Soil Temperature Influences on Root Resistance of Pinus contorta Seedlings

Abstract

The influence of low temperature in the root zone on water uptake in lodgepole pine (Pinus contorta Dougl ex Loud.) was studied under laboratory conditions. To remove soil hydraulic influences, two-year-old seedlngs were transferred to solution cultures and maintained in temperature controlled water baths. Short term measurements of leaf conductance, leaf water potential and tritiated water movement were taken at root temperatures from 22 C down to 0 C. Root resistance was calculated to be 67% of total plant resistance at 7 C and 93% at 0 C. In adtion an Arrhenius break was found in a plant resistance versus temperature plot, suggesting a significant change with temperature in the membrane pathway in the root water uptake system. water potential (4') and/or soil temperature, disregarding morphological development such as degree ofsuberization, and factors such as aeration and root disease. This paper will concentrate on the effect of temperature on root resistance to water transport in the context of whole plant water relations.The primary objective was to develop a functional relation between soil temperature and root resistance for Pinus contorta that was compatible with process modeling efforts of tree water movement (23). To isolate root resistance as the component of plant resistance responding to soil temperature, these water uptake experiments were performed on seedlings in aerated solution culture so there could be no complications caused by soil hydraulic conductivity. In addition, underwater root excision was used to determine the proportion of total water potential drop generated at the root surface. Finally, by comparing seedlings from a greenhouse and a 2 C cold room, influences of preconditioning on root resistance were examined.There has been wide documentation of the influence of V12 on stomatal or k,. Water-limited western conifers exhibit significant stomatal control triggered by *, (8). Consequently, recent efforts to model water movement and transpiration in trees have spent considerable effort in developing functions relating '1 to k, (14, 23).However, a useful process model oftree water movement cannot rely on collected *P data, but must be able to predict P1 over a wide range of conditions. Equations such as *1= * -qR-pgh (1) where I' and I8 are leaf and soil water potential, q is total water flow through the plant, R is total plant resistance, and pgh is the hydrostatic gradient, are useful for dealing with small plants with very little capacitance. They are inadequate for larger trees, because it is not possible to measure q, and prediction of q requires k1 which in a process model requires '1. Also, sapwood capacitance produces hysteresis in the '1 versus q relation (24). Predictions of I1 must be accomplished by defining the individual factors that produce it, and coupling these in the process model. In equation 1, R, total plant resistance, is one factor that must be separated. Much work has been done measuring stomatal resistance (8).Considerably less work has been reported o...

Environmental Controls on Needle Gas Exchange and Growth of White Spruce (Picea glauca) on a Riverside Terrace near the Arctic Treeline

“…When measurements were made in June 2007 and 2008, white spruce needle gas exchange was constrained by cold soils (,7 uC), consistent with observations in the central Brooks Range (Goldstein et al, 1985). Cold soils are thought to reduce water flow into the roots by reducing membrane permeability and by increasing the viscosity of water (Kaufmann, 1975(Kaufmann, , 1977Running and Reid, 1980). Warm and dry conditions in mid-July 2007 led to drought-induced stomatal closure, particularly on shallow parent material, where trees draw water from either a smaller soil volume or a soil volume that is more subject to evaporative water loss.…”

Effect of Soil Water Content on Carbon Dioxide Flux at a Sparse-Canopy Forest in the Canadian Boreal Ecosystem

“…This photosynthetic dormancy during the cold season is consistent with earlier findings that root zone temperatures below 5 °C suppressed water uptake and stomatal conductance (Running and Reid, 1980;Jones, 1992). Daily GPP began to increase in early May as Ts increased rapidly from 0 to 10 °C.…”

Autumn stomatal closure in six conifer species of the Central Rocky Mountains

“…Leaf conductance during the summer increased dramatically to maximum values during mid-August at the same time warming soil temperatures at 25 cm approached 7" C. A similar value of near 7°C was found to be near a limiting threshold for root resistance to water uptake in P. engelmannii (Kaufmann 1975). Running and Reid (1980) also observed an approximate 7" C threshold for increased root conductance to water uptake in P. contorra seedlings. Recently, Teskey et al (1983) reported that cold root temperatures resulted in stomatal closure that was independent of leaf water potentiril in Abies umuhilis.…”

“…As indicated in Fig. 5, a similar reduction in soil water uptake by the roots may also occur when soil temperatures are low (Kaufmann 1975, Dalton and Gardner 1978, Running and Reid 1980, Teskey et al 1983). Other recent work has found a strong correlation between maximum daily leaf conductance and soil temperatures for A .…”

“…Numerous studies have also associated the influence of soil factors such as temperature and moisture on water status and leaf conductance in conifers during the growth season (e.g. Waring and Running 1976;Jarvis 1980;Running and Reid 1980;Schulze and Hall 1982).…”