Polygonum pubescens, known as drooping or lax knotweed is a tropical and subtropical annual herb belonging to Polygonaceae. The weedy and herbaceous nature, wide distribution and availability make this herb an attractive target for useful phytochemicals. This study aimed to investigate the volatile metabolites of this herb which remained unexplored. First, a detailed morphological study established its identity and distinguishing features with closely related Polygonum species. The leaves of this herb produced highest yield of essential oil (0.20%-0.35%) among three aerial parts (leaf, stem, and inflorescence) hydrodistilled. The oil composition was grossly similar across the tissues and exclusively dominated by three eudesmane and cadalane-type sesquiterpene hydrocarbons, namely, β-selinene (36.3%-43.7%, 221.8-254.5 mg/g), α-selinene (11.0%-14.4%, 74.2-86.5 mg/g), and δ-cadinene (29.0%-41.6%, 140.6-197.6 mg/g). This oil was practically composed of sesquiterpenoids which collectively contributed 97.9%-100.0% relative abundance. When phytotoxicity was evaluated, the oil dose-dependently (1.0-200.0 µg/mL) inhibited the growth of wheatgrass coleoptile. However, the inhibitory potency (59%-73%, 200.0 µg/mL) was significantly low for its consideration as an herbicidal candidate. The current study identified P. pubescens as a rich natural source of β-selinene and δ-cadinene, bearing significance in plant defense, chemical synthon and bioactive phytochemicals.

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Wetlands are the largest natural source of terrestrial CH 4 emissions. Afforestation can enhance soil CH 4 oxidation and decrease methanogenesis, yet the driving mechanisms leading to these effects remain unclear. We analyzed the structures of communities of methanogenic and methanotrophic microbes, quantification of mcr A and pmo A genes, the soil microbial metagenome, soil properties and CH 4 fluxes in afforested and non-afforested areas in the marshland of the Yangtze River. Compared to the non-afforested land use types, net CH 4 emission decreased from bare land, natural vegetation and 5-year forest plantation and transitioned to net CH 4 sinks in the 10- and 20-year forest plantations. Both abundances of mcr A and pmo A genes decreased significantly with increasing plantation age. By combining random forest analysis and structural equation modeling, our results provide evidence for an important role of the abundance of functional genes related to methane production in explaining the net CH 4 flux in this ecosystem. The structures of methanogenic and methanotrophic microbial communities were of lower importance as explanatory factors than functional genes in terms of in situ CH 4 flux. We also found a substantial interaction between functional genes and soil properties in the control of CH 4 flux, particularly soil particle size. Our study provides empirical evidence that microbial community function has more explanatory power than taxonomic microbial community structure with respect to in situ CH 4 fluxes. This suggests that focusing on gene abundances obtained, e.g., through metagenomics or quantitative/digital PCR could be more effective than community profiling in predicting CH 4 fluxes, and such data should be considered for ecosystem modeling.

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Paddy soils have been widely recognized as important carbon sinks. However, paddy field abandonment is increasing in the hilly area in subtropical China. Soil waterlogging and weed burning are common practices in abandoned paddy fields, which could affect vegetation cover and carbon sequestration. An rice cultivation experiment was ceased in 2006, and four new treatments were applied as waterlogging (W), drainage (D), waterlogging combined with burning (WB), and drainage combined with burning (DB). Waterlogging altered the vegetation cover and caused an associated change in biomass. Paspalum paspaloides, Murdannia triquetra, and Bidens frondosa dominated W and WB plots, and Microstegium vimineum and Bidens frondosa dominated D and DB plots. Abandonment of paddy fields led to a rapid decrease in soil organic carbon (SOC), and waterlogging accelerates SOC loss which should be attributed mainly to alteration of the vegetation cover. Six years' rice cultivation increased SOC content by 13.5% (2.4 g kg -1 ) on average. In contrast, six years' abandonment reduced SOC content by 14.5% (3.0 g kg -1 ) on average. Decline rate of SOC was 0.38, 0.64, 0.30, and 0.65 g kg -1 a -1 for D, W, DB, and WB, respectively. Such results indicate a significant risk of SOC loss from abandoned paddy fields.

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Polygonum flaccidum Meissn. is an annual herb, native to Bangladesh, and well known for its analgesic, anti-inflammatory, diuretic, purgative and insecticidal properties, and also for its use against snake-bites. The analgesic and the diuretic properties of alpha-santalone (1), isolated from the aerial parts of Polygonum flaccidum, were assessed by the acetic-acid-induced writhing method and the Lipschitz test, respectively. Complete (1)H and (13)C NMR data of 1 are also presented.

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More than 500 plant species, used alone or in combination, are documented in Chinese traditional medicine to have activity against helminth and micro-invertebrate pests of humans. We subjected 153 candidate medicines or their plant sources to multilevel screening for effectiveness against plant-parasitic nematodes. For extracts effective in preliminary screens, we determined time-course and concentration-response relationships. Seventy-three of the aqueous extracts of medicines or their plant sources killed either Meloidogyne javanica juveniles or Pratylenchus vulnus (mixed stages), or both, within a 24-hour exposure period. Of 64 remedies reported as antihelminthics, 36 were effective; of 21 classi- fied as purgatives, 13 killed the nematodes; of 29 indicated as generally effective against pests, 13 killed the nematodes. Sources of extracts effective against one or both species of plant-parasitic nematodes are either the whole plant or vegetative, storage or reproductive components of the plants. Effective plants include both annuals and perennials, range from grasses and herbs to woody trees, and represent 46 plant families.

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