Dynamics of carbon and nitrogen in an extreme alkaline saline soil: A review

The soil of the former lake Texcoco is an ‘extreme’ alkaline saline soil with pH > 10 and electrolytic conductivity (EC) > 150 dS m −1. These conditions have created a unique environment. Application of wastewater sludge to Texcoco soil showed that large amounts of NH 4 + were immobilized, NO 3 − was reduced aerobically, NO 2 − was formed and the mineralization of the organic material in the sludge was inhibited. A series of experiments were initiated to study the processes that inhibited the decomposition of organic material and affected the dynamics of mineral N. The large EC and pH inhibited the decomposition of easily decomposable organic material such as glucose and maize, although cellulolytic activity was observed in soil with pH 9.8 and EC 32.7 dS m −1. The high soil pH favoured NH 3 volatilization of approximately 50 mg N kg −1 soil within a day and a similar amount could be fixed on the soil matrix due to the dispersed minerals and their volcanic origin. Soil microorganisms immobilized large amounts of NH 4 + within a day when glucose was added to soil in excess of what was required for metabolic activity. Removal of NO 3 − from soil amended with glucose was not inhibited by 100% O 2 and NH 4 + indicating that the contribution of denitrification and assimilatory reduction to the reduction of NO 3 − was minimal while the formation of NO 2 − was not inhibited by 0.1% acetylene, known to inhibit nitrification. Additionally, the reduction of NO 3 − in the glucose-amended alkaline saline Texcoco soil was followed by an increase in the amount of NH 4 +, which could not be due to denitrification. It was concluded that the reduction of NO 3 − and the formation of NO 2 − and NH 4 + in the glucose-amended soil was a result of aerobic NO 3 − reduction. A phylogenetic analysis of the archaeal community in the soil of the former lake Texcoco showed that some of the clones identified were capable of reducing NO 3 − aerobically to NO 2 − when glucose was added. A study of the diversity of the bacterial dissimilatory and respiratory nitrate-reducing communities indicated that bacteria could have contributed to the process.