383 | | COEFF_MAINT_INIT regulates the autotropic respiration as a function of temperature. Increasing the parameter will result in more respiration and thus less allocatable biomass. Given that GPP-Ra = NPP, tuning COEFF_MAINT_INIT gives a direct control over the NPP/GPP ratio. A high NPP/GPP implies that the model needs to find N to convert a large share of the GPP into tissue. If this is not possible due to N-limitation, the allocatable carbon that cannot be put away into tissue will end up into the labile and reserve pools. Likewise aiming for a lower NPP/GPP implies that more of the GPP will be required, leaving less allocatable biomass and thus reducing the N-demand to build tissue. As a consequence lower NPP/GPP ratios are likely to results in lower reserve and labile pools but it does not guarantee acceptable labile+reserves (i.e., in cases with extreme N-limitation, even low NPP/GPP ratios may still accumulate C in the labile+reserves.[[BR]] |
| 384 | COEFF_MAINT_INIT regulates the autotropic respiration as a function of temperature. Increasing the parameter will result in more respiration and thus less allocatable biomass. Given that GPP-Ra = NPP, tuning COEFF_MAINT_INIT gives a direct control over the NPP/GPP ratio. A high NPP/GPP implies that the model needs to find N to convert a large share of the GPP into tissue. If this is not possible due to N-limitation, the allocatable carbon that cannot be put away into tissue will end up into the labile and reserve pools. Likewise aiming for a lower NPP/GPP implies that more of the GPP will be required, leaving less allocatable biomass and thus reducing the N-demand to build tissue. As a consequence lower NPP/GPP ratios are likely to results in lower reserve and labile pools but it does not guarantee acceptable labile+reserves (i.e., in cases with extreme N-limitation, even low NPP/GPP ratios may still accumulate C in the labile+reserves).[[BR]] |
417 | | In a formal optimization, the objective function should maximize the LAI while minimizing the labile+reserves. From a plant perspective K_LATOSA should be as high as possible, COEFF_MAINT_INIT should be as low as possible and VMAX_UPTAKE should be as high as possible. Nevertheless, GPP that has to be stored as excessive labile+reserves is a sign of N-limitation and/or a disequilibrium between these parameters. A plant that is well adapted to its environment should only take up the N it can used, develop a canopy that results in a GPP that can be allocated and has a high NPP/GPP ratio as that gives a clear competitive advantage. [[BR]] |
418 | | |
419 | | The combined impact of tuning all three variables may be seen in the accumulated biomass. Biomass, diameter, and tree height remain valuable data sources to evaluate the parameterization of the allocation scheme. It remains difficult to disentangle the impact of single parameters (Previously, Jina has observed some non-linear interactions between parameters). [[BR]] |
| 418 | In a formal optimization, the objective function should maximize the LAI while minimizing the labile+reserves while maintaining a leaf_m_c/root_m_c ratio between 0.5 and 2.0. From a plant perspective K_LATOSA should be as high as possible, COEFF_MAINT_INIT should be as low as possible and VMAX_UPTAKE should be as high as possible. Nevertheless, GPP that has to be stored as excessive labile+reserves is a sign of N-limitation and/or a disequilibrium between these parameters. A plant that is well adapted to its environment should only take up the N it can used, develop a canopy that results in a GPP that can be allocated and has a high NPP/GPP ratio as that gives a clear competitive advantage. [[BR]] |
| 419 | |
| 420 | The combined impact of tuning all three variables may be seen in the accumulated biomass. Biomass, diameter, and tree height remain valuable data sources to evaluate the parameterization of the allocation scheme. It remains difficult to disentangle the impact of single parameters (Previously, Jina has observed some non-linear interactions between parameters. Attempts to refine the parameterization of r7334 resulted in the following insights. Understanding the changes in the absolute values is mostly straightforward but rather subtle changes of several parameters at the same time were required to change the functioning (e.g. higher gpp for the same lai). |
| 421 | |
| 422 | Table. Responses and interactions between variables (columns) and parameters (row). The description assumes that the parameters values were INCREASED. |
| 423 | || PARAMETER|| LEAF_M_c (LAI) || ROOT_M_c || SUGAR_LOAD || PLANT_N_UPTAKE || |
| 424 | || K_LATOSA || K_LATOSA is used in the calculation of the leaf mass, tuning K_LATOSA will thus directly affect LAI. Increasing K_LATOSA will increase LAI up to the point where sugar_load becomes limiting || Root mass will follow the leaf mass as a fixed function of KF and c0_alloc || Increasing LAI requires more N to sustain the higher NPP, sugar_load kicks in when N-limitations occurs and will decrease GPP and thus also NPP || Uptake increases proportional to the root mass but the N-demand will increase proportional to the leaf mass || |
| 425 | || K_BELOWGROUND || Lai decreases because more C is now allocated to the roots so there is less C for the leaves. GPP will decrease but not as fast as LAI because there is more plant available N and leaf_m_n may increase || K_BELOWGROUND is used in the calculation of c0_alloc, tuning K_BELOWGROUND alters the ratio between leaf and root allocation. Increasing K_BELOWGROUND increases the root mass relative to the leaf mass but the absolute root mass may decrease due to the decrease in leaf mass. || N-stress will most likely decrease (the value of sugar_load will therefore increase) because the root mass and increase relative to the leaf mass. Hence, the supply of nitrogen increases whereas the demand is decreasing. || PLANT_N_UPTAKE increases because of an increase in root mass. || |
| 426 | || VMAX_UPTAKE || Increasing the N supply will allow growing larger canopies even if plant growth before parameter tuning was not N-limited. Interestingly these large canopies may generate lots of gpp resulting in N-limitation which will be reflected in a decreasing value of sugar loading. || Root mass will follow LAI. The absolute value of root mass will increase jointly with the increase in LAI. || N-stress will decrease (so sugar_load will increase). Nevertheless, the effect of increasing VMAX_UPTAKE was observed to level off. || PLANT_N_UPTAKE will increase up to the point that soil_n_min becomes the limiting factor. If this point is reached there will be consequences for litter and soil carbon decomposition and thus heterotrophic respiration. || |
| 427 | || COEFF_MAINT_RESP || More respiration leaves less carbon to be allocated to leaves and roots for a given LAI. Note that the absolute value of LAI will decrease. || More respiration leaves less carbon to be allocated to leaves and roots for a given LAI. Note that the absolute value of LAI will decrease. || For a given LAI the N-demand will decrease (as a smaller fraction of the GPP will be allocated towards biomass growth which requires N) resulting in less N-stress (thus a higher value for sugar_load) || Following the decrease in the allocatable C, root mass will decrease resulting in less nitrogen uptake || |
| 428 | |