氮、硫互作对克隆植物互花米草繁殖和生物量累积与分配的影响

氮、硫均是影响入侵植物互花米草（Spartina alterniflora Loisel.）生长与繁殖的重要营养元素，研究其交互作用可能有助于揭示互花米草成功入侵机制。本文在人工控制条件下，以河沙为栽培基质，研究了氮、硫互作对互花米草繁殖和生物量积累与分配的影响。实验结果表明：中氮和高氮处理下的互花米草分支强度、初级分株数、次级分株数、根状茎数及其总长要显著高于低氮，不同硫水平及氮硫互作对互花米草无性繁殖没有显著影响；互花米草的种子数和种子生物量受硫以及氮硫交互作用的影响显著，在高氮水平下，中硫处理的互花米草种子数和种子生物量要远远高于其他处理。中氮和高氮处理下的互花米草叶、茎、根、根状茎和总生物量显著高于低氮处理；只有在高氮水平下，高硫处理的生物量才显著低于其他处理。在中氮和高氮营养条件下，高硫处理会促使互花米草对地上部分投入更多的生物量。中硫-高氮作用对互花米草有性繁殖的促进，使互花米草能在硫浓度较高的滩地保持高有性繁殖率；虽然过高的硫会抑制互花米草的有性繁殖，但却能促进根状茎数目的增加，从而加速其向外短距离扩张；这些特性均有利于互花米草对滨海盐沼的入侵。

Interactive effects of nitrogen and sulfur on the reproduction, biomass accumulation and allocation of the clonal plant Spartina alterniflora

In recent years, interest in sea grass beds and Spartina marshes has grown dramatically. Sea grass beds and Spartina marshes are among the most productive ecosystems in shallow coastal marine environments, at least partially because of the ability of Spartina alterniflora to use nutrients efficiently. Nitrogen and sulfur are the most important nutrients influencing growth and reproduction of S. alterniflora, but their interactive effects have not yet been studied. Addressing such effects may help to understand the invasiveness of S. alterniflora. In this paper, we studied the interactive effects of nitrogen and sulfur on the reproduction, biomass accumulation and allocation of S. alterniflora under controlled levels of nitrogen and sulfur. Branching intensity, number of primary and secondary tillers, number of rhizomes and total rhizome length were significantly higher in the medium and high nitrogen treatments than in the the low nitrogen treatments, whereas sulfur and nitrogen-sulfur (N?S) interactions did not affect these characteristics. Seed number and biomass of S. alterniflora were significantly affected by sulfur levels and the N?S interaction. At high nitrogen levels, seed number and biomass in the intermediate sulfur treatment were much higher than in the other treatments, indicating that sexual reproduction was affected by the sulfur levels. At the same time, leaf biomass, culm biomass, root biomass, rhizome biomass and total biomass of S. alterniflora were significantly higher in the medium and high nitrogen treatments than in the low nitrogen treatments. At high nitrogen levels, these biomass measures were significantly lower at high sulfur levels than at intermediate or low sulfur levels, but this sulfur effect on biomass was not seen at intermediate or low nitrogen levels. Furthermore, at intermediate and high nitrogen levels, high levels of sulfur resulted in greater biomass allocation to aboveground organization. Therefore, the ability to use high levels of nitrogen, combined with high sulfur tolerance, provide an advantage for the invasion of S. alterniflora in the coastal salt marshes. Addressing the tradeoff between sexual and asexual reproduction of S. alterniflora at different nitrogen and sulfur levels, we found that the interaction of high nitrogen and intermediate sulfur levels can result in relatively higher rates of sexual reproduction in the salt marsh, which has sufficient nitrogen and high sulfur concentration (i.e., they are equal to medium nitrogen and intermediate sulfur levels in this experiment). High sulfur can inhibit sexual reproduction of S. alterniflora, but it can increase the number of rhizomes to accelerate short-distance and outward expansion. And this effect provides an other way for S. alterniflora to survive in the costal salt marsh. Nutritional conditions are often reflected in the balance of plant reproductive strategies, and this balance can represent an important influence on the spread of invasive plants; the effects of N and S on S. alternifolia strongly confirm this. Therefore, the efficient use of nutrients by S. alterniflora may be an important reason for its success in beach environments.