BACKGROUND The Eurasian steppe is an important vegetation type characterized by cold, arid and nitrogen poor conditions. At the Eastern edge, including in the Songnen grassland, the vegetation is dominated by Leymus chinensis (henceforth L. chinensis) and is increasing threatened by elevated anthropogenic nitrogen deposition. L. chinensis is a perennial grass that mainly reproduces vegetatively and its sexual reproduction is limited. However, sexual reproduction plays an important role influencing colonization after large disturbances. To develop an understanding of how elevated nitrogen deposition changes the plant community structure and functioning we need a better understanding how sexual reproduction of L. chinensis changes with nitrogen enrichment. Here we report on a field experiment where we added 10 g N m- 2 yr- 1 and examined changes in seed traits, seed germination and early seedling growth. RESULTS Nitrogen addition increased seed production by 79%, contributing to this seed increases were a 28% increase in flowering plant density, a 40% increase in seed number per plant and a 11% increase in seed weight. Seed size increased with a 42% increase in large seeds and a 49% decrease in the smallest seed size category. Seed germination success improved by 10% for small seeds and 18% for large seeds. Combined, the increased in seed production and improved seed quality doubled the potential seed germination. Subsequent seedling above and below-ground biomass also significantly increased. CONCLUSIONS All aspects of L. chinensis sexual reproduction increased with nitrogen addition. Thus, L. chinensis competitive ability may increase when atmospheric nitrogen deposition increases, which may further reduce overall plant diversity in the low diversity Songnen grasslands.

中文翻译：

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多年生根茎草羊草（Leymus chinensis）中，氮的添加增加了有性生殖并改善了幼苗的生长。

背景技术欧亚草原是一种重要的植被类型，其特征是寒冷，干旱和缺氮的条件。在包括松嫩草原在内的东部边缘，植被以羊草（Hysforth L. chinensis）为主导，并因人为氮沉积增加而受到威胁。L. chinensis是多年生草，主要以无性繁殖，其有性繁殖受到限制。然而，有性生殖在发生大的干扰后起着重要的影响定植的作用。为了了解氮沉积的增加如何改变植物群落结构和功能，我们需要更好地了解中华绒螯蟹的有性繁殖如何随着氮的富集而变化。在这里，我们报告了一个田间试验，在该试验中我们添加了10 g N m-2 yr-1并检查了种子性状，种子发芽和幼苗早期生长的变化。结果氮的添加使种子产量增加了79％，这是由于开花植物密度增加了28％，单株种子数量增加了40％，种子重量增加了11％所致。种子大小增加，大种子增加42％，最小种子类别减少49％。小种子的种子发芽成功率提高了10％，大种子的发芽成功率提高了18％。结合起来，种子产量的增加和种子质量的提高使潜在的种子发芽倍增。随后地上和地下生物量的幼苗也显着增加。结论随着添加氮的增加，中华L.有性繁殖的各个方面均增加。因此，L。