Data_Sheet_1_Gravity Reduced Nitrogen Uptake via the Regulation of Brace Unilateral Root Growth in Maize Intercropping.docx

Water, nutrient, light, and interspecific facilitation regulation of soil physicochemical properties and root morphology modulate nitrogen (N) uptake in cereal and legume intercropping systems. However, maize root morphological plasticity and N uptake capability response to gravity in the intercropping system remains to be determined. In this study, maize was grown under 20 cm (I20), 40 cm (I40), and 60 cm (I60) of narrow row spacing in an intercropping system (maize–soybean strip relay intercropping) and equal row spacing of monoculture (M) in a 2-year field experiment. As a supplementary for the field experiment, maize root barrier and plant inclination experiments were conducted. Plant inclination, brace root morphology, N uptake, indole-3-acetic acid (IAA) level, IAA synthesis genes, and grain yield were assessed. The result showed that the plant inclination increased with decreasing narrow row spacing in intercropping system. Also, the brace unilateral root growth ratio (BURR) increased with increasing plant inclination in intercropping treatments. The plant inclination experiment showed the BURR achieved 94% after inclination at 45°. BURR tended to be positively correlated (p = 0.00) with plant inclination. Thus, gravity (plant inclination) causes brace unilateral root growth. The IAA concentration of stem nodes in the wide row increased with increasing plant inclination, while the IAA accumulation decreased in the narrow row. The Zmvt2 and ZM2G141383 genes (associated with IAA biosynthesis) were highly expressed in a wide row. There was a strong correlation (p = 0.03) between the IAA concentration of wide row and the BURR. Therefore, gravity regulates the IAA level, which affects BURR. In addition, the brace root number, volume, and surface area were decreased when BURR was increased. Subsequently, the leaf N, cob N, and kernel N accumulation were reduced. These organs N and grain yield in I60 were not significantly different as compared to the control treatment. The excessive brace unilateral root growth was not conducive to N uptake and increased yield. Our results suggest that gravity is essential in regulating root morphology plasticity by regulating IAA levels and decreasing N uptake capacity. Furthermore, these results indicate that plant inclination can regulate root phenotype and N uptake of maize and by adjusting the spacing of narrow maize row, we can improve the N uptake and yield of the maize–soybean strip relay-intercropping system.

水、养分、光照以及种间促进作用对土壤物理化学性质和根系形态的调节，进而影响禾本科和豆科间作系统中氮（N）的吸收。然而，在间作系统中，玉米根系形态的可塑性及其对重力响应的氮吸收能力尚待确定。本研究中，在两年田间试验中，玉米分别在20厘米（I20）、40厘米（I40）和60厘米（I60）的窄行距间作系统（玉米-大豆条带间作）以及单作（M）的等行距条件下种植。作为田间试验的补充，进行了玉米根系阻隔和植物倾斜实验。评估了植物倾斜、支柱根系形态、氮吸收、吲哚-3-乙酸（IAA）水平、IAA合成基因和籽粒产量。结果显示，在间作系统中，随着窄行距的减小，植物倾斜程度增加。此外，在间作处理中，随着植物倾斜程度的增加，支柱单侧根系生长比（BURR）也增加。植物倾斜实验表明，在45°倾斜后，BURR达到94%。BURR与植物倾斜程度呈正相关（p = 0.00）。因此，重力（植物倾斜）导致支柱单侧根系生长。在宽行中，茎节处的IAA浓度随着植物倾斜程度的增加而增加，而在窄行中，IAA积累减少。Zmvt2和ZM2G141383基因（与IAA生物合成相关）在宽行中高度表达。宽行中的IAA浓度与BURR之间存在强烈的相关性（p = 0.03）。因此，重力调节IAA水平，进而影响BURR。此外，当BURR增加时，支柱根的数量、体积和表面积均减少。随后，叶片氮、穗氮和籽粒氮的积累量减少。与对照处理相比，I60处理中的这些器官氮和籽粒产量没有显著差异。过度的支柱单侧根系生长不利于氮吸收和产量增加。我们的结果表明，重力通过调节IAA水平并降低氮吸收能力，在调节根系形态可塑性方面至关重要。此外，这些结果还表明，植物倾斜可以调节玉米的根系表型和氮吸收。通过调整窄行玉米的行距，我们可以提高玉米-大豆条带间作系统的氮吸收和产量。