Proper assessment of environmental quality or degradation requires knowledge of how terrestrial C pools respond to land use change. Forest plantations offer a considerable potential to sequester C in aboveground biomass. However, their impact on initial levels of soil organic carbon (SOC) varies from strong losses to gains, possibly affecting C balances in afforestation or reforestation initiatives. We compiled paired‐plot studies on how SOC stocks under native vegetation change after planting fast‐growth Eucalyptus species in Brazil, where these plantations are becoming increasingly important. SOC changes for the 0–20 and 0–40 cm depths varied between −25 and 42 Mg ha−1, following a normal distribution centered near zero. After replacing native vegetation by Eucalyptus plantations, mean SOC changes were −1·5 and 0·3 Mg ha−1 for the 0–20 and 0–40 cm depths, respectively. These are very low figures in comparison to C stocks usually sequestered in aboveground biomass and were statistically nonsignificant as demonstrated by a t‐test at p < 0·05. Similar low, nonsignificant SOC changes were estimated after data were stratified into first or second rotation cycles, soil texture and biome (savanna, rainforest or grassland). Although strong SOC losses or gains effectively occurred in some cases, their underpinning causes could not be generally identified in the present work and must be ascribed in a case basis, considering the full set of environmental and management conditions. We conclude that Eucalyptus spp. plantations in average have no net effect on SOC stocks in Brazil. Copyright © 2012 John Wiley & Sons, Ltd.

Specimens of Populus nigra L. cv. Loenen exhibit premature leaf senescence when exposed for a few weeks to realistic air pollution. In this study, the changes in levels of foliar carbohydrates and myo-inositol (MI) due to 30 ± 1 nL/L O3 + 12 ± 1 nL/L SO2 from the onset of exposure to the occurrence of premature abscission is presented. Petioles and laminae of the 12 oldest leaves were separately analysed on days 0, 4, 8, 12, 16, 20, 22, and 32 of continuous exposure, which was performed in open-top chambers (OTC). On days 8 to 12, clearly prior to yellowing (starting on day 22), total nonstructural carbohydrates (TNC; starch + raffinose + sucrose + glucose + fructose + MI) in the fumigated laminae exceeded that in controls by about 30%. This increase was due to higher amounts of different soluble forms, while starch remained unaltered. From day 20 onwards, the level of TNC in the fumigated laminae progressively fell below that in controls. This decrease was due to a progressive decline in starch, which had started on day 16 and was dominating, although glucose and raffinose increased significantly. In the petioles, starch, sucrose, and glucose decreased because of fumigation with the occurrence of leaf yellowing, while raffinose increased. In contrast, MI in the petioles progressively accumulated directly on exposure until leaf yellowing occurred. The results are discussed in terms of the "general adaption syndrome" of H. Selye (1936. Nature (London), 138: 32). The marked MI response in petioles is concluded to be an early indication of phytorelevant O3 + SO2 pollution. Keywords: air pollution, carbohydrates, myo-inositol, pigments, Populus nigra L., senescence, stress.

The expansion of short rotation eucalypt plantations in low soil organic matter (SOM) sandy soils may offer an alternative to improve soil C sequestration. The goal of this study was to estimate the changes in C stocks and emissions in different SOM fractions following conversion of the native Cerrado to pasture and then to eucalypt plantation. Therefore, we studied soils under native Cerrado, planted pasture (cultivated for 34years following the clearing of the Cerrado) and eucalypt plantation (4years). The C and N stocks in particulate organic matter and mineral‐associated organic matter (MAOM) were determined 4years after eucalypt planting. Soil CO2‐C, CH4‐C fluxes and CO2‐C concentrations in soil profile were measured in different seasons over 4years. Variation in the natural abundance of 13C was used to partition the SOM‐C. The soil CO2‐C and CH4‐C fluxes were influenced by soil surface moisture (r= 0.185o and r= 0.430**, respectively), whereas only the soil CH4‐C fluxes correlated with soil surface temperature (r= 0.355**). The highest soil CO2‐C flux in soil under eucalypt occurred after 4years of eucalypt planting (2.5 kg ha−1h−1, approximately 70%). The pasture soil acted as a CH4‐C source to the atmosphere. The pasture MAOM‐C losses in the 0.0–1.0‐m soil layers were not compensated by the new eucalypt C inputs (MAOM‐C lost ~9.6 Mg ha−1). In summary, the recent worldwide expansion of short rotation eucalypt plantations should be carefully considered, particularly under pasture degraded soil sandy soils, because land uses able to increase SOM are priorities.

Eucalyptus forests stand out for their potential to sequestrate atmospheric CO 2 in soil organic matter throughout their growth. Our study evaluated the harvesting and tillage effect in eucalyptus plantations to the soil CO 2 , 13 C-CO 2 , and CH 4 fluxes. This study was carried out in a eucalyptus plantation, on Typic Haplustox soil. The study used stands cultivated with eucalyptus at the end of the first rotation (7 years), established over degraded pastures. The effect of harvesting was assessed through comparisons of samples taken before and after harvesting with Feller + Skidder (F + S) and Harvester + Forwarder (H + F) methods and separate samples of plant rows (R) and plant interrows (IR). The effect of tillage was assessed through comparisons of R and IR samples taken before and after subsoiling tillage in areas harvested with F + S and H + F methods. A nested experimental design was used with eight replicates. The harvest operation (F + S and H + F methods) in eucalyptus plantationsincreased soil CO 2 fluxes, which were primarily derived from eucalyptus materials ('new C'). The F + S harvesting method resulted in the highest soil density and soil moisture reduction in the IR. The tillage operation (subsoiling) resulted in higher soil CO 2 fluxes in eucalyptus plantations harvest with F + S and H + F methods. However, the H + F method preserved the older soil organic carbon (40.8% in R and 50.4% IR of C 4 -CO 2 ). The soil in the eucalyptus plantations showed soil CH 4 influxes, and the harvest and tillage (subsoiling) operations did not negatively affect the net soil CH 4 influx in the studied eucalyptus plantations.

This study aimed: i) to evaluate the influence of fertilization and irrigation management on eucalyptus plantations for soil carbon (C) dynamics; ii) to evaluate the impact of fertilization and irrigation management on eucalyptus plantations in the C allocation in depth compared to the Cerrado biome. This study was carried out in an eucalyptus plantation at the end of the third rotation (7 years), which received different fertilizations and irrigations, and a Cerrado area was used as reference. Soil samples were collected in trenches and the gases (CO 2 and CH 4) on the surface. The total organic carbon (TOC) is more influenced by the availability of water than nutrients. Soils under eucalyptus stands are more efficient at C stocks in depth than the Cerrado and act as a liquid drain of CO 2 and CH 4 from the atmosphere.