Photosynthetic response of soybean and cotton to different irrigation regimes and planting geometries

Authors: PINNAMANENI, SRINIVASA - Oak Ridge Institute For Science And Education (ORISE); ANAPALLI, SASEENDRAN - US Department Of Agriculture (USDA); Reddy, Krishna

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/24/2022
Publication Date: 8/8/2022
Citation: Srinivasa, P.R., Anapalli, S., Reddy, K.N. 2022. Photosynthetic response of soybean and cotton to different irrigation regimes and planting geometries. Frontiers in Plant Science. https://doi.org/10.3389/fpls.2022.894706.
DOI: https://doi.org/10.3389/fpls.2022.894706

Interpretive Summary: Plant species have different mechanisms of sustaining metabolic levels when subjected to moisture deficit stress. Soybean and cotton, predominant crops in Mississippi Delta have C3 photosynthetic mechanism but differ in their tolerance to moisture deficit stress. To understand their differential photosynthetic responses, scientists with the USDA-ARS Crop Production Systems Research Unit and Sustainable Water Management Research Unit, Stoneville, MS, conducted field studies by varying corn and soybean planting geometry and irrigation regimes during 2018-2019. A reduction of 12% and 17% in maximum assimilation rate was observed in rainfed soybean while the reduction is limited to 9% and 6% in rainfed cotton during the 2018 and 2019 seasons, respectively. Both stomatal conductance and transpiration under rainfed declined in both the crops. The photochemical quenching, which protects photosynthesis components declined by 28% in soybean and 26% in cotton. No differences for photosynthetic parameters were observed among single and twin row plantings. These results indicated enhanced electron transport rate in cotton and non-photochemical quenching in soybean play a greater role in maintaining photosynthesis levels under moisture stress.

Technical Abstract: In a two-year study (2018 and 2019), we examined gas-exchange and chlorophyll fluorescence to understand better the adaptation mechanisms of the photosynthetic apparatus of furrow irrigated cotton (Gossypium hirsutum L.,) and soybean (Glycine max L.,) grown under different levels of irrigations and planting geometries, in a split-plot experiment. The main plots were three irrigation regimes, i) all furrow irrigation (AFI), ii) alternate or skipped furrow irrigation (SFI), and iii) no irrigation or rainfed (RF), and subplots were two planting geometries, single-row (SR) and twin-row (TR). The light response curves at vegetative and reproductive phases revealed lower photosynthesis rates in the RF crops than in AFI and SFI. Reduction in maximum assimilation rate (Amax) was higher in soybean than cotton. A reduction of 12% and 17% in Amax was observed in RF soybean while the reduction is limited to 9% and 6% in RF cotton during the 2018 and 2019 seasons, respectively. Both stomatal conductance (gs) and transpiration (E) under RF declined sharply. The moisture deficit stress resulted enhanced operating quantum efficiency of PSII photochemistry (FPSII) which is probably due to increased photorespiration. The non-photochemical quenching (NPQ) and quantum efficiency of dissipation by down-regulation (FNPQ) increased significantly in both crops (up to 50%). The photochemical quenching declined by 28% in soybean and 26% in cotton. It appears soybean preferentially uses non-photochemical energy dissipation while cotton uses probably triggering PSII center and electron transport rate (ETR). No significant differences among SR and TR systems were observed for Amax, gs, E, ETR and various chlorophyll fluorescence parameters.