Microbial population shifts in experimental rice systems uri icon

abstract

  • Biogeochemically relevant constituents of rice soil microbial communities exhibit profound population shifts during a rice cropping cycle on irrigated fields. Greenhouse experiments were designed to examine the effects of the less stable environmental conditions in submergence- and drought-prone rainfed rice cropping systems on soil microbiota. Successions of cultivable groups of microorganisms (guilds) with assumed key functions in nutrient cycling were assessed under different water regimes. Frequently, microbial population dynamics for both planted and unplanted trials converged both in the flooded field and under controlled submergence in the greenhouse. An induced mid season drought as is typical for rainfed rice cropping systems proved not long enough to reverse prevailing trends in population dynamics of most of the functional groups investigated. Irrespective of the water regime, total bacterial cell counts declined toward the end of the cropping period. In contrast, a fast build-up of heterotrophic biomass by copiotrophic bacteria peaked at the flowering stage. This trend was most pronounced under drought conditions, but also significant under submergence. It leveled off towards harvest and the subsequent fallow period.
  • Fungi as primary microbial digesters of crop residues showed a negative correlation with the soil water content and were predominant only under drought or post-harvest fallow conditions. N-remobilizing, proteolytic bacteria declined strongly in the flooded field, whereas drought reversed this trend in the greenhouse. Observations of successive increases of anaerobic guilds in the field were confirmed under permanent flooding in the greenhouse. Peaks of denitrifiers, mainly triggered by post-season puddling, appeared and disappeared early in the plant growth cycle. Ammonium oxidizing nitrifiers showed extremely low titers under submergence, but also in planted trials under drought. This suggested a negative rhizosphere effect under water limitation. For other guilds, differences between planted and unplanted trials were less pronounced. (C) 2001 Elsevier Science B.V. All rights reserved.

publication date

  • 2001
  • 2001
  • 2001