Heavy Metal Contamination Alters the Co-Decomposition of Leaves of the Invasive Tree Rhus typhina L. and the Native Tree Koelreuteria paniculata Laxm

Abstract

Invasive and native plants can coexist in the same habitat; however, the decomposition process may be altered by the mixing of invasive and native leaves. Heavy metal contamination may further alter the co-decomposition of both leaf types. This study evaluated the effects of two concentrations (35 mg·L−1 and 70 mg·L−1) and three types (Pb, Cu, and combined Pb + Cu) of heavy metal contamination on the co-decomposition of leaves of the invasive tree Rhus typhina L. and the native tree Koelreuteria paniculata Laxm, as well as the mixed effect intensity of the co-decomposition of the mixed leaves. A polyethylene litterbag experiment was performed over six months. The decomposition coefficient of the two trees, mixed effect intensity of the co-decomposition, soil pH and enzymatic activities, soil bacterial alpha diversity, and soil bacterial community structure were determined. A high concentration of Pb and combined Pb + Cu significantly reduced the decomposition rate of R. typhina leaves. A high concentration of Pb or Cu significantly reduced the decomposition rate of the mixed leaves. In general, R. typhina leaves decomposed faster than K. paniculata leaves did. There were synergistic effects observed for the co-decomposition of the mixed leaves treated with combined Pb + Cu, regardless of concentration, but there were antagonistic effects observed for the co-decomposition of the mixed leaves treated with either Pb or Cu, regardless of concentration. A high concentration of Pb or Cu may increase antagonistic effects regarding the co-decomposition of mixed-leaf groups. Thus, heavy metal contamination can significantly affect the intensity of the mixed effect on the co-decomposition of heterogeneous groups of leaves.

Do the Leaves of Multiple Invasive Plants Decompose More Easily than a Native Plant’s under Nitrogen Deposition with Different Forms?

“…Thus, the four AIPs may not decompose more easily than those of P. laciniata. This phenomenon is not consistent with the current results, i.e., invasive plants decompose more easily than native plants [18,[51][52][53] or invasive plants decompose more slowly than native plants [54][55][56]. This finding in this study may be due to the similar proportion of soluble (easily decomposed) and recalcitrant (difficult to decompose) components in the leaves of the four AIPs and those of P. laciniata, i.e., the quality of the leaves of the four AIPs and those of P. laciniata was similar because the four AIPs and P. laciniata are Asteraceae species and these species have similar life cycles, life styles, and growing environments, and especially P. laciniata can often coexist with one or more of the four AIPs.…”

Litter Mass Loss of the Invasive Rhus typhina L. and Native Koelreuteria paniculata Laxm. Trees Alters Soil N-Fixing Bacterial Community Composition under Different N Forms

“…Thus, R. typhina litter may decompose more effectively and rapidly than K. paniculate litter under urea. This finding is consistent with the previous studies, i.e., invasive plants decompose more easily and rapidly than native plants [18][19][20][21]. This phenomenon may be due to the higher percentage of soluble components and lower percentage of recalcitrant components in R. typhina litter compared to those of K. paniculate litter, and/or the compounds contained in R. typhina litter may be more readily released into the soil in the presence of urea.…”

“…Thus, contrary to the first hypothesis, R. typhina litter did not degrade more easily than K. paniculata litter. These observations are also inconsistent with the results of previous research which has shown that invasive plants either degrade more rapidly [18][19][20][21], or significantly more slowly than native plants [58][59][60]. This phenomenon may be due to the similar proportions of soluble and recalcitrant components in the litter of the two trees [28].…”

“…As a result, the litter decomposition may be altered when the litter from the two trees is mixed. Non-additive responses in the litter co-decomposition of invasive plants and native plants are often observed, and generally, the litter decomposition of invasive plants can accelerate that of native plants [21,49,61,62]. In this study, the decomposition of the mixed litter from both trees was slower than that of the individual litter of either species (Figure 2).…”

“…In nature, the two trees typically co-exist [21,42]. As a result, the litter decomposition may be altered when the litter from the two trees is mixed.…”