52 ± 3.13^bc	17.65 ± 2.05^c	80.71 ± 8.36^a
6月 June	114.75 ± 12.40^a	67.25 ± 8.67^b	54.39 ± 6.09^b	47.64 ± 4.68^b
7月 July	151.60 ± 18.19^a	100.48 ± 13.22^b	68.15 ± 8.39^bc	43.83 ± 4.80^c
8月 August	119.25 ± 14.83^a	54.28 ± 7.14^b	41.57 ± 5.29^b	35.91 ± 4.17^b
9月 September	48.37 ± 6.25^a	10.15 ± 1.16^b	9.39 ± 1.22^b	4.85 ± 0.61^b

月份 Month	无退化 Non-degradation	轻度退化 Mild degradation	中度退化 Moderate degradation	重度退化 Severe degradation
5月 May	43.54 ± 3.90^b	31.52 ± 3.13^bc	17.65 ± 2.05^c	80.71 ± 8.36^a
6月 June	114.75 ± 12.40^a	67.25 ± 8.67^b	54.39 ± 6.09^b	47.64 ± 4.68^b
7月 July	151.60 ± 18.19^a	100.48 ± 13.22^b	68.15 ± 8.39^bc	43.83 ± 4.80^c
8月 August	119.25 ± 14.83^a	54.28 ± 7.14^b	41.57 ± 5.29^b	35.91 ± 4.17^b
9月 September	48.37 ± 6.25^a	10.15 ± 1.16^b	9.39 ± 1.22^b	4.85 ± 0.61^b

月份 Month	无退化 Non-degradation	轻度退化 Mild degradation	中度退化 Moderate degradation	重度退化 Severe degradation
5月 May	0.077 ± 0.008 4^b	0.106 ± 0.011 0^b	0.070 ± 0.007 8^b	0.220 ± 0.021 0^a
6月 June	0.297 ± 0.039 7^ab	0.337 ± 0.045 0^a	0.219 ± 0.033 7^b	0.213 ± 0.024 9^b
7月 July	0.662 ± 0.102 0^a	0.789 ± 0.102 0^a	0.569 ± 0.072 9^ab	0.367 ± 0.045 2^ab
8月 August	0.372 ± 0.048 0^a	0.265 ± 0.037 2^b	0.242 ± 0.024 6^b	0.255 ± 0.034 0^b
9月 September	0.175 ± 0.014 5^a	0.082 ± 0.006 8^b	0.054 ± 0.007 2^c	0.036 ± 0.006 2^c