Early Influence Of Forest Gap Harvesting On Soil Microbial Biomass And Nutrient In Pinus Massoniana Plantation

We explored the response of soil microbial biomass and nutrient to forest gap disturbance in Pinus massoniana plantation ecosystem, which directed by near natural forest management thoughts. The study took seven size gaps(G1:100 m2, G2:225 m2, G3:400 m2, G4:625 m2, G5:900 m2, G6:1225 m2, G7:1600 m2) as obiects and pure 39-year-old plantation as a control, analyzed the soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial biomass phosphorus (MBP) ammonium nitrogen(NH4+-N), nitrate nitrogen (NO3--N), available phosphorus (AP), soil organic matter (SOM), total nitrogen (TN) and total phosphorus (TP) seasonal variation in gap center and gap edge. The result shows that:(1) Forest gap size was significant effect on MBC both of the two soil layer, but it was significant effect on MBN and MBP only at 0-10 cm depth soil. MBN and MBC had basically the same change trend that lowered after the first change with the increase of forest gap, but MBN in next spring had a high rise, MBP had a resemblance only in gap center. MBC, MBN and MBP were respectively higher in the area of 400-900 m2, 225-625 m2,225-900 m2 of forest gap. Overall, medium-sized forest gap is more advantageous of appreciation of the microbial biomass. The influence of gap size was only significantly on soil AP at 10-20 cm depth about all soil available nutrients. There were higher soil AP in the center of forest gap bigger than 900 m2 and in the edge of gap in area of 225-625 m2 at the soil depth of 0-10 cm, and lower in medium-sized forest gap at 10-20 cm. In addition, forest gap size had a significant effect on SOM both of the soil layer, but the TN and TP were not significant. SOM rose first, and then fall overall.(2) The differences of soil each index between gap center and gap edge were not significant, but the index on the whole, but they had certain improved in gap, especially of MBC, MBN, SOM and AP, compared with pure stand of Pinus massoniana. It was showed that, soil microbial activity had improved greatly, and organic residues were more likely to break into the soil in forest gap. In addition, two levels of soil MBC, MBN, MBP, NH4+-N, SOM and TN had significant difference. It was thus clear that:soil microbial activity is more intense, organic matter is absorbed more quickly at depth of 0-10 cm in early of forest gap being formed.(3) The affected of seasonal variation on MBC, MBN and MBP of two soil layer were significantly. MBC of 0-10 cm soil was higher in summer and lower in twice spring, it were generally higher in autumn and lower in winter at 10-20 cm; MBN in summer and spring was significantly higher than the other seasons; MBP of 0-10 cm was higher in autumn and the next spring, and higher in winter and lower in spring at 10-20 cm. And the soil available nutrients had also high significant seasonal variation. Soil NHU+-N and NO3--N were significantly higher in spring and summer of the first year than other three seasons of 0-10 cm soil; soil NH4+-N was highest in autumn at 10-20 cm, NO3--N in contrast. AP rose first then lowered at 0-10 cm as the whole, the peak frequently found in the summer, but the peak was found in spring at 10-20 cm. In addition, the seasonal variation has a significant influence on soil SOM, TN, but not on TP. Overall, SOM in first upper soil was significantly higher than the other in spring and summer season, while the subsoil was higher in fall. TN was basic conversely with SOM.(4) The correlation analysis results showed that, it had a close relation among soil organic matter, microbial biomass and nutrient. Therefore, the cycle of soil nutrient being improved after forest gap harvesting, this was beneficial to the vegetation recovery and updates. At the same time, soil temperature promoted the increment of microbial biomass carbon and nitrogen, and the accumulation of available nitrogen and organic matter, soil moisture only promoted the accumulation of organic matter, and decreased the MBN and NH4+-N. Thus, soil temperature was the main environmental factors affect soil nutrient cycle after forest gap formed.