Search

Super absorbent polymers (SAP) provide moisture conditions that allow plant growth-promoting rhizobacteria (PGPR) to enter the soil for acclimatization and strain propagation. However, the effects of SAP co-applied with PGPR on the physiological characteristics of leaves and rhizosphere soil enzyme activities of poplar seedlings are not well understood. Here, a pot experiment using one-year-old poplar seedlings with five treatments, normal watering, drought stress (DR), drought stress + SAP (DR+SAP), drought stress + Priestia megaterium (DR +PGPR) and drought stress + SAP + P. megaterium (DR+S+P), was performed to analyze the contents of non-enzymatic antioxidants, osmotic regulators and hormones in leaves, as well as rhizosphere soil enzyme activities. Compared with normal watering, the DR treatment significantly decreased the contents of dehydroascorbate (DHA; 19.08%), reduced glutathione (GSH; 14.18%), oxidized glutathione, soluble protein (26.84%), indoleacetic acid (IAA; 9.47%), gibberellin (GA) and zeatin (ZT), the IAA/abscisic acid (ABA), GA/ABA, ZT/ABA and (IAA+GA+ZT)/ABA (34.67%) ratios in leaves, and the urease and sucrase activities in the rhizosphere soil. Additionally, it significantly increased the soluble sugar, proline and ABA contents in leaves. However, in comparison with the DR treatment, the DR+S+P treatment significantly increased the DHA (29.63%), GSH (15.13%), oxidized glutathione, soluble protein (29.15%), IAA (12.55%) and GA contents, the IAA/ABA, GA/ABA, ZT/ABA and (IAA+GA+ZT)/ABA (46.85%) ratios in leaves, and the urease, sucrose and catalase activities in rhizosphere soil to different degrees. The soluble sugar, proline and ABA contents markedly reduced in comparison to the DR treatment. The effects of the DR+SAP and DR+PGPR treatments were generally weaker than those of the DR+S+P treatment. Thus, under drought-stress conditions, the simultaneous addition of SAP and P. megaterium enhanced the drought adaptive capacities of poplar seedlings by regulating the non-enzymatic antioxidants, osmotic regulators, and endogenous hormone content and balance in poplar seedling leaves, as well as by improving the rhizosphere soil enzyme activities. [ABSTRACT FROM AUTHOR]

Super absorbent polymers can absorb water up to a few hundred or even a few thousand times their own mass. The special physical structure, unique chemical composition and characteristics of high water absorption capacity allow super absorbent polymers to be widely used in water-saving agriculture, horticulture and other industries to relieve drought and reserve water for farmland, seedling protection and crop yield improvement. A large number of studies have showed that super absorbent polymer has the properties of water saving and drought resistance. But the application amount of super absorbent polymer is an important parameter to evaluate. Applying with the improper amount can result in bad effects, either no effect, or soil permeability compromised if excess super absorbent polymer is used. This can cause plant roots to have difficulty in breathing or to get rotten. In the meantime, border irrigation is also an efficient measure which has the advantages of low cost, simple operation and easy popularization. Similarly, the irrigation quantity is a vital factor. Because excess irrigation not only causes the waste of water resource, but also poses a threat to the groundwater. While insufficient irrigation may have no effect. Therefore, it is speculated that super absorbent polymer co-applied with border irrigation should be an interesting thing, and investigating their appropriate proportion has important theoretic value and practical significance. However, there is little information on the effect of border irrigation measure co-applied with super absorbent polymer on the forest-tree plantation. With the purpose of promoting water-saving irrigation and poplar yield, a field experiment of 5 treatments, i.e. CK (conventional border irrigation), I60 (60% conventional border irrigation quantity), I30 (30% conventional border irrigation quantity), I60S (60% border irrigation quantity co-applied with super absorbent polymers) and I30S (30% border irrigation quantity co-applied with super absorbent polymers) was designed and performed. The present study was conducted to determine the effects of different treatments on bulk density, microbial biomass carbon (MBC), microbial biomass nitrogen (MBN) and microbial activity in the forest soil as well as the growth of poplar. Results showed that in comparison to CK treatment, I60S treatment significantly reduced soil bulk density and obviously increased soil total porosity and capillary porosity, indicative of 6.62%, 11.19%, 16.45% and 7.97% decreases in soil bulk density compared to the treatments of CK, I60, I30 and I30S, respectively. The I60S treatment also evidently increased MBC and MBN contents and significantly enhanced microbial respiration, showing 13.89%, 24.24%, 41.38% and 12.33% increases in microbial respiration rate over the treatments of CK, I60, I30 and I30S, respectively. At the same time, the metabolic quotient was reduced by the I60S treatment, demonstrating 5.96%, 8.84%, 11.72% and 4.78% decreases, respectively. Additionally, the volume growth rate of the I60S treatment also reached the maximum, which had significant differences with other treatments (P<0.05). However, in the I30S treatment, less effect on the forest soil characteristics and the volume growth were observed than that in the I60S treatment. The correlation analysis showed that the volume growth rate was extremely significantly correlated with capillary porosity and metabolic quotient, and had significant correlation with soil bulk density, MBC and MBN contents and microbial respiration. In conclusion, the proper water-saving irrigation measure (60% border irrigation quantity co-applied with super absorbent polymers) is beneficial to improving soil physical environment and enhancing microbial activity in forest soil, as well as the growth of poplar. [ABSTRACT FROM AUTHOR]