The influence of soil microbial community structure on carbon and nitrogen partitioning in plant/soil ecosystems

A greenhouse study was conducted to evaluate the influence of increasing soil fungal-to-bacterial ratios (F:B) on the allocation of plant-photosynthate carbon into the carbon (C) and nitrogen (N) partitions (g) of plant components (root, shoot and fruit), New-Soil C and N, and Soil-Respiration C (CO₂). Six (6) experimental treatment soils were formulated to provide linearly increasing: initial-soil C% (0.14% – 5.3%); initial-soil N% (0.01% - 0.40%); and soil microbial community (SMC) populations progressing from bacterial dominant (F:B=0.04) to fungal dominant (F:B=3.68) while still maintaining significant SMC population homogeneity. In an 86-day greenhouse experiment, growing chile plants (Capsicum annuum) in treatment soils with increasing F:B (0.4-3.68), the following was observed: a) a continuous linear increase (3% up to 56%) in the partitioning of total plant-photosynthate C into plant biomass (root, shoot and fruit) when regressed to initial F:B (m=0.13; r²=0.96); b) approximately 93% of the flow of plant-photosynthate C was partitioned into New-Soil C in Treatment 0 (F:B = 0.04), to a minimum of 47% in Treatment 5 (F:B = 3.68) demonstrating a negative linear correlation to treatment Initial-Soil C mass (m= -0.12; r² = 0.97); c) conditional and coordinated flow of system C resources into nitrogen (N) fixation (est. C cost for N fixation at 6:1), with 1.21 g C partitioned to N fixation in Treatment 0 (F:B=0.04), peaking at 6.92 g C in Treatment 2 (F:B=1.6), and final C partitioning to N fixation of 2.91 g C in Treatment 5 (F:B=3.68), following a 3^rd order polynomial trendline (r²=0.99) when correlated with initial treatment soil C mass; d) decreases in soil respiration, from 44% of Initial-Soil C substrate respired in bacterial-dominant low-C (0.14%) soils (F:B = 0.04) to 11% in fungal dominant (F:B = 3.68), high-C percent (5.30% C) soils (y = -0.108ln(x)+ 0.4987; r²= 0.95). Increasing the F:B in the soils of agroecosystems may provide more efficient accumulation and partitioning of photosynthate C into plant and soil biomass, improved N fixation and beneficial increases in total carbon use efficiencies. Collectively, these benefits could provide a practical and cost-effective path towards: improving crop production, reducing N-fertilizer inputs, promoting a more sustainable agricultural system, while providing a cost-effective approach for capturing and storing atmospheric carbon (CO₂) in soils of agroecosystems.