| Vitex negundo,a typical species of shrubs in the southern foot of Taihang Mountains,was selected as the experimental material in this paper.And we have simulated Nitrogen deposition at four different levels of CK(control,0 g Nm-2·a-1),LN(low nitrogen,5 g Nm-2·a-1),MN(middle nitrogen,10 g Nm-2·a-1)and HN(high nitrogen,15 g Nm-2·a-1)to discuss the responses of the morphological characteristics,root characteristics,photosynthetic rate,transpiration rate,intercellular CO2 concentration and enzyme activity to Nitrogen deposition.The main results are as follows.?1?The growth trends of the height,basal diameter,crown width,leaf number and leaf area under different nitrogen application treatments showed MN > HN > LN > CK.And the nitrogen addition levels of 10-15 g Nm-2·a-1 had the most significant effect on the growth and development of Vitex negundo.?2?The changes of the root length,surface area and volume of small fine root?0 0 < D ? 0.5 mm?and large fine root?0.5 < D ? 2.0 mm?under different nitrogen treatments showed MN > CK > LN > HN.The fine root weight,biomass,specific root length and specific surface area of Vitex negundo seedlings were raised with the increase of nitrogen application rate,and reached the highest value at MN and then decreased.Compared with CK,the fine root weight and fine root biomass of seedlings of MN were significantly increased.And compared with CK,the specific root area and specific surface area of fine roots of LN and MN were significantly increased.The indexes of fine roots of seedlings under HN treatment increased but not significantly,and lower than that of LN and MN.?3?The net photosynthetic rate,transpiration rate and stomatal conductance under LN?MN and HN treatments were significantly higher than those of CK,and the highest values appeared in MN.The change of intercellular CO2 concentration showed LN>MN>CK>HN,and MN was significantly higher than CK.Under the condition of artificially controlled light intensity,the maximum net photosynthetic rate,light saturation point,light compensation point and dark respiration rate increased with the increase of nitrogen application rate,and then decreased when MN reached the highest value.Under the artificial control of CO2 concentration,the carboxylation efficiency,maximum net photosynthetic rate,dark respiration rate,and CO2 saturation point under different nitrogen treatments showed an increase trend with the increase of nitrogen application rate,which was reached the highest value under MN.The compensation point of CO2 decreased with the increase of nitrogen application rate.?4?The POD activity of leaves increased with the increase of planting time,and the change was MN > LN > CK > HN in the mass.The SOD activity did not change significantly with planting time,but the highest value all appeared in MN treatment during the whole experiment period.The content of MDA showed a decrease trend with the increase of planting time.The highest value of MDA appeared in LN treatment except at 30 days.The highest value of MDA was observed in CK.The activities of POD and SOD in fine roots under different nitrogen treatments showed an increase trend with the raise of nitrogen application rate,reached the highest value at MN and then decreased.The highest value of fine root MDA content appeared in HN treatment,the lowest value appeared in MN,and HN was significantly higher than CK.?5?The plant height and basal diameter were significantly positively correlated with POD activity,and plant height,crown width,leaf area and leaf length were significantly negatively correlated with leaf MDA content.The biomass of fine roots was significantly positively correlated with POD and SOD activity and significantly negatively correlated with the MDA content.?6?The Vitex negundo seedlings developed best when the nitrogen addition level was 10 g Nm-2·a-1.However,the growth of the seedlings was inhibited when the nitrogen deposition concentration exceeded 10 g N·m-2·a-1 to 15 gN·m-2·a-1. |
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