Irrigated Soybean Leaf Photosynthesis in the Humid Subtropical Midsouth

H Arnold Bruns

doi:10.1155/2014/787945

Abstract

Photosynthesis (CER (μmol CO2mleaf area-2 s−1)), stomatal conductance (gsw), and intercellular [CO2] (Ci) of soybean (Glycine maxL. Merr.) grown using the early soybean production system (ESPS) of the midsouth were determined. Three irrigated cultivars were grown using ESPS on Bosket (Mollic Hapludalfs) and Dundee (Typic Endoaqualf) soils in 2011 and 2012 at Stoneville, MS. Single leaf CER,gsw, andCiwere determined at growth stages R3, R4, and R5 using decreasing photosynthetic photon flux densities (PPFD,μmol m−2 s−1) beginning at 2000 PPFD and decreasing by 250 PPFD increments to 250 PPFD. Photosynthesis changes fit a quadratic polynomial for all fixed variables and range from ~6.0 and 9.0 CER at 250 PPFD and ~22.0 to 28.0 CER at 2000 PPFD. No cultivar differences in CER,gsw, orCiwere noted at any growth stage or site either year. In 2012, CER,gsw, andCiwere lower when measured at R5 than the two previous growth stages, which was not observed in 2011. The R5 sampling in 2012 had accumulated 39 to 70 more growing degree units at 10°C base temperature (GDU 10’s) than in 2011 and were likely more mature. Increased soybean yields from ESPS appear not to result from higher leaf CER.

Highlights

Except for a few hectares seeded in double-crop systems following wheat (Triticum aestivum L.), most soybean crops in the Mississippi Delta are seeded before 1 May with cultivars in the maturity group (MG) 4.0 to MG 5.5 range
Statistical analyses of all other data collected in this experiment showed no significant differences among cultivars at any particular growth stage at either site in 2011 or 2012 and data were pooled for each growth stage at each site both years
Single leaf CER levels for MG 4 and MG 5 cultivars grown in this experiment did not become light-saturated at an indicated 2000 photosynthetic photon flux density (PPFD) at either site or growth stage except possibly at R3 in 2012 on the Bosket sandy loam (Figures 1(a) and 2(a))

Summary

Arnold Bruns

Crop Production Systems Research Unit, USDA-ARS, MSA, P.O. Box 350, 141 Research Road, Stoneville, MS 38776, USA. Photosynthesis (CER (μmol CO2 m−le2af area s−1)), stomatal conductance (gsw), and intercellular [CO2] (Ci) of soybean Merr.) grown using the early soybean production system (ESPS) of the midsouth were determined. Three irrigated cultivars were grown using ESPS on Bosket (Mollic Hapludalfs) and Dundee (Typic Endoaqualf) soils in 2011 and 2012 at Stoneville, MS. No cultivar differences in CER, gsw, or Ci were noted at any growth stage or site either year. In 2012, CER, gsw, and Ci were lower when measured at R5 than the two previous growth stages, which was not observed in 2011. Increased soybean yields from ESPS appear not to result from higher leaf CER

Introduction

Materials and Methods

Results and Discussion