Degradation of soil properties following deforestation and long-term soil cultivation may lead to decreases in soil microbial diversity and functional stability. In this study, we investigated the differences in the stability (resistance and resilience) of microbial community composition and enzyme activities in adjacent soils under either native tropical forest (FST) or in agricultural cropping use for 14 years (AGR). Mineral soil samples (0 to 5 cm) from both areas were incubated at 40 degrees C, 50 degrees C, 60 degrees C, or 70 degrees C for 15 min in order to successively reduce the microbial biomass. Three and 30 days after the heat shocks, fluorescein diacetate (FDA) hydrolysis, cellulase and laccase activities, and phospholipid-derived fatty acids-based microbial community composition were measured. Microbial biomass was reduced up to 25% in both soils 3 days after the heat shocks. The higher initial values of microbial biomass, enzyme activity, total and particulate soil organic carbon, and aggregate stability in the FST soil coincided with higher enzymatic stability after heat shocks. FDA hydrolysis activity was less affected (more resistance) and cellulase and laccase activities recovered more rapidly (more resilience) in the FST soil relative to the AGR counterpart. In the AGR soil, laccase activity did not show resilience to any heat shock level up to 30 days after the disturbance. Within each soil type, the microbial community composition did not differ between heat shock and control samples at day 3. However, at day 30, FST soil samples treated at 60 degrees C and 70 degrees C contained a microbial community significantly different from the control and with lower biomass regardless of high enzyme resilience. Results of this study show that deforestation followed by long-term cultivation changed microbial community composition and had differential effects on microbial functional stability. Both soils displayed similar resilience to FDA hydrolysis, a composite measure of a broad range of hydrolases, supporting the concept of high functional redundancy in soil microbial communities. In contrast, the resilience of the substrate-specific activities of laccase and cellulase were lower in AGR soils, indicating a less diverse community of microorganisms capable of producing these enzymes and confirming that specific microbial functions are more sensitive measurements for evaluating change in the ecological stability of soils.

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Resumo -O objetivo deste trabalho foi avaliar o impacto de plantios fl orestais nos atributos físicos, químicos e biológicos de um Latossolo Vermelho-Amarelo de cerrado. Amostras de solo foram coletadas à profundidade de 0 a 10 cm, em áreas cultivadas há mais de 20 anos com pínus (Pinus tecunumanii), eucalipto (Eucalyptus grandis) ou carvoeiro (Sclerolobium paniculatum). Uma área adjacente de cerrado nativo foi incluída como referência do solo original. Foram observados, em relação ao cerrado, aumentos na densidade do solo sob pínus e eucalipto, redução na macroporosidade sob pínus, menores teores de matéria orgânica sob pínus e eucalipto, além de decréscimos no pH e na saturação por bases e incremento da saturação por alumínio nos cultivos com pínus e carvoeiro. O carbono da biomassa microbiana sob pínus, eucalipto e carvoeiro foi aproximadamente a metade do carbono sob cerrado. Atividades de fosfatase ácida e arilsulfatase foram inibidas pelo pínus e estimuladas pelo carvoeiro. Entre os refl orestamentos avaliados, o pínus promoveu a redução mais acentuada da qualidade do solo de cerrado. As variáveis microbiológicas foram as mais sensíveis em detectar o efeito dos diferentes refl orestamentos na qualidade do solo.Termos para indexação: Eucalyptus grandis, Pinus tecunumanii, Sclerolobium paniculatum, carbono da biomassa microbiana, enzimas do solo, qualidade do solo. Physical, chemical and biological attributes of a cerrado Oxisol under different forest speciesAbstract -The objective of this study was to evaluate the impact of forest plantations on the physical, chemical and microbiological attributes of a cerrado Oxisol. Soil samples were collected at 0-10 cm depth from sites cultivated with pinus (Pinus tecunumanii), eucalyptus (Eucalyptus grandis) and carvoeiro (Sclerolobium paniculatum) for over 20 years. An adjacent native cerrado area was used as a reference of the original soil conditions. It was observed in relation to the native cerrado: increases in soil density under pinus and eucalyptus, reduction in the macroporosity under pinus, lower organic matter contents under pinus and eucalyptus, besides decreases in the soil pH and in the base saturation under pinus and carvoeiro along with an increase in aluminum saturation. Soil microbial biomass carbon under the pinus, eucalyptus and carvoeiro sites was about half of that found under cerrado. The activities of acid phosphatase and arylsulfatase were inhibited by pinus and stimulated by carvoeiro. Among the forest systems evaluated, pinus promoted the greatest reduction on soil quality. The microbiological variables were the most sensitive to detect the effects of these systems on soil quality.

RESUMO -O objetivo deste trabalho foi avaliar a fitomassa de calopogônio, mucuna-preta, mucunarajada, feijão-de-porco, guandu de porte alto, Crotalaria spectabilis e C. breviflora sob diferentes densidades de semeadura (10, 20, 40, 80 e 160 sementes viáveis m -2), e o crescimento de plantas daninhas nessas densidades, em área de tabuleiros costeiros. O experimento foi desenvolvido de maio a agosto de 1996, no Campo Experimental "Antônio Martins" (EMDAGRO/Embrapa-CPATC), em Lagarto, SE. O número de plantas vivas na floração (NPVF) e a matéria seca da parte aérea das leguminosas (MSPA) foram determinados quando, em cada espécie, cerca de 50% das plantas floresceram. Maiores incrementos de MSPA, em resposta ao adensamento populacional, foram observados em C. spectabilis e C. breviflora, seguidas pelo calopogônio, mucuna-preta e mucuna-rajada. Em relação ao feijão-de-porco, a resposta foi negativa, enquanto com o guandu não houve influência. Quanto ao NPVF, as respostas ao adensamento foram lineares e positivas em C. spectabilis, C. breviflora e calopogônio, e quadráticas com ponto de máxima em feijão-de-porco, guandu e mucuna-rajada. Embora nenhum modelo tenha sido ajustado para expressar a relação entre NPVF e adensamento na semeadura de mucuna-preta, a sobrevivência dessa espécie foi reduzida em todas as densidades. Maiores inibições de plantas daninhas ocorreram nas parcelas de mucuna-preta e feijão-de-porco.Termos para indexação: culturas de cobertura, manejo do solo, competição, agricultura sustentável. DRY MATTER OF GREEN MANURE AND CONTROL OF WEEDSAT DIFFERENT SOWING LEGUME DENSITIES ABSTRACT -The objective of this study was to evaluate the dry matter yields of Calopogonium mucunoides, Stizolobium aterrimum, Stizolobium deeringeanum variety "rajada", Canavalia ensiformis, Cajanus cajan, Crotalaria breviflora and C. spectabilis in relation to the sowing densities of 10, 20, 40, 80 and 160 seeds m -2, and the yield of weeds grown in these legume densities. This study was carried out from May to August 1996, in a coastal tableland area of the Antonio Martins Experimental Station (EMDAGRO/Embrapa-CPATC), at Lagarto, State of Sergipe, Brazil. The number of survival plants and the dry matter yields were determined when each species reached the flowering stage. The highest increments of dry matter yield in response to increasing levels of sowing density were observed in plants of Crotalaria spectabilis and C. breviflora followed by C. mucunoides, S. aterrimum and S. deeringeanum. A negative response to the increasing sowing densities was observed in Canavalia ensiformis and sowing densities did not affect the dry matter yield of Cajanus cajan plants. Linear and positive responses of C. spectabilis, C. breviflora and C. mucunoides, and quadratic responses of C. ensiformis, C. cajan and S. deeringeanum were obtained for number of plants in response to increasing sowing density. No equations were found to express the relation between the number of survival plants and sowing densities of S. aterrimum, but the survival ...

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Glyphosate, a broad-spectrum herbicide used for the non-selective control of weeds, inhibits 5enolpyruvylshikimate-3-phosphate synthase, a key enzyme in the synthesis of aromatic amino acids in the shikimic acid pathway in plants, fungi and bacteria, thus impairing the synthesis of proteins required for various life processes. Soybean genetically engineered to be glyphosate resistant (GR or Roundup Ready, RR) represents the most cultivated transgenic crop globally, including Brazil. There are concerns about the effects of RR transgenic soybean and of glyphosate on soil microbial communities and their functioning. Our study was designed to detect changes in soil microbial biomass-carbon (MB-C) and-nitrogen (MB-N) and in enzyme activities [beta-glucosidase (GLU) and acid phosphatase (PHO)] in a large set of field trials performed at six sites in Brazil for two cropping seasons. We evaluated the effects of the RR transgene, glyphosate and weed management (RR soybean + glyphosate vs. conventional soybean + conventional herbicides), with three pairs of nearly isogenic soybean cultivars evaluated per site. Soils were sampled from the 0-10 cm layer, between cropped lines, during the cropping seasons 2004/2005 and 2005/2006, at the R2 stage of soybean growth. Univariate and contrast analyses were performed in addition to multivariate analyses including all four microbial variables, and denominated as soil microbial variables (SMV). In general, microbial parameters and SMV were not affected by the transgene, type of herbicide or weed management. Differences were, rather, related to site, cropping season and cultivar.

All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. T he e ects of land use change and agriculture practices on the composition and diversity of soil microbial communities have been demonstrated using both genetic and physiological techniques. Buckley and Schmidt (2001) showed that elds sharing a history of cultivation possessed di erent T-RFLP pro les, and reduced diversity of rRNA genes associated with α-Proteobacteria, β-Proteobacteria, and Actinobacteria compared with uncultivated elds. Microbial community structure also di ered between cultivated and uncultivated soils based on PLFA analysis (Bossio et al., 2005). Soils that were tilled (Lupwayi et al., 1998) or converted from native vegetation to agriculture (Gomez et al., 2000, 2004; Nsabimana et al., 2004) presented di erent CLPP, and reduced physiological diversity. Despite these well established facts, it remains unclear what delineates a situation where a soil community makes physiological adjustments to environmental disturbance without undergoing community composition change, from one where there is a concomitant community shi (Schimel et al., 2007). Furthermore, it is unknown to what extent a shi in community composition results in greater community resistance to further abuse and buffers against further shi s in composition. In most situations the ability to make this type of association would have been impaired because the responses of microbial communities to treatments might have been in uenced by non-edaphic factors. For example, Yan et al. (2000) associated the reduced physiological diversity of cultivated vertisols assessed by the CLPP method with reduced soil organic C compared with uncultivated vertisols. However, this di erence could also be the result of other factors in uencing soil microbial diversity, such as the history of chemical applications to cultivated elds in the form of fertilizer, insecticides, and herbicides, and higher plant diversity in the uncultivated sites. In another study, the evaluation of a grassland restoration