Soil respiration following Chinese fir plantation clear-cut: Comparison of two forest regeneration approaches

Thinning intensity but not replanting different species affects soil N2O and CH4 fluxes in Cunninghamia lanceolata plantation

Thinning and replanting are effective forest management measures to improve the stand structure and species composition of artificial forests. However, the effects of thinning and replanting on soil N₂O and CH₄ fluxes and their associations with changes in soil environment factors have been poorly understood in plantation forests. A 36-month field experiment was conducted to elucidate the effects of thinning and replanting different species on soil N₂O and CH₄ fluxes and related environmental factors in Cunninghamia lanceolata plantation on shallow soil. The experiment consisted of five treatments, uncut control (CK), moderate thinning + replanting evergreen seedlings (MTE), moderate thinning + replanting deciduous seedlings (MTD), heavy thinning + replanting evergreen seedlings (HTE), heavy thinning + replanting deciduous seedlings (HTD). Compared with the control, moderate and heavy thinning increased cumulative N₂O emissions by 12.4% and 21.4%, respectively, and reduced CH₄ cumulative uptake by 35.4% and 38.8%, respectively. However, the effects on soil N₂O and CH₄ fluxes replanting deciduous or evergreen seedlings were insignificant. The results showed that thinning increased N₂O emissions and decreased CH₄ uptake due to the increased soil temperature, labile C and N concentrations. Soil temperature was the dominant factor, and mineral N was a contributing factor affecting N₂O and CH₄ fluxes. The study concludes that thinning increased the global warming potential with N₂O contributing more than CH₄ (113.5%: -13.5%). Our findings highlight that thinning increased N₂O emissions and decreased CH₄ uptake with the increasing intensity and the replanting had no different effects between deciduous and evergreen seedlings on the fluxes of N₂O and CH₄ during the early years following thinning.

The Effect of the Conversion from Natural Broadleaved Forests into Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) Plantations on Soil Microbial Communities and Nitrogen Functional Genes

The conversion of forests could change soil characteristics and, in turn, impact the microbial community. However, the long-term effect of forest transformation on bacterial and archaeal composition and diversity, especially on nitrogen functional communities, is poorly understood. This study aimed to explore the response of soil bacterial and archaeal communities, as well as nitrogen functional groups, to the conversion from natural broadleaved forests to Chinese fir (Cunninghamia lanceolate (Lamb.) Hook.) plantations in subtropical China by 16S rRNA amplicon sequencing. Except for soil bulk density (BD) and ammonium nitrogen (NH4+–N) content, other soil properties all decreased with the conversion from natural forests to plantations. Alpha diversity of bacteria and archaea declined with the transformation from natural forests to plantations. The composition of bacteria and archaea was significantly different between natural forests and plantations, which could be mainly attributed to the change in the content of soil organic carbon (SOC), total nitrogen (TN), nitrate nitrogen (NO3−–N), and available phosphorus (AP). The conversion of natural forests to plantations decreased the gene copies of ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), and nifH (nitrogen fixation function) but increased denitrification gene copies (i.e., nirS, nirK, and nosZ). In summary, our study emphasizes the long-term negative effect of the conversion from natural broadleaved forests into Chinese fir plantations on the diversity and richness of soil microbial communities, thereby deeply impacting the cycling of soil nitrogen.