不同放牧强度下内蒙古温带典型草原优势种植物防御策略

放牧是草原的主要利用方式, 但对牧草造成了一定的生物胁迫。面对生存压力, 牧草会通过调节初级与次级代谢过程启动防御机制。该研究以内蒙古温带典型草原优势种植物为研究对象, 通过测定其在5个放牧水平下不同营养器官中的次级代谢产物及木质素等含量, 探讨大针茅(Stipa grandis)和羊草(Leymus chinensis)的各营养器官在防御机制中的角色及其碳氮权衡策略。结果表明: 面对放牧胁迫, 大针茅和羊草会产生大量的单宁、总黄酮、酚类以及生物碱等次级代谢产物, 并以叶片为主要的合成及储存器官。中度放牧使羊草的化学防御机制得到较充分的诱导及表达。但二者地上部分木质素含量并无显著增加, 因此, 二者在避牧性机制上更倾向于化学防御而非机械防御。由于羊草有更高的氮利用效率, 这使得羊草可以通过碳氮两种代谢途径进行防御, 但大针茅在生长初期并不能将氮高效地分配到化学防御中。大针茅和羊草在生长初期面对轻度放牧胁迫, 较多的资源仍然用于初级代谢, 增加了植物耐牧性。因此, 轻度放牧有利于提高牧草的碳氮资源利用效率、提高生态系统生产力及稳定性。

Defense strategies of dominant plants under different grazing intensity in the typical temperate steppe of Nei Mongol,China

Aims Grazing is one of the main grassland using modes, which has caused certain biotic stress on pasture. In order to survive, pasture initiates defense mechanisms by regulating the primary and secondary metabolic processes. This article aims to 1) figure out the distribution of defensive substances in different organs produced by the dominant plants Stipa grandis and Leymus chinensis; 2) explore the similarities and differences of the defense mechanisms and carbon-nitrogen trade-off strategies in S. grandis and L. chinensis. Methods We conducted a different grazing intensity experiment in the typical temperate steppe of Nei Mongol. The lignin and secondary metabolites, such as tannins, flavonoids, phenols and alkaloids, as well as the ratio of carbon and nitrogen in different organs of the dominant plants S. grandis and L. chinensis were investigated. Important findings Our results showed that S. grandis and L. chinensis produced a large number of secondary metabolites such as tannins, flavonoids, phenols and alkaloids in the face of grazing stress. The leaves were the main synthesis and storage organs. In addition, the chemical defense mechanism of L. chinensis was well induced and expressed under moderate grazing. There was no significant increase in the lignin content in the aboveground parts of S. grandis and L. chinensis. Therefore, both of them were more inclined to chemical defense than mechanical defense in the mechanism of avoiding grazing. Because of the higher nitrogen use efficiency of L. chinensis, it could be protected by both carbon and nitrogen metabolic pathways. However, Stipa grandis did not efficiently distribute nitrogen into chemical defense in the early stages of growth. More resources still used for primary metabolism in the early stage of S. grandis and L. chinensis growth, under light grazing stress, which increased their grazing resistance. Therefore, light grazing is conducive to improving the carbon and nitrogen use efficiency of pasture, and improving ecosystem productivity and stability.