Studies investigating the mechanisms underlying the variation of photosynthesis along plant phylogeny and especially during domestication are of great importance, and may provide new insights to further improve crop photosynthesis. In the present study, we compiled a database including 542 sets of data of leaf gas exchange parameters and leaf structural and chemical traits in ferns and fern allies, gymnosperms, non-crop angiosperms, and crops. We found that photosynthesis was dramatically improved from ferns and fern allies to non-crop angiosperms, and further increased in crops. The improvement of photosynthesis during phylogeny and domestication was related to increases in carbon dioxide diffusional capacities and, to a lesser extent, biochemical capacity. Cell wall thickness rather than chloroplast surface area facing intercellular airspaces drives the variation of mesophyll conductance. The variation of the maximum carboxylation rate was not related to leaf nitrogen content. The slope of the relationship between mass-based photosynthesis and nitrogen was lower in crops than in non-crop angiosperms. These findings suggest that the manipulation of cell wall thickness is the most promising approach to further improve crop photosynthesis, and that an increase of leaf nitrogen will be less efficient in improving photosynthesis in crops than in non-crop angiosperms.

The double-season rice system plays an important role in ensuring food security in China. However, changes in the grain yield and quality of recently released rice varieties are still not fully understood, especially early indica rice (Oryza sativa). In this study, we collected the yield and quality traits of 224 early indica rice varieties released in China’s Hunan and Jiangxi provinces from 2000 to 2020. The results showed that rice grain yield, but not quality, was significantly improved in early indica rice from 2000 to 2020, and the improvement in grain yield was mainly the result of an increased spikelet number per panicle. Quality traits such as head rice rate, chalky rice rate, and amylose content remained stable while the milled rice rate and degree of chalkiness showed adverse changes during early indica rice breeding. These results suggested that improving grain yield, but not quality, has been prioritized during early indica rice breeding in the past few decades. Further analysis showed that the degree of chalkiness had the largest coefficient of variation among the studied quality traits in the 224 early indica rice varieties, indicating that there is still great potential to decrease the degree of chalkiness through rice breeding. Interestingly, the results showed that lower degrees of chalkiness were associated with lower amylose contents and chalky rice rates but with a higher length-to-width ratios and a gel consistency. Therefore, focusing on the degree of chalkiness seems a promising strategy to synergistically improve the quality traits of early indica rice. Overall, our results have value for guiding future research on high-yield and high-quality breeding in early indica rice.

Plant functional traits, including leaf and root economic traits, are important for understanding the composition and function of ecosystems. However, plant functional traits of crop species and the relationships between them, and their responses to environmental variations are not fully understood. In the present study, the traits in the leaf and root economics spectrum (LES and RES) and plant biomass were investigated in 14 wheat genotypes grown with sufficient or limited nitrogen (N) supply. We found that N had significant impacts on the LES and RES traits and on the relationships among them. Our results generally supported the hypothesized LES, but did not support the RES or plant economics spectrum concept among wheat plants regardless of N treatment. More importantly, we found that more conservative leaf and root economic traits are beneficial for shoot biomass accumulation in wheat plants grown with limited N supply, and for the improvement in the tolerance of wheat to N stress. The data presented suggest that growth conditions should be accounted for when studying trait-to-trait relationships, and that more conservative resource use strategies could be used as promising targets for wheat breeding programs with limited N input.