Leaf phenology and freeze tolerance of the invasive shrub Amur honeysuckle and potential native competitors

The non-native invasive deciduous shrub Lonicera maackii causes a reduction in plant growth and species diversity under its canopy. The mechanisms of these effects are not fully understood, but an apparent difference between L. maackii and native shrub species is its extended leaf duration. We tested the hypothesis that L. maackii has a longer leaf duration than native shrub species found in the same habitats. Leaf phenology of L. maackii and the native deciduous shrubs Asimina triloba and Lindera benzoin was observed at four sites in central Kentucky (USA) from March until December, 2007. Additionally, a late spring freeze allowed for examination of freeze tolerance among the three test species. Lonicera maackii leaf development was two to three weeks earlier than the natives in March and early April. A hard freeze in early April caused significant (P \u3c 0.05) leaf mortality to both of the native species (60–100% leaf mortality at 3 of 4 sites) while L. maackii showed no observable damage. L. maackii had a later transition to fall color and leaf abscission than the native species, which were at a significantly later stage of development (closer to leaf abscission) for a period of four to six weeks. These data suggest two advantages for L. maackii over potential native competitors: 1) greater access to carbon via a longer leaf duration, and 2) a greater capacity to withstand freezing temperatures

Reservoir Water-Level Drawdowns Accelerate and Amplify Methane Emission

Water-level fluctuations due to reservoir management could substantially affect the timing and magnitude of reservoir methane (CH4) fluxes to the atmosphere. However, effects of such fluctuations on CH4 emissions have received limited attention. Here we examine CH4 emission dynamics in six Pacific Northwest U.S. reservoirs of varying trophic status, morphometry, and management regimes. In these systems, we show that water-level drawdowns can, at least temporarily, greatly increase per-area reservoir CH4 fluxes to the atmosphere, and can account for more than 90% of annual reservoir CH4 flux in a period of just a few weeks. Reservoirs with higher epilimnetic [chlorophyll a] experienced larger increases in CH4 emission in response to drawdown (R2 = 0.84, p < 0.01), suggesting that eutrophication magnifies the effect of drawdown on CH4 emission. We show that drawdowns as small as 0.5 m can stimulate ebullition events. Given that drawdown events of this magnitude are quite common in reservoirs, our results suggest that this process must be considered in sampling strategies designed to characterize total CH4 fluxes from reservoirs. The extent to which (and the mechanisms by which) drawdowns short-circuit connections between methanogenesis and methanotrophy, thereby increasing net CH4 fluxes to the atmosphere, should be a focus of future work

Effects of an Experimental Water-level Drawdown on Methane Emissions from a Eutrophic Reservoir

Reservoirs are a globally significant source of methane (CH 4 ) to the atmosphere. However, emission rate estimates may be biased low due to inadequate monitoring during brief periods of elevated emission rates (that is, hot moments). Here we investigate CH 4 bubbling (that is, ebullition) during periods of falling water levels in a eutrophic reservoir in the Midwestern USA. We hypothesized that periods of water-level decline trigger the release of CH 4 -rich bubbles from the sediments and that these emissions constitute a substantial fraction of the annual CH 4 flux. We explored this hypothesis by monitoring CH 4 ebullition in a eutrophic reservoir over a 7-month period, which included an experimental water-level drawdown. We found that the ebullitive CH 4 flux rate was among the highest ever reported for a reservoir (mean = 32.3 mg CH 4 m −2 h −1 ). The already high ebullitive flux rates increased by factors of 1.4–77 across the nine monitoring sites during the 24-h experimental water-level drawdown, but these emissions constituted only 3% of the CH 4 flux during the 7-month monitoring period due to the naturally high ebullitive CH 4 flux rates that persist throughout the warm weather season. Although drawdown emissions were found to be a minor component of annual CH 4 emissions in this reservoir, our findings demonstrate a link between water-level change and CH 4 ebullition, suggesting that CH 4 emissions may be mitigated through water-level management in some reservoirs