| Allelopathy is a hot subject in the recent half century all over the world and it widely exists in nature. Many researches, associated with identification of allelochemicals, investigation of the effect of mono-allelochemicals and mixed allelochemicals, as well as the effect of litterfall and its water leaching solution on growth of plants, etc, have reported that Cinnamomum has strong allelopathic effect. But there are few reports concerning allelopathy of Cinnamomum septentrionale. For its exuberant branches and leaves, beautiful tree appearance and sweet fragrance, C. septentrionale has been widely used as rural four sides gardening and landscape trees (e.g., planted surrounding villages or alongside gardens and vegetable fields) in China. Huang et al. has found that C. septentrionale leaf litter could influence the growth of Brassica rapa. Eucalyptus grandis, as a main tree species for the construction of industrial plantations in southern China, has effectively promoted the timber production in this country. But most Eucalyptus plantations are currently grown as monocultures and bring in many ecological problems, such as the reduction of biological diversity (mainly due to allelopathy), woodland soil degradation, productivity decline, etc. Suitable mixed-forest is favour able to improve the light efficiency, water and nutrient uptake, and overall stand productivity. In recent years, E. grandis plantations have been rapidly developed and some of them were planted largely under or near C. septentrionale forest. Therefore, in this study we added C. septentrionale leaf litter and its water extract into soil to investigate whether the growth of E. grandis saplings could be affected by decomposing C. septentrionale leaf litter (LF) and its water extract (LW), aiming to provide some theoretic reference for interplanting these two species.A pot experiment was implemented in present study to transplant E. grandis saplings and two designs were used:(1) Transplanting E. grandis in soil containing LF (0(A0),40(A1),80(A2) and120(A3) g·pot-1);(2) Transplanting E. grandis in soil and watering LW (B:dosage as above). In addition, Gas chromatography-mass spectrometry (GC-MS) was used to study the release of volatile compounds of decomposing C. septentrionale leaf litter in soil and investigate its underlying allelopathic mechanism. We aimed to examine the possibility of planting E. grandis near the edge and cut-over land of forests containing C. septentrionale or other Lauraceae species. Preliminary results are as follows:(1) Effects of C. septentrionale leaf litter on growth and biomass of E. grandis saplings69d after transplanting, the height and basal diameter increment of E. grandis saplings were significantly reduced (P<0.05) with increasing LF and increasing concentration of LW.11months after transplanting, the basal diameter growth of E. grandis saplings was still significantly suppressed with increasing content of LF and increasing concentration of LW, while the change of height growth was different between these two methods. The height growth of E. grandis was significantly inhibited by LW, while was promoted by LF (A1>A2> A3>Ao).(2) Effects of C. septentrionale leaf litter on protective enzyme activity of E. grandis saplingsLF significantly inhibited the peroxidase (POD) activity of E. grandis saplings and the inhibition strengthened with increasing content of LF, but there was no signigicant difference in superoxide dismutase (SOD) activity between treatments. The POD activity of E. grandis saplings was significantly decreased (P<0.05) with increasing concentration of LW and the inhibition was stronger than that of LF. Furthermore, the SOD activity was stimulated by LW, but no siginificant difference was observed in SOD or POD between B1, B2and B3.(3) Effects of C. septentrionale leaf litter on osmoregulation of E. grandis saplingsThe sugar content of E. grandis showed a sharp decline with increasing content of LF, and the proline content increased first and decreased then, but there was no no significant difference of malondialdehyde (MDA) and soluble protein content among different treatments. As the concentration of LW in the soil increased, the sugar and proline contents of the receptor reduced sharply, but the soluble protein and MDA content increased markedly. Therefore, it is suggested that the LW may have stronger impact on the osmoregulation and membrane lipid peroxidation of E. grandis saplings leaves than its LF.(4) Effects of C. septentrionale leaf litter on photosynthetic physiology of E. grandis saplingsThe net photosynthetic rate (Pn) of E. grandis saplings increased gradually with the increasing content of LF, but the transpiration rate (Tr) and stomatal conductance (Gs) went up dramatically and synthesis of photosynthetic pigment and the ability of assimilation CO2were inhibited. The chlorophyll content was reduced exposed to both LW and LF, but the inhibition of the former was greater than the later. Furthermore, the influence of LW on photosynthetic traits was different from LF, because the Pn and Tr of E. grandis saplings were decreased, and the ability of CO2assimilation was enhanced by LW. The cause of this difference was not clear and it still needs further study.(5) Identification of volatile compounds in the essential oils of C. septentrionale leavesThirty-one volatile compounds, representing94.84%of the total oil contents, were identified in the essential oil extracted from original C. septentrionale leaf litter, which primarily included18terpenoids (49.88%),4alkanes (7.84%),3alkenes (5.57%),2esters (2.64%),1phenol (14.13%),1alcohol (8.87%),1ketone (7.56%) and1steroid (1.33%). Fourteen volatile compounds, representing94.45%of the total oil contents, were identified in the essential oil extracted from treated C. septentrionale leaf litter, which was mixed with soil and used to plant E. grandis saplings for eleven months, suggesting that allelochemicals were released into the soil during decomposition. These compounds included4alkanes (29.07%),4terpenoids (18.98%),2steroids (11.93%),1ketone (36.93%),1Phenanthrene (1.48%) and1phenol (1.61%).In conclusion, LF as well as its LW significantly inhibited the growth of E. grandis saplings. The inhibition of LF and LW on E. grandis saplings strengthened with increasing content of LF and concentration of LF. LW had a stronger allelopathic effect than LF under the same dose (120g and80g) and the order of allelopathic inhibition (from strong to weak) was B3>A3>B2>A2>A1>B1. Furthermore, in the late decomposition process in present study, the LF might release a lot of nutrient to promote the height growth of E. grandis saplings. However, because of the serious damage that occurred during the initial growth stage, the E. grandis saplings could not recover in a short time, and the stem, leaf, branch and root biomass remained diminished. |
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