Pan Guoquan

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.

Effects of groundwater depth on germination and seedling growth of Acorus calamus

Effects of groundwater depth on germination and seedling growth of Acorus calamus were studied by simulating experiment. The experimental barrels (diameter of 35.5cm and depth of 100cm) were filled with fluvial sands of 80cm depth. The water was introduced directly into the bottom of the barrels to build the groundwater depths in -60cm, -50cm, -40cm, -20cm and 0cm in different five barrels respectively. The same rhizomes of A. calamus were selected and planted in each barrel. The results were as follows: (1) Groundwater depth has significant effects on germination and seedling growth of A. calamus. The plant can germinate in the groundwater depth from -60cm to -20cm, when groundwater depth decreased germination ratio reduced. On the 70th day, germination ratio of the -20cm treatment reached 90%, which were 2.25 and 3 times of those in the -50cm and -60cm treatments. Plant of 0cm treatment can not germinate. (2) Leaf length, width and area were positively correlated with groundwater depths and the significant correlations are able to be accepted (P 0.01). With decreasing of groundwater depth, the number of the laminae reduces. The number of the laminae in -20cm and -40cm treatments were very significantly higher than those in -50cm and -60cm treatments (P 0.01). Groundwater depth of -60cm was greatly affected on survival of plant seedling since plant seedling of -60cm treatment began to die after the 70th day. (3) With decreasing of groundwater depth, Chl.a, Chl.b and Car reduced but Chl.a/b increased. Plant leaves captured the light reducibly by the way of morphological adjustment and chlorophyll content reduction. (4) The laminae MDA and membrane permeability increased, which is led by low soil water content caused by low groundwater depth. (5)Groundwater depth has great effects on the rapid responded light-curves of A. calamus. As groundwater depth decreases, the maximal photosynthetic electron transport rate (ETRmax) and the minimal saturated light intensity reduce, and the responded photoresponse capacity is weakened.

Changes of photosynthetic characters of Vallisneria asiatica adhered by Hydrodictyon reticulatum

Chlorophyll fluorescence characters and rapid light curves (RLCs) of Vallisneria asiatica adhered by Hyd- rodictyon reticulatum were measured by a submersible,pulse-amplitude modulated fluorometer:Diving-PAM.Re- suits indicated that on the top of the leaves,F_v/F_m decreased apparently after 15 days,and Photosystem photo- chemical efficiency was reduced remarkably.Dissipated heat of the leaves adhered by H.reticulatum increased in high significant level (P＜0.01) after 15 days.The efficient quantum yield,photochemical quenching,relative Electron-transport rate (rETR),chlorophyll a (abbreviation,Chl.a),carotenoid (abbreviation,Car),the ratio of Chl.a and Chl.b,the ratio of Car and Chl.a of these leaves decreased significantly.It was observed from RLCs that when photosynthetically active radiation excess 104μmol/(m~2·s),rETR of V.asiatica leaves with H.reticu- latum in irradiance were less notablely than that of the control,and photosynthetic ability of these leaves decreased. Meanwhile,the saturating irradiancc (248μmol/(m~2·s))of leaves in the experimental pool was significantly less than 685μmol/(m~2·s)of the control.This indicated that after H.reticulatum adhered to V.asiatica,light re- sponding capacity of V.asiaticas leaves decreased notablely in 15 days.