Autotoxicity And Identification Of Potential Auto Toxins Of Picea Schrenkiana

Picea schrenkiana, the most important zonal vegetation of Tianshan Mountains in China, is an endemic species in Middle Asia and Mountains of Asia. In China, it is mainly distributed in the northern and southern slopes of Tianshan Mountains, and the northern slope of the western part of Kunlun Mountain, accounting for half of the woodland area in Xinjiang province with the area of528,400hm2. As the main tree species and the source of life of Tianshan Mountains and even the forest ecosystems of Xinjiang, P. schrenkiana plays an important role in water conservation. However, with the disturbance on forest ecosystems resulted from human activities, natural regeneration issue of P. schrenkiana is more prominent without fire interference relief. Previous results showed that autotoxicity might be the main cause of the issue for the current forest interference system. Therefore, our study tested the potential autotoxicity of aqueous extract from P. schrenkiana litters and leaves. Water extract from P. schrenkiana litters and leaves was partitioned against diethyl ether, ethyl acetate, and n-butanol sequentially. The organic fractions, original water extract and the residual water after the organic solvent extraction were tested for inhibitory activity on seed germination and seedling growth under climatic cabinate conditions. Furthermore, preliminary identification of the chemical composition of each organic fraction of P. schrenkiana litters and leaves were undertaken by GC-MS-MS analysis.3,4-dihydroxyacetophenone was also isolated and purified from diethyl ether fraction by Silica gel column chromatography and recrystallization. Autotoxicity and allelopathy effects of3,4-dihydroxyacetophenone were also bioassayed. The results were as following:1. Among the five fractions, it showed that the original water extract, diethyl ether fraction, ethyl acetate fraction and n-butanol fraction of P. schrenkiana litters all exhibited different phytotoxic effect. In the seed germination experiments, diethyl ether fraction exhibited the strongest phytotoxicity and reduced seed germination at low concentration (IC50=5mg/mL) and n-butanol fraction had the least effect (IC50>10mg/mL). In the seedling growth experiments, diethyl ether fraction at concentration of1.25mg/mL had significant inhibitory effect on seedling growth (p<0.05). n-Butanol fraction at1.25mg/mL could slightly stimulate seedling growth; while the fraction at concentrations higher than or equal to2.5mg/mL all showed obviously inhibitory effect on seedling growth (p<0.05). Phemolics, long-chain fatty acids, tannic acids and indoles were preliminary identified in the three fractions of aqueous extracts from P. schrenkiana litters.3,4-dihydroxyacetophenone, which was identified but not reported as an allelochemical or autotoxin previously, was isolated and purified from the diethyl ether fraction.2. Among the five fractions, it showed that the original water extract, diethyl ether fraction, ethyl acetate fraction and n-butanol fraction of P. schrenkiana leaves all exhibited different phytotoxic effect. In the seed germination experiments, diethyl ether fraction exhibited the strongest phytotoxicity and reduced seed germination at low concentration (IC50=5.84mg/mL) and n-butanol fraction had the least effect (IC50>10mg/mL). In the seedling growth experiments, diethyl ether fraction at concentration of1.25mg/mL had significant inhibitory effect on seedling growth (p<0.05); while n-butanol fraction at concentrations higher than or equal to2.5mg/mL could show obviously inhibitory effect on seedling growth (p<0.05). Phemolics, long-chain fatty acids, tannic acids, indoles and flavonoids were preliminary identified in the three fractions of aqueous extracts from P. schrenkiana leaves.3,4-dihydroxyacetophenone was also isolated and purified from the diethyl ether fraction.3. Autotoxicity effect of3,4-dihydroxyacetophenone was stronger than its allelopathy effect.3,4-dihydroxyacetophenone treatment solution at concentration of2.5mM had significant inhibitory effect on seed germination of P. schrenkiana (p<0.05); at concentration of0.5mM could significant inhibitory effect on seedling growth of P. schrenkiana (p<0.05). Six different concentrations of3,4-dihydroxyacetophenone treatment solutions had no effect on seed germination of Raphanus sativus, Capsicum frutescens and Cucumis sativus. The treatment solutions at concentrations of0.1mM,0.5mM,1mM could significantly promote seed germination of Allium cepa.(p<0.05) The treatment solutions at concentrations of1mM,10mM could significantly promote seed germination of Oiyza sativa (p<0.05), and seed germination vigor was up to166.69%of control at lOmM. Compared with control, concentrations of3,4-dihydroxyacetophenone treatment solutions higher than or equal to1mM exhibited significant inhibitory effects on seedling growth of R. sativus and C. sativus (p<0.05). Concentrations at higher than or equal to10mM had significant inhibitory effects on seedling growth of C. frutescens and A. cepa (p<0.05), concentrations at0.5mM could significantly promote seedling growth of A. cepa. Concentrations at higher than or equal to2.5mM had significant inhibitory effects on seedling growth of C. frutescens and O. sativa (p<0.05).