Effects of cultivation Polygonatum cyrtonema and Sarcandra glabra under Cunninghamia lanceolata plantation on soil physical and chemical properties

An understory cultivation experiment of Polygonatum cyrtonema and Sarcandra glabra was conducted in C. lanceolata plantation in Luoguopu state-owned forest farm in Linshui County, Guang'an City, Sichuan Province. A randomized block design was adopted to set up cultivation areas for P. cyrtonema and S. glabra, as well as a control area of pure C. lanceolata forest. Soil samples of the 0-20 cm layer were collected to determine the soil moisture content, pH, organic carbon (SOC), total nitrogen (TN), ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃⁻-N), total phosphorus (TP), available phosphorus (AP), total potassium (TK), and available potassium (AK) content. The results showed that the cultivation of P. cyrtonema and S. glabra under C. lanceolata plantation significantly increased the SOC and TN contents by 29.94%, 22.63%, 51.16%, 36.7% respectively, and the promotion effect of P. cyrtonema on SOC and TN was more significant. The cultivation of P. cyrtonema and S. glabra under C. lanceolata plantation also significantly increased the soil NH₄⁺-N and NO₃⁻-N contents by 38.87%, 51.25%, 29.50%, 16.14%, respectively. Additionally, the cultivation of P. cyrtonema and S. glabra under C. lanceolata plantation increased the soil TK and AK contents by 7.56%, 9.45% and 36.12%, 21.50%, respectively. However, there was a tendency for the cultivation of P. cyrtonema and S. glabra under C. lanceolata plantation to reduce soil moisture content, TP, and AP content. To sum up, planting P. cyrtonema and S. glabra under C. lanceolata plantation improved soil fertility on the whole.