Effects of Forest Fires on Soil Labile Organic Carbon in Secondary Forest of Pinus massoniana

Taking the secondary forest of Pinus massoniana in Heshan City of Guangdong Province as the research object. Based on the field investigation, sampling and indoor test, soil labile organic carbon after forest fire were tested, and the content of soil labile organic carbon before and after forest fire were tested. The effect of forest fire on the content of soil labile organic carbon in secondary forest of P. massoniana was analyzed. The findings indicated that compared with the control, the soil labile organic carbon components of young forest, middle-age forest and mature forest decreased by 18.50–26.03%, 17.81–22.96% and 13.50–19.41%. Soil depth explained 70.73%, 28.34%, 79.83%, and 73.35% of soil MBC, DOC, EOC, and POC variations, respectively. Stand age explained 20.09%, 62.27%, 13.92% and 18.13% of soil MBC, DOC, EOC, and POC variations. Forest fires explained 4.69%, 5.39%, 2.61%, and 3.42% of soil MBC, DOC, EOC, and POC variations, respectively. The distribution proportion of each component of soil labile organic carbon in the secondary forest of P. massoniana increased first and then decreased with the increase of stand age, among which the distribution proportion of soil EOC was the largest, the distribution proportion of young forest, middle forest and mature forest were 29.96%, 33.29% and 33.35% respectively. In the vertical direction, the soil MBC and EOC of P. massoniana secondary forest decreased with the deepening of soil depth after the sudden forest fire, while the soil DOC of mature forest increased with the deepening of soil depth, and there was no obvious change rule of soil POC. Forest fires reduced the content of soil labile organic carbon components of P. massoniana secondary forest at different ages, and in the vertical direction, the changes of the content of soil labile organic carbon components of P. massoniana secondary forest at all ages decreased with soil depth.