Climate and breeding determined below-ground biomass allocation strategy in wheat

Abstract

Farmland covers about 12% of the ice-free terrestrial surface, and crop below-ground biomass allocation plays a pivotal role in the sequestration of atmospheric carbon. Nevertheless, our understanding of the integrated response of crop belowground biomass allocation strategy to concomitant variation in key environmental factors related to water and nutrient availability remains limited. Furthermore, it is imperative to conduct further analysis to elucidate the influence of breeding efforts geared toward improving crop yield on the below-ground biomass allocation strategy. Here we compiled a global wheat root mass fraction (RMF) database with 221 observations from 39 studies to analyze the integrated response of RMF to climate, soil properties and filed managements, and the relationship of RMF and yield. We identified an aridity index (AI) threshold of 0.44 for wheat below-ground biomass allocation strategy, based on the effect of long-term climate on plow-layer soil organic carbon and field water capacity (FWC). The negative effect of nitrogen fertilizer rate on RMF along the AI gradient did not significantly change but the main mechanism shifted from indirect to direct effects. For AI < 0.44, the response of RMF to change of water availability was relatively conservative with the insignificant effects of FWC on RMF. However, RMF was highly sensitive to precipitation distribution during the growth stage because RMF decreased as the ratio of precipitation during the reproductive stage to the growth stage increased. We did not observe a significant correlation between RMF and yield within the main range of RMF so a large amount of intraspecific variation in belowground biomass allocation strategies had not been filtered out by breeding. For AI ≥ 0.44, RMF was highly sensitive to water resource availability as RMF significantly decreased with an increase in FWC. Yield decreased significantly with increasing RMF within the main range of RMF, resulting in highly consistent intraspecific belowground biomass allocation strategies under the pressure of breeding. The results suggested long-term climate condition and breeding played critical filters in wheat below-ground biomass allocation strategy and provided a more accurate prediction of RMF for global carbon cycle models and crop growth models.