| 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 of the growth of urban trees. Nutrient seasonal dynamics, nutrient use efficiency, nutrient resorption and N:P ratio of the major urban trees, some soil chemical properties and the characteristics of carbon and nitrogen transformation of the different urban green-lands in Hefei 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. The distribution of P was irregular. The mean pH (H2O) in 0-10 cm soil was 7.70, and pH (KCl) was 6.80. The mean EC in 0-10 cm soil was 147.58μS·cm-1. Total nitrogen concentrations varied from 0.70 to 2.30 g·kg-1. Total phosphorus concentrations varied from 64.18 to 3144.54 mg·kg-1 and available phosphorus varied from 1.05 mg·kg-1 to 130.30 mg·kg-1. Total potassium concentrations varied from 5.12 to 11.02 g·kg-1. Total sodium concentrations varied from 2.49 to 5.35 g·kg-1. Total calcium concentrations varied from 6.22 to 131.80 g·kg-1. Total magnesium concentrations varied from 4.99 to 12.16 g·kg-1.The concentration of DOC in the 0-10 cm soil was the highest in the Liquidamba formosana forest in Shushan park (SPL; 234.48 mg·kg-1) and the lowest in the L. formosana forest on the university campus (UCL; 96.66 mg·kg-1), while for 10-30 cm soil the highest DOC was found in Pinus massoniana forest in Shushan park (SPP; 105.91 mg·kg-1) and the lowest in Cedrus deodara forest in Huancheng park (HPC; 75.35 mg·kg-1).The concentrations of extractable NH4+in the 0-10 cm and 10-30 cm soil were the highest in SPP site (14.28 mg·kg-1 and 13.27 mg·kg-1). The soil under HPC site had the lowest concentrations of extractable NH4+in both 0-10 cm (4.51 mg·kg-1) and 10-30 cm (3.05 mg·kg-1).The concentration of extractable NO3- in the 0-10 cm soils was the highest in HPC site (15.80 mg·kg-1) and the lowest in SPP and SPL sites (7.42 mg·kg-1), while for 10-30 cm soil the highest extractable NO3-was found in C. deodara forest on the campus (UCC; 14.63 mg·kg-1) and the lowest in SPP and SPL sites (6.37 mg·kg-1). Based on the in situ incubation experiment, the annual net rate of DOC was 269.75μg·kg-1·d-1 for 0-10 cm and -323.11μg·kg-1·d-1 for 10-30 cm in UCC site. In reciprocal transplant incubation, the annual net rates of DOC were, respectively,420.75μg·kg-1·d-1 and 195.54μg·kg-1·d-1 for 0-10 cm,-236.19μg·kg-1·d-1 and -169.58μg·kg-1·d-1 for 10-30 cm soil from UCC incubated in both SPP and HPC sites.The annual net rate of DOC was 20.61μg·kg-1·d-1 for 0-10 cm and -16.34μg·kg-1·d-1 for 10-30 cm in HPC site. In reciprocal transplant incubation, the annual net rate of DOC were, respectively,70.29μg·kg-1·d-1 and 93.92μg·kg-1·d-1 for 0-10 cm,51.64μg·kg-1·d-1 and -123.54μg·kg-1·d-1 for 10-30 cm soil from HPC incubated in both UCC site and SPP sites.The annual net rate of DOC was 285.42μg·kg-1·d-1 for 0-10 cm and -213.18μg·kg-1·d-1 for 10-30 cm in SPP site. In reciprocal transplant incubation, the annual net rates of DOC were, respectively,525.35μg·kg-1·d-1 and 689.79μg·kg-1·d-1 for 0-10 cm,-182.76μg·kg-1·d-1 and -211.71μg·kg-1·-1 for 10-30 cm soil from SPP site incubated in both UCC site and HPC sites.The annual net rate of DOC was 8.17μg·kg-1·d-1 for 0-10 cm and -254.82μg·kg-1·d-1 for 10-30 cm in UCL site. In reciprocal transplant incubation, the annual net rates of DOC were 49.93μg·kg-1·d-1 for 0-10 cm,-337.91μg·kg-1·d-1 for 10-30 cm soil from UCL site incubated in SPL site.The annual net rate of DOC was -168.35μg·kg-1·d-1 for 0-10 cm and 290.21μg·kg-1·d-1 for 10-30 cm soil in SPL site. In reciprocal transplant incubation, the annual net rate of DOC were -21.33μg·kg-1·d-1 for 0-10 cm,270.93μg·kg-1·d-1 for 10-30 cm soil from SPL site incubated in UCL site.The annual net rates of ammonification, nitrification and N mineralization were, respectively,-21.32μg·kg-1·d-1,50.86μg·kg-1·d-1 and 4.09μg·kg-1·d-1 for 0-10 cm in UCC site; and for 10-30 cm soil,-51.20μg·kg-1·-1,39.14μg·kg-1·d-1 and 13.40μg·kg-1·d-1. In reciprocal transplant incubation, the net annual rates of ammonification were, respectively, 1.78μg·kg-1·d-1 and -21.35μg·kg-1·d-1 for 0-10 cm,-48.81μg·kg-1·d-1 and -56.27μg·kg-1·d-1 for 10-30 cm soil from UCC site incubated in both SPM and HPC sites. The net annual nitrification rate were, respectively,61.53μg·kg-1·d-1 and 47.95μg·kg-1·d-1 for 0-10 cm,20.19μg·kg-1·d-1 and 64.78μg·kg-1·d-1 for 10-30 cm soil from UCC site incubated in both SPM and HPC sites. The net annual rates of N mineralization were, respectively,6.07μg·kg-1·d-1 and 9.59μg·kg-1·d-1 for 0-10 cm,28.62μg·kg-1·d-1 and 25.53μg·kg-1·d-1 for 10-30 cm soil from UCC site incubated in both SPM and HPC sites. The annual net rates of ammonification, nitrification and N mineralization were, respectively,-33.81μg·kg-1·d-1,75.09μg·kg-1·d-1 and 41.29μg·kg-1·d-1 for 0-10 cm in HPC site; and for 10-30 cm soil,-21.06μg·kg-1·d-1,65.97μg·kg-1·d-1 and 44.91μg·kg-1·d-1. In reciprocal transplant incubation, the net annual rates of ammonification were, respectively,-34.75μg·kg-1·d-1 and -32.91μg·kg-1·d-1 for 0-10 cm,-23.24μg·kg-1·d-1 and-2.47μg·kg-1·d-1 for 10-30 cm soil incubated in both UCC and SPM sites. The net annual nitrification rate were, respectively,51.92μg·kg-1·d-1 and 83.08μg·kg-1·d-1 for 0-10 cm, 75.69μg·kg-1·d-1 and 57.10μg·kg-1·d-1 for 10-30 cm soil incubated in both UCC and SPM sites. The net annual rates of N mineralization were, respectively,17.17μg·kg-1·d-1 and 50.18μg·kg-1·d-1 for 0-10 cm,26.22μg·kg-1·d-1 and 27.31μg·kg-1·d-1 for 10-30 cm soil incubated in both UCC and SPM sites.The annual net rates of ammonification, nitrification and mineralization were, respectively,-124.14μg·kg-1·d-1,81.92μg·kg-1·d-1 and -42.23μg·kg-1·d-1 for 0-10 cm in SPP site; and for 10-30 cm soil,-121.17μg·kg-1·d-1,39.51μg·kg-1·d-1 and -40.83μg·kg-1·d-1. In reciprocal transplant incubation, the net annual rates of ammonification were, respectively,-141.17μg·kg-1·d-1 and -149.14μg·kg-1·d-1 for 0-10 cm,-127.18μg·kg-1·d-1 and -124.12μg·kg-1·d-1 for 10-30 cm soil incubated in both UCC and HPC sites. The net annual nitrification rate were, respectively,139.01μg·kg-1·d-1 and 132.23μg·kg-1·d-1 for 0-10 cm,90.82μg·kg-1·d-1 and 75.74μg·kg-1·d-1 for 10-30 cm soil incubated in both UCC and HPC sites. The net annual rates of N mineralization were, respectively,-2.16μg·kg-1·d-1 and -16.91μg·kg-1·d-1 for 0-10 cm,-18.18μg·kg-1·d-1 and-48.38μg·kg-1·d-1 for 10-30 cm soil incubated in both UCC and HPC sites.The annual net rates of ammonification, nitrification and N mineralization were, respectively,13.66μg·kg-1·d-1,155.66μg·kg-1·d-1 and 169.32μg·kg-1·d-1 for 0-10 cm in UCL site; and for 10-30 cm soil,-18.13μg·kg-1·d-1,137.24μg·kg-1·d-1 and 119.11μg·kg-1·d-1.In reciprocal transplant incubation, the net annual rate of ammonification was-32.54μg·kg-1·d-1 for 0-10 cm,-32.81μg·kg-1·d-1 for 10-30 cm soil incubated in SPL site. The net annual nitrification rate was 116.24μg·kg-1·d-1 for 0-10 cm,45.55μg·kg-1·d-1 for 10-30 cm soil incubated in SPL site. The net annual rate of N mineralization was 83.69μg·kg-1·d-1 for 0-10 cm,12.74μg·kg-1·d-1 for 10-30 cm soil incubated in SPL site.The annual net rates of ammonification, nitrification and mineralization were, respectively,-31.53μg·kg-1·d-1,13.45μg·kg-1·d-1 and -18.08μg·kg-1·d-1 for 0-10 cm in SPL site; and for 10-30 cm soil,-46.97μg·kg-1·d-1,5.97μg·kg-1·d-1 and -41.00μg·kg-1·d-1. In reciprocal transplant incubation, the net annual rate of ammonification was -35.16 μg·kg-1·d-1 for 0-10 cm,-27.90μg·kg-1·d-1 for 10-30 cm soil incubated in UCL site. The net annual nitrification rate was 0.10μg·kg-1·d-1 for 0-10 cm,69.21μg·kg-1·d-1 for 10-30 cm soil incubated in UCL site. The net annual rate of N mineralization was -35.06μg·kg-1·d-1 for 0-10 cm,41.31μg·kg-1·d-1 for 10-30 cm soil incubated in UCL site.Results from the experiment showed that N transformation varied significantly by the reciprocal transplant incubation for the different sampling stands. It suggests that soil N transformation is comtrolled by the substrate quality, and is strongly affected by the environmental condition particullarly temperature as well.The annual mean concentration of soil microbial biomass nitrogen (SMBN) in the 0-10 cm soil was the highest in the Liquidamba formosana forest of campus (104.94 mg-kg-1) and the lowest in the Pinus massoniana forest of campus (12.00 mg-kg-1), while for 10-30 cm soil the highest SMBN was found in Pinus massoniana and Liquidamba formosana mixed forest of Shushan park (80.28 mg-kg-1) and the lowest in the Pinus massoniana forest of campus (15.13 mg-kg-1). There existed a significant difference in SMBN amongst the sampling stands. However, no significant differences in SMBN occurred between 0-10 cm and 10-30 cm soils for all the sampling stands.Nitrogen use efficiency (NUEN) of the common conifers ranged from 59.88 to 149.48 g·g-1, for NUEP from 460.83 to 4545.45 g·g-1, NUEK from 152.67 to 877.19 g·g-1, NUECa from 39.56 to 262.47 g·g-1, NUEMg from 196.46 to 316.46 g·g-1, NUENa from 467.29 to 283.29 g·g-1. NUEP was significantly higher than the other nutrient elements.NUEN in leaf litter for the different deciduous broad-leaved tree species in urban Hefei ranged from 47.53 to 175.44 g·g-1, NUEP from 303.95 to 4617.59 g·g-1, NUEK from 50.94 to 297.97 g·g-1, NUECa from 39.87 to 189.04 g·g-1, NUEMg from 109.60 to 353.61 g·g-1, and NUENa from 211.69 to 970.87 g·g-1.NUEN in leaf litter for the different evergreen broad-leaved tree species in urban Hefei ranged from 35.69 to 172.41 g·g-1, NUEP from 521.71 to 4000.00 g·g-1, NUEK from 76.76 to 559.28 g·g-1, NUENa from 219.88 to 574.71 g·g-1, NUECa from 41.53 to 117.65 g·g-1, NUEMg from 158.23 to 365.50 g·g-1.Cedrus deodara in UCC site had the highest N:P stoichiometrical ratio (27.52) and Sabina procumbens the lowest (8.26) in needles among the different coniferous species in urban Hefei. The N:P ratio varied from 6.21 (Ginkgo biloba)to 19.95 (Quercus acutissima) in leaves for the different deciduous broad-leaved tree species sampled in urban Hefei. Within the evergreen broadleaved tree species, Cinnamomum camphora in the Hezuohua Road had the highest N:P ratio (17.37) and Buxus bodinieri in the campus the lowest (10.15). Within the species studied,22 species (46.81%), with N:P ratio<14, were in N limitation; and 10 species (21.28%) were in P limitation (N:P ratio>16). There were 15 species (31.91%) with N:P ratio in a range of 14-16, indicating that those species were limited by both N and P.
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