Effect of Humic Acids on Soybean Seedling Growth under Polyethylene-Glycol-6000-Induced Drought Stress

Abstract

Humic substances (HS) are the most important natural biostimulant of plants. However, the relationship between their structure and biological activity in plants is still not well recognized. The objective of this paper was to assess the influence of molecular fractions of humic acids (HA) (HA < 30 kDa and HA > 30 kDa) on reducing negative effects of drought stress in soybean (Glycine max (L.) Merr.) seedlings of Progres and Nawiko cultivars. Drought stress was induced in laboratory conditions by the addition of polyethylene glycol 6000 (PEG 6000) to make a water potential of −0.5 MPa. HA were extracted according to the International Humic Substances Society procedure, and then were separated into two molecular fractions by membrane filtration. The following physiological and biometric parameters were determined: chlorophyll content, photosynthesis activity, electrical conductivity, fresh and dry mass of overground and roots, and plant length. The enzyme activity and ion contents were also measured. Differences in response to drought stress with the addition of HA < 30 kDa and HA > 30 kDa or not to the Hoagland’s solution were observed among studied cultivars. Drought stress caused a decrease in the most physiological parameters and increase in peroxidase activity in the case of both studied cultivars. However, the results of biometric measurements showed that the Progres cultivar appears to have better tolerance to drought stress. The significant influence of water deficit on most macroelement content in dry matter leaves of both studied cultivars was not observed, while its effect on microelement uptake by soybean plants was concluded. In the case of the Progres cultivar, the results showed a significant decrease in microelement content in the dry matter of leaves, whereas in the leaves of Nawiko cultivar there was a significant increase. The influence of HA > 30 kDa and HA < 30 KDa fractions on physiological features of both studied cultivars was varied. HA > 30 kDa fraction better up-regulated the antioxidant defense system. Unfortunately, no effect of either HA fraction on the macro- and micronutrients uptake system of both studied cultivars was observed.

Strategies and prospects for biostimulants to alleviate abiotic stress in plants

“…These biostimulants substances can also promote the plant water status by increasing the relative water content and water potential, as well as increase N content leading to higher biomass accumulation in S. officinarum and C. melo plants under drought conditions ( Aguiar et al., 2016 ; Kıran et al., 2019 ). Matuszak-Slamani et al. (2022) also reported that HS (e.g., derived from vermicompost) increases several other morphological features in soybean, like fresh and plant dry matter of root and aboveground, and plant length under drought conditions.…”

Application of humic acid and follar sulfar positively effect yield and related attributes of soybean under the agroclimatic region of Peshawar Pakistan

“…However, the interaction between HA, FS and cultivars was found to be not significant for all the studied traits. In response to HA fertilized at the amount of 9 kg ha -1 , less (56) days to flowering was noted while more days to flowering (60) were seen in control plots. In case of FS, its application at the level of 8% had minimum days to flowering (56) which was not significantly different from 6% (58) in comparison to more days recorded (59) in control plots.…”

“…Improvement in seed protein was seen as result of higher HA and FS application compared to untreated units. Matuszak-Slamani et al [60] found that application of humic acid fractions caused an increase in chlorophyll content, which is an indicator of plant protein content. Additionally, a transcriptomic analysis by [61] revealed that humic acid could relieve the inhibitory effect of high nitrogen on soybean nodulation, which indirectly suggests a potential impact on the protein content of soybean.…”

The role of nanoparticles in plant biochemical, physiological, and molecular responses under drought stress: A review

“…Plants accommodate DS by using various mechanisms, including accumulation of osmolytes, hormones, and activation of the antioxidant defense system ( Hassan et al., 2020 ; Rasheed et al., 2022b ). Climate change and the consequent frequency of DS have adversely affected crop productivity globally ( Matuszak-Slamani et al., 2022 ). To increase crop productivity and counter the effects of DS, various strategies, including screening and breeding of tolerant cultivars, osmolytes, hormones, nutrient application, and microbes, can be used to increase crop production ( Arslan et al., 2021 ).…”