论文部分内容阅读
种子萌发是植物早期生活史中最重要的阶段,决定了植物的生态位和地理分布范围,对外来植物的入侵潜力有重要影响.盐沼植物互花米草(Spartina alterniflora)在中国沿海滩涂的入侵范围最大,并己入侵到比原产地更低的纬度范围,这为我们研究互花米草在不同地理区域之间以及沿纬度梯度的萌发性状差异和适应提供了契机.在控温培养箱中淡水培养条件下,我们比较研究了来自入侵地(19°-40° N)10个地点和原产地(27°-43° N)16个地点不同纬度互花米草种群的种子萌发性状差异,以及这种差异与各种群来源地潮差和气候因素的相关性.原产地互花米草种群种子的萌发率和萌发指数比入侵地种群分别高10％和20％,但入侵地互花米草种群的萌发速度比原产地快3 d.入侵地互花米草种群的萌发率和萌发指数随着纬度升高呈现线性递增的变化趋势,而原产地呈现线性递减的变化趋势.入侵地和原产地互花米草种群的平均萌发时间都与纬度呈现线性负相关.入侵地互花米草种群的萌发率和萌发指数与年日均温、年日最低均温、和年日最高均温呈现负相关,而在原产地呈现相反的相关关系.入侵地和原产地互花米草种群的平均萌发时间分别与年日均温、年日最低均温和年日最高均温呈现正相关关系.我们的研究结果表明,入侵地和原产地互花米草种群的萌发率和萌发指数已沿纬度进化出不同的渐变群格局,但平均萌发时间进化出与原产地一致的纬度渐变群格局,即在生物入侵过程中沿纬度梯度种子萌发策略会随着入侵时间和过程而发生变化.“,”Aims Germination is the earliest life-history transition of a plant species.It determines the ecological breadth and geographic ranges of a species and has major effects on its invasion potential.The largest spread of the invasive salt-marsh cordgrass Spartina alterniflora in China,where it extends to latitudes lower than its native range in North America,provides an opportunity to examine germination trait variation across latitudes within and among its invasive and native ranges.Methods We studied seed germination traits of S.alterniflora using seeds collected from 10 locations across latitudes in its invasive range(China,20°-40° N)and 16 locations across latitudes in its native range(USA,27°-43° N)in growth chambers with 0 PSU sterilized distilled water.We further evaluated how climate and tide range in the original locations influenced germination traits.Important Findings Native populations showed higher(～10％)germination percentage and significantly higher(～20％)germination index than invasive populations did,but invasive populations germinated significantly earlier(～3 days)than native populations.Germination percentage and germination index increased with latitude in the invasive range but decreased with latitude in the native range.The mean germination time decreased with latitude in the invasive range and paralleled that in the native range.Germination percentage and germination index were negatively correlated with mean daily temperature(Tmean),mean daily maximum temperature(Tmax)and mean daily minimum temperature(Tmin),and inversely correlated with Tmean,Tmax and Tmin in the native range.However,the mean germination time was positively correlated with Tmean,Tmax and Tmean in both ranges.Our results demonstrate that invasive and native populations have evolved different latitudinal clines in germination percentage and index,but the mean germination time of the invasive population mirrored the latitudinal cline observed in the native range,suggesting that germination strategy across latitudes may change during invasion process.