Morphological and Physiological Mechanisms of Temperature Compensation in Phosphate Absorption along a Latitudinal Gradient

Abstract

The effects of temperature upon phosphate absorption by marsh plants were examined along latitudinal gradients of temperature and thermal stability in order to (1) document the adaptive differentiation of a physiological system in response to environmental severity and fluctuation, and (2) elucidate the mechanisms and evolutionary implications of compensation for temperature changes occurring over different time scales. Among the species and ecotypes studied, those that had evolved in colder climates differed from their warm—adapted counterparts in having (1) lower temperature optima for root initiation, elongation, and production; (2) larger surface—to—volume ratios of roots; (3) proportionately more nutrient—absorbing tissue; (4) higher phosphate absorption capacities at given measurement and acclimation temperatures; (5) lower potential of the phosphate absorption system to acclimate in response to temperature change; and (6) less temperature sensitivity of the phosphate absorption system. When plants were acclimated to a new temperature over a period of weeks, cold—acclimated individuals had higher rates of phosphate absorption at a given measurement temperature than did warm—acclimated individuals, and temperature sensitivity of phosphate absorption was lowest in those individuals of a population acclimated to a root temperature that most closely approximated the soil temperature at the site of origin of that population. When temperatures were changed over a period of minutes, roots exposed to low temperature had a higher affinity for phosphate than did roots exposed to warm temperature. Consequently, phosphate absorption was less temperature—sensitive at ecological than at saturating concentrations of phosphate, and the change in affinity of roots for phosphate occasioned by a change in temperature compensated for that temperature change.

Kinetics of nutrient uptake by roots: responses to global change

“…Ion movement across the cell membrane is highly sensitive to changes in soil or root temperature (Chapin, 1974 ;BassiriRad et al, 1993), oxygen concentration of the rooting medium (Epstein, 1972), metabolic inhibitors , and light and\or carbohydrate availability (Rufty et al, 1984 ;Glass, 1989 ;Raper et al, 1991), which strongly suggest the presence of an energy-dependent uptake system. Despite the early recognition by Van den Honert (see Glass, 1989) that root ion uptake is an active process, a clear mechanism of uptake was not put forward until Epstein & Hagen (1952) introduced the concept of membrane-bound transporters or carriers.…”

“…Such changes will have a marked effect on soil biology including growth and physiological characteristics of roots. Soil temperature has long been considered as an important ecological factor that determines a variety of structural and functional characteristics in managed and natural ecosystems (Chapin, 1974 ;Rykbost et al, 1975 ;Dixon & Turner, 1991 ;Farnsworth et al, 1995 ;Chapin, 1977 ;Weih & Karlsson, 1999). In some ecosystems, temperature of the root zone is the most important factor in determining net primary productivity (Van Cleve et al, 1981 ;Risser, 1985).…”

“…Indeed, a number of studies have demonstrated that changes in soil temperature can directly effect plant nutrient acquisition by changing root transport properties for NH % + (Chapin et al, 1986), NO $ − (Cumbus & Nye, 1982 ;BassiriRad et al, 1991BassiriRad et al, , 1993, PO % $− (Chapin, 1974(Chapin, , 1977Cumbus & Nye, 1985), and K + (Siddiqi et al, 1984). The exact mechanism for temperature-induced changes in nutrient uptake capacity is not clearly understood.…”

“…BassiriRad et al (1996c) also found that increase in soil temperature from 5 to 15mC significantly increased kinetics of root PO % $− uptake in Eriophorum vaginatum, a tundra species, but a further increase from 15 to 25mC significantly inhibited rates of root PO % $− absorption. In his early work with root P uptake capacity, Chapin (1974Chapin ( , 1977 postulated that the degree of root response to soil temperature changes is determined by the soil thermal characteristics of the habitat of origin. He showed that species from thermally stable cold soil environments were significantly less sensitive to a shift in soil temperature than their counterparts from habitats with warmer and more fluctuating soil environments.…”

Biodiversity, Distributions and Adaptations of Arctic Species in the Context of Environmental Change

“…(111) Increased surface area for nutrient uptake by increased biomass of roots relative to shoots (up to 95% of plant biomass can be below ground) (79,112) associations with mycorrhizal fungi (113) and uptake of N by rhizomes (114) Some Arctic plants can take up nutrients in organic forms, thereby by-passing some of the slow decomposition and mineralization processes (115) Dependence on atmospheric nutrient deposition in mosses and lichens (116) Soil movement at various spatial scales resulting from freeze-thaw cycles, permafrost dynamics and slope processes Freeze-thaw cycles heave ill-adapted plants from the soil and cause seedling death Areas of active movement select for species with elastic and shallow roots or cryptogams without roots. (117)(118)(119) Shallow active layer Limits zone of soil biological activity and rooting depth.…”