On the coexistence mechanisms of a perennial grass with an allelopathic shrub in a semiarid rangeland

ABATRACT: An ecophysiological study was conducted on allelopathic effects of a shrub (Artemisia khorassanica) on a perennial grass (Bromuskopetdaghensis), in Baharkish rangelands, Quchan, Iran. Based on field visits (March – October 2011), Bromus started and terminated its yearly growth respectively one and three months sooner than Artemisia. Water soluble extracts (3% weight/Volume) were taken from Artemisia shoots, at the beginning of the growth season, full vegetative and flowering stages. In a glasshouse experiment, the Artemisia extracts were applied on Bromus seedlings at early vegetative, full vegetative and flowering stages. Artemisia extracts reduced photosynthetic pigment concentration but increased oxidative stress indices in Bromus shoots. Both the allelopathic effects by Artemisia and the adaptive responses from Bromus were reduced by the growth season. Therefore, temporal differences in the phenology, temporal shifts in the allelopathic effects and responses, and Bromus acclimations to mediate the allelopathic stress, may be the reasons for their natural coexistence.