# Allelopathic Activity of Leaf Wastes of _Lriodendron tulipifera_ for Sustainable Management
## 4 Discussion
### An Allelichemical in \(L\). tulipifera Leaves  
The fresh and fallen leaf extracts of \(L\). _tulipifera_ were purified through the bioassay-guided separation process using silica gel chromatography, Sephadex LH-20 chromatography, an ODS cartridge, and reverse-phase HPLC (Figure 2). During the separation process, the allelopathic activity of all separated fractions was determined, and the most active fraction was applied to the next separation process. \(L\). _sativium_ was selected as a bioassay plant species for the isolation process because of its stable germination rate and easy handling [58]. The germination of \(L\). _sativium_ was high (about 90% germination rate at 48 h after sowing) compared with the weed species--_V. myuros, E. crus-galli,_ and_\(L\). _multiform_ (20-40% germination rate). The sensitivity of the \(L\). _sativium_ hypocotyls and roots to the \(L\). _tulipifera_ fresh and fallen leaf extracts was not too high and not too low in comparison with the \(IC_{50}\) values of these weed species (Figures 3-5 and Table 1).  
An active compound, **1**, was isolated from both fresh and fallen leaf extracts and characterized by the spectrum data as lipiferolide (Figure 7). Lipiferolide suppressed the growth of \(L\). _sativium_ and \(L\). _multiform_ in a concentration-dependent manner (Figure 8). Lipiferolide was first isolated from \(L\). _tulipifera_ leaves [59; 60], and has been isolated from other Magnoliaceae species, _Liriodendron chinensis_ ([PERSON].) [PERSON], _Magnolia sirindhorniae, Michelia_ yunnanensis [PERSON] & [PERSON], and _Michelia fuscata_ ([PERSON].) [PERSON]. [61; 62; 63; 64], and the Asteraceae species _Vica pentaema_ [PERSON]. & [PERSON]. [65]. Lipiferolide showed cytotoxic activity against human cancer cell lines, such as KB cells and Hepa lclc7 cells [59; 66], and antiplasmodial activity [23]. However, it is the first report on the biological activity and allelopathic activity of lipiferolide against plant species, including weed species. The mode of action of lipiferolide on allelopathic activity and its concentration in soil should be evaluated in the fur furture. Lipiferolide is only commercially available for laboratories but not for practical use.  
Lipiferolide in the leaves of \(L\). _tulipifera_ may be involved in the allelopathic activity of the fresh and fallen leaf extracts and the leaf powder (Figures 3, 4 and 6). The fresh leaves may contain greater amounts of lipiferolide than fallen leaves because 12 mg and 4 mg of lipiferolide were isolated from the fresh and fallen leaves, respectively. One of the reasons for the lower amount of lipiferolide in the fallen leaves may be the metabolism of the compound during the defoliation and/or degradation process of the leaves [67; 68; 69; 70]. The concentrations of lipiferolide in the fresh and fallen leaves are consistent with the allelopathic activity of the extracts and powder obtained from the fresh and fallen leaves (Figures 3-6). Therefore, lipiferolide in the fresh and fallen leaf powder of \(L\). _tulipifera_ may be liberated into soil at the same proportion and suppress germination.