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ABSTRACT: We examined the timing of root elongation intensity (REI) – the production of newly elongating roots measured in length per unit soil volume per unit time – in a mature white oak-chestnut oak forest in Tennessee, USA, over a 4-year period. We used a network of minirhizotrons to (1) examine environmental control of soil moisture and temperature over REI, (2) evaluate the control of phenology over REI (3) develop a multivariate regression equation using the variables of soil temperature, soil water potential and phenology to predict REI, and (4) delineate soil water potentials that were optimum for growth. Fifteen minirhizotron tubes were installed on the upper slope of an upland oak stand on Walker Branch Watershed in Oak Ridge, Tennessee. Measurements of REI were examined over three growing seasons in the upper 30 cm of the soil profile. Composited sets of data on REI, soil water potential, soil temperature and phenology were analyzed to determine the strength of relationships between the latter three variables and REI. There was no statistically significant relationship between REI and soil temperature during the growing season (March–November). The highly significant (p < 0.0001)="" relationship="" between="" soil="" water="" potential="" and="" rei="" was="" best="" described="" as="" log="" linear,="" using="">10 (-) vs. log10 (REI). The correlation between a phenology index and REI was also highly significant (p < 0.0001),="" as="" the="" 24="" highest="" rei="" levels="" occurred="" between="" late="" april="" and="" early="" august.="" whereas="" soil="" water="" potential="" played="" a="" major="" role="" in="" controlling="" rei,="" our="" data="" indicate="" that="" at="" times="" phenologically="" related="" factors="" appeared="" to="" override="" environmental="" variables.="" the="" fact="" that="" rei="" generally="" peaked="" every="" year="" following="" completion="" of="" leaf="" expansion="" is="" congruent="" with="" the="" fixed="" shoot="" growth="" pattern="" of="" many="" temperate-zone="" deciduous="" tree="" species.="" in="" an="" attempt="" to="" explain="" the="" importance="" of="" phenology="" in="" controlling="" rei,="" we="" refer="" to="" the="" concept="" of="" `phenological="" programming'.="" this="" concept="" contrasts="" with="" more="" environmentally="" determinant="" explanations="" of="" the="" timing="" of="" root="" growth.="" those="" theories="" cannot="" explain="" either="" our="" data="" or="" that="" of="" others,="" wherein,="" during="" late="" summer="" and="" early="" autumn,="" rei="" does="" not="" return="" to="" early="" summer="" rates,="" even="" though="" soil="" moisture="" and="" temperature="" conditions="" are="" equally,="" if="" not="" more,="" favorable.="" the="" particular="" type="" of="" `phenological="" programming'="" hypothesized="" in="" this="" study="" may="" be="" limited="" to="" mature="" deciduous="" trees="" exhibiting="" a="" fixed="" growth="" pattern="" of="" shoot="" expansion="" and="" growing="" in="" a="" temperate="" climate="" with="" a="" mid-summer="" drought="">
Plant and Soil 12/2000; 228(2):201-212. · 2.73 Impact Factor
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ABSTRACT: How ecosystems adapt to climate changes depends in part on how individual trees allocate resources to their components. A review of research using tree seedlings provides some support for the hypothesis that some tree species respond to exposure to drought with increases in root∶shoot ratios but little change in total root biomass. Limited research on mature trees over moderately long time periods (2–10 yr), has given mixed results with some studies also providing evidence for increases in root: shoot ratios. The Throughfall Displacement Experiment (TDE) was designed to simulate both an increase and a decrease of 33% in water inputs to a mature deciduous forest over a number of years. Belowground research on TDE was designed to examine four hypothesized responses to long-term decreases in water availability; (1) increases in fine-root biomass, (2) increases in fine root∶foliage ratio, (3) altered rates of fine-root turnover (FRT), and (4) depth of rooting. Minirhizotron root elongation data from 1994 to 1998 were examined to evaluate the first three hypotheses. Differences across treatments in net fine-root production (using minirhizotron root elongation observations as indices of biomass production) were small and not significant. Periods of lower root production in the dry treatment were compensated for by higher growth during favorable periods. Although not statistically significant, both the highest production (20 to 60% higher) and mortality (18 to 34% higher) rates were found in the wet treatment, resulting in the highest index of FRT. After 5 yr, a clear picture of stand fine-root-system response to drought exposure has yet to emerge in this forest ecosystem. Our results provide little support for either an increase in net fine-root production or a shift towards an increasing root∶shoot ratio with long-term drought exposure. One possible explanation for higher FRT rates in the wet treatment could be a positive relationship between FRT and nitrogen and other nutrient availability, as treatments have apparently resulted in increased immobilization of nutrients in the forest floor litter under drier conditions. Such hypotheses point to the continued need to study the interactions of water stress, nutrient availability and carbon-fixation efficiency in future long-term studies.
New Phytologist 06/2000; 147(1):117 - 129. · 6.64 Impact Factor
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ABSTRACT: Honeylocust (Gleditsia triancanthos L.) root growth response to varying levels of Al and Ca in soil solutions was examined in two horizons each of two forest
soils. With results from all four horizons combined, multiple regression analysis indicated that both Ca and Al were significant
(p<0.01) factors affecting root elongation, branching and biomass production. Over a wide range of Al and Ca concentrations
in soil solutions from four different soil horizons, the Ca:Al ratio was a significantly better predictor of honeylocust root
response to acid soils than Al or Ca alone.
Plant and Soil 08/1989; 119(1):181-185. · 2.73 Impact Factor
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ABSTRACT: Tissue concentrations of Al in red and Norway spruce trees were compared across 5 sites in North America and Europe as part of an investigation of Al biogeochemistry in forested ecosystems (ALBIOS). Fine roots and foliage were sampled and analyzed for Al, Ca, Mg, and P, and the chemistry of soil and soil solutions was characterized at each plot by horizon. Sites exhibited a wide range in soil Al saturation and in concentrations of Al and sulfate in lysimeter solutions. Aluminium concentrations in roots were two orders of magnitude higher than those in foliage. Fine roots (2. soil extracts. Stronger soil Al extractants were generally poor predictors of concentrations of Al in plant tissue. Sites with higher levels of plant-available Al supported spruce trees with correspondingly lower foliar levels of Ca and Mg. As such, these field sites provided circumstantial evidence that Al may be interfering with Ca and Mg uptake and transport. No evidence was found of Al interference with P uptake or transport at these sites.
Water Air and Soil Pollution 01/1988; 40(3):375-390. · 1.63 Impact Factor
