Effects Of Different Sizes Of Quercus Acutissima Seeds On Seedling Growth

Quercus Acutissima Carr.is a typical ectomycorrhizal tree species,an important energy and timber species in China,and is widely distributed,playing an important ecological and economic value.Roots and their symbiotic mycorrhizal fungi are important carriers of plant nutrient acquisition,and photosynthate produced by aboveground leaves meet the carbon demands of roots and mycorrhizal fungi.Therefore,the synergistic changes of aboveground and underground resource harvesting organs are important factors affecting plant growth.Seed size variation,especially within the same species,is a common phenomenon in nature,affecting seed germination and seedling growth.However,there are few studies on the ecological effects(seed germination,seedling size,seedling physiology)of seed size within species,as well as the relationship between seed size and aboveground(leaf)and underground(root and mycorrhizal)resource acquisition strategies of seedlings.These studies are of great value for plantation construction and vegetation restoration.In this study,we took Quercus Acutissima Carr.as the object,the seeds were divided into four size classes: the largest class(XL,seed width greater than 20 mm);Larger grade(L,seed width 18-20 mm);Medium grade(M,seed width 16-18 mm);Minimum grade(S,seed width less than 15 mm).We carried out seed germination experiment for 50 days for the four grades of seeds respectively to determine the seed germination rate.In addition,a 10-month pot experiment was conducted to determine the morphology of the seedlings,as well as root-leaf morphology,physiological and chemical traits.Meanwhile,5 seeds of four grades were selected to determine the nonstructural carbon content of the seeds to compare the non-structural carbon content difference between the seeds and the fine roots of the seedlings.The main experimental results are as follows:Ecological effects of seeds:(1)About seed germination rate: M grade seed germination rate was significantly higher than other grade seeds;There was no significant difference in seed germination rate of S,L and XL grades.(2)Seedling size:there were no significant differences in seed seedling biomass(stem,leaf,taproot,lateral root,above ground,below ground and total biomass),plant height and base diameter of S,M,L and XL classes.(3)Seedling physiology: The transpiration rate of M and XL seed seedlings was significantly higher than that of L seed seedlings,but the photosynthetic rate and stomatal conductance of the four seeds were not significantly different.The respiration rate of M grade seed seedlings was significantly higher than that of L grade seed seedlings based on absorption root weight,but there was no significant difference in respiration rate based on root length.(4)The content of nonstructural carbon in fine roots(diameter less than 2 mm)and seeds: the content of nonstructural carbon in fine roots of seeds of XL and L grades was significantly higher than that of seeds of S and M grades;The non-structural carbon content of S grade seeds was significantly higher than that of the other three grades.Resource acquisition of seedling roots and leaves:(1)Intraspecific variation of root traits: For the absorbent roots(the few roots with primary structure at the end of the root branch,the first 3 order roots in this experiment),the diameter of the absorbent roots was strongly negatively correlated with the root length(root length per unit root biomass),which constituted the foraging dimension of the roots.The tissue density of root is independent of the foraging dimension,which constitutes the economic spectrum dimension of root.(2)Variation of leaf traits: leaf size(represented by single leaf area)was coupled with leaf economic spectrum traits(specific leaf weight and specific leaf area),and they were independent of leaf hydraulics spectrum traits(vein density and vein diameter).(4)Relationship between seed,root and leaf traits: seed size had no relationship with leaf traits(leaf economic spectrum,leaf hydraulics spectrum,leaf size)and root traits(root foraging dimension and root economic spectrum dimension);There was no relationship between the dimensions of leaf character and the absorbent root.(4)In terms of root strategy and mycorrhizal strategy,there was no difference in seedling root strategy traits(root diameter,specific root length,tissue density)and mycorrhizal strategy traits(mycorrhizal fungal infection rate)for seeds of different sizes.The community composition of mycorrhizal fungi in seedling roots(genus level)was significantly different among seeds of different sizes and grades.These results suggest that seedlings produced by larger seeds do not have a growth advantage;This may be due to the resource acquisition strategy of seed size independent of root-leaf,that is,not all large hemp oak seeds have high photosynthetic and root absorption capacity,which is different from the traditional cognition that "larger seeds have more growth advantages".These results provide new insights into the ecological effects and mechanisms of seed size at intraspecific scale,and play an important role in the management,development and utilization of Quercus,an important economic forest.