Volatile and Non-Volatile Allelopathic Characteristics in Thermally Processed Needles of Two Conifers

Abstract

With allelopathic composts, potential merits for preventing initial weed infestations have been observed in crop transplantation. However, previous studies have rarely investigated whether high temperatures, generated during composting, decrease allelopathic ability. This study evaluated the thermal allelopathic effect of two coniferous plants (Pinus densiflora and P. koraiensis) on Brassica napus germination and seedling growth using their characterized allelochemical destinations. The 90 °C dry treatment of P. densiflora extract exhibited stronger inhibitory effect on germination than its 30 °C dry treatment. In a range from 0.25 to 1 mg mL−1, the germination rate was decreased to 38.1 and 64.3% of control with P. densiflora extract dried at 90 and 30 °C, respectively. However, P. koraiensis showed potent inhibition of the germination process with no statistical difference in inhibitory effects regardless of the dry temperature. Regarding B. napus seedling root growth, the allelopathic effects of aqueous extracts of both conifers were not reduced with the 90 °C treatment, but it was lost in seedling shoot growth. GC-MS/MS confirmed that high temperature treatment drastically decreased volatile contents to 53.2% in P. densiflora, resulting in reduced allelopathic abilities. However, a relatively lower decrease to 83.1% in volatiles of P. koraiensis accounts for less loss of the root-specific inhibitory effect on B. napus seedlings even after 90 °C treatment. Foliar tissues of both conifers with species-specific thermal resistance have potentially valuable functions regarding allelopathic use in horticultural compost processing ingredients, demonstrating their weed control ability during the early cultivation season where crops are transplanted in the facilitated area.

The inhibitory potential of green manure return on the germination and seedling growth of Eleusine indica L.

“…Paula et al (2020) found that the extract and fractions of Smilax brasiliensis leaves showed an inhibitory effect on Allium cepa seeds. Gil et al (2022) found the thermal allelopathic effect of two coniferous plants (Pinus densiflora and P. koraiensis) on inhibiting Brassica napus germination and seedling growth. Sakit et al (2022) found the phytotoxic effects of Acacia saligna stem extract on the germination of economically important crops.…”

The other way around: the utility of a plant invader

“…For our study, we preserved the branches by oven drying them at 60°C before use, similar to previous studies (Singh and Sangeeta, 1991; Singh and Thapar, 2003; Gnanavel and Kathiresan, 2007; Saeed et al ., 2011; Khan et al ., 2016). It is known that many allelopathic compounds can be degraded with the heat but there are also many that are thermostable (Gil et al ., 2022). For instance, the allelopathic potential of Pinus koraniensis Siebold & Zucc.…”

“…For instance, the allelopathic potential of Pinus koraniensis Siebold & Zucc. even increased when dried at 90°C (Gil et al ., 2022) and allelopathic properties of Mentha pulgium L. were not altered when dried at 50°C (Ahmed et al ., 2018). Even autoclave temperatures did not reduce the toxicity of A. altissima leaves (Heisey, 1990).…”

Sustainable Weed Management

“…and Pinus koraiensis Siebold & Zucc.) on oilseed rape (B. napus) germination and seedling growth in order to assess whether high temperatures, generated during composting, decrease allelopathic ability [16]. It was found that the allelopathic capacity of two Pinus species showed root-specific inhibition, but the decrease in volatile contents after the thermal process was lesser in P. koraiensis than in P. densiflora.…”