Nutrient Dynamics And Nutrient Use Efficiency Of Major Urban Trees In Hefei

The air,moisture,heat quantity and soil in the urban area were significantly different from those in forest ecosystem because of long-term human disturbances.The characteristics of urban soils were the important controls determining the growth of urban trees.Nutrient seasonal dynamics,nutrient use efficiency,nutrient resorption and N:P ratio of major urban trees in Hefei and some soil chemical properties of different urban green-lands were studied in order to find some orderlinesses which were useful for urban tree management.The soils under urban green-lands in Hefei were badly disturbed by human activities, particularly the pollution from architectural garbage.Urban soil could trend to be alkaline. Urban soils were poor in N but rich in P which distribution was irregular.The mean pH (H₂O)in 0-10 cm soil was 7.4,and pH(KCl)was 6.4.The mean EC in 0-10 cm soil was 107μs/cm.Total nitrogen concentrations varied from 0.07%to 0.18%.Total phosphorus concentrations varied from 86.89 mg/kg to 490.54 mg/kg and available phosphorus varied from 1.05 mg/kg to 84.08 mg/kg.Bischofia polycarpa in the campus had the highest nitrogen concentration(1.57%)in leaf litter and Liquidamba formosana the lowest(0.57%).The mean concentration of all tree species was 1.04%.The highest phosphorus concentration was found in leaf litter of Ginkgo biloba in the campus(3.29 mg/g)and the lowest in Photinia serrulata(0.25 mg/g). The mean P concentration of all tree species was 0.81 mg/g.The highest calcium concentration in leaf litter was Ginkgo biloba in the campus(22.12 mg/g)and the lowest in Sapium sebiferum(5.29 mg/g).The mean concentration of all tree species was 11.57 mg/g.The nitrogen use efficiency(NUE_N)in leaf litter was the highest for Liquidamba formosana in the campus(175.25g/g)while Bischofia polycarpa the lowest(63.76 g/g). The mean value of NUE_N of all tree species was 108.39 g/g.The phosphorus use efficiency (NUE_p)was the highest in leaf litter of Photinia serrulata in the campus(4039.37 g/g)and the lowest was Ginkgo biloba(303.76 g/g).The mean NUE_p was 1869.19 g/g for all tree species.The calcium use efficiency(NUE_Ca)in leaf litter was Sapium sebiferum(189.02 g/g)and the lowest was Ginkgo biloba(45.20g/g).The mean NUE_Cawas 99.98 g/g for all tree species. The mean nitrogen concentration in fresh foliage of Cercis chinensis in the campus was 2.91%,which was 2 fold as high as in Photinia serrulata(1.46%).The highest mean phosphorus concentration was found in the foliage of Ginkgo biloba(3.15 mg/g),while the lowest in Osmanthuum fragrans and Cinnamomum camphora(0.95 mg/g).The mean concentration of calcium in foliage of Ginkgo biloba was 19.12 mg/g which was 2.68 times greater than in Sapiurn sebiferum(5.19 mg/g).The lower concentrations of nitrogen and phosphorus in the foliage appeared in the period of peak leaf fall and procreative stage.Calcium concentration was likely to increase before the peak fall.No significant differences were found in both N,P,Ca concentrations and NUE_N,NUE_p, NUE_Cafor different types,evergreen broad-leaved,deciduous broad-leaved and coniferous tree species.Evergreen broad-leaved trees had higher NUE_N and NUE_P than deciduous broad-leaved trees.Significantly negative correlation was found between P resorption and available P in urban soil R=-0.57(p=0.03).It demonstrates that the trees growing on the site with lower P availability like to increase P resorption.Different characteristics of nutrient limitation were found in urban trees by determination of N:P ratio.The N:P ratios lower than 14 were found in Bischofia polycarpa,Liquidamba formosana,Cinnamomum camphora,Photinia serrulata and Ginkgo biloba in the campus,and Sapium sebiferum in Hezuohua Road,indicating an existence of nitrogen limitation.Photinia serrulata in Changjiang Road,and Sapium sebiferum and Cercis chinensis in the campus had a N:P ratio between 14 to 16,indicating limitation of both nitrogen and phosphorus.However,The N:P ratios in Cedrus deodara, Osmanthuum fragrans,Taxodium distichum,Ligustrum lucidum and Cinnamomum camphora in Hezuohua Road were greater than 16,which suggests that those trees were likely limited by phosphorus.Significantly positive correlations were found between NUE_N and NUE_P R =0.82(p= 0.0001).This suggests that there exists an interaction between N and P in the urban trees.