Liberation of sulfate from sulfate esters by soils

Abstract

When incubated with acid, alkaline, and neutral soils, a variety of synthetic sulfate esters representing the various classes of these compounds was hydrolyzed by enzymes, probably of microbial origin. The appearance of sulfate in the soil water occurred immediately after introduction into the soils with some esters, whereas with others it occurred only after lag periods. Heat treatment destroyed the hydrolytic activity in the soils. The ester sulfate groups-present in humic acid extracted from the soil appeared to be resistant to hydrolysis by a variety of sulfohydrolases extracted from bacteria and other organisms.

Sulfate ester formation and hydrolysis: a potentially important yet often ignored aspect of the sulfur cycle of aerobic soils.

“…Thus, using a variety of mild extractants (176) unlikely to degrade humic acid, Freney et al (88) found that more HI-reducible S was associated with this latter soil colloid than with fulvic acid. This result is consistent with those of Lowe (159) and Houghton and Rose (113) who found that HI-reducible S represented 39 and 51% of the total S present in humic acid isolated from Alberta and Welsh soils, respectively. In the latter study (113), the presence of sulfate ester groups in the humic acid fraction was confirmed by extraction with methanolic hydrogen chloride and by release of S042after hydrolysis in 6 N HCl at 1000C.…”

“…This result is consistent with those of Lowe (159) and Houghton and Rose (113) who found that HI-reducible S represented 39 and 51% of the total S present in humic acid isolated from Alberta and Welsh soils, respectively. In the latter study (113), the presence of sulfate ester groups in the humic acid fraction was confirmed by extraction with methanolic hydrogen chloride and by release of S042after hydrolysis in 6 N HCl at 1000C. The collective results of these studies (88,159,176) and others (90,91,158) suggest that no one procedure is entirely suitable for assessing the heterogeneity of compounds comprising the HIreducible S fraction of soil.…”

“…These soil colloids have been considered (53) to be resistant to S042release by microorganisms, but the available evidence for this is still not convincing. In the only reported study of the degradability of humic acid sulfur, Houghton and Rose (113) found that the sulfate ester groups present in this colloid were resistant to hydrolysis by extracts possessing alkylsulfatase, arylsulfatase, and glycosulfatase activities. It is well established that depolymerization occurs before the desulfation of other sulfated macromolecules (52, 53) and, as the authors (113) pointed out, the desulfation of humic acid may result from a sequential attack by depolymerizing and desulfating enzymes.…”

“…Similarly, Freney and co-workers (86,90) found that HI-reducible S could be extracted from soil using a dilute potassium phosphate solution at pH 7. Although some soils have little capacity to adsorb S042- (90,248), other soils adsorb substantial quantities of this anion (14,108,113,132,158), and there is evidence that HI-reducible S may also be adsorbed to soil particles. Thus, Houghton and Rose (113) found that a wide variety of different mS-labeled sulfate esters were adsorbed to Welsh soils to the extent of 67% (average) of the total concentration of the ester that was initially added to these soils.…”

“…Although some soils have little capacity to adsorb S042- (90,248), other soils adsorb substantial quantities of this anion (14,108,113,132,158), and there is evidence that HI-reducible S may also be adsorbed to soil particles. Thus, Houghton and Rose (113) found that a wide variety of different mS-labeled sulfate esters were adsorbed to Welsh soils to the extent of 67% (average) of the total concentration of the ester that was initially added to these soils. Furthermore, procedures that do not release S042from humic acid (such as heating at neutral pH [13, 234,270] or simple grinding of soil before ex-traction [861) caused a substantial increase in the S042content of some soils.…”