|
|
|
Abstract The Three Gorges Reservoir (TGR), which is the largest water conservancy project ever built in the world, produced a drawdown area of about 348.93km2 due to flooding control. The biological geochemical cycle of the soil in the drawdown zone has been changed as the result of long-term winter flooding and summer drought and vegetation covering. The loss of soil nitrogen in the drawdown zone poses a threat to the water environmental in TGR. Pengxi River, which has the largest drawdown area among all of the tributaries in TGR basin has been selected in present study. The four typical vegetation types, Cynodon dactylon, Cyperus rotundus, Anthium sibiricum and Zea mays L as control, were studied to measure nutrient characteristics and nitrogen forms of rhizosphere and non-rhizosphere soils. The variables included soil physical-chemical proprieties, ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3--N), nitrite nitrogen (NO2--N), nitrogen mineralization in 14d (NN) and 7 types N invertase enzymes including protease (PR), urease (UR), nitrate reductase (NR), nitrite reductase (SNR), dehydrogenase (DE), glutaminase (GL) and asparaginase (AS). The results showed: 1) pH of rhizosphere soil was generally lower than non-rhizosphere soil under different vegetation in different type soils because of the possible organic acid and H+ released from plant roots and cation absorption differences. All nutrient concentrations in rhizosphere soil were higher than those in non-rhizosphere except potassium (Total K and available K). 2) NH4+-N, NO3--N, NO2--N and NN of rhizosphere soil were generally higher than non-rhizosphere soil, by following the order of Cyperus rotundus＞Cynodon dactylon＞Anthium sibiricum and Zea mays L under different vegetation. 3) All 7 types invertases showed the better activeness in the rhizosphere soil compared with them under non-rhizosphere. UR, SNR, DE and GL in the zone covered by Cyperus rotundus and Cynodon dactylon were significantly higher than those in Anthium sibiricum and Zea maysL. 4) There was significant correlation between soil N forms and PR, UR and GL. NO3--N was significantly correlated with SNR. Rhizosphere effects on all N forms and invertase enzyme activity were done to evaluate the incidence of the soil N cycle by different vegetations, and results showed that rhizosphere effects of Cyperus rotundus and Cynodon dactylon were greater than those of Anthium sibiricum and Zea mays L. The present research could provide that the drawdown zone covered with different vegetations has different soil processes and function for N cycle, so the vegetation recovery in the drawdown zone should consider the rhizosphere effect of different vegetations on N cycle.
|
|
Received: 09 February 2015
|
|
|
|
|
|
