Effects Of Root Oxygen Production On Rhizosphere Redox Environment In Typical Wetland Plants

Radical oxygen loss (ROL)of wetland plant roots shapes the rhizospheric redox environment, promotes microbial flourish, which makes rhizosphere the superior active sites of various processes including organism degradation, material circulation and vigorous life activities. Investigation over root radical oxygen loss of wetland plants and rhizospheric redox conditions is crucial to understand material circulation processes of wetland ecosystems, constituting one of the hot areas of current research. In the present study, indoor experimental systems were build up with field collected eutrophic sediment and three typical emergent aquatic plants (Canna indica, Sagittaria sagittifolia, Acorus calamus), ROL of roots was determined with micro-optode technique nondestructively, patterns of ROL and characteristics of root surfacial Fe plaque were compared among plant species, the influence of plant growth on rhizospheric sediments and the relationship between ROL and Fe plaque were discussed. The main conclusions are as follows:(1) The rhizosphere oxygen concentrations of the three wetland plants range as C. indica>S.sagittifolia>A. calamus, averagely 64.9%,58.9%,54.9%. Patterns of ROL along the axis of root show different trends at different growing stages. However, at each stage, there is no difference in ROL patterns among three plants.During the growing stage Ⅰ (the first 10-20 d with lower root number and quickly increasing root length), ROL peaks at the middle part of roots and minimizes at the apex, while during the growing stage Ⅱ (the following 30-40 d with quickly increasing root number and slowly incresing root length), ROL peaks at the basal root.(2) The thichkness of stably-oxidized layer is found positively correlated with shoot height, root length, root number, plant biomass and photosynthetic Yield significantly (P<0.05), ranging as A. calamus>S. sagittifolia> C. indica, averagely 0.71 mm,0.53 mm and 0.46 mm. during growing stage Ⅰ The thichkness of stably-oxidized layer peaks in the basal part in C. indica and S. sagittifolia, while A. calamus at the pex part. during growing stage Ⅱ The thichkness of stably-oxidized layer peaks in the pex part in C. indica and S. sagittifolia, while A. calamus at the midle part.(3) Content of root Fe plaque is found positively correlated with root number, root length and the thickness of stably-oxidized layer significantly (P<0.05). The highest content appears at the middle part while the lowest at the apex and basal root in both A. calamus and S. sagittifolia. The content of Fe plaque in C. indica also peaks at the middle part, but the lowest part differs along growing.(4) During growing stage Ⅰ, the content of Fe plaque ranges as S. sagittifolia>A. calamus>C. indica, while during growing stage Ⅱ, it ranges as A. calamus>S. sagittifolia>C. indica, averagely 1738.4 mg/g root dry biomass,1325.16 mg/g root dry biomass and 423.8 mg/g root dry biomass with statistically significant difference (P<0.05).(5) The growth of wetland plants increases the sedimentary Eh and decreases pH. Eh in sediments cultivated with the thress plant species ranges as A. calamus>S. sagittifolia>C. indica, aeveragely -54 mV、-74 mV、-92 mV. pH ranges as S. sagittifolia<C. indica<A. calamus, decreasing 7.3%、5.9%、2.9% averagely compared with the beginning of the experiment.(6) The growth of wetland plants decreases the content of Fe(Ⅱ) and total phosphorous (TP) in sediments. At the end of the experiment, the sedimentary content of Fe(Ⅱ) ranges as C. indica< S. sagittifolia< A. calamus, decreases by 86.45%、 51.74%、48.38% compared with the beginning of the experiment. The sedimentary content of TP ranges as A. calamus> S. sagittifolia> C. indica.