Soybean photosynthetic and biomass responses to carbon dioxide concentrations ranging from pre-industrial to the distant future

Optimizing cultivars and agricultural management practices can enhance soybean yield in Northeast China

Soybean is an important oil crop in China, and the national focus of soybean production is Northeast China. Crop yield is affected by climate, cultivars and agricultural management practices. Optimizing the composite impacts of these factors on soybean yield and yield gaps is crucial for the local agricultural community. In this study, we used the DSSAT-CROPGRO-Soybean model (validated based on longer-than-20-years agro-meteorological experiments data) to simulate the potential yield (Y_p), attainable yield (Y_a), and potential farmer's yield (Y_pf) of soybean for 56 counties from 1981 to 2017 in Northeast China. Combined with actual farmer's yield (Y_f), we computed different types of yield gaps. Furthermore, we optimized cultivars, agricultural management practices, and those interactions on soybean yield and yield gaps. On county-level, the Y_p, Y_a, Y_pf and Y_f averaged 5528.9, 4762.9, 3786.8 and 1918.8 kg ha^-1, respectively. The total yield gap between Y_f and Y_p was 63.8 % of Y_p. The yield gap between Y_a and Y_p was 12.8 %, which caused by uncontrollable factors; the yield gap between Y_pf and Y_a was 17.6 %, which caused by agronomic factors; and the yield gap between Y_f and Y_pf was 33.5 %, which caused by socioeconomic factors. During 1981-2017, climate, cultivar, sowing date and plant density change affected Y_pf by -7.5, 4.5, -3.0 and - 2.0 %, respectively. By optimizing cultivar, sowing date and plant density, Y_pf would increase by 13.1, 7.9 and 3.1 % and yield gap would close by 9.2, 5.6 and 2.1 %, respectively. By comprehensively optimizing cultivar, sowing date and plant density, Y_pf would increase by 19.4 % and yield gap would close by 13.7 %. This work has practical significance for understanding climate, cultivar and agricultural management impacts on soybean yield, and demonstrates an effective approach, by optimizing cultivars and agricultural management practices to address climate change, increase yield and close yield gaps.

Crops' response to the emergent air pollutants

Consequences of air pollutants on physiology, biology, yield and quality in the crops are evident. Crop and soil management can play significant roles in attenuating the impacts of air pollutants. With rapid urbanization and industrialization, air pollution has emerged as a serious threat to quality crop production. Assessing the effect of the elevated level of pollutants on the performance of the crops is crucial. Compared to the soil and water pollutants, the air pollutants spread more rapidly to the extensive area. This paper has reviewed and highlighted the major findings of the previous research works on the morphological, physiological and biochemical changes in some important crops and fruits exposed to the increasing levels of air pollutants. The crop, soil and environmental factors governing the effect of air pollutants have been discussed. The majority of the observations suggest that the air pollutants alter the physiology and biochemical in the plants, i.e., while some pollutants are beneficial to the growth and yields and modify physiological and morphological processes, most of them appeared to be detrimental to the crop yields and their quality. A better understanding of the mechanisms of the uptake of air pollutants and crop responses is quite important for devising the measures ‒ at both policy and program levels ‒ to minimize their possible negative impacts on crops. Further research directions in this field have also been presented.

A meta-analysis of responses of C3 plants to atmospheric CO2 : dose-response curves for 85 traits ranging from the molecular to the whole-plant level

Generalised dose-response curves are essential to understand how plants acclimate to atmospheric CO₂ . We carried out a meta-analysis of 630 experiments in which C₃ plants were experimentally grown at different [CO₂ ] under relatively benign conditions, and derived dose-response curves for 85 phenotypic traits. These curves were characterised by form, plasticity, consistency and reliability. Considered over a range of 200-1200 µmol mol^-1 CO₂ , some traits more than doubled (e.g. area-based photosynthesis; intrinsic water-use efficiency), whereas others more than halved (area-based transpiration). At current atmospheric [CO₂ ], 64% of the total stimulation in biomass over the 200-1200 µmol mol^-1 range has already been realised. We also mapped the trait responses of plants to [CO₂ ] against those we have quantified before for light intensity. For most traits, CO₂ and light responses were of similar direction. However, some traits (such as reproductive effort) only responded to light, others (such as plant height) only to [CO₂ ], and some traits (such as area-based transpiration) responded in opposite directions. This synthesis provides a comprehensive picture of plant responses to [CO₂ ] at different integration levels and offers the quantitative dose-response curves that can be used to improve global change simulation models.

Elevated CO2 Enhances Dynamic Photosynthesis in Rice and Wheat

Crops developed under elevated carbon dioxide (eCO₂) exhibit enhanced leaf photosynthesis under steady states. However, little is known about the effect of eCO₂ on dynamic photosynthesis and the relative contribution of the short-term (substrate) and long-term (acclimation) effects of eCO₂. We grew an Oryza sativa japonica cultivar and a Triticum aestivum cultivar under 400 μmol CO₂ mol^-1 air (ambient, A) and 600 μmol CO₂ mol^-1 air (elevated, E). Regardless of growth [CO₂], the photosynthetic responses to the sudden increase and decrease in light intensity were characterized under 400 (a) or 600 μmol CO₂ mol^-1 air (e). The Aa, Ae, Ea, and Ee treatments were employed to quantify the acclimation effect (Ae vs. Ee and Aa vs. Ea) and substrate effect (Aa vs. Ae and Ea vs. Ee). In comparison with the Aa treatment, both the steady-state photosynthetic rate (P _N) and induction state (IS) were higher under the Ae and Ee treatments but lower under the Ea treatment in both species. However, IS reached at the 60 sec after the increase in light intensity, the time required for photosynthetic induction, and induction efficiency under Ae and Ee treatment did not differ significantly from those under Aa treatment. The substrate effect increased the accumulative carbon gain (ACG) during photosynthetic induction by 45.5% in rice and by 39.3% in wheat, whereas the acclimation effect decreased the ACG by 18.3% in rice but increased it by 7.5% in wheat. Thus, eCO₂, either during growth or at measurement, enhances the dynamic photosynthetic carbon gain in both crop species. This indicates that photosynthetic carbon loss due to an induction limitation may be reduced in the future, under a high-CO₂ world.

Daytime, Not Nighttime, Elevated Atmospheric Carbon Dioxide Exposure Improves Plant Growth and Leaf Quality of Mulberry (Morus alba L.) Seedlings

Almost all elevated atmospheric CO2 concentrations (eCO2) studies have not addressed the potential responses of plant growth to different CO2 in daytime and nighttime. The present study was to determine the impact of daytime and/or nighttime eCO2 on growth and quality of mulberry (Morus alba L.), a perennial multipurpose cash plant. Six-month-old mulberry seedlings were hence grown in environmentally auto-controlled growth chambers under four CO2 concentrations: (1) ambient CO2 (ACO2, 410 μmol mol-1 daytime/460 μmol mol-1 nighttime), (2) sole daytime elevated CO2 (DeCO2, 710 μmol mol-1/460 μmol mol-1), (3) sole nighttime elevated CO2 (NeCO2, 410 μmol mol-1/760 μmol mol-1), and (4) continuous daytime and nighttime elevated CO2 (D + NeCO2, 710 μmol mol-1/760 μmol mol-1). Plant growth characteristics, nutrient uptake, and leaf quality were then examined after 120 days of CO2 exposure. Compared to control, DeCO2 and (D + N)eCO2 increased plant biomass production and thus the harvest of nutrients and accumulation of leaf carbohydrates (starch, soluble sugar, and fatty acid) and N-containing compounds (free amino acid and protein), though there were some decreases in the concentration of leaf N, P, Mg, Fe, and Zn. NeCO2 had no significant effects on leaf yield but an extent positive effect on leaf nutritional quality due to their concentration increase in leaf B, Cu, starch, and soluble sugar. Meanwhile, (D + N)eCO2 decreased mulberry leaf yield and harvest of nutritious compounds for silkworm when compared with DeCO2. The reason may be associated to N, P, Mg, Fe, and Zn that are closely related to leaf pigment and N metabolism. Therefore, the rational application of mineral nutrient (especially N, P, Fe, Mg, and Zn) fertilizers is important for a sustainable mulberry production under future atmosphere CO2 concentrations.