Agricultural Crop Species Research Articles

Host Range Characterization of Phytophthora sansomeana Across Corn, Soybean, Wheat, Winter Cereal Rye, Dry Bean, and Oats and an In Vitro Assessment of Seed Treatment Sensitivity.

Formally described in 2009, Phytophthora sansomeana is a pathogen of increasing interest in native, agricultural, and horticulturally important plant species. The objective of this study was to elucidate the symptomatic and asymptomatic host range of P. sansomeana on six agricultural crop species commonly used in field crop rotations in Michigan. In addition, sensitivity to oomicides commonly used in seed treatments, including oxathiapiprolin, mefenoxam, ethaboxam, and pyraclostrobin, was performed to aid in disease management recommendations. Plant biomass, quantity of P. sansomeana DNA in roots, and reisolations were used to assess pathogenicity and virulence of 18 isolates of P. sansomeana on each plant species using an inoculated seedling growth chamber assay. Isolates displayed varying levels of virulence to the hosts tested. Reisolations were completed for each plant species tested, and varying quantities of P. sansomeana DNA were found within all plant species root samples. Corn, wheat, soybean, dry bean, and winter cereal rye plants were symptomatic hosts with significant reduction observed in the total plant biomass. No significant reduction in total plant biomass was observed in oats, and oat roots harbored the least amount of P. sansomeana DNA. No P. sansomeana isolates were insensitive to the oomicide compounds tested with mean absolute inhibition (EC50) values of fungicide required for 50% growth inhibition values of 7.8 × 10-2 μg/ml for mefenoxam, 1.13 × 10-1 μg/ml for ethaboxam, 2.6 × 10-2 μg/ml for oxathiapiprolin, and 3.04 × 10-1 μg/ml for pyraclostrobin. These results suggest that common crop rotations in Michigan may not be a viable option to reduce soilborne inoculum accumulation and oomicide seed treatments could be considered for early-season management of P. sansomeana.

Suberin deficiency and its effect on the transport physiology of young poplar roots.

The precise functions of suberized apoplastic barriers in root water and nutrient transport physiology have not fully been elucidated. While lots of research has been performed with mutants of Arabidopsis, little to no data are available for mutants of agricultural crop or tree species. By employing a combined set of physiological, histochemical, analytical, and transport physiological methods as well as RNA-sequencing, this study investigated the implications of remarkable CRISPR/Cas9-induced suberization defects in young roots of the economically important gray poplar. While barely affecting overall plant development, contrary to literature-based expectations significant root suberin reductions of up to 80-95% in four independent mutants were shown to not evidently affect the root hydraulic conductivity during non-stress conditions. In addition, subliminal iron deficiency symptoms and increased translocation of a photosynthesis inhibitor as well as NaCl highlight the involvement of suberin in nutrient transport physiology. The multifaceted nature of the root hydraulic conductivity does not allow drawing simplified conclusions such as that the suberin amount must always be correlated with the water transport properties of roots. However, the decreased masking of plasma membrane surface area could facilitate the uptake but also leakage of beneficial and harmful solutes.

The genetic and physiological basis of Arabidopsis thaliana tolerance to Pseudomonas viridiflava.

The opportunistic pathogen Pseudomonas viridiflava colonizes > 50 agricultural crop species and is the most common Pseudomonas in the phyllosphere of European Arabidopsis thaliana populations. Belonging to the P. syringae complex, it is genetically and phenotypically distinct from well-characterized P. syringae sensu stricto. Despite its prevalence, we lack knowledge of how A. thaliana responds to its native isolates at the molecular level. Here, we characterize the host response in an A. thaliana - P. viridiflava pathosystem. We measured host and pathogen growth in axenic infections and used immune mutants, transcriptomics, and metabolomics to determine defense pathways influencing susceptibility to P. viridiflava infection. Infection with P. viridiflava increased jasmonic acid (JA) levels and the expression of ethylene defense pathway marker genes. The immune response in a susceptible host accession was delayed compared with a tolerant one. Mechanical injury rescued susceptibility, consistent with an involvement of JA. The JA/ethylene pathway is important for suppression of P. viridiflava, yet suppression capacity varies between accessions. Our results shed light on how A. thaliana can suppress the ever-present P. viridiflava, but further studies are needed to understand how P. viridiflava evades this suppression to spread broadly across A. thaliana populations.

Plant and pathogen genomics: essential approaches for stem rust resistance gene stacks in wheat.

The deployment of disease resistance genes is currently the most economical and environmentally sustainable method of crop protection. However, disease resistance genes can rapidly break down because of constant pathogen evolution, particularly when they are deployed singularly. Polygenic resistance is, therefore, considered the most durable, but combining and maintaining these genes by breeding is a laborious process as effective genes are usually unlinked. The deployment of polygenic resistance with single-locus inheritance is a promising innovation that overcomes these difficulties while enhancing resistance durability. Because of major advances in genomic technologies, increasing numbers of plant resistance genes have been cloned, enabling the development of resistance transgene stacks (RTGSs) that encode multiple genes all located at a single genetic locus. Gene stacks encoding five stem rust resistance genes have now been developed in transgenic wheat and offer both breeding simplicity and potential resistance durability. The development of similar genomic resources in phytopathogens has advanced effector gene isolation and, in some instances, enabled functional validation of individual resistance genes in RTGS. Here, the wheat stem rust pathosystem is used as an illustrative example of how host and pathogen genomic advances have been instrumental in the development of RTGS, which is a strategy applicable to many other agricultural crop species.

Global genomic signature reveals the evolution of fall armyworm in the Eastern hemisphere.

The major plant pest fall armyworm (FAW), Spodoptera frugiperda, is native to the Americas and has colonized Africa and Asia within the Eastern hemisphere since 2016, causing severe damage to multiple agricultural crop species. However, the genetic origin of these invasive populations requires more in-depth exploration. We analysed genetic variation across the genomes of 280 FAW individuals from both the Eastern hemisphere and the Americas. The global range-wide genetic structure of FAW shows that the FAW in America has experienced deep differentiation, largely consistent with the Z-chromosomal Tpi haplotypes commonly used to differentiate 'corn-strain' and 'rice-strain' populations. The invasive populations from Africa and Asia are different from the American ones and have a relatively homogeneous population structure, consistent with the common origin and recent spreading from Africa to Asia. Our analyses suggest that north- and central American 'corn-strain' FAW are the most likely sources of the invasion into the Eastern hemisphere. Furthermore, evidence based on genomic, transcriptomic and mitochondrial haplotype network analyses indicates an earlier, independent introduction of FAW into Africa, with subsequent migration into the recent invasive population.

Cytochrome P450 Gene Families: Role in Plant Secondary Metabolites Production and Plant Defense.

Cytochrome P450s (CYPs) are the most prominent family of enzymes involved in NADPH- and O2-dependent hydroxylation processes throughout all spheres of life. CYPs are crucial for the detoxification of xenobiotics in plants, insects, and other organisms. In addition to performing this function, CYPs serve as flexible catalysts and are essential for producing secondary metabolites, antioxidants, and phytohormones in higher plants. Numerous biotic and abiotic stresses frequently affect the growth and development of plants. They cause a dramatic decrease in crop yield and a deterioration in crop quality. Plants protect themselves against these stresses through different mechanisms, which are accomplished by the active participation of CYPs in several biosynthetic and detoxifying pathways. There are immense potentialities for using CYPs as a candidate for developing agricultural crop species resistant to biotic and abiotic stressors. This review provides an overview of the plant CYP families and their functions to plant secondary metabolite production and defense against different biotic and abiotic stresses.

GEOGRAPHIC INFORMATION SYSTEMS FOR AGRICULTURAL SUITABLE LAND AT KABUPATEN SLEMAN

Indonesia is an agricultural country, the growth rate of various food and crops tends to be stable. However, some plants in certain areas are different from what is expected. This study aims to investigate land suitability for crops such as rice, analysis of development potential, and develop recommendations for land use for agricultural types, Sleman Regency, Special Region of Yogyakarta. Landsat 8 imagery is used for land use extraction as input for making land use directions for agricultural and forestry plant species. The method used in this study is a combination of analysis of Landsat 8 imagery and field data processed using a Geographic Information System in making thematic maps of the physical characteristics of the land to obtain land suitability maps for agricultural crop species and with a weighting method in stages based on the physical parameters of the conditions for growing crops. The analysis results are used to formulate land use directions for the types of crops in Sleman Regency. An area very ideal for the type of rice plant and land planted. For crops, it is directed based on the room's function, namely in the cultivation area. Sites that have the potential to be developed for crops are produced and set in buffer zones because more emphasis is placed on conservation aspects and increasing crop productivity. This geographic information system is one of the recommendations to be used as a reference by farmers in increasing the productivity of agricultural land.

Influence of Soil Salinity on Selected Element Contents in Different Brassica Species.

Climate changes in coastal regions cause increased soil salinity, a well-known type of environmental stress for a high number of agricultural crop species, including Brassicaceae, whose growth and development, and consequently the crop quality and yield, are affected by salinity stress. The aim of the present study is to investigate the effect of salt stress on micro- and macro-element homeostasis in different Brassica crops. Kale (Brassica oleracea var. acephala), white cabbage (B. oleracea var. capitata) and Chinese cabbage (B. rapa ssp. pekinensis) were grown hydroponically and treated with 200 mmol/L sodium chloride for 24 h to mimic short-term salt stress. The contents of Al, Ca, K, Mg, Na, B, Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sr, V and Zn were determined in the roots and leaves of the salt-treated plants and corresponding controls by inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry. While Al, Ca, K, Mg and Na were determined in the mg/g range, the contents of the other elements were found at the µg/g level. A statistical analysis of the obtained data showed that the applied salt treatment significantly influenced the single-element contents in different plant parts. The major elements Ca, K and Mg were mainly unaffected in the more-salt-tolerant kale and white cabbage under salinity stress, while K and Mg were significantly decreased in the more-sensitive Chinese cabbage. The levels of micro-elements were found to be species/variety specific. In general, potentially toxic elements were accumulated in the roots of salt-treated plants to a higher extent than in the corresponding controls.

The polyphagous shot hole borer beetle: Current status of a perfect invader in South Africa

The polyphagous shot hole borer (PSHB) beetle is a recent invader in South Africa. Together with its fungal symbiont, Fusarium euwallaceae, it can rapidly kill highly susceptible host plants. Its impact is most profound in urban areas, but it has also been found infesting important forestry, agricultural crop and native species. Since its first detection in 2012, PSHB has spread to all but one province in the country. The beetle–fungus complex has several biological traits that enhance its anthropogenically mediated dispersal, establishment and survival in novel environments – factors that have likely facilitated its rapid spread across the country. We review the history of the PSHB invasion in South Africa, its taxonomic status and the reasons for its rapid spread. We highlight its potential impact and challenges for its management. Finally, we provide an updated distribution map and list of confirmed host plants in South Africa. Of the 130 plant species identified as hosts, 48 of these (19 indigenous and 29 introduced) are reproductive hosts able to maintain breeding PSHB populations. These reproductive hosts may succumb to beetle infestations and act as ‘pest-amplifiers’. The economic impact on urban forests, plantation forestry and agricultural crops may be severe, but the ecological impact of PSHB invasion in native ecosystems should not be underestimated.Significance: We provide an updated host list and distribution map for South Africa of the globally significant tree pest, the polyphagous shot hole borer (PSHB, Euwallacea fornicatus). The South African PSHB invasion represents the largest outbreak of this pest in its global invaded range. PSHB was confirmed to infest 130 plant species in urban, agricultural, and native ecosystems in South Africa, including 44 previously unreported hosts. Impact in South Africa is in its infancy but will likely be substantial to local economies and ecosystems. Mitigation has proven difficult, but numerous research projects have been initiated throughout the country.

Fall acclimation and spring deacclimation of root cold tolerance for two perennial asters1

Snow is an important temperature insulator for overwintering plants, and as the depth and duration of snowpack decreases with warmer weather and the frequency of extreme climate events increases, belowground tissues may be exposed to colder temperatures. Determining the cold tolerance of overwintering plant tissues for native species could help predict species persistence following winter climate change, yet most plant cold tolerance studies are about agricultural crop species, woody plants, or aboveground tissues. Also, plants can acclimate and deacclimate to winter so measuring cold tolerance across seasons provides a more accurate assessment of a species susceptibility to winter climate change. Here, we measure root cold tolerance of two native perennial grassland forbs (Solidago rigida and Silphium integrifolium) in a restored prairie across time to examine cold acclimation and deacclimation to seasonal temperature changes. Average root cold tolerance varied between the two species. Over time, the roots of S. rigida predictably gained cold tolerance as fall progressed and lost cold tolerance in spring. However, roots of S. integrifolium had variable cold tolerance across both seasons. The differences in cold tolerance development between grassland forb species may be a contributing factor explaining species persistence under continued winter climate change. Further research on the cold tolerance of native plant species and belowground tissues is needed to predict the response of temperate plant species and communities to winter climate change.

Growth-Promoting Potential of Rhizobacteria Isolated From Sugarcane

The search for plant growth-promoting rhizobacteria (PGPRs) addresses the ongoing need for new bioinoculants to be used on various agricultural crop species, including sugarcane. Bacterial strains were isolated from the rhizosphere of sugarcane plants and identified by sequencing the 16S ribosomal gene. The main indole acetic acid producers wereEnterobactersp. IP11,Enterobactersp. IP14, andE. asburiaeIP24.Achromobacter spaniusIP23 presented the highest levels of cellulolytic activity and potassium solubilization.Bacillus thuringiensisIP21 andStaphylococcus saprophyticusIJ8 showed the highest levels of fixed nitrogen. The levels of calcium phosphate and aluminum phosphate inB. thuringiensisIP21 were notable, as this strain solubilized 481.00 and 39.33 mg of phosphorus mL−1, respectively; however, for Araxá apatite, the results forB. anthracisIP17 were notable (622.99 mg phosphorus mL−1), while for iron phosphate solubilization,Enterobactersp. IP14, which solubilized 105.66 mg phosphorus mL−1was notable. TheB. thuringiensisIP21 andEnterobactersp. IP11 isolates promoted the growth of the tallest sugarcane plants, inducing increases of 14.1 and 10.4% relative to the control plants, respectively. For shoot dry matter, root dry matter, and total dry matter, plants inoculated withEnterobactersp. IP14,B. anthracisIP17, andA. spaniusIP23 presented higher values than the controls. Furthermore, plants inoculated withB. thuringiensisIP21 presented higher root dry matter and total dry matter values, and those inoculated withEnterobactersp. IP14 also presented higher total dry matter values. These results indicate that bacteria with the potential for use as future inoculants should be investigated since bacteria with plant growth-related characteristics may not impact growth promotion.

Carbon Nanotubes Improved the Germination and Vigor of Plant Species from Peatland Ecosystem Via Remodeling the Membrane Lipidome.

Application of the nanopriming technique to alleviate seed dormancy has shown promising results in various agricultural crop species. However, there is a dearth of knowledge regarding its potential use in native peatland boreal forest species to alleviate seed dormancy and improve their propagation or vigor for forest reclamation activities. Herein, we demonstrate the use of nanopriming with carbon nanotubes (CNT) to alleviate seed dormancy, improved seed germination, and seedling vigor in two boreal peatland species. Bog birch (Betula pumila L.) and Labrador tea (Rhododendron groenlandicum L.) seeds with embryo or seed coat dormancy were nanoprimed with either 20 or 40 µg/mL CNT, cold stratified at 2–4 °C for 15 days, and allowed to germinate at room temperature. The emerged seedlings’ lipidome was assessed to decipher the role of lipid metabolism in alleviating seed dormancy. We observed significant (p < 0.05) improvement in seedling germination and seedling vigor in seeds primed with multiwalled carbon nanotubes functionalized with carboxylic acids. Phosphatidylcholine (PC 18:1/18:3), phosphatidylglycerol (PG 16:1/18:3), and lysophosphatidylcholine (LPC 18:3) molecular species (C18:3 enriched) were observed to be highly correlated with the increased seed germination percentages and the enhanced seedling vigor. Mechanistically, it appears that carbon nanoprimed seeds following stratification are effective in mediating seed dormancy by remodeling the seed membrane lipids (C18:3 enriched PC, PG, and LPC) in both peatland boreal forest species. The study results demonstrate that nanopriming may provide a solution to resolve seed dormancy issues by enhancing seed germination, propagation, and seedling vigor in non-resource boreal forest species ideally suited for forest reclamation following anthropogenic disturbances.

ANALYSIS OF THE PROFITABILITY OF GROWING HERBS AND THE MOST COMMONLY CULTIVATED AGRICULTURAL CROP SPECIES

Background. The aim of this study was to determine the profitability index of herbs (evening primrose, glandular plantain, black caraway, garden dill) and to compare it with the index of dominant species in the cropping system in Poland.Material and methods. Economic analyzes were carried out based on accounting books made available by the owners of two farms located in the Koronowo Gmina (community) of the Kuyavian-Pomeranian Voivodeship and on data provided by the Kuyavian-Pomeranian Agricultural Advisory Centre. The calculations concern the years 2017–2019 and took into account production value, the amount of gross margin, net agricultural income and profitability index.Results. The calculations carried out confirmed the hypothesis that in most cases growing herbs in the field is more profitable than it is for other plant species. The analysis showed that glandular plantain and garden dill had the highest profitability indices. Herbs from which lower financial results were obtained still enabled an income similar to that from sugar beet, pea or winter oilseed rape. The most profitable among the other species was table potato. A farmer's decision regarding the choice of plants for cultivation on a farm should depend on the possibility of selling the produced raw materials on local markets and on their base of machinery and equipment. The study has shown that growing plants from groups that occupy the largest acreage in the cropping structure is characterized by the need to incur very high overheads.Conclusion. Some selected herbs are characterized by a large profitability index that is even several times higher when compared to commonly cultivated agricultural crop species. While other analyzed herb species allow for an income that is at a similar level compared to crops that occupy the largest acreage in Poland. The selection of herbs for cultivation is an economic opportunity, especially for farms with a small area. Their cultivation enables larger agricultural incomes due to their relatively low overhead costs compared to other species. Herb cultivation, however, is a very specific branch of agriculture that requires more human labour.

Contrasting adaptation of xylem to dehydration in two Vitis vinifera L. sub-species

Xylem hydraulic properties of agricultural crop species can be linked to their region of origin, but because crop systems are often irrigated to reach optimum quality and yield, key differences in drought resistance are not often considered. We investigated how hydraulic conductivity and xylem vulnerability to drought-induced cavitation of two grapevine cultivars correspond to their centers of domestication with 'Merlot' (Vitis vinifera subspecies occidentalis) having been domesticated in a temperate forest region, and 'Thompson Seedless' (Vitis vinifera subspecies orientalis) domesticated in a semi-arid region. We used anatomical measurements and xylem vulnerability curves to evaluate hydraulic traits and drought resistance. Our results showed that 'Thompson Seedless' was significantly more vulnerable to drought-induced cavitation than 'Merlot'. Bench dehydration produced significantly different estimations of xylem vulnerability to cavitation in each cultivar. This result was consistent with anatomical measurement, with 'Thompson Seedless' stems having greater maximum stem-specific hydraulic conductivity, more vessels, higher vessel density and a greater lumen fraction than 'Merlot'. The relatively large amount of xylem vessels and lumen area in 'Thompson Seedless' is consistent with domestication in a semi-arid habitat where a greater number and size diversity of xylem vessels would be needed to transport water and meet evaporative demand as opposed to cultivars that were domesticated in temperate forest regions like 'Merlot'. These differences appear to expose 'Thompson Seedless' to high xylem vulnerability to cavitation.

Histochemical and Molecular Quantification of Arbuscular Mycorrhiza Symbiosis.

Arbuscular mycorrhizae (AM) are one of the most widespread and studied plant associations with beneficial microorganisms. Indeed, more than 80% of land plants, including most agricultural and horticultural crop species, are able to establish this mutualistic symbiosis with AM fungi. Through this association the fungus helps the plant in the acquisition of water and mineral nutrients, especially under stress conditions. AM symbiosis affects other ecologically and economically important traits such as plant architecture, flowering, and fruit quality but also tolerance against biotic and abiotic stresses. As a consequence, AM fungi have a great potential as biofertilizers and bioprotection agents in sustainable agriculture. However, in order to take advantage of all these benefits, a good and functional symbiosis is required. Here we present methods for reliable quantification of colonization levels which should be useful not only for research but also from the agronomic point of view.

A simple and efficient method to extract polar metabolites from guar leaves (Cyamopsis tetragonoloba (L.) Taub.) for GC-MS metabolome analysis

Guar (Cyamopsis tetragonoloba (L.) Taub.) is an agricultural crop species new to Russia and is in demand by the gas, oil and food industries. Due to the progress of “omics” technologies and the marker-assisted selection, there is a huge interest in the studies that compare the metabolites of various guar varieties, employing metabolomics as a method of functional genomics. For a large-scale screening of guar germplasm from the VIR collection, it is important to choose an efficient method to extract metabolites from samples. The accuracy of the assessment of the content of metabolites in samples is crucial for distinguishing varieties within the crop, since the metabolome profiles of plants within the same species differ mainly in the quantitative ratio of metabolites, and not in their qualitative composition. In metabolome practice, two methods of extracting polar compounds are usually employed in the preparation of samples for GC-MS analysis. One of the widely used methods of sample preparation is the long-term extraction of metabolites from whole tissues with the aid of a methanol solvent. Another method of sample preparation is based on the short-term methanol extraction of metabolites from frozen and homogenized material. The advantages and disadvantages of these two methods revealed in the course of our work have prompted us to develop a new approach that avoids some difficulties in analyzing the metabolic profiles of leaves of various guar varieties. The method we suggested combines the advantages of the two above-mentioned approaches of sample preparation, namely eliminates the loss of metabolites due to centrifugation and ensures the complete destruction of all cell walls, ensuring the maximum extraction level of polar metabolites. The essence of the new method is that the leaf is rapidly frozen in liquid nitrogen with subsequent thawing in cold methanol. Thus, leaf tissues retain morphological integrity, and subsequent centrifugation, necessary for homogenization, is skipped. We have checked the effectiveness of this improved method by experiments with leaf samples of three guar genotypes. It has been shown that the amount of extracted metabolites increases more than 5-fold compared to extraction with methanol from fresh unfrozen leaf tissues and more than 2-fold compared to extraction with methanol after freezing and homogenization. Extraction of metabolites using the new method allows the GC-MS analysis of guar samples to be conducted with the least loss and high accuracy required to distinguish varieties.

Ranking crop species using mixed treatment comparisons.

The mixed treatment comparison (MTC) method has been proposed to combine results across trials comparing several treatments. MTC allows coherent judgments on which of the treatments is the most effective. It produces estimates of the relative effects of each treatment compared with every other treatment by pooling direct and indirect evidence. In this article, we explore how this methodological framework can be used to rank a large number of agricultural crop species from yield data collected in field experiments. Our approach is illustrated in a meta-analysis of yield data obtained in 67 field studies for 36 different bioenergy crop species. The considered dataset defines a network of comparisons of crop species. We introduce several Bayesian MTC models based on baseline treatment contrasts and evaluate the practical advantages of these models to produce yield ratio estimates. We explore the consistency of some estimates by node-splitting and compare our results to those obtained with a classical two-way linear mixed model. Results reveal that the model showing the lowest deviance information criterion (DIC) includes both study random effects and study-specific residual variances. But all the tested models including study random effects lead to similar yield ratio estimates. The proposed Bayesian framework allows an in-depth analysis of the uncertainty in the species ranking.

Livelihood Improvements Through Agroforestry: Evidence from Northern Bangladesh

Agroforestry is one of the most sustainable land management systems practiced around the world due to the socioeconomic benefits that it brings to farmers. In Bangladesh, farmers practice agroforestry, applying indigenous knowledge. The present study was designed to identify the present status, management practices and its role in improving the livelihoods of farmers in northern Bangladesh. Data for the study were collected through quantitative and qualitative methods. A total of 29 tree and 38 agricultural crop species were planted by the102 farmers interviewed. Mangifera indica (relative prevalence 49%) is the most predominant species, followed by Eucalyptus camaldulensis (relative prevalence 35.4%). Farmers of northern Bangladesh plant trees in cropland for fruits (90%), fuel wood (87%) and timber production (79%). Fruit trees were planted with wider spacing while forest and fuel wood species were planted with narrower spacing. Farmer’s livelihoods improved enormously by practicing agroforestry as they have more access to food, fodder and fuel wood which is reflected by greater access to livelihood capitals (except social capital). However, farmers have experienced increased incidences of pests and diseases to the annual crops and trees. Agroforestry practices increases species diversity, ensure economic return and sustain farmer’s livelihoods.

Biogenic volatile organic compound emissions from senescent maize leaves and a comparison with other leaf developmental stages

Plants are the major source of Biogenic Volatile Organic Compounds (BVOCs) which have a large influence on atmospheric chemistry and the climate system. Therefore, understanding of BVOC emissions from all abundant plant species at all developmental stages is very important. Nevertheless, investigations on BVOC emissions from even the most widespread agricultural crop species are rare and mainly confined to the healthy green leaves. Senescent leaves of grain crop species could be an important source of BVOCs as almost all the leaves senesce on the field before being harvested. For these reasons, BVOC emission measurements have been performed on maize (Zea mays L.), one of the most cultivated crop species in the world, at all the leaf developmental stages. The measurements were performed in controlled environmental conditions using dynamic enclosures and proton transfer reaction mass spectrometry (PTR-MS). The main compounds emitted by senescent maize leaves were methanol (31% of the total cumulative BVOC emission on a mass of compound basis) and acetic acid (30%), followed by acetaldehyde (11%), hexenals (9%) and m/z 59 compounds (acetone/propanal) (7%). Important differences were observed in the temporal emission profiles of the compounds, and both yellow leaves during chlorosis and dry brown leaves after chlorosis were identified as important senescence-related BVOC sources. Total cumulative BVOC emissions from senescent maize leaves were found to be among the highest for senescent Poaceae plant species. BVOC emission rates varied strongly among the different leaf developmental stages, and senescent leaves showed a larger diversity of emitted compounds than leaves at earlier stages. Methanol was the compound with the highest emissions for all the leaf developmental stages and the contribution from the young-growing, mature, and senescent stages to the total methanol emission by a typical maize leaf was 61, 13, and 26%, respectively. This study shows that BVOC emissions from senescent maize leaves cannot be neglected and further investigations in field conditions are recommended to further constrain the BVOC emissions from this important C4 crop species.

Degradation changes in plant root cell wall structural molecules during extended decomposition of important agricultural crop and forage species

Little is known regarding changes in cell wall structural molecules (lignin, cellulose and hemicellulose) as plant roots decompose, despite their importance for soil organic matter (OM) formation. The objectives of this study were to quantify changes in root composition during 270 d incubations of ten important grain and forage crops utilizing forage fiber analysis and to characterize the changes in cell wall composition and structure using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Large, species-dependent variation was observed in the extent of root tissue decomposition over time, ranging from 82.5% of initial mass for alfalfa to 21.5% for switchgrass. Fiber analysis revealed that initial rapid decomposition increased lignin concentration and cellulose concentration while hemicellulose declined, whereas all three moieties degraded proportionally thereafter. Similar trends were found in the ratios between the DRIFTS diagnostic peaks for lignin, cellulose and the carbonyls of hemicellulose and wax components. Spectra illustrated changes during decomposition, particularly in more extensively decomposed roots. Features potentially indicative of suberin preservation were found in the region between 2800 cm−1 and 3000 cm−1. Examination of the region between 1000 cm−1 and 1300 cm−1 revealed possible change in hemicellulose structure. The results illustrate the effect of differences in cell wall composition and structure during root decomposition and expand understanding of the role of roots in soil OM dynamics. Variability in root degradation and change in cell wall composition among species demonstrate that characterization of a broad range of individual species is necessary to predict root contributions to soil C.