| Walnut-mung bean intercropping is one of main agroforestry patterns in hilly region ofTaihang Mountain in China. In this study, spatial distributions of water and nutrients in soilwere investigated in walnut-mung bean intercropping field. A potting experiment wasconducted in a greenhouse to study effects of nitrogen-fixing plant, mung bean, and nitrogenfertilizer on walnut water balance, gas exchange and growth. Moreover, influence of nutrientson walnut water relations was explored through a nutrient control experiment. This study aimsat providing a theoretical basis for understanding the competition and facilitation betweendifferent components in agroforestry systems and improving management model of theagroforestry systems in the Taihang Mountain. The main findings are as follows:1、The spatial distribution of water in soil: The change patterns of soil moisture weresimilar in the walnut and mung bean monocroppings and the walnut–mung bean intercroppingsystems. In vertical direction, soil moisture increased with increasing soil depth, however thevariation magnitude of soil moisture decreased from40to80cm soil layers. In the horizontaldirection, in0-20cm soil layers, the farther the distance was from the forest belt, the lower ofsoil moisture, and in20-80cm soil layers, the closer the distance was from the forest belt, thelower the soil moisture. There was difference in the decline rate of soil moisture in the verticaldirectionin the monocroppings and the intercropping systems. In20-80cm soil layers, the soilmoisture in mung bean monoculture was highest, then was the agroforestry system, and the soilmoisture in walnuts monoculture was lowest. In0-20cm soil layer, the order of soil moisturewas mung bean monoculture the agroforestry system walnut monoculture.The spatial distribution of nutrient in soil: Walnut-mung bean intercropping and mungbean monoculture field had the highest nutrient content in shallow soil layers. In verticaldirection, phosphorus and potassium and soil organic matter content decreased with increasingsoil depth; In horizontal direction, in0-20cm soil layer, the farther the distance was from the forest belt, the lower of soil nutrients; and in20-80cm soil layer, the farther the distance wasfrom the forest belt, the higher the soil nutrients. Soil nutrient content of different layers inagroforestry system were more than walnut monoculture. The requirement of walnut and mungbeans to soil nutrients was available nitrogen> available phosphorus> organic matter>available potassium.2、The study was to explore effects of V. radiata, a nitrogen fixing-crop, on growth, waterbalance and gas exchanges of the intercropping J. regia seedlings and to investigate thehydraulic mechanism involved in photosynthesis and growth. We measured growth, hydrauliccharacteristics, and gas exchanges of J. regia seedlings, analyzed the effects of theintercropping nitrogen fixing V. radiata on xylem anatomic structure, water balance andphotosynthetic characteristics of J. regia seedlings under nitrogen deprivation and abundance.Results showed that under the condition of nitrogen deficiency, the nitrogen fixing V. radiatafacilitated growth of the intercropping J. regia seedlings by improving xylem development,water transport and hydraulic characteristics in high transpiration demand. However, withnitrogen addition, V. radiata plantation inhibited growth of J. regia likely by competing waterand other elements with the intercropping J. regia.3、The growth, hydraulic characteristics, and photosynthetic characteristics of J. regiaseedlings were measured in this study, to explore effects of phosphorous deficient soils withdifferent pH values on growth, water balance and photosynthetic characteristics of J. regiaseedlings. The results showed that: With phosphorous, pH3significantly reduced the P uptakeefficiency and P use efficiency of J. regia seedlings, and had similar reaction with phosphorusstress in the growth and physiological indexes. With phosphorous deficient, pH3increased thepoisoning effect of stress environment on J. regia seedlings. The change of indexes as follows:Under stress conditions the root growth of J. regia seedlings was inhibited, the root area toabsorb water and fertilizer was reduced, the development of petiole xylem was changed, thevessel density decreased, and PLC increased, water transport capacity decreased, inducedstomatal closure. With the stomatal conductance decreased, photosynthesis declined, the phenomenon of photoinhibition of J. regia leaf was induced and photo-oxidative was damaged,Fv/Fm, ΦPSⅡ, qP declined, optical systems starts physiology protection mechanisms, NPQincreased, to reduce photo-oxidative damage, regulated the ability of J. regia seedlings to adaptto environmental, affected the growth of J. regia seedlings.4、This study explored of nitrogen on growth, water balance and photosynthesis of walnutseedlings. The results showed that: leaf area, stomata size and root growth increased undernormal nitrogen supply, while indicators were towards downward trends under high nitrogensupply. Vessel diameter, pit diameter, and perforation diameter of petiole were increased bynitrogen, thus water transport efficiency of vessel was enhanced; While vessel density ofpetiole decreased by both high and low nitrogen, resulting in reducing of leaf water potentialand increasing of water loss rate. Vessel diameter and density were consistent to that of petiole,and root hydraulic conductivity decreased both under high and low nitrogen; While leaf gasexchange and vessel density had the same trend with leaf water potential. Leaf photosyntheticapparatus was damage to a certain degree by high nitrogen treatment and FV/Fmvalue wasbelow0.80. Periodical changes were present in the root pressure of walnut and the maximumvalues could all reach above25Kpa, which was sufficient to repair xylem embolism becauseof strong transpiration.5、Walnut seedlings with different nitrogen concentration conditions response distinctly todrought stress by adopting different coping mechanisms: Low concentration of nitrogentreatment increased root-shoot ratio, leaf stomata density and petioles xylem safety, anddecreased leaf area of seedling. Meanwhile, as soil moisture constant deduced, hydraulicconductivity of petiole and root and stomata conductance were decreased to reduce water loss,furthermore, leaf photosynthesis was also decreased to reduce water consumption fromabover-ground part of plant, which aimed to adjust its strategy of adapting to drought stress.On the other hand, after re-watering treatment, water transporting and photosynthetic ability ofseedlings quickly recovered. Besides, high concentration of nitrogen treatment decreased rootgrowth, root hydraulic conductivity of plant. As soil moisture constant deduced, petiole hydraulic conductivity loss rate was increased, and leaf water potential and were deduced todecrease the leaf transpiration and photosynthesis rate to response to drought stress. However,after re-watering treatment, photosynthetic ability of seedling was decreased. Normal amountsupply of nitrogen promote root growth, water transporting ability, water consumption andphotosynthetic ability of seedlings. Besides, at normal water and mild drought condition,seedling increased root amount, vessel diameter, and water transportation efficiency, to ensurenormal physiological activities. At extreme drought condition, seedling reduced its roothydraulic conductivity and index of leaf gas exchange, also increased petiole hydraulicconductivity loss rate, and adjusted itself to adapt to drought stress. On the one hand, afterre-watering treatment, compensation effect of seedling was most significant. |
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