CarbohydrateModel.cpp

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#include "PlantArchitecture.h"
#include "../include/PlantArchitecture.h"
 
using namespace helios;
 
 
float Phytomer::calculatePhytomerConstructionCosts() const {
    float leaf_carbon_percentage = plantarchitecture_ptr->plant_instances.at(this->plantID).carb_parameters.leaf_carbon_percentage;
    float SLA = plantarchitecture_ptr->plant_instances.at(this->plantID).carb_parameters.SLA;
 
    float leaf_construction_cost_base = leaf_carbon_percentage * 0.1 / (C_molecular_wt * SLA); // mol C/m^2
 
    float phytomer_carbon_cost = 0.f; // mol C
 
    // leaves (cost per area basis)
    float leaf_area = 0;
    uint p = 0;
    for (const auto &petiole: leaf_objIDs) {
        for (uint leaf_objID: petiole) {
            if (context_ptr->doesObjectExist(leaf_objID)) {
                float obj_area = context_ptr->getObjectArea(leaf_objID);
                float scale_factor = current_leaf_scale_factor.at(p);
                float scaled_area = obj_area / powi(scale_factor, 2);
                leaf_area += scaled_area;
            }
        }
        p++;
    }
    phytomer_carbon_cost += leaf_construction_cost_base * leaf_area;
 
    return phytomer_carbon_cost;
}
 
float Phytomer::calculateFlowerConstructionCosts(const FloralBud &fbud) const {
    float flower_carbon_cost = 0.f; // mol C
 
    for (uint flower_objID: fbud.inflorescence_objIDs) {
        flower_carbon_cost += plantarchitecture_ptr->plant_instances.at(this->plantID).carb_parameters.total_flower_cost;
    }
 
    return flower_carbon_cost;
}
 
void PlantArchitecture::initializeCarbohydratePool(float carbohydrate_concentration_molC_m3) const {
    for (auto &plant: plant_instances) {
        auto shoot_tree = &plant.second.shoot_tree;
 
        for (auto &shoot: *shoot_tree) {
            // calculate shoot volume
            float shoot_volume = shoot->calculateShootInternodeVolume();
            // set carbon pool
            shoot->carbohydrate_pool_molC = shoot_volume * carbohydrate_concentration_molC_m3;
            context_ptr->setObjectData(shoot->internode_tube_objID, "carbohydrate_concentration", carbohydrate_concentration_molC_m3);
            context_ptr->setObjectData(shoot->internode_tube_objID, "carbohydrate_pool_molC", shoot->carbohydrate_pool_molC);
        }
    }
}
 
void PlantArchitecture::initializePlantCarbohydratePool(uint plantID, float carbohydrate_concentration_molC_m3) {
 
    // Make sure that the plant exists in the context
    if (plant_instances.find(plantID) == plant_instances.end()) {
        helios_runtime_error("ERROR (PlantArchitecture::initializePlantCarbohydratePool): Plant with ID of " + std::to_string(plantID) + " does not exist.");
    } else if (carbohydrate_concentration_molC_m3 < 0.f) {
        helios_runtime_error("ERROR (PlantArchitecture::initializePlantCarbohydratePool): Carbohydrate concentration must be greater than or equal to zero.");
    }
 
    // loop over all shoots
    for (auto &shoot: plant_instances.at(plantID).shoot_tree) {
        initializeShootCarbohydratePool(plantID, shoot->ID, carbohydrate_concentration_molC_m3);
    }
}
 
void PlantArchitecture::initializeShootCarbohydratePool(uint plantID, uint shootID, float carbohydrate_concentration_molC_m3) {
    if (plant_instances.find(plantID) == plant_instances.end()) {
        helios_runtime_error("ERROR (PlantArchitecture::initializeShootCarbohydratePool): Plant with ID of " + std::to_string(plantID) + " does not exist.");
    } else if (shootID >= plant_instances.at(plantID).shoot_tree.size()) {
        helios_runtime_error("ERROR (PlantArchitecture::initializeShootCarbohydratePool): Shoot with ID of " + std::to_string(shootID) + " does not exist.");
    } else if (carbohydrate_concentration_molC_m3 < 0.f) {
        helios_runtime_error("ERROR (PlantArchitecture::initializeShootCarbohydratePool): Carbohydrate concentration must be greater than or equal to zero.");
    }
 
    // calculate shoot volume
    float shoot_volume = plant_instances.at(plantID).shoot_tree.at(shootID)->calculateShootInternodeVolume();
 
    // set carbon pool
    plant_instances.at(plantID).shoot_tree.at(shootID)->carbohydrate_pool_molC = shoot_volume * carbohydrate_concentration_molC_m3;
}
 
void PlantArchitecture::accumulateHourlyLeafPhotosynthesis() const {
    for (const auto &[plantID, plant_instance]: plant_instances) {
        auto shoot_tree = &plant_instance.shoot_tree;
 
        for (auto &shoot: *shoot_tree) {
            // Set cumulative photosynthesis of dormant shoots equal to zero.
            if (shoot->isdormant) {
                for (const auto &phytomer: shoot->phytomers) {
                    for (const auto &leaf_objID: flatten(phytomer->leaf_objIDs)) {
                        for (uint UUID: context_ptr->getObjectPrimitiveUUIDs(leaf_objID)) {
                            context_ptr->setPrimitiveData(UUID, "cumulative_net_photosynthesis", 0);
                        }
                    }
                }
            } else {
                for (const auto &phytomer: shoot->phytomers) {
                    for (auto &leaf_objID: flatten(phytomer->leaf_objIDs)) {
                        for (uint UUID: context_ptr->getObjectPrimitiveUUIDs(leaf_objID)) {
                            float lUUID_area = context_ptr->getPrimitiveArea(UUID);
                            float current_net_photo = 0;
 
                            float leaf_A = 0.f;
                            if (context_ptr->doesPrimitiveDataExist(UUID, "net_photosynthesis")) {
                                context_ptr->getPrimitiveData(UUID, "net_photosynthesis", leaf_A);
                            }
 
                            float new_hourly_photo = leaf_A * lUUID_area * 2 * 3600.f * 1e-6f;
                            ; //net photosynthesis (mol C hr-1) from umol CO2 m-2 sec-1
 
                            if (context_ptr->doesPrimitiveDataExist(UUID, "cumulative_net_photosynthesis")) {
                                context_ptr->getPrimitiveData(UUID, "cumulative_net_photosynthesis", current_net_photo);
                            }
                            current_net_photo += new_hourly_photo;
                            context_ptr->setPrimitiveData(UUID, "cumulative_net_photosynthesis", current_net_photo);
                        }
                    }
                }
            }
        }
    }
}
 
void PlantArchitecture::accumulateShootPhotosynthesis() const {
    uint A_prim_data_missing = 0;
 
    for (auto &[plantID, plant_instance]: plant_instances) {
 
        const auto shoot_tree = &plant_instance.shoot_tree;
 
        for (const auto &shoot: *shoot_tree) {
            uint shootID = shoot->ID;
            float net_photosynthesis = 0;
            float shoot_volume = plant_instances.at(plantID).shoot_tree.at(shoot->ID)->calculateShootInternodeVolume();
 
            if (shoot->isdormant) {
                for (const auto &phytomer: shoot->phytomers) {
                    for (const auto &leaf_objID: flatten(phytomer->leaf_objIDs)) {
                        for (uint UUID: context_ptr->getObjectPrimitiveUUIDs(leaf_objID)) {
                            context_ptr->setPrimitiveData(UUID, "cumulative_net_photosynthesis", 0.f);
                        }
                    }
                }
            } else {
                for (const auto &phytomer: shoot->phytomers) {
                    for (const auto &leaf_objID: flatten(phytomer->leaf_objIDs)) {
                        for (uint UUID: context_ptr->getObjectPrimitiveUUIDs(leaf_objID)) {
                            if (context_ptr->doesPrimitiveDataExist(UUID, "cumulative_net_photosynthesis")) {
                                float A;
                                context_ptr->getPrimitiveData(UUID, "cumulative_net_photosynthesis", A);
                                net_photosynthesis += A;
                                context_ptr->setPrimitiveData(UUID, "cumulative_net_photosynthesis", 0.f);
                            } else {
                                A_prim_data_missing++;
                                context_ptr->setPrimitiveData(UUID, "cumulative_net_photosynthesis", 0.f);
                            }
                        }
                    }
                }
            }
            if (net_photosynthesis >= 0.f) {
                shoot->carbohydrate_pool_molC += net_photosynthesis;
            }
            context_ptr->setObjectData(shoot->internode_tube_objID, "carbohydrate_concentration", shoot->carbohydrate_pool_molC / shoot_volume);
            context_ptr->setObjectData(shoot->internode_tube_objID, "carbohydrate_pool_molC", shoot->carbohydrate_pool_molC);
            context_ptr->setObjectData(shoot->internode_tube_objID, "daily_net_photosynthesis", net_photosynthesis);
        }
    }
 
    if (A_prim_data_missing > 0) {
        std::cerr << "WARNING (PlantArchitecture::accumulateShootPhotosynthesis): " << A_prim_data_missing << " leaf primitives were missing net_photosynthesis primitive data. Did you run the photosynthesis model?" << std::endl;
    }
}
 
void PlantArchitecture::subtractShootMaintenanceCarbon(float dt) const {
    for (const auto &[plantID, plant_instance]: plant_instances) {
        auto shoot_tree = &plant_instance.shoot_tree;
 
        const CarbohydrateParameters &carbohydrate_params = plant_instances.at(plantID).carb_parameters;
 
        float rho_cw = carbohydrate_params.stem_density * carbohydrate_params.stem_structural_carbon_percentage / C_molecular_wt; // Density of carbon in almond wood (mol C m^-3)
 
        for (auto &shoot: *shoot_tree) {
            if (context_ptr->doesObjectExist(shoot->internode_tube_objID)) {
                if (shoot->isdormant && shoot->old_shoot_volume >= 0.f) {
                    shoot->carbohydrate_pool_molC -= shoot->old_shoot_volume * rho_cw * carbohydrate_params.stem_maintenance_respiration_rate  * carbohydrate_params.dormant_respiration_fraction * dt; // remove shoot maintenance respiration (0.5 correction for living wood fraction, 0.2 correction for
                    shoot->carbohydrate_pool_molC -= shoot->old_shoot_volume * rho_cw * carbohydrate_params.root_maintenance_respiration_rate / carbohydrate_params.shoot_root_ratio  * carbohydrate_params.dormant_respiration_fraction * dt; // remove root maintenance respiration portion
                    float net_respiration = (shoot->old_shoot_volume * rho_cw * carbohydrate_params.stem_maintenance_respiration_rate * carbohydrate_params.dormant_respiration_fraction * dt) + (shoot->old_shoot_volume * rho_cw * carbohydrate_params.root_maintenance_respiration_rate / carbohydrate_params.shoot_root_ratio * carbohydrate_params.dormant_respiration_fraction * dt);
                    context_ptr->setObjectData(shoot->internode_tube_objID, "daily_respiration", net_respiration);
                } else if (shoot->old_shoot_volume >= 0.f) {
                    shoot->carbohydrate_pool_molC -= shoot->old_shoot_volume * rho_cw * carbohydrate_params.stem_maintenance_respiration_rate * dt; // remove shoot maintenance respiration
                    shoot->carbohydrate_pool_molC -= shoot->old_shoot_volume * rho_cw * carbohydrate_params.root_maintenance_respiration_rate / carbohydrate_params.shoot_root_ratio * dt; // remove root maintenance respiration portion
                    float net_respiration = (shoot->old_shoot_volume * rho_cw * carbohydrate_params.stem_maintenance_respiration_rate * dt) + (shoot->old_shoot_volume * rho_cw * carbohydrate_params.root_maintenance_respiration_rate / carbohydrate_params.shoot_root_ratio * dt);
                    context_ptr->setObjectData(shoot->internode_tube_objID, "daily_respiration", net_respiration);
                }
            }
        }
    }
}
 
void PlantArchitecture::subtractShootGrowthCarbon() {
    for (auto &[plantID, plant_instance]: plant_instances) {
        const auto shoot_tree = &plant_instance.shoot_tree;
 
        const CarbohydrateParameters &carbohydrate_params = plant_instances.at(plantID).carb_parameters;
 
        float rho_cw = carbohydrate_params.stem_density * carbohydrate_params.stem_structural_carbon_percentage / C_molecular_wt; // Mature density of carbon in almond wood (mol C m^-3)
 
        for (const auto &shoot: *shoot_tree) {
            float shoot_volume = plant_instances.at(plantID).shoot_tree.at(shoot->ID)->calculateShootInternodeVolume();
            uint parentID = shoot->parent_shoot_ID;
            float shoot_growth;
 
            float phytomer_shoot_volume = 0;
 
            for (int p = 0; p < shoot->phytomers.size(); p++) {
                float phytomer_volume = plant_instances.at(plantID).shoot_tree.at(shoot->ID)->phytomers.at(p)->calculatePhytomerVolume(p);
                float phytomer_age = plant_instances.at(plantID).shoot_tree.at(shoot->ID)->phytomers.at(p)->age;
                float density_dynamic = phytomer_age / carbohydrate_params.maturity_age;
                // Clamp dynamic carbon density between minimum value and density at full maturity
                float rho_cw_dynamic = rho_cw * std::clamp(density_dynamic, carbohydrate_params.initial_density_ratio, 1.f); // Carbon density of the stem for the given phytomer (mol C / m^3 wood)
                float phytomer_growth_carbon_demand = 0.f;
                if (plant_instances.at(plantID).shoot_tree.at(shoot->ID)->old_shoot_volume > 0.f) {
                    phytomer_growth_carbon_demand = rho_cw_dynamic * (phytomer_volume - plant_instances.at(plantID).shoot_tree.at(shoot->ID)->phytomers.at(p)->old_phytomer_volume); // Structural carbon - mol C / m^3 wood
                    shoot->carbohydrate_pool_molC -= phytomer_growth_carbon_demand ; // Subtract construction carbon from the shoot's carbon pool
                    shoot->carbohydrate_pool_molC -= phytomer_growth_carbon_demand  / carbohydrate_params.shoot_root_ratio; // Subtract construction carbon for the roots from the carbon pool
                    shoot_growth += (phytomer_growth_carbon_demand ) + (phytomer_growth_carbon_demand / carbohydrate_params.shoot_root_ratio);
                }
                phytomer_shoot_volume += phytomer_volume;
 
                plant_instances.at(plantID).shoot_tree.at(shoot->ID)->phytomers.at(p)->old_phytomer_volume = phytomer_volume; // Update the old volume of the phytomer
            }
 
            // Update shoot's carbohydrate_concentration value (mol C / m^-3)
            if (context_ptr->doesObjectExist(shoot->internode_tube_objID)) {
                context_ptr->setObjectData(shoot->internode_tube_objID, "carbohydrate_concentration", shoot->carbohydrate_pool_molC / shoot_volume);
                context_ptr->setObjectData(shoot->internode_tube_objID, "carbohydrate_pool_molC", shoot->carbohydrate_pool_molC);
                context_ptr->setObjectData(shoot->internode_tube_objID, "daily_growth", shoot_growth);
            }
        }
    }
}
 
 
float Phytomer::calculateFruitConstructionCosts(const FloralBud &fbud) const {
    const CarbohydrateParameters &carbohydrate_params = plantarchitecture_ptr->plant_instances.at(this->plantID).carb_parameters;
 
    float fruit_construction_cost_base = carbohydrate_params.fruit_density * carbohydrate_params.fruit_carbon_percentage / C_molecular_wt; // mol C/m^3
 
    float fruit_carbon_cost = 0.f; // mol C
 
    // fruit (cost per fruit basis)
    for (uint fruit_objID: fbud.inflorescence_objIDs) {
        float mature_volume = context_ptr->getPolymeshObjectVolume(fruit_objID) / fbud.current_fruit_scale_factor; // mature fruit volume
        fruit_carbon_cost += fruit_construction_cost_base * (mature_volume) * (fbud.current_fruit_scale_factor - fbud.previous_fruit_scale_factor);
    }
 
    return fruit_carbon_cost;
}
 
void PlantArchitecture::checkCarbonPool_abortOrgans(float dt) {
    for (auto &[plantID, plant_instance]: plant_instances) {
        const auto shoot_tree = &plant_instance.shoot_tree;
        const CarbohydrateParameters &carbohydrate_params = plant_instances.at(plantID).carb_parameters;
 
        float fruit_construction_cost_base = carbohydrate_params.fruit_density * carbohydrate_params.fruit_carbon_percentage / C_molecular_wt; // mol C/m^3
 
        for (const auto &shoot: *shoot_tree) {
            uint shootID = shoot->ID;
 
            float shoot_volume = plant_instances.at(plantID).shoot_tree.at(shootID)->calculateShootInternodeVolume();
            // Establish a working carbon pool to see if you could stay above the carbon threshold by aborting fruits.
            float working_carb_pool = shoot->carbohydrate_pool_molC;
            if (dt > carbohydrate_params.bud_death_threshold_days) {
                shoot->days_with_negative_carbon_balance += dt / 2; // Make sure you have at least two timesteps before starting to abort buds
            } else {
                shoot->days_with_negative_carbon_balance += dt;
            }
 
            // No need to mess with anything if you already have a carbon surplus
            if (shoot->carbohydrate_pool_molC > carbohydrate_params.carbohydrate_abortion_threshold * carbohydrate_params.stem_density * shoot_volume / C_molecular_wt) {
                shoot->days_with_negative_carbon_balance = 0;
                goto shoot_balanced;
            }
            // Prevent any shoots from reaching negative carbon values: instant death
            if (shoot->carbohydrate_pool_molC <= 0.f) {
                pruneBranch(plantID, shootID, 0);
                goto shoot_balanced;
            }
            if (shoot->sumShootLeafArea() == 0.f && shoot->sumChildVolume() == 0.f && shoot->isdormant == false) {
                pruneBranch(plantID, shootID, 0);
                goto shoot_balanced;
            }
            // Prune branches that can't stay above a sustainable threshold
            if (shoot->carbohydrate_pool_molC < carbohydrate_params.carbohydrate_pruning_threshold * carbohydrate_params.stem_density * shoot_volume / C_molecular_wt &&
                shoot->days_with_negative_carbon_balance > carbohydrate_params.branch_death_threshold_days) {
                pruneBranch(plantID, shootID, 0);
                goto shoot_balanced;
            }
            // Keep track of how many days the shoot has been below the threshold
            if (shoot->days_with_negative_carbon_balance <= carbohydrate_params.bud_death_threshold_days) {
                continue;
            }
 
            // Loop over fruiting buds and abort them one at a time until you would be able to stay above the threshold
            const auto phytomers = &shoot->phytomers;
 
            bool living_buds = true;
            while (living_buds) {
                living_buds = false;
 
                for (const auto &phytomer: *phytomers) {
                    bool next_phytomer = false;
 
                    for (auto &petiole: phytomer->floral_buds) {
                        if (next_phytomer) {
                            break;
                        }
 
                        bool next_petiole = false;
                        for (auto &fbud: petiole) {
                            if (next_petiole) {
                                break;
                            }
                            if (fbud.state == BUD_DORMANT || fbud.state == BUD_DEAD) {
                                continue;
                            }
 
                            for (uint fruit_objID: fbud.inflorescence_objIDs) {
                                float mature_volume = context_ptr->getPolymeshObjectVolume(fruit_objID) / fbud.current_fruit_scale_factor; // mature fruit volume
                                working_carb_pool += fruit_construction_cost_base * (mature_volume) * (fbud.current_fruit_scale_factor - fbud.previous_fruit_scale_factor);
                            }
                            phytomer->setFloralBudState(BUD_DEAD, fbud);
                            // Kill a floral bud to eliminate it as a future sink
 
                            if (working_carb_pool > carbohydrate_params.carbohydrate_abortion_threshold * carbohydrate_params.stem_density * shoot_volume / C_molecular_wt) {
                                goto shoot_balanced;
                            } // If the amount of carbon you've eliminated by aborting flower buds would have given you a positive carbon balance, move on to the next shoot
 
                            living_buds = true;
                            // There was at least one living bud, so stay in the loop until there aren't any more
                            next_petiole = true;
                            // As soon as you've eliminated one bud from a given petiole, move to the next one
                            next_phytomer = true;
                            // As soon as you've eliminated one bud from a given phytomer, move to the next one
                        }
                    }
                }
            }
        }
 
    shoot_balanced:; // empty statement after the label to avoid a compiler warning
    }
}
 
 
void PlantArchitecture::checkCarbonPool_adjustPhyllochron(float dt) {
    for (auto &[plantID, plant_instance]: plant_instances) {
        const auto shoot_tree = &plant_instance.shoot_tree;
        const CarbohydrateParameters &carbohydrate_params = plant_instances.at(plantID).carb_parameters;
 
        for (const auto &shoot: *shoot_tree) {
            uint shootID = shoot->ID;
 
            float shoot_volume = plant_instances.at(plantID).shoot_tree.at(shootID)->calculateShootInternodeVolume();
 
            float phyllochron_carbon_ratio = shoot->carbohydrate_pool_molC / (carbohydrate_params.carbohydrate_phyllochron_threshold * carbohydrate_params.stem_density * shoot_volume / C_molecular_wt);
 
            shoot->phyllochron_instantaneous = std::fmax(shoot->shoot_parameters.phyllochron_min.val(), shoot->phyllochron_min / (phyllochron_carbon_ratio * dt));
        }
    }
}
 
void PlantArchitecture::checkCarbonPool_transferCarbon(float dt) {
    for (auto &[plantID, plant_instance]: plant_instances) {
        const auto shoot_tree = &plant_instance.shoot_tree;
        const auto shoot_tree_ptr = &plant_instances.at(plantID).shoot_tree;
        const CarbohydrateParameters &carbohydrate_params = plant_instances.at(plantID).carb_parameters;
 
        // Transfer carbon from parent shoots to distal child shoots (gradient-driven flux)
        for (const auto &shoot_inner: *shoot_tree) {
            if (!shoot_inner) {
                continue; // Skip null shoots
            }
            uint shootID_inner = shoot_inner->ID;
            float shoot_volume_inner = plant_instances.at(plantID).shoot_tree.at(shootID_inner)->calculateShootInternodeVolume();
            float shoot_carb_pool_molC_inner = shoot_inner->carbohydrate_pool_molC;
            float shoot_carb_conc_inner = shoot_carb_pool_molC_inner / shoot_volume_inner;
            if (shoot_inner->carbohydrate_pool_molC > carbohydrate_params.carbohydrate_transfer_threshold_up * shoot_volume_inner * carbohydrate_params.stem_density / C_molecular_wt) {
                float totalChildVolume = shoot_inner->sumChildVolume(0);
                if (totalChildVolume <= 0.0f) {
                    continue;
                }
                // Determine carbon pool (mol C) available for transfer from parent shoot.
                float available_fraction_of_carb =
                        (shoot_inner->carbohydrate_pool_molC - carbohydrate_params.carbohydrate_transfer_threshold_up * shoot_volume_inner * carbohydrate_params.stem_density / C_molecular_wt) / shoot_inner->carbohydrate_pool_molC;
 
                for (int p = 0; p < shoot_inner->phytomers.size(); p++) {
                    // call recursively for child shoots
                    if (shoot_inner->childIDs.find(p) != shoot_inner->childIDs.end()) {
                        for (int child_shoot_ID: shoot_inner->childIDs.at(p)) {
                            float child_volume = plant_instances.at(plantID).shoot_tree.at(child_shoot_ID)->sumChildVolume(0) + plant_instances.at(plantID).shoot_tree.at(child_shoot_ID)->calculateShootInternodeVolume();
                            float child_ratio = child_volume / totalChildVolume;
 
                            float child_shoot_volume = plant_instances.at(plantID).shoot_tree.at(child_shoot_ID)->calculateShootInternodeVolume();
 
                            if (child_shoot_volume > 0.f) {
                                float child_shoot_carb_pool_molC = shoot_tree_ptr->at(child_shoot_ID)->carbohydrate_pool_molC;
                                float child_shoot_carb_conc = child_shoot_carb_pool_molC / child_shoot_volume;
                                // Only tranfer carbon if the parent shoot has greater carbon concentration than the child shoot.
                                if (shoot_carb_conc_inner > child_shoot_carb_conc) {
                                    float transfer_volume = shoot_volume_inner;
                                    if (child_shoot_volume < shoot_volume_inner) {
                                        transfer_volume = child_shoot_volume;
                                    }
                                    float delta_C = shoot_carb_conc_inner - child_shoot_carb_conc;
                                    float transfer_mol_C_demand = delta_C * child_ratio * transfer_volume * carbohydrate_params.carbon_conductance_up * dt;
 
                                    float transfer_mol_C = std::clamp(transfer_mol_C_demand, 0.f, shoot_inner->carbohydrate_pool_molC * available_fraction_of_carb * child_ratio);
 
                                    // Mass-balance transfer of carbon between shoots
                                    plant_instances.at(plantID).shoot_tree.at(child_shoot_ID)->carbohydrate_pool_molC += transfer_mol_C;
                                    shoot_inner->carbohydrate_pool_molC -= transfer_mol_C;
                                }
                            }
                        }
                    }
                }
            }
        }
 
        // Transfer carbon from distal child shoots to parent shoots (gradient-driven flux)
        for (const auto &shoot: *shoot_tree) {
            if (!shoot) {
                continue; // Skip null shoots
            }
            uint shootID = shoot->ID;
            uint parentID = shoot->parent_shoot_ID;
 
            float shoot_volume = plant_instances.at(plantID).shoot_tree.at(shootID)->calculateShootInternodeVolume();
 
            if (shoot_volume <= 0.0f) {
                continue;
            }
 
            float shoot_carb_pool_molC = shoot->carbohydrate_pool_molC;
            float shoot_carb_conc = shoot_carb_pool_molC / shoot_volume;
 
            // Only transfer carbon if child shoot has greater carbon concentration than parent
            if (shoot_carb_pool_molC > carbohydrate_params.carbohydrate_transfer_threshold_down * shoot_volume * carbohydrate_params.stem_density / C_molecular_wt) {
                float available_fraction_of_carb = (shoot->carbohydrate_pool_molC - carbohydrate_params.carbohydrate_transfer_threshold_down * shoot_volume * carbohydrate_params.stem_density / C_molecular_wt) / shoot->carbohydrate_pool_molC;
                if (parentID < 10000000) {
                    float parent_shoot_volume = plant_instances.at(plantID).shoot_tree.at(parentID)->calculateShootInternodeVolume();
 
                    float parent_shoot_carb_pool_molC = plant_instances.at(plantID).shoot_tree.at(parentID)->carbohydrate_pool_molC;
                    float parent_shoot_carb_conc = parent_shoot_carb_pool_molC / parent_shoot_volume;
 
                    float delta_C = shoot_carb_conc - parent_shoot_carb_conc;
                    float transfer_mol_C_demand = delta_C * shoot_volume * carbohydrate_params.carbon_conductance_down * dt;
                    // Ensure only available carbon is transferred
                    float transfer_mol_C = std::clamp(transfer_mol_C_demand, 0.f, shoot->carbohydrate_pool_molC * available_fraction_of_carb);
                    // Mass balance transfer of C (mol) from child to parent shoot
                    plant_instances.at(plantID).shoot_tree.at(parentID)->carbohydrate_pool_molC += transfer_mol_C;
                    shoot->carbohydrate_pool_molC -= transfer_mol_C;
                }
            }
        }
    }
}
 
 
void PlantArchitecture::incrementPhytomerInternodeGirth_carb(uint plantID, uint shootID, uint node_number, float dt, bool update_context_geometry) {
    // Slow Radial growth of shoots if their carbon concentration falls below a sustainable threshold
    const CarbohydrateParameters &carbohydrate_params = plant_instances.at(plantID).carb_parameters;
 
    if (plant_instances.find(plantID) == plant_instances.end()) {
        helios_runtime_error("ERROR (PlantArchitecture::incrementPhytomerInternodeGirth): Plant with ID of " + std::to_string(plantID) + " does not exist.");
    }
 
    auto shoot = plant_instances.at(plantID).shoot_tree.at(shootID);
 
    if (shootID >= plant_instances.at(plantID).shoot_tree.size()) {
        helios_runtime_error("ERROR (PlantArchitecture::incrementPhytomerInternodeGirth): Shoot with ID of " + std::to_string(shootID) + " does not exist.");
    } else if (node_number >= shoot->current_node_number) {
        helios_runtime_error("ERROR (PlantArchitecture::incrementPhytomerInternodeGirth): Cannot scale internode " + std::to_string(node_number) + " because there are only " + std::to_string(shoot->current_node_number) + " nodes in this shoot.");
    }
 
    auto phytomer = shoot->phytomers.at(node_number);
 
    // float leaf_area = phytomer->calculateDownstreamLeafArea();
    float leaf_area = phytomer->downstream_leaf_area;
    if (context_ptr->doesObjectExist(shoot->internode_tube_objID)) {
        context_ptr->setObjectData(shoot->internode_tube_objID, "leaf_area", leaf_area);
    }
 
    float phytomer_age = phytomer->age;
    float girth_area_factor = shoot->shoot_parameters.girth_area_factor.val();
    if (phytomer_age > 365) {
        girth_area_factor = shoot->shoot_parameters.girth_area_factor.val() * 365 / phytomer_age;
    }
 
 
    float internode_area = girth_area_factor * leaf_area * 1e-4;
 
    float phytomer_radius = sqrtf(internode_area / PI_F);
 
    float rho_cw = carbohydrate_params.stem_density * carbohydrate_params.stem_structural_carbon_percentage / C_molecular_wt; // Density of carbon in almond wood (mol C m^-3)
    float max_shoot_volume = internode_area * shoot->calculateShootLength();
    float current_shoot_volume = shoot->calculateShootInternodeVolume();
    float max_carbon_demand = (max_shoot_volume - current_shoot_volume) * rho_cw; //(mol C)
 
    float threshold_carbon_pool = carbohydrate_params.carbohydrate_growth_threshold * current_shoot_volume * carbohydrate_params.stem_density / C_molecular_wt; //(mol C)
 
    auto &segment = shoot->shoot_internode_radii.at(node_number);
    for (float &radius: segment) {
        if (phytomer_radius > radius) { // radius should only increase
            float carbon_availability_ratio = std::clamp((shoot->carbohydrate_pool_molC - threshold_carbon_pool) / max_carbon_demand, .05f, 1.f);
            radius = radius + carbon_availability_ratio * 0.5 * (phytomer_radius - radius);
        }
 
 
        if (update_context_geometry && context_ptr->doesObjectExist(shoot->internode_tube_objID)) {
            context_ptr->setTubeRadii(shoot->internode_tube_objID, flatten(shoot->shoot_internode_radii));
        }
    }
}
 
 
bool Shoot::sampleVegetativeBudBreak_carb(uint node_index) const {
    const CarbohydrateParameters &carbohydrate_params = plantarchitecture_ptr->plant_instances.at(plantID).carb_parameters;
    float shoot_volume = calculateShootInternodeVolume();
 
    if (node_index >= phytomers.size()) {
        helios_runtime_error("ERROR (PlantArchitecture::sampleVegetativeBudBreak): Invalid node index. Node index must be less than the number of phytomers on the shoot.");
    }
 
    float probability_min = plantarchitecture_ptr->plant_instances.at(this->plantID).shoot_types_snapshot.at(this->shoot_type_label).vegetative_bud_break_probability_min.val();
    float probability_max = 1.f;
    float probability_decay = plantarchitecture_ptr->plant_instances.at(this->plantID).shoot_types_snapshot.at(this->shoot_type_label).vegetative_bud_break_probability_decay_rate.val();
 
    if (carbohydrate_pool_molC < carbohydrate_params.carbohydrate_vegetative_break_threshold * shoot_volume * carbohydrate_params.stem_density / C_molecular_wt) {
        probability_max = carbohydrate_pool_molC / (carbohydrate_params.carbohydrate_vegetative_break_threshold * shoot_volume * carbohydrate_params.stem_density / C_molecular_wt);
    }
 
    float bud_break_probability;
    if (!shoot_parameters.growth_requires_dormancy && probability_decay < 0.f) {
        bud_break_probability = probability_min;
    } else if (probability_decay > 0.f) { // probability maximum at apex
        bud_break_probability = std::fmax(probability_min, probability_max - probability_decay * float(this->current_node_number - node_index - 1));
    } else if (probability_decay < 0.f) { // probability maximum at base
        bud_break_probability = std::fmax(probability_min, probability_max - fabs(probability_decay) * float(node_index));
    } else {
        if (probability_decay == 0.f) {
            bud_break_probability = probability_min;
        } else {
            bud_break_probability = probability_max;
        }
    }
 
    bool bud_break = true;
    if (context_ptr->randu() > bud_break_probability) {
        bud_break = false;
    }
 
    return bud_break;
}