Climate change regulate tree growth and intrinsic water use efficiency of Populus simonii at different levels of degradation

doi:10.17521/cjpe.2023.0363

Abstract

Abstract:

Aims As one of the important species in shelterbelt forests of the northern China, the large-scale decline of the Populus simonii has a serious impact on the healthy development of the ecosystem and the sustainable management of shelterbelt forests, and the investigation on the causes of P. simonii degradation in the context of climate change can provide a reference for the management of plantation forests.

Methods The study investigated three P. simonii plantation forests with different degradation levels in Zhangbei, and compared their basal area increment (BAI), intrinsic water use efficiency (iWUE), tree ring carbon stable isotopes ratio, and stomatal regulation strategies, in order to analyze the impacts of climate change on the growth of P. simonii and its intrinsic water use efficiency.

Important findings The results showed that: 1) CO₂ concentration and air temperature were the main drivers of iWUE changes, with a significant increasing trend in iWUE under the combined effects of increasing atmospheric CO₂ concentration, climate change and physiological conditions. 2) The tree growth in the three P. simonii stands with different levels of degradation was mainly determined by air temperature, and in most cases the increase in iWUE did not promote tree growth. 3) Declining trees were more sensitive to drought in the context of climate change, and more stringent stomatal strategies were adopted by highly degraded stands under drought stress. 4) The negative effects of increased drought stress on tree physiology could not be counteracted by increased CO₂ concentrations and increased air temperatures, and prolonged drought stress might lead to further decline in the growth of degraded trees.

Key words: climate change, drought, stomatal regulation, tree ring, stable isotope, plantation

WANG Kun-Ying, QIU Gui-Fu, LIU Zi-He, MENG Jun, LIU Yu-Xuan, JIA Guo-Dong. Climate change regulate tree growth and intrinsic water use efficiency of Populus simonii at different levels of degradation[J]. Chin J Plant Ecol, 2025, 49(2): 343-355.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2023.0363

https://www.plant-ecology.com/EN/Y2025/V49/I2/343

Figures/Tables 11

Fig. 1 Location and sampling sites distribution of Populus simonii plantation forests with three degradation levels in Zhangbei.

Table 1 Statistical information on sample plots of Populus simonii plantations at different levels of degradation (mean ± SD)

退化等级 Degradation level	衰退树木比率 Rate of dieback trees (%)	树高 Height (m)	胸径 DBH (cm)	叶面积指数 LAI	密度 Density (·hm^-2)	采样点数量 (小区数量) Sites (subplots)	海拔 Altitude (m)
正常生长 Normal growth	<20	13.88 ± 4.25^a	22.15 ± 2.25^a	2.06 ± 0.96^a	1 042 ± 532	9 (3)	1 250-1 275
轻度退化 Mild degradation	20-60	10.82 ± 2.25^a	17.62 ± 1.86^a	1.30 ± 0.53^ab	1 650 ± 839	9 (3)	1 238-1 285
重度退化 Severe degradation	>60	8.95 ± 2.25^b	13.71 ± 1.64^b	0.98 ± 0.21^c	728 ± 230	9 (3)	1 256-1 286

Fig. 2 Characterization of Palmer Drought Index (PDSI) in Zhangbei.

Fig. 3 Interannual variation of temperature, precipitation, relative humidity and annual vapor pressure deficit (VPD) in Zhangbei.

Fig. 4 Basal area increment (BAI) and intrinsic water use efficiency (iWUE) of Populus simonii at different degradation levels in Zhangbei (mean ± SD). Different uppercase letters indicate significant differences in iWUE between degradation levels, and different lowercase letters indicate significant differences in BAI between degradation levels (p < 0.05).

Fig. 5 Trends and comparisons of carbon stable isotope values of tree ring cellulose (δ13C) and 13C discrimination in the tree ring (Δ13C) changes in Populus simonii with different degradation levels in Zhangbei (mean ± SD). Significant differences (p < 0.05) in δ13C between different degrees of degradation are indicated by different uppercase letters, and significant differences (p < 0.05) in Δ13C between different degrees of degradation are indicated by different lowercase letters.

Fig. 6 Intercellular CO2 concentration (Ci) and the ratio of Ci to atmospheric CO2 concentration (Ca) in Populus simonii with different degradation levels. Significant differences (p < 0.05) in Ci between different degrees of degradation are indicated by different lowercase letters, and significant differences (p < 0.05) in Ci/Ca between different degrees of degradation are indicated by different uppercase letters.

Fig. 7 Correlation coefficients among basal area increment (BAI), intrinsic water use efficiency (iWUE) and inter-annual meteorological factors of Populus simonii with different degradation levels. * and ** represent significance levels less than 0.05 and 0.01, respectively. Figures A, B and C show BAI and iWUE correlations with pre-2000 meteorological factors, and Figures D, E and F show post-2000 meteorological factor correlations. BAIn, BAIm and BAIs represent BAI in normal, mild and severely degraded stands, respectively. P, precipitation; PDSI, Palmer drought severity index; RH, relative humidity; T, air temperature; VPD, vapor pressure deficit.

Table 2 Akaike Information Criterion (AIC) values of stepwise regression between basal area increment (BAI) and meteorological factors for Populus simonii

选取指标 Selection of indicators	正常生长 Normal growth		轻度退化 Mild degradation		重度退化 Severe degradation
选取指标 Selection of indicators	2000年前 Pre-2000	2000年后 Post-2000	2000年前 Pre-2000	2000年后 Post-2000	2000年前 Pre-2000	2000年后 Post-2000
T	60.35	16.71	49.18	14.19	35.99	16.71
T+PDSI	61.41	18.50	49.82	15.53	35.50	18.50
RH+PDSI	59.31	14.75	59.31	16.63	43.72	17.99
P+T+PDSI	63.14	20.46	51.53	17.44	36.87	20.46
T+RH+VPD+PDSI	53.52	17.63	53.52	18.67	39.32	21.84
P+T+RH+VPD+PDSI	67.07	19.61	55.32	20.66	40.74	23.80

Table 3 Akaike Information Criterion (AIC) values of stepwise regression between intrinsic water use efficiency (iWUE) and meteorological factors for Populus simonii

选取指标 Selection of indicators	正常生长 Normal growth		轻度退化 Mild degradation		重度退化 Severe degradation
选取指标 Selection of indicators	2000年前 Pre-2000	2000年后 Post-2000	2000年前 Pre-2000	2000年后 Post-2000	2000年前 Pre-2000	2000年后 Post-2000
PDSI	56.09	40.80	73.23	58.40	78.36	59.71
T+PDSI	58.06	40.39	45.22	60.36	77.94	59.23
T+VPD	65.48	37.12	74.35	60.63	79.61	61.78
P+PDSI	54.72	42.80	75.14	59.98	79.36	61.71
T+VPD+PDSI	60.05	39.03	76.05	62.36	78.79	60.14
P+T+RH+PDSI	58.19	44.33	78.27	63.90	80.80	63.14
P+T+RH+VPD+PDSI	60.14	42.54	79.00	65.89	81.99	63.67

Table 4 Effect of monthly mean air temperature on basal area increment (BAI) for Populus simonii

月份 Month	BAI_n	BAI_m	BAI_s
1	0.18	0.24	0.26
2	<0.01^**	<0.01^**	<0.01^**
3	0.26	0.28	0.22
4	0.23	0.22	0.19
5	0.20	0.19	0.16
6	0.04^*	0.04^*	0.29
7	<0.01^**	<0.01^**	0.27
8	<0.01^**	<0.01^**	0.04^*
9	<0.01^**	<0.01^**	<0.01^**
10	0.11	0.05	0.01^*
11	0.20	0.23	0.20
12	0.06	0.01	0.12

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