Physiological and antioxidant responses of cotton and spurred anoda (Anoda cristata) under nitrogen deficiency

Abstract

Spurred anoda is a major competitor with cotton in the southern United States. Physiological and antioxidant responses of two species of cotton (Gossypium barbadenseL. cv. ‘Pima S-7’ andGossypium hirsutumL., Delta and Pine Land Company cv. ‘Delta Pine 5415’) and two accessions of spurred anoda [New Mexico (NM) and Mississippi (MS)] were investigated under nitrogen (N) -sufficient and -deficient conditions in the greenhouse. Pima S-7 had the highest leaf N content of all the plants regardless of treatment. Biomass decreased in all species when N was withheld, with Pima S-7 exhibiting the least reduction and MS the greatest. Plant height decreased in cotton but not spurred anoda under N stress. Height:node ratio increased 9% in MS, but decreased 8% in DP 5415 when they were deprived of N. Withholding N reduced photosynthesis 45% regardless of species. Comparable decreases were found in stomatal conductance and transpiration, suggesting strong stomatal regulation of gas exchange under N stress. The quantum efficiency of photosystem II (dark-adaptedFv/Fm) decreased 4% under N deficiency. Alpha-carotene decreased for all species when N was withheld, except for the NM accession, in which the levels increased. Total chlorophyll and lutein decreased under N stress regardless of species, but alpha-tocopherol and the xanthophyll cycle conversion state increased. Pima S-7 had the most chlorophyll and lutein, and both cotton species had more alpha-tocopherol, anthocyanins, and free-radical scavenging capacity than spurred anoda. These enhanced pigment and antioxidant profiles of cotton, particularly Pima S-7, may contribute to cotton's ability to compete for N with spurred anoda.