Characteristics Of Drought And Salt Resistance Of Robinia Pseudoacacia

This paper studies the characteristics of drought resistance and saltresistance of young tree clones as well as germination physiology of seed of Robiniapseudoacacia. Resistance experiments were carried out in pots with 1-year oldroot-cutting plants of 6 clones: Robinia pseudoacacia CL. 'Luci 1'(L1), R.pseudoacacia CL. 'Luci 59'(L59), R. pseudoacacia CL. 'Luci 78'(L78);R.pseudoacacia CL. 'Anhui 1'(W1), R. pseudoacacia CL. 'Dongying 56'(D56), and R.pseudoacacia CL. 'dongying 327'(D327). Germination tests were performed usingseeds of 2 families (61 and 07). The germination physiology of seed were studied byPEG simulated drought and different concentrations of NaCl solution. The changes ofgrowth, photosynthesis, osmotic adjustment, defensive enzymes, distribution of14C-photosynthates and water status were investigated and the limiting factors ofphotosynthesis of young tree clones were analyzed under continuous drought,controlling gradient of water in soil, continuous adding salt and controllinggradient of salt in soil, respectively. The impacts of water stress on polyamine and theABA quantity changes in young tree caused by root-shoot communication in responseto drought were examined. The growth and characteristics of ionic distribution,absorption and selective transportation were studied under various degrees of saltstresses. The stress resistance mechanisms of black locust clones were elucidated forthe first time, and the suitability of black locust clones on water, salt solution, andwater-salt stress was put forward and preliminarily conformed. The main results of thestudy are as follows:The germination physiology of black locust seed under stress: Black locustseeds had rather high germination capacities and vigor level under –2bar waterpotential or 0.3% salt concentration. There was the difference of stress resistancesamong different families. Suitable pretreatments could improve germinationcapacities of black locust seed. The result showed that seed germination would beinhibited by salt solution infusion and enhanced by 3-5℃ low temperature treatment.10% PEG solution treatment could improve seed germination under drought stressand alleviated inhibition of salt on seed germination. There were cross-adaptationphenomenon between drought resistance and salt resistance.The drought resistance characteristics and drought resistance physiology ofblack locust clones: Black locust had strong automatic regulation ability and couldrapidly respond to drought by adjusting its metabolism under the condition of droughtstress. For four black locust clones, as the intensity of drought stress increases, thephysiological indexes fluctuated more violently under the condition of sustained soilwater stress than under the treatment of controlled soil water content gradient.Drought stress significantly inhabited the growth of clones. After 12 days'continuous soil water stress and when the soil water content reaches 10%, the heightgrowth of L78,W1 and L59 were small, and L1 nearly stopped growing. Black locustincreased its root-shoot ratio to adapt to drought stress. for example;L78 increased itsmoisture of leaves to preserve leaves' function and contained more photosynthesisand higher vigor of NR enzyme under 30%FFC. In terms of the height increment,collar diameter, physiology and biochemistry characteristics, the drought resistanceabilities of four black locust clones were ranked as follows: L78> W1>L59>L1.Black locust clones' photosynthesis was very sensitive to drought stress, Pn ofblack locust clones decreases linearly with decreasing soil water contents. Andtemperature is an important factor, the suitable temperature ranges from 20 to 30℃.Following drought stress degree increases, intercellular CO2 concentration(Ci),chlorophyll contents increase and transpiration rate(sTr), stomatal conductance(Gs),CO2 assimilation ability decrease. The responses of W1, L1 were more rapid than L59,L78. Four clones were divided into two groups on the base of their photosynthesischaracteristics and mechanisms of drought résistance. High-WUE group included W1and L1, and high-photosynthesis rate group included L59 and L78.Black locust has a strong osmotic adjustment and the order is L78> L1> L59> W1.Under water stress, soluble sugars and Pro increased quickly and soluble proteindecreased. It was apparent that there was a critical point. And the critical value ofeach clone's is different.Polyamine (spermine SPM, spermdine SPD, and putrescencePUT) and defensive enzymes of black locust clones also expressed different changes.Under water stress, PUT and SPD gradually increased while SPM decreased (W1 wasan exception). W1 and L1 improved the activity of SOD, CAT and POD to protect cellstability, but L59 and L78 only improve the activity of SOD and CAT. Studies showsthat root can sense the soil water deficit and synthesize the drying signal —ABA tocommunication with shoots. Therefore stomatal movements can be adjusted andtogether with other additional adjustments (e.g. osmotic adjustment) was consideredinvolved in creating a new water balance under soil adverse condition. Afterwards,changes of ABA level in droughted-plants of black locust clones were typically astress response in root-shoot communication. After serious soil water deficit, ABAcontinues to rise up the level that can induce leaf abscission. Therefore,stressed-plants of black locust clones create a new water balance mainly bydecreasing evaporative surface area.According to water consumption characteristics, the 4 clones can be divided into2 groups, W1 and L78was in one group, L59 and L1 another.The salt resistance characteristics and drought resistance physiology ofblack locust clones Salt stress obviously suppressed growth of black locust clonesand raised their root-stem ratio .There were differences among different clones. D56belonged to the species of powerful salt resistance type;D327 and W1 was medium,L78was inferior.Pn of black locust clones decreases linearly under continuous increasing saltconcentration. Tr, Gs, Chl contents (including Chla Chla+b Chla/b) all decrease. Themore the salt solution concentration increase, the less Chlorophyll contents. There wereno significant differences among the 4 clones.Under salt stress, malondialdehydel(MDA), soluble sugar and Pro increasedquickly and soluble protein decreased. The studies showed that soluble sugar played aimportant role in osmotic adjustment. The osmotic adjustment capacity's order is L78>>W1 >D327>D56。Cell salt ions of black locust appeared compartmentation. Young trees activelyabsorb salt ions for osmotic adjustment under lower soil salt concentrations andselective absorption of mineral nutrition ions to contain ionic balance. The saltresistance ability of W1 and D56 was explained by that they could control absorptionof ions quite well and keep ionic balance.The drought resistance and salt resistance of black locust clones under soilwater and salt stress: It was most important to keep good growth under stressconditions. Using growth as an evaluating criterion, the research results showed thatthe ranked consequence were different under different stress combinations ofcontinuous time and salt grades. Comprehensive appraisal sequences were: W1> D327> L78.