Divergence in root functional trait variation for yield improvement

Functional traits are fundamental for understanding and predicting crop responses to abiotic stress and yield improvement. Root functional traits are key determinants of carbon allocation and water transport efficiency. However, there are few studies integrating the effects of physiological and anatomical traits relevant to carbon allocation and water transport in roots on yield.We performed a global scale data analysis to quantify the ecological effects of root functional traits on yield under abiotic stress. A field study was also conducted to test the relationships between yield and root anatomical traits such as cortex area and xylem area in two semi-arid regions in China.The search of the literature on the relationships between the effects of abiotic stress on crop yield and root functional traits was consistent with the results in the field. Meta-analysis showed that critical thresholds of root respiration and xylem area were observed for yield under abiotic stress. Yield initially increased, then declined as root respiration and xylem area increased under stress. It also showed that root hydraulic conductance was positively correlated with xylem area under stress. The similar results were observed in the field study that there were inverse relationships between yield and cortex areaand root xylem area was positively related to yield of wheat at both sites.<b> </b>Our study suggests that there are inverse relationships between yield and cortex area and respiration. Increased yield was associated with decreased respirationwith potentially smaller cortical tissue when the respiration under abiotic stress was reduced by less than 36.5% compared withcontrol. However, increased water transport capacity with increased xylem area has contributed to high yields at both sites under rain-fed conditions.