Photosynthetic compensation of maize in heterogeneous light is impaired by restricted photosynthate export

Nitrogen allocation for CO2 fixation promotes nitrogen use in the photosynthetic compensation of soybean under heterogeneous light after a pre-shading

The spatial and temporal distribution of sunlight around plants is constantly changing in natural and farmland environments. Previous studies showed that the photosynthesis of crops responds significantly to heterogeneous light conditions in fields. However, the underlying mechanisms remain unclear. In the present study, soybean plants were treated by heterogeneous light after a pre-shading (SH-HL) to simulate the light condition in relay strip intercropping. Gas exchange and nitrogen (N) of leaves were measured to evaluate the photosynthetic performance, as well as photosynthetic N- and water-use efficiency (PNUE and PWUE). Chlorophylls (Chl) and Rubisco were analyzed as representative photosynthetic N components. Results suggest that SH-HL treated soybean exhibited evident photosynthetic compensation as the net photosynthetic rate (Pn) increased significantly in unshaded leaves, from which the export of photosynthates was enhanced. Under SH-HL, leaf N concentration remained relatively stable in unshaded leaves. While Chl concentration decreased but Rubisco concentration increased in unshaded leaves, indicating preferential allocation of leaf N for CO2 fixation. Results also showed that PNUE increased and PWUE decreased in unshaded leaves under SH-HL. Therefore, we suggest that within-leaf N allocation for CO2 fixation in unshaded leaves rather than within-plant N distribution to unshaded leaves drives the photosynthetic compensation under heterogeneous light after a pre-shading. However, enhanced water loss from unshaded leaves is a cost for efficient N-use under these conditions.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01392-8.

Row ratio increasing improved light distribution, photosynthetic characteristics, and yield of peanut in the maize and peanut strip intercropping system

Changes in the canopy microclimate in intercropping systems, particularly in the light environment, have important effects on the physiological characteristics of photosynthesis and yield of crops. Although different row ratio configurations and strip widths of dwarf crops in intercropping systems have important effects on canopy microclimate, little information is available on the effects of intercropping on chlorophyll synthesis and photosynthetic physiological properties of dwarf crops. A 2-year field experiment was conducted in 2019 and 2020, with five treatments: sole maize (SM), sole peanut (SP), four rows of maize intercropping with eight rows of peanut (M4P8), four rows of maize intercropping with four rows of peanut (M4P4), and four rows of maize intercropping with two rows of peanut (M4P2). The results showed that the light transmittance [photosynthetically active radiation (PAR)], photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs) of intercropped peanut canopy were reduced, while the intercellular carbon dioxide concentration (Ci) was increased, compared with SP. In particular, the M4P8 pattern Pn (2-year mean) was reduced by 5.68%, 5.33%, and 5.30%; Tr was reduced by 7.41%, 5.45%, and 5.95%; and Gs was reduced by 8.20%, 6.88%, and 6.46%; and Ci increased by 11.95%, 8.06%, and 9.61% compared to SP, at the flowering needle stage, pod stage, and maturity, respectively. M4P8 improves the content of chlorophyll synthesis precursor and conversion efficiency, which promotes the utilization efficiency of light energy. However, it was significantly reduced in M4P2 and M4P4 treatment. The dry matter accumulation and pod yield of peanut in M4P8 treatment decreased, but the proportion of dry matter distribution in the late growth period was more transferred to pods. The full pod number decreases as the peanut row ratio decreases and increases with year, but there is no significant difference between years. M4P8 has the highest yield and land use efficiency and can be used as a reference row ratio configuration for maize-peanut intercropping to obtain relatively high yield benefits.

Effect of Mn Deficiency on Carbon and Nitrogen Metabolism of Different Genotypes Seedlings in Maize (Zea mays L.)

Manganese deficiency critically impairs the function and stability of photosystem II (PSII) and negatively impacts crop growth and yield. However, the response mechanisms of carbon and nitrogen metabolism to Mn deficiency in different genotypes of maize and the differences in Mn deficiency tolerance are unclear. Herein, three different genotypes of maize seedlings (sensitive genotype: Mo17, tolerant genotype: B73, and B73 × Mo17) were exposed to Mn deficiency treatment for 16 days using liquid culture with different concentrations of MnSO₄ [0.00, 2.23, 11.65, and 22.30 mg/L (control)]. We found that complete Mn deficiency significantly reduced maize seedling biomass; negatively affected the photosynthetic and chlorophyll fluorescence parameters; and depressed nitrate reductase, glutamine synthetase, and glutamate synthase activity. This resulted in reduced leaf and root nitrogen uptake, with Mo17 being most severely inhibited. B73 and B73 × Mo17 maintained higher sucrose phosphate synthase and sucrose synthase activities and lower neutral convertase activity compared to Mo17, which resulted in higher accumulation of soluble sugars and sucrose and maintenance of the osmoregulation capacity of leaves, which helped mitigate damage caused by Mn deficiency. The findings revealed the physiological regulation mechanism of carbon and nitrogen metabolism in different genotypes of maize seedlings that resist Mn deficiency stress, providing a theoretical basis for developing high yield and quality.