Fluxes of carbon to the microbial pool from the humus, litter and faeces pools

The size of the microbial pool may vary over time depending on the consumption and mortality of the micro organisms. The net result of these two processes will determine the transfer of carbon to the microbial pool from the humus, litter and faeces pools respectively. These carbon fluxes from the litter, humus and faeces pools to the microbial biomass, C_{Litter1 and 2→Microbe} , C_{Humus→Microbe} and C_{Faeces→Microbe} are calculated as:

                          (6.9)

 

 

where f_e,m is an efficiency parameter, f_cons,l1 is a parameter that gives the fraction of consumption for the litter pool compared to the whole consumption, f_mort,l1 is a parameter that gives the fraction of mortality for the litter pool compared to the whole mortality and k_m,mort is the microbial mortality rate. f(CN_l1) and f(C_Litter1) are response functions for the carbon nitrogen ratio and the total carbon content in the litter pool respectively. These response functions are not considered for the humus pool and can also optionally be switched off for the other organic pools (see switch CN Ratio Influence). Finally f(A_mort) is an abiotic response function on mortality and M_potcons is the potential microbial consumption. The equation is used analogously for the faeces, litter 2 and humus pools by the parameters f_cons,l2, f_cons,f, f_mort,l2 and f_mort,f. For the humus pool the parameters f_cons,h and f_mort,h are the fractions of the microbial biomass that remains when the rest of the biomass has been allocated to the litter and faeces pools for consumption and mortality respectively.

The potential microbial consumption is calculated as:

                                               (6.10)

where k_m,cons is the microbial consumption rate and f(A_cons) is an abiotic response function on consumption (see below). If the consumption is dependent only on the carbon content in the microbes (see switch Microbes) the C_dep equals the carbon content in the microbial pool, C_Microbe. If, on the other hand, the consumption depends of the carbon content in the substrate, the C_dep is the sum of the carbon contents in the litter and faeces pools, when calculating flows from these pools, but from the humus pool, C_dep is instead equal to C_Humus.

The response function f(CN_l1) assumes an optimal range when the actual CN ratio is lower then a minimum value, r_CN,min, and it approaches zero when a maximal CN ratio, r_CN,max, is reached:

                           (6.11)

 

 

See viewing function Decomposition – Substrate dependence, CN ratio.

The response because of the total amount of substrate available, f(C_Litter1), is given by a Michaeli-Menton approach:

                                            (6.12)

 

 

where s_cons is a parameter that corresponds to a 50% reduction of potential consumption rate and Δz is the soil layer thickness. See viewing function Decomposition – Substrate dependence, Carbon content.

The response function for abiotic influence on microbial mortality, f(A_mort), and consumption, f(A_cons), can be described together as f(A_i), and are determined by the switches Microbial mortality and Microbial consumption:

•      “static”
f(A_i) = 1

•      “F(Temp)”                                                 (6.13)
f(A_i) = f(T)

•      “F(Temp, Moisture)”
f(A_i) = f(θ)⋅f(T)

The response functions for soil moisture and temperature, f(θ) and f(T), are described in the section Common abiotic functions.