Net ecosystem carbon exchange characteristics in Stipa breviflora desert steppe with different stocking rates

doi:10.17521/cjpe.2017.0066

Abstract

Abstract:

Aims Grassland ecosystem is the largest terrestrial ecosystem type in China. The dynamic changes in carbon cycle play an important role in global carbon budget balance. Grazing is the main use of grassland ecosystem. Different grazing intensity has different effects on the grassland ecosystem.

Methods In the growing seasons (May to October) from 2014 to 2016, we used portable optical LI-6400 and the method of static chamber to measure net ecosystem carbon exchange in Stipa breviflora desert steppe with 3 different stocking rates (CK, no grazing control; LG, lightly grazing; HG, heavily grazing). At the same time, the soil temperature and moisture of 10 cm depth were also measured. The effects of stocking rate and hydrothermal factors on the carbon exchange were discussed.

Important findings Stocking rate had a significant impact on net ecosystem carbon exchange. With the increase of stocking rate, the net ecosystem carbon exchange, ecosystem respiration, gross ecosystem productivity decreased by 48.6%, 35.3% and 40.4% respectively. Heavily grazing significantly reduced grassland carbon sequestration, but lightly grazing had no significant effect. The inter-annual changes in net carbon exchange was mainly controlled by precipitation. Throughout the growing season, Stipa breviflora desert steppe were carbon sinks. The contribution of soil temperature to the variations of net ecosystem carbon exchange was higher than that of soil moisture.

http://jtp.cnki.net/bilingual/detail/html/ZWSB201803011

Key words: Stipa breviflora desert steppe, stocking rate, net ecosystem carbon exchange, ecosystem respiration, gross ecosystem productivity

JIN Yu-Xi, LIU Fang, ZHANG Jun, HAN Meng-Qi, WANG Zhong-Wu, QU Zhi-Qiang, HAN Guo-Dong. Net ecosystem carbon exchange characteristics in Stipa breviflora desert steppe with different stocking rates[J]. Chin J Plant Ecol, 2018, 42(3): 361-371.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2017.0066

https://www.plant-ecology.com/EN/Y2018/V42/I3/361

Figures/Tables 8

Fig. 1 Daily mean air temperature and precipitation in the growing seasons from 2014 to 2016. Each data point is the observation value of the day.

Fig. 2 During the growing season 2014-2016, 10 cm surface soil temperature and moisture under different stocking rates. Each data point is the average of all repeated observations for that day under that treatment.

Table 1 Effect of grazing, year and their interactions on ecosystem carbon exchange

	生态系统净碳交换 Net ecosystem carbon exchange	生态系统呼吸 Ecosystem respiration	生态系统总初级生产力 Gross ecosystem productivity	土壤温度 Soil temperature	土壤湿度 Soil moisture
载畜率 Stocking rate	<0.001^**	<0.000 1^***	<0.000 1^***	0.740	0.085
年 Year	<0.000 1^***	<0.000 1^***	<0.000 1^***	0.080	<0.000 1^***
载畜率×年 Stocking rate × Year	0.287	0.022^*	0.071	0.984	0.808

Fig. 3 Variations of ecosystem carbon exchange in plots with different stocking rates from 2014 to 2016 (mean ± SE). CK, no grazing control; LG, lightly grazing; HG, heavily grazing. Capital letters indicate significant differences (p < 0.05) in sites with different stocking rates in the same year. Lowercase letters indicate significant differences (p < 0.05) in different years at sites with the same rate of stocking. The same letters mean no significant difference (p > 0.05).

Fig. 4 The monthly dynamic of net ecosystem carbon exchange from 2014 to 2016 (mean ± SE). NEE, net ecosystem carbon exchange. Each data point is the observed value of each stocking rate treatment observed on the day.

Table 2 The relative contribution of soil temperature and soil moisture to the variations of net ecosystem carbon exchange

子模型 Sub-model	2014年额外方差贡献 Extra variance contribution in 2014			2015年额外方差贡献 Extra variance contribution in 2015			2016年额外方差贡献 Extra variance contribution in 2016
子模型 Sub-model	R²	ST	SM	R²	ST	SM	R²	ST	SM
K = 0	0	0.075	0.041	0	0.094	0.003	0	0.228	0.21
ST	0.075		0.004	0.094		0.090	0.228		0.154
SM	0.041	0.039		0.003	0.181		0.206	0.176
K = 1		0.039	0.004		0.181	0.090		0.176	0.154
ST, SM	0.079			0.184			0.382
总平均贡献 Total average contribution		0.057	0.022		0.137	0.046		0.202	0.180
在方差中的比例 Ratio in variance		72.28%	27.72%		74.71%	25.29%		52.88%	47.12%

Fig. 5 Relationship between gross primary productivity (GEP) and net ecosystem carbon exchange (NEE) (left panel) and ecosystem respiration (ER) and net ecosystem carbon exchange (NEE) (right panel) in plots with different stocking rates from 2014 to 2016. CK, no grazing control; LG, lightly grazing; HG, heavily grazing. Each data point in the graph is the value of each replicate to each stocking rate observed during the day.

Fig. 6 The relationship between ecosystem carbon exchange and soil temperature and soil moisture from 2014 to 2016. NEE, net ecosystem carbon exchange; ER, ecosystem respiration; GEP, gross primary productivity. In 2014, the exponential model was used to fit the relationship between carbon flux and soil temperature and soil moisture, In 2015, the exponential model was used to fit the relationship between ER and soil temperature, and the linear model was used to fit the relationship between NEE, GEP and soil temperature. In 2016, the linear model was used to fit the relationship between carbon flux and soil temperature and soil moisture. Each data point is the observed value of the day.

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