Assessing silvopasture management as a strategy to reduce fuel loads and mitigate wildfire risk

Managing private forests for wildfire resilience is challenging due to conflicting social, economic, and ecological decisions that may result in an increase of surface fuel loads leading to greater fire risk. Due to fire suppression and a changing climate, land managers in fire-prone regions face an increasing threat of high severity fires. Thus, land managers need fuel treatment options that match their forest types and management objectives. One potential option for producers that graze livestock is silvopasture management, where livestock, forages, and overstory vegetation are carefully managed for co-benefits on the same unit of land. This study compared forest composition and structure, fuel types, and vegetative biomass between silvopasture and non-grazed managed forests in Washington, U.S. We show that silvopasture management results in reductions in grass biomass, litter, and duff depth when compared to non-grazed managed forest. These findings point to the integrated nature of silvopasture, where management of overstory composition and structure, understory vegetation, and grazing can reduce fuel loads and potential wildfire risk.

Effect of soil amendments on antioxidant activity and photosynthetic pigments in pea crops grown in arsenic contaminated soil

The mechanism of arsenic (As) immobilization in soils is crucial for improving photosynthetic pigments and antioxidants in food crops. The effects of soil amendments with arbuscular mycorrhizal fungi (AMF), biochar (BC), selenium (Se), sulfur (S) and Si-gel on the concentrations of chlorophyll, carotenoid, proline, malondialdehyde (MDA), and the activity of ascorbate peroxidase (APX), guaiacol peroxidase (POD), and catalase (CAT) were studied in BARI pea (Pisum sativum) under As stress. Soil amendments with AMF, Se, Si-gel and S enhanced chlorophyll a and total chlorophyll contents by 31–35% and 60–75%, respectively. Likewise, CAT activity was increased by 24–46% in BC, AMF, Se, Si-gel and S-treated pea, respectively. APX and POD activity was also found to be enriched with the treatment of BC, AMF and Se. In contrast, the content of MDA and proline was found lower than that of control in peas. These findings indicate that oxidative damage, osmotic stress and cell injury were possibly reduced in As-stressed peas. Particularly, AMF and Se both were comparatively more potential in comparison to BC. Thus, soil amendments with AMF, BC and Se are significantly important for improving antioxidant enzyme activity of food crops grown in soil with elevated As levels.

Arbuscular mycorrhizal fungi reduce arsenic uptake and improve plant growth in Lens culinaris

Arsenic (As) is a carcinogenic and hazardous substance that poses a serious risk to human health due to its transport into the food chain. The present research is focused on the As transport in different lentil genotypes and the role of Arbuscular Mycorrhizal Fungi (AMF) in mitigation of As phyto-toxicity. Arsenic transport from soil to root, shoot and grains in different lentil genotypes was analyzed by flow injection hydride generation atomic absorption spectrophotometry. AMF were applied for the reduction of As uptake as well as the improvement of plant growth in lentil genotypes. Arsenic phyto-toxicity was dose-dependent as evidenced by relatively higher shoot length, fresh and dry weight of root and shoot in 5 and 15 mgkg-1 As-treated lentil plants than that in 100 mgkg-1 As-treated lentil. Arsenic accumulation occurred in roots and shoots of all BARI-released lentil genotypes. Arsenic accumulation in grains was found higher in BARI Mashur 1 than other lentil genotypes. AMF treatment significantly increased growth and biomass accumulation in lentil compared to that in non-AMF plants. Furthermore, AMF effectively reduced the As concentrations in roots and shoots of lentil plants grown at 8 and 45 mgkg-1 As-contaminated soils. This study revealed remarkable divergence in As accumulation among different BARI-released lentil genotypes; however, AMF could reduce As uptake and mitigate As-induced phyto-toxicity in lentil. Taken together, our results suggest a great potential of AMF in mitigating As transfer in root and shoot mass and reallocation to grains, which would expand lentil cultivation in As-affected areas throughout the world.

Effect of Arbuscular Mycorrhizal Fungi, Selenium and Biochar on Photosynthetic Pigments and Antioxidant Enzyme Activity Under Arsenic Stress in Mung Bean (Vigna radiata)

Environmental perturbations alter biochemical compounds in food crops. Arsenic (As), a toxic metalloid, is known to affect the cultivation of food crops in many regions of the world; however, the changes in chlorophyll, catalase (CAT), and proline in response to As stress and the role of stress relief substances remain largely unknown in mung bean (Vigna radiate L.). In this study, biochar (BC), arbuscular mycorrhizal fungi (AMF), and selenium (Se) were applied to soils as stress relief substances (under 30 mg kg-1 As stress), and the effects of BC, AMF, and Se on chlorophyll a, chlorophyll b, total chlorophyll, CAT activity, and proline content were studied in different mung bean genotypes. Under As stress, the chlorophyll a, chlorophyll b, and total chlorophyll contents in BARI mung 3, BARI mung 5, and BARI mung 8 were found statistically similar. Meanwhile, CAT activity increased in comparison to the control due to the application of BC, AMF, and Se in mung bean crops. However, proline was found significantly lower in AMF, BC, and Se-treated mung bean. This indicates that oxidative stress was potentially minimized in As-stressed mung bean crops due to the application of these stress relief substances. Notably, AMF was relatively effective against As stress in comparison to BC and Se. It is concluded that BC, AMF, and Se are all highly effective in enhancing antioxidant defenses as well as the nutritional quality of mung bean crops under As stress.

Bacteria and Competing Herbivores Weaken Top-Down and Bottom-Up Aphid Suppression

Herbivore suppression is mediated by both plant defenses and predators. In turn, plant defenses are impacted by soil fertility and interactions with soil bacteria. Measuring the relative importance of nutritional and microbial drivers of herbivore resistance has proven problematic, in part because it is difficult to manipulate soil-bacterial community composition. Here, we exploit variation in soil fertility and microbial biodiversity across 20 farms to untangle suppression of aphids (Brevicoryne brassicae) through bottom-up and top-down channels. We planted Brassica oleracea plants in soil from each farm, manipulated single and dual infestations of aphids alone or with caterpillars (Pieris rapae), and exposed aphids to parasitoid wasps (Diaeretiella rapae) in the open field. We then used multi-model inference to identify the strongest soil-based predictors of herbivore growth and parasitism. We found that densities of Bacillus spp., a genus known to include plant-growth-promoting rhizobacteria, negatively correlated with aphid suppression by specialist parasitoids. Aphid parasitism also was disrupted on plants that had caterpillar damage, compared to plants attacked only by aphids. Relative abundance of Pseudomonas spp. bacteria correlated with higher aphid growth, although this appeared to be a direct effect, as aphid parasitism was not associated with this group of bacteria. Non-pathogenic soil bacteria are often shown to deliver benefits to plants, improving plant nutrition and the deployment of anti-herbivore defenses. However, our results suggest that these plant growth-promoting bacteria may also indirectly weaken top-down aphid suppression by parasitoids and directly improve aphid performance. Against a background of varying soil fertility, microbial biodiversity, competing herbivores, and natural enemies, we found that effects of non-pathogenic soil microbes on aphid growth outweighed those of nutritional factors. Therefore, predictions about the strength of plant defenses along resource gradients must be expanded to include microbial associates.

Nitrogen Fixation by US and Middle Eastern Chickpeas with Commercial and Wild Middle Eastern Inocula

Chickpeas (Cicer arietinum L.) are native to the Middle East (ME) and must be inoculated with symbiotic bacteria (Mesorhizobium ciceri) to fix nitrogen (N) in North American soils. Whether commercial M. ciceri strains are more or less effective than wild strains from ME soils when paired with various chickpea hosts must be elucidated. Wild N-fixing bacterial strains were isolated from ME soils, and their effectiveness was compared against commercial strains on US and ME chickpea varieties. Chickpeas were inoculated with individual strains and grown in chambers for 8 weeks. Plants received 2 mM (15NH4)2 SO4 (5% atom excess) to measure N fixation by isotope dilution. Plant below- and above-ground biomass and proportion of N fixed (PNF) were determined. Commercial and wild ME strains were examined for genetic diversity by sequencing their 16 S rDNA region. The PNF was significantly influenced by inoculant strains and chickpea varieties. Among varieties, Sierra, Troy, and Almaz had the highest PNF of 86.7%, 85.3%, and 85.2%, respectively. Among strains, Jord-M1 contributed to greater PNF (84.7%) compared to Syr-M1 (81.4%). Overall, chickpea varieties had greater effect on PNF than strain selection. These findings support efforts focusing on varietal breeding and strain selection to increase agricultural N fixation.

Influence of biodynamic preparations on compost development and resultant compost extracts on wheat seedling growth

Biodynamic (BD) agriculture, a form of organic agriculture, includes the use of specially fermented preparations, but peer-reviewed studies on their efficacy are rare. Composting of a grape pomace and manure mixture was studied in two years (2002 and 2005) with and without the BD compost preparations. Water extracts of finished composts were then used to fertigate wheat seedlings, with and without added inorganic fertilizer. BD-treated mixtures had significantly greater dehydrogenase activity than did untreated (control) mixtures during composting, suggesting greater microbial activity in BD-treated compost. In both years there was a distinct compost effect on wheat shoot and root biomass irrespective of supplemental fertilizer. Shoot biomass was highest in all treatments receiving 1% compost extract. Wheat seedlings that received 1% compost extract in 2005 grew similar root and shoot biomass as fertilized seedlings, despite only containing 30% as much nitrogen as the fertilizer treatment. In both years seedlings that received fertilizer plus 1% compost extract produced 22-61% more shoot biomass and 40-66% more root biomass than seedlings that received fertilizer alone, even at higher rates. In 2002 a 1% extract of BD compost grew 7% taller wheat seedlings than did 1% extract of untreated compost. At 0.1% only BD extract grew taller plants than water, but in 2002 only. No effect on shoot or root biomass was seen at 0.1%. Our results support the use of compost extracts as fertilizer substitutes or supplements, testimonial reports on the growth promoting effects of compost extracts, and the occasional superiority of BD compost to untreated compost.

Citrus Black Rot is Caused by Phylogenetically Distinct Lineages of Alternaria alternata

ABSTRACT Phylogenetic analysis revealed that isolates of Alternaria alternata causing black rot of citrus were associated with six well-supported evolutionary lineages. Isolates recovered from brown spot lesions on Minneola tangelo, leaf spot lesions on rough lemon, and healthy citrus tissue and noncitrus hosts were related closely to isolates from black-rotted fruit. Phylogenies estimated independently from DNA sequence data from an endopolygalacturonase gene (endoPG) and two anonymous regions of the genome (OPA1-3 and OPA2-1) had similar topologies, and phylogenetic analysis was performed on the combined data set. In the combined phylogeny, isolates from diverse ecological niches on citrus and noncitrus hosts were distributed in eight clades. Isolates from all lineages, regardless of ecological or host association, caused black rot in fruit inoculation assays, demonstrating that small-spored Alternaria isolates associated with different ecological niches on citrus and other plant hosts are potential black rot pathogens. These data also indicated that the fungi associated with black-rotted fruit do not form a natural evolutionary group distinct from other Alternaria pathogens and saprophytes associated with citrus. The use of the name A. citri to describe fungi associated with citrus black rot is not justified and it is proposed that citrus black rot fungi be referred to as A. alternata.

Molecular systematics of citrus-associated Alternaria species

The causal agents of Alternaria brown spot of tangerines and tangerine hybrids, Alternaria leaf spot of rough lemon and Alternaria black rot of citrus historically have been referred to as Alternaria citri or A. alternata. Ten species of Alternaria recently were described among a set of isolates from leaf lesions on rough lemon (Citrus jambhiri) and tangelo (C. paradisi × C. reticulata), and none of these isolates was considered representative of A. alternata or A. citri. To test the hypothesis that these newly described morphological species are congruent with phylogenetic species, selected Alternaria brown spot and leaf spot isolates, citrus black rot isolates (post-harvest pathogens), isolates associated with healthy citrus tissue and reference species of Alternaria from noncitrus hosts were scored for sequence variation at five genomic regions and used to estimate phylogenies. These data included 432 bp from the 5' end of the mitochondrial ribosomal large subunit (mtLSU), 365 bp from the 5' end of the beta-tubulin gene, 464 bp of an endopolygalacturonase gene (endoPG) and 559 and 571 bp, respectively, of two anonymous genomic regions (OPA1-3 and OPA2-1). The mtLSU and beta-tubulin phylogenies clearly differentiated A. limicola, a large-spored species causing leaf spot of Mexican lime, from the small-spored isolates associated with citrus but were insufficiently variable to resolve evolutionary relationships among the small-spored isolates from citrus and other hosts. Sequence analysis of translation elongation factor alpha, calmodulin, actin, chitin synthase and 1, 3, 8-trihydroxynaphthalene reductase genes similarly failed to uncover significant variation among the small-spored isolates. Phylogenies estimated independently from endoPG, OPA1-3 and OPA2-1 data were congruent, and analysis of the combined data from these regions revealed nine clades, eight of which contained small-spored, citrus-associated isolates. Lineages inferred from analysis of the combined dataset were in general agreement with described morphospecies, however, three clades contained more than one morphological species and one morphospecies (A. citrimacularis) was polyphyletic. Citrus black rot isolates also were found to be members of more than a single lineage. The number of morphospecies associated with citrus exceeded that which could be supported under a phylogenetic species concept, and isolates in only five of nine phylogenetic lineages consistently were correlated with a specific host, disease or ecological niche on citrus. We advocate collapsing all small-spored, citrus-associated isolates of Alternaria into a single phylogenetic species, A. alternata.

Use of phospholipid fatty acids and carbon source utilization patterns To track microbial community succession in developing compost

Carbon source utilization and phospholipid fatty acid analyses were used to track the rapidly changing microbial community in composting dairy waste. Microbial abilities to utilize common plant sugars increased during composting. Community phospholipid profiles changed significantly over time. Phospholipids suggested the presence of more thermophiles and fewer bacteria with continued compost development.