O uso de resíduos vegetais carbonizados vem sendo resgatado e avaliado como alternativa para melhorar a qualidade do solo. O material gerado, denominado biocarvão, é o produto formado a partir da pirólise, que é a alteração térmica da biomassa em ambiente fechado, com suprimento limitado de oxigênio e em temperaturas relativamente baixas. A composição química e estrutural do biocarvão é altamente heterogênea, mas o pH é normalmente maior que sete. Algumas propriedades estão presentes em todos os biocarvões, incluindo alto teor de carbono e grau de aromaticidade, o que explica seu alto nível de recalcitrância. Contudo, a exata composição química e estrutural é dependente da combinação da matéria-prima e das condições de pirólise. Quando aplicado ao solo, o biocarvão pode aumentar o pH, a capacidade de troca de cátions, o teor de carbono orgânico e a disponibilidade de nutrientes; alterar a abundância e funcionamento de fungos micorrízicos e prover refúgio para microrganismos nos microporos do biocarvão; e melhorar a estrutura do solo e disponibilidade de água. Todas estas características de interação com o solo fazem com que a sua utilização no meio agrícola apresente normalmente efeitos positivos para o crescimento vegetal. Acredita-se também que a utilização de biocarvão possa contribuir para o sequestro de carbono, sendo considerado por muitos como “carbono negativo”, devido a sua capacidade de promover o crescimento vegetal e pela sua estabilidade no solo. Estudos com o biocarvão já atingiram proporções de escala mundial envolvendo diversas áreas e têm crescido muito nos últimos anos. No entanto, ainda existem muitas incertezas sobre a sua utilização na agricultura, devido principalmente ao fato de que os trabalhos publicados têm dado mais atenção a sua capacidade de manutenção e melhoria da fertilidade do solo e aumento da produtividade agrícola do que esclarecimentos dos possíveis riscos envolvidos na utilização do biocarvão.

& Key message In loblolly pine land use of 17-32 years following forest clearing, CH 4 consumption and N 2 O emission diminished by 17 years, due to high soil moisture (~80% WFPS, N 2 O into N 2), but increased by 32 years, where medium moisture favoured methanotrophy and denitrification into N 2 O. Soil greenhouse gases (GHG) emission was positive by 17 years, but negative by 32, when soil sequestered carbon. & Context Much of the role of planted forests in the gaseous soil-atmosphere exchanges in the subtropics remains to be evaluated. & Aims To assess the impacts of loblolly pine (Pinus taeda L.) on soil nitrous oxide (N 2 O) and methane (CH 4) fluxes in a subtropical Cambisol. & Methods Fluxes were monitored over 1 year with static chambers, in forest stands under natural forest (NF) and pine plantation for 17 (P17) and 32 years (P32). & Results The NF soil showed the lowest N 2 O emission and the highest CH 4 consumption, because of the lowest water-filled pore space (WFPS, < 40%) and highest soil macroporosity. In P17, N 2 O emission was still low, but CH 4 consumption diminished sixfold, possibly because of the predominance of methanotrophy, favoured by the highest WFPS (~80%) and lowest macroporosity that together with low mineral N concentration also did not favour the formation of N 2 O. In P32, the improved soil mineral N, macroporosity and intermediate WFPS (~60%) increased CH 4 consumption and also N 2 O emission, in an environment supposedly favourable to methanotrophy and also to N 2 O production. Considering soil organic carbon (SOC) from a concurrent study, the net GHG emission (Mg C eq ha −1 year −1

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RESUMOO objetivo deste trabalho foi investigar a influência da variação de temperatura foliar associada à suspensão de irrigação sobre as trocas gasosas de plantas jovens de taxi-branco (Sclerolobium paniculatum Vogel). O estudo foi realizado em casa de vegetação na área experimental da Embrapa Amazônia Ocidental. As plantas cresceram em casa de vegetação e depois de quatro meses de aclimatização foram submetidas a três regimes hídricos (mantidas irrigadas até a capacidade de campo do solo, irrigação suspensa por oito e 14 dias). Foram avaliados os parâmetros fisiológicos de trocas gasosas, taxa de assimilação líquida de CO 2 (A), transpiração foliar (E), condutância estomática (g s ) e eficiência no uso da água (EUA) os quais foram obtidos por meio do medidor portátil de fotossíntese (CI-340, CID, Inc.). Os resultados mostraram que houve redução das taxas de assimilação líquida de CO 2 em função da elevação da temperatura foliar e da suspensão da irrigação. Após oito dias de suspensão da irrigação houve redução das taxas de assimilação líquida de CO 2 fotossintéticas em 62, 65, 75, 58, 50 e 64% e aos 14 dias esta redução foi de 80, 85, 85, 84, 86 e 93% em comparação as plantas mantidas irrigadas, nas temperaturas de 25, 30, 35, 40, 45 e 50°C, respectivamente. O comportamento das taxas de transpiração foliar foi inversamente proporcional às taxas de fotossíntese líquida, mostrando incremento em função do aumento da temperatura foliar. O comportamento fisiológico de trocas gasosas de Sclerolobium paniculatum apresentou variações tanto em relação ao efeito da temperatura foliar, quanto da suspensão de irrigação. Palavras-chave: Sclerolobium paniculatum; fotossíntese; estresse hídrico. ABSTRACTThe study aimed to investigate the influence of leaf temperature variation associated with irrigation suspension on gas exchange of seedlings of Sclerolobium paniculatum Vogel. The study was carried out in a greenhouse at experimental area of Embrapa, Amazônia Ocidental. Plants were grown in a greenhouse and, after four months were subjected to three treatments (irrigated maintained until the field capacity, irrigation suspended for eight and 14 days). We evaluated the physiological parameters of gas exchange, net assimilation rate of CO 2 (A), leaf transpiration (E), stomatal conductance (g s ) and water use efficiency (WUE) which were obtained through a photosynthesis portable meter (CI-340, CID, Inc). The results showed reduction of net assimilation rate of CO 2 depending on the elevation of the leaf temperature and without irrigation. After eight days without irrigation, decreased rates of photosynthetic assimilation of CO 2 in 62, 65, 75, 58, 50 and 64%, and after 14 days the reduction was 80, 85, 85, 84, 86 and 93% compared to plants irrigated maintained at temperatures of 25, 30, 35, 40, 45 and 50 °C, respectively. The leaf transpiration was inversely proportional to rates of net photosynthetic assimilation of CO 2 , which has increased with an increased leaf temperature. The physiological behavior of gas exchange of ...

Quantifying soil organic carbon (SOC) inputs in the surface soil is a critical component for assessing the potential for carbon sequestration of managed pine forests. This study used a sequential exclusion of aboveground litter inputs (L, litter exclusion) and aboveground plus belowground inputs (LR, litter and root exclusion) to segregate carbon sources contributing to the development and maintenance of SOC in the surface soil supporting juvenile loblolly pine (Pinus taeda L.) in its rapid growth phase. The study spanned the 7th to 10th year of stand growth. Soil physical size fractions (>2 mm, ≤2 mm, 2000–250 μm, 250–150 μm, 150–53 μm, and <53 μm) were used to investigate the change in native SOC over time in the untreated control plots (UC, untreated control) and the effects of exclusion treatments. An accretion rate of 4.6 Mg SOC·ha−1 of soil·year−1 was observed in the fine earth fraction (≤2 mm), reflecting the rapid phase of stand growth. The accretion was primarily observed in the upper 10 cm of the soil. Treatment effects were most apparent in soil bulk density, SOC of the fine earth, and 150–53 μm size fractions. In general, changes in SOC observed in the L treatment was an intermediate increase between the UC and LR treatments, where only the removal of roots provided no change in SOC and was significantly different from the control (p = 0.05). We conclude that a major contributor to the maintenance and increase of SOC in this fast-growing pine ecosystem was due to root turnover (60%), with 40% due to aboveground litter inputs.

Although Eucalyptus is the most commonly cultivated genus in Brazil, more information is needed on how these forests can act as a sink for greenhouse gases. This study assessed the potential greenhouse gas (GHG) mitigation of eucalyptus forests by quantifying both the seasonal rates of exchange of methane (CH4) and nitrous oxide (N2O) gases at the soil–atmosphere interface and their relationships with soil variables (moisture, temperature and physicochemical attributes). Soil organic carbon sequestration rate was used together with soil GHG emission to estimate net global warming potential. This study was conducted at an experimental forestry station in the south-central region of the state of São Paulo, Brazil. No differences were found between treatments in the seasonal fluxes of N2O and CH4, which may have resulted from similar soil properties, particularly bulk density and nitrate (NO3−) contents. CH4 flux dynamics were mainly controlled by the concentrations of ammonium (NH4+) in the soil. In all treatments, the soil acted as a continuous sink for CH4, absorbing it at an average rate of −65 μg C m−2 h−1, which was higher than the results of other studies conducted in native areas of the Cerrado biome and planted forests. However, although CH4 removal helped offset greenhouse gas emissions, net emissions were seen in most treatments due to N2O emissions in greater magnitude and soil carbon losses.

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