Impact of severe dry season on net ecosystem exchange in the Neotropical rainforest of French Guiana

Abstract

The lack of information on the ways seasonal drought modifies the CO2 exchange between Neotropical rainforest ecosystems and the atmosphere and the resulting carbon balance hinders our ability to precisely predict how these ecosystems will respond as global environmental changes force them to face increasingly contrasting conditions in the future. To address this issue, seasonal variations in daily net ecosystem productivity (NEPd) and two main components of this productivity, daily total ecosystem respiration (REd) and daily gross ecosystem productivity (GEPd), were estimated over 2 years at a flux tower site in French Guiana, South America (511605400N, 5215404400W). We compared seasonal variations between wet and dry periods and between dry periods of contrasting levels of intensity (i.e. mild vs. severe) during equivalent 93-day periods. During the wet periods, the ecosystem was almost in balance with the atmosphere (storage of 9.0 gCm_2). Seasonal dry periods, regardless of their severity, are associated with higher incident radiation and lower REd combined with reduced soil respiration associated with low soil water availability. During the mild dry period, as is normally the case in this region, the amount of carbon stored in the ecosystem was 32.7 gCm_2. Severe drought conditions resulted in even lower REd, whereas the photosynthetic activity was only moderately reduced and no change in canopy structure was observed. Thus, the severe dry period was characterized by greater carbon storage (64.6 gCm_2), emphasizing that environmental conditions, such as during a severe drought, modify the CO2 exchange between Neotropical rainforest ecosystems and the atmosphere and potentially the resulting carbon balance

C, N and P fertilization in an Amazonian rainforest supports stoichiometric dissimilarity as a driver of litter diversity effects on decomposition

“…The soil of the study area is characterized as acrisol developed over a Precambrian metamorphic formation called the Bonidoro-series. The tree species richness is around 140 species per hectare with a mean density of 620 individual trees per hectare (individuals of a diameter more than 0.1 m at breast height) [21].…”

“…The amount of fertilizers were chosen in order to allow for comparison among different fertilization studies in tropical rainforests [23][24][25] These amounts correspond roughly to half (C), double (N) and 50-fold (P) of the total natural annual input via leaf litter fall at our study site [21,26]. Starting in April 2009, fertilizers were applied twice a year during the drier periods of the year (from mid-August to mid-November and in March-April) in order to avoid lateral and vertical wash off during heavy rainfalls during the wet seasons.…”

Automatic high-frequency measurements of full soil greenhouse gas fluxes in a tropical forest

“…The automated soil GHG flux system was deployed in the footprint of the Guyaflux site, which holds a 55 mtall tower upon which canopy CO2, H2O and energy fluxes have been monitored since 2004 using the eddy covariance technique (Aguilos et al, 2018;Bonal et al, 2008). The site is covered with tropical pristine forest and located in the northernmost part of the Guiana shield.…”

The African contribution to the global climate-carbon cycle feedback of the 21st century

“…The El Niño/Southern Oscillation (ENSO) climate variability induces large excursions in photosynthesis and/or decomposition and fires (Page et al, 2002) leading to anomalous CO 2 release from tropical ecosystems during El Niño events, and conversely to anomalous uptake during the cooler and wetter La Niña episodes. However, the effect of drought in decreasing C uptake as simulated by all global models, was recently challenged by field measurements showing locally more C uptake by tropical forests during the dry periods (Saleska et al, 2007;Bonal et al, 2008). 514 P. Friedlingstein et al: The African contribution to the global climate-carbon cycle feedback However, so far, within the tropical forest, most of the focus has been given to the Amazon basin Betts et al, 2004;Huntingford et al, 2004).…”