Because of its characteristics such as high pH value，high-salt content，poor structure and low fertility，saline and alkali soil has harmful effect on both plant growth and eco-environment. Therefore，it is important to improve and utilize the saline and alkali soil. According to the relevant research in China and abroad，this paper reviewed the main causes of the saline and alkali soil，including soil parent material，texture，landform，neotectonics，hydrological condition，human activities，and analyzed biotechnologies such as germplasm screening，distant hybridization and genetic engineering as well as non-biological technologies including tillage fertilization，covering technique，hydraulic measures，chemical measures and electro-magnetic methods. And suggestions are raised，namely further improving regional salt forecast system and giving play to plant-microorganism combined bioremediation for the soil.［Ch，52 ref.］
Pot experiments were conducted to research vegetative and physiological changes of Prunus maritima seedlings under NaCl stress. The results showed that its biomass was firstly increased,and then decreased with an increase in NaCl concentration,and its growth was restrained under high level of salinity. Contents of MDA,relative electric conductivity in its leaves were increased to different extents and so were contents of both proline and soluble protein; and the activity of superoxide dismutase,of peroxidase,of root reached a maximum under 6 g/L NaCl in the irrigation water, then reduced significantly at 9 g/L. Changes of net photosynthetic rate,of water use efficiency,of apparent photosynthetic electron transport rate,and of real photochemical efficiency were similar to those of the two enzymes,and also achieved maximun under 6 g/L NaCl,while alterations of intercellular CO2 concentration were contrary to those of the above photosynthetic indexes. In summary,Prunus maritima has high salt resistance,and grows well under condition that NaCl concentration is about 6 g/L.
Through the research on the trees' phytoextraction of heavy metals in the soil of South China,the results were as follows:the content of different heavy metals such as Pb,Cd,Hg,As differed widely in same tree's leaves,and that of the same element also differed in different trees.The content of heavy metals in the leaves usually went up as environmental pollution increased,so the heavy metals' content of the trees in downtown area was more than that in suburb areas.The mean contents of Pb,Cd,Hg,As in downtown area were increased by 62%,103%,187%,104%respectively than those in suburb areas.It also showed that Ficus beniamina'Exotica',F.religiosa,Delonix regia,Araucaria cunninghamii had the phytoextraction of Pb,Cd,Hg,As respectively,thus planting these trees could be a good way to remedy the heavy metal pollution.Bauhinia variegata,Araucaria cunninghamii,F.altissima,F.microcarpa could be used to monitor the pollution of heavy metal as a result of their sensitivity to Pb,Cd,Hg,As respectively.Thus it is significant for rational planting sensitive trees and hyperaccumulating trees in urban afforestation and other ecological construction,which can monitor and repair heavy metal pollution.
As we all known,a well-planned fertilization method plays a very important role in poplar seedling production.This paper focused on the question whether formulated fertilization is good for the the growth of poplar seedling and it explores the best one in final.In the relative experiment for this question,nine kinds of formulated fertilizer solutions mixed with N,P,K at different concentration ratio were used during the growing process of poplars named as Populus deltoids Bartr.cv.'Lux'× P.deltoides Bartr.cv.'Havard'.The results showed that the nine kinds are all favorable for poplar seedling growth and the third one with N,P,K at concentration ratio of respectively 17 mg/L,10 mg/L and 8.5 mg/L,mostly increased the biomass for the root,bark,branch,leaf and all of them as a whole.Comparing with the control,they are increased by 294%,66%,96%,126% and 118% respectively.According to the regression equation for the data obtained from the experiment above,the rational concentration of N,P,K for seedling's growth of poplar was 13.03 mg/L,3.76 mg/L and 2.24 mg/L respectively,while for the root growth that was 2.36 mg/L,2.12 mg/L and 4.71 mg/L respectively.Therefore,the amount of fertilizer N should be increased in the early stage of growth when the fertilizer P and fertilizer K were being used,but in later stage of growth the amount of fertilizer N should be controlled properly and in turn the amount of fertilizer P and fertilizer K should be increased,which was favorable for improving stress resistance and equality of the poplar's seedlings.So the formulated fertilization would promote the growth of seedling and root of poplar and increase the biomass production,in particular,N was good for growth of seedling height and tissue biomass,while as K was favorable for root growth.
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