The Early Effects of Forest Gap Harvesting on Soil Microbial Biomass in Pinus massoniana Plantations
There are a certain degree of low-efficient Pinus massoniana plantations in a hilly area of the upper reaches of the Yangtze River. To understand the forest gap formed by artificial tending thinning to regulate forest structure and the impact on ecological effect of low-efficient plantation, which to provide critical scientific basis for the optimum control mode of forest gap size of masson pine plantation in the hilly area. The study takes seven gaps with different sizes(G1: 100 m2, G2: 225 m2, G3: 400 m2, G4: 625 m2, G5: 900 m2, G6: 1225 m2, G7: 1600 m2) as objects and pure 39-year-old plantation as a control, analyzes the seasonal variations of soil microbial biomass carbon(MBC), microbial biomass nitrogen(MBN) and microbial biomass phosphorus(MBP) at the centers and edges of the gaps. The results show that: 1) the gap size has significant effect on soil MBC and MBP at different locations, but has no significant impact on the soil MBN. MBN and MBC vary with the same trend, both showing unimodal type change with the increase of gaps, but MBN changes in a smaller range. MBP has only a single peak variation at the gap center. The soil MBC, MBN and MBP are respectivly higher in gaps with area of 400-900 m2, 225-625 m2 and 625-900 m2. 2) Seasonal changes have significantly influence on soil MBC, MBN and MBP. MBC is higher in summer and lower in spring. MBN is higher in summer and lower in winter. MBP changes in more complicated way, and it is relatively high in autumn. Among them, the MBC in 100- 900 m2 gaps is significantly higher in summer than in spring by an increase of more than twice. 3) MBC, MBN and MBP at the center and the edge of the gaps are not significantly different, but the soil MBC and MBN in the forest gaps are significantly higher than those at the understory. 4) Soil temperature has significant influence on MBC and MBN, while soil moisture has significant influence on MBN and MBP. Our findings support that medium- sized gaps are more conducive to microbial biomass appreciation. Compared with pure pine forest, soil microbial activity in the gaps improves greatly. Soil temperature and moisture are important environmental factors affecting soil microbial biomass of Pinus massoniana plantations after gap's formation. The above results provide certain scientific basis to rebuild low-efficient plantation and deeply understand the belowground ecological process.