| Pinus elliottii×P.caribaeais the vital species for industrial raw material forest and fast-growing and high-yield plantation,and it plays an important role in solving the contradiction between supply and demand in wood and resin in C hina.Currently,Pinus elliottii×P.cariabea has the problem on the extensive management,especially the mistaken and abusive fertilization.According to the pot and field trials,the research was carried out by exploring the rules of nutrient requirements at seed ling stage,and the main limiting factors that made an influence on the trees in high-yield.Further,taking phosphorus which was the main limiting factor as the main research object,and thegenotypic variation in phosphorus efficiency was evaluated in different Pinus elliottii×P.caribaea clones.The main results are as follows:?1?In soil culture,phosphorus deficiency decreased the heights and diameters obviously with 16.3%and 12.1%,respectively,compared to the control at the seedling stage.The field trial indicated that calcium superphosphate or the diammonium orthophosphate as base fertilizer increased the height with 11%-24%at Yangjiang experimental site,while the calcium magnesium phosphate increased the height with 11%at Jiangxi.It can be seen from the results that phosphorus was the main limiting nutrient factor at the seedling stage of Pinus elliottii×P.caribaea.?2?The nutrient deficiency had significant effects on chlorophyll fluorescence parameters of needles,but the difference among clones was not significant.The F v/Fm,qN and NPQ were reduced,and qP increased in nitrogen and potassium deficient treatments,but the lack of phosphate had no significant effect on chlorophyll fluorescence parameters.?3?In the field trial,the total phosphorus concentrations were low in the needles.Sixteen months later with diammonium orthophosphate application in Yangjiang plantation,the needles of total phosphorus concentration at seedling stage were increased from0.67g·kg-1to 0.8-1.02g·kg-1.In Jiangxi plantation,the calcium magnesium phosphate increased the total magnesium concentration in needles remarkably rather than phosphorus,and the total boron concentration was also increased with borax and zinc sulfate added.?4?The P-efficient clones 23#and 38#,the P-inefficient clones 8#?12#?32#?22#?29#were screened initially with soil and sand cultured trials.The height,the aboveground and underground biomass of 23#and 38#were 33%and 34%,181%and 75%higher than the mass average in the sand culture under low P condition.?5?The low phosphorus stress had no significant effect on each indices in hydroponics.The P-inefficient clones had the same performance in soil and sand culture.However,4#?31#had a good performance in one culture and medium in another culture.It showed that sand culture was suitable for evaluation of Pinus elliottii×P.caribaea P-inefficient clones rather than hydroponic culture.The growth performances in every medium should be considered comprehensively for the selective breeding of P-efficient clones.?6?The root traits of clones in sand cultured trial varied largely.In low phosphorus treatment,the total root length and surface area of 23#?38#were higher than the mass avearge with 182%and 53%,21%and 48%,respectively.C lone 17#and 39#had excellent performances in aboveground biomass in soil cuture,while the total root lengths in sand culture were 36%and 35%lower than the mass avearge.C lone 29#had poor performance in the soil culture,in contrast,the total root length and surface area were outstanding in sand culture.The results indicated that the root traits at seedling stage could not be the main mechanism of forming P-efficient trait in Pinus elliottii×P.caribaea.?7?The root-shoot ratio of hydroponic cultured clones in low phosphorus treatment was apparently higher than the control.In the low phosphorus treatment,3#and 9#were twice than that in the control,31#and 38#were 70%higher than that in control,however,clone 46 had no obvious difference in different treaments.The result suggested that regulating the distribution ratio of dry matters in different tissues,which was probably one of the mechanism about P-efficient trait formation.?8?Phosphorus concentration in low phosphorus treatment was no significant difference in hydroponic cultured clones,but N/P of the mass avearge were increased from7.45 to 30.72,and the 38#ranked the last.In the no mal phosphorus treatment,the phosphorus concentration in aboveground parts of clones were remarkable different.C lone9#had the lowest and non-significant difference.In summary,as for the Pinus elliottii×P.caribaea at the seedling stage,P was the nutrient limiting factor for growth and accumulation of biomass.There were significant genotypic variation in phosphorus efficiency.The research had screened and obtained clone38#as P-efficient clone,and it could be used for resolving the forming mechanism of the P-efficient trait. |
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