Response of decomposition and nutrient release in different diameter fine roots of Pinus tabuliformis plantation to N addition
We examined the effects of four nitrogen (N) addition treatments,i.e.,N0 (0 g N · m-2 a-1),N3 (3 g N · m-2 a-1),N6 (6 g N · m-2 a-1) and N9 (9 g N · m-2 a-1) on the decomposition and nutrient release processes of fine roots with different diameters in Pinus tabuliformis plantation using litterbag method.The results showed that the decomposition process of fine roots could be divided into rapid (0-60 d) and slow (60-300 d) decomposition stages.The decomposition mass percentages of fine roots with 0-0.4 mm,0.4-1 mm and 1-2 mm were 7.6％,10.4％ and 11.4％ on the 60th day and 19.8％,23.5％ and 30.5％ on the 300th day,respectively,indicating that finer root had lower decomposition rates.N addition reduced significantly the decomposition rates of fine roots with 0-0.4 mm diameter,but had no significant influence on those of root with 0.4-1 mm and 1-2 mm diameters.Compared with the control,N3,N6 and N9 treatments reduced the decomposition rates by 2.1％,4.5％ and 5.8％,respectively.N addition increased both the C and N remaining percentages of fine roots with 0-0.4 mm and 0.4-1 mm diameters,but had no significant influence on those with 1-2 mm diameters.Additionally,P remaining percentages of fine roots had no response to the N addition.Compared with the control,N3,N6 and N9 treatments increased the root C remaining percentages by 8.1％,9.4％ and 4.5％ in 0-0.4 mm diameter roots,and 2.5％,2.5％ and 0.9％ in 0.4-1 mm diameter roots,respectively.Similarly,N3,N6 and N9 treatments also increased the root N remaining percentages by 5.3％,16.3％ and 16.7％ in 0-0.4 mm diameter roots and 0.9％,2.3％ and 3.9％ in 0.4-1 mm diameter roots,respectively.The transfer models for C,N and P in 0-0.4 mm and 0.4-1 mm diameters were direct releasing,and the transfer models for N showed an enriching-releasing model.N deposition may decrease the fine root decomposition rates mainly by affecting the decomposition process of fine roots with 0-0.4 mm diameters (mainly the first two order roots).
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