Date Published: April 23, 2019
Publisher: Public Library of Science
Author(s): Lanlan Sun, Hongle Xu, Hongdan Hao, Shiheng An, Chuantao Lu, Renhai Wu, Wangcang Su, Haitao Shi.
A potted soil experiment was conducted to investigate the effects of bensulfuron-methyl (BSM) residue on the growth and photosynthesis of seedlings of a local cucumber variety (Xia Feng No.1). When the residue of bensulfuron-methyl in soil exceeded 50μg kg-1, it significantly inhibited the growth of cucumber, chlorophyll content and photosynthetic capacity of cucumber. BSM treatment caused significant decreases in the biomass, chlorophyll content, net photosynthesis rate, stomatal conductance, and transpiration rate, photosystem II (PSII) maximum quantum yield, actual quantum yield, photochemical quenching coefficient, and electron transport rate in cucumber seedlings, but increased the minimal fluorescence yield and dark respiration rate. Moreover, comparisons of the patterns of absorbed light energy partitioning revealed that the fractions of excess and thermally dissipated energy increased with rising concentrations of the BSM residue, but the fraction of PSII photochemistry declined. The BSM residues caused reversible destruction in the PSII reaction centers and decreased the proportion of available excitation energy used in PSII photochemistry. The results suggested that rice or wheat fields sprayed with BSM will not be suitable for planting cucumbers in succession or rotation.
Herbicides are necessary for weed control in intensive crop production, and play an important role in modernization of agriculture. Bensulfuron-methyl (BSM) has been used since the 1970s and now is widely used in paddy fields in the world. In China, BSM was first used in paddy fields to control sedge and broadleaf weeds, and now it is also used to control broadleaf weeds in wheat fields .
The shoot length, root length, SDM, RDM, and TDM of cucumber seedlings decreased significantly with the presence of the BSM residue, and the degree of decrease was directly related to the BSM concentration added to soil. The R:S ratio in seedlings initially decreased and then increased with rising BSM concentrations. The BSM residue had a more pronounced effect on RDM than SDM at lower concentrations. As the BSM residue concentration increased, the growth of both above- and belowground parts of cucumber seedlings were severely suppressed. These results were consistent with the results of Su et al., but inconsistent with those of Su et al. . Su et al. reported that the inhibition of the root length of soybean and peanut were greater than those of plant height in the presence of BSM residue. This indicated that different crops responded differently to BSM residues. The reasean may be that at the lower concentrations, the critical threshold that the cucumber seedlings can tolerate has not yet been reached, so the BSM residue had a more pronounced effect on RDM than SDM. With the increase of the BSM residue concentration, it exceeds the critical threshold that the cucumber seedlings can tolerate, so the root and stem were significantly inhibited.