Responses Of Bud Bank Dynamics Of Nitraria Tangutorum To Nitrogen Addition

In recent decades,anthropogenic factors such as fertilization,deforestation and fossil fuel combustion have led to a significant increase in nitrogen（N）activity in terrestrial ecosystems.N deposition and its ecological effects have become one of the hot topics in ecology.Inner Mongolia Ulan Bub Desert is located in the west of China,where N is a limiting factor for local vegetation growth compare to water limitation.Bud bank is the set of buds in clonal plant,which bears the role of vegetation regeneration and has a decisive effect on plant growth patterns.However,researcher mainly concerned with the bud bank of perennial herb,and ignored woody plant bud bank.In this paper,our object is to understand the effects of N addition on the temporal and spatial dynamics and structure of the bud bank by establishing the pot and field N addition experiments and investigating the growth index and bud bank characters.Additionally,the ecological stoichiometry of carbon,N and phosphorus were analyzed.（1）Effects of different N addition on aboveground bud bank traits of Nitraria tangutorum seedlingsIn order to investigate the potential effects of N addition on bud bank,we studied bud bank traits of N.tangutorum seedlings with the application of N using pot experiments.The N addition levels consist of 0,12,24,49,73,98 and 122 gN·m^-2.The results showed that: N addition significantly increased the number of buds and vegetative shoots in bud bank,and significantly reduced the number of dormant buds and dormant shoots;meanwhile,N addition promoted the bud production of secondary shoots and tertiary shoots;With the increasing of N addition,the relative position of vegetative shoots in bud bank had a tendency to move from base to tip;There was a quadratic nonlinear positive correlation between nitrogen balance index（NBI）and buding intensity,branching intensity,bud production of secondary and tertiary shoots of N.tangutorum seedling;The N content,accumulation amount（NAA）and the morphological traits underground were positively related to the number of buds and vegetative shoots,and negatively related to the number of dormant buds and dormant shoots;Shoots,leaves and total aboveground dry mass were significant positive correlated with buds number,shoots number,budding intensity and branching intensity,and negatively correlated with the number of dormant buds and shoots.These results suggest that N.tangutorum seedlings response to N availability through changing bud bank size and spatial distribution.Additionally,N supply affected plants growth by adjusting bud bank structure.This provides a better understanding of bud bank and contributes to explain and predict the effects of N deposition on dynamic of desert plants.（2）Effects of N addition on bud bank demography of Nitraria tangutorum rametsWe investigate the potential effects of N addition on bud bank demography by using field fertilization experiments.The N addition levels consist of 0,10 and 20 gN·m^-2.The results showed that: low and high N addition both reduced the survival rate of dormant buds,and increased the probability of vegetative shoots survival,reproductive shoots survival and bud translating to vegetative shoots;However,low N addition increased the probability of reproductive growth,and high N additon increased the probability of vegetative growth;Lastly,the probability of dormant bud translating to vegetative shoots had most important role on the population growth rate（λ）,and the probability of bud production of vegetative and reproductive shoots had little impact on λ.In summary,N addition significantly affected the population demography of N.tangutorum ramets and increased λ.The probability of dormant bud translating to vegetative shoots was the key to ramets population demography.（3）Effects of N addition on bud bank allocation of Nitraria tangutorum rametsWe investigate the potential effects of N addition on bud bank allocation by using field fertilization experiments.The N addition levels consist of 0,5,10,15 and 20 gN·m^-2.The results showed a significant allometric relationships between bud bank allocation and plant size for each bud fate throughout development;Allometry and plasticity tended to be strongest early in development;C:N was significant linearly positive correlated with apical dominance,and negative correlated with branching intensity and reproductive effort;N:P was significant linearly negative correlated with apical dominance,and positive correlated with branching intensity and reproductive effort The results showed that N.tangutorum ramets response to N addition by changing their bud bank allocation,and C:N ratio and N:P ratio had indicative role of bud bank allocation.