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  1. Free, publicly-accessible full text available November 1, 2024
  2. Abstract

    Soil CO2concentrations and emissions from tropical forests are modulated seasonally by precipitation. However, subseasonal responses to meteorological events (e.g., storms, drought) are less well known. Here, we present the effects of meteorological variability on short‐term (hours to months) dynamics of soil CO2concentrations and emissions in a Neotropical wet forest. We continuously monitored soil temperature, moisture, and CO2for a three‐year period (2015–2017), encompassing normal conditions, floods, a dry El Niño period, and a hurricane. We used a coupled model (Hydrus‐1D) for soil water propagation, heat transfer, and diffusive gas transport to explain observed soil moisture, soil temperature, and soil CO2concentration responses to meteorology, and we estimated soil CO2efflux with a gradient‐flux model. Then, we predicted changes in soil CO2concentrations and emissions under different warming climate change scenarios. Observed short‐term (hourly to daily) soil CO2concentration responded more to precipitation than to other meteorological variables (including lower pressure during the hurricane). Observed soil CO2failed to exhibit diel patterns (associated with diel temperature fluctuations in drier climates), except during the drier El Niño period. Climate change scenarios showed enhanced soil CO2due to warmer conditions, while precipitation played a critical role in moderating the balance between concentrations and emissions. The scenario with increased precipitation (based on a regional model projection) led to increases of +11% in soil CO2concentrations and +4% in soil CO2emissions. The scenario with decreased precipitation (based on global circulation model projections) resulted in increases of +4% in soil CO2concentrations and +18% in soil CO2emissions, and presented more prominent hot moments in soil CO2outgassing. These findings suggest that soil CO2will increase under warmer climate in tropical wet forests, and precipitation patterns will define the intensity of CO2outgassing hot moments.

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  3. Summary

    Arbuscular mycorrhizal (AM) fungi are the most abundant plant symbiont and a major pathway of carbon sequestration in soils. However, their basic biology, including their activity throughout a 24‐h day : night cycle, remains unknown.

    We employed thein situSoil Ecosystem Observatory to quantify the rates of diurnal growth, dieback and net productivity of extra‐radicalAMfungi.AMfungal hyphae showed significantly different rates of growth and dieback over a period of 24 h and paralleled the circadian‐driven photosynthetic oscillations observed in plants.

    The greatest rates (and incidences) of growth and dieback occurred between noon and 18:00 h. Growth and dieback events often occurred simultaneously and were tightly coupled with soil temperature and moisture, suggesting a rapid acclimation of the external phase ofAMfungi to the immediate environment.

    Changes in the environmental conditions and variability of the mycorrhizosphere may alter the diurnal patterns of productivity ofAMfungi, thereby modifying soil carbon sequestration, nutrient cycling and host plant success.

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  4. Abstract

    Leaf‐cutter ants are a prominent feature in Neotropical ecosystems, but a comprehensive assessment of their effects on ecosystem functions is lacking. We reviewed the literature and used our own recent findings to identify knowledge gaps and develop a framework to quantify the effects of leaf‐cutter ants on ecosystem processes.

    Leaf‐cutter ants disturb the soil structure during nest excavation changing soil aeration and temperature. They mix relatively nutrient‐poor soil from deeper layers with the upper organic‐rich layers increasing the heterogeneity of carbon and nutrients within nest soils.

    Leaf‐cutter ants account for about 25% of all herbivory in Neotropical forest ecosystems, moving 10%–15% of leaves in their foraging range to their nests. Fungal symbionts transform the fresh, nutrient‐rich vegetative material to produce hyphal nodules to feed the ants. Organic material from roots and arbuscular mycorrhizal fungi enhances carbon and nutrient turnover in nest soils and creates biogeochemical hot spots. Breakdown of organic matter, microbial and ant respiration, and nest waste material decomposition result in increased CO2, CH4,and N2O production, but the build‐up of gases and heat within the nest is mitigated by the tunnel network ventilation system. Nest ventilation dynamics are challenging to measure without bias, and improved sensor systems would likely solve this problem.

    Canopy gaps above leaf‐cutter ant nests change the light, wind and temperature regimes, which affects ecosystem processes. Nests differ in density and size depending on colony age, forest type and disturbance level and change over time resulting in spatial and temporal changes of ecosystem processes. These characteristics remain a challenge to evaluate rapidly and non‐destructively.

    Addressing the knowledge gaps identified in this synthesis will bring insights into physical and biological processes driving biogeochemical cycles at the nest and ecosystem scale and will improve our understanding of ecosystem biogeochemical heterogeneity and larger scale ecological phenomena.

    Aplain language summaryis available for this article.

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