Background <p>Studying how economic vegetable adapt to stressful environment is important not only for plant biology application but also to agronomy. In this study, we selected two commonly used genotypes of pak choi, i.e., larger green pak choi (<i>Brassica rapa</i> ssp. <i>chinensis</i>) and smaller purple pak choi (<i>Brassica rapa</i> var. <i>chinensis</i>, ‘Rubi F1’) to examine the divergent response of the two genotypes to drought and shading in the semi-arid region of Xinjiang. We compared the differences in biomass accumulation and plant morphological traits of the two pak choi in response to the interaction effects of drought (55-70% of field water capacity) and shading (24% reduction of canopy light radiation).</p> Results <p>The results showed drought and shading significantly reduced the aboveground and belowground biomass of the two pak choi, with a particularly pronounced decrease in shoot biomass under the combined effect of shading + drought. The decline in shoot biomass was mostly resulted from decreasing in the number of leaves rather than in plant height and crown width in response to drought and shading. In terms of morphological traits, green pak choi sensitively responded to increased drought and shading, with aboveground biomass mostly determined by leaf number and root mass. In contrast, purple pak choi likely more resistant to the stressful environment, as its aboveground biomass was also influenced by plant height and crown width.</p> Conclusions <p>Hence it is important to consider not only the effects of drought but also the role of adequate light, which plays a key part in promoting the cultivation and growth of pak choi in stressful environments. The research and application of plant biology and agronomy in the region also need to consider the diversity of key economic plants to promote sustainability of vegetable farming in adapting to changing environmental stresses.</p>