Wang Wenlin

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.

The litter and residue of Eichhornia crassipes(Mart.) Solms

The litter and the residue of the aquatic plants play an important role in the nutrient cycle and energy flow. Under natural conditions, the sediment was collected in situ at different stages of Eichhornia crassipes, and its changes of the litter and residue were studied. The weight of sediment had an obviously increasing trend from waterhycinth death to its disappearance from water surface. When the litter and residue disappeared completely from water surface, the weight of sediment and the downward fluxes reached the maximum value 579.59g/m2, 7.54g/(m2·d) respectively. Both of them had a significantly positive correlation with the water temperature. When the litter and residue disappeared completely from water surface, the organic carbon, total nitrogen and total phosphorus were low in the growth but high in the floating, and reached the maximum values 40.29%, 3.66%, 0.90% respectively, then they gradually decreased, and tended to be stable.