The effects of global dimming on the wheat crop grown in the Yangtze Basin of China simulated by SUCROS_LL, a process-based model

Low light spell, one of the major causes of reduction in global radiation (global dimming), has become a new challenge to crop production. For assessing impacts of low light spells on wheat yield, we proposed a low light index (LLI) and quantified the effects of low light spell conditions occurring at different development stages on five key crop parameters of wheat (leaf photosynthetic capacity, photosynthetic initial light-use efficiency, specific leaf area, dry matter partitioning index for green leaf and harvest index) as functions of LLI using data from field experiments with different levels (50%, 66% and 84% of reduction in incident radiation from ambient) and durations (2d, 4d, 6d and 8d) of shading treatments. These functions were then incorporated into the generic process-based crop growth model SUCROS97 to develop a model, called SUCROS_LL hereafter, for assessing potential yield loss of wheat caused by low light spells. SUCROS_LL was validated and tested using independent data from field shading experiments and 19 agro-meteorological experimental stations, and then used for assessing the potential yield loss of wheat caused by low light spells in the Middle-Lower Reaches of Yangtze River Basin during 1961–2010. Our field experimental data showed that responses of wheat parameters and yield to low light depended on not only LLI, but also the development stages. Plant adaptive responses cannot fully mitigate the negative effects of short-term substantial reduction in incident radiation on wheat crop yield. Compared with SUCROS97, SUCROS_LL significantly improved prediction accuracy of wheat yield by 37% under field shading experimental conditions and 29% under natural low light spell conditions at the 19 agro-meteorological experimental stations. The simulated potential yield loss of wheat caused by low light spells averaged over 1961–2010 increased from the North (below 10%) to the South (above 40%) in the studied region. Potential yield loss averaged over the whole studied region was estimated to increase from the 1960s to the 1990s by 2.9% per decade, but decrease in the 2000s by 9.1% per decade. Although potential wheat yield loss caused by low light spells has been decreased in the past decade in the studied region, the trends of global dimming suggests that breeding/choice of cultivars with better morphological plasticity in response to light availability is in need to mitigate the negative effects of reduction in incident radiation on wheat growth and yield.