Mixed plantations of Alnus formosana and Pinus massoniana improve ecosystem multifunctionality than monoculture plantations
Abstract
Long-term management of Pinus massoniana monoculture faces significant challenges, including low productivity, nutrient depletion, and weakened ecological functions. Alnus formosana , a native nitrogen-fixing species in southern China, can increase soil fertility and accelerates nutrient cycling. However, the impact of its mixed cultivation with P. massoniana on ecosystem multifunctionality (EMF) remains unclear. This study assessed tree growth, soil characteristics, enzyme activity, and EMF in monocultures and mixed forests at 1:2, 1:1, and 2:1 ratios (APP, AP, and AAP). Results showed that mixed-species treatment significantly increased tree growth index (TGI) of A. formosana but decreased that of P. massoniana ( P <0.05) . In mixed forests, A. formosana had higher diameter at breast height (DBH), tree height (TH), crown width (CW), clear bole height (CBH) and tree volume (V) than P. massoniana , and exhibited stronger competitive effects (Slope-A=1.12∼1.27) on DBH and CW compared to P. massoniana (Slope-P=0.65∼0.96). Soil quality index (SQI) and EMF significantly increased in mixed forests than in monocultures, as evidenced by higher soil C- and N-acquisition enzyme activities and related nutrients. In mixed forests, TGI was positively correlated with SQI of A. formosana but negatively correlated with that of P. massoniana , which led to the growth of A. formosana being more sensitive to available nutrients (nitrate nitrogen, available phosphorus, and ammonium nitrogen), while the growth of P. massoniana was more reliant on soil total nutrients (total nitrogen and total phosphorus). Notably, A. formosana exhibited the highest TGI, SQI, and EMF in the AAP treatment. Thus, the 2:1 (AAP) mixing ratio is recommended for the scientific management of P. massoniana and A. formosana mixed forests.