典型草原建群种羊草对氮磷添加的生理生态响应

doi:10.3724/SP.J.1258.2014.00010

摘要/Abstract

摘要：

由于人类活动和气候变化的共同作用, 大气氮(N)沉降日益加剧, 使得陆地生态系统中的可利用性N显著增加, 生态系统更易受其他元素如磷(P)的限制。然而, 目前关于N、P养分添加对草原生态系统不同组织水平的影响研究较少, 相关机制尚不清楚。该文以内蒙古典型羊草(Leymus chinensis)草原为研究对象, 通过连续两年(2011-2012年)的N和P养分添加实验, 研究建群种羊草的生理生态性状、种群生物量和群落初级生产力对N、P添加的响应及其适应机制。结果表明: 羊草草原不同组织水平对N、P添加的响应不同。群落水平上, 地上净初级生产力在不同降水年份均受N和P元素的共同限制, N、P共同添加显著提高了地上净初级生产力; 物种水平上, N、P添加对羊草种群生物量和密度, 以及相对生物量均没有显著影响, 表明羊草能够维持种群的相对稳定; 个体水平上, 在正常降水年份(2011年), 羊草生长主要受N素限制, 而在湿润年份(2012年), 降水增加使得羊草生长没有受到明显的养分限制。羊草通过增加比叶面积、叶片大小和叶片N含量, 提高整体光合能力, 以促进个体生长。总之, 内蒙古典型草原群落净初级生产力受N、P元素共同限制, 作为建群种的羊草, 其对N、P添加的响应因组织水平而异, 也受年际间降水变化的影响。

关键词: 地上净初级生产力, 羊草, 形态性状, 氮磷添加, 组织水平, 生理性状, 典型草原

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

白雪, 程军回, 郑淑霞, 詹书侠, 白永飞. 典型草原建群种羊草对氮磷添加的生理生态响应. 植物生态学报, 2014, 38(2): 103-115. DOI: 10.3724/SP.J.1258.2014.00010

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. Chinese Journal of Plant Ecology, 2014, 38(2): 103-115. DOI: 10.3724/SP.J.1258.2014.00010

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

图/表 7

图1 实验样地的月降水量和月平均温度的变化。

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

表1 N、P添加处理和年份对群落初级生产力、羊草种群特征和功能性状的影响

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

图2 N、P添加对群落地上净初级生产力、羊草种群生物量、密度和相对生物量的影响(平均值±标准误差, n = 5)。CK, 对照; N, 氮添加; P, 磷添加; N + P, 氮、磷共同添加。不同小写字母表示处理间差异显著(p < 0.05); NS表示处理间差异不显著(p > 0.05)。

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).

图3 羊草的整株性状对N、P添加的响应(平均值±标准误差, n = 9)。CK, 对照; N, 氮添加; P, 磷添加; N + P, 氮、磷共同添加。不同小写字母表示处理间差异显著(p < 0.05)。NS表示处理间差异不显著(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).

图4 羊草的叶片形态性状对N、P添加的响应(平均值±标准误差, n = 9)。CK, 对照; N, 氮添加; P, 磷添加; N + P, 氮、磷共同添加。不同小写字母表示处理间差异显著(p < 0.05)。NS表示处理间差异不显著(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).

图5 羊草叶片N和P含量对N、P添加的响应(平均值±标准误差, n = 9)。CK, 对照; N, 氮添加; P, 磷添加; N + P, 氮、磷共同添加。不同小写字母表示处理间差异显著(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).

图6 羊草个体生物量与比叶面积(A)、光合产量(B)响应值之间的关系。N, 氮添加; P, 磷添加; N + P, 氮、磷共同添加。样本量(n) = 9。

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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