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PT. XYZ yang bergerak dalam industri pembuatan ban mengalami kegagalan yang terjadi pada unit mesin curing Type B45 dimana terjadi kegagalan pada bagian poros low ring, yang mengakibatkan terhentinya proses produksi. Penelitian dilakukan dengan tujuan, mengidentifikasi masalah yang terjadi.Dari hasil penelitian dapat di identifikasi penyebab terjadinya kegagalan pada poros yaitu tegangan geser yang terjadi pada poros low-ring (τ) lebih besar dari tegangan geser yang diijinkan (τa) maka hal ini yang menyebabkan terjadinya retak pada poros tersebut ( > 102,35 N/mm ). Dari hasil analisis gaya silinder (F2), adalah gaya silinder pada saat silinder retract, adalah model yang signifikan dalam penentuan optimasi desain silinder dalam rangka mengurangi kegagalan pada mesin curing karena korelasinya paling besar dari ketiga model. Pengaruh diameter silinder terhadap gaya sangat tinggi, hal ini dikarenakan koefisien korelasinya sebesar R=0,99985 menunjukan mendekati angka 1. Untuk tindakan perbaikan pada masalah tersebut bisa dilakukan dengan cara mendesain ulang silinder hidrolik. Yaitu dengan merubah ukuran silinder dengan luas penampang yang mendapat tekanan hidrolik (2,1 MPa)) tidak lebih dari 12957,28 mm2.

1. Drylands are among the most threatened ecosystems in the world because of the effects of global change and because they are not particularly resilient. Regeneration after disturbance is quite slow and secondary succession can be delayed to the point of nearly stop. This is exacerbated when the community is strongly dominated by a single species able to quickly respond after disturbance. One example of such monospecific dominance is the colonization of abandoned fields in SE Spain by an early successional and native tussock grass, Lygeum spartum, that seems to halt succession. 2. Here we tested the competitive ability of Lygeum against Salsola oppositifolia, a shrub species that can be found interspersed with Lygeum in mid‐successional stages, and assessed how plant–soil interactions mediate the outcome of plant– plant competition. To do so, we sowed seeds and grew plants of Lygeum and Salsola in either intra‐ or interspecific competition under controlled conditions using sterile field soils inoculated with either live (i.e., with micro‐organisms) or sterile soil extracts from the understories of either Lygeum or Salsola. Soil nutrient content, seed germination rate, and shoot mass growth were determined after 5 months, and soil bacterial communities were characterized by sequencing. 3. Lygeum soil micro‐organisms and soil properties, such as the high content of N and organic matter, enhanced seed germination rate of Lygeum individuals. By contrast, Salsola adults outperformed Lygeum when growing in interspecific competition. 4. Synthesis. The enhanced competitive ability of Lygeum, which was mediated by soil micro‐organisms, may lead to complete dominance of Lygeum in the plant community right after abandonment of agricultural fields. However, when the plant community is already developed, Lygeum would be unable to enforce such dominance. We conclude that positive plant–soil feedbacks combined with certain plant traits such as clonal growth support the strong resilience of Lygeum and allow for its dominance in extreme habitats., AEI, Grant/Award Number: CGL2017‐84515‐R; Junta de Andalucía Regional Government, Grant/Award Number: P09‐RNM‐4821

Inovasi dan pengembangan berkelanjutan selalu dilakukan di bidang otomotif, terutama untuk kendaraan guna memaksimalkan efisiensi bahan bakar yang dikonsumsi. Inovasi ini juga digunakan untuk meningkatkan keselamatan dan kenyamanan saat mengemudi. Kondisi jalan yang tidak selalu rata menyebabkan kehilangan konsumsi bahan bakar yang terpisah karena pengemudi harus memperlambat kendaraan untuk menghindari getaran yang berlebihan. Inovasi penting yang dikembangkan adalah sistem suspensi regeneratif, yang berfungsi untuk menyerap energi getaran yang dihasilkan oleh sistem suspensi. Suspensi regeneratif mengubah energi getaran menjadi listrik melalui penempatan generator linier. Pengembangan teknologi Permanent Magnet Linear Generator (PMLG) masih sangat baru dan perlu dibuat dalam satu kerangka desain konseptual. Peneltiian ini menggunakan kerangka desain VDI 2221 dan metode eksperimen untuk memvalidasi hasil dari desain PMLG. VDI 2221 dipilih karena sistem PMLG telah memasuki tahap pengembangan. Fokus desain adalah pada pemilihan ukuran kawat stator, dan ditemukan bahwa penggunaan kabel yang berbeda memberikan kinerja dengan karakteristik masing-masing. Hasil pengujian pada desain dipilih dengan variable ukuran kawat stator AWG 28, 27 dan 25 menunjukan nilai konstanta generator tertinggi ada pada ukuran 27. Nilai konstanta generator menjadi indikator penting untuk mengetahui performa dari PMLG dan nilai ini dapat dijadikan sebagai rujukan awal untuk penerapan sistem PMLG pada suspensi regenerative.

A recent study by Sugiura and coworkers reported the non-symbiotic growth and spore production of an arbuscular mycorrhizal (AM) fungus, Rhizophagus irregularis, when the fungus received an external supply of certain fatty acids, myristates (C:14). This discovery follows the insight that AM fungi receive fatty acids from their hosts when in symbiosis. If this result holds up and can be repeated under nonsterile conditions and with a broader range of fungi, it has numerous consequences for our understanding of AM fungal ecology, from the level of the fungus, at the plant community level, and to functional consequences in ecosystems. In addition, myristate may open up several avenues from a more applied perspective, including improved fungal culture and supplementation of AM fungi or inoculum in the field. We here map these potential opportunities, and additionally offer thoughts on potential risks of this potentially new technology. Lastly, we discuss the specific research challenges that need to be overcome to come to an understanding of the potential role of myristate in AM ecology.

Background and Aims Our understanding of plant responses to biotic and abiotic drivers is largely based on above-ground plant traits, with little focus on below-ground traits despite their key role in water and nutrient uptake. Here, we aimed to understand the extent to which above- and below-ground traits are co-ordinated, and how these traits respond to soil moisture gradients and plant intraspecific competition. Methods We chose seedlings of five tropical tree species and grew them in a greenhouse for 16 weeks under a soil moisture gradient [low (drought), medium and high (well-watered) moisture levels] with and without intraspecific competition. At harvest, we measured nine above- and five below-ground traits of all seedlings based on standard protocols. Key Results In response to the soil moisture gradient, above-ground traits are found to be consistent with the leaf economics spectrum, whereas below-ground traits are inconsistent with the root economics spectrum. We found high specific leaf area and total leaf area in well-watered conditions, while high leaf dry matter content, leaf thickness and stem dry matter content were observed in drought conditions. However, below-ground traits showed contrasting patterns, with high specific root length but low root branching index in the low water treatment. The correlations between above- and below-ground traits across the soil moisture gradient were variable, i.e. specific leaf area was positively correlated with specific root length, while it was negatively correlated with root average diameter across moisture levels. However, leaf dry matter content was unexpectedly positively correlated with both specific root length and root branching index. Intraspecific competition has influenced both above- and below-ground traits, but interacted with soil moisture to affect only below-ground traits. Consistent with functional equilibrium theory, more biomass was allocated to roots under drought conditions, and to leaves under sufficient soil moisture conditions. Conclusions Our results indicate that the response of below-ground traits to plant intraspecific competition and soil moisture conditions may not be inferred using above-ground traits, suggesting that multiple resource use axes are needed to understand plant ecological strategies. Lack of consistent leaf–root trait correlations across the soil moisture gradient highlight the multidimensionality of plant trait relationships which needs more exploration.

Microplastics are a complex contaminant suite that are now understood to affect plants and soil biota and the processes they drive. However, the role of microplastic in plant-soil feedbacks, a key feature in plant-soil interactions, is still unknown. We address this here, using soil from a previous experiment, which has been conditioned with 12 different microplastic types including fibers, films, foams, and fragments. To evaluate the feedback effect, we grew a native and a range-expanding plant species with inocula extracted from each one of these soils. At harvest, plant biomass and root morphological traits were measured.Films gave rise to a positive feedback on shoot mass (higher mass with soil inocula conditioned with microplastics than without), likely via negative effects on harmful soil biota. Foams and fragments also caused positive feedback on shoot mass likely via effects on enzymatic activities and mutualistic soil biota. Fibers led to negative feedback on root mass as they may promote the abundance of soil pathogens.Microplastics also have a legacy effect on root traits: Daucus had thicker roots probably for promoting mycorrhizal associations while Calamagrostis had reduced root diameter probably for diminishing pathogenic infection. Microplastic legacy on plants is species-specific and may affect plant biomass primarily via root traits. Microplastics, as a function of their shape and polymer type, have a feedback effect on plant performance.

1. Drought causes soil feedback effects on plant performance. However, how the linkages between conditioned soil biota and root traits contribute to explain plant–soil feedback (PSF) as a function of drought is unknown. 2. We utilized soil inoculum from a conditioning experiment where grassland species grew under well-watered and drought conditions, and their soil fungi were analyzed. Under well-watered conditions, we grew 21 grassland species with those inocula from either conspecific or heterospecific soils. At harvest, plant biomass and root traits were measured. 3. Negative PSF (higher biomass in heterospecific than in conspecific soils) was predominant, and favored in drought-conditioned soils. Previous drought affected the relationship between root traits and fungal groups. Specific root surface area (SRSA) was higher in heterospecific than in conspecific droughted soils and was linked to an increase in saprotroph richness. Overall, root diameter was higher in conspecific soils and was linked to mutualist and pathogen composition, whereas the decrease of root : shoot in heterospecific soils was linked to pathogenic fungi. 4. Drought legacy affects biomass and root morphological traits via conditioned soil biota, even after the drought conditions have disappeared. This provides new insights into the role that soil biota have modulating PSF responses to drought.

Microplastics and plant litter are ubiquitous in the soil environment, and both materials can influence soil properties and biota. Plant litter releases secondary metabolites (e.g., phenolic compounds) during the decomposition process, including chemical compounds active in plant defense. Effects of microplastics and plant litter on soil biota have been studied independently but we have limited information about the combined effects of both sources of chemicals. Here, we specifically focused on the interaction between plant litter and microplastics, as well as their potential effects on soil biota (i.e., nematodes). We used soils from a previous experiment that included three different types of microplastic fibers (MFs) and four different types of plant litter, which were incubated in the soil in all combinations of materials. After soil incubation (42 days) in the previous experiment, we here tested for effects on nematodes (Caenorhabditis elegans). Plant litter treatments negatively affected the reproduction of nematodes, but these effects were reduced when the soils were incubated along with MFs. We measured the phenolic concentrations in plant litter extracts in a kinetic experiment and found that phenolic concentrations significantly decreased with some of the MF additions. Our results suggest that microplastics can affect the potential effects of natural chemicals such as plant phenolic compounds. We urge future studies to consider this possibility as a key explanatory process underpinning effects of microplastic in the soil environment.

Microplastics are an increasing concern in terrestrial systems. These particles can be incorporated into the soil in a wide range of shapes and polymers, reflecting the fact that manufacturers produce plastics in a variety of physical and chemical properties matching their intended use.Despite of this, little is known about the effects that the addition into the soil of microplastics of different shapes, polymer type and concentration levels may have on soil properties and plant performance.To fill this gap, we selected four microplastic shapes: fibers, films, foams and fragments; and for each shape we selected three microplastics made of one of the following polymers: polyester, polyamide, polypropylene, polyethylene, polyethylenterephthalat, polyurethane, polystyrene and polycarbonate. In a glasshouse experiment, each microplastic was added to a soil from a dry grassland at a concentration of 0.1%, 0.2%, 0.3% and 0,4%. A carrot (Daucus carota) plant grew in each pot during four weeks. At harvest, shoot and root mass, soil aggregation and microbial activity were measured.Our results showed that all microplastic shapes increased shoot and root masses. As concentration increased, microfibers increased plant biomass probably as fibers may hold water in the soil for longer. In contrast, microfilms decreased biomass with concentration, likely because they can create channels in the soil that promote water evaporation affecting plant performance. All microplastic shapes decreased soil aggregation, probably since microplastics may introduce fracture points in the aggregates affecting their stability and also due to potential negative effects on soil biota. The latter may also explain the decrease in microbial activity with, for example, polyethylene films. Similar to plant biomass, microfilms decreased soil aggregation with increasing concentration.Our study tested the microplastic shape mediation and dissimilarity hypotheses, highlighting the importance of microplastic shape, polymer type and concentration when studying the effects of microplastics on terrestrial systems.

Microplastics in soils have become an important threat for terrestrial systems, which can be exacerbated by drought as microplastics may affect soil water content. Thus, the interaction between these two factors may alter ecosystem functions such as litter decomposition, stability of soil aggregates, as well as functions related to nutrient cycling. Despite this potential interaction, we know relatively little about how microplastics, under different soil water conditions, affect ecosystem functions and ecosystem multifunctionality.To address this gap, we carried out a controlled-environment study using grassland plant communities. We applied the two factors microplastic fibers (absent, present) and soil water conditions (well-watered, drought), in all possible combinations in a factorial experiment. At harvest, we measured multiple ecosystem functions linked to nutrient cycling, litter decomposition, and soil aggregation and as terrestrial systems provide these functions simultaneously, we also assessed ecosystem multifunctionality.Our results showed that the interaction between microplastic fibers and drought affected ecosystem functions and multifunctionality. Overall, drought had negatively affected nutrient cycling by decreasing potential enzymatic activities and increasing nutrient leaching, while microplastic fibers had a positive impact on soil aggregation and nutrient retention by diminishing nutrient leaching. Microplastic fibers also impacted enzymatic activities, soil respiration and ecosystem multifunctionality, but importantly, the direction of these effects depended on soil water status (i.e., they decreased under well watered conditions, but tended to increase or had similar effects under drought conditions). Litter decomposition had a contrary pattern.Synthesis and applications. As soil water content is affected by climate change, our results suggest that areas with sufficiency of water would be negatively affected in their ecosystem functioning as microplastics increase in the soil; however, in areas subjected to drought, microplastics would have a neutral or slightly positive effect on ecosystem functioning.

PT. X adalah perusahaan yang bergerak dalam bidang manufaktur khususnya memproduksi AsepticTank. PT X mempunyai misi perbaikan berkesinambunan (Continunous Improvement),dalam hal ini PT. Xselalu melakukan perbaikan salah satunya adalah perbaikan pada lini produksi tangki guna meningkatkanefisiensi pada lini tersebut. Tesis ini di fokuskan pada line of balancing lini produksi tangki untukmengoptimalkan kinerja produksi. Dengan meningkatkan efisiensi pada lini produksi tangki tersebut makakapasitas produksi dapat meningkat karena hal ini akan mempengaruhi produktifitas agar tidak terjadi idletime yang berlebihan. Untuk menyelesaikan masalah tersebut data yang dikumpulkan adalah waktu siklustiap elemen kerja, setelah itu dilakukan pengolahan data yaitu melakukan pengujian, menghitung waktusiklus rata-rata, takt time, idle time, efisiensi dan balance delay sebelum serta sesudah perbaikan. Denganhasil tersebut maka dapat disimpulkan bahwa perbaikan lini produksi sangat perlu dilakukan.

Penggunaan serat alam sebagai bahan komposit untuk pembuatan komponen kendaraan dewasa inibanyak digunakan, diantaranya adalah serat kelapa, jerami, dan resam. Kondisi ini sangatlah sulit bila hanyabergantung pada beberapa serat, padahal masih banyak tanaman lain yang belum tersentuh. Oleh karena itu,perlu alternatif lain misalnya dengan serat daun nanas. Pemanfaatan serat daun nanas hanya untuk bahanbaku kerajinan tangan. Untuk itu perlu dilakukan penelitian terhadap serat daun nanas agar memilikipemanfaatan lebih luas. Penelitian yang sudah dilakukan oleh peneliti lain menunjukkan bahwa penggunaanserat alam sebagai bahan komposit dapat ditingkatkan dengan NaOH.Tujuan penelitian ini adalah untuk mendapat bahan komposit baru, hasil dari perlakuan kimia denganlarutan NaOH terhadap serat daun nanas. Tahapan penelitian ini yaitu: pembuatan sampel uji, pengujianmekanik dan analisis data. Bahan-bahan untuk pembuatan sampel uji diantaranya adalah serat daun nanas,resin epoxy sebagi hardener, dan wax glasses sebagai pencegah menempelnya resin ke cetakan. Benda ujidibuat dengan cara menganyam serat yang sudah siap pakai lalu mencampurkan ke resin. Parameterprosentase serat 20%, 30%, dan 40% dan prosentase matrik 70%, 80%, dan 90%. Ukuran benda ujiberdasarkan standar uji tarik (ASTM D 638 - 14), uji impact (ISO-179 - 2010) dan uji heat resistance padatemperatur 85° selama 12 jam. Nilai paling tinggi uji tarik adalah 39,60 ± 3,70 MPa, regangannya 1,94 ±0,73%, heat resistance 1,96 % ± 1,31 %. Sedangkan nilai paling tinggi uji impact adalah 39,20 ± 3,97 kJ/m2.Selain itu hasil uji heatresistancenya pun sangat baik tidak mengalami kerusakan. Hasil ini menunjukkan ujitarik, uji impact dan uji heat resistancenya sudah memenuhi standar plastik yang digunakan interior mobil.

Human activities can dramatically alter natural plant communities which, after disturbance cessation, undergo secondary succession. In arid environments plant succession is quite slow, and its link to the carbon (C) cycle is not well known. We assessed changes in C balance on a semiarid plant community along a chronosequence spanning ca. 100 years after land abandonment in an arid environment in SE Spain to examine temporal changes in C following human disturbance. We selected 5 individuals of the dominant plant species along five plant community stages differing in the time since land abandonment occurred, and we used a closed-chamber infrared gas analyzer method to estimate the contribution of whole plants and bare soil to community C exchange. We estimated CO2 fluxes for each plant community stage and calculated temporal differences along the chronosequence. Plant community composition and plant cover changed throughout the chronosequence. Carbon balance was related to changes in plant photosynthesis and plant and soil respiration along the chronosequence. Overall, community C exchange shifted from source to sink as plant colonization progressed. It took 65 years for the system to recover the equivalent C sink capacity of the undisturbed site. Recovery of arid plant communities after land abandonment may enhance long-term C sequestration and significantly contribute to C balance at the global level.

Drought can strongly modify plant diversity and ecosystem processes. As droughts are expected to intensify in the future, it is important to better understand plant responses to this global driver. Root traits are an overlooked but powerful predictor of plant responses to drought because they are in direct contact with the soil environment and are responsible for taking up nutrients and water. Here, we determine which root traits are sensitive to drought and the magnitude of that response. We also tested whether root trait relationships with shoot biomass are affected by drought and to what extent all these responses depend on plant species identity. To do so, we conducted a glasshouse experiment with 24 plant species grown in pots (10 replicates per species), which included grasses, forbs and legumes. All replicates were well watered during the first month and then half of them were kept under drought (30% water holding capacity [WHC]), with the other half serving as control (70% WHC). After 2 months of treatment, leaf and root traits were measured. Leaf traits had a strong and more uniform response to drought compared to root traits. Root trait responses were variable and differed among plant species. Overall, grasses and several forbs had increased root diameter with drought while forbs had decreased specific root surface area (SRSA) and specific root length (SRL). Increase of root diameter and reduction of root elongation or sacrificing fine roots are different strategies that may promote nutrient and water acquisition, depending on plant species identity. Our results identify changes in root morphological traits as mechanisms to likely tolerate drought and highlight that, although such drought responses are species-specific, they are phylogenetically clustered. A freePlain Language Summarycan be found within the Supporting Information of this article.

Microplastics in soils can affect plant performance, as shown in studies using individual plants. However, we currently have no information about potential effects on plant community productivity and structure. In a plant community consisting of seven plant species that co-occur in temperate grassland ecosystems, we thus investigated the effect of microplastics (i.e., microfibers) and drought, a factor with which microfibers might interact, on plant productivity and community structure. Our results showed that at the community level, shoot and root mass decreased with drought but increased with microfibers, an effect likely linked to reduced soil bulk density, improved aeration, and better penetration of roots in the soil. Additionally, we observed that microfibers affected plant community structure. Species such as Calamagrostis, invasive in Europe, and the allelophatic Hieracium, became more dominant with microfibers, while species that potentially have the ability to facilitate the establishment of other plant species (e.g., Holcus), decreased in biomass. As microfibers affect plant species dominance, the examination of cascade effects on ecosystem functions should be a high priority for future research.

Drought can strongly modify plant diversity and ecosystem processes. As droughts are expected to intensify in the future, it is important to better understand plant responses to drought. We expect that roots traits constitute an overlooked but powerful predictor of plant responses as roots are in direct contact with the soil environment, taking up nutrients and water.Here, we determine which root traits are sensitive to drought, the magnitude of that response, whether their predictive power and relationships with shoot biomass are affected by drought and whether all these responses depend on plant functional group. To do so, we conducted a glasshouse experiment with 24 plant species grown in pots (10 replicates per species), which represent three different functional groups: grasses, herbs and legumes. All replicates were well watered during the first month and then half of the replicates were kept under drought (30 % water holding capacity (WHC)) with the other half serving as control (kept at 70% WHC). After two months of the treatment, leaf and root traits were measured.Leaf traits had a strong but more uniform response to drought compared to root traits. Root trait response was variable and differed by plant functional group. Most grasses had increased root diameter, specific root surface area (SRSA) while decreased root tissue density (RTD) with drought. Production of thicker roots with a low tissue density could allow grasses to achieve greater nutrient and water acquisition through mycotrophy and would be linked to an increase in the reserve of non-structural carbohydrates needed for osmoregulation. Herbs had decreased SRSA and specific root length (SRL) while increase root carbon allocation. Reduction of root elongation or sacrifice of fine roots would be compensated by an increase in root carbon allocation, which allow herbs to improve water uptake. Legumes did not alter root morphological traits but promote an early flowering in order to scape drought.Our results identify changes in root morphological traits as mechanisms to likely face drought, a response that is species-specific and differed among functional groups.

Nurse plants promote establishment of other plant species by buffering climate extremes and improving soil properties. Soil biota plays an important role, but an analysis to disentangle the effects of soil microorganisms, soil properties and microclimate on facilitation is lacking. In three microhabitats (gaps, small and large Retama shrubs), we placed six microcosms with sterilized soil, two per soil origin (i.e. from each microhabitat). One in every pair received an alive, and the other a sterile, inoculum from its own soil. Seeds of annual plants were sown into the microcosms. Germination, survival and biomass were monitored. Soil bacterial communities were characterized by pyrosequencing. Germination in living Retama inoculum was nearly double that of germination in sterile inoculum. Germination was greater under Retama canopies than in gaps. Biomass was up to three times higher in nurse than in gap soils. Soil microorganisms, soil properties and microclimate showed a range of positive to negative effects on understory plants depending on species identity and life stage. Nurse soil microorganisms promoted germination, but the effect was smaller than the positive effects of soil properties and microclimate under nurses. Nurse below-ground environment (soil properties and microorganisms) promoted plant growth and survival more than nurse microhabitat.

Plant growth dynamics are shaped by the diversity of associating pathogenic, saprotrophic, and mutualistic soil fungi., Feedbacks between plants and soil microbial communities play an important role in vegetation dynamics, but the underlying mechanisms remain unresolved. Here, we show that the diversity of putative pathogenic, mycorrhizal, and saprotrophic fungi is a primary regulator of plant-soil feedbacks across a broad range of temperate grassland plant species. We show that plant species with resource-acquisitive traits, such as high shoot nitrogen concentrations and thin roots, attract diverse communities of putative fungal pathogens and specialist saprotrophs, and a lower diversity of mycorrhizal fungi, resulting in strong plant growth suppression on soil occupied by the same species. Moreover, soil properties modulate feedbacks with fertile soils, promoting antagonistic relationships between soil fungi and plants. This study advances our capacity to predict plant-soil feedbacks and vegetation dynamics by revealing fundamental links between soil properties, plant resource acquisition strategies, and the diversity of fungal guilds in soil.

Competition is a key process that determines plant community structure and dynamics, often mediated by nutrients and water availability. However, the role of soil microorganisms on plant competition, and the links between above- and belowground processes, are not well understood. Here we show that the effects of interspecific plant competition on plant performance are mediated by feedbacks between plants and soil bacterial communities. Each plant species selects a singular community of soil microorganisms in its rhizosphere with a specific species composition, abundance and activity. When two plant species interact, the resulting soil bacterial community matches that of the most competitive plant species, suggesting strong competitive interactions between soil bacterial communities as well. We propose a novel mechanism by which changes in belowground bacterial communities promoted by the most competitive plant species influence plant performance and competition outcome. These findings emphasise the strong links between plant and soil communities, paving the way to a better understanding of plant community dynamics and the effects of soil bacterial communities on ecosystem functioning and services.

Secondary succession studies have mainly focused on plants, but little is known about the fate of soil microbial communities and their relationship with plant succession after disturbance, particularly in dry ecosystems. We examined changes in soil properties and of plant and soil microbial communities across a chronosequence of abandoned arable fields that included five successional stages according to time of abandonment stretching near a century. We hypothesized the existence of a parallel secondary succession above- and below-ground and explored the possible linkages between plant and microbial communities as well as the role of changes in soil properties over the successional gradient. Soil microbial communities were characterized by PLFAs analysis, enzymatic activities, and pyrosequencing of the 16S rDNA. We found clear patterns of plant and microbial secondary succession characterized by an increase in organic C, NH4+, and silt content as well as in soil microbial biomass and activity along the successional stages, linked to an increase in plant productivity and diversity. Plant and microbial composition were significantly different among successional stages, although no distinct microbial communities were observed in the two initial stages, suggesting that microbial succession may lag behind plant succession. However, the degree of change in the composition of soil microbial communities and plant communities across our chronosequence evidenced that above- and below-ground secondary succession developed with similar patterns and correlated with changes in multiple ecosystem functions such as increases in above-and below-ground productivity, diversity and nutrient accumulation as plant and microbial succession progressed.

Shrubs in semiarid ecosystems facilitate the establishment of other plant species under their canopies and promote changes in the understory plant communities as they grow. To better understand whether plant community dynamics are linked to changes in soil microbes, we characterized soil microbial communities in gaps (open spaces) and under Retama sphaerocarpa shrubs of three different size classes. Different methodological approaches including pyrosequencing of 16S rDNA, phospholipid-fatty acid (PLFA) analysis and microbial activity indicators were combined to characterize both the structure and function of soil microbial communities in the different treatments. Soil microbial communities under small shrubs showed higher microbial biomass and activity, as well as different relative abundance of several bacterial groups, than communities in gaps. Shrubs were associated with a higher relative abundance of Bacteroidetes , Betaproteobacteria and Gammaproteobacteria in detriment of Actinobacteria and Firmicutes without changes in overall bacterial diversity. Soil microbial community changed with shrub size, being most different in gaps and under the canopy of large shrubs. We suggest that changes in composition and function of soil microbial communities may promote the increase in the understory plant growth and species richness previously reported for this shrub species. Our data emphasize the importance of plant–soil interactions in defining the structure and composition of both plant and soil microbial communities and their impact on ecosystem functioning.

En esta tesis doctoral pretendemos aclarar aspectos fundamentales relacionados con la interacción entre plantas y microorganismos del suelo y sus consecuencias para la dinámica de las comunidades vegetales. Pretendemos comprobar si las comunidades microbianas están determinando interacciones negativas y/o positivas entre plantas; si tras el abandono de tierras dedicadas al cultivo, las plantas y los microorganismos del suelo siguen patrones sucesionales, y si los microorganismos asociados a las especies vegetales son los que determinan su éxito competitivo en una comunidad vegetal. Para evaluar esto realizamos diferentes experimentos en campo y en invernadero apoyados por una serie de análisis físicos, químicos, biológicos y moleculares del suelo y de sus comunidades microbianas., Proyecto de excelencia de la Junta de Andalucía ha financiado esta tesis doctoral.

Microplastics may enter the soil in a wide range of shapes and polymers. However, little is known about the effects that microplastics of different shapes, polymers, and concentration may have on soil properties and plant performance. To address this, we selected 12 microplastics representing different shapes (fibers, films, foams, and fragments) and polymers, and mixed them each with soil at a concentration of 0.1, 0.2, 0.3, and 0.4%. A phytometer (Daucus carota) grew in each pot during 4 weeks. Shoot, root mass, soil aggregation, and microbial activity were measured. All shapes increased plant biomass. Shoot mass increased by ∼27% with fibers, ∼60% with films, ∼45% with foams, and by ∼54% with fragments, as fibers hold water in the soil for longer, films decrease soil bulk density, and foams and fragments can increase soil aeration and macroporosity, which overall promote plant performance. By contrast, all shapes decreased soil aggregation by ∼25% as microplastics may introduce fracture points into aggregates and due to potential negative effects on soil biota. The latter may also explain the decrease in microbial activity with, for example, polyethylene films. Our findings show that shape, polymer type, and concentration are key properties when studying microplastic effects on terrestrial systems.

1. Microplastics in soils have become an important threat for terrestrial systems as they may potentially alter the geochemical/biophysical soil environment and can interact with drought. As microplastics may affect soil water content, this could exacerbate the well-known negative effects of drought on ecosystem functionality. Thus, functions including litter decomposition, soil aggregation or those related with nutrient cycling can be altered. Despite this potential interaction, we know relatively little about how microplastics, under different soil water conditions, affect ecosystem functions and multifunctionality. 2. To address this gap, we performed an experiment using grassland plant communities growing in microcosms. Microplastic fibres (absent, present) and soil water conditions (well-watered, drought) were applied in a fully factorial design. At harvest, we measured soil ecosystem functions related to nutrient cycling (beta-glucosaminidase, beta-D-cellobiosidase, phosphatase, beta-glucosidase enzymes), respiration, nutrient retention, pH, litter decomposition and soil aggregation (water stable aggregates). As terrestrial systems provide these functions simultaneously, we also assessed ecosystem multifunctionality, an index that encompasses the array of ecosystem functions measured here. 3. We found that the interaction between microplastic fibres and drought affected ecosystem functions and multifunctionality. Drought had negatively affected nutrient cycling by decreasing enzymatic activities by up to similar to 39%, while microplastics increased soil aggregation by similar to 18%, soil pH by similar to 4% and nutrient retention by up to similar to 70% by diminishing nutrient leaching. Microplastic fibres also impacted soil enzymes, respiration and ecosystem multifunctionality, but importantly, the direction of these effects depended on soil water status. That is, under well-watered conditions, these functions decreased with microplastic fibres by up to similar to 34% while under drought they had similar values irrespective of the microplastic presence, or tended to increase with microplastics. Litter decomposition had a contrary pattern increasing with microplastics by similar to 6% under well-watered conditions while decreasing to a similar percentage under drought. 4. Synthesis and applications. Single ecosystem functions can be positively or negatively affected by microplastics fibres depending on soil water status. However, our results suggest that microplastic fibres may cause negative effects on ecosystem soil multifunctionality of a similar magnitude as drought. Thus, strategies to counteract this new global change factor are necessary.