Prospects for high-resolution microwave spectroscopy of methanol in a Stark-deflected molecular beam

Recently, the extremely sensitive torsion-rotation transitions in methanol have been used to set a tight constraint on a possible variation of the proton-to-electron mass ratio over cosmological time scales. In order to improve this constraint, laboratory data of increased accuracy will be required. Here, we explore the possibility for performing high-resolution spectroscopy on methanol in a Stark-deflected molecular beam. We have calculated the Stark shift of the lower rotational levels in the ground torsion-vibrational state of CH3OH and CD3OH molecules, and have used this to simulate trajectories through a typical molecular beam resonance setup. Furthermore, we have determined the efficiency of non-resonant multi-photon ionization of methanol molecules using a femtosecond laser pulse. The described setup is in principle suited to measure microwave transitions in CH3OH at an accuracy below 10^{-8}

The demography of fine roots in response to patches of water and nitrogen

Fine root demography was quantified in response to patches of increased water and nitrogen availability in a natural, second-growth, mixed hardwood forest in northern Michigan, USA. As expected, the addition of water and water plus nitrogen resulted in a significant overall increase in the production of new fine roots. New root production was much greater in response to water plus nitrogen when compared with water alone, and the duration of new root production was related to the length of resource addition in the water plus nitrogen treatments; the average difference in new root length between the 20 vs. 40 d additions of water plus nitrogen amounted to almost 600%. Roots produced in response to the additions of water and water plus nitrogen lived longer than roots in the control treatments. Thus, additions of water and water plus nitrogen influenced both the proliferation of new roots and their longevity, with both proliferation and longevity related to the type and duration of resource supply. Results suggest that root longevity and mortality may be plastic in response to changes in soil resource availability, as is well known for root proliferation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65770/1/j.1469-8137.1993.tb03905.x.pd

The relationship between fine root demography and the soil environment in northern hardwood forests

We used minirhizotrons to measure growing-season fine root dynamics at 0-30 and 50-100 cm depths in two northern hardwoods forests. Concomitant measurements of several soil and site environmental variables were also made. We then used regression models to quantify the relationships between these environmental variables and fine root demography. Generally, environmental factors had a moderate effect on broad, inherent phenological patterns of root activity and abundance. For example, both shallow fine root length density and potential evapotranspiration reached their maximum in mid-summer, but the relationship between the two was not strong at either site (R2 = 0.12). Deep root length density was not significantly related to any measured environmental factor. Periods of high water demand during which soil moisture was also abundant (i.e., late spring and early summer) were related to increased shallow root production. Root length mortality was low at these times, but the correlation with soil moisture was statistically significant only in the shallow depth increment. Quantifying the relative importance of the environment on root growth in large field studies like ours is complicated by a number of factors. These include the difficulty of intensive sampling, interactive effects of environmental factors, and the uncertainty of encountering environmental conditions sufficiently severe to elicit a measurable root response during the study period

Regulation of fine root dynamics by mammalian browsers in early successional Alaskan taiga forests.

Abstract. The effects of browsing by moose and snowshoe hares on fine root production, mortality, and decomposition in early successional forest ecosystems along the Tanana River floodplain in interior Alaska were studied over a 3-yr period using minirhizotrons placed inside and outside large permanent exclosures. Fine root production and mortality varied seasonally, with greatest rates of production occurring during June each year, and greatest rates of mortality occurring in fall and over winter. Annual production and mortality during 1993, a year of unusually low precipitation, were significantly higher than during either 1992 or 1994. Aboveground herbivory significantly reduced monthly rates of fine root production, and on an annual basis, fine root production of browsed plots (311.4 Ϯ 31.7 mm·tube Ϫ1 ·yr Ϫ1 ) was significantly less than that of unbrowsed plots (453.8 Ϯ 49.8 mm·tube Ϫ1 ·yr Ϫ1 ) when averaged over 3 yr. Because herbivory had less of an effect on monthly or annual rates of fine root mortality, fine root turnover was higher for browsed stands. Browsed plants had a higher percentage of annual production in surface soil layers. Production on all plots shifted to deeper soil layers as the growing season progressed; this shift occurred deeper in the profile for unbrowsed plants than for browsed plants. We used a parameter estimation program (Program MARK) to generate fine root survival and decomposition estimates from models testing the direct and interactive effects of time period, cohort (i.e., when the root first appeared) age of the root, browsing, and site on fine root longevity and decomposability. Cohort effects showed that survival of fine roots was greatest for roots that first appeared in May, and that survival progressively declined for roots first appearing during subsequent time periods, while age-based estimates showed a rapid decline in survival over the interval following first appearance. Survival and decomposition estimates were inversely correlated within a growing season, with the lowest survival but highest decomposition occurring over winter. Two-factor models indicated that time-dependent survival and decomposition rates of fine roots differed significantly between browsed and unbrowsed stands, among the 10 fine root age groups, and among the three study sites. Browsing significantly reduced fine root survival, but this effect varied among sites. Fine root decomposition rates were consistently lower (Ϫ21%) in browsed stands. Two important features distinguish fine root dynamics in our stands from temperate and more southerly boreal ecosystems: (1) low overwinter survival of fine roots, and (2) a substantial time lag between leaf-out and maximum fine root growth, suggesting greater reliance on aboveground stores for spring regrowth. Herbivores appear to play an important role in linking these two events, first by exacerbating overwinter mortality, and second by consuming a substantial amount of aboveground stores. Thus, not only do herbivores have pronounced direct effects on carbon and nutrient cycling processes, but climatically driven effects on fine root processes may be linked with herbivory in complex ways that define fundamental latitudinal patterns in plant growth and allocation to defense against herbivory