| A randomized block design was used to study the effects of simulated nitrogen deposition on fine root in a mid-subtropical evergreen broadleaf forest located at the Castanopsis kawakamii Nature Reserve, sanming, Fujian province. Three nitrogen (N) addition-level treatments were designed, each receiving 0 g Nm-2 yr-1 (CK),4 g N m-2 yr-1 (LN) and 8 gN mr-2 yr-1 (HN), four replicate plots, respectively. N application was started in early October,2012. Soil coring and minirhizotrons were used to observe and analyze the change of fine root biomass, production and morphologies over 3 years of N application. And the significance of fine root biomass and production were also analyzed among different N application levels. The soil coring results showed:(1) As soil depth increase, the fine root biomass, root surface area density, root length density and root biomass density were all decrease in the three N application treatments. And the fine root biomass in the 0-1 Ocm soil depth was significant with the 10-20cm,20-40cm and 40-60cm soil depth (P<0.05). The fine root biomass of three treatments in the 0-20cm soil depth accounted for 69%-76% of the 0-60cm soil depth, existing an enrichment characteristic in the surface layer. The main reason may be the soil bulk density was small in the surface layer while big in the deep soil layer. (2) Treatment and soil depth had no interactive effects on fine root biomass (P=0.574), but different N application level had different influence on the fine root bioomass in the 0-10cmtopsoil. As to CK treatment topsoil biomass, LN had significant increase, while HN had no significant. The possible reason is that LN still not reached the experiment field N threshold while HN did. (3) The LN treatment fine root biomass was greater man CK and HN among 0-1 mm, 1-2mm and 2-5mm root diameter, and also significant with CK and HN in each root diameter (except the 0-1 mm root diameter in HN treatment); while HN fine root biomass was only significant in the 0-1 mm root diameter. The reason was similar to (3), and the 0-1 mm root enriched in the surface layer and sensitive to the resource acquisition. (4) SRL was only significant in the CK treatment between 20-40cm and 40-60cm soil depth, the others did not show significance between each other. The possible reason is that the fertilizaton time and the change of root morphologies may not important than the change of leaf morphologies aboveground. (5) Root morphologies were responsed significantly to the N application, soil depth, root diameter and pairwise interaction. It may own to the woods inherent trait, the rich diversity of plants and the diffferent resource acquisition strategy of fine root in different plants. The minirhizotrons results indicated:(1) For root length production, no significance existed in each treatment, each season, within-treatment and within-season. It may cause by the length of fertilization, the different plants with different response to N application, the change of plants diversity and the great heterogeneity of the study plot and so on, which needs further research. (2) As to CK treatment, the entire fine root diameter bacame thinner in LN, but thicker in HN. This suggests the possibility that more roots were put into the transportation and storage of nutrients in HN, while the change in LN may contribute to the absorption of soil nutrients and water, which leads to the increasement in root length production, especially the finest fine root (D<0.19mm). (3) Different distribution in root diameter were existed between root length production and root volume production. (4) The fine root length production in CK, LN and HN treatments were all unimodal distribution with diameter. Owning to minirhizotrons its own feature of capturing pitures, the fine root diameter was relatively smaller than the soil coring method. These results provided a basis data for how the fine root respond to the N deposition in subtropical evergreen broad-leaved forest and a scientific basis for the establishment of model. |
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