McMaster Gregory S, Wilhelm W W, Palic D B, Porter John R, Jamieson P D
USDA-ARS, Great Plains Systems Research, 301 S. Howes St, Room 353, Fort Collins, CO 80521, USA.
Ann Bot. 2003 May;91(6):697-705. doi: 10.1093/aob/mcg074.
Extensive research shows temperature to be 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, leaf appearance in spring wheat ('Nordic') was measured in a 2-year field experiment (Nunn clay loam soil; fine, smectitic, mesic Aridic, Argiustoll) with three planting dates and two soil temperature treatments. One temperature treatment (denoted +3C) consisted of heating the soil at crown depth to 3 degrees C above the ambient soil temperature (denoted +0C). Main stem cumulative leaf number was measured at least weekly until flag leaf emergence. Leaf appearance was essentially linear with both air and soil growing degree-days (GDD), although there was a stronger linear relationship with soil GDD in the +0C plants than in +3C plants. A weak positive relationship between planting date and the phyllochron was observed. Unexpectedly, we found that heating the soil 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 in leaf appearance: (1) cell division at the shoot apex forms the primordium; (2) cell division in the intercalary meristem forms the cells that then (3) expand to produce the leaf. Cell division is predominantly controlled by temperature, but cell expansion is considerably more affected by factors other than temperature, explaining the influence of other factors on the phyllochron. Secondly, the vertical distribution of the two meristems and region of cell expansion occur over a significant distance, where temperature varies considerably, and temperature at a specific point (e.g. crown depth) does not account for the entire temperature regime under which leaves are developing.
大量研究表明，温度是控制小麦（Triticum aestivum L.）叶龄期或叶片出现速率的主要环境因素。实验结果表明，冠层深度处的土壤温度，而非冠层上方的气温，能更好地预测小麦叶片出现速率。为验证这一假设，在一项为期两年的田间试验（纳恩粘壤土；细质、蒙脱石质、半湿润干旱型、粘化干润软土）中，对春小麦（‘北欧’品种）在三个播种日期和两种土壤温度处理下的叶片出现情况进行了测量。一种温度处理（标记为+3°C）包括将冠层深度处的土壤加热至比环境土壤温度（标记为+0°C）高3摄氏度。在旗叶出现之前，至少每周测量一次主茎累积叶片数。叶片出现与气温和土壤生长度日（GDD）基本呈线性关系，不过在+0°C处理的植株中，与土壤GDD的线性关系比在+3°C处理的植株中更强。观察到播种日期与叶龄期之间存在微弱的正相关关系。出乎意料的是，我们发现加热土壤并未如范例所预测的那样提高叶片出现速率。为解释这些结果，我们建议从两个方面扩展该范例。首先，叶片出现涉及三个过程：（1）茎尖的细胞分裂形成原基；（2）居间分生组织中的细胞分裂形成随后（3）扩展以产生叶片的细胞。细胞分裂主要受温度控制，但细胞扩展受温度以外的因素影响要大得多，这就解释了其他因素对叶龄期的影响。其次，这两个分生组织和细胞扩展区域的垂直分布跨越相当大的距离，温度在该距离内变化很大，特定点（如冠层深度）的温度并不能解释叶片发育所处的整个温度状况。
