A global meta-analysis reveals the positive effect of invasive alien plants on soil heterotrophic respiration

Plant invasions represent a major global change in the carbon cycle. Soil respiration (Rs) comprises autotrophic respiration (Ra) and heterotrophic respiration (Rh). Understanding the impacts of plant invasions on different components of soil respiration is critical for predicting how invasive alien plants (IAPs) affect the exchange of C between the atmosphere and terrestrial ecosystems. However, the responses of Rs, Rh and Ra to IAPs are poorly understood on a global scale. We conducted a meta-analysis based on 54 published papers and 256 observations to explore the effects of IAPs on Rs, Rh and Ra. Overall, the results showed that at the global scale, IAPs significantly increased the Rh by an average of 87.91% but had no significant effects on Rs or Ra. Regarding the life forms, we found that invasive forbs significantly increased Rh regardless of ecosystem type, and the subgroup analysis of ecosystem types showed that invasive forbs significantly increased Rh only in grasslands. However, the effects of IAPs on soil Rs and Rh did not differ among ecosystem types. Soil respiration is substantially influenced by soil biotic and abiotic properties. We found IAPs significantly increased microbial biomass carbon (MBC) by 9.28% (mainly from invasive forbs) and soil β-glucosidase activity by 80.35% (mainly from invasive shrubs), but the IAPs had no significant effect on invertase activity. The effect size of Rh was significantly positively correlated with the changes in soil pH, MBC and β-glucosidase. In addition, the response of Rh differed depending on the ecosystem management approach. IAPs significantly increased the Rh in abandoned ecosystems but had no significant effects on the Rh in managed ecosystems or natural ecosystems. These results emphasize the importance and complexity of the relationship between IAPs and soil respiration and highlight the need for better management to reduce soil respiration due to plant invasion.