Forest soil CO 2 fluxes as a function of understory removal and N-fixing species addition

Abstract

We report on the effects of forest management practices of understory removal and N-fixing species ( Cassia alata) addition on soil CO 2 fluxes in an Eucalyptus urophylla plantation (EUp), Acacia crassicarpa plantation (ACp), 10-species-mixed plantation (Tp), and 30-species-mixed plantation (THp) using the static chamber method in southern China. Four forest management treatments, including (1) understory removal (UR); (2) C. alata addition (CA); (3) understory removal and replacement with C. alata (UR+CA); and (4) control without any disturbances (CK), were applied in the above four forest plantations with three replications for each treatment. The results showed that soil CO 2 fluxes rates remained at a high level during the rainy season (from April to September), followed by a rapid decrease after October reaching a minimum in February. Soil CO 2 fluxes were significantly higher ( P < 0.01) in EUp (132.6 mg/(m 2·hr)) and ACp (139.8 mg/(m 2·hr)) than in Tp (94.0 mg/(m 2·hr)) and THp (102.9 mg/(m 2·hr)). Soil CO 2 fluxes in UR and CA were significantly higher ( P < 0.01) among the four treatments, with values of 105.7, 120.4, 133.6 and 112.2 mg/(m 2·hr) for UR+CA, UR, CA and CK, respectively. Soil CO 2 fluxes were positively correlated with soil temperature ( P < 0.01), soil moisture ( P < 0.01), NO 3 −-N ( P < 0.05), and litterfall ( P < 0.01), indicating that all these factors might be important controlling variables for soil CO 2 fluxes. This study sheds some light on our understanding of soil CO 2 flux dynamics in forest plantations under various management practices.