Responses of soil inorganic nitrogen to increased temperature and plant removal during the growing season in a Sibiraea angustata scrub ecosystem of eastern Qinghai-Xizang Plateau

doi:10.17521/cjpe.2017.0086

Abstract

Abstract:

Aims Little information has been available on the soil nitrogen transformation process of alpine scrubland under global warming and changing climate. This study aimed at clarifying seasonal dynamics of the soil nitrate and ammonium contents and their responses to increased temperature under different plant treatments.

Methods We conducted a field experiment including two plant treatments (removal- or unremoval-plant) subjected to two temperature conditions (increased temperature or control) in Sibiraea angustata scrub ecosystem on the eastern Qinghai-Xizang Plateau. The contents of soil nitrate and ammonium were measured at the early, middle and late growing seasons.

Important findings The results showed that soil nitrate and ammonium contents exhibited obvious seasonal dynamics. Throughout the entire growing season, the soil nitrate contents increased firstly and then decreased, while the soil ammonium contents increased continually. Particularly, in the early and middle growing season, the soil nitrate contents were significantly higher than those of ammonium, regardless of increased temperature and plant treatments; however, in the late growing season, the soil nitrate contents were significantly lower than those of ammonium. These results implied that soil nitrification was the major process of soil nitrogen transformation in the early and middle growing season; soil ammonification contributed mostly to soil nitrogen transformation in the late growing season. Furthermore, different responses of soil nitrate and ammonium contents to increased temperature and plant removal treatments were observed at the different stages in the growing season. The effects of increased temperature on soil nitrate contents mainly occurred in the middle and late growing season, but the effects varied with plant treatments. Increased temperature only significantly increased soil ammonium contents in the unremoval-plant plots during the middle growing season. The effects of plant treatments on soil nitrate contents only occurred in the control plots (controlled temperature). Plant removal only increased soil nitrate contents in the early and middle growing season, but significantly decreased soil nitrate contents in the late growing season. Plant removal significantly decreased soil ammonium contents in the increased temperature plots during the middle growing season. Probably, in the early and middle growing season, scrub vegetation mainly absorbed soil nitrate and the absorption process was not affected by increased temperature. These results would increase our understanding of the soil nitrogen cycling process in these alpine scrub ecosystems under global warming and changing climate.

http://jtp.cnki.net/bilingual/detail/html/ZWSB201801009

Key words: alpine scrub, warming, plant removal, soil nitrogen transformation, nitrate, ammonium

MA Zhi-Liang, ZHAO Wen-Qiang, ZHAO Chun-Zhang, LIU Mei, ZHU Pan, LIU Qing. Responses of soil inorganic nitrogen to increased temperature and plant removal during the growing season in a Sibiraea angustata scrub ecosystem of eastern Qinghai-Xizang Plateau[J]. Chin J Plant Ecol, 2018, 42(1): 86-94.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2017.0086

https://www.plant-ecology.com/EN/Y2018/V42/I1/86

Figures/Tables 6

Fig. 1 Seasonal transitions of daily mean soil temperature at 5 cm below the soil surface, daily mean air temperature at 70 cm high and soil volumetric moisture at 5 cm below the soil surface under different treatments (mean ± SD) during the experiment period. P0W0, P0W1, P1W0, P1W1 are refer to the different treatments, indicated removal-plant + controlled temperature, removal-plant + increased temperature, unremoval-plant + controlled temperature, unremoval-plant + increased temperature, respectively.

Fig. 2 Seasonal dynamics of the soil nitrate contents under different treatments (mean ± SD). P0W0, P0W1, P1W0, P1W1 are refer to the different treatments, indicated removal-plant + controlled temperature, removal-plant + increased temperature, unremoval-plant + controlled temperature, unremoval-plant + increased temperature, respectively. Differences lowercase letters indicated significant differences between different treatments at the same sampling dates (p < 0.05).

Table 1 Results of the repeated measures ANOVA showing the p values for the responses of the soil nitrate and ammonium contents and nitrate/ammonium to increased temperature (W), plant treatments (P), and sampling dates (D)

因子 Factor	D	D × P	D × W	D × P × W	P	W	P × W
硝态氮 Nitrate	<0.001	<0.001	<0.001	0.002	0.002	0.001	0.086
铵态氮 Ammonium	<0.001	0.949	0.232	0.368	0.051	0.496	0.516
硝态氮/铵态氮 Nitrate/ammonium	<0.001	<0.001	0.015	0.025	<0.001	0.001	0.046

Fig. 3 Seasonal dynamics of the soil ammonium contents under different treatments (mean ± SD). P0W0, P0W1, P1W0, P1W1 are refer to the different treatments, indicated removal- plant + controlled temperature, removal-plant + increased temperature, unremoval-plant + controlled temperature, unremoval- plant + increased temperature, respectively. Differences lowercase letters indicated significant differences between different treatments at the same sampling dates (p < 0.05).

Table 2 Correlation between soil moisture and temperature, nitrate and ammonium

指标 Index	温度 Temperature	水分 Moisture	硝态氮 Nitrate	铵态氮 Ammonium	硝态氮/铵态氮 Nitrate/ammonium
温度 Temperature	1
水分 Moisture	-0.527^**	1
硝态氮 Nitrate	0.457^**	-0.159	1
铵态氮 Ammonium	0.047	0.294^*	-0.404^**	1
硝态氮/铵态氮Nitrate/ammonium	0.232	-0.228	0.829^**	-0.813^**	1

Fig. 4 Seasonal dynamics of soil nitrate/ammonium under different treatments (mean ± SD). P0W0, P0W1, P1W0, P1W1 are refer to the different treatments, indicated removal-plant + controlled temperature, removal-plant + increased temperature, unremoval-plant + controlled temperature, unremoval-plant + increased temperature, respectively. Differences lowercase letters indicated significant differences between different treatments at the same sampling dates (p < 0.05).

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