入侵藤本薇甘菊的耐盐能力

薇甘菊Mikania micrantha Kunth为原产中南美洲的入侵藤本植物，现已在全球热带和亚热带地区照成严重的生态问题。野外观察发现薇甘菊已在珠三角沿海植被中滋生。为揭示薇甘菊的耐盐能力及其对滨海盐生植被的潜在危害性，分别对薇甘菊种子、根系和茎干在不同盐度胁迫下的响应进行了测定。在珠三角地区采集了薇甘菊3个批次的种子，并选取珠江三角洲6种常见植物（菊科假臭草Eupatorium catarium、藿香蓟Ageratum conyzoides、野茼蒿Crassocephalum crepidioides、鬼针草Bidens pilosa、翅果菊Pterocypsela indica和旋花科小花假番薯Ipomoea triloba）作为对照，测定了它们在不同NaCl盐度（质量分数）胁迫下的萌发率和幼苗生长；为揭示薇甘菊种子是否可由海水传播，将薇甘菊和对照植物假臭草、藿香蓟和鬼针草在不同盐度条件下浸泡不同时间后解除胁迫再观测其种子萌发率；为确定薇甘菊能否在滨海盐土中无性繁殖，分别对薇甘菊的根系和茎干在盐水浸泡下的植株生长进行了测定。研究结果表明：1）总体而言，薇甘菊3个种群在≤0.6%盐度胁迫下的种子萌发率均与对照组无显著差异，个别种群的这一阈值可高达1.5%，明显高于其他对照植物；同一盐度胁迫条件下，薇甘菊幼苗根系和苗高生长受抑制程度明显低于对照植物。2）即使经高达3.0%盐度胁迫浸泡长达12 d后，薇甘菊、藿香蓟和假臭草种子的萌发率也没有受到显著影响，而鬼针草种子的萌发率有明显下降；四种植物受浸泡后萌芽的幼苗生长均正常。3）薇甘菊根系受0.5%盐度胁迫时没有植株死亡，但苗高增长仅为对照组的53.3%；根系在1.0%盐度胁迫下有95%的植株能存活至少25 d，但苗高增长仅为对照的18.9%；根系在≥1.5%盐度胁迫下薇甘菊无法存活。4）被清水浸泡的薇甘菊茎茎叶均能存活且在全部被浸泡的节上萌芽。当薇甘菊茎干受≥1.0%盐水浸泡时，受浸泡的叶片全部死亡，在1.0%、2.0%和3.0%盐度胁迫下受试茎第21天的死亡率分别为42.9%、40.9%和86.4%。以上结果表明薇甘菊对盐生生境具一定的适应能力，可能通过种子萌发或无性繁殖扩张的方式对滨海盐生植被构成威胁，应当引起重视。

Salt tolerance of the invasive vine Mikania micrantha Kunth

Mikania micrantha Kunth is a noxious invasive species in tropical and subtropical regions. This weed has been found to grow on the coast of the Pearl River Delta and off-coast islands in China. In the present study, we assessed the salt tolerance of M. micrantha seeds, roots, and stems separately. Seed germination and seedling growth in different concentrations of NaCl were tested for three M. micrantha populations and six common species （Eupatorium catarium, Ageratum conyzoides, Crassocephalum crepidioides, Bidens pilosa, Pterocypsela indica, and Ipomoea triloba） in the Pearl River Delta. Seed germination of M. micrantha, E. catarium, A. conyzoides, and B. pilosa were tested after 3, 6, and 12 days of submergence in different concentrations of NaCl to determine whether seeds can be transferred by seawater. Responses of submerged cultured M. micrantha root and stem in different concentrations of NaCl were also recorded to determine whether the weed can disperse by vegetative propagation in coastal saline soils. Experiments produced the following results. 1） In general, the seed germination rates of M. micrantha did not differ significantly from those of the controls at ≤0.6% salinity, and the highest threshold value of 1.5% was greater than those for all control species. Radicle and seedling height growth rates of M. micrantha were less suppressed than those of control plants under the same salinity stress. 2） In comparison with controls, no significant decline in germination rate was observed in treated （submerged in up to 3.0%NaCl for up to 12 days） M. micrantha, A. conyzoides, or E. catarium, whereas submergence in 3.0%NaCl for 12 days caused a significant decline in B. pilosa. However, seedlings of all four tested species grew well. 3） All tested M. micrantha plants survived 0.5%salinity stress to root systems, with a decline in the average seedling height growth rate to 53.3%those of controls;95%of tested plants survived up to 1.0%salinity stress to root systems for at least 25 days, with a decline in the average seedling height growth rate to 18.9%;no M. micrantha plant survived 1.5%salinity stress to the root system. 4） All leaves of M. micrantha survived stem submergence in water, with sprouting observed in all submerged nodes, whereas all submerged leaves died when stems were exposed to ≥1.0%salinity stress. Mortality rates of the tested stems at day 21 were 42.9%, 40.9%, and 86.4%for 1.0%, 2.0%, and 3.0% salinity stress, respectively. We conclude that M. micrantha can disperse in coastal saline soils by seed and vegetative propagation. More attention should be paid to the potential threat of M. micrantha populations near coastal halophytic vegetation.