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Soil is the world’s largest terrestrial carbon (C) sink, and is estimated to contain approximately 1600 Pg of carbon to a depth of one metre. The distribution of soil organic C (SOC) largely follows gradients similar to biomass accumulation, increasing with increasing precipitation and decreasing temperature. As a result, SOC levels are a function of inputs, dominated by plant litter contributions and rhizodeposition, and losses such as leaching, erosion and heterotrophic respiration. Therefore, changes in biomass inputs, or organic matter accumulation, will most likely also alter these levels in soils. Although the soil microbial biomass (SMB) only comprises 1-5% of soil organic matter (SOM), it is critical in organic matter decomposition and can provide an early indicator of SOM dynamics as a whole due to its faster turnover time, and hence, can be used to determine soil C dynamics under changing environmental conditions.¶ Approximately 932 million ha of land worldwide are degraded due to salinity and sodicity, usually coinciding with land available for agriculture, with salinity affecting 23% of arable land while saline-sodic soils affect a further 10%. Soils affected by salinity, that is, those soils high in soluble salts, are characterised by rising watertables and waterlogging of lower-lying areas in the landscape. Sodic soils are high in exchangeable sodium, and slake and disperse upon wetting to form massive hardsetting structures. Upon drying, sodic soils suffer from poor soil-water relations largely related to decreased permeability, low infiltration capacity and the formation of surface crusts. In these degraded areas, SOC levels are likely to be affected by declining vegetation health and hence, decreasing biomass inputs and concomitant lower levels of organic matter accumulation. Moreover, potential SOC losses can also be affected from dispersed aggregates due to sodicity and solubilisation of SOM due to salinity. However, few studies are available that unambiguously demonstrate the effect of increasing salinity and sodicity on C dynamics. This thesis describes a range of laboratory and field investigations on the effects of salinity and sodicity on SOC dynamics.¶ In this research, the effects of a range of salinity and sodicity levels on C dynamics were determined by subjecting a vegetated soil from Bevendale, New South Wales (NSW) to one of six treatments. A low, mid or high salinity solution (EC 0.5, 10 or 30 dS/m) combined with a low or high sodicity solution (SAR 1 or 30) in a factorial design was leached through a non-degraded soil in a controlled environment. Soil respiration and the SMB were measured over a 12-week experimental period. The greatest increases in SMB occurred in treatments of high-salinity high-sodicity, and high-salinity low-sodicity. This was attributed to solubilisation of SOM which provided additional substrate for decomposition for the microbial population. Thus, as salinity and sodicity increase in the field, soil C is likely to be rapidly lost as a result of increased mineralisation.¶ Gypsum is the most commonly-used ameliorant in the rehabilitation of sodic and saline-sodic soils affected by adverse soil environmental conditions. When soils were sampled from two sodic profiles in salt-scalded areas at Bevendale and Young, SMB levels and soil respiration rates measured in the laboratory were found to be low in the sodic soil compared to normal non-degraded soils. When the sodic soils were treated with gypsum, there was no change in the SMB and respiration rates. The low levels of SMB and respiration rates were due to low SOC levels as a result of little or no C input into the soils of these highly degraded landscapes, as the high salinity and high sodicity levels have resulted in vegetation death. However, following the addition of organic material to the scalded soils, in the form of coarsely-ground kangaroo grass, SMB levels and respiration rates increased to levels greater than those found in the non-degraded soil. The addition of gypsum (with organic material) gave no additional increases in the SMB.¶ The level of SOC stocks in salt-scalded, vegetated and revegetated profiles was also determined, so that the amount of SOC lost due to salinisation and sodication, and the increase in SOC following revegetation relative to the amount of SOC in a vegetated profile could be ascertained. Results showed up to three times less SOC in salt-scalded profiles compared to vegetated profiles under native pasture, while revegetation of formerly scalded areas with introduced pasture displayed SOC levels comparable to those under native pasture to a depth of 30 cm. However, SOC stocks can be underestimated in saline and sodic landscapes by setting the lower boundary at 30 cm due to the presence of waterlogging, which commonly occurs at a depth greater than 30 cm in saline and sodic landscapes as a result of the presence of high or perched watertables. These results indicate that successful revegetation of scalded areas has the potential to accumulate SOC stocks similar to those found prior to degradation.¶ The experimental results from this project indicate that in salt-affected landscapes, initial increases in salinity and sodicity result in rapid C mineralisation. Biomass inputs also decrease due to declining vegetation health, followed by further losses as a result of leaching and erosion. The remaining native SOM is then mineralised, until very low SOC stocks remain. However, the C sequestration potential in these degraded areas is high, particularly if rehabilitation efforts are successful in reducing salinity and sodicity. Soil ecosystem functions can then be restored if organic material is available as C stock and for decomposition in the form of either added organic material or inputs from vegetation when these salt-affected landscapes are revegetated.

Doctor of Philosophy / Department of Agronomy / Charles W. Rice / Gretchen F. Sassenrath / Soil microorganisms are a critical component of ecosystem services provided by soil. Soil management drives soil physical, chemical, and biological properties. Pedogenesis and management interact to change microbial structure and function in the soil profile. Soil microbial properties may vary temporally with crop development and crop species. The objective of this study was to explore the pedogenetic and anthropogenic controls on key soil microbial properties by (i) assessing the profile of a claypan soil under conventional tillage (CT), no-till (NT), and hay meadow (HM); (ii) assessing seasonal changes of soil microbial properties in a corn/winter wheat/soybean rotation under CT and NT; and (iii) assessing vertical changes of soil microbial properties in response to long-term (28 yrs) tillage and mineral and organic fertilization. Selected microbial properties included extracellular enzyme activity, microbial structure as measured by phospholipid fatty acid (PLFA), as well as soil chemical properties. Soil C, enzyme activities, and microbial biomass were greatest in HM soils, followed by NT and then CT in the claypan soil. Wheat in the rotation increased hydrolase activity and bacterial biomass more than corn, while microbial activities were stable during soybean growth. Increased enzyme activities in the claypan layer resulted from the combination of clay-enzyme interaction and impacts from management practices. In a Mollisol soil, an increase in C-acquiring enzyme activity and microbial PLFAs in a buried A horizon was a result of root growth under no-till practice and mineral fertilization. Surprisingly, long-term mineral fertilizer applications had little effect on enzyme activities and microbial biomass. Long-term organic fertilization increased soil C, enzyme activities, and PLFAs but decreased arbuscular mycorrhizal fungi (AMF) throughout the soil profile to a depth of 90 cm. Microbial properties are controlled by crop and soil management at the soil surface and by the interaction of management and pedogenetic properties deeper in the soil profile. Incorporating grasses in the crop rotation may allow nutrients to be extracted from deeper within the soil profile, enhancing the utilization of the entire soil profile and providing additional nutrient resources to cash crops. Incorporating wheat in the crop rotation supports greater microbial activity and biomass after corn harvest, especially in no-till management. Additional research is required to delineate further causative factors impacting enzyme activity in the claypan layer, a finer resolution in soil microbial community at the species level to explore the linkage between ecological function and microbiome structure, and a network analysis for the soil-plant-microbe interactions.

Made available in DSpace on 2014-06-11T19:31:35Z (GMT). No. of bitstreams: 0 Previous issue date: 2002-05Bitstream added on 2014-06-13T21:02:53Z : No. of bitstreams: 1 rocha_mm_dr_botfca.pdf: 1150326 bytes, checksum: 893acd7e01d7f269b3eaa875876c771e (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O manejo agrícola altera, em muito, as características físicas, químicas e biológicas dos solos. A cultura e as condições climáticas, assim como o tipo de solo propriamente dito, afetam a decomposição da matéria orgânica do solo e, consequentemente, a biogeociclagem dos nutrientes. A matéria orgânica é uma característica importante em relação à fertilidade do solo, de modo que o impacto do uso do solo precisa ser avaliado principalmente em agroecossistemas. O conhecimento dos efeitos do uso da terra e das práticas agrícolas sobre a comunidade microbiana é de fundamental importância, em vista das importantes funções que os microorganismos desempenham no solo e que irão se refletir na produtividade agrícola. Neste sentido, uma avaliação da biomassa microbiana e de microorganismos do solo pode evidenciar diversas alterações no ecossistema do solo que estão associadas ao teor de argila e/ou sistemas de plantio. No presente estudo, caracterizou-se a camada superficial do perfil de solos sob plantio direto e plantio convencional em quatro fazendas no Brasil em relação a alguns de seus componentes microbiológicos. Para tanto, analisou-se, mensalmente, a respiração do solo, a biomassa microbiana e grupos de microorganismos. A avaliação da biomassa microbiana foi feita através da técnica da fumigação-incubação (FI), utilizando-se a Equação: [(C-CO2 liberado pelo solo fumigado, no período de 0-10 dias de incubação) - (C-CO2 liberado pelo solo não-fumigado, ao longo de 10-20 dias de incubação)]/0,45. Os cálculos indicaram um conteúdo de carbono da biomassa microbiana significativamente maior nos solos sob sistema de plantio direto em relação àqueles sob plantio convencional, na camada amostrada (0-10 cm de profundidade). Quantidades significativamente maiores... / The crop management changes greatly the physical, chemical and biological soil properties. Furthermore, the crop and soil types, and the climatic conditions would affect on soil organic matter decomposition and on nutrients biogeociclying. Soil organic matter is a important characteristic in relationship soil fertility. The knowledge about effects on soil using and agriculture practices on soil microbial communities is very important, due to the function that microorganisms have in soil and it was going to in soil fertility. In this sense, evaluation of the soil microbial biomass and micro-organisms greatly aids predictions several changes in the soil ecosystems are associated with reduced tillage as compared with conventional tillage. Surface soils from long-term no-till and conventional tillage plots at four Brazil farms were characterised for microbial components. Soil respiration, microbial biomass carbon and counts of microorganisms were measured at intervals monthly. The evaluation of microbial biomass carbon was done by fumigation-incubation technique (FI). For calculating the soil microbial biomass carbon, the equation used was: Equation = [(CO2-C evolved by fumigated soil, 0-10 days) - (CO2-C evolved by unfumigated soil, 10-20 days)]/0,45. Significantly greater amounts of CO2-C were released from no-till than from conventional tilled soils. qCO2 values were not significantly different between tillage systems. This observation confirms that the tillage affected biological activity in those soils, further that qCO2 values didn't have significantily different which two tillage systems, in studied soils. Number both fungi and bacteria were assayed by Most Probable Number (MPN) by the agar drop counting technique and the microorganisms groups were calculated using by traditional Most Probable Number (MPN) method...(Complete abstract, click electronic access below)

Submitted by Angela Maria de Oliveira (amolivei@uepg.br) on 2018-05-18T12:54:48Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Carlos Henrique Antunes.pdf: 1490715 bytes, checksum: 395b47451425b08679ea95cbb4e672d7 (MD5) / Made available in DSpace on 2018-05-18T12:54:48Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Carlos Henrique Antunes.pdf: 1490715 bytes, checksum: 395b47451425b08679ea95cbb4e672d7 (MD5) Previous issue date: 2018-02-28 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O aporte de N na forma assimilável pelas plantas (NH4+) em diversos ecossistemas é realizado principalmente pelos organismos diazotróficos, e os mesmos vêm sendo pesquisados amplamente em todo o mundo. O N se configura como um dos nutrientes que apresenta grande importância no crescimento e desenvolvimento das plantas devido a sua função estrutural, pois faz parte da molécula de compostos orgânicos,como os aminoácidos e proteínas, sendo ainda ativador de muitas enzimas. Os adubos amoniacais são os mais comumente utilizados como fonte de nitrogênio nas atividades agrícolas. Contudo, a sua utilização acarreta em aumentos significativos da acidificação do solo, provenientes dos processos de nitrificação. O solo é um sistema complexo e as práticas de manejo podem afetar significativamente as comunidades microbianas que realizam muitos processos de suma importância para a produtividade e sustentabilidade. O objetivo desse trabalho foi avaliar o impacto na comunidade microbiana de um solo com a adição de N e calagem sob cobertura na aveia preta em um sistema de plantio direto de longa duração. As coletas de solo foram realizadas em cinco tratamentos distintos, distribuídos aleatoriamente em triplicatas na área experimental: SC (sem cobertura de inverno); CC (com cobertura de inverno); CC+ N (com cobertura de inverno + nitrogênio); CC+C (com cobertura de inverno + calcário) e CC+C+N (com cobertura de inverno + calcário + nitrogênio). Avaliaram-se os atributos químicos do solo, o carbono da massa microbiana, a respiração basal, o quociente metabólico, o NMP dos diazotrofos, o número de nódulos, a massa seca dos nódulos, a massa seca da raiz e parte aérea da soja, bem como utilizou-se a técnica da Biolog Ecoplate para analisar o consumo de fontes de carbono entre os tratamentos, a fim de verificar suas similaridades e diferenças. Constatou-se que as condições químicas como o pH influenciaram diretamente o crescimento e o desenvolvimento da comunidade microbiana em vários parâmetros estudados. Os níveis de carbono da massa microbiana do solo, bem como a respiração basal e o quociente metabólico variaram entre os tratamentos, sendo o tratamento CC+ N o que apresentou um maior distúrbio na biomassa microbiana causado pelo seu manejo. Em relação às bactérias diazotróficas do solo, ficou evidente que a população teve forte influência da aplicação de N e de calcário, se mostrando nula no tratamento CC+C+N, contudo a população de bactérias noduladoras não teve influência negativa nos diferentes tratamentos.Observou-se que o houve um consumo diferente pelas comunidades de para determinados subgrupos de fontes de carbono. É notável a importância do estudo acerca das características e potenciais das bactérias diazotróficas, a fim de promover um avanço nas tecnologias para maximizar a produtividade de culturas que apresentam grande valor econômico para os produtores. / The contribution of N in the form assimilable by the plants (NH4 +) in several ecosystems is carried out mainly by the diazotrophic organisms, and they have been researched widely around the world. N is one of the nutrients that has great importance in the growth and development of plants due to its structural function, since it is part of the molecule of organic compounds, such as amino acids and proteins, being still activator of many enzymes. Ammoniac fertilizers are most commonly used as a source of nitrogen in agricultural activities. However, their use leads to significant increases in soil acidification from nitrification processes. Soil is a complex system and management practices can significantly affect microbial communities that perform many processes of paramount importance for productivity and sustainability. The objective of this work was to evaluate the impact on the microbial community of a soil with the addition of N and liming under cover in black oats in a long - term no - tillage system. Soil samples were collected in five different treatments, randomly distributed in triplicates in the experimental area: SC CC (without winter cover); CC (with winter cover); CC + N (with winter + nitrogen coverage); CC + C (with winter cover + limestone) and CC + C + N (with winter cover + limestone + nitrogen).Soil chemical, microbial mass carbon, basal respiration, metabolic quotient, diazotrophs NMP, number of nodules, nodule dry mass, dry mass of the root and shoot of the soybean were evaluated, as well as using the Biolog Ecoplate technique to analyze the consumption of carbon sources between treatments in order to verify their similarities and differences. It was found that chemical conditions such as pH directly influenced the growth and development of the microbial community in several parameters studied. The carbon levels of the soil microbial mass, as well as the basal respiration and the metabolic quotient varied among the treatments, being the treatment CC + N that presented a greater disturbance in the microbial biomass caused by its handling. In relation to the diazotrophic bacteria of the soil, it was evident that the population had a strong influence of the application of N and limestone, if it was null in the treatment CC + C + N, however the population of nodulating bacteria did not have negative influence in the different treatments. It was observed that there was a different consumption by the communities of for certain subgroups of carbon sources. The importance of the study of the characteristics and potentials of diazotrophic bacteria is remarkable in order to promote an advance in the technologies to maximize the productivity of crops that present great economic value to the producers.

Orientador: Marli Teixeira de Almeida Minhoni / Resumo: O manejo agrícola altera, em muito, as características físicas, químicas e biológicas dos solos. A cultura e as condições climáticas, assim como o tipo de solo propriamente dito, afetam a decomposição da matéria orgânica do solo e, consequentemente, a biogeociclagem dos nutrientes. A matéria orgânica é uma característica importante em relação à fertilidade do solo, de modo que o impacto do uso do solo precisa ser avaliado principalmente em agroecossistemas. O conhecimento dos efeitos do uso da terra e das práticas agrícolas sobre a comunidade microbiana é de fundamental importância, em vista das importantes funções que os microorganismos desempenham no solo e que irão se refletir na produtividade agrícola. Neste sentido, uma avaliação da biomassa microbiana e de microorganismos do solo pode evidenciar diversas alterações no ecossistema do solo que estão associadas ao teor de argila e/ou sistemas de plantio. No presente estudo, caracterizou-se a camada superficial do perfil de solos sob plantio direto e plantio convencional em quatro fazendas no Brasil em relação a alguns de seus componentes microbiológicos. Para tanto, analisou-se, mensalmente, a respiração do solo, a biomassa microbiana e grupos de microorganismos. A avaliação da biomassa microbiana foi feita através da técnica da fumigação-incubação (FI), utilizando-se a Equação: [(C-CO2 liberado pelo solo fumigado, no período de 0-10 dias de incubação) - (C-CO2 liberado pelo solo não-fumigado, ao longo de 10-20 dias de incubação)]/0,45. Os cálculos indicaram um conteúdo de carbono da biomassa microbiana significativamente maior nos solos sob sistema de plantio direto em relação àqueles sob plantio convencional, na camada amostrada (0-10 cm de profundidade). Quantidades significativamente maiores ...(Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The crop management changes greatly the physical, chemical and biological soil properties. Furthermore, the crop and soil types, and the climatic conditions would affect on soil organic matter decomposition and on nutrients biogeociclying. Soil organic matter is a important characteristic in relationship soil fertility. The knowledge about effects on soil using and agriculture practices on soil microbial communities is very important, due to the function that microorganisms have in soil and it was going to in soil fertility. In this sense, evaluation of the soil microbial biomass and micro-organisms greatly aids predictions several changes in the soil ecosystems are associated with reduced tillage as compared with conventional tillage. Surface soils from long-term no-till and conventional tillage plots at four Brazil farms were characterised for microbial components. Soil respiration, microbial biomass carbon and counts of microorganisms were measured at intervals monthly. The evaluation of microbial biomass carbon was done by fumigation-incubation technique (FI). For calculating the soil microbial biomass carbon, the equation used was: Equation = [(CO2-C evolved by fumigated soil, 0-10 days) - (CO2-C evolved by unfumigated soil, 10-20 days)]/0,45. Significantly greater amounts of CO2-C were released from no-till than from conventional tilled soils. qCO2 values were not significantly different between tillage systems. This observation confirms that the tillage affected biological activity in those soils, further that qCO2 values didn't have significantily different which two tillage systems, in studied soils. Number both fungi and bacteria were assayed by Most Probable Number (MPN) by the agar drop counting technique and the microorganisms groups were calculated using by traditional Most Probable Number (MPN) method...(Complete abstract, click electronic access below) / Doutor

Currently, 74% of cotton acres in the United States are planted with glyphosatetolerant varieties. The average glyphosate-tolerant cotton crop is treated with glyphosate 2.1 times each year in addition to other herbicides, insecticides, and fungicides. The primary objectives of this research were to: 1) describe the influence of glyphosate and pesticides commonly applied at or near the time of cotton planting on soil microbial activity and biomass; 2) study the effect of glyphosate on fluometuron degradation; 3) evaluate the response of Rhizoctonia solani to glyphosate and fluometuron; 4) study changes in glyphosate metabolism that occur as a result of repeated glyphosate applications; and 5) define shifts in the soil microbial community. Additionally, methods for accelerated solvent extraction (ASE) of fluometuron from soils were developed. In one experiment, the addition of glyphosate reduced C-mineralization in soils treated with fluometuron, aldicarb, or mefenoxam + PCNB formulations. However, in a second experiment, C-mineralization increased when glyphosate was applied with fluometuron relative to fluometuron applied alone. Accelerated solvent extraction was used in experiments which demonstrated that application of glyphosate with fluometuron increased the rate of fluometuron degradation in soil relative to fluometuron alone. When glyphosate was added to minimal medium, degradation of fluometuron by R. solani was reduced and less fungal biomass was produced. The total amount of 14C-glyphosate mineralized was reduced when glyphosate was applied 5 times relative to 1, 2, 3, or 4 times. Incorporation of 14Cglyphosate residues into soil microbial biomass was greater following five glyphosate applications than one application 3 and 7 days after application (DAA). Soil fatty acid methyl ester (FAME) profiles were altered by five glyphosate applications relative to one application. Additionally, FAMEs common to gram-negative bacteria were present in higher concentrations following five applications relative to 1, 2, 3, or 4 applications both 7 and 14 DAA. These studies indicated that: 1) glyphosate altered the soil microbial response to other pesticides; 2) fluometuron-degrading microorganisms in soil responded differently to glyphosate; 3) changes in the dissipation or distribution of glyphosate following repeated glyphosate applications were associated with changes in the structural diversity of the soil microbial community.

Woody plant invasion of grasslands is prevalent worldwide, but the biogeochemical consequences of this vegetation shift remain largely unquantified. In the Rio Grande Plains, TX, grasslands and savannas dominated by C4 grasses have undergone succession over the past century to subtropical thorn woodlands dominated by C3 trees/shrubs. To elucidate mechanisms of soil organic carbon (SOC) and soil total N (STN) storage and dynamics in this ecosystem, I measured the mass and isotopic composition (δ13C, δ15N) of C and N in whole-soil and soil size/density fractions in chronosequences consisting of remnant grasslands (Time 0) and woody plant stands ranging in age from 10-130 years. Rates of SOC and STN storage averaged 10-30 g C m-2yr-1 and 1-3 g N m-2yr-1, respectively. These accumulation rates increased soil C and N pools 80-200% following woody encroachment. Soil microbial biomass (SMB-C) also increased after woody invasion. Decreasing Cmic/C org and higher qCO2 in woodlands relative to grasslands suggests that woody litter is of poorer quality than grassland litter. Greater SOC and STN following woody invasion may also be due to increased protection of organic matter by stable soil structure. Soil aggregation increased following woody encroachment; however, most of the C and N accumulated in free particulate organic matter (POM) fractions not protected within aggregates. Mean residence times (MRTs) of soil fractions were calculated based on changes in their δ13C with time after woody encroachment. Free POM had the shortest average MRTs (30 years) and silt+clay the longest (360 years). Fine POM had MRTs of about 60 years, reflecting protection by location within aggregates. δ15N values of soil fractions were positively correlated with their MRTs, suggesting that higher δ15N values reflect an increased degree of humification. Increases in SOC and STN are probably being sustained by greater inputs, slower turnover of POM (some biochemical recalcitrance), and protection of organic matter in aggregates and association with silt and clay. Grassland-to-woodland conversion during the past century has been geographically extensive in grassland ecosystems worldwide, suggesting that changes in soil C and N dynamics and storage documented here could have significance for global C and N cycles.

The ecological significance of coarse woody debris (CWD) is usually highlighted in forests where CWD constitutes much of an ecosystem's carbon (C) source and stores. However, a unique addition of CWD is occurring in semi-deserts for which there is no ecological analog. To stem catastrophic wildfires and create firebreaks, whole Juniperus osteosperma (Torr.) and Pinus edulis (Engelm.) trees are being mechanically shredded into CWD fragments and deposited on soils previously exposed to decades of tree-induced changes that encourage "tree islands of fertility." To investigate consequences of CWD on C and nitrogen (N) cycling, we evaluated microbial metabolic activity and N transformation rates in Juniperus and Pinus surface and subsurface soils that were either shredded or left untreated. We sampled three categories of tree cover on over 40 tree cover encroachment sites. Tree cover categories (LOW = 0-15%, MID ≥ 15-45%, HIGH ≥ 45%) were used to indicate tree island development at time of treatment. In conjunction with our microbial measurements, we evaluated the frequency of three exotic grasses, and thirty-five native perennial grasses to identify links between belowground and aboveground processes. The addition of CWD increased microbial biomass by almost two-fold and increased microbial efficiency, measured as the microbial quotient, at LOW Juniperus cover. C mineralization was enhanced by CWD only in Pinus soils at the edge of tree canopies. The addition of CWD had little impact on microbial activity in subsurface soils. CWD enhanced the availability of dissolved organic C (DOC) and phosphorus (P) but tended to decrease the overall quality of labile DOC, measured as the ratio of soil microbial biomass to DOC. This suggested that the increase in DOC alone or other environmental factors novel to CWD additions lead to the increase in biomass and efficiency. P concentrations were consistently higher following CWD additions for all encroachment levels. The CWD additions decreased N mineralization and nitrification in Juniperus and Pinus soils at LOW and MID tree cover but only in surface soils, suggesting that less inorganic N was available to establishing or residual plants. The frequency of native perennial grasses, especially Elymus elymoides (Raf.), was at least 65% higher under CWD additions for all categories of tree cover, while the frequencies of exotic annual and perennial grasses were not impacted by CWD. The frequency of all perennial grasses ranged from 10-27%. Our results suggest that CWD enhanced microbial activity even when the quality of C substrates declined requiring microbes to immobilize more N. The reduction in inorganic N may promote the establishment and growth of native perennial grasses. Ultimately, the addition of CWD improved soil conditions for microbes in tree islands of fertility.