Denton Matthew D, Sasse Camille, Tibbett Mark, Ryan Megan H
School of Plant Biology, M084, The University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia.
Centre for Land Rehabilitation, School of Earth and Geographical Sciences, The University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia.
Funct Plant Biol. 2006 Dec;33(12):1091-1102. doi: 10.1071/FP06176.
Many Australian plant species have specific root adaptations for growth in phosphorus-impoverished soils, and are often sensitive to high external P concentrations. The growth responses of native Australian legumes in agricultural soils with elevated P availability in the surface horizons are unknown. The aim of these experiments was to test the hypothesis that increased P concentration in surface soil would reduce root proliferation at depth in native legumes. The effect of P placement on root distribution was assessed for two Australian legumes, Kennedia prorepens F. Muell. and Lotus australis Andrews, and the exotic Medicago sativa L. Three treatments were established in a low-P loam soil: amendment of 0.15 g mono-calcium phosphate in either (i) the top 50 mm (120 µg P g) or (ii) the top 500 mm (12 µg P g) of soil, and an unamended control. In the unamended soil M. sativa was shallow rooted, with 58% of the root length of in the top 50 mm. K. prorepens and L. australis had a more even distribution down the pot length, with only 4 and 22% of their roots in the 0-50 mm pot section, respectively. When exposed to amendment of P in the top 50 mm, root length in the top 50 mm increased 4-fold for K. prorepens and 10-fold for M. sativa, although the pattern of root distribution did not change for M. sativa. L. australis was relatively unresponsive to P additions and had an even distribution of roots down the pot. Shoot P concentrations differed according to species but not treatment (K. prorepens 2.1 mg g, L. australis 2.4 mg g, M. sativa 3.2 mg g). Total shoot P content was higher for K. prorepens than for the other species in all treatments. In a second experiment, mono-ester phosphatases were analysed from 1-mm slices of soil collected directly adjacent to the rhizosphere. All species exuded phosphatases into the rhizosphere, but addition of P to soil reduced phosphatase activity only for K. prorepens. Overall, high P concentration in the surface soil altered root distribution, but did not reduce root proliferation at depth. Furthermore, the Australian herbaceous perennial legumes had root distributions that enhanced P acquisition from low-P soils.
许多澳大利亚植物物种具有特定的根系适应性，以便在缺磷土壤中生长，并且通常对高浓度的外部磷敏感。澳大利亚本土豆科植物在表层土壤磷有效性提高的农业土壤中的生长反应尚不清楚。这些实验的目的是检验以下假设：表层土壤中磷浓度的增加会减少本土豆科植物根系在深层的增殖。研究了磷的施用位置对两种澳大利亚豆科植物（匍匐肯氏豆（Kennedia prorepens F. Muell.）和南方百脉根（Lotus australis Andrews））以及外来的紫花苜蓿（Medicago sativa L.）根系分布的影响。在低磷壤土中设置了三种处理：在土壤的（i）顶部50毫米（120微克磷/克）或（ii）顶部500毫米（12微克磷/克）添加0.15克磷酸二氢钙，以及一个不添加的对照。在未添加的土壤中，紫花苜蓿根系浅，58%的根长在顶部50毫米。匍匐肯氏豆和南方百脉根在花盆深度上的分布更为均匀，它们分别只有4%和22%的根在花盆0 - 50毫米部分。当在顶部50毫米添加磷时，匍匐肯氏豆顶部50毫米的根长增加了4倍，紫花苜蓿增加了10倍，尽管紫花苜蓿的根系分布模式没有改变。南方百脉根对添加磷的反应相对不明显，根系在花盆中分布均匀。地上部磷浓度因物种而异，但不受处理影响（匍匐肯氏豆2.1毫克/克，南方百脉根2.4毫克/克，紫花苜蓿3.2毫克/克）。在所有处理中，匍匐肯氏豆地上部总磷含量高于其他物种。在第二个实验中，对直接从根际附近采集的1毫米厚的土壤切片中的单酯磷酸酶进行了分析。所有物种都向根际分泌磷酸酶，但向土壤中添加磷仅降低了匍匐肯氏豆的磷酸酶活性。总体而言，表层土壤中的高磷浓度改变了根系分布，但没有减少深层根系的增殖。此外，澳大利亚多年生草本豆科植物的根系分布有利于从低磷土壤中获取磷。
