Han Ruiming

Spatio-temporal patterns in rhizosphere oxygen profiles in the emergent plant species Acorus calamus.

Rhizosphere oxygen profiles are the key to understanding the role of wetland plants in ecological remediation. Though in situ determination of the rhizosphere oxygen profiles has been performed occasionally at certain growing stages within days, comprehensive study on individual roots during weeks is still missing. Seedlings of Acorus calamus, a wetland monocot, were cultivated in silty sediment and the rhizosphere oxygen profiles were characterized at regular intervals, using micro-optodes to examine the same root at four positions along the root axis. The rhizosphere oxygen saturation culminated at 42.9% around the middle part of the root and was at its lowest level, 3.3%, at the basal part of the root near the aboveground portion. As the plant grew, the oxygen saturation at the four positions remained nearly constant until shoot height reached 15 cm. When shoot height reached 60 cm, oxygen saturation was greatest at the point halfway along the root, followed by the point three-quarters of the way down the root, the tip of the root, and the point one-quarter of the way down. Both the internal and rhizosphere oxygen saturation steadily increased, as did the thickness of stably oxidized microzones, which ranged from 20 µm in younger seedlings to a maximum of 320 µm in older seedlings. The spatial patterns of rhizosphere oxygen profiles in sediment contrast with those from previous studies on radial oxygen loss in A. calamus that used conventional approaches. Rhizosphere oxygen saturation peaked around the middle part of roots and the thickness of stably oxidized zones increased as the roots grew.

Diversity and community structure of epiphytic bacteria on different submerged macrophytes in Lake Hongze

Algae, epiphytic bacteria and other substances attached to the surface of submerged macrophytes affected not only the growth of submerged macrophytes but also the mass cycling in aquatic ecosystems. Previously, many reports were focus on the influ⁃ ence from algae, far few were related to epiphytic bacteria. Terminal Restriction Fragment Length Polymorphism (T⁃RFLP) method was used to investigate the epiphytic bacteria communities attached to three common submerged macrophytes (Potamogeton pectina⁃ tus, Potamogeton crispus and Ceratophyllum demersum) in Lake Hongze. The relationship between environmental factors and the a⁃ bundance of epiphytic bacteria were analyzed by means of redundancy analysis (RDA). The results showed that: (1) Epiphytic bacteria varied greatly in community structure among the three macrophytes. The relative abundance of 143 bp T⁃RF in P. crispus and P. pectinatus reached 20% and 11% in average respectively, while less than 1% in C. demersum; the relative abundance of 89 bp T⁃RF in C. demersum has an average of 13% while less than 5% in P. crispus and P. pectinatus. The relative abundance of 94 bp T⁃RF in P. crispus was more than 15% , but it was even not detected in other two macrophytes. (2) The diversity of epiphytic bac⁃