Phosphorus rather than nitrogen enhances CO₂ emissions in tropical forest soils: Evidence from a laboratory incubation study

Abstract

Ecosystem functional responses such as soil CO 2 emissions are constrained by microclimate, available carbon (C) substrates and their effects upon microbial activity. In tropical forests, phosphorus (P) is often considered as a limiting factor for plant growth, but it is still not clear whether P constrains microbial CO 2 emissions from soils. In this study, we incubated seven tropical forest soils from Brazil and Puerto Rico with different nutrient addition treatments (no addition, Control; C, nitrogen (N) or P addition only; and combined C, N and P addition (CNP)). Cumulative soil CO 2 emissions were fit with a Gompertz model to estimate potential maximum cumulative soil CO 2 emission (C m ) and the rate of change of soil C decomposition (k). Quantitative polymerase chain reaction (qPCR) was conducted to quantify microbial biomass as bacteria and fungi. Results showed that P addition alone or in combination with C and N enhanced C m , whereas N addition usually reduced C m , and neither N nor P affected microbial biomass. Additions of CNP enhanced k, increased microbial abundances and altered fungal to bacterial ratios towards higher fungal abundance. Additions of CNP, however, tended to reduce C m for most soils when compared to C additions alone, suggesting that microbial growth associated with nutrient additions may have occurred at the expense of C decomposition. Overall, this study demonstrates that soil CO 2 emission is more limited by P than N in tropical forest soils and those effects were stronger in soils low in P. Highlights• A laboratory incubation study was conducted with nitrogen, phosphorus or carbon addition to tropical forest soils. Soil CO 2 emission was fitted with a Gompertz model and soil microbial abundance was quantified using qPCR. Phosphorus addition increased model parameters C m and soil CO 2 emission, particularly in the Puerto Rico soils. Soil CO 2 emission was more limited by phosphorus than nitrogen in tropical forest soils.

Modeling Soil Responses to Nitrogen and Phosphorus Fertilization Along a Soil Phosphorus Stock Gradient

“…Jena Soil Model was able to reproduce the R s decreases to N addition, but only simulated an R s increase to P addition in the most P-poor site LUE and R s decreases at other sites ( Table 5 and Figure 3). The fact that in JSM, R s increased after P addition only at the very P-poor site agrees with the finding that P-poor tropical soils usually have positive R s responses to P addition while other soils not (Hui et al, 2019;Zhu, 2019, Fanin et al, 2012). Although R s decreases can be simulated after N and P addition in JSM, the reasons are different for N and P. N addition leads to a decreased N mining and thus decreased respiration, while P addition leads to increased SOC sequestration thus decreased respiration.…”

Higher carbon sequestration potential and stability for deep soil compared to surface soil regardless of nitrogen addition in a subtropical forest

“…Long-term experiments were needed to monitor the processes of C sequestration. Third, new C sequestration also varied with the quality and quantity of the exogenous C. Four, compared to N availability, P availability was suggested to be more important to soil C cycling in tropical and subtropical forests (Hui et al, 2019). The ignoring of P availability and CNP stoichiometry in this study would constrain the application of our results.…”

Phosphorus addition decreases microbial residual contribution to soil organic carbon pool in a tropical coastal forest

“…Hui et al. (2019) also found that soil CO 2 emission was more limited by P than N in tropical forest soils. Our results indicated that N addition significantly decreased NAG activity, but increased BG activity.…”