环境因子对蒙古莸种子萌发及幼苗建成的影响

Effects of environmental factors on seed germination and seedling establishment of Caryopteris mongolica

蒙古莸(Caryopteris mongolica)是珍稀濒危的资源性植物,具较高的观赏和药用价值。其分布范围正日渐缩小。通过对内蒙古中西部干旱草原区蒙古莸天然种群实生苗的调查,以及在室内模拟不同环境条件,对蒙古莸种子萌发和幼苗建成进行研究,旨在探究这一物种珍稀、濒危的原因。结果显示:1)自然条件下蒙古莸种子在5—7月大量萌发,但在幼苗生长初期死亡率较高,使得自然种群更新强度仅为0.11株/m^2。2)蒙古莸种子不存在休眠现象,成熟采收后很快即可萌发。萌发对水分要求较宽范,但适宜其种子萌发的温度范围较窄,为25—30℃。3)蒙古莸幼苗生长的最适温度为25℃,能耐受每日短暂的高温胁迫(50℃)。持续的高温、低温和频繁的降水显著增大幼苗死亡率。研究认为,蒙古莸种子萌发的条件与幼苗存活的条件差异较大,同时满足其萌发和幼苗存活和生长的窗口条件比较严苛。其野生生长地的生境条件往往难以满足要求,这是限制蒙古莸通过有性繁殖进行自然种群扩散的主要原因之一。

Caryopteris mongolica, a rare and endangered small shrub, is mainly found in arid grasslands in northern China. Its distribution areas have rapidly contracted in recent years. In this study, an attempt was made to investigate the causes of the low survival rate of seedlings under local field conditions. The study combined a field survey of seedling survival with laboratory assessments of seed germination and seedling growth under different environmental conditions to establish the difficulties for C. mongolica seedling establishment. We selected a C. mongolica community in arid grasslands. The survival capacity of seedlings, seed germination, and seedling establishment under different temperatures, water cycles, and water quantities were determined. Climate and soil conditions were also studied. The following results were obtained. （1） Under field conditions, a large number of seeds germinated during the period from May to July, but few seedlings survived due to a high seedling mortality. The natural regeneration rate for the plant seedlings was 0.11 plant/m^2, because of the very high mortality rate of seedlings. （2） Seeds of C. mongolica had no dormancy after ripening. Seed germination requirements showed a relatively wide range of moisture conditions, but a narrow temperature range of 25-30℃. The optimum burial depth for seed germination was 10-15 mm. The seeds of C. mongolica can complete germination within 15 days when sown under suitable conditions. The water cycle had no significant effect on germination. The seeds buried in shallow soil were able to imbibe rapidly after full precipitation. （3） The most suitable temperature for seedling growth was approximately 25℃, although seedlings could tolerate a high temperature of up to 50℃ for a short period. Prolonged high or low temperature and frequent watering increased seedling death. The water cycle significantly influenced plant height and stem basal diameter. Shortening the water cycle can increase the height and stem thickness of C. mongolica. There was a significant influence of temperature on leaf age. The optimum temperature for leaf growth of C. mongolica was 25℃. Furthermore, variable temperature conditions were beneficial for erect growth and the thickening of stems. It was concluded that C. mongolica has relatively strict requirements for seed germination and seedling growth. The discrepancy between germination and seedling growth requirements narrowed the seedling establishment window. In the natural habitats of C. mongolica, the conditions are often not able to meet the requirements for the entire process from seed germination to seedling establishment. This is the main reasons for the relatively poor dispersion of C. mongolica populations through sexual propagation under field conditions.