SPRING WHEAT LEAF APPEARANCE AND TEMPERATURES:EXTENDING THE PARADIGM

Authors: McMaster, Gregory; Wilhelm, Wallace; Palic, Daniel; PORTER, J - UNIVERSITY DENMARK; JAMIESON, P - NEW ZEALAND GOV

Submitted to: Annals of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2003
Publication Date: 6/1/2003
Citation: Mcmaster, G.S., Wilhelm, W.W., Palic, D.B., Porter, J.R., Jamieson, P.D. 2003. Spring wheat leaf appearance and temperatures:extending the paradigm. Annals Of Botany. Volume 91, pg. 697-705.

Interpretive Summary: The rate of leaf appearance is fundamental in understanding how plants develop and grow, which in turn is useful in better managing our agricultural systems. Extensive research has shown that temperature is the primary environmental factor controlling the phyllochron, or rate of leaf appearance of wheat (Triticum aestivum L) and most plant species. Experimental results suggest that soil temperature at crown depth, rather than air temperature above the canopy, would better predict wheat leaf appearance rates. We tested this hypothesis in a 2-yr field experiment with three planting dates and two soil temperature treatments using the spring wheat cultivar Nordic. One temperature treatment (denoted +3C) consisted of heating the soil at crown depth to 3oC above the ambient soil temperature treatment (denoted +0C). Seedling emergence and the main stem cumulative leaf number were measured at least weekly until flag leaf emergence. Leaf appearance was essentially linear with both air and soil growing degree-days (GDD), although plants in the +0C treatment had a stronger linear relationship with soil GDD than the +3C plants. A weak positive relationship between planting date and the phyllochron was observed. Unexpectedly, we found heating the soil at crown depth did not increase the rate of leaf appearance, as the paradigm would predict. To explain these results, we propose extending the paradigm in two ways. First, three processes are involved with leaf appearance: a) cell division at the shoot apex forms the primordium, b) cell division in the intercalary meristem forms the cells that then c) expand to produce the leaf. Cell division is predominately controlled by temperature, but cell expansion is considerably more affected by factors other than temperature, explaining where other factors influence the phyllochron. Second, the vertical distribution of processes involved in leaf appearance (i.e., two meristems and region of cell expansion) occurs over a significant distance where temperature varies considerably, and temperature at a specific point (e.g. crown depth) does not account for these factors. Based on our findings we do not recommend that the effort and expense of collecting soil temperature data is expended as using readily available air temperature is sufficient.

Technical Abstract: Extensive research has shown that temperature is the primary environmental factor controlling the phyllochron, or rate of leaf appearance of wheat (Triticum aestivum L). Experimental results suggest that soil temperature at crown depth, rather than air temperature above the canopy, would better predict wheat leaf appearance rates. To test this hypothesis, a 2-yr field experiment (Nunn clay loam soil; fine, smectitic, mesic Aridic, Argiustoll) with three planting dates and two soil temperature treatments was performed using the spring wheat cultivar Nordic. One temperature treatment (denoted +3C) consisted of heating the soil at crown depth to 3oC above the ambient soil temperature treatment (denoted +0C). Seedling emergence and the main stem cumulative leaf number were measured at least weekly until flag leaf emergence. Leaf appearance was essentially linear with both air and soil growing degree-days (GDD), although plants in the +0C treatment had a stronger linear relationship with soil GDD than the +3C plants. A weak positive relationship between planting date and the phyllochron was observed. Unexpectedly, we found heating the soil at crown depth did not increase the rate of leaf appearance, as the paradigm would predict. To explain these results, we propose extending the paradigm in two ways. First, three processes are involved with leaf appearance: a) cell division at the shoot apex forms the primordium, b) cell division in the intercalary meristem forms the cells that then c) expand to produce the leaf. Cell division is predominately controlled by temperature, but cell expansion is considerably more affected by factors other than temperature, explaining where other factors influence the phyllochron. Second, the vertical distribution of processes involved in leaf appearance (i.e., two meristems and region of cell expansion) occurs over a significant distance where temperature varies considerably, and temperature at a specific point (e.g. crown depth) does not account for these factors.