Effects Of Flooding Stress On Growth And Physiological Characteristics Of Cerasus Campanulata Seedlings

For the attracting flowers and excellent adaptability,Cerasus campanulata has been widely cultivated in China.In the horticultural production and application,flooding is one of the most serious threats for ornamental plants.To discover the flooding tolerance of C.campanulata and the potential flooding recovering method,we carried out two sets of experiment with C.campanulata seedlings.For the flooding experiment,we stressed seedlings with three different levels of waterlogging(mild stress-the water merged half of the substrate,moderate stress-the water merged the whole substrate,severe stress-the water merged 2 cm higher than substrate).We studied the response mechanism of the growth and physiological characteristics of C.campanulata seedlings under different flooding gradients and different flooding time(3,6,9 and 12 days),and determined the adaptability of C.campanulata to flooding stress.In the flooding recovering experiment,we compared physiological characters of flooding C.campanulata seedlings with or without exogenous spermidine treatment.The physiological characters detected here included chlorophyll content,antioxidant enzyme activities and osmotic adjustment substances of C.campanulata.The main results are as follows:(1)The seedling height,ground diameter,total biomass accumulation and root-shoot ratio of C.campanulata seedlings decreased along with the aggravation of the stress.Flooding also affected the biomass accumulation and distribution of above-ground and underground organs.The biomass distribution of CK group was root>stem>leaf,while the trend turns to stem>root>leaf under flooding stress.Flooding promotes the C.campanulata transfer the biomass from under-to above-ground organs.The root length,root surface area,root volume,average root diameter and number of root tips in the stress group were significantly lower than those in the CK.(2)Flooding stress had a significant response to the water content of the leaves of C.campanulata seedlings.The relative water content of leaves gradually decreased with the aggravation of the stress.The relative water content in the stress groups decreased by 6.08%to 23.45%,which was significantly different from that of CK(P<0.05).However,the specific leaf weight increased 22.30%-31.57%after 12 days treatment(P<0.05).(3)Flooding stress inhibited the photosynthesis of C.campanulata seedlings,resulting in a significant decrease in Pn,Gs and Tr.Among them,after 12 days of flooding,the Pr of T1,T2 and T3 groups decreased by 64.17%,86.26%and 91.56%compared with that of CK.However,the Ci decreases at the initial stage and increases at the later stage,and the Ls and WUEinst was the opposite.By comparing the relationship between the Ci and the Ls,we found that the Pn decreased at the initial stage of flooding due to stomatal limitation,and this inhibition was caused by non-stomatal limitation at the later stage of stress.(4)Flooding stress significantly affected the membrane lipid oxidation,osmotic regulation system and free radical scavenging system of C.campanulata seedlings.The content of malondialdehyde,soluble sugar and proline increased with the increase of stress degree and time,and the soluble protein showed a trend of increasing at the initial stage and decreasing at the later stage.This indicated that flooding stress promoted the increase of SOD,POD and CAT enzyme activities,and with the extension of stress time,the three enzyme activities gradually decreased.These results indicated that C.campanulata may resist the damage caused by flooding by regulating the osmotic regulation system and reactive oxygen species scavenging system.(5)The correlation analysis was carried out on the various indicators of C.campanulata,and the correlation of some indicators are significant(P<0.01).For example,Tr was positively correlated with Gs,the correlation coefficient(R)was 0.983,between proline and soluble sugar(R=0.955)and between SOD and CAT(R=0.929)and between root length and SPAD value(R=0.900).(6)In this experiment,we found that C.campanulata seedlings outperformed at the 0.25 mmol/L concentration of exogenous spermidine.Spraying spermidine the flooding-stressed C.campanulata seedlings can increase the POD activity of leaves,reduce the content of malondialdehyde,soluble sugar and soluble protein,and reduce membrane damage.It also reduced the decline rate of chlorophyll a,chlorophyll b and carotenoids.These indicated that spraying spermidine can recover the damage of C.campanulata by flooding stress.The above results show that long-time flooding stress leads to death,and the C.campanulata seedlings can only cope with the short-term flooding stress.In addition,exogenous spermidine could recover the flooding-stressed C.campanulata by regulating the antioxidant capacity and reducing the content of osmotic regulating substances.This study provides a certain reference for the planting and management of C.campanulata in Hunan and similar areas with high rainfall and high groundwater level.