Response of Soil CO2 Emissions to Straw-returning in Citrus/Mushroom Intercropping Systems

Abstract

Based on the pattern of citrus tree/stropharia mushrooms intercropping, returning-straw was used as the raw material for the stropharia mushrooms, and an in-situ experiment was conducted to monitor soil CO2 emissions under different dosage of straw application during the stropharia growth period. Soil CO2 emissions and the influencing factors were analyzed under different treatments of cultivated (HSM, ASM, and DSM) and uncultivated stropharia mushrooms (HS, AS, and DS). The mushroom yield and soil carbon emission efficiency (CEE) were used to provide a theoretical basis for improving the use of land under citrus orchards. The results showed that:① Straw return increased the cumulative CO2 emissions compared with the control system (conventional planting, CK) and cumulative CO2 emissions increased with the dosage of straw application. Cumulative CO2 emissions from soil treated with cultivated stropharia mushrooms were higher than those from soil treated with uncultivated stropharia mushrooms, in the order of DSM (52.09 t·hm-2) > ASM (41.10 t·hm-2) > HSM (33.20 t·hm-2) > DS (27.15 t·hm-2) > AS (25.34 t·hm-2) > HS (18.94 t·hm-2) > CK (12.16 t·hm-2). Cumulative CO2 emissions under the DSM treatment significantly increased by 328.37% compared with CK. ② For the treatment of cultivated stropharia mushrooms, peak soil CO2 emissions occurred during the period of mycelium growth. The highest cumulative CO2 emissions during this period were obtained under the DSM treatment and accounted for 43.27% of the total cumulative emissions. This was followed by ASM and HSM which accounted for 42.63% and 40.57% of emissions, respectively. ③ Cultivated stropharia mushrooms reduced the temperature sensitivity coefficient (Q10). The soil temperature (5 cm depth) had a significant effect on the soil CO2 emission rate (P<0.01) but soil moisture did not (P>0.05). Soil temperature explained 27% to 71% of the variation in soil CO2 emissions rates, and the two-factor fitting of soil temperature and soil moisture explained 36% to 82% of the variation. ④ For the treatment of cultivated stropharia mushrooms, the ranked yield of each treatment was DSM (49.7 t·hm-2) > ASM (47.0 t·hm-2) > HSM (23.3 t·hm-2), and ASM had the highest soil CEE (1.14). Therefore, under the system of citrus tree/stropharia mushroom intercropping, straw return can increase soil CO2 emissions, with the highest emissions being obtained when a double dosage of straw was applied. However, the optimal amount of straw still needs to be determined in combination with changes in soil nutrients and crop yields.