Non-Structural Carbohydrate and Biomass Characteristics of Pinus yunnanensis Seedlings under Continuous Drought Stress
[Objective]This study aims to reveal the changes of Pinus yunnanensis seedling growth and non-structural carbohydrates(NSC)in response to persistent drought stress,in order to provide theoretical support for the population dynamics of this species and the formulation of rational management measures,as well as a basis for plantation establishment,especially seedling management,under drought conditions.[Method]A pot experiment was carried out on 2-year-old P.yunnanensis seedlings,and a weighed water control method was used to control the relative soil water content at 75％-85％(control),60％-70％(mild drought),45％-55％(moderate drought)and 30％-40％(severe drought)of the field water holding capacity to study the effects of different drought treatments on seedling ground diameter,seedling height,biomass accumulation and distribution and NSC content.[Result]1)The seedling ground diameter and seedling height growth,needles,stems,coarse roots and whole plant biomass all gradually decreased with increasing soil drought.However,fine root biomass gradually increased,with a significant increase of 22.79％under severe drought.2)The NSC content of seedling needles,stems and crude roots all increased to different degrees with increasing soil climate,with significant increases of 10.89％,45.37％and 30.70％under severe drought,respectively,while the NSC content of fine roots decreased to different degrees.There was difference in the ratio of soluble sugars to starch in various organs in response to drought stress,and the ratios were all greater than 1.Starch was the most important form of NSC storage in P.yunnanensis seedlings,mainly in stems and thick roots.3)Under drought stress,the biomass and NSC organ allocation ratios of P.yunnanensis seedlings changed in a similar pattern,i.e.the biomass and NSC allocation ratios of leaves gradually decreased with increasing soil drought,those of stems and fine roots gradually increased,and those of coarse roots first decreased and then increased.4)Seedling growth was generally significantly correlated with non-structural carbohydrates.Plasticity and PCA analyses showed that the plasticity indices for seedling height and ground diameter were relatively small,while the plasticity indices for needle biomass,fine root biomass ratio,stem starch,needle and stem soluble sugars/starch were higher and the load on the principal components was greater.[Conclusion]Drought stress significantly inhibits the growth of P.yunnanensis seedlings.When carbon availability is limited by drought stress,there is a trade-off between growth and NSC storage,i.e.biomass and NSC are allocated less to needles but more to fine roots,which is an important cause of slow growth in P.yunnanensis seedlings.P.yunnanensis seedlings adapt to drought conditions mainly by regulating needle and fine root growth,increasing storage of starch in stems,and maintaining a dynamic balance of NSC in needles and stems.
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