Abstract
Roots are an important water transport pathway between soil and plant. Root water uptake (RWU) plays a key role in water and heat exchange between plants and the atmosphere. Inaccurate RWU schemes in land surface models are one crucial reason for decreased model performance. Despite some types of RWU functions being adopted in land surface models, none have been certified as suitable for maize farmland ecosystems. Based on 2007–2009 data observed at the maize agroecosystem field station in Jinzhou, China, the RWU function and root distribution (RD) in the Common Land Model (CoLM) were optimized and the effects of the optimizations on model performance were compared. Results showed that RD parameters calculated with root length density were more practical relative to root biomass in reflecting soil water availability, and they improved the simulation accuracy for water and heat fluxes. The modified RWU function also played a significant role in optimizing the simulation of water and heat fluxes. Similarly, the respective and integrated roles of two optimization schemes in improving CoLM performance were significant during continuous non-precipitation days, especially during the key water requirement period of maize. Notably, the improvements were restrained within a threshold of soil water content, and the optimizations were inoperative outside this threshold. Thus, the optimized RWU function and the revised RD introduced into the CoLM model are applicable for simulation of water and heat fluxes for maize farmland ecosystems in arid areas.
Highlights
Roots are an important pathway for water and energy exchange between the soil, vegetation and the atmosphere [1]
According to the partitioning of soil layers in the Common Land Model (CoLM), the thickness of the third soil layer in the model corresponded to a soil water content (SWC) observation depth of 0–10 cm, represented as SWC10; the fifth layer was a depth of 20–30 cm, represented as SWC20–30; and the sixth layer was a depth of 30–50 cm, represented as SWC30–50
The observed SWC values were little influenced by small amounts of rain, possibly because the penetration of drizzle could not reach a depth of 10 cm
Summary
Roots are an important pathway for water and energy exchange between the soil, vegetation and the atmosphere [1]. The root water uptake (RWU) process as a key link in the surface water cycle, which distributes precipitation through evaporation, transpiration and infiltration, and closely connects with carbon cycle processes through coupling with photosynthesis [2]. Water 2018, 10, 1090 relates to the distribution of RWU at various soil depths [4,5], but available data are very scarce because of difficulties with observation, leading to simplifications of corresponding parameters thereby affecting simulation of the RWU process. There are three root distribution parameterization schemes in existing mainstream land surface models. The first one proposed by Jackson et al [6] has an exponential relationship between accumulated root fraction and soil depth, as applied in the Land
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