| Quercus vuriabilis is a typical oak species in China,as well as an important support tree species for ecological construction in northern regions.It makes up a huge part of the forest vegetation in China and even around the world.More importantly,Q.variabilis has remarkable values in wood production,industrial production and landscape construction.The regeneration and/or recover of this species is extremely important for its founctional status,which is tightly related acorn nutrient and surrounding conditions.However,Q.variabils is large-seeded species,acorns usually varied several folds,which results in remarkably nutrient variation.In addition,acorns contain large amount of starch,thus,are easily be predated by wild animal,such as partial consumption during dispersal and completely removal after seedling emergence,which both result in differences in acoren nutirnt availability.Such acorn nutrient variation mayaffect seedling development and therefore renegeration efficiency.In this study,we classified acorn sizes,and simulated partial consumption and complete predation of acorn before or after seedling emergence,implementing two contrastiong nursery fertilization,to determine their effects on seedling emergence charactristics,growth,photosynthetic characteristic,nutrient status and outplanting performance.The aims of this study were to undertand the important role of acorn nutrients in seedling lifetime sycle and how it interacts with soil fertility to affect seedling development,and also to reveal the knicks of acorn nutrient during seedling emergence and development.The main results and conlusions are as below:(1)Acorn size significantly affected seedling emergence.The small acorn only had 38.8%emerged,wich is much lower than large and medium acorns.Moreover,acorn size affected seedling performance in nursery and seedlings from small acorns consistently had smaller size,lower photosynthetic characteristics and poorer nutrient content compared with seedlings from large or medium acorns;nursery fertilization can not remendy the differences between seedling from small and large or medium acorns;wherease seedlings from large and medium acorns had quite similar attributes After field planting,survival for small-seeded seedlings was more than half lower than large-/medium-seeded seedlings in both of the first and second seasons;the same with that in nursery,seedlings performed similarly for large and medium acorns.In comprehensive consideration of seedling performance in nursery and field,small acorns may decrease the efficiency of seedling cultivation,while increase seedlings cost,and therefor have very limited contribution for Q.variabilis regeneration or recovery;but medium acorns have equal potential in seedling emergence and growth,thus,can both be ultilized in regeneration or recovery efforts.Moreover,the effects of acorn size on seedling emergence and growth are not only a consequence of nutrient variation,but also relate to acorn physiological maturation and vitality,which need further study in the future(2)The influence of partial cotyledon loss on Q.variabilis seedling cultivation is two-sided,varying with nursery fertilization regimes.As suggested in this study,cotyledon excision resulted in increased seedling emergence and also accelerated emergence speed,specially the Intermediate excision(E1/2)treatment had the best emergence characteristics.However,cotyledon excision before sowing had some disadvantages such as reduction of seedling growth and root development in the nursery compared with seedlings from nonexcised acorns,depending on the intensities of excision.Under nonfertilized(FO)condition,seedling growth and nutrient accumulation would be restrained onece cotyledon was excised,wherease under fertilized(F+)codition,slight(E1/3)and/or intermediate(E1/2)excision had minor negative effects on seedling quality,and even promoted root vitality,but extrem excision(E2/3)always strongly decreased seedling performance.After planting,the response of seedling performance to cotyledon excision was a little different with that in nursery,intermediate excision combined with nursery fertilization(E1/2-F+),following by E1/3-F+,resulted in highest seedling mass,nutrient content and photosynthetic charactristics compared with other treatments.Thus,we conclude that Q.variabilis seedling development can endure a certain degree of cotyledon loss,which is toughly related to soil fertility conditions.(3)The knicks of acorn nutrient translocation were tightly related to requirements of seedling development,irrespective of soil fertility.More than 80%of acorn nutrients were translocated in early developmental stages(?2 weeks after emergence),while N and P translocated fater than K.Acorn/cotyledon loss before 2 wekks after emergence strongly restrained seedling development,therefor negatively affected seedling growth and nutrient absoption,decreased the proportion of lower layer roots,and even increase seedling mortality.Notablely,the effects of acorn loss in very early stages on seedling development can not be reverted by nursery fertilization.Acorn loss later than 2 weeks after emergence had minor effects on seedling growth and root development,the improvement function of nursery fertilization can therefor be prominent.Overall,differences of acorn nutrient availability due to acorn size variation and aorn fate have congenital and persistent effects on seedling growth,and therefor affect Q.variabilis regeneration.The effects of acorn nutrient on seedling cultivation and regeneration may varied with soil fertility,but soil fertility can not remedy the differences in seedling growth,as well as seedling quality,caused by acorn nutrient variation.Thus,in order to increase seedling quality and regeneration efficiency of Q.variabilis,a clear understand and high emphasis of the importance acorn nutrient for seedling development are needed in seedling cultivation efforts,and foresters should trengthen the comprehensive control of acorn nutrient and soil fertility. |
PDF Full Text Request