Effect of Litter Decomposition on Soil Polarization in Two Typical Planted Pure Broadleaved forests in the Gully Region of Loess Plateau, China

Soil polarization is a new concept which describes the deviation of soil properties of planted pure forest from its original equilibrium status towards an extreme condition due to long-term growth or continuous planting of single tree species. It is thought to be one obstacle of forest. In order to investigate the effect of litter decomposition on soil polarization of planted forests in the gully region of Loess Plateau, China, humus soil and litter were sampled in two typical broadleaved forests, and 4 treatments as "soil + leaf litter", "soil + ischolar_mains", "soil + leaf litter + ischolar_mains", and CK were set for laboratory incubation experiment in this research. The results showed that polarizations of different properties were variable, in both direction and degree, after the incubation with litters. Based on analyzing the polarization ratios by PCA (principal component analysis) method, the results of comprehensive soil properties were showed as follows: in the Robinia pseudoacia forest soil, both of leaf litter and ischolar_mains resulted in negative polarization, and leaf litter showed greater effect than ischolar_mains; in the Betula platyphylla forest soil both of leaf litter and ischolar_mains resulted in negative polarization, and also leaf litter showed greater effect than ischolar_mains. When leaf litter and ischolar_mains mixed-together with the soil, the interaction sequence is R. pseudoacia (0.497) > B. platyphylla (-0.466). The result indicated that leaf litter and ischolar_mains when mix-incubated with forest soil showed promoting effect on soil properties in the R. pseudoacia forest soil, and showed inhibitory effect on soil properties in B. platyphylla forest soil. In general, litter decomposition in R. pseudoacia forest soil was more beneficial for soil properties than B. platyphylla.