| The loess plateau ecological environment is fragile, and the water is the most important factor for plant growth in this eara. Black locust as the one of tree species is main detected soil-water conservation and afforestation pioneer in the loess plateau. Because of this species can be growth well in both environment as the moist fertile soil and dry conditions be barren, also it has high adaptability and resistance, so this speices has performed important roles in vegetation restoration and ecological construction in the loess arid and semiarid region. The study of photosynthetic characteristic of Black locust under different soil water status, which is has important theoretical and paractical significance for the scientific palnation and forest management of black locust. In this study, we used the annual cocust potted plants as research object, anysised the photosynthetic characteristic of Black locust under different soil water status, and discussed the environment factor on the influence of the cocust photosynthesis way and degree. The main results as follows:(1) under the condition of different soil moisture locust photosynthetic physiological parameters contrastIn different soil moisture conditions, the leaf photosynthetic physiological parameters with the order of the day is a trend change is consistent. Net photosynthetic rate of diurnal variation present diauxie curve form, there is a clear at noon nap phenomenon, and the morning peak number is significantly bigger than the afternoon peak number.Under the condition of different soil moisture detected, physiological parameters in the contrast of photosynthesis different soil moisture conditions, leaves the same photosynthetic physiological parameters detected; the day is a trend change is consistent.The dynamic process of net photosynthetic rate and dynmic process of stomatal conductance has similar trendency of black locust leaves.The net photosynthetic rate and the stomatal limitation of black locust leave reduced in two ways. From8:00to10:00, the net photosynthetic rate was decrease by non-stomatal control; from10:00to12:00, the net photosynthetic rate was decrease bystomatal control;(2) Although the photosynthetic physiological parameters in different soil moisture conditions, the change trend of similar, but to drought stress have a remarkable effect on them. In a full day seven test time point, the net photosynthetic rate, stomatal conductance, and transpiration rate, stomatal limitation value, and carboxylation efficiency are performanced as: Normal soil moisture> Moderate drought stress> Severe drought stress. The intercellular CO2concentration is behaved for Severe drought stress> Moderate drought stress> Normal soil moisture. Vapor pressure deficit in three kinds of soil moisture conditions change of small scale.(3) The black locust leave’s water use efficiencies have showed different results under different water status, from6:00ot12:00:Normal soil moisture> Moderate drought stress> Severe drought stress; at14:00:Moderate drought stress> Normal soil moisture>> Severe drought stress. Under severse drought stress, although the black locust leaves showed low water use efficiencies in most time, but it start to increase from12:00. The water use efficiency increased high level at18:00, which is higher than Normal soil moisture and severe drought stress.The net photosynthetic rate, stomatal conductance, and transpiration rate, stomatal limitation value and carboxylation efficiency are performanced significant difference in mean number among one day:Normal soil moisture> Moderate drought stress> Severe drought stress. The intercellular CO2concentration is behaved significant difference for Severe drought stress> Moderate drought stress> Normal soil moisture.(4) Different environment factors effect on physiological parameters under different soil moisture statusDifferent environment factors are including photosynthetically active radiation, air temperature, air CO2concentration, and air relative humidity. The net photosynthetic rate, stomatal conductance, and transpiration rate, stomatal limitation value and carboxylation efficiency were choosen as main physiological parameters. We discussed different environment factors effect on the physiological parameters using path analysis.(5) After comprehensive consideration of the direct size coefficient, indirect size coefficient, simple correlation coefficient, we got the results as air temperature and air relative humidity are important environment factors effect on the black locust physiological parameters under different water status (Severe drought stress, Moderate drought stress, and Normal soil moisture).Photosynthetic physiological behavior has sensitive changes in different environment while the water stress performanced on the black locust seeding. So, environment factors are direct to infulunce the physiological parameters in this study. Along with the soil drought stress increased, the black locust seedings depend on the water in the air sensitively and denpendently in order to effective to add the water for them. The different physiological parameters have high correlation with air relative humidity and increased constantly. Moreover, four multiple regression equation were build as the net photosynthetic rate, stomatal conductance, and transpiration rate, stomatal limitation value and carboxylation efficiency in different environment factors. |
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