Biomass properties in association with plant species and assortments. II: A synthesis based on literature data for ash elements

A study was carried out based on ash composition data (relative proportion of SiO2, K2O, CaO, MgO, Na2O, P2O5, Al2O3, Fe2O3 and SO2 in ash) in a large number of biomass species and assortments. The data were collected from 109 peer-reviewed publications and consisted of 367 objects for ash composition analysis. Principal component analysis (PCA) was used to analyze the data. The analyses were performed at five levels of plant classifications respectively: level 1–3 for life-forms/species groups, level 4 for assortments and level 5 for species. species data points tended to differ from herbaceous ones in terms of PCA for level 1 analysis. The loading plot of the two first components (PC1 and PC2) indicated that the woody species tended to be associated with Ca–Mg–P–K–S, while the herbaceous ones were closer to Si. Ca and Si had the largest contributions in forming the pattern. The woody group had a larger variation than the herbaceous group in terms of ash composition but this could be explained only by differentiation in assortments as illustrated with the level 4 analysis. The PCA analyses at levels 2 and 3 did not generate significant patterns, as the variations within the groups were larger than between the groups. The variation of the herbaceous data, however, could be explained by all level 2–5 analyses and attributed to differences between herbaceous dicots and graminoids, between C3 and C4 plants, and between assortments such as husk, fruit residues and bagasse. The robust analysis had in general the same results. These results could be further interpreted by the trend that Si decreased but Ca increased gradually in the following order: C3 graminoids → C4 graminoids → herbaceous dicots → woody groups. It was also found that K, P, Mg and S were higher in herbaceous dicots than in graminoids.