Montagu K D, Conroy J P, Atwell B J
Centre for Horticulture and Plant Sciences, University of Western Sydney, Hawkesbury, Richmond, NSW 2753, Australia.
J Exp Bot. 2001 Nov;52(364):2127-33. doi: 10.1093/jexbot/52.364.2127.
Plants growing in soils typically experience a mixture of loose and compact soil. The hypothesis that the proportion of a root system exposed to compact soil and/or the timing at which this exposure occurs determines shoot growth responses was tested. Broccoli (Brassica oleracea var. italica cv. Greenbelt) seedlings were grown in pot experiments with compact, loose and localized soil compaction created by either horizontal (compact subsoils 75 or 150 mm below loose topsoil) or vertical (adjacent compact and loose columns of soil) configurations of loose (1.2 Mg m(-3)) and compact (1.8 Mg m(-3)) soil. Entirely compact soil reduced leaf area by up to 54%, relative to loose soil. When compaction was localized, only the vertical columns of compact and loose soil reduced leaf area (by 30%). Neither the proportion of roots in compact soil nor the timing of exposure could explain the differing shoot growth responses to localized soil compaction. Instead, the strong relationship between total root length and leaf area (r(2)=0.92) indicated that localized soil compaction reduced shoot growth only when it suppressed total root length. This occurred when isolated root axes of the same plant were exposed to vertical columns of compact and loose soil. When a single root axis grew through loose soil into either a shallow or deep compact subsoil, compensatory root growth in the loose soil maintained total root length and thus shoot growth was unaffected. These contrasting root systems responses to localized soil compaction may explain the variable shoot growth responses observed under heterogeneous conditions.
生长在土壤中的植物通常会经历疏松土壤和紧实土壤的混合环境。我们对以下假设进行了测试：根系暴露于紧实土壤的比例和/或这种暴露发生的时间决定了地上部的生长反应。在盆栽试验中种植西兰花（Brassica oleracea var. italica cv. Greenbelt）幼苗，通过水平（紧实底土在疏松表土以下75或150毫米）或垂直（相邻的紧实和疏松土柱）配置疏松（1.2 Mg m(-3)）和紧实（1.8 Mg m(-3)）土壤，创造出紧实、疏松和局部土壤紧实的环境。相对于疏松土壤，完全紧实的土壤使叶面积减少了高达54%。当紧实是局部的时，只有紧实和疏松土壤的垂直土柱减少了叶面积（减少了30%）。紧实土壤中根系的比例和暴露时间都无法解释地上部对局部土壤紧实的不同生长反应。相反，总根长与叶面积之间的强相关性（r(2)=0.92）表明，局部土壤紧实只有在抑制总根长时才会减少地上部生长。当同一植株的孤立根轴暴露于紧实和疏松土壤的垂直土柱时，就会出现这种情况。当单个根轴从疏松土壤生长到浅或深的紧实底土中时，疏松土壤中的补偿性根系生长维持了总根长，因此地上部生长不受影响。根系对局部土壤紧实的这些不同反应可能解释了在异质条件下观察到的地上部生长反应的变化。
