Only 16% of all experiments studied (24 from 151) had specifically looked at soil C, suggesting that eCO2 effects on below-ground C dynamics are poorly understood at the global scale. Importantly, results from a limited number of whole ecosystem studies involving total experimental areas of between 10 m2 and 3000 m2 (25) have detected gains for soil C in the most studied temperate deciduous forest biome, but for all other biomes the data are too limited to discern any reliable patterns (see Fig. 3b). Tropical forest ecosystems possess the largest biologically

active C stocks (de Deyn et al., 2008), which account for ~ 70% of the gross C uptake by the world’s forests (Pan et al., 2011). Tropical forest litter and soils are also a significant reservoir of C, accounting for ~ 34% of all litter and soil forest C globally. Selleck Selisistat As highlighted by Hickler et al. (2008), certain functional characteristics of tropical ecosystems, combined with high rates of productivity, suggest Ibrutinib that this biome has a capacity for stronger eCO2 responses than its temperate equivalent. Modeling and atmospheric sampling analyses support such a widespread biological response, repeatedly implicating tropical forests as the major global sink for anthropogenic C (Fisher et al., 2013, Hickler et al., 2008 and Stephens et al., 2007), yet the spatial

extent and characteristics that support this tropical “sink” are yet to be verified from ground-truthing surveys using limited scale measurements of tropical tree growth rates over time to investigate this (Clark et al., 2003 and Clark et al., 2010). Leguminous N-fixing species and evergreen broadleaved species are a large component of tropical forest biomass and also known to be especially physiologically responsive to eCO2 (Rogers et al., 2009 and Niinemets et al., 2010). Furthermore, Astemizole eCO2 can also lower the photosynthetic light compensation point, thereby increasing photosynthetic efficiency,

particularly in the deeply shaded tropical understory (Korner, 2009). In short, a combination of ecophysiological mechanisms such as these could potentially account for increased tropical CO2 uptake, yet none have been extensively studied under eCO2 conditions in tropical forest. Hypothetically, tropical habitats enriched with certain plant functional types (such as legumes), particular soil characteristics (e.g. differences in nutrient cycling capacity), or vegetation disturbance history (Foody et al., 1996 and Pan et al., 2011), could each modulate the tropical eCO2 sink capacity, either individually or in combination. Addressing the influence of factors such as these alongside eCO2 would address a present research shortfall and identify the specific ecosystem characteristics allowing this sink to function. If such research were developed in order to define the tropical sink it would provide invaluable information and potentially demonstrate which habitat types are most important for CO2 sequestration.