Regulatory mechanism of root-mycelial-microorganism interactions on soil phosphorus transformation of Pinus massoniana plantation under mixed renovation

Objective This paper aims to reveal the regulation mechanisms of soil phosphorus fraction conversion in Pinus massoniana plantations under multi-layered, uneven-aged mixed transformation, providing theoretical support for alleviating soil phosphorus limitation and ecological function decline caused by continuous planting of coniferous pure forests.

Method Using Pinus massoniana pure forest and its mixed plantation of different aged with Castanopsis hystri and Erythrophleum fordii as research object, the effects of root-mycelium-microbe interactions on phosphorus cycling were resolved by means of inter-root limiting devices with mesh sizes of 1.45 mm (root + mycelium) and 53 μm (mycelium).

Result (1) Introducing Castanopsis hystri and Erythrophleum fordii mixed transformation into the pure forest, soil total labile phosphorus content was elevated by 41.34% and 44.42%, total moderately labile phosphorus content was elevated by 36.84% and 40.26%. (2) In the mixed forest, total microbial biomass phosphorus content was significantly increased by 91.21% and 79.52%, and the total acid phosphatase activity was significantly increased by 86.25% and 103.46%. Soil total nitrogen, total microbial biomass phosphorus, and L-leucine aminopeptidase were main environmental factors regulating the transformation of soil phosphorus fractions. (3) Only after increasing the involvement of mycelium, phosphorus activation coefficients in the soil of three stands were significantly increased by 24.37%, 20.24%, 20.69%, respectively. (4) Compared with only increasing mycelium involvement, root inputs resulted in total active phosphorus and total moderately active phosphorus in pure forests to decrease by 35.55% and 30.25%, respectively, and the active inorganic phosphorus in Castanopsis hystri and Erythrophleum fordii mixed forests to drop by 28.14% and 34.59%, respectively.

Conclusion The cycling and transformation of soil phosphorus fractions in a mixed mosaic forest are influenced by soil microorganisms, enzyme activities, and soil nitrogen. Roots play a major role in transformation of phosphorus in soil, and the interaction between root system and mycelium can complicate the interactions of microbial communities in their soils, affecting the transformation and effectiveness of soil phosphorus.