Effects of seasonal variation of photosynthetic capacity on the carbon fluxes of a temperate deciduous forest

Abstract

[1] Seasonal variation in photosynthetic capacity is an important part of the overall seasonal variability of temperate deciduous forests. However, it has only recently been introduced in a few terrestrial biosphere models, and many models still do not include it. The biases that result from this omission are not well understood. In this study, we use the Ecosystem Demography 2 model to simulate an oak-dominated stand in the New Jersey Pine Barrens. Two alternative model configurations are presented, one with seasonal variation of photosynthetic capacity (SPC-ON) and one without seasonal variation of photosynthetic capacity (SPC-OFF). Under typical climate conditions, the two configurations simulate values of monthly gross primary productivity (GPP) as different as 0.05 kg C m À2 month À1 in the early summer and 0.04 kg C m À2 month À1 in the fall. The differences between SPC-ON and SPC-OFF are amplified when there is temporal correlation between photosynthetic capacity and climate anomalies or disturbances. Warmer spring temperatures enhance GPP in SPC-ON more than in SPC-OFF, but warmer fall temperatures enhance GPP in SPC-OFF more than in SPC-ON. Defoliation by gypsy moth, a class of disturbance that typically happens in late spring in the New Jersey Pine Barrens, has a disproportionately negative impact on GPP in SPC-ON. It is concluded that including seasonal variation of photosynthetic capacity in models will improve simulations of monthly scale ecosystem functioning as well as of longer-term responses to climate change and disturbances.

Stand age and species richness dampen interannual variation of ecosystem-level photosynthetic capacity

“…These parameters are typically assumed to be constant over time, but may vary spatially according to forest types 23 . Our findings suggest that stand age and species richness should be accounted for to dynamically adjust parameters related to photosynthetic capacity.…”

A roadmap for improving the representation of photosynthesis in Earth system models

“…When this effect was accounted for with a photoperiod correction of V c , max in CLM, the model's ability to capture seasonal patterns of atmospheric C a was improved (Bonan et al ., ; Bauerle et al ., ). Other papers have noted that incorporating a photoperiod scalar with direct effects on V c , max improves estimates of seasonal carbon fluxes in eddy flux studies, supporting a role for photoperiod in modulating V c , max (Medvigy et al ., ; Stoy et al ., ). In controlled environments, photoperiod is tightly correlated with total leaf protein content, suggesting a tradeoff between the value of protein and the cost of its maintenance and provides a possible mechanistic explanation for the impact of photoperiod on V c , max (Hannemann et al ., ).…”

Estimation of vegetation photosynthetic capacity from space‐based measurements of chlorophyll fluorescence for terrestrial biosphere models

“…To more accurately quantify global and regional terrestrial GPP, information is needed on the seasonal variability of V cmax (Wilson et al, 2001;Medvigy et al, 2013). As Bonan et al (2011) has pointed out, it is important to parameterize V cmax for simulating GPP because model structural errors can be partially compensated for by adjusting this parameter.…”

“…For example, in the widely used Community Land Model (CLM) (Oleson et al, 2010) V cmax is assigned a specific value for each broadly defined plant functional type (PFT) and then adjusted with day length. There is increasing evidence that the assumption of time-invariant photosynthetic parameters can cause significant errors if large seasonal variability in photosynthetic capacity occurs (Wilson et al, 2001;Kosugi et al, 2003;Medvigy et al, 2013). As a consequence, the broad implications of seasonal variations of V cmax on the carbon cycle are not well understood.…”