| Proplems of decline of productivity and protective function due to continous plantation exist in Casuarina equisetifolia shelfer-forest. Many scholars have been studying on the causes for decline of productivity of Casuarina after regeneration from these aspects such as decline of species , insect pest and changing of soil physical and chemical character in recent few decades. However, The research on Casuarina self-allelopathy to cause the decline of productivity of Casuarina was rarely reported. Ms. Deng Guilan reported in 1996 that the leaves extracts of Casuarina could inhibited the growth of Casuarina seedlings. Moreover, she isolated and identified five self-allelochemicals from leaves extract. But the studies on that Casuarina can produce self-allelochemicals to inhibit itself growth through root and litter leaves, self-allelochemicals affect physiology and biochemical of Casuarina, effect factors and relief measures on Casuarina self-allelopathy have never been carried out.This research paper studied the effects of Casuarina allelochemicals on the growth , nutritional absorption , Carbon, AOS and endogenous hormone, the factors to affect Casuarina self-allelopathy and the measure of Casuarina self-allelopathy relief through using the seedlings of Casuarina as experimental material and water extract of roots, fresh leaves, litters and surface soil of middle age Casuarina as allelochemicals and method of nutritional culture. The main results were submitted as follows:1 Effects of allelochemicals of Casuarina on the growth of Casuarina seedlings Using water extract of roots, fresh leaves, litters and surface soil of 15-year old Casuarina to handle Casurina seedlings. The results showed that water extract of various organs of Casuarina inhibited the growth of seedlings height and diameter, weight and activity of root, weight of leaves and stems, and this inhibition was strengthened with the increasing of water extract concentration. The inhibition extent of water extract on the growth of seedlingsshowed that roots>fresh leaves>litter>surface soil. It indicated that Casuarina can produce allelochemicals to inhibit itself growth through roots, leaves, litter, and allelochemicals keep jn the soil to affect the growth of next generation. 2 Effects of allelochemicals of Casuarina on nutritional absorption2.1 Under low concentrative water extract (1:40 and 1:20) of roots, the content of P in seedling roots increased 26.3% and 28.8%compared with CK while high concentration (l:10and 1:5) made the content of P reduced 5.1% and 28.8% which indicated that low concentrative allelochemicals promoted the absorption of P of seedling roots while high concentrative allelochemicals inhibited the absorption of P. The content of P in seedling stems and leaves reduced with the increasing of the concentration of Casuarina root water extract. The above mentioned showed that allelochemicals inhibited the absorption of P of Casuarina seedling stems and leaves and prevented the transportation of P from roots to stems and leaves.2.2 Low concentrative water extract of Casuarina roots promoted the absorption of K of seedling roots and stems while high concentrative extract inhibited the absorption and transportation of K. The content of K in seedling roots increased 11.4% when the concentration of water extract was 1:40. Then with the increasing of root water extract, the content of K in the root decreased. The content of K in seedling roots reduced 59.1 %^ 80.1 % and 175% when the concentration of root extract was 1:20. And the content of K reduced with the increasing of water extract of roots. The content of K in the stems reduced 24.4% and 74.9% compared with CK when root extract of Casuarina were 1:10 and 1:5. The content of K in seedling leaves dramatically reduced with the increasing of root extract. The content of K reduced 15.8% to 167.6% compared with CK. The above mentioned showed that allelochemicals could inhibit the absorption of seedlings on K. But low concentration of allelochemicals promoted the absorption of K of seedling roots and stems.2.3 The content of Ca and Mg of seedlings reduced dramatically under water extract of roots. The content of Ca in seedling roots > stems and leaves reduced 31.6%~122.6% ^ 35.5%~226.7%and 34.0%~176.8% respectively compared with CK and the content of Mg declined 90.4%~180.2%, 6.7%~31.4%and 23.7%~I76.7% respectively. The above mentioned indicated that allelochemicals inhibited Casuarina seedlings to absorb Ca and Mg. Moreover, the higher the concentration of allelochemicals, the stronger the inhibition.2.4 Under water extract of Casuarina root, the content of Fe in seedling leaves continuously declined with 4.0%~108.3% compared with CK while it in the roots and stems added 3.7% and 5.3% respectively compared with CK when water extract of seedling roots was 1:40. However, the content of Fe in roots and stems of seedlings reduced 35.0%~107.7% and 35.7%~146.8% respectively when the concentration of water extract of roots was more than 1:40. The content of Cu of seedling stems and leaves increased 33.8%~48.0% and 38.4%~49.1% when the concentration of water extract of seedling roots was less than 1:20 while it declined 35.5%~49.0% and 97.6%~105.0% respectively when the concentration of water extract of roots was more than 1:20. However, the content of Cu in seedling roots reduced 12.7%~214.4% compared with CK with the increasing of water extract of roots. The content of Mn in seedling roots and leaves declined 32.4%~212.1% and 22.3%~151.9% respectively with the increasing of water extract of Casuarian roots. Low concentrationl:40and 1:20) of water extract of roots caused the content of seedling stem to increase 22.5% and 44.4% respectively compared with CK while high concentration (1:10and l:5)made the content of Mn decline 72.6%~134.8%. The content of Zn in roots> stems and leaves of seedlings reduced 15.9%~276.3%> 31.6%~99.6% and 5.7%~110.2% respectively.It could be concluded that self-allelochemicals Casuarina produced inhibited seedlings of Casuarina to absorb the nutrition from the soil. The reason was that self-allelochemicals of Casuarina poisoned the roots of Casuarina seedlings which reduced the activity of Casuarinaseedlings. However, the fact that low concentration allelochemicals promoted seedlings to absorbed some nutrition perhaps was related to the defensive response that seedlings made under the stimulation of allelochemicals.3 Effects of self-allelochemicals of Casuarina on Carbon of Casuarina seedlings3.1 self-allelochemicals declined the content of Chi of seedlings. Self-allelochemicals reduced the content of Chi a, band a/b. Meanwhile, the extent of declining of Chi a> b and a/b was strengthened with the increasing of the concentration of allelochemicals. The content of Chi a > b and (a+b) of leaves(unit.Fw) of seedlings reduced 9.09%~68.77% ^ 5.76%~60.27%and 7.45%~54.9% respectively, and Chi a/b reduced 5.76%~60.27%. The declining of Chi is unfavorable to photosynthesis of Casuarina. The extent of Chi a declining was more than Chi b which was obvious when the concentration of allelochemicals was high. The content of Chi mainly a reduced largely when the concentration of allelochemicals was high.3.2 Photosynthesis efficiency of seedlings reduced under self-alleiopathy of Casuarina. net photosynthetic rate, light staturation point, CO2 staturation point, carboxylation efficiency and photophosphorylation activities of casuarinas were reduced under self-allelopathy and glycolate oxidase activities were strengthened .3.3 The accumulation of C in seedlings of Casuarina declined under self-allelopathy the content and accumulation of C of casuarinas were declined and content of total soluble sugars in casuarinas roots and items were increased under self-allelopathy, while content of total soluble sugars in casuarinas leaves was increased under low concentration of self-allelopathy, but high one caused its dropping.4 Effects of self-allelochemicals of Casuarina on AOS and endogenous hormone of seedlings 4.1 the content of the growth promoting hormones of seedlings declined under self-allelopathy of Casuarian.the content of the growth promoting hormones in leaves and roots of casuarina IAA> GF^ iPAs and ZRs decreased under self-allelopathy and the content ofdecreasing was strengthened with the increasing of concentration of self-allelopathy. And the balance of endogenous hormones were broken and the content of ABA increased as well as ABA/lAA,ABA/GA,ABA/iPAs and ABA/ZRs. Under self-allelopathy, the increment and biomass of roots,items and leaves of casuarina has close relation to the reducing of content of IAA,GR,iPAs and ZRs.increasing of content of ABA and the damage of the balance of endogenous hormones.4.2 the balance of AOS was damaged and AOS greatly acumulated in the casuarina under self-allelopathy. It showed that permeability of plasma membrane increased construction and function of membrane were damaged . The content of MDA increased and membrane lipid peroxidation became serious.The producing speed of O2" and the content of H2O2 in leaves cells increased, and the balance of AOS on producing and clearing was broken. AOS acumulated greatly in leaves cells.The defense system of AOS was damaged and the activity of SOD,CAT,GR and POD decreasd as well as the ability of cells on clearing O{ and H2O2. 5 Effect factors and relief of self-allelopathy of Casuarina5.1 Selection of proper clone of Casuarina relieved self-allelopathy of Casuarina. Inhibition of self-allelochemicals of different clone of Casuarina on seedlings and resistance of different clone seedlings on allelochemicals of Casuarina were different. The inhibition extent of allelochemicals of experimental clone showed seed breeding >clone Dongl> clone Pingl>clone Yue601>clone Yue701. Clone Yue501> clone Yue701 and clone Huil had high resistance and adaptability. In practical plantation, Casuarina could relieve to inhibit its growth because of self-allelopathy through selecting clone Yue50k Yue601 , Yue701 and Hui 1 to plant.5.2 Density of stand affected Casuarina self-allelopathy. Low density relieved the growth inhibition of Casuarina. Under high density, Casuarina strengthened the producing of self-allelochemicals and the growth inhibition, relieved photosynthesis and Pn. Moreover,... |
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