Lichen Sulfur Contents as Bioindicators of Crop Sulfur: Deficiency or Luxury Uptake

Abstract

The most important, immediate source of sulfur (S) for agricultural crops is the soil, but the soil supply is augmented by anthropogenic and natural S additions. In either case, lichen S contents provide a means for evaluating the effective S supply. Thus, lichen S content may be a way of determining locations where S emissions are large and extensive and why soil levels may vary from sufficient to deficient. Lichen S and phosphorus (P) contents were determined in two contrasting areas of the North Central United States, one east and one west of the Mississippi River. Mean contents were in µg g⁻¹ S 4100 and P 1550 in Area East and S 2100 and P, 1660 in Area West. Population density and S emissions are much greater in Area East. Sulfur deficiencies are not generally recognized there. Area West includes regions that range from severely S deficient to adequate in soil S, with regions that are borderline predominating. Lichen S in the Gulf Coast Plain area and northwest of the Great Lakes was in the range 1000–2000 µg g⁻¹. Sulfur deficiencies are well documented in the region, suggesting that 2000 µg g⁻¹ lichen S‐represents a boundary between near adequate and S‐deficient crops unless soil sources are adequate. An east‐west lichen S transect from southern Indiana to southwest Missouri suggests that a response to S fertilizer can be expected if the soil is sandy or lichen S is less than 2000 µg g⁻¹ and crops are well supplied with other nutrients. High‐S contents observed along the transect may have resulted from long‐distance S transport from cities along the Missouri and Mississippi Rivers and the west shore of Lake Michigan. Lichen S contents along transects from Ontario, Canada, to the Gulf of Mexico ranged from 6000 µg g⁻¹ near the Great Lakes to 1000 µg g⁻¹ near the Gulf of Mexico. By using 2000 µg g⁻¹ as the desired S level, half of the area is, to a certain extent, potentially S deficient.

Keywords:

• Environment
• bioindicator
• S deficiency
• S excess
• lichen S