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

Abstract

The total uptake of carbon dioxide by ecosystems via photosynthesis (gross primary productivity, GPP) is the largest flux in the global carbon cycle. A key ecosystem functional property determining GPP is the photosynthetic capacity at light saturation (GPPsat), and its interannual variability (IAV) is propagated to the net land–atmosphere exchange of CO2. Given the importance of understanding the IAV in CO2 fluxes for improving the predictability of the global carbon cycle, we have tested a range of alternative hypotheses to identify potential drivers of the magnitude of IAV in GPPsat in forest ecosystems. Our results show that while the IAV in GPPsat within sites is closely related to air temperature and soil water availability fluctuations, the magnitude of IAV in GPPsat is related to stand age and biodiversity (R2 = 0.55, P < 0.0001). We find that the IAV of GPPsat is greatly reduced in older and more diverse forests, and is higher in younger forests with few dominant species. Older and more diverse forests seem to dampen the effect of climate variability on the carbon cycle irrespective of forest type. Preserving old forests and their diversity would therefore be beneficial in reducing the effect of climate variability on Earth's forest ecosystems

Employing stable isotopes to determine the residence times of soil water and the temporal origin of water taken up by Fagus sylvatica and Picea abies in a temperate forest

“…Here we show that the two most common tree species in European temperate forests are partly complementary with respect to the temporal origin of water that they use throughout a water uptake season. Our finding thus provides a new mechanistic explanation for the recently detected positive relationships between tree diversity and ecosystem functioning (Grossiord et al ., ; Musavi et al ., ).…”

Global importance of large‐diameter trees

“…Large‐diameter tree richness in tropical forests suggests more resilience to projected climate warming in two ways. First, absolute large‐diameter tree richness was highest in tropical forests, suggesting that the large‐diameter tree guild may have different adaptations that will allow at least some species to persist (Musavi et al, ). Secondly, the pool of species that can reach large diameters may have been undersampled in the plots used here, implying an even higher level of richness may exist in some forests than captured in these analyses.…”

Dry‐Season Greening and Water Stress in Amazonia: The Role of Modeling Leaf Phenology

“…Global estimates of GPP are still highly uncertain (Badgley et al, ), and tropical carbon fluxes are poorly resolved in existing DGVMs (Restrepo‐Coupe et al, ). Tropical forest GPP is a major component of the global carbon cycle (Musavi et al, ), and understanding its seasonal and interannual variability is crucial to predict global climate dynamics. Here we have provided a novel mechanistic approach to represent leaf phenology and GPP seasonality that requires a single parameter and is general enough to be used in any DGVM that has a prognostic phenology and simulates leaf age.…”