| The growth, root biomass, root horizontal and vertical distribution,root activities and purification efficiency of wastewater of four plants inSurface Flow Constructed Wetland were studied in this paper. Theseplants are Vetiveria zizanioides (Linn.) Nash., Cyperus alternifolius subsp.flabelliformis (Rottb.) Kukenth., Phragrnitas communis Trin. andHymenocallis littoralis (Jack.) Salisb. Meanwhile, the relationshipbetween root biomass and purification efficiency, root activities andpurification efficiency, root biomass and up-ground of plants, as well asroot activities and root biomass were also analyzed. The results are shownas follows:1. Different season patterns were shown by the growth of four plants.The growth of V. zizanioides and C. flabelliformis were much faster withhigher accumulation of plant height from April to September. The twoplants became wilting, leaves turned yellow and parts of root were dieafter September. Whereas, in P. communis, the tillering number and thediameter of the new bud were increased with fully growth of the plant.However, the growth of H. littoralis was much stable within a year. Thegrowth quantity of the root of V. zizanioides and P. communis reached theclimax in July, whereas it was in October in C. flabelliformis and H.littoralis. The annual root biomass of V. zizanioides, C. flabelliformis, P.communis and H. littoralis are 92.3125g·m-2, 404.6275g·m-2, 384.71g·m-2 and505.2275g·m-2, respectively.2. Different plants have different root distributions. The root systemof V. zizanioides was accumulated under 20cm of under-ground with45.8% of total biomass. It has a vertical distribution, rarely growinghorizontally. However, the other three root systems were mainlydistributed in 10cm of under-ground. The root biomass of C.flabelliformis, P. communis and H. littoralis are 76.1%, 68.2% and 82.5%of there total biomass, respectively. The root system of P. eommunis wasmainly rhizomorphous stem. The root of C. flabelliformis is radicel,whereas that of H. littoralis is thicker. But both of two kinds of root arehorizontal distributed. 3. The average root activity of V. zizanioides, C. flabelliformis, P.communis and H. littoralis are 473.9526μg·DWg-1·h-1, 700.6479μg·DWg-1·h-1, 715.7995μg·DWg-1·h-1 and 683.2747μg·DWg-1·h-1,respectively. The changes of root activity are not synchronized, with timelag in the summits. The root activity of V. zizanioides is much lowercompared with others. Following with the summit in August (724.5046μg·DWg-1·h-1), the root activity of V. zizanioides is sharply declined afterSeptember. The climax of root activity of C. flabelliformis was alsoobserved in August (1507.5176μg·DWg-1·h-1). Although it was slightlydecreased after August, the root activity is still highest among four plants.Same trends as in P. communis, the summit of root activity was in July(1351.2574μg·DWg-1·h-1), followed with steeply declining after August.Between April and August, the root activity of H. littoralis is relativelystable. The climax was shown in August (1063.8053μg·DWg-1·h-1), with itdecreasing then. However, the root activity of all four plants is slightlyincreased in January, 2007.4. The leaf area index of V. zizanioides, C.flabelliformis, P.communis and H. littoralis are 2.79, 4.40, 3.01 and 2.99 in December,respectively. The changes of leaf area index in every month are different.The highest leaf area index was shown in C. flabelliformis, which havelargest plant cover. The quickest increase rate of leaf area index wasobserved during May to August, following with slower rate. However, thelowest leaf area index was shown in V. zizanioides, with quickest increaserate during June to October. The average increase rate of leaf area indexafter September was much higher than the annual rate in P. communis.Moreover, the higher rate was shown during May to July and September toNovember in H. littoralis.5. In plant wetland, the CODcr removal efficiency of V. zizanioides, C.flabelliformis, P. communis and H. littoralis are 57.9%, 57.6%, 55.0%,51.5%, respectively. The TP removal efficiency are 84.3%, 75.0%, 84.1%,80.1% respectively. The TN removal efficiency are 59.5%, 63.1%, 63.2%,59.1%, respectively. However, there is no significant difference inremoval efficiency of all pollutants among four plant wetlands (P＞0.05).The removal efficiency in different wetlands is season-dependent, which is shown the highest removal efficiency between June andSeptember and lowest in September.6. There is significant relativity between the root activity of V.zizanioides and removal efficiency of TN, NH4-N and SP (P＜0.05) andso that between the root activity of C. flabelliformis and removalefficiency of NH4-N (P＜0.05). Moreover, most significant relativity wasshown between the root activity of H. littoralis and removal efficiency ofNH4-N (P＜0.01) and significant relativity with the removal efficiency ofSP (P＜0.05). The differentiations of the relativities were observedbetween the root activity of different plants and removal efficiency ofdifferent pollutants.
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