Study Of Growth Decline Mechanism Based On Root Of Robinia Pseudoaatcia On Coastal Saline-alkali Soil

Growth decline mechanism based on root of Robinia pseudoacacia in coastal saline-alkali soil wasclosely related to salt stress. In-depth study of root distribution law in the soil of different declineR.pseudoacacia individuals, effects of salt stress on physiologic characteristics and morphologicdevelopments of Robinia pseudoacacia roots were essential to reveal the growth decline mechanism ofblack locust in Coastal Saline-alkali Soil.Test I: The test was based on the pure R.pseudoacacia forest of25a in the coastal saline-alkali soil, bystand survey, felling and sampling, trunk analysis and total digging to study the relevance of root biomassand aboveground; by drilling the soil core to research25a R.pseudoacacia plantation root samples taken inthe growing season in Coastal Saline-alkali Soil; The spatial distribution characteristics of the root simple(fine root and coarse root) biomass, specific root length (SRL), root length density (RLD), the root surfacearea index were studied. The research shows the results as follows:(1) The difference of roots morphological characters of different R.pseudoacacia degrees wassignificant. Quality and basal diameter increased with the increases of diameter class; root parameters ofmedium and dying tree compared with healthy tree appeared different degree decreased: root length,quality of root and basal diameter of root of first lateral root of medium and dying tree compared withhealthy was decreased45.31%,60.11%,62.38and32.51%,56.92%,57.62%; root length, quality of rootand basal diameter of root of second lateral root of medium and dying tree compared with healthy wasdecreased38.54%,49.61%,36.76%,38.18%and40.12%,68.99%,39.71%,76.06%.(2) The standing root biomass of different degree decline R.pseudoacacia was different. The healthtotal fine root biomass was14960.73g·m-3, fine living root (less than2mm) biomass was2040.24g·m-3,account for13.64%, death fine root (less than2mm) biomass was339.11g·m-3, account for2.27%, fineliving root (more than2mm) biomass was12581.38g·m-3, account for84.09%; The medium tree total fineroot biomass was12707.93g m-3, fine living root (less than2mm) biomass was1754.18g·m-3, accountfor13.89%, death fine root (less than2mm) biomass was497.3g·m-3, account for3.28%, fine living root(more than2mm) biomass was10456.45g m-3, account for82.83%; The dying tree total fine root biomasswas14960.73g·m-3, fine living root (less than2mm) biomass was413.73g·m-3, account for10.59%,death fine root (less than2mm) biomass was255.05g·m-3, account for5.43%, fine living root (more than2mm) biomass was3940.75g·m-3, account for83.97%.(3) The fine root seasonal sensitivity of different decline degree black locust population was different.The coarse root biomass of medium tree and healthy tree was at a significant level (P=0.016), the dead fineroot biomass of medium tree and healthy tree was at a very significant level (P=0.001), the fine living root biomass of medium tree and healthy tree was at a significant level (P=0.034). The difference of rootbiomass of dying tree and healthy tree was at a very significant level (P=0.009, P=0.003, P=0.009).(4) The vertical distribution characters of root parameters of different decline degree plantation wasdifferent, all could withquadratic polynomial. With increased of soil depth and decline degree, rootparameters value decreased, differences of groups was significantly (P＜0.05). The specific root length(SRL) of different decline degree manifested as: health was better than medium tree and better than dyingtree at the same soil layer.(5)The biomass between above-ground, whole-tree, lateral branch, crown, trunk and root weresignificant correlation, the relevance could established a simple linear model; tree height was notsignificantly related to root biomass; DBH with root biomass was at a very significant level.Test Ⅱ: The test used annual black locust seedling as testmaterial, according to actual content in soilof coastal saline-alkali, setting4concentration gradient, root physiologic indexes, and photosyntheticcharacteristics were studied respectively at the8thd,15thd,22ndd,29thd,36thd and42ndd after treated withsalt stress, and data of morphologic characteristics were obtained at the42ndd.(1)Morphologic Characteristics: Salt stress significantly affected the growth and development of blacklocust seedling. With the increased of salt stress, the indicator includes mean root length, mean root surfacearea, average number of roots, relative growth of basal diameter, relative growth of seedling height, etcshowed decrease trends. The higher the salt stress level was, the longer the mean root length was.(2) Physiology and biochemistry Characteristics: low salt stress could promote the activity of SOD, whilehigh salt stress could inhibite it, and under medium salt stress, the activity of SOD showed S curve. On thecontrary, activity of POD in low and medium salt stress indicates "rise gradually-drop rapidly-risegradually", and in high salt stress, it demonstrated "rise first and then drop"; with the time passing, theactivity of roots would decline when the salt stress increase; moreover, when the processing time becamelonger and the salt stress became higher, the degree of root hurt and content of MDA was increasing.(3) Photosynthetic indexes: with the increase of salinity, water saturation deficit (WSD) becamesignificantly high; while stomata conductance of low concentration salt stress treatment was higher thanthat of control, medium and high concentrations salt stress treatments were lower than that of control, andnet photosynthetic rate had a close relation with stomata conductance.(4) Results of the correlation analysis: mean root length with mean root area, relative growth of basaldiameter with mean root length, relative growth of seedling height with mean root length, the number ofroots with mean root length, branchs dry weight with mean root length, relative growth of basal diameterwith mean root area, the number of roots with mean root area, branches dry weight with mean root area,relative growth of seedling height with the number of roots, the number of roots with branches dry weight,root dry weight with leaf dry weight, root activity with root POD activity, branches WSD with root WSD,leaf WSD with root WSD, total chlorophyll content with root WSD, total chlorophyll with branches WSD,net photosynthetic rate with stomatal conductance showed very significantly positive correlation; root dryweight with mean root length, leaf dry weight with mean root length, relative growth of seedling heightwith mean root area, root dry weight with mean root area, leaf dry weight with mean root area, relative growth of seedling height with relative growth of basal diameter, the number of roots with relative growthof basal diameter, root dry weight with relative growth of basal diameter, leaf dry weight with relativegrowth of basal diameter, root dry weight with relative growth of seedling height had significantly positivecorrelation; net photosynthetic rate with root with root WSD, net photosynthetic rate with branches WSD,net photosynthetic rate with leaf WSD, net photosynthetic rate with total chlorophyll, root activity with rootinjury degree were negative relationships; mean root diameter with root dry weight, root injury degree withroot SOD activity, stomatal conductance with root WSD, stomatal conductance with leaf WSD hadsignificant negative correlation.