The Study of Selenium: Its Chemical Form in Rhizosphere Soil and Absorption By Different Rice Varieties As Regulated By Nitrogen.

Using rhizobag methods, the author investigated 1) Selenium speciation distribution characteristics in rhizosphere and non-rhizosphere paddy soils, 2) the relationship between Se accumulation and rhizosphere nutrients, and 3) the influence of nitrogen forms on Se dynamic accumulation. Through hydroponic experimentation, the author also studied the effects of nitrate on selenium accumulation on local sites and long distances. The main results are listed below.

(1) In low-Se paddy soil, the Se （mainly OM-Se） in rhizosphere soil is more concentrated than in non-rhizosphere soil. Soluble Se, Exc-Se (exchangeable and bound to carbonates Se), OM-Se (bound to organic-sulfide matter and elemental Se), and total-Se contents in rhizosphere soils are significantly higher than those in non-rhizosphere soils.

(2) The shoot Se accumulating ability is significantly different among four rice cultivars and has no direct relationship with rice color, but does have higher transport ability from roots to shoots. The Se-enrichment cultivars Longqing4 and Xiushui48 have a higher ratio of (shoot Se)/(root Se) than non-Se-enrichment cultivars Heimi and S.Andrea, and also show higher NP-utilizing abilities. The relationship analysis revealed that Se accumulation and assimilation in rice plants have a close relation with N and P, but not with K.

(3) Different N forms in soils have distinct effects on Se accumulation in rice seedlings.

(4) Nitrate could significantly inhibit selenite uptake by excised rice roots, and the inhibition was influenced by solution pH. The inhibition might result from the competition for non-specific anion transport carriers on root surface, but not from inhibition in the assimilation process inside roots.

(5) The split-root experiments suggested that nitrate could influence selenite uptake through local site and long distance regulation.