Water Use and Growth of Honey Locust and Tree-of-Heaven at High Root-zone Temperature

Abstract

<jats:p>Honey locust <jats:italic>(Gleditsia triacanthos</jats:italic> var. <jats:italic>inermis</jats:italic> Wind.) and tree-of-heaven <jats:italic>Ailanthus altissima</jats:italic> (Mill.) Swingle] sometimes are exposed to high root-zone temperatures in urban microclimates. The objective of this study was to test the hypothesis that seedlings of these species differ in how elevated root-zone temperature affects growth, leaf water relations, and root hydraulic properties. Shoot extension, leaf area, root: shoot ratio, and root and shoot dry weights were less for tree-of-heaven grown with the root zone at 34C than for those with root zones at 24C. Tree-of-heaven with roots at 34C had a lower mean transpiration rate (E) than those grown at 24C, but leaf water potential (ψ<jats:sub>1</jats:sub>) was similar at both temperatures. In contrast, shoot extension of seedlings of honey locust grown with roots at 34C was greater than honey locust at 24C, E was similar at both temperatures, and ψ<jats:sub>1</jats:sub> was reduced at 34C. Hydraulic properties of root systems grown at both temperatures were determined during exposure to pressure in solution held at 24 or 34C. For each species at both solution temperatures, water flux through root systems (J<jats:sub>v</jats:sub>) grown at 34C was less than for roots grown at 24C. Roots of tree-of-heaven grown at 34C had lower hydraulic conductivity coefficients (L<jats:sub>p</jats:sub>) than those grown at 24C, but L<jats:sub>p</jats:sub> of roots of honey locust grown at the two temperatures was similar.</jats:p>

Growth and phosphorus, zinc, and manganese content of tomato, muskmelon, and honey locust at high root‐zone temperatures1

“…Honey locust whole plant dry mass, and P and Zn contents did not change over the range of RZT tested, but Mn content was highest at 24*C. The predicted threshold RZT for honey locust growth is 34* to 35*C (3,6) . Equations for manganese are: y = -7.5 + 0.6x -0.01x2, r2 = 0.62 (tomato); y = -0.14 + 0.02x, r^ = 0.91 (muskmelon); y = 0.29 -0.006x, r2 = 0.56 (honey locust).…”

“…Tolerance to supraoptimal RZT has been assessed singly in a few temperate horticultural crops, but few comparisons have been conducted on differences in growth and nutrient absorption of horticultural crops with differing tolerances to RZT > 30*C. Seedlings of thornless honey locust had greater shoot extension at 34*C RZT than honey locust seedlings at 24*C RZT (6). Muskmelons also had rapid vegetative growth in response to soil temperatures > 30*C (15,20).…”

Heat Stress and Roots

“…For plants, temperature increases will be compounded by CO 2 -induced decreases in stomatal conductance, and hence transpiration, and by increases in leaf size, both of which will increase leaf temperatures [4]. Although not widely appreciated, roots are also subject to high temperatures under natural conditions, especially when plant canopies are not closed and sunlight illuminates the soil directly (e.g., above 70 C near the soil surface and 40 C at 15 cm depth in deserts [5,6] or above 30 C in urban settings in the United States [7]); soil temperatures can also reach very high levels during fire (e.g., above 35 C just below the soil surface) [6]. Heat stress in plants can decrease ecosystem productivity and change community composition (e.g., [8][9][10]), and heat stress decreases food production in agricultural plants [11,12], including root heat stress [13,14].…”

Supraoptimal Soil Temperatures Induced Oxidative Stress in Leaves of Creeping Bentgrass Cultivars Differing in Heat Tolerance

“…Leaf injury under high soil temperatures has been attributed to direct inhibition of root growth (Xu and Huang, 2000), hormone synthesis and transport (Udomprasert, et al, 1995), water uptake (Graves et al, 1991; Huang et al, 1991), and nutrient uptake (Gur and Shulman, 1979; Huang and Xu, 2000). Other biochemical processes may be involved in leaf senescence at high soil temperatures.…”