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This paper is part of a series considering the impact of activated carbon (AC) on the composition of plant tissue culture media. Using liquid culture media for initiation of Norway spruce embryogenic tissue and eight different ACs, we present a method for achieving target plant growth regulator (PGR) levels in AC-containing medium based on sorption isotherms for individual PGRs. Linear relationships were found between PGR adsorption and specific BET (Brunauer, Emmett, Teller theory) surface area and specific total pore volume of AC. When using a new AC, this linear relationship allows one to achieve multiple PGR levels similar to historic levels through adjustment of the mass of AC based on its relative BET surface area or relative total pore volume. Target levels of PGRs and an initiation success similar to that in medium without AC were achieved with several different AC types when AC mass was adjusted on the basis of pore volume.

This study considered the elemental composition of plant tissue culture media in response to pH and two different types of activated C (AC; tissue culture and non acid-washed grades) in liquid media. When tissue culture medium is supplemented with AC the method of AC addition and pH adjustment can greatly impact the final medium pH, in turn, altering mineral availability. Over the pH range of 4-7, Cu and Zn adsorbed (95% and 50%) onto the two physically different ACs to the same extent. As the pH exceeded 5.8, precipitation became pronounced, resulting in 50% reductions in Mn and Fe and smaller reductions in Ca (20%), and P (15%), independent of AC. Non acid-washed AC released significant levels of Mg (65% increase) and Ca (10% increase) at pH 5.8 compared to the no-AC control. No adsorption was indicated for inorganic anions. Low levels for Cu and Zn are a concern when using AC, and low levels of Fe and Mn are a concern when the pH of the medium exceeds 5.8. Due to its impurity content and difficulty associated with its neutralization, non-acid-washed AC may be a poor choice for use in tissue culture medium.

The elemental composition of plant tissue culture media was studied in response to (1) different levels of Gelrite and activated carbon (AC) in semisolid media and (2) different levels and types of AC in liquid media. Doubling the level of Gelrite from 2 g/l to 4 g/l reduced available magnesium (20%), calcium (16%), zinc (17%) and manganese (24%) and increased potassium (6%). AC adsorbed copper (90-95%) and zinc (35-51%) from both liquid and semisolid media. Two significantly different ACs gave minor differences in adsorption. No adsorption was indicated for inorganic anions. Nonacid-washed AC released significant levels of magnesium (44% increase), calcium (16% increase) and silica (a 75% increase to 1.8 mg/l). The elemental composition of media may need to be adjusted when increasing the Gelrite level or adding AC.