Figure 4 - available via license: Creative Commons Attribution 4.0 International
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Outputs of the leaf cohort model in two contrasted K fertilisation regimes. The K content present in each individual leaf of the cohort is represented through the lifespan of a cohort (x-axis) for the different cohort created along the first 60 months of the rotation (a, c). The symptom area proportion for each leaf of the cohort is also represented (b, d). Top subplots (a, b) were simulated in +K conditions, while bottom subplots were oK simulations (c, d).
Source publication
The extent of the potassium (K) limitation of forest productivity is probably more widespread than previously thought, and K-limitation could influence the response of forests to future global changes. To understand the effects of K-limitation on forest primary production, we have developed the first ecophysiological model simulating the K cycle an...
Contexts in source publication
Context 1
... k LA and t50 LA were assumed not to vary along the stand rotation. LA max was also assumed to be constant since the leaf scans did not show 210 any explainable trends of mean leaf area during the rotation (Fig.S4). ...
Context 2
... leaf area (SLA) of individual leaves showed a decreasing relationship with tree height (Fig.S5a), while LA max was more constant as described before (Fig.S4). We thus assumed that BF max increased with tree height: ...
Context 3
... +K condition, K availability was high during the whole rotation with symptom area proportion of the canopy always below 2.5% (Fig.5b) throughout the leaf lifespan, that reached its 560 maximum (LLS, fixed value). On the other hand, in oK simulations, leaf lifespan was greatly reduced (less than half of the leaf lifespan of fertilised stands, Fig.4c) and symptom proportions reached more than 40% during a major part of the rotation (Fig.4d,5b). ...
Context 4
... +K condition, K availability was high during the whole rotation with symptom area proportion of the canopy always below 2.5% (Fig.5b) throughout the leaf lifespan, that reached its 560 maximum (LLS, fixed value). On the other hand, in oK simulations, leaf lifespan was greatly reduced (less than half of the leaf lifespan of fertilised stands, Fig.4c) and symptom proportions reached more than 40% during a major part of the rotation (Fig.4d,5b). The patterns of the leaf K content in the different cohorts during the oK rotation had two phases (Fig.4c): a first phase of the rotation where soil K bioavailability was high and a second phase with very low K concentrations in leaves. ...
Context 5
... the other hand, in oK simulations, leaf lifespan was greatly reduced (less than half of the leaf lifespan of fertilised stands, Fig.4c) and symptom proportions reached more than 40% during a major part of the rotation (Fig.4d,5b). The patterns of the leaf K content in the different cohorts during the oK rotation had two phases (Fig.4c): a first phase of the rotation where soil K bioavailability was high and a second phase with very low K concentrations in leaves. ...
Context 6
... the oK condition, symptoms appeared very early during the leaves' lifespan (Fig.4d). The proportion of symptomatic leaf area was slightly higher in the simulations of the EUCFLUX site than measurements at the Itatinga site (Fig.S6). ...
Context 7
... difference of GPP between fertilisation regimes was not constant during the rotation. During the first phase (i.e. the first year), the difference was small due to similar low leaf areas in both fertilisation conditions resulting in low K demand, fulfilled by sufficient K availability for both treatments (Fig.4a,c). The difference was also quite small during the major 2014 drought (Fig.6a) where water-limitation dominated in the +K stand. ...
Context 8
... the oK condition, contrary to +K, the model was not sensitive to the parameter controlling maximum leaf lifespan (LLS, Fig.7. Indeed, the maximum leaf lifespan was almost never reached because of earlier leaf fall due to K limitation (Fig.4c). Other parameters (t50 LA , k LA ) controlling maximum leaf growth had also a much lower impact for similar reasons. ...
Similar publications
The extent of the potassium (K) limitation of forest productivity is probably more widespread than previously thought, and K limitation could influence the response of forests to future global changes. To understand the effects of K limitation on forest primary production, we have developed the first ecophysiological model simulating the K cycle an...
Citations
... The study of the limitation of gross primary production (GPP, C source) by K deficiency was explored at the stand level in Part 1 (Cornut et al., 2023) of this series of two papers, using a coupled C-H 2 O-K mechanistic model (CASTANEA-MAESPA-K). The simulations showed a strong response of GPP to K deficiency. ...
... To this end, the C and K allocation schemes of CASTANEA-MAESPA-K were adapted to Brazilian eucalypt stands. The model was evaluated against data obtained in a K fertilisation-omission experiment (Cornut et al., 2023). To test the hypothesis of sink limitation of wood NPP, the parsimony principle was applied. ...
... CASTANEA-MAESPA-K (Cornut et al., 2023) is a coupled C-H 2 O-K mechanistic model that simulates forest growth at the stand level. The original CASTANEA model (Dufrêne et al., 2005), generally used to simulate temperate forest stands, was adapted to tropical eucalypt plantations. ...
Potassium (K) availability constrains forest productivity. Brazilian eucalypt plantations are a good example of the K limitation of wood production. Here, we built upon a previously described model (CASTANEA-MAESPA-K) and used it to understand whether the simulated decline in C source under K deficiency was sufficient to explain the K limitation of wood productivity in Brazilian eucalypt plantations. We developed allocation schemes for both C and K and included these in CASTANEA-MAESPA-K. Neither direct limitations of the C-sink activity nor direct modifications of the C allocation by K availability were included in the model. Simulation results show that the model was successful in replicating the observed patterns of wood productivity limitation by K deficiency. Simulations also show that the response of net primary productivity (NPP) is not linear with increasing K fertilisation. Simulated stem carbon use and water use efficiencies decreased with decreasing levels of K availability. Simulating a direct stoichiometric limitation of NPP or wood growth was not necessary to reproduce the observed decline of productivity under K limitation, suggesting that K stoichiometric plasticity could be different to that of N and P. Confirming previous results from the literature, the model simulated an intense recirculation of K in the trees, suggesting that retranslocation processes were essential for tree functioning. Optimal K fertilisation levels calculated by the model were similar to nutritional recommendations currently applied in Brazilian eucalypt plantations, paving the way for validation of the model at a larger scale and of this approach for developing decision-making tools to improve fertilisation practices.
