Reconciling simulations of seasonal carbon flux and soil water with observations using tap roots and hydraulic redistribution: A multi-biome FLUXNET study

• Published in: Agricultural and forest meteorology Vol. 198-199; pp. 309 - 319
• Main Author: Alton, Paul B.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.11.2014; Elsevier
• Subjects: Agricultural and forest climatology and meteorology. Irrigation. Drainage; Agronomy. Soil science and plant productions; Biological and medical sciences; Carbon; Carbon cycle; climate; Computational fluid dynamics; Computer simulation; deciduous forests; Drought; dry season; ecosystems; energy flow; evapotranspiration; Fluid flow; Flux; FLUXNET; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; Hydraulics; Land-surface modelling; Moderate resolution imaging spectroradiometer (MODIS); Physical properties; Physics, chemistry, biochemistry and biology of agricultural and forest soils; Roots; shrubs; Simulation; Soil science; soil water; soil water content; tap roots; trees; tropical forests; Water and solute dynamics; Water cycle; Carbon cycle; Land-surface modelling; Drought; Water cycle; Moderate resolution imaging spectroradiometer (MODIS); FLUXNET; On board equipment; Biometeorology; Carbon exchange rate; Soil moisture; Hydraulics; Measurement sensor; Property of soil; Earth surface; Physical properties; Time variation; Modeling; Soil water properties; Biome; Redistribution; Simulation; Seasonal variation; Observation
• ISSN: 0168-1923; 1873-2240
• DOI: 10.1016/j.agrformet.2014.08.019

•Land-surface models overestimate seasonal drought for trees and shrubs.•Tap root required in standard land-surface models to reproduce seasonal carbon flux.•Tap roots most important in tropical broadleaf forest.•Land-surface models too dry with respect to observed soil moisture.•Tap root rather than hydraulic redistribution affects seasonal totals. Understanding the response of plants to soil moisture stress is important given a future climate subject to greater extremes, including drought. Nevertheless, major discrepancies still exist between observed and simulated seasonal carbon, water and energy fluxes at the vegetated land-surface. For tropical forest, these discrepancies have been reduced, especially during the dry season, by taking account of tap roots and hydraulic redistribution. The expanding FLUXNET open-access archive allows the current study to extend the investigation of seasonal drought-stress to ten different vegetation types. A state-of-the-art land-surface model is enhanced to take account of tap roots and hydraulic redistribution in order to compare with traditional simulations. Carbon fluxes and fractional soil water content are simulated and compared against observations. We find that a traditional approach, by neglecting tap roots, simulates a seasonal drought for trees and shrubs which is generally too severe compared to observed net carbon flux. The introduction of a tap root benefits tropical broadleaf forest and other ecosystems with high annual potential evapotranspiration in reducing observation-model discrepancies. Our simulations suggest a minor role for hydraulic redistribution, modifying weekly soil moisture rather than substantially changing seasonal water flux totals.