Allelopathic effects of volatile organic compounds released from Pinus halepensis needles and roots

Abstract

The Mediterranean region is recognized as a global biodiversity hotspot. However, over the last decades, the cessation of traditional farming in the north part of the Mediterranean basin has given way to strong afforestation leading to occurrence of abandoned agricultural lands colonized by pioneer expansionist species like Pinus halepensis . This pine species is known to synthesize a wide range of secondary metabolites, and previous studies have demonstrated strong allelopathic potentialities of its needle and root leachates. Pinus halepensis is also recognized to release significant amounts of volatile organic compounds (VOC) with potential allelopathic effects that have never been investigated. In this context, the objectives of the present study were to improve our knowledge about the VOC released from P. halepensis needles and roots, determine if these VOC affect the seed germination and root growth of two herbaceous target species ( Lactuca sativa and Linum strictum ), and evaluate if soil microorganisms modulate the potential allelopathic effects of these VOC. Thirty terpenes were detected from both, needle and root emissions with β‐caryophyllene as the major volatile. Numerous terpenes, such as β‐caryophyllene, δ‐terpinene, or α‐pinene, showed higher headspace concentrations according to the gradient green needles < senescent needles < needle litter. Seed germination and root growth of the two target species were mainly reduced in presence of P. halepensis VOC. In strong contrast with the trend reported with needle leachates in literature, we observed an increasing inhibitory effect of P. halepensis VOC with the progress of needle physiological stages (i.e., green needle < senescent needle < needle litter). Surprisingly, several inhibitory effects observed on filter paper were also found or even amplified when natural soil was used as a substrate, highlighting that soil microorganisms do not necessarily limit the negative effects of VOC released by P. halepensis on herbaceous target species.

Influence of drought on allelopathic properties of Pinus sylvestris L.

“…Germination and seedling development are the main life stages usually affected by allelochemicals. Frequent allelopathic influence often inhibits (Fernandez et al, 2013;Santonja et al, 2019) and results in a delay of seed germination (Fernandez et al, 2013;Hashoum et al, 2017). It also inhibits the seedling growth (Gavinet et al, 2019) by altering physiological processes (e.g., photosynthesis, nutrient uptake, cell division, or elongation (Inderjit & Duke, 2003)).…”

Soil scarification favors natural regeneration of Pinus pinea in Lebanon forests: Evidences from field and laboratory experiments

“…In addition, several previous studies clearly demonstrated allelopathic potentialities of both green needles and needle litter (e.g. Nektarios et al 2005;Santonja et al 2019) that can act simultaneously on target species under field conditions. Emergence was slightly but significantly lower in the litter burning treatment than in the soil scarification treatment (Fig.…”

“…Ten replicates were performed for each treatment (3 substrate types × green needle aqueous extract concentrations) for a total of 90 microcosms. The bioassays were conducted under controlled conditions in climaticcontrolled room (Panasonic, France) under optimal conditions favoring P. pinea seed germination and seedling growth (Agrimi and Ciancio; (Hashoum et al, 2017;Santonja et al, 2019). Germination speed was calculated using the Kotowski velocity coefficient (Mazliak, 1982;Santonja et al, 2018) as: Cv = 100 (ΣNi / ΣNiTi), where Ni is the number of seeds germinated at time i, and Ti is the number of days since the start of the experiment.…”

Allelopathic Effect of Serphidium kaschgaricum (Krasch.) Poljak. Volatiles on Selected Species

“…In most circumstances, the allelopathic effect of allelochemicals are species selective and concentration dependent. Santonja et al found VOCs produced by Pinus halepensis exerted more potent effect on Linum strictum than Lactuca sativa ; meanwhile, strength of allelopathy was enhanced along with the increase of VOC concentration [ 52 ]. In another study, Ercoli et al evaluated the allelopathic effect of the aqueous extracts of Secale cereal , Brassica juncea and Vicia villosa on A. retroflexus , Chenopodium album and Polygonum aviculare , and found that the strength of inhibitory effect differed significantly among test species, and the magnitude of reduction on shoot growth was always lower than on root growth, which responded in a dose-dependent manner; the aqueous extract of S. cereale significantly reduced the shoot length of A. retroflexus by 25% at the concentration of 1:10 whereas by 83% at 1:5 [ 53 ].…”