RHIZOME DYNAMICS AND AGE STRUCTURE OF PHRAGMITES AUSTRALIS POPULATIONS IN HETEROGENEOUS HABITATS OF NORTHEAST GRASSLANDS IN CHINA

Rhizomes are important for both reproductive organs and nutrient storage; thus, rhizomes have the functions for vegetative propagation and expansion of population as well as for physiological integration of clonal family channels. Using soil samples excavated from Northeast meadow steppe, five rhizomes of single dominant rhizome species (Phragmites australis) from meadow soil habitat and saline-alkali soil habitat were investigated and compared within a growing season on growing period length, biomass and dry storage with the amount of seasonal variation. The results showed that: rhizome length, biomass and dry storage of the species from the meadow soil habitat are significantly greater than the species from the saline-alkali soil habitat. Over the entire growth period, rhizome length gradually increased to a maximum at the 3rd, while at the 6th the smallest rhizome biomass occurred. Dry material storage, after an initial decline, increased to the largest biomass at the 3rd and was the minimum at the 1st year. Maximum dry matter storage occurred at the 5th, and was the lowest for the 1st year. Among age classes, the relationship was significant between rhizome length and age spectrum month fitting a straight line. A quadratic function was found to fit the relationship between amount of months and the biomass of the age spectrum. Further, there is also a significant relationship between the five growth stages and age class of the rhizome dry storage defined by quadratic functions. Rhizome length, biomass and dry storage and soil moisture, soil organic matter, and soil available nitrogen content were significantly positively correlated with soil pH, while soil available phosphorus content was significantly negatively correlated with soil pH. All of the rhizome dynamics have the same seasonal variation; the rhizome life span of different age classes is closely related to nutrient output depletion and nutrient input compensation. Over the entire growth period, the impact of habitat heterogeneity on rhizome age structure dynamics is evident with the relatively stable differences.