A robust CWM-PCA for evaluating chemospace of metabolome of root exudates across 9 tropical species

Root exudate is comprised of complex compounds which have multiple function for plant performance and plant-soil interactions. Although the carbon fluxes of root exudates is considered as an important trait towards the fast-slow growing axis in the multidimensional root economics space, the complexity of the metabolome in root exudates is not well evaluated. Here, we present a community-weighted PCA for species chemospace. Compounds are aggregated to species with two weightings: presence (detection proportion) and relative (softmax of logabundance). Isomer candidates are pooled using Dirichlet priors (A1 symmetric; A2 similarityweighted). Dimensions are selected by Horn's parallel analysis, and robustness is assessed with leave-one-out principal angles. Of 22 descriptors, nine were near-constant or missing and were excluded. Variance concentrated in two components: presence 55.7% and 28.4%; relative 75.8% and 15.5%; both PCs exceeded the 95th percentile noise envelope. The PC1 and PC2 subspace was stable (mean cosine 0.993 to 0.994; largest deletion about 22 degrees), and A1 and A2 produced nearly identical subspaces. PC1 reflected hydrophobicity versus polarity and hydrogen bonding (higher LogP/LogD, lower H-bond acceptors/donors and polar surface area). PC2 captured adsorption and bioconcentration together with molecular flexibility and optical proxies (higher KOC and BCF, more freely rotating bonds, higher refractive index). Relative weighting is recommended as primary; presence serves as a concordant robustness check.