Methanogenic abundance and changes in community structure along a rice soil chronosequence from east China

Abstract

Summary Changes in abundance, community structure and activity of archaea were investigated for rice paddy soil under long‐term cultivation along a chronosequence that spans 700 years in a coastal area of east China. Topsoil samples were analysed for archaeal abundance and community structures, which were determined with archaeal 16S rRNA and methanogenic mcrA genes. Methane production potential (MPP) was evaluated concurrently with a laboratory anaerobic incubation of treated topsoil samples. Gene abundance of archaea and methanogenic archaea increased from 6.70 × 106 and 1.53 × 105 copies g−1 in marsh to 2.89 × 108 and 2.73 × 107 copies g−1 in rice soil cultivated for seven centuries, respectively. Compared with the uncultivated marsh, diversity indices for both archaea and methanogenic archaea increased markedly with rice cultivation. Methanogenic archaeal community structure was dominated by Methanosarcinales and changed to a lesser extent after 100 years. The measured MPP varied over a range from 241.3 to 301.1 µg CH4 g−1 for the rice soil, whereas it was 101.3 µg CH4 g−1 for the uncultivated marsh soil. Therefore, gene abundance of both archaea and methanogenic archaea appeared to increase with the accumulation of organic matter following long‐term rice cultivation. The changes in MPP and community structure, however, were independent of differences in archaeal abundance. This suggests a complex interaction of soil organic matter, archaeal abundance and community structure, which could change the potential methanogenic activity in rice soil with long histories of rice cultivation. Highlights How do archaeal and methanogenic archaeal communities change in response to long‐term rice cultivation? Improve understanding of archaeal communities and their function in rice soil over hundreds of years. Change in the archaeal community structure was controlled by soil desalinization and decalcification. Archaeal community diversity precedes soil morphological and mineralogical development.

Rice paddy soils are a quantitatively important carbon store according to a global synthesis

“…Consequently, leaching of dissolved organic matter will be reduced. Furthermore, low soil pH values slow down litter decomposition by reducing enzyme activity 28,29 and by changing the composition of microbial communities 30,31 .…”