Abstract
Garlic is considered to have a strong positive effect on the growth and yield of receptors under soil cultivation conditions. However, how this positive promotion is produced by changing the growth environment of the receptors or directly acting on the receptors is still not very clear. The direct influence of co-culturing with different quantities of garlic plants (the control 5, 10, 15, 20) on the growth and biochemical processes of cucumber plants was studied using a hydroponic co-culture system. Different numbers of garlic bulbs inhibited the growth of cucumber plants and increased the production and induction of reactive oxygen species, which accompanied the enhancement of lipid peroxidation and oxidative damage to cucumber. This allelopathic exposure further reduced the chlorophyll contents and photosynthesis rate, and consequently impaired the photosynthetic performance of photosystem II (PSII). Garlic root exudates increased the leaves’ carbohydrates accumulation, such as soluble sugar contents and sucrose levels by regulating the activities of metabolismic enzymes; however, no such accumulation was observed in the roots. Our results suggested that garlic root exudates can mediate negative plant–plant interactions and its phytotoxic influence on cucumber plants may have occurred through the application of oxidative stress, which consequently imbalanced the source-to-sink photo-assimilate flow.
Highlights
Chemical-mediated plant–plant interference is an important allelopathic mechanism by which certain plant species produce and release organic compounds into the growth environment through leaching, volatilization, root exudation, and passive discharge through decomposition, which have beneficial and harmful effects from the donor plant on the receptor plant [1]
The negative response of receptors to allelochemicals manifests as growth retardation and tissue destruction, which results in oxidative damage to the plant system, where oxidative stress is thought to be a putative mode of action of allelochemicals induced by the overproduction of reactive oxygen species, and causes lipid peroxidation [10]
Our results show that the proportion of the stomatal closures, together with the loss of leaf turgor, progressively leads to showing stress symptoms, followed by parallel decreases of the net photosynthesis rate in cucumber caused by allelopathic agents [46]
Summary
Chemical-mediated plant–plant interference is an important allelopathic mechanism by which certain plant species produce and release organic compounds into the growth environment through leaching, volatilization, root exudation, and passive discharge through decomposition, which have beneficial and harmful effects from the donor plant on the receptor plant [1]. Many plant organs, such as root tissues or leachates, play diverse physiological functions in term of resource competition and root-mediated rhizospheric interactions that have strong allelopathic significance by involving the secretion of potent phytotoxins or organic chemicals, defined as allelochemicals [2]. The inhibition of photo-assimilate output to the sink tissues results in the accumulation of soluble sugars and sucrose in source leaves, which leads to the inhibition of photosynthetic feedback [13]
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