Root quality and decomposition environment, but not tree species richness, drive root decomposition in tropical forests

Abstract

Background and aims Tropical forests contribute significantly to the global carbon cycle, yet the relative importance of tree diversity on key ecosystem processes such as root decomposition remains unknown.Methods We examined the influence of tree species richness on root decomposition over 485 days at two sites in Panama with contrasting soil fertility. Diversity effects on decomposition rates were calculated where 1) overstory tree species richness and composition matched that occurring inside root decomposition bags and 2) where roots of contrasting species richness decomposed under a common tree overstory. In addition, we tested 27 root traits to identify those that contribute to predict root decomposition in tropical forests. Results Tree species richness did not affect root decomposition rates, neither when species were manipulated within bags nor with varying tree overstory richness. Root carbon quality and micronutrient concentrations such as manganese explained 47 and 81 % of the variation in decomposition rates in the fertile and infertile site, respectively, demonstrating that the relative importance of traits was modulated by the soil environment. Conclusions Our results suggest that root decomposition in tropical forests is mediated by root functional composition and the soil environment rather than by species richness.

Decomposition of leaf litter mixtures across biomes: The role of litter identity, diversity and soil fauna

“…These litter identity effects mostly were interpreted based on few, commonly measured traits such nitrogen (N), C and lignin concentrations (Adair et al., 2008; Hättenschwiler & Jørgensen, 2010), which have been assumed to exert the strongest control on litter decomposition rates. However, there is increasing evidence that other litter traits regulating decomposer and enzyme activities, including concentrations of plant secondary compounds as well as micronutrients such as calcium (Ca), magnesium (Mg) and manganese (Mn), can be more important in driving litter decomposition than the more commonly used nutrient and C quality traits (Berg et al., 2017; Berg, Steffen, & McClaugherty, 2007; García‐Palacios, McKie, Handa, Frainer, & Hattenschwiler, 2016; Guerrero‐Ramírez et al., 2016; Makkonen et al., 2012; Pérez‐Harguindeguy et al., 2000; Vaieretti, Harguindeguy, Gurvich, Cingolani, & Cabido, 2005). Therefore, to better understand the underlying drivers of litter identity effects on decomposition, and how they interact with climate at large spatial scales and across biomes, decomposition studies should assess a large number of leaf litter traits, including those that, like micronutrients, are not commonly considered.…”

Mycorrhizal and environmental controls over root trait–decomposition linkage of woody trees

“…For example, root decomposition has been reported to be negatively (Hobbie et al ., 2010) or not (Sun et al ., 2018) correlated with root diameter. In addition, studies have reported positive (Guerrero‐Ramírez et al ., 2016; Prieto et al ., 2016) or negative (Hobbie et al ., 2010; Jo et al ., 2016) relationships between root decomposition and specific root length (SRL). Such discrepancies could be attributed to the arbitrary definition of fine roots based on a diameter threshold of 2 mm (Pregitzer et al ., 2002).…”

Soil carbon stocks across tropical forests of Panama regulated by base cation effects on fine roots

“…Particularly in humid tropical forests, decomposition of leaf litter on the forest floor is rapid (<3 years) (11), and a large proportion of surface litter is likely respired back to the atmosphere as CO 2 rather than transported downward and stored in mineral soils. Root C, in contrast, is transferred directly into mineral soils, where tough, lignin-rich tissues, saturated conditions, and low oxygen levels can slow decomposition, leading to greater C retention of root tissues relative to leaf litter (12,13). Thus, estimates of root biomass, rather than aboveground C stocks, are likely to be more useful for predicting tropical soil C stocks.…”