Ecosystem-dependent responses of soil carbon storage to phosphorus enrichment.

Phosphorus deposition can stimulate both plant carbon inputs and microbial carbon outputs. However, how P enrichment affects soil organic carbon (SOC) storage and the underlying mechanisms remain unclear. We conducted a meta-analysis of 642 SOC observations from 213 field P addition experiments world-wide and explored the regulations of plant inputs, microbial outputs, plant characteristics, and environmental and experimental factors on SOC responses. We found that, globally, P addition stimulated SOC by 4.0% (95% CI: 2.0-6.0%), but the stimulation only occurred in forest and cropland rather than in grassland. Across sites, the response of SOC correlated with that of plant aboveground rather than belowground biomass, suggesting that the change in plant inputs from aboveground was more important than that from belowground in regulating SOC changes due to P addition. Among multiple factors, plant N fixation status and mean annual temperature were the best predictors for SOC responses to P addition, with SOC stimulation being higher in ecosystems dominated by symbiotic nitrogen fixers and ecosystems in high-temperature regions like tropical forests. Our findings highlight the differential and ecosystem-dependent responses of SOC to P enrichment and can contribute to accurate predictions of soil carbon dynamics in a P-enriched world.

Fertilization makes strong associations between organic carbon composition and microbial properties in paddy soil.

Fertilization changes the soil organic carbon (SOC) composition, affecting the carbon cycle of paddy soil. Understanding the mechanisms of physical fraction and chemical composition of SOC responding to fertilization can help regulate the nutrient release and carbon sequestration. However, it is unclear whether these changes in SOC composition to fertilization are consistent and how these are regulated by biotic and abiotic properties. Therefore, a positioning experiment in a rice field was conducted with a total of nine treatments. Chemical fertilizers (0, 337.5, and 675 kg ha-1; C0, C50, and C100, respectively) and fungal residue (0, 10,000, and 20,000 kg ha-1; F0, F50, and F100, respectively) were applied to evaluated (i) changes in the physical fraction and chemical composition of SOC, (ii) changes in soil properties, microbial biomass and community, and (iii) establish relationships among soil properties, microbial community, microbial biomass, and SOC composition. Our results showed that the application of fungal residue exhibited more significant effects on SOC physical fractions than those with the chemical fertilizers. Furthermore, the chemical composition of SOC was more respond to the application of chemical fertilizers than fungal residue. The partial least squares path model indicated that soil properties mainly affected the mineral-associated organic carbon (MAOC) by microbial biomass. In addition, bacterial diversity played an important role in improving the accumulation of MAOC. The SOC chemical composition was mediated by fungal community composition and bacterial diversity. In conclusion, fungal residue application affected SOC physical fraction by increasing soil properties, microbial biomass, and bacterial diversity. Chemical fertilizers application mainly mediated the chemical composition of SOC by altering fungal community composition and decreasing bacterial diversity.

Climate warming alters subsoil but not topsoil carbon dynamics in alpine grassland.

Subsoil contains more than half of soil organic carbon (SOC) globally and is conventionally assumed to be relatively unresponsive to warming compared to the topsoil. Here, we show substantial changes in carbon allocation and dynamics of the subsoil but not topsoil in the Qinghai-Tibetan alpine grasslands over 5 years of warming. Specifically, warming enhanced the accumulation of newly synthesized (14 C-enriched) carbon in the subsoil slow-cycling pool (silt-clay fraction) but promoted the decomposition of plant-derived lignin in the fast-cycling pool (macroaggregates). These changes mirrored an accumulation of lipids and sugars at the expense of lignin in the warmed bulk subsoil, likely associated with shortened soil freezing period and a deepening root system. As warming is accompanied by deepening roots in a wide range of ecosystems, root-driven accrual of slow-cycling pool may represent an important and overlooked mechanism for a potential long-term carbon sink at depth. Moreover, given the contrasting sensitivity of SOC dynamics at varied depths, warming studies focusing only on surface soils may vastly misrepresent shifts in ecosystem carbon storage under climate change.