Impact of Thinning Intensity on Ectomycorrhizal Fungal Communities in Pinus Massoniana Plantations

Ectomycorrhizal (ECM) fungal play an indispensable role in promoting nutrient cycling within forest ecosystems. However, the mechanism by which thinning regulates ECM fungal communities through its effects on soil and plant fine roots are still unclear. To elucidate this, we established a thinning experiment in a 29-year-old low production Pinus Massoniana plantation in southwest China, subjected to four thinning intensities in 2018: 0% (CK, control), 10% (low-intensity thinning; LIT), 30% (moderate-intensity thinning; MIT), and 50% (high-intensity thinning; HIT). Results demonstrated that thinning significantly reduced soil pH (1.45%), soil bulk density (9.70%), and available phosphorus (13.59%), while leaving other soil factors unaffected. All thinning intensities (LIT, MIT, HIT) significantly increased fine root biomass (by 32.36%, 54.47%, and 18.78%, respectively) and fine root total nitrogen (by 53.76%, 116.73%, and 107.71%, respectively). Furthermore, it induced significant shifts in the diversity and composition of the ECM fungal community. The complexity of the ECM fungal co-occurrence network initially increased and then decreased with increasing thinning intensity, exhibiting a recurring complexity pattern. The RDA identified the soil C/P ratio as the key factor shaping the community. A partial least squares regression-structural equation model (PLS-SEM) confirmed that thinning directly altered ECM community composition and fine root nutrients, largely independent of soil nutrient changes. In conclusion, our study highlights that thinning regulates Ectomycorrhizal fungal communities primarily through the modification of host fine root traits rather than direct soil nutrient shifts, emphasizing the importance of plant-soil-microbe feedback in forest ecosystem recovery.