Functional traits of expanding, thicket-forming shrubs: contrasting strategies between exotic and native species

Woody expansion has been documented for decades in many different systems globally, often yielding vast changes in ecosystem functioning. While causes and consequences of woody expansion have been well documented, few studies have addressed plant functional traits that promote dramatic and rapid expansion in range. Our objectives were to investigate plant functional traits that contribute to the colonization, rapid expansion, and thicket formation of an invasive, N-fixing shrub, Elaeagnus umbellata Thunb. (Elaeagnaceae), and a native, N-fixing shrub Morella cerifera (L.) Small (Myricaceae) and compare to native, sympatric, non-expanding shrub species. Quantified functional traits included morphological (e.g., specific leaf area, leaf area) and physiological characteristics (e.g., electron transport rate, hydraulic conductivity) and were linked to two primary resources: light and water, which directly influence plant growth. Elaeagnus umbellata and M. cerifera rely on different strategies to maximize carbon gain, yet resulting physiological efficiency is similar. Elaeagnus umbellata invests a substantial amount of energy into growth during a short amount of time (i.e., deciduous growing season), using an acquisitive trait strategy to outcompete co-occurring woody species, while M. cerifera is productive year-round and uses a combination of conservative and acquisitive traits to outcompete co-occurring woody species. The majority of quantified functional traits of E. umbellata and several of M. cerifera are indicative of efficient light capture, utilization, and internal water movement. These factors contribute to rapid range expansion and thicket formation by promoting enhanced productivity while simultaneously inhibiting colonization and expansion of co-occurring species. Suites of functional traits are important for expansive success and thicket formation, yet differences in functional traits represent alternative strategies for colonization, rapid expansion, and thicketization

Hammett Correlations of Half-Wave Reduction Potentials in a Series of N-(Aryl substituted)-Dichloronicotinamides

Excellent correlations of Hammett substituent constants (sigmaR) of a series of N-(R-substituted aryl) -2,6-, 2,5-, and 5,6- dichloronicotinamides with polarographic half-wave potentials were observed. Although the correlations demonstrate that all three series of amides experience comparable sensitivity to the R groups at the carbonyl reduction site, the relative ease of reduction varies according to the chlorine substitution pattern on the pyridine ring. These differences are suggested to be due to combinations of mesomeric, inductive, and field effects which operate differently in the three systems. Correlation analysis also revealed that Hammett heteroatomic replacement constants previously determined by NMR studies are valid in the present polarographic studies