A preliminary exploration: Why Myricaria laxiflora so immersion-resistant and so soil-selective?

摘要

Myricaria laxiflora is a shrub and also an endemic, rare and endangered plant species in Three Gorges Reservoir Area. It is of highly immersion resistant and soil selective. In this paper, the probable immersion-resistant structures of stem were identified, and the relationships between components of its inhabiting soil and the structures of stem were explored. Results showed that the parenchyma cells in cortical and pith could produce lysigenous intercellular lacuna acting as aerenchyma. The compact periderm, as well as loose-arrayed and star-shaped xylem parenchyma cells might be two fortifications of the stem to isolate water from inner tissues. We estimated that the vessel cavitation conducive to oxygen-store might likely be arisen. Our result indicated that the plant stem structures greatly depended on the soil particle fractions, especially the fractions of coarse sand and above. The fractions of residual parent rock and fine gravel of soil predominated structures of stem which could act as barriers of radial oxygen loss when plant immersed in flood. This suggested that the sand-gravel soil might play an important role in determining whether survival or not of M. laxiflora when immersed. Of all 7 studied mineral elements i.e. N, P, K, Ca, Mg, Mn, Zn, P and K contents of soil were positively predominant factors of vessel, especially vessel diameter which directly related to the likelihood of vessel cavitation and the capacity of water transportation. This also indicated that they played an important role in determining immersion resistance and the post immersion growth of the species. Therefore, for M. laxiflora, the traits of immersion-resistance and soil-selection were closely interrelated. The immersion-resistance ability of M. laxiflora would be stronger when soil has larger fractions of coarse sand and gravels.