Inhibition of continuous cropping obstacle of celery by chemically modified biochar: An efficient approach to decrease bioavailability of phenolic allelochemicals.

The accumulation of allelochemicals released by plants is commonly found in continuous monocropping systems. These chemicals, such as phenolic acids, were shown to be the major sources of autotoxin or pathogen accumulation in soils, leading to a direct or indirect continuous cropping obstacle. In this study, three types of agricultural residuals, i.e., rice husk, tea waste, and wood meal, were chosen as feedstocks. Biochar samples were prepared from these feedstocks to examine their abilities to remove gallic acid, a representative phenolic acid. Biochar, which was prepared from wood meal soaked with H3PO4 (1:1.5, w/w) and pyrolyzed at 400 °C (symbolized as WP400), exhibited the highest adsorption capacities of gallic acids and other phenolic acids. The mechanisms of phenolic acid removal by WP400 were evaluated via experimental and spectroscopic investigations to elucidate the notable adsorption capacity of WP400. The adsorption of gallic acids was pH-dependent and followed a pseudo-second-order kinetic model. The combination of high surface area, the existence of O-containing groups, and the enhancement of H bonds between CC groups and phenolic acids may contribute to the high adsorption capacity of WP400. In a pot experiment, we found that celery growth was promoted with the addition of 0.3% (w/w) WP400 to soils that were continuously monocropped with celery. A large decrease in the water-soluble phenolic compound by more than 40% may be responsible for the results. However, WP400 scavenged nitrate, and this study showed that the synergistic actions of WP400 and nutrients exhibited the greatest efficiencies in mitigating the continuous cropping obstacles of celery.

Historical spatial range expansion and a very recent bottleneck of Cinnamomum kanehirae Hay. (Lauraceae) in Taiwan inferred from nuclear genes.

BACKGROUND: Species in the varied geographic topology of Taiwan underwent obvious demographic changes during glacial periods. Cinnamomum kanehirae has been exploited for timber and to obtain medicinal fungi for the past 100 years. Understanding anthropogenic factors influencing the demography of this species after the last glacial maximum (LGM) is critically important for the conservation of this species. RESULTS: Populations of C. kanehirae were classified into four geographic regions: northwestern (NW), west-central (WC), southwestern (SW), and southeastern (SE). In total, 113 individuals from 19 localities were sampled, and variations in the chalcone synthase gene (Chs) intron and leafy (Lfy) intron-2 sequences of nuclear DNA were examined in order to assess phylogeographic patterns, the timescales of demographic and evolutionary events, and recent anthropogenic effects. In total, 210 Chs and 170 Lfy sequences, which respectively constituted 36 and 35 haplotypes, were used for the analyses. Estimates of the migration rate (M) through time revealed a pattern of frequent gene flow during previous and the present interglacials. The isolation-by-distance test showed that there generally was no significant correlation between genetic and geographic distances. The level of among-region genetic differentiation was significant when comparing eastern to western populations. However, no significant among-region genetic differentiation was found in comparisons among the four geographic regions. Moreover, essentially no genetic structuring was found for the three regions west of the CMR. A fit of spatial range expansion was found for pooled and regional samples according to the non-significant values of the sum of squared deviations. Using the Bayesian skyline plot (BSP) method, a recent bottleneck after the LGM expansion was detected in both regional and pooled samples. CONCLUSIONS: Common haplotype distributions among geographic regions and the relatively shallow genetic structuring displayed are the result of historical gene flows. Southward dispersals in an earlier time frame from the NW region and in a later time frame from the SE region were inferred. The BSP analysis suggested a postglacial expansion event. Recent trends, however, refer to a bottleneck due to human interventions observed for both pooled and regional C. kanehirae samples.