Effect Of Salt-isolated Treatments On Soil Water And Salt Movement And Growth Characteristics And Photosynthesis Of Four Trees In Coastal Saline-alkaline Land

In order to explore the regularity that different salt-isolated measures affected on water-salt movement in coastal saline-alkaline land and the growth characteristics and photosynthesis of four trees(sophora japonica, ash trees, acacia and robinia idaho) and provide theoretical basis for afforestation tree species selection of corrective measures on inshore saline, we did a lot of work. According to field experiments, field tests and indoor tests, as the inshore saline with no salt-isolated measures was set to be the blank control, we studied the space-time change of soil particles and soil water content and electrical conductivity of soil on sample plots disposed by laying slag and sand on the bottoms of planting hole as salt-isolated covers and the relationship and change regulations between water-salt movement and both meteorological factors and unconfined water depth, and the effect different salt-isolated measures worked on the growth characteristic (livability, height, diameter, new shoots growth) of the four trees and Photosynthetic characteristics (photosynthetic diurnal variation characteristics and light response characteristics) . The study maked some contributions:(1) Effected by rainfall, evaporation and plant growth, groundwater depth in test sites was changed with time. The growing seasons could be divided into three stages, which were relatively stable period (from April to May), cataclymically period (from June to July) and lasting decline period (From September to Octomber).(2) Soil water content and soil conductivity movement on experimental area changed with seasons obviously. Soil water content was low and the salt was accumulated in the soil in spring; Soil water content was high and salt was washed in summer and salt content was steady in autumn. The proportion of evaporation and drop and groundwater depth was significant correlations with soil conductance, while the soil water content was significantly negative correlation with the proportion of evaporation and drop, and the soil water content were correlations with groundwater depth and significant correlations with soil conductance.(3)The salt-isolated treatments of slag and sand significantly reduce the soil electrical conductivity above the salt-isolated layer. In dry season, the salt-isolated layers can prolong the degree of soil salt accumulation. In rainy season, the salt-isolated layers strengthened the eluviation effect of rainfall. The soil desalinization ratio was between10% and 40% under salt-isolated treatments, while the ratio was 5% in the control. The salt-isolated layers influenced the soil moisture on its limited range of around little, and the influence on the overall is not obvious. From soil layers,the salt-isolated layers firstly had effect in 80¹00 cm soil profile. Then its influence scope was enlarged upwards, and it can slowdown soil salt fluctuation. From the reducing effect of salt-isolated treatments, slag treatment was better than sand treatment.(4)After taking the measurement of segregating salt, the content of main salt ions(Na⁺,Cl^- and HCO₃^-)in the soil significantly reduced. The soil ion content of surface layer is much more than other layers. After taking the measurement of segregating salt, the reduction is also significantly greater than the other layers. Seen from the material for segregating salt, slag is better than sand.(5)The conservative rate of each testing plant increased after salt-isolated treatments were taken. After salt-isolated treatments were taken, growth status of each species are better than the control, and new branches growth amount of slag treatment was 30% biger than the control, and that of sand treatment was 10% biger than the control, the growth increment of tree height and diameter at breast height varied significantly from different species and treatments. The effect of salt-isolated treatments on Sophora japonica was more effective than that on the other three species. The effect of slag salt-isolated treatment performence was the most significant amang all treatments.(6) As for the four tree species, salt-isolation measures can improve the photosynthetic capacity at different levels, effectively improve the diurnal variation of the mean of the net photosynthetic rate and transpiration rate , improve the moisture deficit situation at noon and afternoon, make photosynthetic diurnal variation curve stable (tending to typical single-peak and typical double-peaks). Salt-isolation measures have different influence with the four tree species in photosynthetic characteristics, which plays an important role in photosynthesis for Sophora japonica Linn. and Fraxinus chinensis Roxb., and does not play a significant role for Robinia pseudoacacia cv.idaho. and Robinia pseudoacacia Linn.. Salt-isolation measures can enhance the metabolic activity in the plant leaves, and the maximum net photosynthetic rate, the light saturation point, light compensation point,dark respiratory rate and apparent quantum efficiency of the four tree species are given different degrees of improvement than the contrast, of which the amplitude improved is more than 15%.From the improvements of the photosynthetic capacity of the salt-isolation measures, the effect of the slag is better than that of sand. From the seasonal change of the photosynthetic characteristics, the influence of the dry season is greater than that of the rain reason.