Organic anion-to-acid ratio influences pH change of soils differing in initial pH

Purpose

This study aimed to investigate the effect of initial soil pH and organic anion-to-acid ratio on changes in soil pH.

Materials and methods

Two soils (Podosol and Tenosol) along with two carboxylic acids (malic and citric acid) and their anions (sodium malate and citrate), commonly found in plant residues, were used in this study. Stock solutions of either malic acid and disodium malate or citric acid and trisodium citrate were added to pre-incubated soils at anion-to-acid ratios of 0:100, 10:90, 25:75, 50:50, 75:25, 90:10, 100:0 and at 0.25 g C kg^?1 soil. Soils were adjusted to 80 % field capacity and mixed thoroughly, and three replicates of 50 g of each soil were transferred into individual plastic cores and incubated at 25 °C in the dark for 30 days. Soil pH, respiration, NH₄ ⁺, and NO₃ ^? were determined.

Results and discussion

Soil pH increased linearly with increasing organic anion-to-acid ratio. The addition of organic anions to soil resulted in net alkalinisation. However, the addition of organic acids immediately decreased soil pH. During subsequent incubation, soil pH increased when the organic anions were decomposed. Alkalinity generation was lower in the Podosol (initial pH 4.5) than in the Tenosol (initial pH 6.2), and was proportional to anion-to-acid ratio across all the treatments. Cumulative CO₂-C release was approximately three times lower in the Podosol than the Tenosol at day 2 due to lower microbial activity in the low-pH Podosol.

Conclusions

Increasing anion-to-acid ratio of organic compounds increased soil pH. Increases in soil pH were mainly attributed to direct chemical reactions and decomposition of organic anions. Low pH decreased the amount of alkalinity generated by addition of organic compounds due to incomplete decomposition of the added compounds. This study implies that organic anion-to-acid ratio in plant residues plays an important role in soil pH change.     

Oxygen isotopes: experimental vapor fractionation and variations in tektites

High-temperature (about 2800 degrees C) vapor fractionation of a silicate glass that originally contained 82 percent by weight of SiO(2) resulted in a decrease of the silica content to 45 percent. Oxygen isotope analyses show that the O(18)/O(16) ratio increased from 13.80 per mil in the starting material to 14.47 and 15.03 per mil in the residuum. This suggests that bediasites, which also exhibit an increase in this ratio with decreasing content of silica, have been subjected to a process of vapor fractionation.     

A mammalian mitochondrial RNA processing activity contains nucleus-encoded RNA

Ribonuclease mitochondrial RNA processing, a site-specific endoribonuclease involved in primer RNA metabolism in mammalian mitochondria, requires an RNA component for its activity. On the basis of copurification and selective inactivation with complementary oligonucleotides, a 135-nucleotide RNA species, not encoded in the mitochondrial genome, is identified as the RNA moiety of the endoribonuclease. This finding implies transport of a nucleus-encoded RNA, essential for organelle DNA replication, to the mitochondrial matrix.