| Artificial forestation is one of the core contents in environment management and resource utilization of waterlogged floodplain currently. Poplar, which is a fast-growing, flood-resistence and widely-used tree, has become one of the preferred species in the seasonally flooded lands of the middle and low reaches of the Yangtze River.But flooding-stress is still the main limited factor of hindering poplar growth in waterlogged floodplains, resulting in huge losses of timber production, and even plant death. At present, the mechanism of flood-tolerance in poplar is unclear, and the influence of the roots and aerial parts on the tolerance of poplar to flooding stress is also rarely reported.Two full-sib family clones LS1 and LS2,origin from Populus deltoides cv.Lux ex. 1-69/55 (flood-tolerant)× P.simonii (flood-susceptible), respectively tolerant (LS1) and susceptible (LS2) to flooding stress,were used as the materials in the re-search.The two materials were used as rootstocks and scions for grafting respectively.So six combinations (scion/rootstock) of LSI and LS2:namely, self-grafted LS1 (LS1/LS1) and LS2 (LS2/LS2),LS1 grafted onto LS2 (LS1/ LS2),and LS2 grafted onto LSI (LS2/LS1),non-grafted LSI (LS1) and LS2 (LS2),were exposed to two water regime treatments. The research used the non-grafted LS1 and LS2 as the control materials to investigate the growth conditions, photosynthetic characteristics, membrane permeability and the indicators of physiology and biochemistry about plants of the six combinations,and explore the roots and aerial parts (stems and leaves) on the tolerance of poplar to flooding stress.The main results are as follows:1.During the flooding treatment, all the watered (CK) plants grew vigorously, and no defoliation and death occurred.Flooded plants was obviously influenced in morphology and growth, including decreased stem growth,retarded leaf initiation and development,chlorosis and abscission of leaves,as well as development of hypertrophied lenticels. The more seriously adverse changes were observed in LS1/LS2, LS2/LS2 and LS2 plants. At the end of the research, survival rate of all the six combination plants were 100% in CK, while 100%,100%,93.33%,26.67%, 6.67%and 20.00% survival rates,respectively, were observed in flooded plants of LS1,LS1/LS1,LS2/LS1,LS1/LS2,LS2/LS2 and LS2. Additionally, flooding stress resulted in rot and death of the old roots.After drainage, the plants with roots of LSI (LS1,LS1/LS1 and LS2/LS1) regenerated much more new vigorous roots than the plants with roots of LS2 (LS1/LS2,LS2/LS2, LS2).Therefore,we thought that the plants behaved better when root is flood-tolerant LS1.2. Flooding stress significantly restrained the growth of six combination plants.Growth of height, root-collar diameter and total biomass accumulation were significantly lower in flooded plants when compared to controls in all the six combinations plants. The plants with rotots of LS1 (LS1, LS1/LS1, LS2/LS1) were displayed significantly superior growth rate than the plants when the root is LS2 (LS1/LS2, LS2/LS2, LS2) in all the indicators of growth.On day 21 of the flooding period, reduction of height growth due to flooding was 11.46%,13.34%,19.91%, 47.28%,54.88% and 50.16%in LS1, LSI/LS1, LS2/LS1, LS1/LS2, LS2/LS2 and LS2,respectively.These values in root-collar diameter growth,were 6.20%,7.41%, 12.00%,41.45%,40.74% and 36.99%.For total biomass accumulation,these values were 24.35%,28.79%,30.54%,65.69%,68.54% and59.91%. We would know that the decrease of values due to flooding in plants with roots of LS2 (LS1/LS2, LS2/LS2, LS2) was more serious than the plants with roots of LS1 (LS1, LS1/LS1, LS2/LS1). Thus, flooding stress affected the plants with roots of LS2 more adversely than the plants with roots of LS1.For the grafted plants, which have the same genotype rootstock and different genotype scion, these change values were similar.On the contrary,the plants with the same genotype scion and different genotype rootstock,these change values were greatly different.Mean while,the ratio of roots/shoots in the six combinations plants was 2.33%,2.93%,8.05%,15.92%,36.50% and 34.68% respectively. Changes in the roots/shoots ratios illustrated that the roots underwent more severe flood injury than the aboveground organs, especially when the roots are LS2.3. Flooding stress significantly influenced the values of leaf gas exchange. With the prolonged soil flooding,values of Pn,Tr and Gs gradually decreased in all of the flooded plants,and reached their minimum values on day 21 of the flooding period, which was significantly different with the control plants,but not of Ci/Ca. At this time, greatly superior change rate to flooding of Pn,Tr and Gs were found in the plants with roots of LS2 (LS1/LS2,LS2/LS2,LS2) indicating severe injury in photosynthetic system and inhibition of photosynthetic activity.During the terminal recovery stage, all of the leaf gas exchange parameters increased rapidly.And the plants when roots are LS2 had slower recovery speed.than the plants with roots of LS1.Thereby, throughout the whole flooding period, the plants with roots of LS1 (LS1, LS1/LS1, LS2/LS1) displayed significantly slighter flood injury than the plants with roots of LS2.4.Throughout the whole flooding period, all the values of Fv,Fv/Fm and Fv/Fo in all flooded plants significiently declined.The plants with roots of LS2 (LS1/LS2, LS2/LS2,LS2) had greatly superior change rate to flooding of Fv,Fv/Fm and Fv/Fo than the plants when the roots were LS1.The values of Fv,Fv/Fm and Fv/Fo in all of the flooded plants increased rapidly after flooding were removed.and the plants with roots of LS2 (LS1/LS2,LS2/LS2,LS2) had a slower recover speed.At the end of the recovery stage, the plants with roots of LS1 (LS1,LS1/LS1,LS2/LS1) recovered to the control level,while values were still much lower than control when roots are LS2.5.Under flooding treatment, all of the flooded plants declined root activities gra-dually at different degree and reached the lowest values on day 21.At the time,change rate to flooding in LS1,LS1/LS1,LS2/LS1, LS1/LS2, LS2/LS2 and LS2 were 48.70%,48.27%,60.87%,82.18%,87.73% and 81.71%, respectively.Thus less changes were found in the plants when roots are LS1 (LS1,LS1/LS1,LS2/LS1) than the plants have roots of LS2.During the recovery stage, root activities increased rapidly, accompanied with regeneration of new vigorous roots.And the plants with roots of LS2 regenerated less vigorous roots.than the plants when the roots are LS1, resulting a slower recover speed,indicating more severe flood injury in the plants with roots of LS2.6. Soil flooding significantly elevated the relative membrane permeability (RMP) of leaves and Malonaldehyde (MDA) contents of leaves and roots in the flooded plants. On day 21, rate of change due to flooding of RMP in LS1,LS1/LS1, LS2/LS1, LS1/LS2,LS2/LS2 and LS2 were-185.46%,-218.88%,-213.02%,-488.13%,-459.33% and-479.23%,respectively.These values of leaf MDA contents were-64.10%,-55.29%,-62.16%,-135.14%,-138.40% and-137.02%, For MDA contents of roots, these values were respectively,-190.91%,-166.3%,-150.32%,-216.97%,-229.54% and -215.89%. It is clear that, significantly higher changes in the plants with roots of LS2 indicated more severe flood injury in the plants.The values of RMP and MDA contents reduced after the flooding stress was removed.The plants with roots of LS2 had a lower recover speed than the plants when roots are LS1.In conclusions, performance of the plants with flood-tolerant root of LS1 (LS1, LS1/LS1, LS2/LS1) were significantly better under soil flooding than the plants with flood-susceptible root of LS2 (LS1/LS2, LS2/LS2, LS2).Thereby,we deduce that root genotype play a vital role in flood-tolerance of poplar,regardless of scion or stem.Meanwhile plants with flood-tolerant genotype root behaved better than with flood-susceptible genotype root under flooding conditions. |
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