To understand the origin of the ultrafine pedogenic components responsible
for the magnetic susceptibility (MS) enhancement remains a major challengin
g problem, in linking the magnetic signal with paleoclimatic conditions. He
re we examine the influence of natural fires on the MS signal of both plant
s and modern soils and in particular the MS difference between C3 and C4 pl
ant ashes and their influence possibly on soil magnetic susceptibility. We
demonstrate that burning of C3 and C4 plants can enhance MS signal of moder
n soils. We show that C4 plants have greater potential to enhance the MS si
gnal. The average MS value of C4 plant ashes is (532+/-61) x 10(-8)m(3) kg(
-1), much higher than the average MS value of (120 +/-65) x 10(-8)m(3) kg(-
1) of C3 plant ashes. The Fe2O3 concentration in C4 plant is two to four ti
mes higher than that in C3 pliant. One burning of the grassland, mainly con
sisting of C4 plants, can enhance MS value of the surface soil up to about
30-40%.