Anthropogenic and climate influences on biogeochemical dynamics and molecular-level speciation of soil sulfur.
The soil environment is a primary component of the global biogeochemical sulfur (S) cycle, acting as a source and sink of various S species and mediating oxidation state changes. However, ecological significance of the various S forms and the impacts of human intervention and climate on the amount and structural composition of these compounds are still poorly understood. We investigated the long-term influences of anthropogenically mediated transitions from natural to managed ecosystems on molecular-level speciation, biogeochemical dynamics, and the apparent temperature sensitivity of S moieties in temperate, subtropical, and tropical environments with mean annual temperature (MAT) ranging from 5 degrees C to 21 degrees C, using elemental analysis and X-ray absorption near-edge structure (XANES) spectroscopy. Land-use and land-cover changes led to the depletion of total soil S in all three ecoregions over a period of up to 103 years. The largest decline occurred from tropical forest agroecosystems (67% Kakamega and 76% Nandi, Kenya), compared to losses from temperate (36% at Lethbridge, Canada, and 40% at Pendleton, USA) and subtropical (48% at South Africa) grassland agroecosystems. The total S losses correlated significantly with MAT. Anthropogenic interventions profoundly altered the molecular-level composition and resulted in an apparent shift in oxidation states of organic S from native ecosystems composed primarily of S moieties in intermediate and highly reduced oxidation states toward managed agroecosystems dominated by organic S rich in strongly oxidized functionalities. The most prominent change occurred in thiols and sulfides, the proportion of which decreased by 46% (Lethbridge) and 57% (Pendleton) in temperate agroecosystems, by 46% in subtropical agroecosystems, and by 79% (Nandi) and 81% (Kakamega) in tropical agroecosystems. The proportion of organic S directly linked to O increased by 81%, 168%, 40%, 92%, and 85%, respectively. Among the various organic S functionalities, thiols and sulfides seem to have higher apparent temperature sensitivity, and thus these organic S moieties may become prone to losses due to land-use changes, even from the cooler regions of the world if MAT of these regions rise in the future.
Solomon
Dawit
D
Cornell University, College of Agriculture and Life Sciences, Ithaca, New York 14853, USA. ds278@cornell.edu
Lehmann
Johannes
J
Kinyangi
James
J
Pell
Alice
A
Theis
Janice
J
Riha
Susan
S
Ngoze
Solomon
S
Amelung
Wulf
W
Du Preez
Chris
C
Machado
Stephen
S
Ellert
Ben
B
Janzen
Henry
H
D002980:Climate; D017753:Ecosystem; D006801:Humans; D007630:Kenya; D009656:North America; D010084:Oxidation-Reduction; D012987:Soil / Q000032:analysis*; D013019:South Africa; D013455:Sulfur / Q000032:analysis*; D013457:Sulfur Compounds / Q000032:analysis*; D013696:Temperature; D013997:Time Factors
D012987:Soil; D013457:Sulfur Compounds; D013455:Sulfur