Abstract:

Staghorn Sumac(Rhus typhina) is an alien tree species. It is a clonal woody plant with the distinguished characteristics, which the front part of the horizontal lateral root in the Staghorn Sumac is much bigger than the back part. In order to analyze the causes of the distinctive asymmetry of the lateral root diameter of the clonal ramets in Staghorn Sumac, samples were taken during the growth period in 2003.Nine individual plants at age of 1 year with their intact underground organs were carefully digged out and planted in the potters for feeding ¹⁴C isotope. The lateral roots of each individual plants at age from one to three or four were also taken for testing or observing in laboratory. Then the distribution of photosynthetic products in the clonal ramets were tested by means of isotope ¹⁴C tracer technique, the contents of hormone such as IAA,GA₃ and ABA of different organs in Staghorn Sumac were determined and the anatomical structure characteristics were observed. The experimental results showed that: 1)The abundances of isotope ¹⁴C in different organs of 9 clonal ramets of Staghorn Sumac were ranked as follows: feeding leaves>stem>the front part of the lateral root>the back part. 2) As the result of the higher density and larger diameter of vessel in the front part(RDF) of the lateral root of the clonal ramets, the abundant nutrition in the central part of the lateral root and the much numerous layer in the cambium, the width of the secondary xylem of the front part in the clonal ramets at age from 1 to 4 years was much larger than that of the back part(RDB). 3)IAA/GA₃ ratio of the front part in the clonal ramet at age of 1 and 3 was much higher than that of the back part. Therefore, it was concluded that the asymmetry of the lateral root diameter between the front part and the back part in Staghorn Sumac clonal ramet would be induced by the nonbalance accumulation of photosynthetic products, which accumulated in the front part of the lateral root of the clonal ramet much more than the back part, and related to the hormone level and the cambium activity closely. The stem of the clonal ramet and its front part of the lateral root would belong to the dominant and subdominant growth and the store center of photosynthetic products respectively.

Key words: alien species, horizontal lateral root diameter, clonal growth, reproductive investment strategy, ¹⁴C isotope