Ecophysiological Characteristics and Productivity of Agroforestry System in the Loess Area of the Northern Wei River, Shaanxi, China
|School||Northwest University of Science and Technology|
|Keywords||Agroforestry photosynthetic characteristics productivity loess|
Considering the fragile ecological environment, economic backwardness in the loess area and the sustainability, diversity, efficiency and stability of agroforesty system, taking the agroforestry system （walnut, plum intercropping with corn, soybean, mung bean and pepper, respectively） as research object, ecophysiological characteristics of photosynthesis, biological characteristics and productivity of the intercropping crops were monitored under different intercropping models, and the effects of different models on photosynthesis, growth and yields of intercropping crops were studied in order to design, manage and control the agroforestry system rationally and to provide theoretical basis for further probing into theincreasing yield mechanism of agroforestry system. The main conclusions are as follows: （1）Compared with the monoculture system, during the growing season, the intercropping systems could reduce the air temperature, wind speed, soil temperature, photosynthetic active radiation（PAR） and the atmospheric CO2 concentration by 1.55-2.65℃, 39.2%-53.6%, 2.02-3.4℃, 10.1-42.8%, 16.1-20.32μmol·mol-1, respectively; but increase the relative atmospheric humidity by 3.49-5.13%; and the narrower the tree spacing, the more significant effects of microclimate.（2）At a distance from walnuts, plums from 2.5m to 1m, PAR and crop photosynthetic rate showed a gradual decrease trend in different intercropping systems, and PAR and crop photosynthetic rate in 3m×3m intercropping models were significant lower than those in 5m×3m. With the aggravation of shade, the relative chlorophyll content of corn decreased gradually, however that of soybean, mung bean and pepper increased. This indicated that soybean, mung bean and pepper could enhance the adaptability to shade environment by increasing chlorophyll content. PAR and atmospheric CO2 concentration were two main factors influencing the photosynthetic rate of corn, soybean, mung bean and pepper. Though agroforestry system reduced PAR of understory, it prevented midday depression of photosynthesis appeared in crops. It is an important aspect of interoperability of the synergistic use of solar energy. During the whole growth period, the average WUE of crops were: mung bean > soybean>corn>pepper. Compared with monoculture, the average WUE of soybean and mung bean increased by 78.6%, 82.8% respectively in different intercropping models.Compared with monoculture, Fv / Fm,ФPSⅡand qP of soybean, mung bean and pepper planted at 1m distance from the trees increased in different extents, yet qN P decreased gradually. As to corn, Fv / Fm showed an opposite trend. It indicated that, with increasing the degree of shade, the photochemical efficiency and the potential activity of light reaction center （PSⅡ） in soybean, mung bean and pepper increased. With more and more closer to trees, PAR, light compensation point （LCP） and light saturation point （LSP） of soybean, mung bean and pepper decreased, but apparent quantum yield （Ф） of three crops increased gradually. However, corn’sФshowed an opposite trend with other three crops. It indicated that the former three crops could adapt to low light condition, which could be able to use low-light at a relatively low light condition, so as to ensue the leaves to carry out normal photosynthesis.（3）During the growth period, mean soil moisture at 0-80cm layer of intercropping systems was lower than that of monoculture system. At a distance from walnut and plum from 2.5m to 1m, soil moisture decreased gradually in each treatment. Compared with monoculture, mean soil moisture of corn, soybean, mung bean and pepper was decreased by 1.91-11.49%, 0.5-13.24%, 0.5-10.17% and 0.6-9.68%, respectively. And the mean soil moisture of 3m×3m models was significantly lower than that of 5m×3m models. However soil moisture at 0-20cm layer of some intercropping models was slightly higher than that of monoculture. It may be the result of the“water effect”of walnut and plum that cause the redistribution of soil water.（4）Crop height, leaf area, leaf area index and leaf weight of four crops in agroforestry system less than those in monoculture system. At a distance from walnuts, plums from 2.5m to 1m, crop height, leaf area, leaf area index and leaf weight of four decreased gradually in different intercropping systems, and they were significantly lower in 3m×3m intercropping models than those in 5m×3m. In comparison with monoculture, crop height of corn, soybean, mung bean and pepper in the mature period decreased by 4.8-37.6%, 6.6-47.3%, 8.2-47.2% and 4.6-31.6% respectively; leaf area decreased by13.7-56%, 15.9-66.6%, 15.3-63.6% and 6.2-32.2% respectively; leaf area index decreased by 2.5-35.1%, 2-36.3%, 3.6-47.8% and 3.2-40.7% respectively, and leaf weight decreased by 8.4-55.2%, 23.6-66.1% and 26.1-54.4% , 9.1-48.9% respectively.（5）At a distance from walnuts, plums from 2.5m to 1m, biomass and yield of four crops were reduced gradually in different intercropping models, and they were significantly less in than 3m×3m intercropping models than those in 5m×3m. Compared with monoculture, mean biomass of corn, soybean, mung bean and pepper in the mature period was reduced by 22-62.3%, 1.6-47.2%, 12.6-40.9% and 21.2-56.7% respectively; mean yield reduced by 24.8-65.3%, 13.3-50.2%, 26.3-62.7% and 37-67.4% respectively.The correlation analysis results indicated that competition for light is one of the key factors decreasing the yield of corn, soybean, mung bean and pepper. Soil moisture at 0-40cm layer had a positive correlation with crop height, biomass and yield of corn, soybean, mung bean and pepper. It showed that soil moisture was one of main factors that influenced the crop productivity.（6）Analysis on combined effects of improving ecological environment, enhancing land use efficiency and increasing the economic effects of the different intercroppting models showed that walnut intercropping with soybean and mung bean, and plum with soybean in the 5m×3m tree spacing system were three models suitable for the test area.