【作者】 李羿桥；

【导师】 胡庭兴；

【作者基本信息】 四川农业大学 ， 森林培育， 2013， 博士

【摘要】 林草复合模式是国家生态建设中重要的生态恢复模式,也是长江上游生态屏障建设中最有效的植被恢复措施之一。在长江上游地区,巨桉是重要的造林树种之一,目前巨桉人工林种植方式多以纯林为主。造林初期,为增加农民收入,常在林下套种或间种牧草、粮食、蔬菜等农作物,在林分近熟或成熟后则多为林下混生多种野草的经营模式。巨桉林凋落叶通过分解能为林下草类的生长提供的一定的养分,但其分解释放的化感物质也会对林下植物的生长造成一定的负面影响。然而,关于巨桉凋落物分解过程中化感物质的产生、降解以及对周围植物的影响效应,人们还知之甚少。因此,研究巨桉凋落叶分解及其化感物质释放动态对作物的影响规律,对巨桉人工林生态系统生物多样性的维护以及可持续经营具有重要的意义。本研究以10a生巨桉人工林林下收集的新近凋落叶为试验材料,置于相对含水量分别为40%和80%土壤湿度条件下及野外自然分解,测定其分解过程中养分及化感物质的释放动态(相对含量的动态变化情况),分析其化感作用可能的持续期；通过盆栽试验探讨了凋落叶处理量分别为30g/盆(A1)、60g/盆(A2)和90g/盆(A3)条件下其分解对菊苣、假俭草和狗尾草生长以及生理特性的影响；同时以三个草种种子进行发芽试验,研究了0.5%、1%、10%三个浓度凋落叶水浸提液对种子萌芽的影响。主要研究结果如下：1.巨桉凋落叶在土壤相对含水量为80%的状态下分解率最高,自然水分条件次之,40%条件下分解率最低；凋落叶分解具有季节性,在夏季高温高湿条件下,分解速度最快,冬季分解较慢；80%土壤湿度和自然水分条件下的凋落叶干物质残留率在7月后都显著低于40%土壤湿度条件下凋落叶干物质的残留率,且从8月开始,80%土壤湿度条件下的凋落叶干物质残留率也显著低于自然水分条件。2.40%和80%土壤湿度处理下,巨桉凋落叶中除N元素含量表现为先上升后下降外,木质素、纤维素以及C、P、K、Mg和Ca的含量均单调的下降；自然水分条件下,凋落叶中纤维素的释放模式为淋溶-积累-释放,木质素和N为富集-释放,C和K为持续释放,而Mg和Ca为先释放后积累,而P则表现为积累。3.巨桉凋落叶初始样品中共检测到36种有机化合物,根据各组分的化学性质与结构的不同可分为9大类,其中有萜类物质19种,为主要的化感物质,占总数的52.78%,此外桉叶油醇(19.61%),α-蒎烯(12.48%)的相对含量较高。这类化学组分大多呈现随凋落叶分解而下降的趋势,表现为自然水分条件下分解最快,40%土壤湿度下损失最少；各化学组分在凋落叶分解前期下降速度较快；萜类物质在三种条件下释放率都超过了80%。4.巨桉凋落叶在土壤中分解时能抑制菊苣、假俭草和狗尾草的生长以及生物量的积累,随凋落叶添加量的增多,抑制作用越明显；用经过蒸馏浸提后的凋落叶(尽可能去除其中化感物质)处理三个草种,其生长性状表现为,在不同试验组之间的差异均不显著,说明添加的凋落叶对土壤的物理性质(通气透水性以及对根系的物理阻隔)影响不大,表明化感物质是影响草种生长的主要因素。5.巨桉凋落叶的分解明显抑制了菊苣、假俭草以及狗尾草叶片中光合色素(叶绿素a、叶绿素b和类胡萝卜素)的合成,随着凋落叶施加量的增加抑制作用增强,具体表现为A3>A2>A1>CK (P<0.05)。3个处理组中草种叶片的光合速率、气孔导度、蒸腾速率及其对环境中光照和CO2浓度改变的适应能力与对照组相比都显著降低(P<0.05),从而减弱了叶片的光合作用,最终抑制草种的生长以及生物量积累。6.三种草种叶片的抗性生理指标都受巨桉凋落叶化感作用的影响。在低凋落叶量和短时间处理下,草种叶片中的SOD、CAT和POD活性与对照组差异不显著或有所上升,但随着处理时间推移和处理量加大,3种酶的活性都降低,90d时各处理均显著低于对照组(P<0.05)。土壤中凋落叶含量越高,分解时对草种中MDA含量的影响越显著,30d、60d以及90d时,经90g凋落叶处理的草种叶片中MDA含量都显著高于其它试验组(P<0.05)。叶片中游离脯氨酸和可溶性糖含量随凋落叶施加量增多而上升,可溶性蛋白含量则相反；60g和90g凋落叶处理时,这3个指标在不同时间与对照组之间差异都达到显著水平(P<0.05)。7.除0.5%和1%浓度的巨桉凋落叶水浸提液能提高假俭草的发芽势和发芽指数外,狗尾草、假俭草和菊苣种子的发芽率、发芽势、发芽指数、胚根和胚芽的长度以及幼苗的鲜重和干重均受到浸提液中化感物质的抑制,随浸提液的浓度增加,抑制效果增强。10%浓度的浸提液对3个草种种子萌发及幼苗生长的影响程度显著大于1%和0.5%浓度处理组以及对照组(P<0.05)。综上,巨桉凋落叶的分解可为林下植物生长提高养分,但其释放的化感物质也会对植物种子萌芽以及生长、发育表现出不同程度的抑制效应。本研究结果可为巨桉人工林生态系统多样性保护和林草复合种植模式的开展提供理论依据,为科学地开发巨桉林+草复合种植模式以及进行合理的经营管理提供理论依据和技术参考,并为科学合理地评价巨桉+作物人工复合种模式的生态经济价值提供参考。更多还原

【Abstract】 Forest-grass compound is an important ecological restoration mode in the national ecological construction, and is also one of the most effective ways to restoring the vegetation in the construction of ecological defense in the upper reaches of Yangtze River, where Eucalyptus grandis is one of the most important planting tree species, and is usually planted by forest-grass compound. In order to increase the income of farmers, crops like pasture, food, and vegetable are usually intercropped or interplanted in the forest at the early of period of the afforestation. But the intercropping of forest and various grasses are carried out at the near ripe or ripe forest. On one hand, the decomposing leaf litter of E grandis can provide nutrition to the undergrowth, but on the other hand allelochemicals from decomposing leaf litter also negatively affect the growth of grass in the intercropping system of E. grandis plantation and grass. However, there is little knowledge on the produce, degradation, and its allelopathic effect on the peripheral plants under the decomposition of E grandis leaf litter. Hence, the research of influence rule of allelopathy and degradation dynamic of E grandis leaf litter on crop is very meaningful for the restoration of ecosystem diversity and sustainable forest management in the E. grandis plantation.Fresh leaf litter were randomly collected from a10-yaer-old E. grandis plantation as experimental materials in this study, and the dynamic change of the relative content of allelochemicals and nutrient in leaf litter were compared under the conditions of40%soil moisture,80%soil moisture, and natural terms. Pot experiment was used to study the effect of decomposing leaf litter with three different contents include30g/pot (A1),60g/pot (A2), and90g/pot (A3) on growth and physiological characteristics of Cichorium intybus, Setaira viridis (L.) Beauv, and Eremochloa ophiuroides. Additionally, the mehod of culture was used to investigate the effect of water extract of fresh failed leves with three concentrations (0.5%,1%, and10%) on the seed germination and seeding growth of the three grasses. The main results are followed:1. The decomposition rate of E grandis leaf litter was highest in80%soil moisture, lowest in40%soil moisture, and that in natural condition was medium. The decomposition rate in summer was relatively higher, and that in winder was relatively slower. The dry matter remaining rate in80%soil moisture and natural condition was significant lower than that in40%soil moisture after July, and the dry matter remaining rate in80%soil moisture was also lower natural condition from August.2. Under the40%and80%soil moisture, the content of Nitogen in E. grandis leaf litter first incrased and then decreasd, and the content of lignose, cellulose, Carbon (C), Phosphorus (P), Potassium (K), Magnesium (Mg), and Calcium (Ca) decreased monotomously. In the natural condition, the release pattern of lignos was leaching-accumulation-release, C and K was continuous release, Mg and Ca released first and then accumulated, and the pattern of P was accumulation.3. There were36chemical substances detected in the initial samples of leaf litter of E. grandis, and which can be divided into9categories due to their chemical structures and properties, and nineteen of which were terpenoids, and accouting for52.78percent of them, which are the main allelochemicals. The relative content of alpha-Pipene nd1,8-Cineole were12.48%and19.61%, respectively, and were higher among all the chemical substances. The relative content of total chemical compositions and major allelochemicals decreased over time, and the biggest dorp was found in natural condition, whereas, smallese decrease was observed in40%soil humidity. Furthermore, the rates of decline were faster in early stage of decomposition, and the release rates of terpenoids were more than80%under these three contitions.4. The decomposing leaf litter of E. grandis can inhibit the growth and the accumulation of biomass of Cichorium intybus, Setaira viridis (L.) Beauv, and Eremochloa ophiuroides, the inhibition effect went up with the increase of the content of leaf litter. There was no significant difference found in the growth traits among the different experiment groups in the three grasses, when the distilled leaf litter of E. grandis were added in the soil. This shows that no significant influence of leaf litter on the physical properties of soil, and allelochemical was the main factor to influence the grass growth.5. The decomposing leaf litter of E. grandissignificantly inhibited the synthesis of photosynthetic pigments (chlorophyll a, chlorophyll b and cartenoids) of C. intybus, S. viridis, and E. ophiuroides. The photosynthetic rate, stomatal conductance, transpiration rate, and the response to CO2concentration and lingt intensity in three treatments were significantly lower than those in control group (P<0.05). The photosynthesis of leaf decreased that unltimately inhibited the the growth and the accumulation of biomass of grasses.6. The resistance physiology traits of C. intybus, S. viridis, and E ophiuroides’were influenced by allelopathy from the decomposing leaf litter of E. grandis. There was no significant difference in the activity of SOD, CAT, and POT between CK and treatments. The activity of three enzymes decreased with time and the amoungt of processing. At the day of90, the activity of three enzymes in treatments were significant lower than those in CK (P<0.05). The more leaf litter contained in the soil, the moer significant effect had in the content of MDA. The MDA content in the treatment with90g leaf litter was significant hiher than that in CK at the dat of30,60, and90(P<0.05). The soluble sugar and free proline content went up with the increase of leaf litter content at all time points, while the change of soluble protein contents was opposite. There were significant diffenerces found between CK and treatments with60and90g leaf litter in these three indexes at all tested time points (P<0.05).7. Besides, the extracts of fresh leaf litter of E grandis with concentration of0.5%and1%can improve the germination potential and germination index of E. ophiuroides, the germination potential, germination index, germination rate, the length of radicle and germ, and the fresh weight and dry weight of seedling were inhibited by the allelochemicals of extracts, and the inhibitory effect enhanced with the increase of concentration. The effect level of10%concentration was significant greater in germination and seedling growth than those of1%and0.5%concentractions, and CK (P<0.05).In conclusion, the decomposing of E. grandis leaf litter can not only provide nutrients to the undergrowth, but allelochemicals had various degrees of inhibitory on the germination, growth and development of grasses at different growth stages. Results of this study could provide scientific theoretical basis for the Forest-grass compound, biodiversity conservation, rational management in the intercropping system of E. grandis plantation and grass, and also provide some reference to evaluate scientifically the ecological value of E. grandis plantation.更多还原