Topography as a factor driving small‐scale variation in tree fine root traits and root functional diversity in a species‐rich tropical montane forest

Abstract

We investigated the variation in tree fine root traits and their functional diversity along a local topographic gradient in a Neotropical montane forest to test if fine root trait variation along the gradient is consistent with the predictions of the root economics spectrum on a shift from acquisitive to conservative traits with decreasing resource supply. We measured five fine root functional traits in 179 randomly selected tree individuals of 100 species and analysed the variation of single traits (using Bayesian phylogenetic multilevel models) and of functional trait diversity with small‐scale topography. Fine roots exhibited more conservative traits (thicker diameters, lower specific root length and nitrogen concentration) at upper slope compared with lower slope positions, but the largest proportion of variation (40–80%) was explained by species identity and phylogeny. Fine root functional diversity decreased towards the upper slopes. Our results suggest that local topography and the related soil fertility and moisture gradients cause considerable small‐scale variation in fine root traits and functional diversity along tropical mountain slopes, with conservative root traits and greater trait convergence being associated with less favourable soil conditions due to environmental filtering. We provide evidence of a high degree of phylogenetic conservation in fine root traits.

Leaf trait variation in species-rich tropical Andean forests

“…We thus conclude that filtering through an increasingly cold and nutrient-limited environment seems to be only partly shaping the functional trait composition of these communities. In addition, small-scale heterogeneity in soil physical and chemical conditions, enhanced through topographic gradients in the rugged mountain terrain, is one possible factor that might allow maintaining a higher trait variability also at higher elevations, as it creates different edaphic niches at short distance 8 , 43 , 45 . Yet, environmental filtering apparently has increased the integration of leaf traits in higher-elevation trees, as is suggested by the trait network analysis.…”

Factors controlling the productivity of tropical Andean forests: climate and soil are more important than tree diversity

“…Various studies have identified WSG as a good predictor of the diameter increment of tropical trees, and high WSG has been linked to low aboveground productivity in tropical lowland forests (Malhi et al, 2004;Poorter et al, 2008;Finegan et al, 2015). In the Ecuadorian Andes, the negative effect of average WSG on productivity was as strong as the positive biomass (AGB) influence, suggesting that negative edaphic effects on productivity, notably high soil acidity and low availability of basic cations, are exerted in part indirectly through an increase in wood specific gravity (Unger et al, 2012).…”

Carbon cycle in tropical upland ecosystems: a global review

“…This way it is possible to scale from the individual to ecosystem level by studying informative traits related to carbon balance such as maximum rate of photosynthesis, maximum chlorophyll flu- orescence, and time to maximum photosynthesis (Rawat et al, 2015). Additionally, functional traits can also be critical for understanding the dynamics of fine roots in the carbon storage and nutrient acquisition, but this is still in its infancy (Pierick et al, 2021). Traits such as root diameter, specific root length, root branching intensity, root tissue density, root nitrogen concentration, mycorrhizal association type, carbon translocation to symbionts, and others (Freschet et al, 2021;Pierick et al, 2021) may have important effects on soil carbon and nutrient cycling in upland ecosystems.…”

“…Additionally, functional traits can also be critical for understanding the dynamics of fine roots in the carbon storage and nutrient acquisition, but this is still in its infancy (Pierick et al, 2021). Traits such as root diameter, specific root length, root branching intensity, root tissue density, root nitrogen concentration, mycorrhizal association type, carbon translocation to symbionts, and others (Freschet et al, 2021;Pierick et al, 2021) may have important effects on soil carbon and nutrient cycling in upland ecosystems. It is important to note that correlations between above-and belowground traits can be integrated at the whole-plant level , showing the level of coordination between both compartments from which significant functions can emerge like plant growth and carbon accumulation.…”

“…In particular, tropical upper montane ecosystems are highly idiosyncratic because of their ecological and evolutionary singularities, which are very different from the lowland tropics (Malhi et al, 2010). Beyond constituting an upslope extension of lowlands, tropical upland forests are characterized by extraordinary local endemism and high rates of beta-diversity (Olson and Dinerstein, 2002;Calbi et al, 2021;Hurtado-Martilleti et al, 2021), which are mainly explained by the topographic heterogeneity (Pierick et al, 2021), the broad range of climatic environments (Malhi et al, 2010), and the complex geophysical structures (Körner, 2007;Körner and Spehn, 2019). These characteristics, at the same time, hinder mountain research, and many ecological questions remains to be answered, especially in ecosystem functioning.…”