Effects of freeze-thaw changes on soil physicochemical properties and enzyme activities in root zone of Picea asperata and Fargesia nitida under subalpine forests of southwest China

doi:10.17521/cjpe.2022.0031

Abstract

Abstract:

Aims The subalpine forests of southwest China belongs to a typical seasonal frozen soil area. This study aimed to explore the effects of freeze-thaw changes on the soil physicochemical properties and enzyme activities under forest soils in response to climate warming.

Methods Infrared radiation heaters were applied to simulate climate warming. Soils in the root zone of Picea asperata and Fargesia nitida were collected to explore the effects of warming on soil freeze-thaw cycles, soil physicochemical properties and enzyme activities. Meanwhile, soil incubation experiments were conducted to further analyze the effects of different freeze-thaw cycles on soil properties.

Important findings Our results showed that (1) Experimental warming increased the soil temperatures by 2.85 and 2.13 °C, decreased freezing days by 60 and 32 days, and also declined freeze-thaw cycles from 1-3 times to 0 time at the 5 cm and 15 cm soil depths, respectively. (2) Warming increased the contents of soil total nitrogen (TN), dissolved organic nitrogen (DON) and microbial biomass nitrogen (MBN), but significantly reduced the content of ammonium nitrogen (NH₄⁺-N) under both P. asperata and F. nitida plots. The soil freezing days and number of freeze-thaw cycles were significantly negatively correlated with TN and DON contents, and significantly positively correlated with NH₄⁺-N content. (3) Warming significantly promoted the activity of β-N-acetylglucosaminidase (NAG), but significantly inhibited the activity of urease (Ure) under the root zone soil of the two species. The activities of NAG and Ure were significantly correlated with freezing days and the number of freeze-thaw cycles. (4) Similar to results of the field study, the simulated freeze-thaw cycles significantly increased NH₄⁺-N content and 4-methylumbelliferyl-β-D-glucoside (BG) activity, but decreased NAG activity under the root zone soil of P. asperata. On the other hand, freeze-thaw cycles increased NH₄⁺-N content and reduced the activities of NAG and BG under the root zone soil of F. nitida. However, the effects of freeze-thaw cycles on the contents of nitrate nitrogen (NO₃^--N) and DON as well as the activities of Ure and protease (Pro) were different based on the results of field experiment. Redundancy analysis showed that soil enzyme activities under the root zone of F. nitida were mainly affected by DON content, whereas those parameters under the root zone of P. asperatawere significantly correlated with pH, NH₄⁺-N and DON contents. These results suggested that the disappearance of freeze-thaw cycles caused by future climate warming would significantly affect the soil physicochemical properties (especially soil nitrogen pool) and enzyme activities during non-growing season under subalpine forests of southwest China. But the underlying mechanism needs further study.

Key words: freeze-thaw cycle, simulated warming, Picea asperata, Fargesia nitida, soil physicochemical property, enzyme activity

GUO Min, LUO Lin, LIANG Jin, WANG Yan-Jie, ZHAO Chun-Zhang. Effects of freeze-thaw changes on soil physicochemical properties and enzyme activities in root zone of Picea asperata and Fargesia nitida under subalpine forests of southwest China[J]. Chin J Plant Ecol, 2023, 47(6): 882-894.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2022.0031

https://www.plant-ecology.com/EN/Y2023/V47/I6/882

Figures/Tables 8

Fig. 1 Temperature and humidity of 5 cm soil layer of sample plot under subalpine forests of southwest China (2018-12-06 to 2019-03-31).

Table 1 Freeze-thaw cycles of the warming and control plots during December 2018 to March 2019 under subalpine forests of China (mean ± SE)

处理 Treatment	土深5 cm Soil depth 5 cm		土深15 cm Soil depth 15 cm
处理 Treatment	冻结时间 Freezing time (d)	冻融循环次数 Freeze thaw cycle (times)	冻结时间 Freezing time (d)	冻融循环次数 Freeze thaw cycle (times)
对照 Control	65 ± 2.9	3 ± 0	36 ± 1.1	1 ± 0
增温 Warming	5 ± 0.6	0 ± 0	4 ± 0.5	0 ± 0

Fig. 2 Effects of warming on soil physicochemical properties of sample plot under subalpine forests of southwest China (mean ± SE). CK, control treatment; W, warming treatment. FN, Fargesia nitida; PA, Picea asperata. DON, dissolved organic nitrogen; MBN, microbial biomass nitrogen; NH4+-N, ammonium nitrogen; NO3--N, nitrate nitrogen. *, p < 0.05; ns, p > 0.05.

Fig. 3 Effects of warming on soil enzyme activities of sample plot under subalpine forests of southwest China (mean ± SE). CK, control treatments; W, warming treatments. FN, Fargesia nitida; PA, Picea asperata. BG, activity of 4-methylumbelliferyl-β-D-glucoside; NAG, activity of β-N-acetylglucosaminidase; Pro, activity of protease; Ure, activity of urease. *, p < 0.05; **, p < 0.01; ***, p < 0.001; ns, p < 0.05.

Table 2 Correlation analysis between soil physicochemical factors, enzyme activities and freeze-thaw cycles

	SM	pH	TC	TN	NO₃^--N	NH₄⁺-N	MBN	DON	BG	NAG	Pro	Ure
T5	-0.33	-0.27	0.08	-0.67^*	-0.38	0.72^**	-0.14	-0.62^**	0.94	-0.93^**	0.02	0.72^**
T15	-0.33	-0.27	0.08	-0.48^*	-0.51	0.83^**	-0.01	-0.85^**	0.889	-0.91^**	0.16	0.76^**
D5	-0.33	-0.30	0.01	-0.66^*	-0.43	0.80^**	-0.08	-0.71^**	0.906	-0.96^**	0.04	0.74^**
D15	-0.34	-0.29	0.02	-0.68^*	-0.42	0.79^**	-0.08	-0.69^**	0.898	-0.97^**	0.03	0.74^**

Fig. 4 Effects of freeze-thaw cycles on soil physicochemical properties of sample plot under subalpine forests of southwest China (mean ± SE). 0, control treatment; 5, five freeze-thaw cycles; 15, fifteen freeze-thaw cycles. FN, Fargesia nitida; PA, Picea asperata. Different lowercase letters represent significant difference between treatments (p < 0.05).

Fig. 5 Effects of freeze-thaw cycles on soil enzyme activities of sample plot under subalpine forests of southwest China (mean ± SE). 0, control treatment; 5, five freeze-thaw cycles; 15, fifteen freeze-thaw cycles. FN, Fargesia nitida; PA, Picea asperata. BG, activity of 4-methylumbelliferyl-β-D-glucoside; NAG, activity of β-N-acetylglucosaminidase; Pro, activity of protease; Ure, activity of urease. Different lowercase letters represent significant difference between treatments (p < 0.05).

Fig. 6 Redundancy analysis (RDA) of soil enzyme activities and physicochemical factors of sample plot under subalpine forests of southwest China. A, Fargesia nitida. B, Picea asperata. BG, activity of 4-methylumbelliferyl-β-D-glucoside; DON, dissolved organic nitrogen content; MBN, microbial biomass nitrogen content; NAG, activity of β-N-acetylglucosaminidase; NH4+-N, ammonium nitrogen content; NO3--N, nitrate nitrogen content; Pro, activity of protease; TC, total carbon content; TN, total nitrogen content; Ure, activity of urease.

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