Short-Term Wavelike Dynamics of Bacterial Populations in Response to Nutrient Input from Fresh Plant Residues

Abstract

The objectives of the research were to investigate short-term dynamics of bacterial populations in soil after a disturbance in the form of fresh organic matter incorporation and to investigate how these dynamics are linked to those of some environmental parameters. To reach these objectives, soil bacterial populations, mineral nitrogen, pH, and redox potential (ROP) were monitored daily for 1 month after incorporation of clover-grass (CG) plant material in microcosm experiments. Colony-forming units (CFUs) and direct microscopic counts of FDA-stained and FTTC-stained bacteria increased immediately after incorporation of the plant material, dropped within 2 days, and fluctuated thereafter. Harmonics analysis demonstrated that there were significant wavelike fluctuations with three or four significant peaks within 1 month after incorporation of clover-grass material. Peaks in CFUs were 1-2 days ahead of those in direct counts. Ammonium (NH4) concentrations increased from the start of the experiments until nitrification commenced. Nitrate (NO3) concentrations dropped immediately after plant incorporation, and then rose monotonically until the end of the experiments. There were no wavelike fluctuations in NH4 and NO3 concentrations, so that bacterial fluctuations could not be attributed to alternating mineral N shortages and sufficiencies. pH levels rose and declined with NH4 levels. ROP dropped shortly before NH4 concentrations rose, and increased before NH4 concentrations decreased; there were no regular fluctuations in ROP, so that temporary oxygen shortages may not have been responsible for the observed fluctuations in bacterial populations. Thus, for the first time, regular wavelike dynamics were demonstrated for bacterial populations after perturbation by addition of fresh organic matter to soil, and several potential reasons for the death phase of the fluctuations could be excluded from further consideration.

Legume and gramineous crop residues stimulate distinct soil bacterial populations during early decomposition stages

“…While the larger soil DNA pool size can partly be attributed to the DNA content of residues, higher soil RNA contents should be strictly correlated to real-time enhanced bacterial metabolic activities and cell division as RNAs are highly labile and reactive molecules that were undoubtedly degraded in original plant materials owing to their physical treatment before incorporation into soil. Thus, this fast increase in RNA contents strongly suggests an immediate stimulation of microbial activity following residues application, and is in agreement with studies focusing on the evolution of various bacterial features following soil enrichment with plant material, such as clover (Zelenev et al 2005), rye (Lundquist et al 1999), ryegrass (McMahon et al 2005 or pea (Ha et al 2008), and including a first sampling at early stages similar to our timescale (3Á5 d).…”

Successional Change in Microbial Communities of Benthic Phormidium-Dominated Biofilms

“…Sime-Ngando et al [59] suggested that these oscillations were linked to biotic factors and interactions, whereas Zelenev et al [60] indicated that they were controlled by the interaction between bacteria and their carbon substrate in soil ecosystems. Availability of organic carbon, for example, from algal photosynthates, can affect alkaline phosphatase production [57].…”

Relation between soil health, wave-like fluctuations in microbial populations,and soil-borne plant disease management

“…This question was addressed in another time-series experiment with and without grass-clover incorporated into a sandy soil. The response of copiotrophic bacterial CFUs (de Vos and van Bruggen, 2001;Zelenev et al, 2005) to the disturbance was determined daily over a period of nine days, both for the grassclover (GC) and the non-amended control series (CO). Copiotrophic bacteria are fast-growing bacteria, with a relatively low substrate affinity and high half saturation constant.…”