Effect of different levels of nitrogen addition on aboveground and belowground net primary productivity in Leymus secalinus grassland in Northern Shanxi, China

doi:10.17521/cjpe.2024.0453

Abstract

Abstract:

Aims Nitrogen (N) addition can significantly affect the aboveground net primary productivity (ANPP) and belowground net primary productivity (BNPP) of grassland ecosystems. However, the mechanisms underlying different responses of plant ANPP and BNPP to N addition and their saturation response thresholds at different levels of N addition are not clear.

Methods Eight N addition levels (0, 1, 2, 4, 8, 16, 24, 32 g·m^-2·a^-1) were set up in the Leymus secalinus grassland in Northern Shanxi, and the changes of plant ANPP, BNPP and total net primary productivity (NPP) were monitored for five years from 2017 to 2021. The temporal stability, N saturation threshold and N response efficiency of plant productivity were also calculated.

Important findings The results showed that: (1) ANPP and NPP were increased nonlinearly with the increase of N addition levels. The saturation response thresholds of ANPP and NPP across five years (2017-2021) were 25.7 g·m^-2·a^-1and 21.3 g·m^-2·a^-1, respectively. (2) ANPP and BNPP had different sensitivities to N addition, and the sensitivity of ANPP was higher than that of BNPP. The change in NPP was mainly caused by changes in ANPP, suggesting that plant productivity distribution to the aboveground increased as the level of N addition increased. (3) Nitrogen response efficiency of ANPP (NRE_ANPP)showed an exponential downward trend with the increase of N addition levels, while the nitrogen response efficiency of BNPP (NRE_BNPP) and nitrogen response efficiency of NPP (NRE_NPP) showed a linear downward trend with the increase of N addition levels. (4) Structural equation model analysis showed that soil NO^-₃-N content and pH regulated the effects of N addition and duration on plant ANPP and BNPP. There were different regulatory mechanisms of ANPP and BNPP under low N and high N addition treatments. Both ANPP and BNPP were directly affected by N addition under low N addition treatments, while the soil inorganic N content indirectly regulated the response of ANPP and BNPP to N addition under high N addition treatments. This study indicates that plant productivity in grassland ecosystem responds nonlinearly with N addition levels, which provided dataset supporting for ecosystem service function of Leymus secalinus grassland in Northern Shanxi under the scenario of N deposition.

Key words: nitrogen deposition, aboveground net primary productivity, belowground net primary productivity, nitrogen response efficiency, response threshold

BIAN Jia-Chen, WANG Rui, GAO Yang-Yang, LIANG Wen-Jun, JIN Hong, ZHANG Wen-Xuan, ZHANG Xiao-Rong, HAO Jie, $\boxed{\hbox{WANG Chang-Hui}}$, DONG Kuan-Hu, DIAO Hua-Jie. Effect of different levels of nitrogen addition on aboveground and belowground net primary productivity in Leymus secalinus grassland in Northern Shanxi, China[J]. Chin J Plant Ecol, 2025, 49(12): 2043-2053.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2024.0453

https://www.plant-ecology.com/EN/Y2025/V49/I12/2043

Figures/Tables 7

Fig. 1 Annual precipitation and air temperature during 2017-2021 at the study site in Leymus secalinus grassland in Northern Shanxi.

Table 1 Results (F value) of two factors analysis of variance of the effects of year, nitrogen addition, and their interactions on plant productivity and soil physicochemical properties of Leymus secalinus grassland in Northern Shanxi

因子 Factor	ANPP	BNPP	NPP	NH₄⁺-N	NO^-₃-N	ST	SWC	pH
年 Year (Y)	12.732^***	60.957^***	42.353^***	1164.145^***	336.475^***	648.398^***	86.091^***	45.046^***
氮添加 Nitrogen addition (N)	12.502^***	3.222^**	10.075^***	22.508^***	75.519^***	3.824^**	0.522	4.051^**
年×氮添加 Y × N	0.832	0.931	0.776	22.805^***	7.085^***	0.413	0.535	0.456

Fig. 2 Effect of nitrogen addition on soil temperature (A), pH (B), NH4+-N content (C), and NO-3-N content (D) in Leymus secalinus grassland in Northern Shanxi (mean ± SE).

Fig. 3 Threshold of net primary productivity with the increase of nitrogen addition levels in Leymus secalinus grassland in Northern Shanxi of 2017-2021 (mean ± SE). ANPP, aboveground net primary productivity; BNPP, belowground net primary productivity; NPP, net primary productivity. Solid line represents a significant fitted equation (p < 0.05), and dashed line represents an insignificant fitted equation (p > 0.05).

Fig. 4 Response efficiency of aboveground net primary productivity (NREANPP, A), underground net primary productivity (NREBNPP, B), and net primary productivity (NRENPP, C) under different nitrogen addition levels in Leymus secalinus grassland in Northern Shanxi (mean ± SE).

Fig. 5 Annual variation (A-C) and temporal stability (D-F) of plant productivity in Leymus secalinus grassland under different nitrogen (N) addition levels in Northern Shanxi (mean ± SE). ANPP, aboveground net primary productivity; BNPP, belowground net primary productivity; NPP, net primary productivity; N0, N1, N2, N4, N8, N16, N24, N32 represent N addition levels are 0, 1, 2, 4, 8, 16, 24, 32 g∙m-2∙a-1, respectively. *, p < 0.05; **, p < 0.01; ns, p > 0.05.

Fig. 6 Structural equation model of the directly and indirectly effects of low nitrogen addition (A) and high nitrogen (N) addition (B) on aboveground net primary productivity (ANPP) and belowground net primary productivity (BNPP). Blue and red lines represent significant positive and negative correlation, respectively, and black dashed line represents no significant correlation. Line width is proportional to the strength of the correlation. Low N addition: significance p = 0.373, Akaike Information Criterion (AIC) = 51.36, Chi-square = 5.36, df = 5; high N addition: p = 0.614, AIC = 45.22, Chi-square = 7.22, df = 9. NH4+-N, soil NH4+-N content; NO-3-N, soil NO-3-N content; pH, soil pH; ST, soil temperature; SM, soil water content. *, p < 0.05; **, p < 0.01; ***, p < 0.001.

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