埋深和播种密度对豚草种子出苗及幼苗生长的影响

豚草是一种全球性的恶性入侵杂草，给我国生物多样性及经济发展造成了巨大威胁。为研究豚草种子出苗和幼苗生长的影响因素，采用盆栽实验分析了种子大小（L、M、S）与埋深（2、4 cm和6 cm）或播种密度（2、4粒/盆和8粒/盆）对豚草（Ambrosia artemisiifolia）种子的出苗和幼苗生长的影响。研究结果表明，埋深对豚草种子出苗的影响高于播种密度及种子大小的影响，较浅的埋深有利于豚草种子出苗；出苗率在不同播种密度下均具有较高水平，达到67.9%-100%，这种高出苗率是豚草在不同生境成功定植的原因之一。豚草的幼苗生长受埋深或播种密度的影响大于种子大小的影响，且小种子更易受埋深或播种密度的影响。种子大小显著影响豚草幼苗的株高和基径（P<0.05），总体上较大种子的株高和基径高于小种子，此外更小的种子会将生物量更多的分配给根以促进幼苗的生长。幼苗的株高和基径在较浅的埋深下更高，而豚草幼苗的单株生物量、单株地上和地下生物量随埋深的增加而增加。播种密度的增加会加剧豚草幼苗之间对水分、营养、光照等资源的竞争，导致其单株地上、地下及总生物量显著降低（P<0.05）。研究发现豚草在浅埋深、低密度生境中更容易入侵成功，因此可以通过对土壤进行深翻，采取替代控制，种植竞争能力强的本地植物等手段有效管理和防治豚草。

Effects of burial depth and planting density on seedling emergence and growth of Ambrosia artemisiifolia of different seed sizes

Ambrosia artemisiifolia, native to North America, is a notorious invasive plant worldwide. It has posed a serious threat to the biodiversity, stability of ecosystem, economic development and human health in China. Research on the seeding emergence and growth process of A. artemisiifolia, which are important stages in its life history, is essential for invasive management. However, little attention has been paid to the effects of seed characteristics, sowing depth and density at the emergence and growth stages of A. artemisiifolia. In order to study the influence factors of seed emergence and seedling growth of A. artemisiifolia, we conducted a pot experiment to examine the effects of seed size (L, M, S) and burial depth (2, 4 and 6 cm) or planting density (2, 4 and 8 seeds per pot) on the emergence and seedling growth of A. artemisiifolia. It was found that the effect of burial depth on the emergence of A. artemisiifolia was much stronger than that of planting density and seed size, and we also found that the shallower burial depth promoted the emergence of seeds. Under the three different planting densities, A. artemisiifolia showed a relatively high emergence rate at about 67.9%-100%, which was one of the reasons why A. artemisiifolia could successfully colonize in different habitats. The seedling growth was more affected by burial depth and planting density than seed size, and small seeds were more susceptible to the effects of burial depth and planting density. The seedling height and basal diameter were affected by seed size significantly (P<0.05). In general, the seedling height and basal diameter of larger seeds were higher than those of small seeds. In addition, smaller seeds would distribute more biomass to the roots to promote the growth of seedlings. The seedling height and basal diameter were higher at shallower burial depth, while the total individual biomass, individual aboveground and underground biomass increased with the increase of burial depth. As planting density increased, the intraspecific competition of seedlings for water, nutrition, light and other resources increased, resulting in a significant decrease in the aboveground, underground and total biomass of individual (P<0.05). In this study, we found that A. artemisiifolia was more inclined to invade habitats with shallow burial depth and low density successfully. Therefore, for the purpose of preventing A. artemisiifolia invasion, deep ploughing and replacement control technology, which use competitive native plants to compete with invasive plants, can be conducted to inhibit the growth of A. artemisiifolia in China.