Submitted by Celso Magalhaes (celsomagalhaes@ufrrj.br) on 2017-05-05T13:43:03Z No. of bitstreams: 1 2012 - Diego Campana Loureiro.pdf: 6292509 bytes, checksum: 5485d752378d7d1a430cdb431c98ed44 (MD5) / Made available in DSpace on 2017-05-05T13:43:03Z (GMT). No. of bitstreams: 1 2012 - Diego Campana Loureiro.pdf: 6292509 bytes, checksum: 5485d752378d7d1a430cdb431c98ed44 (MD5) Previous issue date: 2012-03-22 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / The objective of this study was to evaluate the influence of the plant management and soil vegetation cover in the microbial biomass and labile soil organic matter (SOM) levels, with the possibility of prediction about the fate of soil organic carbon in the Atlantic Forest biome. We studied different crop areas under organic cultivation of vegetables (intensive cultivation, minimum tillage and crop rotation), grazing areas of Paspalum notatum (PAS); remaining fragments of Atlantic Forest (RMA), and degraded soil areas (ADR). Three composite soil samples were collected in each area to a depth of 0-10 cm in a Red Yellow Podzolic soil. In each sample we determined the levels of C and N associated with the SMB, labile C, labile N, free light fraction and intra-aggregate SOM, microbial respiration, microbial quotient and metabolic quotient. It was also determined mineral fractions as sand, silt, and clay, gravimetric moisture content, as well as the chemical attributes (Ca2+, Mg2+, P2O5, K+, organic C, total N, Al3+, CEC and pH in water). The pasture area had the highest accumulation of carbon in the soil microbial biomass (SMB) with 384 mg C kg-1 soil, about 35% above the level seen in the remaining Atlantic Forest fragments, which was attributed to the intense development and cycling of the root system of grasses in the upper soil layer, a horizon with higher concentration of microorganisms. About 2% of total organic C is stored in the SMB in pasture areas. The introduction of agricultural practices in farming system considerably affected the levels of SMB, showing reduction average of 30% compared to the remaining forest fragments. The metabolic quotient (qCO2) indicated losses of soil C for the managed areas with crops, and among the different systems of agriculture, greater losses of C were observed in areas managed with short cycle crops, with frequent use of plowing and harrowing, prompting the search for management systems that minimize soil disturbance and prioritize the maintenance of vegetation cover. The degraded soil area was the environment that contributed the most to the separation of the multivariate groups, showing the area of higher differences for the microbial activity and SOM levels. The attributes with higher importance in the multivariate grouping were clay content and the microbial C/N ratio showing the significance of the use of SMB and soil texture attributes in distinguishing between different crop management systems and soil vegetation cover, showing the prediction potential for the fate of soil organic carbon. / O objetivo do estudo foi avaliar a influ?ncia do manejo fitot?cnico e da cobertura vegetal do solo na biomassa microbiana e fra??es l?beis da mat?ria org?nica do solo (MOS), com a possibilidade de progn?stico sobre o destino do carbono org?nico do solo em um sistema integrado de produ??o agroecol?gica. Foram estudadas diferentes ?reas de lavoura sob cultivo org?nico de hortali?as (cultivo intensivo, cultivo m?nimo e cultivo rotacionado); ?reas de pastagens de Paspalum notatum (PAS); remanescentes florestais da Mata Atl?ntica (RMA); e ?reas degradadas (ADR). Tr?s amostras compostas de solo foram coletadas em cada ?rea a uma profundidade de 0-10 cm em Argissolo Vermelho-Amarelo. Em cada amostra determinou-se os teores de C e N associados ? BMS, C e N l?beis, fra??o leve livre e intra-agregado da MOS, respira??o microbiana, quociente microbiano e quociente metab?lico. Determinaram-se tamb?m as fra??es granulom?tricas areia, silte, argila, umidade gravim?trica, bem como os atributos qu?micos (Ca2+, Mg2+, P2O5, K+, C org?nico, N total, Al3+, CTC e pH em ?gua). A ?rea de pastagem apresentou o maior ac?mulo de carbono da biomassa microbiana do solo (BMS), com 384 mg C kg-1 solo, cerca de 35 % acima dos valores observados nos remanescentes florestais da Mata Atl?ntica, o que foi atribu?do ao intenso desenvolvimento e ciclagem do sistema radicular das gram?neas forrageiras na camada superior do solo, regi?o que ocorre maior concentra??o de microrganismos. Cerca de 2 % do total de Corg org?nico est? estocado na BMS nas ?reas de pastagens. A introdu??o de pr?ticas agr?colas no sistema de lavoura afetou consideravelmente os teores de BMS-C, apresentando redu??o m?dia de 30% com rela??o aos remanescentes florestais. O quociente metab?lico (qCO2) indicou perdas de C do solo para as ?reas manejadas com culturas agr?colas, e dentre os diferentes sistemas de cultivo agr?cola, maiores perdas de C foram observados nas ?reas manejadas com culturas de ciclo curto, com uso freq?ente de ara??o e gradagem, alertando para a procura de sistemas de manejo que minimizem o revolvimento do solo e priorizem a manuten??o da cobertura vegetal. A ?rea degradada foi o ambiente que mais contribuiu para a separa??o dos grupos de an?lise multivariada, mostrando ser a ?rea mais discrepante em rela??o ? atividade microbiana e teores de MOS. As vari?veis com maior peso na forma??o dos agrupamentos foram o teor de argila e a rela??o C/N microbiana, mostrando a import?ncia do uso da BMS e atributos granulom?tricos do solo na distin??o de diferentes sistemas de manejo fitot?cnico e cobertura vegetal do solo, ampliando a possibilidade de progn?stico sobre o destino do carbono org?nico do solo.

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.