The influence of soils on heterotrophic respiration exerts a strong control on net ecosystem productivity in seasonally dry Amazonian forests

[摘要] Net ecosystem productivity of carbon (NEP) in seasonally dry forestsof the Amazon varies greatly between sites with similarprecipitation patterns. Correctly modeling the NEP seasonality withterrestrial ecosystem models has proven difficult.Previousmodelling studies have mostly advocated for incorporating processes thatact to reduce water stress on gross primary productivity (GPP)during the dry season, such as deep soils and roots,plant-mediated hydraulic redistribution of soil moisture, andincreased dry season leaf litter generation which reduces leaf ageand thus increases photosynthetic capacity. Recent observations,however, indicate that seasonality in heterotrophic respiration alsocontributes to the observed seasonal cycle of NEP. Here, we use thedynamic vegetation model CLASS-CTEM (Canadian LandSurface Scheme–Canadian TerrestrialEcosystem Model) – without deep soils or roots,hydraulic redistribution of soil moisture, or increased dry seasonlitter generation – at two Large-Scale Biosphere–AtmosphereExperiment (LBA) sites (Tapajós km 83 and JarúReserve). These LBA sites exhibit opposite seasonal NEP cyclesdespite reasonably similar meteorological conditions. Our simulations are ableto reproduce the observed NEP seasonality at both sites. SimulatedGPP, heterotrophic respiration, latent and sensible heat fluxes,litter fall rate, soil moisture and temperature, and basicvegetation state are also compared with available observation-basedestimates which provide confidence that overall the model behavesrealistically at the two sites.Our results indicate thatrepresenting the effect of soil moisture on heterotrophic respiration in terms of soil matric potential and constrainingheterotrophic respiration when absolute soil matric potential is both low (wetter soils) and high (drier soils), with optimum conditions in between, allows%appropriately representing the influence of soil texture and depth,%through soil moisture, on seasonal patterns of GPP and, especially,%heterotrophic respiration is importantto correctly simulate NEPseasonality.

[学科分类] 地球化学与岩石