EFFECTS OF SOIL PROPERTIES AND TRACE-ELEMENTS ON ETHYLENE PRODUCTION IN SOILS

Soils vary widely in their capacity to produce ethylene (C2H4). This laboratory study was conducted to assess various California soils for their potential to produce C2H4 and to evaluate the effects of trace elements on C2H4 evolution in soil. Soils unamended and amended with L-methionine and/or D-glucose were monitored for C2H4 production over 7 days at ambient laboratory conditions (24 +/- 3-degrees-C). Unamended soils varied in their potential to generate C2H4 ranging from 1.1 to 348.4 nmol C2H4 kg-1 soil. In most cases, organic amendments (L-methionine and/or D-glucose) significantly promoted C2H4 production in soils. There was a significant negative linear correlation between soil pH and C2H4 production in the unamended soils (r = 0.54*) and in L-methionine-amended soils (r = 0.53*). The effects of various trace elements on L-methionine-dependent C2H4 generation in soil was highly concentration-dependent. Seven trace elements [Ag(I), Cu(II), Fe(II), Mn(II), Ni(II), Zn(II), Al(III)] significantly inhibited C2H4 production when applied at concentrations greater-than-or-equal-to 100 mg.kg-1 soil. The most effective trace elements in promoting synthesis of C2H4 were Co(II) and As(III) when added at 100 mg.kg-1 soil. Ethylene generation was inhibited in the presence of Hg(II), Fe(III), and Mo(VI) at greater-than-or-equal-to 10 mg.kg-1 soil. Application of Fe(II) at greater-than-or-equal-to 100 mg.kg-1 promoted the abiotic production of C2H4 in soil. The influence of trace elements on C2H4 production in soil may be related to their effects on E(h), the catalytic activity (cofactors versus inhibitors), and toxicity to the microflora.