The lack of mechanistic grounding for soil moisture constraints on carbon and water fluxes in terrestrial biosphere models

The gap

Evidence profile

Sourced from the future work and stated research gap and abstract of the source papers, classified as general, drawn from work published between 2024 and 2026, spanning 2 journals. Those papers have been cited 13 times in total.

Supporting evidence — 3 representative gaps

• Factors Affecting CO2, CH4, and N2O Fluxes in Temperate Forest Soils (2025) · Forests · cited 5× · doi

  While significant progress has been made in understanding the factors driving soil GHG fluxes, key research gaps remain that limit our ability to predict and manage these fluxes under changing environmental and soil conditions. Future research should focus on the following directions: Current research often relies on soil properties such as temperature and moisture; however, our synthesis reveals that site-specific factors, including soil texture, substrate availability, and hydroclimatic conditions, strongly influence these properties. This is es- pecially critical for CH4 and N2O fluxes, which exhibit distinct moisture thresholds, CH4 peaking at 60%–80% WFPS and N2O at approximately 60% WFPS [21,187]. Additionally, soil moisture mediates the temperature sensitivity of soil respiration over long timescales [30,187]. Therefore, considering the interactions between soil properties and hydrocli- matic drivers is important in field studies to improve the accuracy of GHG flux modeling under both variable and similar environmental conditions. Tree species can influence soil microclimate through their canopy structure and phys- iological traits, such as root-mediated water consumption, which differs among tree types and may affect microbial processes and GHG fluxes. Studies on this aspect remain rare in temperate forest ecosystems. Our review demonstrates that these tree-mediated effects Forests 2025, 16, 1723 20 of 32 directly regulate GHG-producing microbial processes: monoterpenes from F. sylvatica and P. abies inhibit CH4 oxidation by up to 90% [141], while ectomycorrhizal hyphae in Pinus spp. enhance CH4 uptake through labile compounds [32,140–142]. Deciduous species with N-rich litter simultaneously stimulate both CO2 emissions through enhanced microbial biomass [51,125] and N2O production through denitrifier activity [126]. Despite these mechanistic insights, the net global warming potential when integrating all three GHGs across different tree species compositions remains unquantified. This knowledge gap lim- its our ability to predict how changes in forest composition, disturbance, or management practices will alter ecosystem C and N fluxes and hinders optimization of forest manage- ment for climate mitigation rather than single-gas fluxes. In forest ecosystems, the soil substrate is complex and depends on both tree species litter and root exudates. Soil substrate complexity depends on tree species’ litter chemistry and root exudates, ranging from simple labile compounds to complex molecules like hydrolysable tannins and recalcitrant lignin. These species-specific traits shape microbial diversity, functional gene abundances (pmoA, nirK, nirS, nosZ, amoA [68,148,150–152] and GHG flux balances. Thus, examining the variation in substrate complexity and microbial response, especially in chemically diverse forest rhizospheres, is crucial because it influences microbial diver- sity, GHG

  generalfuture work
  Keywords: soil uxes tree species microbial forest substrate conditions properties moisture root litter factors remain ability
• Extending the least-cost theory of stomatal regulation to include soil moisture stress (2026) · bioRxiv (Cold Spring Harbor Laboratory) · doi

  The lack of mechanistic grounding for soil moisture constraints on carbon and water fluxes in terrestrial biosphere models. The need for a more coherent alternative to existing soil moisture parameterisations.

  generalstated research gapevidence 5/5
  Keywords: lack mechanistic grounding soil moisture constraints carbon water
• Stand Density Management of Cypress Plantations Based on the Influence of Soil Hydrothermal Conditions on Fine Root Dynamics in Southwestern China (2024) · Forests · cited 8× · doi

  The mechanisms by which the soil physical structure, nutrient conditions, understory vegetation diversity and forest meteorological factors influence fine root (<2 mm diameter) characteristics mediated by soil moisture content (SMC) and soil heat flux (SHF) remain uncertain under climate change.

  generalabstractevidence 5/5
  Keywords: soil mechanisms physical structure nutrient conditions understory vegetation diversity forest meteorological factors influence fine root

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