Shoot growth inhibition occurs in cool season turfgrasses at supraoptimal temperatures. To identify possible mechanisms of growth inhibition, temperature influences on the concentration and distribution of nutrients were evaluated.
Kentucky bluegrass (Poa pratensis L.) cultivars ‘Merion’ and ‘Nugget’ were established from seed on coarse sand in a greenhouse propagation bed for 10 weeks. Sod pieces were then transferred to pots, allowed to acclimate for 2 weeks, and placed in an environmental growth chamber where air temperatures were increased 4 C every 2 weeks from 22 to 38 C. The effects of root temperature maintained at 22 C in half of the pots (controlled root temperatures, CRT) were compared to the other half where root temperatures were allowed to equilibrate with air temperatures (non-controlled root temperatures, (NRT). Shoot growth above 4.0 cm was clipped weekly from plants grown at 22 to 34 C. After the 38 C period, the plants were separated into verdure (live, green tissue), thatch (dead, brown tissue), crowns, and roots. The distribution of dry weight, N, P, K, Ca, Mg, Na, Mn, Fe, Zn, Cu, B, and Al was determined among the four plant fractions.
The N content of leaves was significantly lower at 26, 30, and 34 C compared to 22 C. Significant reductions in Mn, Fe, and Zn content occurred in leaves at 30 C compared to 22 and 26 C. Significant increases in Al, B, and Na content were found at 34 C compared to 22 C. Compared to dry weight distribution, roots were found to accumulate proportionally high levels of P, Fe, Cu, and Al; while K, Ca, Na, Mg, and B were at very low levels in the root. Nitrogen was essentially non-detectable in thatch, but occurred at high levels in leaf and verdure tissue. The thatch accumulated high levels of the other nutrients while leaf and verdure tissue exhibited low levels.
Where growth and high temperature survival of both cultivars was improved at CRT compared to NRT, no major change in the pattern of mineral nutrient concentration or distribution was detected. Thus, even though changes occurred in mineral nutrient levels as temperature increased from 26 to 38 C, changes in these levels do not appear to be involved in high temperature growth inhibition of cool-season turfgrasses.