Acidity of Soil and Water Decreases in Acid-Sensitive Forests of Tropical China.

Acid deposition in China has been declining since the 2000s. While this may help mitigate acidification in forest soils and water, little is known about the recovery of soils and water from previous severe acidification in tropical China. Here, we assessed the chemistry of mineral soils, water, and acid gases (SO2 and NOx) from three successional forest types in tropical China from 2000 to 2022. Our results showed that soil pH increased synchronously from 3.9 (2000-2015) to 4.2 (2016-2022) across all three forest types, with exchangeable acid initially decreasing and thereafter stabilizing. Surface and ground water pH also gradually increased throughout the monitoring period. Soil pH recovery was stronger in the primary than in the planted forest. However, soil pH recovery lagged behind the increase in rainfall pH by approximately a decade. The recovery of soil pH was likely related to the positive effects of the dissolution of Al/Fe-hydroxysulfate mineral and subsequent sulfur desorption on soil acid-neutralizing capacity, increased soil organic matter, and climate warming, but was likely moderated by increased exchangeable aluminum and potentially proton-producing hydroxysulfate mineral dissolution that caused the lagged soil pH recovery. Surface and ground water pH recovery was attributed to increased water acid-neutralizing capacity. Our study reports the potential for the recovery of acidified soil and water following decreased acid deposition and provides new insights into the functional recovery of acid-sensitive forests.

Comparative microbiome analysis of Diaphorina citri and its associated parasitoids Tamarixia radiata and Diaphorencyrtus aligarhensis reveals Wolbachia as a dominant endosymbiont.

Microbiome analysis in a host-parasitoid interaction network was conducted to compare the taxonomic composition of bacterial communities of Diaphornia citri, Tamarixia radiata, and Diaphorencyrtus aligarhensis. The comparative analysis revealed differences in the composition and diversity of the symbiont populations across the host and its associated parasitoids. Proteobacteria was the most dominant phylum, representing 67.80% of the total bacterial community, while Candidatus Profftella armature and Wolbachia were the dominant genera across the host and parasitoids. There were clear differences observed in alpha and beta diversity of microbiota through the host and its associated parasitoids. The function prediction of bacterial communities and Pearson correlation analysis showed that specific bacterial communities displayed positive correlations with the carbohydrate metabolism pathway. Furthermore, when symbiotic bacteria were eliminated using a broad-spectrum antibiotic, tetracycline hydrochloride, the parasitoids' median survival time and longevity were significantly reduced. We confirmed the physiological effects of symbiotic bacteria on the fitness of parasitoids and demonstrated the effect of antibiotics in decreasing the food intake and measurement of amino acids in the hemolymph. This study sheds light on basic information about the mutualism between parasitoids and bacteria, which may be a potential source for biocontrol strategies for citrus psyllid, especially D. citri.

Isolation and characterization of Metarhizium anisopliae TK29 and its mycoinsecticide effects against subterranean termite Coptotermes formosanus.

The entomopathogenic fungus Metarhizium anisopliae is widely used as biocontrol agent against many insect pests. In the present study, the potential isolate of M. anisopliae TK29 was isolated from the agricultural soils in Thekkady, India. The taxonomic identity of the isolate was confirmed based on its morphology and 18S rDNA gene sequence homology. Phylogenetic analysis confirmed that the isolated strains were related to the same species. A potential isolate (TK29) was optimized for mass cultivation and conidial spore production was enhanced using three different raw substrates (Rice, Maize, black gram) by solid-state fermentation. The results showed higher conidial spore yield from rice (2.6 ±â€¯0.32%) compared to black gram (2.1 ±â€¯0.28%) and maize (1.9 ±â€¯0.23%) substrates. Dry green conidia were applied against Formosan subterranean termite, Coptotermes formosanus at three different concentrations (1 × 106, 1 × 107, and 1 × 108 conidia/ml-1). The highest mortality rate was obtained from 1 × 108 conidia/ml-1 at 120 h post-treatment. Our study indicated that M. anisopliae TK29 had desirable attributes for the development of a mycoinsecticide against C. formosanus.

Managing antimony pollution: Insights into Soil-Plant system dynamics and remediation Strategies.

Researchers are increasingly concerned about antimony (Sb) in ecosystems and the environment. Sb primarily enters the environment through anthropogenic (urbanization, industries, coal mining, cars, and biosolid wastes) and geological (natural and chemical weathering of parent material, leaching, and wet deposition) processes. Sb is a hazardous metal that can potentially harm human health. However, no comprehensive information is available on its sources, how it behaves in soil, and its bioaccumulation. Thus, this study reviews more than 160 peer-reviewed studies examining Sb's origins, geochemical distribution and speciation in soil, biogeochemical mechanisms regulating Sb mobilization, bioavailability, and plant phytotoxicity. In addition, Sb exposure effects plant physio-morphological and biochemical attributes were investigated. The toxicity of Sb has a pronounced impact on various aspects of plant life, including a reduction in seed germination and impeding plant growth and development, resulting from restricted essential nutrient uptake, oxidative damages, disruption of photosynthetic system, and amino acid and protein synthesis. Various widely employed methods for Sb remediation, such as organic manure and compost, coal fly ash, biochar, phytoremediation, microbial-based bioremediation, micronutrients, clay minerals, and nanoremediation, are reviewed with a critical assessment of their effectiveness, cost-efficiency, and suitability for use in agricultural soils. This review shows how plants deal with Sb stress, providing insights into lowering Sb levels in the environment and lessening risks to ecosystems and human health along the food chain. Examining different methods like bioaccumulation, bio-sorption, electrostatic attraction, and complexation actively works to reduce toxicity in contaminated agricultural soil caused by Sb. In the end, the exploration of recent advancements in genetics and molecular biology techniques are highlighted, which offers valuable insights into combating Sb toxicity. In conclusion, the findings of this comprehensive review should help develop innovative and useful strategies for minimizing Sb absorption and contamination and thus successfully managing Sb-polluted soil and plants to reduce environmental and public health risks.

Carbon sequestration and storage capacity of Chinese fir at different stand ages.

In southern China, Chinese fir Cunninghamia lanceolata is one of the most important native conifer trees, widely used in afforestation programs. This area has the largest forestland atmospheric carbon sink, and a relatively young stand age characterizes these forests. However, how C. lanceolata forests evolved regarding their ability to sequester carbon remains unclear. Here we present data on carbon storage and sequestration capacity of C. lanceolata at six stand ages (5-, 10-, 15-, 20-, 30- and 60 - year-old stands). Results show that the carbon stock in trees, understory, vegetation, litter, soil, and ecosystem significantly increased with forest age. The total ecosystem carbon stock increased from 129.11 to 348.43 Mg ha-1 in the 5- and 60 - year-old stands. The carbon sequestration rate of C. lanceolata shows an overall increase in the first two stand intervals (5-10 and 10-15), peaks in the 15-20 stand intervals, and then decreases in the 20-30 and 30-60 stand intervals. Our result revealed that carbon sequestration rate is a matter of tree age, with the highest sequestration rates occurring in the middle age forest (15-20 - year-old). Therefore, this information may be useful for national climate change mitigation actions and afforestation programs, since forests are primarily planted for this purpose.

Comprehensive genome-wide identification and expression profiling of ADF gene family in Citrus sinensis, induced by endophytic colonization of Beauveria bassiana.

Endophytic entomopathogenic species are known to systematically colonize host plants and form symbiotic associations that benefit the plants they live with. The actin-depolymerizing factors (ADFs) are a group of gene family that regulate growth, development, and defense-related functions in plants. Systematic studies of ADF family at the genome-wide level and their expression in response to endophytic colonization are essential to understand its functions but are currently lacking in this field. 14ADF genes were identified and characterized in the Citrus sinensis genome. The ADF genes of C. sinensis were classified into five groups according to the phylogenetic analysis of plant ADFs. Additionally, the cis-acting analysis revealed that these genes play essential role in plant growth/development, phytohormone, and biotic and abiotic responses; and the expression analysis showed that the symbiotic interactions generate a significant expression regulation level of ADF genes in leaves, stems and roots, compared to controls; thus enhancing seedlings' growth. Additionally, the 3D structures of the ADF domain were highly conserved during evolution. These results will be helpful for further functional validation of ADFs candidate genes and provide important insights into the vegetative growth, development and stress tolerance of C. sinensis in responses to endophytic colonization by B. bassiana.

Carbon storage capacity of Castanopsis hystrix plantations at different stand-ages in South China.

The establishment of forest plantations is an excellent silvicultural alternative to improve atmospheric carbon (C) sequestration for climate change mitigation. In recent years, the importance of forest growth and C dynamics at different stand ages have drawn huge attention for investigation. To evaluate the impacts of different stand ages on the C storage capacity of Castanopsis hystrix plantations ecosystems, we measured biomass and C content in trees, understory, litter, and soil components from field measurements at different stand ages, i.e., 6-, 10-, 15-, 25-, and 34-year-old stands. Results showed that the C stocks in trees, understory vegetation, litter, soil and the whole ecosystem increased steadily with stand age. C. hystrix C storage capacity in the 6-, 10-, 15-, 25-, and 34-year-old stands were 29.17, 56.18, 85.60, 132.19 and 157.79 Mg ha-1, respectively, while the total ecosystem C storage capacity was 68.11, 106.11, 136.13, 187.34 and 226.14 Mg ha-1, respectively. Meanwhile, the C sequestration rate in the 6-10, 10-15, 15-25 and 25-35-year-old stands were 675.28, 588.35, 465.97 and 284.39 g m2 year-1, respectively. Similarly, total biomass of trees, understory, and litter increased with stand age. Our study indicated that C. hystrix plantations are still developing in the area, since live biomass and soil C continue to accumulate despite reduced C sequestration rates. The information provided here highlight the C stock and C sequestration rates of C. hystrix at different stand ages, providing baseline information on the C dynamics of young and older stand of C. hystrix in this region; Hence, such knowledge could be useful for designing more realistic policies to mitigate climate change, such as programs to maintain continuous forest growth.

Host-Parasitoid Phenology, Distribution, and Biological Control under Climate Change.

Climate change raises a serious threat to global entomofauna-the foundation of many ecosystems-by threatening species preservation and the ecosystem services they provide. Already, changes in climate-warming-are causing (i) sharp phenological mismatches among host-parasitoid systems by reducing the window of host susceptibility, leading to early emergence of either the host or its associated parasitoid and affecting mismatched species' fitness and abundance; (ii) shifting arthropods' expansion range towards higher altitudes, and therefore migratory pest infestations are more likely; and (iii) reducing biological control effectiveness by natural enemies, leading to potential pest outbreaks. Here, we provided an overview of the warming consequences on biodiversity and functionality of agroecosystems, highlighting the vital role that phenology plays in ecology. Also, we discussed how phenological mismatches would affect biological control efficacy, since an accurate description of stage differentiation (metamorphosis) of a pest and its associated natural enemy is crucial in order to know the exact time of the host susceptibility/suitability or stage when the parasitoids are able to optimize their parasitization or performance. Campaigns regarding landscape structure/heterogeneity, reduction of pesticides, and modelling approaches are urgently needed in order to safeguard populations of natural enemies in a future warmer world.

Comparative transcriptome analysis of Tamarixia radiata (Hymenoptera: Eulophidae) reveals differentially expressed genes upon heat shock.

Temperature is a key parameter that affects insect population, abundance, and distribution in tropical and subtropical regions. Tamarixia radiata Waterson (Hymenoptera: Eulophidae) is a species-specific ectoparasitoid widely used as a biological control agent for the major citrus pest Diphornia citri Kuwayama (Hemiptera: Liviidea). To date, T. radiata response to high temperature at the molecular level still is unclear. In this study, we conducted a comparative analysis of the transcriptomes of T. radiata exposed at 25 °C and 38 °C for 15 min. A total of 51,072 unigenes were obtained, 22,413 annotated with a mean length of 1054 bp. Differential expression analysis showed that 502 genes were identified, including 476 genes significantly up-regulated and 26 genes down-regulated after heat stress exposure. The Gene Ontology analysis showed that most enriched DEGs are categorized into "cellular process", "metabolic process" and "DNA binding." In addition, "Lysosome," "Longevity regulating pathway-multiple species," and "starch and sucrose metabolism" were highly enriched in Kyoto Encyclopedia of Genes and Genomes pathways. Transcriptome analyses showed that heat stress significantly induced the transcription of the molecular chaperone, immune response, stress signaling transduction, and oxidation resistance, including highly expressed heat shock proteins, ATPases, and detoxifying enzymes. Furthermore, the expression patterns of thirteen genes including heat shock proteins (HSP), glutathione S-transferase (GST) and cytochrome P450 were consistent with the transcriptome results obtained through qRT-PCR. Together, our results provided a comprehensive study of the molecular response of T. radiata to heat stress and provides new insight for the future functional validation of heat resistance-related genes.

Genome-Wide Identification and Characterization of Toll-like Receptors (TLRs) in Diaphorina citri and Their Expression Patterns Induced by the Endophyte Beauveria bassiana.

Toll-like receptors (TLRs) are pathogen recognition receptors (PRRs), which play key roles in helping the host immune system fight pathogen invasions. Systematic information on TLRs at the genome-wide level and expression profiling in response to endophytic colonization is very important to understand their functions but is currently lacking in this field. Here, a total of two TLR genes were identified and characterized in Diaphorina citri. The TLR genes of D. citri were clustered into five families according to the phylogenetic analysis of different species' TLRs. The domain organization analyses suggested that the TLRs were constituted of three important parts: a leucine-rich repeat (LRR) domain, a transmembrane region (TR) and a Toll/interleukin-1 receptor (TIR) domain. The mRNA expression levels of the two TLR genes (DcTOLL and DcTLR7) were highly regulated in both nymphs and adults of D. citri. These results elucidated the potentiated TLR gene expression in response to endophytically colonized plants. Furthermore, the 3D structures of the TIR domain were highly conserved during evolution. Collectively, these findings elucidate the crucial roles of TLRs in the immune response of D. citri to entomopathogens systematically established as endophytes, and provide fundamental knowledge for further understanding of the innate immunity of D. citri.

General Limitations to Endophytic Entomopathogenic Fungi Use as Plant Growth Promoters, Pests and Pathogens Biocontrol Agents.

The multiple roles of fungal entomopathogens in host plants' growth promotion, pest and pathogen management have drawn huge attention for investigation. Endophytic species are known to influence various activities of their associated host plants, and the endophyte-colonized plants have been demonstrated to gain huge benefits from these symbiotic associations. The potential application of fungal endophytes as alternative to inorganic fertilizers for crop improvement has often been proposed. Similarly, various strains of insect pathogenic fungi have been formulated for use as mycopesticides and have been suggested as long-term replacement for the synthetic pesticides that are commonly in use. The numerous concerns about the negative effects of synthetic chemical pesticides have also driven attention towards developing eco-friendly pest management techniques. However, several factors have been underlined to be militating the successful adoption of entomopathogenic fungi and fungal endophytes as plant promoting, pests and diseases control bio-agents. The difficulties in isolation and characterization of novel strains, negative effects of geographical location, vegetation type and human disturbance on fungal entomopathogens, are among the numerous setbacks that have been documented. Although, the latest advances in biotechnology and microbial studies have provided means of overcoming many of these problems. For instance, studies have suggested measures for mitigating the negative effects of biotic and abiotic stressors on entomopathogenic fungi in inundative application on the field, or when applied in the form of fungal endophytes. In spite of these efforts, more studies are needed to be done to achieve the goal of improving the overall effectiveness and increase in the level of acceptance of entomopathogenic fungi and their products as an integral part of the integrated pest management programs, as well as potential adoption as an alternative to inorganic fertilizers and pesticides.

Temperature-Dependent Biological Control Effectiveness of Tamarixia radiata (Hymenoptera: Eulophidea) Under Laboratory Conditions.

The parasitism rate and host-feeding rate of Tamarixia radiata (Hymenoptera: Eulophidae), an ectoparasitoid of Diaphorina citri (Hemiptera: Liviidae), were evaluated at 20, 27.5, 30, and 35°C, at 70 ± 5% RH, and 14 h of photoperiod. The biological control efficacy of T. radiata was evaluated by linking the age-stage predation rate with the two-sex life table. The net host-feeding rate (C0) by T. radiata was 32.05, 54.40, 17.25, and 1.92 nymphs per female parasitoid at 20, 27.5, 30, and 35°C, respectively. The total net nymphs killing rate (Z0) was 103.02, 223.82, 72.95, and 6.60 nymphs per female parasitoid at 20, 27.5, 30, and 35°C, respectively. Noneffective parasitism rate was observed at 35°C because of high mortality at this temperature. Our results indicated that temperature had meaningful effects on parasitism and host-feeding rate parameters in the laboratory, and may affect biological control efficiency of the parasitoid in the field. The highest host-feeding rate and total biological control efficiency of T. radiata were recorded at 27.5°C. Most importantly, we found that host-feeding activity of the parasitoid is temperature-dependent, and changed across temperature regimes: the host-feeding rate increased as the temperature increased up to 30°C, started to decrease after this temperature and declined to its minimum level at 35°C. This information is valuable for developing biological control and integrated pest management techniques for Asian citrus psyllid management.

Temperature-Dependent Demography and Population Projection of Tamarixia radiata (Hymenoptera: Eulophidea) reared on Diaphorina citri (Hemiptera: Liviidae).

Tamarixia radiata Waterson (Hymenoptera: Eulophidea) is the principal natural enemy used for the control of the major citrus pest Diaphorina citri Kuwayama (Hemiptera: Liviidae). In this study, we collected the life-history data of T. radiata at four different temperatures (20, 27.5, 30, and 35°C) and analyzed them by using the age-stage, two-sex life table. The longest preadult developmental time (16.53 d) was observed at 20°C, whereas the shortest one was 7.29 d at 35°C. The preadult development rate was well-fitted to a linear equation. The lower threshold temperature (T0) was 7.85°C and the thermal summation (K) was 193.36 degree-day. The highest fecundity (F) was 322.7 eggs per female was at 27.5°C, whereas the lowest one was 10.8 eggs per female at 35°C. The net reproductive rate (R0) were 70.97, 169.42, 55.70, and 3.25 offspring at 20, 27.5, 30, and 35°C, respectively; the intrinsic rate of increase (r) were 0.1401, 0.3167, 0.3517, and 0.1143 d-1, respectively. The highest values of fecundity, net reproductive rate, intrinsic rate of increase, and finite rate of increase were observed at 27.5°C. The relationships among F, R0, Nf, and N in all treatments were consistent with R0=F×(Nf/N). The age of peak reproductive value was close to the total preoviposition period in all treatments. Population projections based on the age-stage, two-sex life table showed the dynamics of stage structure and its variability. Faster population growth was observed at 27.5 and 30°C.

Effects of Seedling Age on Colonization Patterns of Citrus limon Plants by Endophytic Beauveria bassiana and Metarhizium anisopliae and Their Influence on Seedlings Growth.

The inoculation methods, the fungal strains, and several other factors are known to influent the success of fungal entomopathogens colonization in plants. The physiological status of the plant could also be another determinant. In the present study, the ability of three strains of Beauveria bassiana and one strain of Metarhizium anisopliae to successfully colonize Citrus limon plants and the influence of seedling age on endophytic colonization success was examined. Three, 4, and 6 months old seedlings were inoculated with 10 mL of 1 × 108 conidial·mL-1 suspensions of each of the four fungal strains via foliar spraying. All fungal strains successfully colonized citrus seedlings and were sustained up to 2 months in colonized plants irrespective of the seedling age, with differences in the mean percentage colonization recorded at various post-inoculation periods among the fungal strains. The highest percent endophytic fungi recovery rate was recorded in the 3 months old seedlings, where fungal mycelia of inoculated fungi were successfully re-isolated from 65.6% of the untreated newly developed leaf and stem tissues. One strain of B. bassiana, BB Fafu-12, significantly improved seedling height and leaf number. The study demonstrates the influence of seedling age on B. bassiana and M. anisopliae successful colonization in the citrus plant.

Endophytic Beauveria bassiana in Foliar-Treated Citrus limon Plants Acting as a Growth Suppressor to Three Successive Generations of Diaphorina citri Kuwayama (Hemiptera: Liviidae).

Entomopathogenic fungi are commonly applied as inundative sprays to protect plants against insect pests. Their artificial establishment as fungal endophytes to provide other benefits to the host plants aside mere protection against the primary pests has also been widely demonstrated. In the present study, two fungal strains of Beauveria bassiana and one strain of Isaria fumosorosea were assessed in a pathogenicity test against adults of Asian citrus psyllid (Diaphorina citri) and found to induce 50% reduction in the survival rate of D. citri adults within 5 days of exposure. The ability of the three fungal strains to endophytically colonize Citrus limon, the impact on plant growth and the effects of systemic colonization on 3 successive generations of D. citri feeding on colonized plants was evaluated. Citrus seedlings at 4 months post-planting were inoculated with each of the fungal strains via foliar spraying. Both strains of B. bassiana successfully colonized the seedlings. One of the B. bassiana strains (BB Fafu-13) was sustained up to 12 weeks in the colonized seedlings, whereas the other B. bassiana strain (BB Fafu-16) was only recovered up to 8 weeks post-inoculation. Isaria fumosorosea (IF Fafu-1) failed to colonize the plant. Both strains of B. bassiana induced significant improvement in plant height and flush production in endophytically colonized seedlings. In addition, endophytic B. bassiana caused 10-15% D. citri adult mortality within 7 days of exposure. Female D. citri feeding on B. bassiana challenged plants laid fewer eggs as compared to those feeding on endophyte-free seedlings, while reduction in adult emergence was recorded on B. bassiana treated plants. With this study, we present the first evidence of B. bassiana artificial establishment as fungal endophyte in citrus plants and its negative effects on D. citri.