为了探究棉花中上部叶片首先出现缺钾症状的生理机制，以中棉所41为供试材料，于2013—2014年在中国农业大学上庄实验站缺钾(K)土壤上(速效 K 含量64.0~70.9 mg kg–1)进行试验，设置低钾(225 kg K2O hm–2)和高钾(375 kg K2O hm–2)2个钾处理，以不施钾为对照，观察蕾期至花铃后期主茎叶缺 K 症状的发展动态，并测定了叶片的K+含量。结果表明，棉花叶片缺 K 症状并不是简单的自下部老叶逐步向上发展，而是从第10节位左右向上推移，并且这种推移呈跳跃式，植株中部某些叶位的叶片一直未出现缺 K 症状或症状很轻微。棉花这种缺 K 症状模式与叶片K+含量无必然联系。叶片 K+含量基本遵循随叶位上升而增加的规律，符合缺 K 条件下的一般特征，但这种自下而上增加的幅度及增幅较大的部位在不同生育时期和不同年份存在差异。大部分叶片的 K+含量随叶龄增长呈或快或慢的下降趋势，但在蕾期至盛花期某些幼叶和功能叶的 K+含量会出现上升现象，如2013年的第7~第14叶、2014年的第13~第16叶。要揭示棉花缺 K 症状的生理机制，还需要从不同叶片对 K+的敏感性、K+在整株水平的再分配等方面深入研究。%In order to explore the physiological mechanism of an unusual phenomenon that potassium (K) deficiency symptom first occurs in medium and upper leaves rather than lower leaves of cotton plants, field experiments were conducted at Shangzhuang Experimental Station of China Agricultural University with a low K soil (64.0 to 70.9 mg kg–1 of available K) in Beijing (40º08′N, 116º10′E) during 2013 and 2014 growing season, using CCRI 41 (Gossypium hirsutum L.; susceptible to K deficiency) as material. There were three potassium treatments: control (no potassium applied), low potassium (225 kg K2O hm–2) and high potassium (375 kg K2O hm–2). We observed potassium deficiency symptoms of the main stem leaves from squaring stage to late stage of flowering and boll period and determined the content of K + of blade. It was found that K deficiency symptoms developed upward from the leaf located at the tenth node or so of mainstem, and those leaves below this node did not show symptoms during the whole season. However, this type of upward development of K deficiency symptoms was not successive;some leaves at medium part of mainstem (the 16th node or so) were always normal or near normal. There was no necessary link between the pattern of K deficiency symptoms and K+ concentration in cotton leaves. The latter generally increased with the leaf position raised from bottom to top, which is in accord with the common pattern under K deficiency. However, the increased mag-nitude from bottom to top and the leaf position with a larger increase in K+ concentration were different at contrasting growth stages, as well as between 2013 and 2014. The K+ concentration in most leaves decreased faster or slower over time. Nevertheless, some young or functional leaves (e.g. from the 7th to 14th node in 2013, and from the 13th to 16th node in 2014) showed an in-crease of K+ concentration during the period from squaring stage to peak blooming stage. In conclusion, the spatiotemporal pat-tern of K deficiency symptoms in cotton leaves is more complicated than expected; and according to K+ concentration in leaves we cannot explain it well. The further study should focus on the susceptibility to K deficiency in leaves at different positions, and K+ redistribution in whole plant.
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