Responses of Pinus tabulaeformis Seedlings to Different Soil Water Moistures in Ecophysiological Characteristics

In our present study,seedlings of Pinus tabulaeformis were subjected to four levels of soil water content:80% maximum field capacity(FC),60%FC,40%FC and 20%FC,respectively regarded as well-watered,mild,moderate and severe water stress.Our results showed that water stress significantly decreased dry matter accumulation(including leaf,shoot,root and total dry matter production),relative growth rate,plant height and basal stem diameter except that root/shoot ratio showed an increasing trend with increasing water stress.Also,leaf gas exchange parameters(net photosynthetic rate,stomatal conductance and transpiration rate) were significantly decreased with the increase of water stress and the reduction in net photosynthetic rate was mainly due to the stomatal closure.Furthermore,when severe water stress was imposed,both instantaneous water use efficiency and long term water use efficiency,indicated by stable carbon isotope composition(δ13C) significantly increased.In addition,leaf nitrogen concentration(per mass,N%) showed a decreasing trend with increasing soil water stress while leaf carbon concentration(per mass,C%) showed an opposing trend,which directly resulted in an increase in C/N ratio with decreasing soil water content.We also found a positive correlation between photosynthetic rate and leaf nitrogen concentration in our study.In conclusion,our results indicated that changes in growth and structural characteristics,leaf nitrogen and carbon concentrations and improving water use efficiency with increasing soil water stress in P.tabulaeformis may facilitate its adaptation to low soil water availability conditions.