Climate seasonality limits leaf carbon assimilation and wood productivity in tropical forests

Abstract

International audienceThe seasonal climate drivers of the carbon cycle in tropical forests remain poorly known, although these forests account for more carbon assimilation and storage than any other terrestrial ecosystem. Based on a unique combination of seasonal pan-tropical data sets from 89 experimental sites (68 include aboveground wood productivity measurements and 35 litter productivity measurements), their associated canopy photosynthetic capacity (enhanced vegetation index, EVI) and climate, we ask how carbon assimilation and aboveground allocation are related to climate seasonality in tropical forests and how they interact in the seasonal carbon cycle. We found that canopy photosynthetic capacity seasonality responds positively to precipitation when rainfall is < 2000 mm yr(-1) (water-limited forests) and to radiation otherwise (light-limited forests). On the other hand, independent of climate limitations, wood productivity and litterfall are driven by seasonal variation in precipitation and evapotranspiration, respectively. Consequently, light-limited forests present an asynchronism between canopy photosynthetic capacity and wood productivity. First-order control by precipitation likely indicates a decrease in tropical forest productivity in a drier climate in water-limited forest, and in current light-limited forest with future rainfall < 2000 mm yr(-1)

Chlorophyll Fluorescence Data Reveals Climate-Related Photosynthesis Seasonality in Amazonian Forests

“…The positive relationship between ChlF and radiation observed for 76% of the Amazon forest suggests that photosynthesis responds to an increase in radiation and is coherent with independent results obtained with Enhanced Vegetation Index (EVI), which is a proxy for photosynthetic capacity [9][10][11][12][13][14][15][16]50] and Leaf Area Index (LAI) [10,13]. Both EVI and LAI exhibit an increase with sunlight during the dry season in central and eastern Amazon rainforests [7,[9][10][11][12][13][14][15][16][19][20][21].…”

Litter production in a natural stand of Brazil nut trees (Bertholletia excelsa Bonpl.)

“…The Shapiro-Wilk, PCO, t-test, and the correlations were conducted using the Past statistical program, version 3.14 (Veloso et al, 1991), and the CRA was done using the program Canoco, version 4.5 (Ter Braak and Smilauer, 2002). The choice of these statistical tests is supported by the analyses done in Valentin (2012), Vasconcellos et al (2013) and Wagner et al (2016).…”

“…Meteorological factors are frequently included in research on litterfall, principally air temperature and precipitation (Bianchin et al, 2016;Chave et al, 2010;Ferreira et al, 2015;Santos Neto et al, 2015;Zhang et al, 2014) and also evapotranspiration (Wagner et al, 2016). Borchert et al (2015) related that insolation is also a relevant climatic factor for litter production.…”

“…Borchert et al (2015) related that insolation is also a relevant climatic factor for litter production. The degree of influence of these environmental factors can vary depending on the region studied (Godinho et al, 2015;Wagner et al, 2016).…”

Reviews and syntheses: Field data to benchmark the carbon cycle models for tropical forests

“…In many tropical forests, leaf litterfall typically peaks at the time of the yearly maximum soil dry-down (Wagner et al, 2016); this timing can be distinct from that of actual leaf production. Such a timing disjunct will complicate attempts to evaluate the seasonality of tropical-forest NPP and C allocation when leaf litterfall is used as the surrogate for production (e.g., Doughty et al, 2014).…”