Coastal Saline Land Research Articles

Straw incorporation: A more effective coastal saline land reclamation approach to boost sunflower yield than straw mulching or burial

In coastal lands, soil salinity greatly impedes crops growth and severely affects the agricultural productivity. Returning the crop straw and residual to soil was considered an important land reclamation method; however, the approach of straw return varied, including mulching (SM), burial (SB), and incorporation (SI). This study aimed to determine which approach was most effective to ameliorate coastal saline land and boost crop yield. Field experiments were conducted under different straw amelioration treatments on dry farming sunflowers (Helianthus annuus Linn.) in Bohai coastal land of Northern China. The results indicated that SM and SB changed the soil salt profile and significantly reduced the topsoil (0–0.2 m) salt content mainly by their direct effects on soil water transport, with little impacts on soil structure changes. Differently, SI significantly increased 21.8 % soil organic carbon and 52.3 % soil mean weight diameter in straw incorporated layer. The improvement on soil aggregates and porosity reduced 24.1–38.9 % of topsoil salt content, by limiting soil salt accumulation and promoting salt leaching. Furthermore, SI significantly boosted the sunflower fine root (d< 1.0 mm) growth and resulted in the highest sunflower yield (4.7 t/ha in 2020 and 4.6 t/ha in 2021) among those straw treatments. Compared to SM and SB, the net revenues of two-years sunflower cultivation under SI were improved by 40.68 % and 31.22 %, respectively. Therefore, it concluded that straw incorporation was more effective to reclaim coastal saline soil than straw mulching or burial. In addition, a back propagation artificial neural network model was developed to predict the dynamic of sunflower yield. This outcome provides an insight into the management of coastal farmland by establishing an easily desalinized and fertile topsoil profile structure.

Soil Organic Matter and Bulk Density: Driving Factors in the Vegetation-Mediated Restoration of Coastal Saline Lands in North China

Coastal saline soils are an important soil resource that, when restored, can enhance arable land and preserve the natural ecology. With the aim of improving the use of coastal saline soils, we conducted a spot survey at Bohai coastal saline land to investigate the differences in soil properties between different vegetation types. The soil physical and chemical properties of various vegetation types, including Aeluropus sinensis, Imperata cylindrica, Tamarix chinensis, Lycium chinense, Hibiscus moscheutos, Helianthus annuus, Gossypium hirsutum, and Zea mays, were examined at two depth layers: 0–20 cm and 20–40 cm, and in two seasons, spring and autumn. The soil properties were compared with bare land as a control. The results indicated that the electrical conductivity, total soil salt content, sodium adsorption ratio, and bulk density of soils with vegetation cover were lower than those with bare land. On the other hand, soil pH, organic matter content, mean weight diameter, and saturated hydraulic conductivity were higher. The redundancy analysis results revealed a substantial positive correlation between soil pH, saturated hydraulic conductivity, water content, mean weight diameter, and organic matter content, as well as a significant positive correlation between soil electrical conductivity, total soil salt content, sodium adsorption ratio, and bulk density. Soil pH, saturated hydraulic conductivity, water content, mean weight diameter, organic matter content, and soil electrical conductivity, total soil salt content, sodium adsorption ratio, and bulk density were negatively correlated. The results of the structural equation model and variance decomposition showed that soil organic matter and bulk density were the key factors affecting the degree of soil salinization, and compared with their independent effects, their combined effect on soil salinization was greater. This study’s conclusions can provide a point of reference for further research on the mechanisms of soil improvement and desalinization in coastal saline land.

Spatial patterning and species coexistence: A case study using concentric circular vegetation patches in saline land

Spatial patterns in plant community structures within stressed ecosystems have drawn much attention in the field of ecology. However, the mechanisms underlying spatial formation and its impact on species coexistence and diversity remain controversial. In this study, we investigated concentric circular vegetation patches in coastal saline land, and analysed the spatial patterning of plant communities and associated soil physicochemical properties. Thereafter, we tested how the soil conditioned by plant communities from different locations within the vegetation patches influence the species growth and inter-specific competition. Our results show soil salinity enlarges in a centrifugal manner in horizontal direction in all patches. Soil salinity decreased and species diversity increased along with the increase of patch size. In addition, we found significant shifts in both the composition of plant communities and in soil physicochemical properties from outer to center. The results indicate that the pioneer species Suaeda salsa facilitated the subsequent species. However Suaeda salsa was inhibited and became inferior competitor in the soil conditioned by the subsequent species. We infer that the less-visible spatial patterns of soil physicochemical properties at small scales create ecological niches for specialized species, allowing them to coexist but not mix. We suggest that a trade-off between tolerance to salt stress and competitive ability under ameliorated conditions may underlie mechanisms of pattern formation in small scale. Our findings lend support to the idea that soil stress constraints community assembly and triggers spatial patterns, which, in turn, buffer the stress on plant communities and enhance species diversity.

Partial substitution of chemical fertilizer by Trichoderma biofertilizer improved nitrogen use efficiency in wolfberry (Lycium chinense) in coastal saline land.

A two-year field trial was conducted to investigate the effects of partial substitution of chemical fertilizer (CF) by Trichoderma biofertilizer (TF) on nitrogen (N) use efficiency and associated mechanisms in wolfberry (Lycium chinense) in coastal saline land. As with plant biomass and fruit yield, apparent N use efficiency and plant N accumulation were also higher with TF plus 75% CF than 100% CF, indicating that TF substitution promoted plant growth and N uptake. As a reason, TF substitution stabilized soil N supply by mitigating steep deceases in soil NH4 +-N and NO3 -N concentrations in the second half of growing seasons. TF substitution also increased carbon (C) fixation according to higher photosynthetic rate (Pn) and stable 13C abundance with TF plus 75% CF than 100% CF. Importantly, leaf N accumulation significantly and positively related with Pn, biomass, and fruit yield, and structural equation modeling also confirmed the importance of the causal relation of N accumulation coupled with C fixation for biomass and yield formation. Consequently, physiological and agronomical N use efficiencies were significantly higher with TF plus 75% CF than 100% CF. Overall, partial substitution of CF by TF improved N use efficiency in wolfberry in coastal saline land by stabilizing soil N supply and coupling N accumulation with C fixation.

Effects of Supplementation of Different Amendments on Soil Heavy Metals and Enzyme Activities in Coastal Saline Land

The supplementation of soil amendments may not only improve the soil physical and chemical properties but also lead to the accumulation of heavy metals in soil. This experiment included six treatments:control (CK), organic manure (OM), polyacrylamide+organic manure (PAM+OM), straw mulching+organic manure (SM+OM), buried straw+organic manure (BS+OM), and bio-organic manure+organic manure (BM+OM) to explore the effects of different soil amendments on heavy metals and soil enzyme activities in coastal saline land and the relationship between them. The results revealed that compared with that in the CK treatment, the contents of soil Cr, Cu, Ni, and Pb exhibited an upward trend after the supplementation of soil amendments, among which the SM+OM and PAM+OM treatments had the most significant effects on the contents of soil Cr and Cu, respectively, whereas the BM+OM treatment had the most significant effects on the contents of soil Ni and Pb. Compared with those in the CK treatment, the activities of soil invertase and urease increased significantly following supplementation of soil amendments, and the BM+OM treatment had the best effect. The alkaline phosphatase activity exhibited a slightly upward trend after the supplementation of soil amendments, whereas the catalase activity did not change significantly. The redundancy analysis revealed that the first two axes cumulatively accounted for 70.3% of the variability in enzyme activities, and the importance of single soil heavy metals on soil enzyme activity was as follows:Ni>Cu>Cr>Pb.

Porous Minerals Improve Wheat Shoot Growth and Grain Yield through Affecting Soil Properties and Microbial Community in Coastal Saline Land

Soil salinization has become a major environmental factor severely threatening global food security. The application of porous minerals could significantly ameliorate soil fertility and promote plant productivity under salt stress conditions. However, the effects of porous minerals on improving the salt resistance of grain crops in coastal saline soils is not fully studied. In this work, the shoot growth and grain yield of wheat plants grown in coastal saline fields, respectively amended with the four naturally available porous minerals, diatomite, montmorillonite, bentonite and zeolite, were assessed. The application of porous minerals, especially zeolite, significantly improved the biomass and grain yield of wheat plants under saline conditions, as demonstrated by the augmented plant fresh mass (14.8~61.2%) and increased seed size (3.8~58.8%) and number (1.4~57.5%). Soil property analyses exhibited that porous-mineral amendment decreased soil sodium content and sodium absorption ratio, and increased soil nutrients in both the rhizosphere and nonrhizosphere of wheat plants. Further quantitative-PCR and 16S high-throughput sequencing analysis revealed that porous-mineral application also remarkably increased the abundance of bacterial 16S rRNA (0.8~102.4%) and fungal 18S rRNA (89.2~209.6%), and altered the composition of the soil microbial community in the rhizosphere of wheat. Our findings suggest that zeolite could be used as an ideal salt soil amendment, and the changes in soil properties and microorganisms caused by the application of porous minerals like zeolite improved the salt resistance of wheat plants in coastal saline land, leading to increased shoot growth and seed production.

Soil Physicochemical Properties and Salt Leaching Associated with Typical Plant Communities in Coastal Saline Land

Soil Physicochemical Properties and Salt Leaching Associated with Typical Plant Communities in Coastal Saline Land

Biomass composite with exogenous organic acid addition supports the growth of sweet sorghum (Sorghum bicolor 'Dochna') by reducing salinity and increasing nutrient levels in coastal saline-alkaline soil.

In coastal saline lands, organic matter is scarce and saline stress is high. Exploring the promotion effect of intervention with organic acid from biological materials on soil improvement and thus forage output and determining the related mechanism are beneficial to the potential cultivation and resourceful, high-value utilization of coastal mudflats as back-up arable land. Three exogenous organic acids [humic acid (H), fulvic acid (F), and citric acid (C)] were combined with four kinds of biomass materials [cottonseed hull (CH), cow manure (CM), grass charcoal (GC), and pine needle (PN)] and applied to about 0.3% of medium-salt mudflat soil. The salinity and nutrient dynamics of the soil and the growth and physiological differences of sweet sorghum at the seedling, elongation, and heading stages were observed under different treatments to screen for efficient combinations and analyze the intrinsic causes and influencing mechanisms. The soil salinity, nutrient dynamics, and forage grass biological yield during sweet sorghum cultivation in saline soils differed significantly (p < 0.05) depending on the type of organic acid-biomass composite applied. Citric acid-pine needle composite substantially reduced the soil salinity and increased the soil nutrient content at the seedling stage and improved the root vigor and photosynthesis of sweet sorghum by increasing its stress tolerance, allowing plant morphological restructuring for a high biological yield. The improvement effect of fulvic acid-pine needle or fulvic acid-cow manure composite was manifested at the elongation and heading stages. Citric acid-pine needle composite promoted the growth of saline sweet sorghum seedlings, and the effect of fulvic acid-pine needle composite lasted until the middle and late stages.

Application of biochar and polyacrylamide to revitalize coastal saline soil quality to improve rice growth.

Poor soil quality is affected by salinity, which limits land productivity and sustainable agricultural development in coastal China. Hence, it is essential to choose suitable and efficient approaches to revitalize coastal saline soil quality and improve agricultural productivity. Biochar and polyacrylamide (PAM) have been widely applied as soil amendments to enhance soil structure, but the interactive effects of biochar and PAM on rice growth are unclear. The experiment described in this study was conducted over five consecutive growing seasons (from 2016 to 2020) with biochar (at 0, 32, and 79 t/hm2) and PAM (at 0, 0.6, and 1.6 t/hm2) applications to study the effects of amendments on soil properties, rice photosynthesis, and rice yield in coastal saline land. The soil property results showed that wheat straw biochar and PAM lowered soil total salt and bulk density, but increased the soil organic matter (SOM), mean weight diameter of water-stable aggregates (MWD), and macroaggregate (> 0.25 mm) content. The application of either biochar or PAM increased the rice net photosynthetic rate, transpiration rate, and stomatal conductance. The combined application of 32 t/hm2 biochar + 0.6 t/hm2 PAM increased the net photosynthetic rate by 26.0% and the transpiration rate by 24.8% relative to the control. The application of 32 t/hm2 biochar and 1.6 t/hm2 PAM significantly increased the rice grain yield. The path analysis model showed that spikelets per panicle and canopy gross photosynthesis had strong and significant positive effects on grain yield, whereas soil total salt had a negative effect on grain yield. The combined application of 32 t/hm2 biochar + 0.6 t/hm2 PAM was identified as the most effective for rice growth. Biochar and PAM amendments at an optimal level may enhance soil properties by reducing salinity. These findings indicate that biochar and PAM have the potential to remediate coastal saline soil quality and the environment, which would simultaneously increase the sustainable use of coastal land resources and food production to preserve the ecological environment.Supplementary InformationThe online version contains supplementary material available at 10.1007/s11356-022-23511-w.

Long-Term Effect of Tamarisk Plantation on Soil Physical Properties and Soil Salt Distribution in Coastal Saline Land

Ecological restoration of coastal land by planting salt-tolerant plants has been widely used to construct vegetation. The aim of this study was to evaluate the changes induced by tamarisk (Tamarix chinensis) shrub on coastal soil physical quality and as well as the corresponding impact on salt distribution in the soil. A field study was conducted on coastal saline land, North China, where tamarisk plantation was established 5-year-old (T-5yr) and 11-year-old (T-11yr), and compared with barren land as control (CK). Quantitative soil physical properties, soil physical quality index, soil salt distribution, and salt leaching were examined. The results indicated that planting tamarisk improved the coastal soil properties at higher degree in topsoil than in deep soil layers. Tamarisk plantation significantly increased soil organic carbon content and pH. It also enhanced the formation of soil large aggregates and porosity; however, reduction soil bulk density and salt content in topsoil were recorded. Soil physical quality index was positively correlated with root weight density of tamarisk, and soil of T-11 yr plantation exhibited the highest soil physical quality index, with promoted soil physical functions of supporting root growth and the resistance to soil degradation. In addition, tamarisk induced soil physical changes which enhanced the salt-leaching in rainy season and contributed to the homogeneous salt distribution in soil profile. Consequently, the ecological benefits of tamarisk vegetation turned coastal saline land into a fertile land by plant–soil interaction and the soil structure improvement, therefore, it prevented the natural soil accumulation by accelerating the salt leaching after tamarisk was restored. This study provides some insights into the mechanism of tamarisk on coastal soil restoration and its regulation of soil salt distribution.

A Root Density Tradeoff in an Okra-Assisted Subsurface Pipe Drainage System for Amelioration of Saline Soil

Subsurface pipe drainage technology can effectively improve coastal saline land in Northern China. We explored an okra (Abelmoschus esculentus L.)-assisted subsurface pipe drainage system to improve the water and salt discharge performance and benefits. In this study, the simulation box experiment was conducted to research the response of water and salt discharge performance in subsurface pipe drainage to okra root weight density (RWD). The drain outflow, soil salinity, and sodium adsorption ratio were determined. The results showed that okra RWD affected the vertical distribution of okra roots. Okra with an appropriate RWD (about 116 μg·cm−3) could significantly increase the cumulative drain outflow. Okra with an appropriate RWD (about 136 μg·cm−3) could significantly increase the desalting effect. Moreover, the RWD of okra also influenced the ability of subsurface pipe drainage to inhibit soil alkalization. The above results show that planting okra and installing subsurface pipe drainage to control drainage at the coastal saline land in Northern China can effectively improve the water and salt drainage effect when okra RWD is about 116–136 μg·cm−3. When using subsurface pipe drainage to improve coastal saline soils, planting okra with proper density may be an appropriate choice to improve the effect and benefit.

Straw retention coupled with mineral phosphorus fertilizer for reducing phosphorus fertilizer input and improving cotton yield in coastal saline soils

Straw return can improve soil nutrient availability, but its interaction with phosphorus (P) fertilizer on cotton (Gossypium hirsutum L.) production and soil P availability has rarely been studied. Therefore, we carried out a four-year field trial to evaluate the effects of straw management (retention or removal) with P fertilizer (0, 22, 44, 66, 88 kg P ha–1) additions on seed cotton yield, cotton P uptake, soil fertility, and P apparent recovery efficiency (PRE) in a continuous barley–cotton rotation system in a coastal saline soil field from 2016-2019. Our results showed that the year and the interaction of P fertilization and straw management had significant effects on seed cotton yield and boll numbers, but there was no significant effects of straw management and the interaction of P fertilization and straw management on seed cotton weight per boll. An increase in P activation coefficient (14-28%) was observed due to the higher soil available P content following straw retention compared to the straw removal. Compared with straw removal, straw retention reduced mineral P fertilization by about 27-38% without affecting seed cotton yield, while increasing PRE by 14‒27% over the four years. In the 0-20 cm soil layer, straw retention reduced the Langmuir P sorption maximum (Qmax) and maximum buffer capacity (BCmax), and also increased the degree of P saturation (DPS), but it did no effect on the soil adsorption equilibrium constant (k). Straw retention significantly decreased the soil Qmax compared to straw removal under 0, 22, and 44 kg P ha–1, while no significant straw effects were found on Qmax under 66 and 88 kg P ha–1. Cotton P uptake and seed cotton yield were negatively correlated with the Qmax (P<0.01). Our results suggest that straw return may be a promising management practice to reduce mineral P fertilization without significant loss of seed cotton yield on coastal saline lands.

Kosteletzkya pentacarpos: A Potential Halophyte Candidate for Phytoremediation in the Meta(loid)s Polluted Saline Soils.

Kosteletzkya pentacarpos (L.) Ledebour is a perennial facultative halophyte species from the Malvacea family that grows in coastal areas with high amounts of salt. The tolerance of K. pentacarpos to the high concentration of salt (0.5–1.5% salinity range of coastal saline land) has been widely studied for decades. Nowadays, with the dramatic development of the economy and urbanization, in addition to the salt, the accumulation of mate(loid)s in coastal soil is increasing, which is threatening the survival of halophyte species as well as the balance of wetland ecosystems. Recently, the capacity of K. pentacarpos to cope with either single heavy metal stress or a combination of multiple meta(loid) toxicities was studied. Hence, this review focused on summarizing the physiological and biochemical behaviors of K. pentacarpos that has been simultaneously exposed to the combination of several meta(loid) toxicities. How the salt accumulated by K. pentacarpos impacts the response to meta(loid) stress was discussed. We conclude that as a potential candidate for phytoremediation, K. pentacarpos was able to cope with various environmental constrains such as multiple meta(loid) stresses due to its relative tolerance to meta(loid) toxicity.

Effects of mosaic biological soil crusts on vascular plant establishment in a coastal saline land of the Yellow River Delta, China

Abstract Aims The effects of biocrusts on vascular plants are rarely evaluated in coastal saline lands. Our aim was to examine whether and how a mosaic of biocrusts affect seed germination of two typical herbaceous plants in a coastal saline land of the Yellow River Delta, to enhance our understanding by which substrate heterogeneity influences plant community dynamics. Methods We conducted growth chamber experiments to investigate the effects of biocrusts and uncrusted soil from bare patch-, Phragmites australis-, Suaeda glauca- and Tamarix chinensis-dominated habitats on seed germination percentage and mean germination time of two herbaceous plants: the perennial P. australis and the annual S. glauca. We also explored the mechanisms underlying the effects of substrate on seed germination. Important Findings Compared with uncrusted soil, biocrusts increased water content, nutrient accumulation and concentration of most salt ions, but they reduced soil pH value. Biocrusts with mosses directly decreased soil pH value and concentration of Mg2+, resulting in an indirect increase in seed germination percentage of S. glaucas. The low soil pH value also resulted in an indirect decrease in seed germination speed of P. australis in their own habitats. Bare patch directly increased accumulation of Cl−, resulting in an indirect decrease in seed germination speed of P. australis. These results suggest that biocrusts with mosses in P. australis habitats offer a window of opportunity for germination of S. glaucas. Biocrusts combined with habitat type have the potential to influence plant community structure through an effect on seed germination and establishment.

Dose-Effect Relationship of Water Salinity Levels on Osmotic Regulators, Nutrient Uptake, and Growth of Transplanting Vetiver [Vetiveria zizanioides (L.) Nash

Vetiver grass [Vetiveria zizanioides (L.) Nash] without seeds, suitable for growing on coastal saline land, has attracted attention because of oil extraction from its roots and industrial and agricultural use. In this study, a pot experiment with different NaCl contents was used to investigate the influence of water salinity levels on vetiver, salt tolerance, and the feasibility of transferring it to coastal saline regions. The results indicated that the fresh weight of roots and shoots increased initially and then gradually decreased with an increase in NaCl content, and the maximum was attributed to a water salinity of 0.3%. The vetiver can tolerate a maximum saline content of up to 2%. The promotion of vetiver growth under water salinity could be attributed to the acceleration of nutrient uptake-induced saline, including K, N, and Cl. The growth of vetiver was insignificantly inhibited with 0.5% water salinity (mild stress), significantly inhibited with 1.0% water salinity (moderate stress: biomass decrease), and severe inhibited with >1.5% water salinity (intense stress: biomass decrease). The salt tolerance of vetiver was due to osmotic regulation by reducing sugars under mild stress and of proline under intense stress, and Na+ sequestration in roots and the transformation of Cl− away from sensitive roots. The vetiver could be cultivated in slightly coastal saline soil (0.1–0.2% soil salinity) and even moderately saline coastal soil (0.2–0.4% soil salinity) under irrigation with low salt water during transplanting.

Physiological, morphological and anatomical responses of Hibiscus moscheutos to non-uniform salinity stress

Plant growth in the heterogeneous salinity soil is better than that of in the uniform salinity soil, thus, planting salt tolerant plants in the partial zone desalinated soil of the saline land may reduce the revegetation costs. The swamp rose mallow (Hibiscus moscheutos, SRM), which is an important landscape plant that grows in coastal saline lands, may be an optional plant that can adapt to the non-uniform salinity soil. In this study, SRM seedlings grown in split-root pots irrigated with different concentration of NaCl solutions were studied. There were four treatments, a control (0 mM NaCl), uniform salinity (200 mM NaCl), and two non-uniform salinities (0/200 mM and 0/400 mM NaCl). We determined the growth, gas exchange properties of the leaves, morphological parameters of the leaves and roots, water potential and consumption, and ion accumulation of the seedlings. The aim was to reveal the physiological and anatomical responses of SRM to non-uniform salinity. Under non-uniform salinity, the total biomass, shoot height, and leaf area of SRM seedlings were significantly higher and the leaf Na+ and Cl− contents were significantly lower than under uniform salinity. The total biomass was negatively corelated with the mean root zone salinity. Once the parts of the roots were in the salt-free zone, the leaf water potential and the daily water consumption of the seedlings under non-uniform salinity were much higher than the uniform salinity treatment. The leaf gas exchange of SRM under non-uniform salinity was not significantly inhibited compared to the control, but was significantly higher than under uniform salinity. The leaf electron transport rate (ETR) and maximum quantum yield (Fv/Fm) of the PSII, leaf SOD activity, and the MDA content of the seedlings subjected to non-uniform salinity treatments were at unstressed level. In terms of leaf anatomical traits, that the palisade and spongy parenchyma was significantly thicker than the uniform salinity. Early senescence of the leaves was observed under both uniform and non-uniform salinity conditions. More roots, especially fine roots, were distributed in the non-saline zone. These results indicate that under non-uniform salinity, SRM seedling growth was significantly inhibited, however, the salt stress was alleviated by the partial salt-free root zone compared to uniform the salinity. Non-uniform salinity led to moderate Na+ accumulation in the leaves, which in turn caused slight oxidative and osmotic stress, but had little influence on the morphological or anatomical traits of the leaves. SRM could adapt to the saline soil where partial zone desalinated or partial zone replaced by the non-saline soil.

Contrasting photosynthesis, photoinhibition and oxidative damage in honeysuckle (Lonicera japonica Thunb.) under iso-osmotic salt and drought stresses

Honeysuckle (Lonicera japonica Thunb.) is a traditional Chinese medicinal crop and belongs to the glycophyte with certain salt tolerance. This study aimed to deeply dissect its salt adaptability by contrasting photosynthesis, photoinhibition and oxidative damage under moderate and severe iso-osmotic salt (150 and 300 mM NaCl) and drought (19.3 % and 28 % PEG-6000) stresses with hydroponic protocol. Photosynthesis was more susceptible to drought stress than iso-osmotic salt stress in honeysuckle according to drought-induced greater decrease in photosynthetic rate. In contrast to salt-induced mild PSⅡ and PSI photoinhibition, severe photosystem II (PSⅡ) and photosystem I (PSI) photoinhibition arose upon iso-osmotic drought stress, indicated by greater decreased the maximal photochemical efficiency of PSⅡ and PSI and remarkable loss of their reaction center proteins. However, PSⅡ and PSI interaction hardly contributed to salt stability of photosynthetic apparatus because of salt-induced finite restriction on electron flow from PSⅡ to PSI. Consistent with photosystems photoinhibition, leaf lipid peroxidation, H2O2 production and electrolyte leakage were elevated much greater by drought stress than iso-osmotic salt stress, confirming drought-induced severe oxidative stress in honeysuckle. Furthermore, the principal components analysis comprehensively showed higher salt adaptability in honeysuckle due to larger cluster separation upon drought stress than iso-osmotic salt stress. As an apparent reason, honeysuckle could prevent drought-induced tremendous leaf water loss upon iso-osmotic salt stress, and had a capacity to dispose accumulated Na+. Therefore, honeysuckle resembles halophytes in this respect and seems appropriate for planting in coastal saline land.

Potato (Solanum tuberosum L.) Cultivation by Zero Tillage and Paddy Straw Mulching in the Saline Soils of the Ganges Delta

In the coastal region of the Ganges Delta, rice is the predominant crop during the wet/kharif season and most of the land remains fallow during dry/rabi season due to soil salinity and irrigation water scarcity. Sustainable intensification of coastal saline land needs an improved package of practices which conserves soil moisture, facilitates early crop establishment, ensures profitability and has a positive effect on soil health. To achieve these objectives, we evaluated seven treatments for the potato crop in a randomized complete block design with five replications (farms) during the rabi season of 2017–2018 and again in 2018–2019, viz. T1, ridge planting (control); T2, zero tillage planting with 15 cm (9 t ha−1) paddy straw mulching; T3, T2 + foliar spray of nutrients; T4, zero tillage planting with 20 cm (12 t ha−1) paddy straw mulching; T5, T4 + foliar spray of nutrients; T6, zero tillage planting with 25 cm (15 t ha−1) paddy straw mulching; and T7, T6 + foliar spray of nutrients. Tuber yield was higher in T5, T6 and T7 (37.9–41.5 t ha−1) during the second year over other treatments (21.5–32.3 t ha−1). About 200 mm of irrigation water can be saved by zero tillage planting with paddy straw mulching compared with ridge planting. The tuber quality in terms of crude protein, fat, crude fibre and carbohydrate was better under zero tillage planting with paddy straw mulching. The cost of cultivation of potato was reduced by about 27% due to zero tillage planting (US$ 1211.6 ha−1) compared with conventional tillage, intensive ridge planting practice (US$ 1660.4 ha−1). Zero tillage planting with paddy straw mulching resulted in a net return of US$ 1779.2 ha−1, whereas under conventional cultivation, it was US$ 589.6 ha−1. Zero tillage planting of potato with paddy straw mulching reduced soil salinity (ECe) from 5 to 3 dS m−1, conserved soil moisture (4–8%), improved soil bulk density from 1.49 to 1.44 Mg m−3 and increased soil organic carbon from 0.39 to 0.44%. The results of this study suggest that zero tillage potato cultivation in the dry/rabi season can increase cropping intensity in the salt-affected Ganges Delta and increase income of the farmers.

Comparison of random forest and multiple linear regression models for estimation of soil extracellular enzyme activities in agricultural reclaimed coastal saline land

The alternations in soil physicochemical properties caused by the reclamation of coastal tidal land can strongly affect the activities of soil extracellular enzymes. Soil extracellular enzymes are one of the most active organic components in soil ecosystem, which is involved in almost all the biochemical reactions. Determining the importance of potential influencing factors of soil extracellular enzymes and thus estimating their activities are important for clarifying the biological mechanism of soil carbon and nitrogen cycling. In this study, the multiple linear regressions (MLR) and random forest (RF) models were conducted to estimate the activities of soil amylase and urease activities using covariates, such as soil water content (SWC), electrical conductivity (EC), total nitrogen (TN), total phosphorus (TP), and soil organic carbon (SOC) as well as the soil bulk density (BD) and pH. The results reveals that the amylase activity of fishpond was significantly higher than that of other land use types, while the urease activity of rape land, broad bean land, and fishpond were notably higher than that of bare flat, Spartina alterniflora, and uncultivated land. The RF model indicated that the SWC and TN is the main variable affecting amylase and urease activity, respectively. The RF model performed much better than MLR model in estimating the soil amylase and urease activity as it revealed much lower error indices (MAE and RMSE) and higher R2 value. The superiority of RF model in estimating amylase and urease activity is due to its advantages to handle the nonlinear and hierarchical relationships between enzyme activities and covariates, and insensitivity to overfitting and the presence of noise in the data.

De novo transcriptome assembly and population genetic analyses of an important coastal shrub, Apocynum venetum L

BackgroundApocynum venetum L. is an important medicinal plant that is mainly distributed in the coastal areas and northwest of China. In addition to its high medical and economic value, its adaptation to saline-alkali and coastal saline lands makes A. venetum an ideal candidate for use in vegetation restoration. To date, the study of A. venetum has been limited in the northwest region of China, little attention has been paid to the genetic diversity and population structure of A. venetum populations in the coastal region. Here, we performed transcriptome sequencing of total RNA from A. venetum leaves and developed efficient expressed sequence tag-simple sequence repeat (EST-SSR) markers for analyzing the genetic diversity and population structure of A. venetum in the coastal region.ResultsA total of 86,890 unigenes were generated after de novo assembly, and 68,751 of which were successfully annotated by searching against seven protein databases. Furthermore, 14,072 EST-SSR loci were detected and 10,243 primer pairs were successfully designed from these loci. One hundred primer pairs were randomly selected and synthesized, twelve primer pairs were identified as highly polymorphic and further used for population genetic analysis. Population genetic analyses showed that A. venetum exhibited low level of genetic diversity (mean alleles per locus, NA = 3.3; mean expected heterozygosity, HE = 0.342) and moderate level of genetic differentiation among the populations (genetic differentiation index, FST = 0.032–0.220) in the coastal region. Although the contemporary (mean mc = 0.056) and historical (mean mh = 0.106) migration rates among the six A. venetum populations were moderate, a decreasing trend over the last few generations was detected. Bayesian structure analysis clustered six populations into two major groups, and genetic bottlenecks were found to have occurred in two populations (QG, BH).ConclusionsUsing novel EST-SSR markers, we evaluated the genetic variation of A. venetum in the coastal region and determined conservation priorities based on these findings. The large dataset of unigenes and SSRs identified in our study, combining samples from a broader range, will support further research on the conservation and evolution of this important coastal plant and its related species.