Heat Stress and Roots

Abstract

As with above-ground tissues, plant roots can be subjected to stressful high temperatures that can limit whole-plant function and decrease crop productivity. Further, with impending climate change, the frequency, duration, and severity of root heat stress will increase. In comparison to shoot function, especially photosynthesis, much less is known regarding heat stress and roots. Most previous research on roots and heat stress has been conducted on detached roots or by heating only roots or parts of root systems (but not shoots too) in intact herbaceous plants, and most past studies on intact plants have imposed chronic heat stress, with few examining effects of abrupt heat stress (e.g., heat waves). Importantly, plant responses to heat stress often differ in detached roots or when only roots are heated, compared to plants wherein both shoots and roots (or shoots only) are heated, and responses to chronic and abrupt heat stress can differ. Hence, many past results do not inform as to how natural heat stress often impacts roots in intact plants or do not inform as to the effects of heat waves on roots. Both chronic and abrupt heat stress can decrease root growth and function, including nutrient and water uptake, and studies in which both roots and shoots were heat-stressed indicate that roots are often more sensitive to heat stress than shoots. Heat stress may affect roots both directly and indirectly, and indirect effects likely involve decreases in shoot carbon provided to roots or changes in root water relations driven by increased shoot water demand, which then affect root growth and nutrient uptake. Interactive effects between heat stress and other global environmental change factors (e.g., elevated carbon dioxide, drought) on roots are likely. We conclude that further research on roots and heat stress is strongly warranted.

Effects of Prior Heat Stress on the Growth and Phytochemical Contents Accumulation of Amaranthus hybridus (Linn.)

“…The results from the current study showed that exposure of Amaranthus hybridus at different duration of heat negatively affects their growth, but the effect on the phytochemical constituents at different stages of growth enhanced the quantity of some phytochemicals and inhibit the quantity of others. As in other previous studies (Heckathorn et al, 2013), among roots and shoots subjected to the same high temperatures, roots were more sensitive to heat stress than shoots. In the hereby study, both root and shoot growth as expressed by their fresh and dry weights decreased at high duration of heat stress at 45 o C. This might have contributed to the decrease observed in the leaf fresh and dry weights, consistent with results of a study on abrupt heat stress in a heat-tolerant grass (Mainali, 2007).…”

Heat Stress Decreases Levels of Nutrient-Uptake and -Assimilation Proteins in Tomato Roots

“…Both shoots and roots are sensitive to heat-related damage, and roots are often as sensitive, or more, as shoots to a heat stress [7,11]. Further, roots are often subjected to high and potentially-stressful temperatures; e.g., when canopies are not closed and soil receives direct sunlight [12,13,14] or in cool-season species during hot summer months [15].…”

“…Further, roots are often subjected to high and potentially-stressful temperatures; e.g., when canopies are not closed and soil receives direct sunlight [12,13,14] or in cool-season species during hot summer months [15]. The tolerance of roots to heat stress scales with the mean temperatures of the habitats to which the species are adapted, such that optimal temperatures for root growth are lower in cool-season species, higher in warm-season species, and still higher in warm-desert plants [11]. For example, soil temperatures can exceed 30 °C in the top 5 cm of the soil profile in cool-season wheat fields in cool-temperate locations [15], 33 °C to 10 cm depth in oat fields in Texas [14], 35 °C–40 °C to 10 cm depth in a sub-tropical maize field [16], and 70 °C to 40 °C from the surface to 15 cm depth in deserts dominated by succulents [17]; in each of these cases, these soil temperatures exceed optimal temperatures for root growth for the respective species.…”

“…Relative to shoots, less research has examined the effects of heat stress on roots, and most of this past research had focused on root growth and carbon relations (especially respiration) [7]. Relatively little past research has investigated how heat stress affects plant nutrient relations [7,8,11,19], and most of this previous work has measured only heat effects on nutrient content or concentration. In addition, most of the past research on root heat stress has focused on chronic heat stress, but the responses of roots to chronic warming can differ from abrupt heat stress [11]; hence, the effects of abrupt heat stress on root nutrient-uptake is especially poorly understood.…”

“…Based on the few past studies, it is known that heat stress often decreases the concentration of nutrients in plant tissues or decreases the total content of nutrients in the plants, though effects can vary among nutrients and species [11]. Heat stress can also disrupt enzymes involved in nutrient metabolism (e.g., nitrate and ammonium assimilation) [20,21].…”