ABSTRACT
Fire, as a natural disturbance, significantly shapes and influences the functions and services of terrestrial ecosystems via biotic and abiotic processes. Comprehending the influence of fire on soil greenhouse gas dynamics is crucial for understanding the feedback mechanisms between fire disturbances and climate change. Despite work on CO2 fluxes, there is a large uncertainty as to whether and how soil CH4 and N2O fluxes change in response to fire disturbance in terrestrial ecosystems. To narrow this knowledge gap, we performed a meta-analysis synthesizing 3615 paired observations from 116 global studies. Our findings revealed that fire increased global soil CH4 uptake in uplands by 23.2 %, soil CH4 emissions from peatlands by 74.7 %, and soil N2O emissions in terrestrial ecosystems (including upland and peatland) by 18.8 %. Fire increased soil CH4 uptake in boreal, temperate, and subtropical forests by 20.1 %, 38.8 %, and 30.2 %, respectively, and soil CH4 emissions in tropical forests by 193.3 %. Additionally, fire negatively affected soil total carbon (TC; -10.3 %), soil organic carbon (SOC; -15.6 %), microbial biomass carbon (MBC; -44.8 %), dissolved organic carbon (DOC; -27 %), microbial biomass nitrogen (MBN; -24.7 %), soil water content (SWC; -9.2 %), and water table depth (WTD; -68.2 %). Conversely, the fire increased soil bulk density (BD; +10.8 %), ammonium nitrogen (NH4+-N; +46 %), nitrate nitrogen (NO3--N; +54 %), pH (+4.4 %), and soil temperature (+15.4 %). Our meta-regression analysis showed that the positive effects of fire on soil CH4 and N2O emissions were significantly positively correlated with mean annual temperature (MAT) and mean annual precipitation (MAP), indicating that climate warming will amplify the positive effects of fire disturbance on soil CH4 and N2O emissions. Taken together, since higher future temperatures are likely to prolong the fire season and increase the potential of fires, this could lead to positive feedback between warming, fire events, CH4 and N2O emissions, and future climate change.
ABSTRACT
A significant increase in reactive nitrogen (N) added to terrestrial ecosystems through agricultural fertilization or atmospheric deposition is considered to be one of the most widespread drivers of global change. Modifying biomass allocation is one primary strategy for maximizing plant growth rate, survival, and adaptability to various biotic and abiotic stresses. However, there is much uncertainty as to whether and how plant biomass allocation strategies change in response to increased N inputs in terrestrial ecosystems. Here, we synthesized 3516 paired observations of plant biomass and their components related to N additions across terrestrial ecosystems worldwide. Our meta-analysis reveals that N addition (ranging from 1.08 to 113.81 g m-2 year-1 ) increased terrestrial plant biomass by 55.6% on average. N addition has increased plant stem mass fraction, shoot mass fraction, and leaf mass fraction by 13.8%, 12.9%, and 13.4%, respectively, but with an associated decrease in plant reproductive mass (including flower and fruit biomass) fraction by 3.4%. We further documented a reduction in plant root-shoot ratio and root mass fraction by 27% (21.8%-32.1%) and 14.7% (11.6%-17.8%), respectively, in response to N addition. Meta-regression results showed that N addition effects on plant biomass were positively correlated with mean annual temperature, soil available phosphorus, soil total potassium, specific leaf area, and leaf area per plant. Nevertheless, they were negatively correlated with soil total N, leaf carbon/N ratio, leaf carbon and N content per leaf area, as well as the amount and duration of N addition. In summary, our meta-analysis suggests that N addition may alter terrestrial plant biomass allocation strategies, leading to more biomass being allocated to aboveground organs than belowground organs and growth versus reproductive trade-offs. At the global scale, leaf functional traits may dictate how plant species change their biomass allocation pattern in response to N addition.
