Effects of Nitrogen Addition and Drought on Sapling Growth of Four Subtropical Tree Species
To explore the effects of nitrogen deposition and drought on plant growth in subtropical forests,the responses of four typical subtropical tree species,such as Pinus massoniana,Cunninghamia lanceolata,Ormosia pinnata and Schima superba,to different nitrogen levels and drought degrees were studied.The results showed that drought and nitrogen addition treatment for 2.5 years had different effects on the growth of different tree species.Nitrogen addition significantly increased the total biomass,plant height,and basal diameter of S.superba and C.lanceolata under the control and moderate drought treatment,but constrained the root and stem biomass and basal diameter of P.massoniana under moderate drought treatment,and had no significant effect on the growth of four tree species under severe drought treatment.Drought and nitrogen addition decreased height and total biomass of O.pinnata,P.massoniana and S.superba,and the inhibition effect became more obvious with the increase of drought degree.Without nitrogen addition,drought had no significant effect on the total biomass and plant height of S.superba.However,severe drought and nitrogen addition significantly reduced the basal diameter and total biomass of S.superba.Drought significantly increased the root-shoot ratio of C.lanceolata,but had no significant effect on other tree species.Furthermore,the effects of nitrogen addition and drought on the growth of non-leguminous species(e.g.,S.superba)were more obvious than that of leguminous plants(e.g.,O.pinnata).Therefore,it was that nitrogen deposition might exacerbate the inhibitory effect of extreme drought on the growth of some tree species in subtropical regions.
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