Measuring Nitrogen and Phosphorus Uptake by Intact Roots of Mature Acer saccharum Marsh., Pinus resinosa Ait., and Picea abies (L.) Karst

Abstract

A common method for measuring uptake by intact roots in situ is the depletion method, wherein intact fine roots are separated from soil and placed in nutrient solution. The difference between initial and final amounts of nutrient in solution is attributed to root uptake. Variations on this method include applying pretreatment solutions, training roots to grow into bags or trays, and varying concentrations of nutrient solution. We tested whether variations in methods affected measured net uptake rates of NH 4 + , NO 3 ) , and PO 43) . Intact roots of 60 year-old sugar maple (Acer saccharum Marsh.), red pine (Pinus resinosa Ait.), and Norway spruce (Picea abies (L.) Karst.) were given one of four treatments prior to measuring net uptake. ''Trained'' roots were grown in a sand-soil mixture. ''Recovered'' roots were excavated and allowed to recover in nutrient solution for two or four days (''two-day recovery'' and ''four-day recovery'', respectively). ''No recovery'' roots were excavated and used immediately in experiments. We exposed roots to three concentrations of nutrient solutions to observe the effects of initial nutrient solution concentration. Initial nutrient solution concentration was an important source of variation in measured uptake rates, and N uptake was stimulated by low antecedent concentrations. We found no significant differences in net uptake rates between pretreatments for any of the species studied, indicating that our pretreatments were not effective in improving measurement of uptake. Such pretreatments may not be necessary for measuring net uptake and may not hinder the comparison of rates measured using variations of the depletion method.

Root Morphology and Nutrient Uptake Kinetics by Australian Cedar Clones

“…For the C min value, nutrient concentrations present in the depleted solution after 24 hours were calculated. The liquid inflow (IL) was estimated according to Equation 1, as proposed by Michaelis-Menten and modified by Nielsen and Barber (1978). (1) After separating the shoots and roots, they were washed in distilled water and placed in plastic pots containing 70% alcohol, to determine the length, volume, surface area, average diameter, and extension of roots per diameter class.…”

“…The kinetic parameters vary, especially with genotype and species (ALI et al, 2010;BRIX et al, 2010;LIMA et al, 2005;McFARLANE;YANAI, 2006;PINTO, 2009;SCHONINGER;GATIBONI;ERNANI, 2013;SILVEIRA;CARDOSO, 2004), as they determine the characteristics of the plant itself, and provide it with a higher or lower nutrient uptake capacity at a given concentration in the external medium. A genotype or species is considered efficient in the uptake of a particular nutrient when it presents kinetic parameters that qualify it as such.…”

“…A genotype or species is considered efficient in the uptake of a particular nutrient when it presents kinetic parameters that qualify it as such. In principle, it would be expected that the plant achieves a high initial rate of nutrient uptake as a consequence of an existing high-affinity between the transporter and the element, resulting from a low K m value, and when extracting the maximum possible amount of the nutrient, low concentrations are found in the soil solution (C min ) (NIELSEN; BARBER, 1978).…”

“…Moreover, the nutrient uptake efficiency may be influenced by physiological variations, as well as kinetic parameters, such as the maximum uptake velocity (V max ), the Michaelis-Menten constant (K m ), and the minimum nutrient concentration in the soil (C min ). The interaction of these parameters is estimated through the inflow of nutrients (ALVES et al, 2012;FURTINI NETO, 1994;LIMA et al, 2005;NIELSEN;BARBER, 1978;PINTO, 2009). …”

Estimating nutrient uptake by mature tree roots under field conditions: challenges and opportunities

“…In a depletion study with mature trees, roots of four tree species were exposed to pretreatments designed to reduce the effects of disturbance on uptake measurements (McFarlane and Yanai 2006). Roots were either excavated directly from the soil, excavated and allowed to recover for 2 or 4 days, or grown in bags containing a sand-soil mixture to reduce damage to the roots.…”