| The allelopathy on seed germination and sprout growth of wheat, kidney bean, cucumber and pepper in root exudates of soil and substrates extracts of1-3years continuous cropping pepper were studied by bioassay methods. Major allelochemicals were identified by GC-MS analyzing methods in the separated components of soil and substrates extracts of3years continuous cropping pepper combined with results of bioassay methods, which held the highest allelopathy on pepper. Further, throughing exogenous SNP (NO donor,150μmol·L-1) and ABA (100μmol·L-1) treated by foliar spray pepper seedlings under soil and substrates extracts, physiological and biochemical mechanisms of nitric oxide (NO) and abscisic acid (ABA) on alleviation to autotoxicity in pepper seedlings were studied, which related to growth, photosynthesis, antioxidant enzyme systems, nitrogen assimilation, and so on. The main results were as folllows:1. Radicle length, shoot length, germination rate and sprout fresh weight of wheat, kidney bean, cucumber and pepper were reduced to different extents with soil and substrates extracts of1-3years continuous cropping pepper treated, which indicated that root exudates suppressed strongly seed germination and sprout growth of four vegetables. Suppression action on seed germination and sprout growth of four vegetables was strengthener with continuous cropping years of pepper prolonged,and that of soil extracts was better obviously that of substrates extracts. Suppression action on seed germination and sprout growth of wheat was strongest among four vegetables of soil and substrates extracts of3years continuous cropping pepper, which was gradually weakened on pepper. kidney bean and cucumber. Major allelochemicals by GC-MS were difference in soil and substrates extracts of3years continuous cropping pepper, and major allelochemicals were3-methyl-1-butanol, ethylene glycol,2,2,4-trimethylpentane,1,2-benzenedicarboxylic acid, mono(2-ethylhexyl) ester in soil extracts, while major allelochemicals were hexadecanoic acid, methyl ester,1,2-benzenedicarboxylicacid, bis(2-methylpropyl) ester in substrates extracts, we found that soil extracts diethylether+ethylacetate component and substrates extracts ethylacetate component held the highest allelopathy. Finally, the component of soil extracts diethylether+ethylacetate and substrates extracts ethylacetate was analyzed by GC-MS. The result showed that the main allelochemicals were identified as1,2-epoxyethylbenze1,2-benzenedicarboxylicacid, bis(2-methylpropyl) ester,1,2-benzenedicarboxylicac bis(2-methylpropyl) ester in Soil extracts diethylether+ethylacetate component, and the main allelochemicals were identified as acenaphthene,1,2-epoxyethylbenzen,1,2-benzenedicarboxylicacid, bis(2-methylpropyl) ester in Substrates extracts ethylacetate component. Common allelochemical was1,2-Benzenedicarboxylicacid, bis(2-methylpropyl) ester in both components.2. Stem diameter, plant height, leaf length, leaf width, leaf number, fresh and dry weight, ratio of root to top and root activity of pepper seedlings were declined under both soil and substrates extracts, especially, stem diameter, plant height, leaf length, root fresh weight, R/T of fresh weight, top dry weight, root dry weight and root activity were lower significantlly than that under autotoxicity stress, which indicated that both soil and substrates extracts suppressed obviously growth and root activity of pepper seedlings. NO and ABA both promoted obviously increasement of the above index under autotoxicity, and promoting role of NO on top fresh and dry weight of seedlings was stronger than that of ABA, while which of ABA on root fresh and dry weight of seedlings was stronger than that of NO. In all, promoting role of NO on growth index and activity of pepper seedlings was higher significantlly than that of ABA under autotoxicity stress.3. All of soil and substrates extracts reduced Pn, Gs, Tr, Fv/Fm, ΦPS II, qP, chlorophyll content and ratio of chlorophyll a/b obviously, but increased Ci and NPQ significantly. Under autotoxicity stress, exogenous NO treatments significantly increased Pn、Gs、Fv/Fm、ΦPS Ⅱ、qP and chlorophyll content, but reduced Ci and NPQ significantly, and had no obvious influence on Tr. Exogenous ABA treatments significantly increased Pn、Fv/Fm、ΦPS Ⅱ、qP and chlorophyll content, but reduced Ci and NPQ significantly, and had no obvious influence on Gs and Tr under autotoxicity stress. The reduction in net photosynthesis rate caused by autotoxicity stress was considered to be a result of non-stomatal restriction mainly, and autotoxicity on pepper of soil extracts was serious greatly than substrates extracts. Under autotoxicity stress, exogenous NO and ABA application increased chlorophyll content, maintained PSII center activities and photo synthetic capacity, and enhanced autoxicity tolerance in pepper.4. Superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) activities, and dehydroascorbate (DHA) content declined under all of soil and substrates extracts stress, while ascorbic acid (AsA), proline (Pro), soluble protein, malondialdehyde (MDA) contents, relative conductivity and AsA/DHA ratio increased. Autotoxicity pepper of soil extracts was serious greatly than that of substrates extracts. NO and Al significantly increased SOD, POD and CAT activities, Pro and soluble protein contents, while reduced MDA content and relative conductivity significantly. At the same time, AsA/DHA ratio was significantly higher through promoting significantly to increase AsA content and decrease DHA content. Alleviate effect to autotoxicity of NO was significantly better than that of ABA in pepper seedlings. The above results suggested that NO and ABA effectively prevented malondialdehyde accumulation and electrolyte leakage, mitigated lipid peroxidation, through increasing antioxidant enzymes activities, osmotic adjustment substance content and AsA/DHA ratio in pepper seedlings under autoxicity stress.5. Total nitrogen, total phosphorus and total potassium content, nitrate reductase (NR) and glutamine synthetase (GS) activities declined under drought stress, while the content of ammonia nitrogen and nitrate nitrogen content increased. Exogenous application of NO and ABA in the condition of autotoxicity stress significantly increased the content of total nitrogen total phosphorus and total potassium, while decreased the accumulation of inorganic nitrogen. Also, NO application obviously increased the activities of NR and GS under autotoxicity stress. The above results suggested that NO and ABA enhanced the ability of nitrogen reduction and assimilation under autotoxicity stress, which might be a key reason for improving the autotoxicity tolerance of plants. |
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