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Droughts and other extreme precipitation events are predicted to increase in intensity, duration, and extent, with uncertain implications for terrestrial carbon (C) sequestration. Soil wetting from above (precipitation) results in a characteristically different pattern of pore-filling than wetting from below (groundwater), with larger, well-connected pores filling before finer pore spaces, unlike groundwater rise in which capillary forces saturate the finest pores first. Here we demonstrate that pore-scale wetting patterns interact with antecedent soil moisture conditions to alter pore-scale, core-scale, and field-scale C dynamics. Drought legacy and wetting direction are perhaps more important determinants of short-term C mineralization than current soil moisture content in these soils. Our results highlight that microbial access to C is not solely limited by physical protection, but also by drought or wetting-induced shifts in hydrologic connectivity. We argue that models should treat soil moisture within a three-dimensional framework emphasizing hydrologic conduits for C and resource diffusion. [ABSTRACT FROM AUTHOR]

Threats to biodiversity from increasing populations and poverty has resulted in the use of investments in livelihoods support activities as economic incentives for natural resource and biodiversity conservation in Ghana. Examples of such activities include woodlots, beekeeping, snail breeding, and mushroom farming. In order to assess and evaluate the effectiveness of these activities as tools for conservation planning and resource allocation, it is essential to document their use for environmental conservation. This study presents a consolidated documentation of the use of livelihoods support activities for natural resource and biodiversity conservation in Ghana. This documentation includes the specific activities, the number of such interventions since they were first used until 2010, their geographical distribution in the country, and implementation strategies. The methods used in this study include thematic and chronological analysis of conservation project reports, interviews with project managers, collection of primary data on the specific activities, and focus group discussions with participants of livelihoods support activities in rural Ghana. Seventy-one different types of livelihoods support activities belonging to eight categories have been employed for conservation in Ghana since 1993. The majority of these activities were based on non-timber forest products. A chronological trend analysis indicated an increasing tendency to make livelihoods support activities part of conservation projects in Ghana. These activities have become very relevant to Ghana’s current collaborative policy because they are used to buy-in local support for natural resource and biodiversity conservation. [ABSTRACT FROM PUBLISHER]

Disturbance affects most terrestrial ecosystems and has the potential to shape their responses to chronic environmental change., Scrub-oak vegetation regenerating from fire disturbance in subtropical Florida was exposed to experimentally elevated carbon dioxide ( CO2) concentration (+350 μl l−1) using open-top chambers for 11 yr, punctuated by hurricane disturbance in year 8. Here, we report the effects of elevated CO2 on aboveground and belowground net primary productivity ( NPP) and nitrogen ( N) cycling during this experiment., The stimulation of NPP and N uptake by elevated CO2 peaked within 2 yr after disturbance by fire and hurricane, when soil nutrient availability was high. The stimulation subsequently declined and disappeared, coincident with low soil nutrient availability and with a CO2-induced reduction in the N concentration of oak stems., These findings show that strong growth responses to elevated CO2 can be transient, are consistent with a progressively limited response to elevated CO2 interrupted by disturbance, and illustrate the importance of biogeochemical responses to extreme events in modulating ecosystem responses to global environmental change. [ABSTRACT FROM AUTHOR]

Uncertainty surrounds belowground plant responses to rising atmospheric CO2 because roots are difficult to measure, requiring frequent monitoring as a result of fine root dynamics and long-term monitoring as a result of sensitivity to resource availability., We report belowground plant responses of a scrub-oak ecosystem in Florida exposed to 11 yr of elevated atmospheric CO2 using open-top chambers. We measured fine root production, turnover and biomass using minirhizotrons, coarse root biomass using ground-penetrating radar and total root biomass using soil cores., Total root biomass was greater in elevated than in ambient plots, and the absolute difference was larger than the difference aboveground. Fine root biomass fluctuated by more than a factor of two, with no unidirectional temporal trend, whereas leaf biomass accumulated monotonically. Strong increases in fine root biomass with elevated CO2 occurred after fire and hurricane disturbance. Leaf biomass also exhibited stronger responses following hurricanes., Responses after fire and hurricanes suggest that disturbance promotes the growth responses of plants to elevated CO2. Increased resource availability associated with disturbance (nutrients, water, space) may facilitate greater responses of roots to elevated CO2. The disappearance of responses in fine roots suggests limits on the capacity of root systems to respond to CO2 enrichment. [ABSTRACT FROM AUTHOR]

This study reports the aboveground biomass response of a fire-regenerated Florida scrub-oak ecosystem exposed to elevated CO2 (1996–2007), from emergence after fire through canopy closure. Eleven years exposure to elevated CO2 caused a 67% increase in aboveground shoot biomass. Growth stimulation was sustained throughout the experiment; although there was significant variability between years. The absolute stimulation of aboveground biomass generally declined over time, reflecting increasing environmental limitations to long-term growth response. Extensive defoliation caused by hurricanes in September 2004 was followed by a strong increase in shoot density in 2005 that may have resulted from reopening the canopy and relocating nitrogen from leaves to the nutrient-poor soil. Biomass response to elevated CO2 was driven primarily by stimulation of growth of the dominant species, Quercus myrtifolia, while Quercus geminata, the other co-dominant oak, displayed no significant CO2 response. Aboveground growth also displayed interannual variation, which was correlated with total annual rainfall. The rainfall × CO2 interaction was partially masked at the community level by species-specific responses: elevated CO2 had an ameliorating effect on Q. myrtifolia growth under water stress. The results of this long-term study not only show that atmospheric CO2 concentration had a consistent stimulating effect on aboveground biomass production, but also showed that available water is the primary driver of interannual variation in shoot growth and that the long-term response to elevated CO2 may have been caused by other factors such as nutrient limitation and disturbance. [ABSTRACT FROM AUTHOR]

We report the results of a 2-year study of effects of the elevated (current ambient plus 350 μmol CO2 mol−1) atmospheric CO2 concentration ( Ca) on net ecosystem CO2 exchange ( NEE) of a scrub–oak ecosystem. The measurements were made in open-top chambers (OTCs) modified to function as open gas-exchange systems. The OTCs enclosed samples of the ecosystem (ca. 10 m2 surface area) that had regenerated after a fire, 5 years before, in either current ambient or elevated Ca. Throughout the study, elevated Ca increased maximum NEE ( NEEmax) and the apparent quantum yield of the NEE ( φNEE) during the photoperiod. The magnitude of the stimulation of NEEmax, expressed per unit ground area, was seasonal, rising from 50% in the winter to 180% in the summer. The key to this stimulation was effects of elevated Ca, and their interaction with the seasonal changes in the environment, on ecosystem leaf area index, photosynthesis and respiration. The separation of these factors was difficult. When expressed per unit leaf area the stimulation of the NEEmax ranged from 7% to 60%, with the increase being dependent on increasing soil water content ( Wsoil). At night, the CO2 effluxes from the ecosystem ( NEEnight) were on an average 39% higher in elevated Ca. However, the increase varied between 6% and 64%, and had no clear seasonality. The partitioning of NEEnight into its belowground ( Rbelow) and aboveground ( Rabove) components was carried out in the winter only. A 35% and 27% stimulation of NEEnight in December 1999 and 2000, respectively, was largely due to a 26% and 28% stimulation of Rbelow in the respective periods, because Rbelow constituted ca. 87% of NEEnight. The 37% and 42% stimulation of Rabove in December 1999 and 2000, respectively, was less than the 65% and 80% stimulation of the aboveground biomass by elevated Ca at these times. An increase in the relative amount of the aboveground biomass in woody tissue, combined with a decrease in the specific rate of stem respiration of the dominant species Quercus myrtifolia in elevated Ca, was responsible for this effect. Throughout this study, elevated Ca had a greater effect on carbon uptake than on carbon loss, in terms of both the absolute flux and relative stimulation. Consequently, for this scrub–oak ecosystem carbon sequestration was greater in the elevated Ca during this 2-year study period. [ABSTRACT FROM AUTHOR]

Abstract We report effects of elevated atmospheric CO2 concentration (C a ) on leaf area index (LAI) of a Florida scrub-oak ecosystem, which had regenerated after fire for between three and five years in open-top chambers (OTCs) and was yet to reach canopy closure. LAI was measured using four nondestructive methods, calibrated and tested in experiments performed in calibration plots near the OTCs. The four methods were: PAR transmission through the canopy, normalized difference vegetation index (NDVI), hemispherical photography, and allometric relationships between plant stem diameter and plant leaf area. Calibration experiments showed: (1) Leaf area index could be accurately determined from either PAR transmission through the canopy or hemispherical photography. For LAI determined from PAR transmission through the canopy, ecosystem light extinction coefficient (k ) varied with season and was best described as a function of PAR transmission through the canopy. (2) A negative exponential function described the relationship between NDVI and LAI; (3) Allometric relationships overestimated LAI. Throughout the two years of this study, LAI was always higher in elevated C a , rising from, 20% during winter, to 55% during summer. This seasonality was driven by a more rapid development of leaf area during the spring and a relatively greater loss of leaf area during the winter, in elevated C a . For this scrub-oak ecosystem prior to canopy closure, increased leaf area was an indirect mechanism by which ecosystem C uptake and canopy N content were increased in elevated C a . In addition, increased LAI decreased potential reductions in canopy transpiration from decreases in stomatal conductance in elevated C a . These findings have important implications for biogeochemical cycles of C, N and H2 O in woody ecosystems regenerating from disturbance in elevated C a . [ABSTRACT FROM AUTHOR]

AbstractThe effect of elevated atmospheric CO2 concentration (C a ) on the aboveground biomass of three oak species, Quercus myrtifolia , Q. geminata , and Q. chapmanii , was estimated nondestructively using allometric relationships between stem diameter and aboveground biomass after four years of experimental treatment in a naturally fire-regenerated scrub-oak ecosystem. After burning a stand of scrub-oak vegetation, re-growing plants were exposed to either current ambient (379 µL L-1 CO2 ) or elevated (704 µL L-1 CO2 ) C a in 16 open-top chambers over a four-year period, and measurements of stem diameter were carried out annually on all oak shoots within each chamber. Elevated C a significantly increased aboveground biomass, expressed either per unit ground area or per shoot; elevated C a had no effect on shoot density. The relative effect of elevated C a on aboveground biomass increased each year of the study from 44% (May 96–Jan 97), to 55% (Jan 97–Jan 98), 66% (Jan 98–Jan 99), and 75% (Jan 99–Jan 00). The effect of elevated C a was species specific: elevated C a significantly increased aboveground biomass of the dominant species, Q. myrtifolia , and tended to increase aboveground biomass of Q. chapmanii , but had no effect on aboveground biomass of the subdominant, Q. geminata . These results show that rising atmospheric CO2 has the potential to stimulate aboveground biomass production in ecosystems dominated by woody species, and that species-specific growth responses could, in the long term, alter the composition of the scrub-oak community. [ABSTRACT FROM AUTHOR]

SummaryWe report changes in nitrogen cycling in Florida scrub oak in response to elevated atmospheric CO2 during the first 14 months of experimental treatment. Elevated CO2 stimulated above-ground growth, nitrogen mass, and root nodule production of the nitrogen-fixing vine, Galactia elliottii Nuttall. During this period, elevated CO2 reduced rates of gross nitrogen mineralization in soil, and resulted in lower recovery of nitrate on resin lysimeters. Elevated CO2 did not alter nitrogen in the soil microbial biomass, but increased the specific rate of ammonium immobilization (NH4+ immobilized per unit microbial N) measured over a 24-h period. Increased carbon input to soil through greater root growth combined with a decrease in the quality of that carbon in elevated CO2 best explains these changes. These results demonstrate that atmospheric CO2 concentration influences both the internal cycling of nitrogen (mineralization, immobilization, and nitrification) as well as the processes that regulate total ecosystem nitrogen mass (nitrogen fixation and nitrate leaching) in Florida coastal scrub oak. If these changes in nitrogen cycling are sustained, they could cause long-term feedbacks to the growth responses of plants to elevated CO2. Greater nitrogen fixation and reduced leaching could stimulate nitrogen-limited plant growth by increasing the mass of labile nitrogen in the ecosystem. By contrast, reduced nitrogen mineralization and increased immobilization will restrict the supply rate of plant-available nitrogen, potentially reducing plant growth. Thus, the net feedback to plant growth will depend on the balance of these effects through time. [ABSTRACT FROM AUTHOR]

The article discusses a study on effects of elevated carbon dioxide on herbivore densities, herbivore feeding rates and levels of attack of herbivores by natural enemies. Topics discussed include decline in leafminer densities under elevated carbon dioxide, increase in leaf production under elevated carbon dioxide, increase in death rates of leafminers under elevated carbon dioxide due to reduced leaf quality and elevated levels of parasitism in leafminers due to big size of mines.

Abstract: Fine root dynamics play an important role in the cycling of carbon belowground. Previous studies have indicated that CO2 enrichment results in increased root productivity, mortality and relative turnover; however, our understanding of the duration and long-term trends of this effect are limited. Non-destructive minirhizotron observation tubes were used to measure effects of elevated CO2 on root dynamics and survivorship in a fire dominated scrub-oak ecosystem. Open-top chambers were exposed to elevated atmospheric CO2 for 10 years at Kennedy Space Center, Florida. In this study, initial fine root dynamics from an earlier published study from this experiment () were compared to our findings 5 years later. Significant increases in root productivity, mortality, and turnover due to CO2 enrichment were no longer present after 9 years of treatment. However, the vertical variation in these parameters suggests the upper 50cm of the soil are the most dynamic. A greater proportion of the fine roots were deeper in the soil profile later in the study, but no CO2 effect was observed. Survivorship analysis suggested the smallest fine roots (i.e. <0.1mm in diameter and <0.25mm in length) were most susceptible to mortality. In addition, increased root persistence was correlated with greater soil depth, suggesting that a nutrient and water limited scrub-oak ecosystem at root closure or carrying capacity produces larger, longer-lived fine roots at greater depths. Mean root diameter increased in the upper and lower portions of the soil profile. Seasonal cohort analysis implied that roots appearing in the spring and summer typically had the highest risk of mortality in the fall, although environmental factors influencing this relationship are not clear. The results from this study indicated that CO2 enrichment is no longer driving changes in fine root dynamics, but rather root closure in the upper portions of the soil profile seem to be the strongest influence. Fine roots comprise nearly 25% of the total plant biomass in the scrub-oak ecosystem and their turnover and persistence is an important pathway for carbon inputs into the soil. In order to develop accurate predictive models of the impacts of increasing anthropogenic CO2 on carbon cycling, it is imperative to examine long-term fine root dynamics rather than just shorter observations that could result in misleading conclusions regarding ecosystem responses. [Copyright &y& Elsevier]

Rising atmospheric carbon dioxide (C[suba]), a product of fossil fuel burning, land-use change, and cement manufacture, is expected to cause a large carbon sink in land ecosystems, partly mitigating human-driven climate change. As in many short-term experiments, the authors found that C[suba] enrichment increased nitrogen-fixation during the first year of treatment in an oak woodland. N-fixing plants are sensitive to light availability, so increased shading through greater leaf area could have been responsible for the declining response of N fixation to elevated C[suba].