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LandscapeDNDC
1.36.0
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LandscapeDNDC
1.36.0
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The PSIM runs in sub-daily (hourly) time steps and gets assimilated carbon based on a Farquhar approach [20], calculated in the photofarquhar.cpp, which is considered along with the ideas of Ball et al. [5] regarding consideration of stomatal conductance (ld_berryball.cpp).
Processes are generally calculated specifically for species (as cohorts containing trees of equal dimensions), canopy- (2-40) and soil layers (individually set in the site properties). In addition, long-living foliage is considered in different age classes.
In the module itself, respiration is considered to originate from either biomass growth, nitrate conversion, or maintenance of different compartments (foliage, fine roots, structural reserves, living wood) and depends on temperature and nitrogen concentrations [10]. Allocation from net photosynthesis (or nitrogen uptake) into the respective compartments is realized according to its sink strength that is determined from targed allometric relations and dynamic gain and loss processes [28]. Therefore, the model assumes a certain longevity of each compartment, resulting in an empirically determined senescence.
Specifically, the main physiological processes of carbon and nitrogen in the plant are:
In addition, a change in enzymatic capacity is derived indicating a seasonality and stress-dependence of photosynthetic enzyme activity (PSIM_PhotosynthesisRates).
Besides from the photosynthesis input (see PhotoFarquhar), the module depends on variables describing:
The calculations are reduced to the seasonality, flushing and senescence modules if the model runs in the MoBiLE_IsOneLeaf mode where plant growth is not of interest.
Available options (default options are marked with bold letters):
The hydraulic approach calculates canopy water potential based on soil water potential, which then affects stomal conductance following the 'Stomata on Xylem' (SOX) model (see: Farquhar model): First, xylem water potential is derived from the soil conditions, weighting soil layer importance by fine root abundance and considering a threshold soil water potential at which plant tissues are decoupled from the soil:
\[ psi\_{sr} = Sum[(min(CSR\_{REF}; psi_{sl} \cdot fFrt_{sl})] \]
with
Canopy water potential is then calculated from the gradient between the water potential in the xylem and from evaporative demand, also including the gravitational force.
\[ psi\_{can} = (psi\_{sr} + psidecline\_{cum}) - (\frac {transp}{CWP\_{REF} \cdot kxyl} ) - dpsi \]
with
The water deficit is build from the water that is transpired but was not available from the rooting zone. It is supposed to reflect the water resources within a tree, i.e. the stem water content. Surplus on water supply will refill this storage while additional deficits will empty it further.
The total plant, or xylem, conductance is calculated based on empirical relations with species-specific parameters (PSI_REF, PSI_EXP).
\[ kxyl = 1.0 - (1.0 - exp(-((\frac {psi\_{can}} {PSI\_{REF}})^{PSI\_{EXP}} ))) \]
Leaf flushing is calculated using the growing degree days approach, which is using the temperature sum since this years 1st January, considering chilling requirements and drought stress limitations.
Therefore, temperature sum (cumulative growing degree days, gdd),is first calculated from daily temperature sum ([45]):
\[ gdd\_cum = temp \cdot \frac{dayl}{12.0} \]
with
When cumulative gdd reaches a threshhold value (gdd_thresh) that depends on the degree chilling requirements are met, flushing is initiated. This value is calculated as:
\[ gdd\_thresh = 100.0 + GDDSTART \cdot exp( -0.0075 \cdot chilldays) \]
with
Chilling days (chilldays) are calculated from average temperature and amplitude [50] :
\[ chilldays = 2.0 \cdot arcos( 1.0 - ( max( 0.0, - \frac {temp\_avg - 0.5 \cdot temp\_ampl} {0.5 \cdot temp\_ampl} )) \cdot \frac {diy}{2.0 \cdot PI} \]
with
After temperature requirements are met, flushing goes on provided water supply is above a species-specific treshold value (H2OREF_FLUSHING) and there is no water deficit in the stem.
Dry matter senescence loss is calculated assuming fixed tissue longevity separately for foliage, fine roots, and living (sap-)wood. Fine root and sapwood senescence is decreased by a species-specific fraction each day. Senescence of buds is directly related to foliage growth, which is driven by a similar function than foliage senescence (see Carbon allocation and growth).
Foliage senescence (sFol) is empirically determined (for evergreen species in every age class, na) based on a mortality factor ranging between 1 and 0:
\[ sFol = mFol\_{na} \cdot (1.0 - \frac {1.0 - dvsmort} {1.0 - dvsmort\_{old}} ) \]
\[ dvsmort = exp( -1.0 \cdot \frac { foliage\_{age} - DLEAFSHED)^{ 2 } } { (0.5 \cdot NDMORTA)^ { 2 } \cdot log(2.0) } ) \]
with:
The nitrogen loss is defined by the nitrogen concentration in the tissue considering a species-specific retranslocation rate that is the same for all tissues. The maximum retranslocation rate is reduced if the overall nitrogen demand is smaller than the maximum amount of nitrogen that could be retranslocated.
Under some circumstances, stress induced senescence (i.e. xylem and foliage loss due to extensive drought stress) is also considered. This part is under development.
Carbon provided by photosynthesis (minus growth respiration) is distributed into any compartment that didn't comply with parameterized allometric relations which define the optimum biomass. Allocation strength is linearly related to the difference between actual and optimum biomass [28] .
\[ dc_{C} = cPool \cdot afc_{C} - res_{C}Old \]
\[ afc_{C} = \frac {dem_{C} }{cPool } \]
\[ dem_{C} = \frac { max(0.0, m_{C}Opt - m_{C}) \cdot CCDM }{1.0 - FYIELD} + res_{C}Old \]
with
The foliage compartment is primarily increased by the depletion of reserves (bud compartment), and therefore has no 'demand' to its own. The transfer and thus the increase of foliage biomass is triggering the demand of buds, sapwood, and fine roots via allometric relations:
\[ m_{Frt}Opt = QRF \cdot mFol; \]
\[ m_{Sap}Opt = qsfm \cdot mFol; \]
\[ m_{Bud}Opt = MFOLOPT \cdot farea \cdot fheight \cdot \frac{qsfm}{qsfm_act}; \]
\[ m_{Fac}Opt = sum( m_{C} ) \cdot (FACMAX - fac); \]
with
qsfm is derived from a desired relation between sapwood area and foliage area (Huber value, QSFA) and the dimension of the tree (assuming species-specific taper functions and fixed fractions for branchiness and coarse roots.
Sink-limitations apply for the compartments 'buds', which is only supported if sapwood area is sufficient to supply current leaves, and 'sapwood', which is not growing under drought stress (positive plant water deficit).
If the supply is larger than all demands, the surplus is distributed between buds, foliage, and fine roots in case of herbaceous plants, wood and buds in case of determined growth (FREEGROWTH = false) or into foliage growth if species are growing leaves continously (FREEGROWTH = true).
Free available carbon can be depleted only by respiration demands higher than supply rates.
Carbon exudation is assumed to be species specific fraction of total fine root growth (see: PSIM_SoilCarbonRelease).
The nitrogen provided from uptake and retranslocation is distributed according to biomass growth and optimum tissue concentrations [28].
Respiration consists of growth (rGro) and maintenance respiration, with the latter split up into respiration that is related to nutrient uptake and transport (rTra), and into remaining (residual) respiration (rRes). I Growth respiration is a fraction of growth is assumed to apply equally for every tissue
\[ rGro = sum( dc_{C} \cdot (1.0 - FYIELD) ) \]
with
II Transport respiration summarizes carbon costs due to uptake of nitrogen and other nutrients (rUpt), phloem transport of carbon into the roots (rPhl), and the reduction of oxygenized nitrogen compounds (rNit). Uptake of nitrogen compounds is explicitly modeleled, while additional costs from uptake and incorporation of other nutrients are estimated from biomass growth, assuming a that all requirements are met.
\[ rTra = rUpt + rPhl + rNit \]
\[ rUpt = PAMM \cdot (uptNH4 + uptNH3) + PNIT \cdot (uptNO3 + uptNOx) + PMIN \cdot growth \cdot \frac{FMIN}{CCDM} \]
\[ rPhl = PPHLOE \cdot (dcFrt + dcSap + exsuLoss) \]
\[ rNit = PREDFRT \cdot uptNO3 \cdot FRFRT + PREDSAP \cdot uptNO3 \cdot (1.0 - FRFRT) + PREDSAP \cdot uptNOx \]
with
III Residual (maintenance) respiration according to temperature and nitrogen content [10]
\[ rRes = sum( km \cdot fsub \cdot n_{C} ) \]
\[ km = KM20 \cdot (temp_{C} - TRMIN) ^ { 2 } \cdot (TRMAX - temp_{C}) \cdot \frac{1.0}{ ( TROPT - TRMIN) ^ { 2 } \cdot ( TRMAX - TROPT) } \]
\[ fsub = \frac { \frac {ffac}{FFACMAX} }{ KMMM + \frac {ffac}{FFACMAX} } \]
with
Uptake of ammonia and nitrate from the soil and canopy is calculated according to supply, soil water availability and fine root density. Total nitrogen uptake is limited to the current whole plant demand. Nitrogen uptake/emission from the canopy depends on NOx air concentration.
\[ v25_{E} = V25_{E} \cdot fdorm \cdot fnit \cdot fwat \]
with
The reduction factor for phenology is differently calculated for deciduous species, where enzyme activity is assumed to develop in parallel to flushing and senescence, and for evergreen species, where the activity is determined from temperature development according to Maekelae et al [57] :
\[ fdorm = C1 \cdot (tFol24 + \frac{24.0}{TAU} \cdot ( temp - tFol24) - PSNTFROST) \]
with
The reduction factor for nitrogen supply is defined as the degree to which the optimum (equal to maximum) foliage nitrogen concentration has been established:
\[ fnit = \frac {ncFol - NCFOL\_{MIN} }{NCFOL\_{OPT} - NCFOL\_{MIN} } \]
with
The reduction factor for water supply is based on the same function as has been used for determining the loss of hydraulic conductance according to [67]. The recovery of the water damaged enzyme activity is not very well determined. In the literature, periods between 3 (33% recovery rate) and >20 (about 5% recovery rate are indicated [53]. The value is currently set to 5% for all species.
\[ fwat = \frac {1.0 + exp(A\_{REF} \cdot A\_{EXP}) } {1.0 + exp((A\_{REF} - psi\_{mean}) \cdot A\_{EXP}) } \]
with
1.8.13