Translocation of assimilates in Undaria and its cultivation in China

Undaria cultivation on a commercial scale began in China only in the last decade. Today, Undaria pinnatifida is the main species under cultivation concentrated in two provinces, Liaoning and Shandong. The annual production in the early nineties was 8000-13 000 tons dry weight, which is two or three times the pre-1980 figures. The raft cultivation method maintaining the alga at the desired depths generally ensures the light saturated rate of photosynthesis on clear days, and enhances production. Under the cultivated condition, the calculated annual primary productivity of this alga is 160 gC m⁻² y⁻¹. Translocation of ¹⁴C-labelled photoassimilates in rapidly growing sporophyte of Undaria pinnatifida was studied in the open sea. Samples from different parts of the blade with counterparts exposed to tracer (NaH¹⁴CO₃) showed that the translocation that occurred mainly from the tip of the blade to the growing region had obvious source-sink relationship. It took 20 minutes to translocate the labelled photoassimilates from the epidermis, via cortex, to the medulla of the midrib, where rates of translocation averaging 42–48 cm h⁻¹ were observed in the open sea. Production experiments of tip-cutting of the blades showed an increased production of 9%. This revised version was published online in August 2006 with corrections to the Cover Date.