Effects Of Soil Acidification Research Articles

Plant functional traits modulate the effects of soil acidification on above- and belowground biomass

Abstract. Atmospheric sulfur (S) deposition has been increasingly recognized as a major driver of soil acidification. However, little is known about how soil acidification influences above- and belowground biomass by altering leaf and root traits. We conducted a 3-year S-addition experiment to simulate soil acidification in a meadow. Grass (Leymus chinensis (Trin.) Tzvelev) and sedge (Carex duriuscula C.A.Mey) species were chosen to evaluate the linkage between plant traits and biomass. Sulfur addition led to soil acidification and nutrient imbalances. Soil acidification decreased specific leaf area (SLA) but increased leaf dry-matter content (LDMC) in L. chinensis, showing a conservative strategy and thus suppressing aboveground instead of belowground biomass. However, in C. duriuscula, soil acidification increased plant height and root nutrients (N, P, S, and Mn), favoring competition for natural resources through enhanced above- and belowground biomass, i.e., adoption of an acquisitive strategy. Increased soil acidity resulted in an overall reduction in aboveground community biomass by 3 %–33 %, but it led to an increase in community root biomass by 11 %–22 % due to upregulation as a result of higher soil nutrient availability. Our results demonstrate that both above- and belowground plant biomass is affected by S-induced acidification. Understanding the linkage between plant biomass and functional traits contributes to a better understanding of plant–soil feedback in grassland ecosystems.

Effect of Soil Acidification on Temperature Sensitivity of Soil Respiration

Soil pH significantly impacts microbial activity and community assembly, which in turn determines the temperature sensitivity (Q10) of soil respiration. Due to the high soil acidification in China, it is necessary to understand how soil acidification impacts Q10. Here, the Q10 of soil respiration was examined in a long-term field experiment (1982–present) with different soil pH caused by fertilization management. In this experiment, we selected treatments with neutral pH: (1) no crops and fertilization (CK); (2) crops without fertilization (NF); low pH with (3) crops with chemical fertilization (NPK); and (4) crops with chemical fertilization combined with wheat straw incorporation (WS). Under natural soil temperature changes, we observed that soil acidification lowered the Q10 value of soil respiration. Considering only temperature changes, the Q10 of soil respiration was strongly associated with microbial community composition, alpha diversity, and soil ammonium nitrogen. Considering the interaction between soil pH and temperature, warming strengthened the negative effect of soil pH on the Q10 of soil respiration, and the pathway through which soil pH mediated Q10 included not only microbial community composition, alpha diversity, and biomass but also the soil’s available phosphorus. This work enhanced our insights into the relationships between Q10, temperature, and soil pH by identifying important microbial properties and key soil environmental factors.

A Review on the Impact of Soil Acidification on Plant Nutrient Availability, Crop Productivity, and Management Options in the Ethiopian Highlands

Soil acidity is a type of soil deterioration that has a negative impact on Ethiopia's overall and Western Oromia's specific sustainable agricultural production. Currently, soil acidity in highland portions of Western Oromia, including Gimbi, Nedjo, and surrounding areas, is a major problem that can impede agricultural productivity. Reviewing the mechanisms of soil acidification, which can affect soil nutrient availability and agricultural production, as well as management choices, were done in this context for this review topic. The main causes of acid soils are leaching of exchangeable basic cations and topsoil erosion caused by high temperatures and heavy rains, which promote the loss of organic matter the most. In most of Ethiopia's highland regions, the removal of agricultural waste and ongoing use of inorganic fertilizers that produce acidity are major factors in the development of soil acidity. Al and Mn toxicity are caused by acid soil, which also reduces nutrient availability. Furthermore, agricultural yield decreases due to acidity in the soil. The management options for acid soils include crop types resistant to Al toxicity, liming, and the use of organic materials as integrated forms of soil fertility control. Therefore, lime and organic fertilizers should be employed as crucial agricultural techniques for small-holder farmers in acidic soil locations in order to decrease the effects of soil acidity.

Lime microdosing: A new liming strategy for increased productivity in acid soils

AbstractDespite the effectiveness of the fertilizer microdosing technique, lime microdosing (LMD) to alleviate the negative impacts of soil acidity has not been comprehensively assessed. In a 3‐year study at four sites across three countries (one in the United States, two in Ghana, and one in Burkina Faso), we evaluated the effectiveness of the microdosing technique for lime application to alleviate the adverse effects of soil acidity in cropping systems, using corn (Zea mays L.) as the study crop. LMD was evaluated at four lime application rates, including 5%, 10%, 25%, and 50% of the calculated lime‐requirement rate (LR), which was compared to the traditional lime broadcasting strategy using 75% and 100% LR. Averaged across all experimental sites for the duration of the study, LMD with 25% LR resulted in similar grain yield, and nitrogen, phosphorus, and potassium recovery efficiency as those of the traditional lime broadcast techniques with 100% LR, but significantly greater than those of the lime broadcast techniques with 75% LR. Postharvest rhizosphere aluminum saturation percentage of the LMD with 25% LR was similar to that of the traditional lime broadcast techniques with 100% LR. However, LMD with lime application rates lower than 25% LR was not agronomically effective. The combined results suggest that LMD could be an efficient liming technique, and that with this technique, as little lime material as 25% LR could be used to mitigate the negative impacts of Al toxicity associated with soil acidity. Nevertheless, economic analyses are required to determine the profitability of utilizing the LMD technique to mitigate the negative impacts of soil acidity on crop production relative to the traditional lime‐broadcast approach.

Biochar derived from invasive plants improved the pH, macronutrient availability and biological properties better than liming for acid rain-affected soil

Rapid development in industrialization and urbanization causes serious environmental issues, of which acid rain is one of the quintessential hazards, negatively affecting soil ecology. Liming has been investigated for a long time as the most effective amendment to alter the adverse effects of soil acidity resulting from acid rain. Herein, this study tested the biochar produced from invasive plants as an alternative amendment and hypothesized that biochar can maintain better availability of macronutrients under acid rain than liming by improving soil chemical and biological properties. Therefore, a pot experiment was conducted to compare the effects of lime and biochar at two rates (1% and 3%) on soil available nitrogen (N), phosphorous (P) and potassium (K) under simulated acid rain of two pH levels (4.5: pH4.5 and 2.5: pH2.5) as compared with tap water (pH7.1) as a control treatment. Biochar was produced using different invasive plants, including Blackjack (Biden Pilosa), Wedelia (Wedelia trilobata) and Bitter Vine (Mikania micrantha Kunth). Liming decreased the availability of soil N, P, and K by 36.3% as compared with the control due to the great increment in soil pH and exchangeable calcium (Ca2+) by 59% and 16-fold, respectively. Moreover, liming reduced the alpha diversity of soil bacteria and fungi by 27% and 11%, respectively. In contrast, biochar at different types and rates resulted in a fourfold increment in the available N, P, and K as an average under acid rain (pH4.5 and pH2.5) owing to maintaining a neutral pH (6.5–7), which is the most favorable level for soil microbial and enzymatic activites, and the bioavailability of soil nutrients. Furthermore, biochar caused balanced increments in Ca2+ by threefold, cation exchange capacity by 45%, urease activity by 16%, and fungal diversity by 10%, while having a slight reduction in bacterial diversity by 2.5%. Based on the path, correlation, and principal component analyses, the exchangeable aluminum was a moderator for the reductions in macronutrients’ availability under acid rain, which decreased by 40% and 35% under liming and biochar, respectively. This study strongly recommended the use of biochar from invasive plants instead of lime for sustainable improvements in soil properties under acid rain.Graphical

Amelioration of Soil Acidity in Ferralsols of Central Uganda

Soil acidity is one of the major constraints limiting crop productivity in Central Uganda. Thus, the ideal soil pH for crop production ranges from 5.5 to 6.8, but in Central Uganda, crops are believed to be cultivated in soils with pH below these ranges. Given the adverse effects of soil acidity to agricultural production, appropriate measures such as the use of lime could be an option to improve the productive capacity. Henceforward, soils were sampled from farmers’ fields in Mpigi, Mubende and Wakiso Districts representing Central Uganda to evaluate rates of CaCO3 and corncob biochar in a greenhouse incubation study. Afterwards, 2 kg of soil was weighed, placed in a plastic container and thoroughly mixed with 0, 1, 3 and 5 g equivalent to 0, 1, 3 and 5 tons/ha CaCO3 and corncob biochar. Soils were arranged in a Complete Randomized Design (CRD) and moistened with 500 ml of water to bring it to about field capacity and pH determination done for a period of three (3) months until equilibration. The analysis of variance (ANOVA) showed significant effect (P<0.001) on soil pH when CaCO3 and corncob biochar were applied with the three districts recording a near neutral pH of 6.7.
 After pH equilibration in the greenhouse, rates of CaCO3 and corncob biochar that raised the soil pH in each medium were used to calculate the lime rates i.e., 0, 120, 360 and 600 g applied in the fields. In a Complete Randomized Design (CRD) consisting of four replications, soybean varieties were applied as the main plots while rates of CaCO3 and corncob biochar were applied as the sub plots. The analysis of variance (ANOVA) showed that CaCO3 had significant effect (p<0.001) on soil pH with Mpigi recording the highest soil pH (6.7) followed by Mubende (pH 6.6). Rates of CaCO3 and corncob biochar also showed significant effect (p<0.001) on soybean grain yield compared to 0 g CaCO3 and corncob biochar. Application of 600 g of corncob biochar showed significant effect (p<0.001) on soil pH in the different study locations. Besides, increased in CaCO3 rate to 600 g recorded the highest (7137.5 kg ha-1) soybean grain yield in Wakiso District while 600 g of corncob biochar recorded the highest (5637.5 kg ha-1) soybean grain yield in Mpigi District thus signifying the potential effect of CaCO3 and corncob biochar in Acid Ferralsols.

Long-term risk assessment of uprooting and stem breakage under drought conditions and at high N deposition in beech and Norway spruce

Damage by wind in forests has increased in recent decades, counteracting possible growth increases by nitrogen (N) deposition. This is also shown by the long-term forest monitoring data from this study. The main factors affecting uprooting and stem breakage in Fagus sylvatica (L.) (9′846 individual beech trees in 102 plots) and Picea abies (Karst.) (9′168 Norway spruce trees in 72 plots) have been analysed by binomial mixed regression models. Our long-term forest observations showed that drought increased uprooting of beech and increased both uprooting and stem breakage of Norway spruce. In beech, high N deposition interacted with drought, resulting in increased uprooting under drought. In Norway spruce, N deposition increased stem breakage directly. Foliar potassium (K) deficiency increased uprooting of both beech and Norway spruce. Moreover, we found an indirect effect of soil acidification in increasing uprooting of beech by decreasing foliar calcium (Ca) concentrations. In Norway spruce, the soil acidification effect was confounded by foliar K concentrations. In beech, stem breakage increased with higher temperature which can be explained by a temperature-mediated growth increase of white rot fungi. In contrast, temperature was negatively related with stem breakage in Norway spruce, which may be interpreted as an inhibition of the heartrot fungus Heterobasidion at higher temperatures.In summary, drought and high N deposition increase the risk of mechanical damage to both beech and Norway spruce and thus endanger sustainable growth rates. We therefore suggest that wind damage must be taken in account in productivity calculations and carbon budgets of temperate forests.

Effect of Soil Acidification on the Production of Se-Rich Tea.

Selenium (Se)-enriched tea is a well-regarded natural beverage that is often consumed for its Se supplementation benefits. However, the production of this tea, particularly in Se-abundant tea plantations, is challenging due to soil acidification. Therefore, this study aimed to investigate the effects of changes in Se under acidified soil conditions. Eight tea plantation soil monitoring sites in Southern Jiangsu were first selected. Simulated acid rain experiments and experiments with different acidification methods were designed and soil pH, as well as various Al-ion and Se-ion concentrations were systematically determined. The data were analyzed using R statistical software, and a correlation analysis was carried out. The results indicated that as the pH value dropped, exchangeable selenium (Exc-Se) and residual selenium (Res-Se) were transformed into acid-soluble selenium (Fmo-Se) and manganese oxide selenium (Om-Se). As the pH increased, exchange state aluminum (Alex) and water-soluble aluminum (Alw) decreased, Fmo-Se and Om-Se declined, and Exc-Se and Res-Se increased, a phenomenon attributed to the weakened substitution of Se ions by Al ions. In the simulated acid rain experiment, P1 compared to the control (CK), the pH value of the YJW tea plantation decreased by 0.13, Exc-Se decreased by 4 ug mg-1, Res-Se decreased by 54.65 ug kg-1, Fmo-Se increased by 2.78 ug mg-1, and Om-Se increased by 5.94 ug mg-1 while Alex increased by 28.53 mg kg-1. The decrease in pH led to an increase in the content of Alex and Alw, which further resulted in the conversion of Exc-Se to Fmo-Se and Om-Se. In various acidification experiments, compared with CK, the pH value of T6 decreased by 0.23, Exc-Se content decreased by 8.35 ug kg-1, Res-Se content decreased by 40.62 ug kg-1, and Fmo-Se content increased by 15.52 ug kg-1 while Alex increased by 33.67 mg kg-1, Alw increased by 1.7 mg kg-1, and Alh decreased by 573.89 mg kg-1. Acidification can trigger the conversion of Exc-Se to Fmo-Se and Om-Se, while the content of available Se may decrease due to the complexation interplay between Alex and Exc-Se. This study provides a theoretical basis for solving the problem of Se-enriched in tea caused by soil acidification.

Long-term nitrogen fertilization and sweetpotato cultivation in the wheat-sweetpotato rotation system decrease alkaline phosphomonoesterase activity by regulating soil phoD-harboring bacteria communities

The alkaline phosphomonoesterase (ALP)-harboring community (phoD-harboring community) plays a crucial role in the conversion of organic phosphorus (P) into available P (AP). However, the response mechanisms of phoD-harboring communities to fertilization strategies, crop types, and their interactions within the wheat-sweetpotato rotation are poorly understood. A nine-year field experiment of different fertilization strategies was established under the wheat-sweetpotato rotation. After harvesting the crop, we collected soil samples without fertilization (CK), inorganic NK fertilization (NK), inorganic NPK fertilization (NPK), and a combined application of inorganic NPK and organic fertilizer (NPKM). We employed high-throughput sequencing and enzymology techniques to analyze the composition and functional activity of phoD-harboring bacterial communities as well as their correlation with soil physicochemical properties. The results showed that long-term nitrogen (N) fertilization, especially inorganic N, significantly reduced soil pH and ALP activity while increasing AP compared with CK. The AP content in sweetpotato season was significantly higher than that in wheat season. Inorganic N fertilization dramatically reshaped the communities of phoD-harboring bacteria and decreased diversity. The phoD-harboring bacterial communities in sweetpotato season were significantly different from those in wheat season. The N fertilization significantly reduced the relative abundance of Acuticoccus, Methylibium, Rhizobacter, and Roseivivax, which was positively correlated with ALP activity. These groups in sweetpotato season decreased significantly compared with wheat season. A structural equation model indicates that pH and AP play a significant role in regulating the phoD-harboring bacteria communities, ALP activity, and their interactions. We demonstrate that fertilization strategies and crop types have a substantial impact on the phoD-harboring bacteria communities and functions, which are closely linked to soil pH and AP levels. Our study highlights the detrimental effects of soil acidification resulting from inorganic N fertilization on P-cycling bacterial communities and functions. However, the combination of inorganic and organic fertilizer can mitigate these adverse effects.

Effects of soil acidity on soil nitrogen-transforming microorganisms, biochemical intensity and tea quality

Effects of soil acidity on soil nitrogen-transforming microorganisms, biochemical intensity and tea quality

Soil acidification induced variation of nitrifiers and denitrifiers modulates N2O emissions in paddy fields

Soil acidification is a major land degradation process globally, and impacts soil nitrogen (N) transformation. However, it is still not well known how soil acidification affects net N mineralization and nitrification, especially N-cycling microbes and nitrous oxide (N2O) emissions. Hence, three soils characterized by different soil pH values (5.5, 6.3, and 7.7) were collected from the paddy fields, and experiments were conducted to evaluate the effect of soil acidification on net N mineralization and nitrification, and N2O emissions. Compared to those in the soils with pH 7.7 and 6.3, net N mineralization, net nitrification, and N2O emissions were decreased by 75–76 %, 89–91 %, and 19–48 %, respectively, in the soil with pH 5.5, while net N nitrification and N2O emissions decreased by 18 % in the soil with pH 6.3 when compared to those in the soil with pH 7.7. The significantly decreased net nitrification in the soils with pH 6.3 and 5.5 was mainly attributed to the limited N availability and abundance of nitrification-related microbes including ammonia-oxidizing bacteria and complete ammonia-oxidizers. The decrease in N2O emissions of soils with pH 6.3 and 5.5 had mainly resulted from decreasing nitrification and denitrification via suppressing microbes including nirS and fungal nirK and limiting N availability. Hence, this study provides new insights and improves our understanding of how soil acidification regulates N mineralization, nitrification, and N2O emissions in paddy soils, which gives guidance on developing N management strategies for sustainable production and N2O mitigation in acid soils.

Lime and Vermicompost Application to Acid Soils and Their Effects on Maize Yield and Yield Components in Lalo Asabi District, West Wollega Zone, Oromia, Ethiopia

Soil acidity is one of the major yield-limiting factors for crop production worldwide, particularly on highly weathered and leached tropical soils. Different reports have indicated that there is significant soil acidity coverage in Ethiopia. In particularly, in the western part of the country, soil acidity is a well-known problem limiting crop production and productivity. As part of the solution to such a problem in soils, the combined application of lime and VC on maize has not been investigated in the area, in which maize was one of the potential cereal crops in the area. A field experiment was conducted at Lalo Asabi district in western Wollega during the 2020 cropping season to evaluate the responses of maize to the combined application of lime and vermicompost (VC). The experimental treatments were five rates of lime (CaCO3) (0, 25, 50, 75, and 100% of lime requirement (LR)) and three levels of vermicompost (0, 2.5, and 5 t ha-1). The treatments were arranged in factorial combinations in a randomized complete block design with three replications. One composite surface soil samples from a depth of (0-15 cm) was collected from the experimental field before the commencement of the experiment. Maize yield and yield components were measured following standard procedures. The yield components and yield results revealed the main effects of lime and VC showed a significant effect (p<0.05) on the number of days to 50% tasseling and silking, ear height, number of cobs per plant, number of grains per cob, thousand grain weight, above ground biomass, and harvest index of maize. However, days to 90% physiological maturity, plant height, cob length and grain yield of maize were significantly affected (p<0.05) by lime and VC interactions. Even though both were statistically equal, the combined application of lime at 100% LR + 5 t VC ha-1 yielded the highest grain yield (7.99 t ha-1) followed by the combined application of lime at 75% LR + 2.5 t VC ha-1 whereas the lowest grain yield (2.97 t ha-1) from control plots. The results of economic analysis indicated that the combination of lime at 75% LR + 2.5 t VC ha-1 showed a marginal rate of return of 2322.74%, with the highest net benefit of 49980 Ethiopian Birr compared to other treatments. This study indicates combined use of lime and VC could ameliorate the adverse effect of soil acidity, and application of 75% LR + 2.5 t VC ha1 enhances grain yield and produces the highest net benefit of maize grown on acidic soil of the Lalo Asabi district.

Saprotrophic fungi buffer the adverse effects of soil acidification on the soil nutrient supply ability of Chinese fir (Cunninghamia lanceolata) plantations

Soil nutrient supply is critical in maintaining plantation productivity and sustainable management. However, long-term continuous planting can result in soil acidification, and the underlying mechanisms of how soil microorganisms maintain soil nutrient supply ability under the stress of soil acidification remain elusive. Here, we investigated soil physicochemical properties and assessed soil fertility levels in mature Chinese fir (Cunninghamia lanceolata) plantations (MatCFPs) and middle-aged Chinese fir plantations (MidCFPs). 16S and ITS rRNA amplicon sequencing were performed to examine the soil bacterial and fungal community structure. Compared with MidCFPs, the soil organic carbon, total nitrogen, total phosphorus, ammonium nitrogen, and available phosphorus contents in MatCFPs soil were significantly higher, thus significantly improving the soil fertility level of MatCFPs. Additionally, we observed a significant decrease in soil pH in MatCFPs compared to MidCFPs. Resulting soil acidification in MatCFPs not only decreased soil bacterial abundance and network stability but also limited bacterial functions related to nitrogen and carbon cycling. In contrast, compared with MidCFPs, fungal abundance and network stability increased in acidified MatCFP soils. Fungal abundance rather than bacterial abundance was positively correlated with the soil fertility level, and saprotrophic fungi were the main microbial driver of soil fertility, which explained the 21.4% of the variation in the soil fertility level. This study improves our understanding of the importance of saprotrophic fungi in maintaining soil nutrient supply ability under the adverse effect of soil acidification and provides insight into sustainable plantation management.

Higher pH is associated with enhanced co-occurrence network complexity, stability and nutrient cycling functions in the rice rhizosphere microbiome.

The rice rhizosphere microbiota is crucial for crop yields and nutrient use efficiency. However, little is known about how co-occurrence patterns, keystone taxa and functional gene assemblages relate to soil pH in the rice rhizosphere soils. Using shotgun metagenome analysis, the rice rhizosphere microbiome was investigated across 28 rice fields in east-central China. At higher pH sites, the taxonomic co-occurrence network of rhizosphere soils was more complex and compact, as defined by higher average degree, graph density and complexity. Network stability was greatest at medium pH (6.5 < pH < 7.5), followed by high pH (7.5 < pH). Keystone taxa were more abundant at higher pH and correlated significantly with key ecosystem functions. Overall functional genes involved in C, N, P and S cycling were at a higher relative abundance in higher pH rhizosphere soils, excepting C degradation genes (e.g. key genes involved in starch, cellulose, chitin and lignin degradation). Our results suggest that the rice rhizosphere soil microbial network is more complex and stable at higher pH, possibly indicating increased efficiency of nutrient cycling. These observations may indicate routes towards more efficient soil management and understanding of the potential effects of soil acidification on the rice rhizosphere system.

Soil metagenomic analysis on changes of functional genes and microorganisms involved in nitrogen-cycle processes of acidified tea soils.

Nitrogen (N) is the first essential nutrient for tea growth. However, the effect of soil acidification on soil N cycle and N forms in tea plantation are unclear. In this study, the nitrogen contents, soil enzyme activity and N mineralization rate in acidified soil of tea plantation were measured. Moreover, the effects of soil acidification on N cycling functional genes and functional microorganisms were explored by soil metagenomics. The results showed that the NH4 +-N, available N and net N mineralization rate in the acidified tea soil decreased significantly, while the NO3 --N content increased significantly. The activities of sucrase, protease, catalase and polyphenol oxidase in the acidified tea soil decreased significantly. The abundance of genes related to ammonification, dissimilatory N reduction, nitrification and denitrification pathway in the acidified tea soil increased significantly, but the abundance of functional genes related to glutamate synthesis and assimilatory N reduction pathway were opposite. In addition, the abundance of Proteobacteria, Actinobacteria, Chloroflexi, Nitrospirae, Actinomadura, Nitrospira etc. microorganisms related to nitrification, denitrification and pathogenic effect increased significantly in the acidified tea soil. The correlation results showed that soil pH and N forms were correlated with soil enzyme activity, N cycling function genes and microbial changes. In conclusion, soil acidification results in significant changes in enzyme activity, gene abundance and microorganism involved in various N cycle processes in acidified tea soil, which leads to imbalance of soil N form ratio and is not conducive to N transformation and absorption of tea trees.

Subcellular Element Distribution in Shoots of Wheat Grown in an Acidic Soil with Native AMF Extraradical Mycelium

Soil acidity can reduce crop growth by increasing bioavailable soil Al, Fe, and/or Mn to toxic levels. The presence of an intact extraradical mycelium (ERM) of arbuscular mycorrhizal fungi (AMF), developed by the native Ornithopus compressus in the acidic soil, can increase wheat growth and prevent symptoms of Mn toxicity. To understand the protective effect of the intact ERM of this native plant on wheat element balance and distribution, in the present study, shoot Al, Fe, K, Zn, Na, and Si levels and their subcellular partitioning were determined by inductively coupled plasma mass spectrometry (ICP-MS), for the first time, for this system. In undisturbed soil, where an intact ERM structure is maintained, wheat shoot growth was promoted, probably due to faster root mycorrhizal colonization. The levels of potentially toxic Al and Fe were reduced, the proportions of the macronutrient K and micronutrient Zn were higher in the symplast, and the Na proportion increased in the vacuole, while Si increased in the apoplast. Overall, the undisturbed soil from O. compressus treatment appeared to influence the uptake and distribution of essential and beneficial elements, as a strategy to reduce the negative effect of soil acidity on wheat growth. Understanding the dynamics of element distribution influenced by stress-adapted AMF on wheat growth can provide more sustainable approaches to intensive agriculture.

Root-Associated Microbiota Response to Ecological Factors: Role of Soil Acidity in Enhancing Citrus Tolerance to Huanglongbing.

The citrus orchards in southern China are widely threatened by low soil pH and Huanglongbing (HLB) prevalence. Notably, the lime application has been used to optimize soil pH, which is propitious to maintain root health and enhance HLB tolerance of citrus; however, little is known about the interactive effects of soil acidity on the soil properties and root-associated (rhizoplane and endosphere) microbial community of HLB-infected citrus orchard. In this study, the differences in microbial community structures and functions between the acidified and amended soils in the Gannan citrus orchard were investigated, which may represent the response of the host-associated microbiome in diseased roots and rhizoplane to dynamic soil acidity. Our findings demonstrated that the severity of soil acidification and aluminum toxicity was mitigated after soil improvement, accompanied by the increase in root activity and the decrease of HLB pathogen concentration in citrus roots. Additionally, the Illumina sequencing-based community analysis showed that the application of soil amendment enriched functional categories involved in host-microbe interactions and nitrogen and sulfur metabolisms in the HLB-infected citrus rhizoplane; and it also strongly altered root endophytic microbial community diversity and structure, which represented by the enrichment of beneficial microorganisms in diseased roots. These changes in rhizoplane-enriched functional properties and microbial composition may subsequently benefit the plant's health and tolerance to HLB disease. Overall, this study advances our understanding of the important role of root-associated microbiota changes and ecological factors, such as soil acidity, in delaying and alleviating HLB disease.

Metabarcoding of organic tea (Camellia sinensis L.) chronosequence plots elucidates soil acidification-induced shifts in microbial community structure and putative function

Tea (Camellia sinensis L.) agroecosystem soil acidification (TASA) is occurring at epidemic rates relative to other crops, however TASA remains poorly defined in its pathogenesis and effects on soil microbiota. The present study examined bulk soil physicochemical and bacterial 16S rDNA sequence data to elucidate TASA-associated changes through 10 tea agroecosystem sites, including an organic-certified tea field chronosequence of 3-year- (Young), 8-year- (Middle), and 13-year-old (Old) plots. Soil pH declined linearly with age through chronosequence plots. Hierarchical clustering based on community β-diversity revealed a tipping point in community composition as soil acidified below pH 4.5, which had occurred between Middle and Old plots. Tipping point-associated changes in predicted community functionality included a precipitous decline in nitrogenase-encoding communities and concurrent proliferations of Al-detoxifiers, anti-oxidative specialists, and pathogen virulence factor-encoding communities. PERMANOVA modeling revealed that Streptomyces was the genus with population abundance corresponding most significantly with whole microbiome composition at both OTU- (r2 = 0.460, p < 0.001) and genus-levels (r2 = 0.512, p < 0.001), despite ranking 74th in total abundance among 186 core genera, providing computationally-modeled evidence of a keystone role of Streptomyces under tea agroecosystem conditions. Correlations of soil pH with Rhizobiales (r = 0.713, p < 0.001), Acidibacter (r = −0.717, p < 0.001), and predicted β-glucosidase-encoding communities (r = −0.622, p < 0.001) across all samples indicated potential utility as community-level TASA biomarkers. Moreover, two phylogenetically diverse OTU co-abundance modules also corresponded (p < 0.01) with soil pH across all samples, suggesting that TASA-induced shifts were interfaced by networks of diverse and interactive taxa, or keystone guilds. Presently, organic management per se was unable to retain soil pH within the optimal range for tea plant cultivation (pH 4.5–5.5), therefore additional considerations not currently encompassed by organic management guidelines, such as lower tea planting density, may be necessary to avoid the detrimental effects of soil acidification described above. Moreover, future studies may seek to further elucidate the keystone functions of Streptomyces spp. under tea agroecosystem conditions.

Polarisation‐induced covalent interactions between H+ and surface O atoms promote clay aggregation

AbstractAccumulation of H+ can cause soil acidification, affect soil particle interactions, and alter soil processes. In this study, aggregation kinetics of montmorillonite colloids induced by monovalent ions of Li+ and H+ were determined by dynamic light scattering. The experimental results indicated that the critical coagulation concentration (CCC) value of Li+ was 4.5 times that of H+, indicating that H+ can strongly promote montmorillonite colloids aggregation. Joint analysis of the adsorption force type and energy of Li+ and H+ as well as the infrared spectroscopy of Li+ and H+ montmorillonite indicated that there was only electrostatic adsorption for Li+, while there was not only electrostatic adsorption but also a new type of covalent adsorption for H+: polarisation‐induced covalent adsorption. The total adsorption energy of H+ is thus much higher than that of Li+ on montmorillonite surfaces. Moreover, the polarisation‐induced covalent adsorption energy of H+ increased linearly with increasing electric field strength, which is consistent with the quantum mechanical analysis of the asymmetric orbital hybridisation of surface O atoms on montmorillonite. On this basis, the polarisation‐induced covalent adsorption energy of H+ was employed to predict the CCC value of H+ induced montmorillonite aggregation, and it was 7.40 mmol L−1. The high agreement with experimental results (7.26 mmol L−1) proved that the polarisation‐induced covalent interactions between H+ and surface O atoms promotes montmorillonite aggregation. This polarisation induced covalent effect between H+ and surface O atoms might further affect the formation and stability of soil aggregates and the pore status of soil structure, especially as soil acidification is currently becoming a global issue. The discovery from this study will improve our understanding of the effects of soil acidification on soil properties and processes.Highlights H+ greatly promoted clay aggregation. Polarization‐induced covalent between H+ and surface O presented at clay surface. Polarization‐induced covalent bonding energy increase with increasing electric field. Electrostatic and covalent bonding forces jointly determined clay aggregation.

Effects of Liming on the Morphologies and Nutrients of Different Functional Fine Roots of Cunninghamia lanceolata Seedlings

Soil acidification is an important cause of the productivity decline of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook)—one of the most important timber species in China. Although liming is an effective measure for reversing the effects of soil acidification, the effects on the morphologies and nutrients of different functional roots remain ambiguous. Thus, this study aimed to investigate the effects of liming on fine root traits of Chinese fir seedlings between two root function types (absorptive roots (AR) and transport roots (TR)). Chinese fir seedlings with equal performance were planted in each pot with two acidification soils (pH 3.6 and pH 4.3) and three levels of liming (0, 1000, and 4000 kg CaO ha−1). Our data showed that liming had no effect on the root biomass (RB) of AR and TR in mildly acidified soil, but it decreased the RB in severely acidified soil. Specific root length (SRL) of AR and TR were significantly increased by 24% and 27% with a high liming dose in mildly acidified soil, respectively. The specific root areas (SRA) of AR and TR were significantly increased by 10% and 22% with a high liming dose in mildly acidified soil, respectively. Furthermore, root N concentrations were significantly increased by 26% and 30% in AR and TR with a high liming dose in mildly acidified soil, respectively. Root P concentration of AR was significantly increased by 21% with a high liming dose in mildly acidified soil while root Ca concentration was significantly increased with all treatments. A similar trend was also observed in the Ca/Al ratio of roots. Both low and high doses of liming decreased the root Al concentration of AR by 26% and 31% in mildly acidified soil, respectively; however, there was no significant effect on TR in both soils. Our findings indicated that liming could alleviate Al toxicity to fine roots and increase root investment efficiency and absorption capacity. Liming also had coordinate effects on SRL, SRA, Root tissue density (RTD), N, P, Ca and Ca/Al between AR and TR. Our study suggested that to gain a comprehensive understanding of plant growth strategy, researchers in future studies must consider different functional roots rather than just the absorption part. Our results also revealed that the root system became more “acquisitive” due to the remediation of Al toxicity, which may be an important mechanism underlying the increment of the productivity of Chinese fir plantations undergoing liming.