Ecophysiological responses of Leymus chinensis to nitrogen and phosphorus additions in a typical steppe

doi:10.3724/SP.J.1258.2014.00010

Abstract

Abstract:

Aims The accelerated atmospheric nitrogen (N) deposition due to human activity and climate change greatly increases the availability of reactive N in terrestrial ecosystems, leading to limitations of other nutrient elements such as phosphorus (P). The effects of N and P additions on grassland ecosystems across different organizational levels, however, have rarely been studied; particularly the underpinning mechanisms remain unclear. Our objective is to examine the effects of N and P additions on aboveground net primary productivity and functional traits of Leymus chinensis, which is a dominant species in the typical steppe of Inner Mongolia, and to study nutrient limitations at different organizational levels in a L. chinensis steppe induced by N and P additions.
Methods We conducted a field manipulation experiment with additions of N (10.5 g N·m^-2·a^-1) and P (32 g P₂O₅·m^-2·a^-1) in a L. chinensis steppe ecosystem in Inner Mongolia in 2011 and 2012. The aboveground primary productivity, population biomass and density, whole-plant traits (e.g., individual biomass and stem-leaf biomass ratio), leaf physiological (e.g., photosynthetic rate, water use efficiency, and leaf N content) and morphological traits (e.g., leaf area and specific leaf area) of L. chinensis were investigated.
Important findings Our results showed that N and P additions had different effects on the aboveground biomass at different organizational levels. The aboveground net primary productivity was greatly enhanced by the combined N and P additions in 2011 (normal precipitation) and 2012 (above average precipitation), indicating the co-limitation of N and P at the community level. At the species level, N and P additions had no significant effects on population biomass, density, and relative biomass of L. chinensis in both years, indicating that this species could maintain population stability. The individual biomass of L. chinensis was increased by N addition in 2011; whereas it was not affected by either N or P addition in 2012. It is suggested that the growth of L. chinensis may be subjected to N limitation in the dry year, but not to any nutrient limitation in the wet year due to water mediation. Leymus chinensis exhibited high specific leaf area, leaf size and leaf N content, and high photosynthetic yield in response to N enrichment. In conclusion, our results indicate that the primary productivity of typical steppe in Inner Mongolia is co-limited by N and P availability. The functional traits of L. chinensis in response to N and P additions are dependent on the organizational level and mediated by interannual precipitation fluctuations.

Key words: aboveground net primary productivity, Leymus chinensis, morphological traits, nitrogen and phosphorus additions, organizational level, physiological traits, typical steppe

BAI Xue, CHENG Jun-Hui, ZHENG Shu-Xia, ZHAN Shu-Xia, BAI Yong-Fei. Ecophysiological responses of Leymus chinensis to nitrogen and phosphorus additions in a typical steppe[J]. Chin J Plant Ecol, 2014, 38(2): 103-115.

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URL: https://www.plant-ecology.com/EN/10.3724/SP.J.1258.2014.00010

https://www.plant-ecology.com/EN/Y2014/V38/I2/103

Figures/Tables 7

Fig. 1 Monthly precipitation and monthly mean air temperature of the study site.

Table 1 Effects of N and P additions and year on community aboveground net primary productivity, population traits and plant functional traits of Leymus chinensis

	因素 Factor	df	群落特征和植物功能性状 Community characteristics and plant functional traits
群落地上净生产力和羊草种群特征 ANPP and population traits of L. chinensis			ANPP	PB	PD	RAB
	处理 Treatment (T)	3	<0.000 1	0.788	0.505	0.373
	年份 Year (Y)	1	0.001	<0.000 1	<0.000 1	<0.000 1
	T × Y	3	0.278	0.493	0.828	0.980
羊草形态性状 Morphological traits of L. chinensis			IB	LB	SB	SLR	SLA	LA	LM
	处理 Treatment (T)	3	0.069	0.075	0.114	0.701	0.144	0.007	0.069
	年份 Year (Y)	1	0.885	0.203	0.106	0.001	0.066	0.993	0.885
	T × Y	3	0.140	0.234	0.073	0.368	0.649	0.539	0.140
羊草生理性状 Physiological traits of L. chinensis			N	P	P_n	T_r	G_s	C_i	WUE	L_s
	处理 Treatment (T)	3	<0.000 1	<0.000 1	0.117	0.085	0.293	0.731	0.282
	年份 Year (Y)	1	0.817	0.001	0.980	0.135	<0.000 1	<0.000 1	0.279	<0.000 1
	T × Y	3	0.871	0.001	0.667	0.626	0.930	0.612	0.079	0.656

Fig. 2 Effects of N and P additions on aboveground net primary productivity (ANPP), population biomass, density, and relative biomass of Leymus chinensis (mean ± SE, n = 5). CK, control; N, N addition; P, P addition; N + P, N and P additions. Different lower-case letters indicate significant differences among treatments (p < 0.05); NS indicates non-significant difference among treatments (p > 0.05).

Fig. 3 The whole-plant traits of Leymus chinensis in response to N and P additions (mean ± SE, n = 9). CK, control; N, N addition; P, P addition; N + P, N and P additions. Different lower-case letters indicate significant differences among treatments (p < 0.05). NS indicates non-significant difference among treatments (p > 0.05).

Fig. 4 Leaf morphological traits of Leymus chinensis in response to N and P additions (mean ± SE, n = 9). CK, control; N, N addition; P, P addition; N + P, N and P additions. Different lower-case letters indicate significant differences among treatments (p < 0.05). NS indicates non-significant difference among treatments (p > 0.05).

Fig. 5 Responses of leaf N and P contents to N and P additions of Leymus chinensis (mean ± SE, n = 9). CK, control; N, N addition; P, P addition; N + P, N and P additions. Different lower-case letters indicate significant differences among treatments (p < 0.05).

Fig. 6 Relationships of individual biomass response ratio with the response ratios of specific leaf area (SLA) (A) and photosynthetic yield (B) of Leymus chinensis. N, N addition; P, P addition; N + P, N and P additions. Sampling size (n) = 9.

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