Litter model configuration#

The litter model only requires one configuration section:

The litter model constants ([litter.constants])

Litter constants#

[litter.constants]
litter_decomp_reference_temp = 40.0
litter_decomp_offset_temp = 31.79
litter_decomp_temp_response = 3.36
litter_decay_water_potential_optimum = -10.0
litter_decay_water_potential_halt = -28800.0
moisture_response_curvature = 1.0
litter_decay_constant_metabolic_above = 0.08
litter_decay_constant_structural_above = 0.021714285714285714
litter_decay_constant_woody = 0.006666666666666667
litter_decay_constant_metabolic_below = 0.1
litter_decay_constant_structural_below = 0.02702702702702703
cue_metabolic = 0.45
cue_structural_above_ground = 0.55
cue_woody = 0.55
cue_structural_below_ground = 0.45
lignin_inhibition_factor = -5.0
max_metabolic_fraction_of_input = 0.85
metabolic_split_nitrogen_sensitivity = 0.018
metabolic_split_phosphorus_sensitivity = 0.0011613
metabolic_to_structural_n_ratio = 5.0
metabolic_to_structural_p_ratio = 5.0

litter.constants.litter_decomp_reference_temp

Reference temperature for litter decomposition [Celsius].

Value is taken from Kirschbaum and Paul (2002). Default = 40.0

litter.constants.litter_decomp_offset_temp

Offset temperature for litter decomposition [Celsius].

Value is taken from Kirschbaum and Paul (2002). Default = 31.79

litter.constants.litter_decomp_temp_response

Parameter controlling the temperature response strength of litter decomposition.

[unitless]. Value is taken from Kirschbaum and Paul (2002). Default = 3.36

litter.constants.litter_decay_water_potential_optimum

The water potential at which below ground litter decay is maximised [kPa].

Value is taken from Moyano et al. (2013). Default = -10.0

litter.constants.litter_decay_water_potential_halt

The water potential at which below ground litter decay stops entirely [kPa].

Value is taken from Moyano et al. (2013). Default = -28800.0

litter.constants.moisture_response_curvature

Curvature of the litter decay moisture response function [unitless].

Value is taken from Moyano et al. (2013). Default = 1.0

litter.constants.litter_decay_constant_metabolic_above

Decay constant for the above ground metabolic litter pool [day^-1].

Value is taken from Kirschbaum and Paul (2002). Default = 0.08

litter.constants.litter_decay_constant_structural_above

Decay constant for the above ground structural litter pool [day^-1].

Value is taken from Kirschbaum and Paul (2002). Default = 0.021714285714285714

litter.constants.litter_decay_constant_woody

Decay constant for the woody litter pool [day^-1].

Value is taken from Kirschbaum and Paul (2002) as the average of fine wood and coarse wood decay. Default = 0.006666666666666667

litter.constants.litter_decay_constant_metabolic_below

Decay constant for the below ground metabolic litter pool [day^-1].

Value is taken from Kirschbaum and Paul (2002). Default = 0.1

litter.constants.litter_decay_constant_structural_below

Decay constant for the below ground structural litter pool [day^-1].

Value is taken from Kirschbaum and Paul (2002). Default = 0.02702702702702703

litter.constants.cue_metabolic

Carbon use efficiency of metabolic litter decay [unitless].

The value given here is taken from Fatichi et al. (2019), but I can’t track down an empirical source. This carbon use efficiency is constant with temperature, soil moisture and substrate stoichiometry. These assumptions are not made in the soil model, but are used for the sake of simplicity here. If an improved version of the litter model gets made, this is a key area to address. Default = 0.45

litter.constants.cue_structural_above_ground

Carbon use efficiency of aboveground structural litter decay [unitless].

The value given here is taken from Fatichi et al. (2019); see documentation for LitterConstants.cue_metabolic for details. Default = 0.55

litter.constants.cue_woody

Carbon use efficiency of woody litter decay [unitless].

The value given here is taken from Fatichi et al. (2019); see documentation for LitterConstants.cue_metabolic for details. Default = 0.55

litter.constants.cue_structural_below_ground

Carbon use efficiency of belowground structural litter decay [unitless].

The value given here is taken from Fatichi et al. (2019); see documentation for LitterConstants.cue_metabolic for details. Default = 0.45

litter.constants.lignin_inhibition_factor

Exponential factor expressing the extent that lignin inhibits litter breakdown.

[unitless]. The more negative this value the greater the strength of the inhibition. This value is taken from Kirschbaum and Paul (2002). Default = -5.0

litter.constants.max_metabolic_fraction_of_input

Maximum proportion of input plant biomass that can go to metabolic litter.

[unitless]. The value is taken from Krinner et al. (2005). Default = 0.85

litter.constants.metabolic_split_nitrogen_sensitivity

Sensitivity to nitrogen of the split between metabolic and structural litter.

i.e. how much the split of input biomass between these two litter pools changes in response to changes in the product of the nitrogen and lignin concentrations [unitless]. These factors are combined as lignin is assumed to colimit litter breakdown along with limiting nutrients. The value is taken from Krinner et al. (2005). Default = 0.018

litter.constants.metabolic_split_phosphorus_sensitivity

Sensitivity to phosphorus of the split between metabolic and structural litter.

i.e. how much the split of input biomass between these two litter pools changes in response to changes in the product of the phosphorus and lignin concentrations [unitless]. These factors are combined as lignin is assumed to colimit litter breakdown along with limiting nutrients.

The default value was calculated following Orwin et al. (2011), by rescaling the sensitivity constant for nitrogen by how limiting phosphorus is relative to nitrogen. For this we used, an (atomic) C:N:P ratio of soil microbial biomass of 60:7:1, we took this from Cleveland and Liptzin (2007). This was then converted to a mass terms ratio by using their atomic masses. Default = 0.0011613

litter.constants.metabolic_to_structural_n_ratio

Ratio of nitrogen concentrations for input to metabolic and structural litter.

Following Kirschbaum and Paul (2002), we assume that the nitrogen concentrations (relative to the carbon mass) of inputs to the metabolic and structural litter pools are in a fixed proportion. This parameter sets how many times higher the nitrogen concentration is for inputs to the metabolic pool relative to inputs to the corresponding structural pool. The default value is also taken from Kirschbaum and Paul (2002). Default = 5.0

litter.constants.metabolic_to_structural_p_ratio

Ratio of phosphorus concentrations for input to metabolic and structural litter.

This follows the same logic as for phosphorus (see LitterConstants.metabolic_to_structural_n_ratio). The default value used is the same as for the nitrogen case as we saw no sense treating them differently. Default = 5.0