摘要
农林复合生态系统是一种经济、高效、可持续的土地利用方式。发展农林复合生态系统具有重要的经济、社会、生态效益。在本研究中,首先采用生物检测的方法,测定了香樟叶片、根和根际土壤的化感作用,然后选取不同林分郁闭度的香樟林地,分别配植紫背天葵、芝麻菜、辣菜三种蔬菜,以无林地和纯林地为对照,研究林-菜系统生态耦合后土壤理化性质的变化规律,林下小气候的变化规律以及林-菜复合生态系统的植物生产特点,探讨发展林-菜复合生态系统的可行性,通过研究得到结论如下:
①香樟叶、根、根际土壤的水浸提液对蔬菜种子萌发、幼苗生长均有化感作用,化感作用随着浸提液浓度的增大而增加,受试蔬菜种类不同,其化感作用也不相同,化感能力以叶水浸提液最大,根水浸提液次之,土壤水浸提液的抑制作用最小。高浓度的根水浸提液处理下,红苋菜和荠菜种子均不能萌发,发芽速度指数I为0。低浓度的土壤水浸提液出现对受试植物生长的作用,如对萝卜根长的化感作用效应指数为49.69,对根长生长有明显的促进作用。这和其他一些研究结果相同,即该化感物质对植物生长出现低促高抑的作用。
②林-菜系统耦合后土壤的理化性质有比较明显的变化。结果表明,低林分郁闭度与蔬菜构建的林菜复合系统能够降低土壤容重,改善土壤物理性状。林菜复合生态系统土壤有机质含量明显高于对照,有利于维持土壤有机质的稳定。
③林-菜复合系统中,由于蔬菜生长吸收较多养分,土壤速效养分逐渐减少,但与无林对照地K相比,养分损失较少,在蔬菜采收期林-菜复合系统土壤养分含量与纯林地相比差异不显著,说明林-菜系统耦合能够有效利用土壤中的有效养分,减少养分淋溶带来的损失。
④林-菜系统耦合后土壤pH值有所下降,接近中性,说明林-菜系统复合经营能够降低土壤pH值,使之趋于有利于作物生长的pH区间;且合理的复合模式能够有效调控土壤TDS含量达到动态平衡。
⑤林-菜复合生态系统中,由于林木的存在,外界气温较高时,能够显著降低林下的大气温度,与无林对照地气温相比,最多能降低10.92℃,外界气温较低时,能够延缓林下温度的下降,林-菜系统耦合以后,能够显著减小温度的日较差,维持气温稳定。系统内部的大气相对湿度也有较为明显的升高,土壤蒸发减少,系统保水性增加。
⑥林-菜系统耦合构建的农林复合生态系统形成了独特的林下小气候,能够提高蔬菜光合效率,其生物量较高,固定和转化CO2的效率得到提高。林木、蔬菜的存在,减少了裸露土壤受光照、气候条件的影响,因而其各层土壤温度的变化幅度均有减小。尤其是在蔬菜生长初期,处理H的表层土壤温度比对照CK下降了5.65℃。
⑦林-菜系统耦合对蔬菜的一些生化指标影响显著,不同处理的蔬菜叶绿体色素含量、可溶性糖和可溶性蛋白质的含量差异显著,通过分析数据可将三种蔬菜分为两类,芝麻菜、辣菜的含量随着郁闭度的下降基本呈上升趋势,紫背天葵恰恰相反,更适合在有一定郁闭度的林下栽培。
⑧林分郁闭度对林-菜系统内蔬菜的株高、叶面积影响显著,在蔬菜生长初期,高郁闭度降低了大气温度,减少了水分蒸发,H内蔬菜生长较好;随着时间进行,温度下降,环境越来越适宜蔬菜生长,低郁闭度和无林对照地的蔬菜迅速生长,株高,叶面积迅速增加。蔬菜的根冠比与林分郁闭度成负相关关系,随着郁闭度的降低根冠比逐渐增大。不同林分郁闭度下蔬菜的鲜重和产量差异显著,其鲜重变化规律同株高、叶面积基本相同;低郁闭度林地与三种蔬菜耦合后,紫背天葵和辣菜产量均高于无林对照地,说明合理模式的林-菜复合生态系统具有更大的经济、生态效益。
In the paper, the allelopathy of leaves, roots and the rhizosphere soil of Cinnamomum camphora L. on three vegetables (Raphanus sativus L., Amaranthus mangosfanus L. and Capsella bursa-pastoris (L.) Medic.) were studied by using the biological examination, and then the change of soil physicochemical properties, microclimate and the plant growth in compound ecosystem of Cinnamomum camphora L. and three vegetables Gynura bicolor D.C, Eruca sativa L., Brassica juncea (L.) var. foliosa Bailey were investigated to research the feasibility of developing forest-vegetable compound ecosystem. Results showed as follows:
①The water extracts of leaves, roots and rhizosphere soil of Cinnamomum camphora L. have allelopathy effects on the seed germination and seedling growth of radish, amaranth and capsella and different vegetables have different responses on the allelopathy of Cinnamomum camphora L.. Meanwhile, allelopathy effect increased with increasing the concentration of each extract, which order is: leaves>root>rhizosphere soil. However, low concentration of rhizosphere soil extract can improve plant growth, but high restrict. Therefore, developing forest-vegetable compound system is feasibility through reasonable agricultural measurement and scientific management.
②The change of soil physicochemical properties in the forest-vegetable system coupling process is very obvious. The result indicated that the reasonable canopy density forest compounded appropriate vegetables can reduce the soil bulk specific gravity and leaching loss, and maintain and increase the content of organic matter and availability of nutrient in the soil. Moreover, the reasonable management of forest-vegetable compound system can reduce the soil pH value to advantageous range for growth and development of crops, and effectively regulate the soil TDS content to achieve the dynamical equilibrium.
③The forest-vegetable coupling ecological system can reduce the difference of day-night temperature and the soil moisture evaporation and the vegetable transpiration, and increase the atmospheric humidity and the CO2 efficiency of fixation and transformation. The biomasses of vegetables in the forest-vegetable system have a high affinity with the canopy density of forest. The low canopy density can significantly increase vegetables photosynthesis compared to the control. Meanwhile, the total efficiency of photosynthesis in the reasonable disposed compound ecosystem is higher than the control (non-forest) and the economic outputs are also significantly high. The change of soil temperature is small and there is a quite stable microclimate under the forest because the influence of the light and other climatic conditions on soil reduced.
④The forest-vegetable coupling system had a significantly effect on some physicochemical characteristic of vegetables. The contents of the chloroplast pigment, soluble sugar and soluble protein in the vegetables present the regular changes, but the relative of Gynura bicolor D.C is different with other two kinds of vegetables. Gynura bicolor D.C displayed shade-resistant, possibly due to its specifically physiological structures, which should be deeply studied for us.
⑤Vegetables' height, leaf area, fresh weight and outputs have remarkable difference compared to the control. In the initial period of vegetables growth, the high canopy density reduced the air temperature and moisture evaporation, and makes the vegetable growing well. The temperature drops with the time in high canopy density and this environment is suitable for the growth of vegetables. The high of vegetable and leaf area in the low canopy density rapidly grow compared to the control (non-forest). Moreover, outputs of vegetables are highest among the treatments and the control.
Therefore, it is very important to select reasonable canopy density forest land and the kinds of compounded vegetables and introduce appropriate agronomy method and pattern of scientific management for optimizing forest-vegetable compound system to achieve the maximization of economic, ecological and social benefits.
引文
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