Comparison of the Roles of Optimizing Root Distribution and the Water Uptake Function in Simulating Water and Heat Fluxes within a Maize Agroecosystem

Abstract

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.

The Decreased Availability of Soil Moisture and Canopy Conductance Dominate Evapotranspiration in a Rain-Fed Maize Ecosystem in Northeastern China

“…Rain-fed maize was generally sown every year during mid-April to mid-May, and harvested from mid-September to early October, depending on air temperature and soil moisture conditions without irrigation [33,34]. Ji et al [35] pointed out that the threshold of water supply for maize growth was 361-741 mm, and that the appropriate threshold was 451-556 mm in the northeast China.…”

Interannual variability in net ecosystem carbon production in a rain-fed maize ecosystem and its climatic and biotic controls during 2005–2018

“…Therefore, the agroecosystem in the area has a potentially large capacity for carbon sequestration or release depending on climatic and biotic factors. A prolonged drought affected 52.3-62.0% of the area in northeastern China in the past 15 years [31], and there is an increasing trend in temperature of 0.035˚C/a and a decreasing trend in precipitation of −13.3 mm/10a [29]. An increased understanding the relationships between interannual variability in NEP and climatic and biotic controls will aid in efforts to improve the carbon sequestration potential.…”

Interannual variability of net ecosystem carbon production and its climatic and biotic mechanism during 2005-2018 in a rain-fed maize ecosystem

“…As a part of the China FLUX network, the eddy fluxes of carbon dioxide and water vapor of a typical rain-fed maize agroecosystem were measured at the Jinzhou site (41°08' N, 121°12'E, and 23.3 m above sea level) in the northeast China. This flux site is operated by Jinzhou Ecology and Agriculture Meteorological Center, Liaoning Meteorological Bureau, and located in a representative temperate monsoon climate area with an mean annual temperature of 9.4 °C and annual precipitation of 565.9 mm, obtained according to the long-term records (1981-2010) of the adjacent weather station [33]. There were two prevailing wind directions, including north-northeast in winter and south-southeast in summer.…”

“…In northeast China, the average growth rate of air temperature is 0.35℃/10a, and that of precipitation is −13.3 mm/10a, based on the 1961-2010 ground observations from 91 meteorological stations [31,32]. However, the rain-fed spring maize is the dominant crop, and it accounts for 57.2% of the planted area and 64.3% of the crop yield in northeast China, and 33.8% of the total maize yield in China [31,33].…”