Jones Melanie D, Durall D M, Tinker P B
Plant Mycorrhizal Unit, Natural Environment Research Council, Department of Plant Sciences, Parks Road, Oxford, OXI 3PF, UK.
Terrestrial and Freshwater Science Directorate, Natural Environment Research Council, Polaris House, North Star Avenue, Swindon, SN2 1EU, UK.
New Phytol. 1991 Sep;119(1):99-106. doi: 10.1111/j.1469-8137.1991.tb01012.x.
One way of viewing a mycorrhizal symbiosis is as a balance between the nutritional 'benefits' and carbon 'costs' to the phytobiont. Phosphorus acquisition efficiency (the amount of phosphorus taken up per unit of carbon allocated belowground) can be used as an indicator of this balance. In this study, phosphorus uptake and belowground carbon allocation were measured using ectomycorrhizal (M) (Thelephora terrestris (Ehrh.) Fr.) and non-mycorrhizal (NM) Salix viminalis L. cv. Bowles Hybrid. Following 50, 60, 85 or 98 d of growth in a gamma-irradiated soil/sand mixture containing 4 mg bicarbunate-extractable P kg , seven randomly-selected cuttings of each treatment were harvested and their P contents determined. Nine d prior to each harvest, the three median plants from the group of seven were pulse labelled with C to determine the relative allocation of C aboveground and belowground. Mycorrhizal colonization of willow caused a two-fold increase in growth owing to substantially higher P uptake. Phosphorus inflow rates were almost three times as high for M root systems as for NM root systems over the interval up to the first harvest (3.2 × 10 and 1.2 × 10 mol m s-1, respectively). Over the interval from 50 to 98 d, inflows into M plants were 50% higher than into NM plants (1.4 × 10 and 0.9 × 10 mol m s respectively). The M plants allocated about 25 times as much carbon belowground as the NM plants for both periods. The P acquisition efficiency was higher in M than in NM plants during the first interval (16% and 40% higher using two different calculation methods), whereas during the second interval it was higher in NM than in M plants (33% and 44% higher using the two different methods). Thus, ectomycorrhizas can be very effective in supplying P to their hosts even at an early stage of infection. Furthermore, it is suggested that a temporal separation exists in the maximal fluxes of P and C between the fungus and the host of the mycorrhizal association. The results are discussed in the context of the nutrient requirements and carbon economies of field-grown woody plants.
一种看待菌根共生关系的方式是将其视为植物共生体在营养“益处”和碳“成本”之间的一种平衡。磷获取效率（每单位分配到地下的碳所吸收的磷量）可作为这种平衡的一个指标。在本研究中，利用外生菌根（M）（土生棱柄盘菌（Ehrh.）Fr.）和非菌根（NM）的垂柳（Salix viminalis L. cv. Bowles Hybrid）来测量磷吸收和地下碳分配情况。在含有4毫克碳酸氢盐可提取磷/千克的经γ射线辐照的土壤/沙子混合物中生长50、60、85或98天后，对每个处理随机选取七株插条进行收获，并测定其磷含量。在每次收获前九天，对七株植株中的三株中间植株用¹⁴C进行脉冲标记，以确定地上和地下碳的相对分配情况。柳树的菌根定殖由于磷吸收大幅增加而使生长增加了两倍。在首次收获前的时间段内，M根系的磷流入速率几乎是NM根系的三倍（分别为3.2×10⁻⁹和1.2×10⁻⁹摩尔·米⁻²·秒⁻¹）。在50至98天的时间段内，M植株的磷流入量比NM植株高50%（分别为1.4×10⁻⁹和0.9×10⁻⁹摩尔·米⁻²·秒⁻¹）。在这两个时期，M植株分配到地下的碳量大约是NM植株的25倍。在第一个时间段内，M植株的磷获取效率高于NM植株（使用两种不同计算方法分别高16%和40%），而在第二个时间段内，NM植株的磷获取效率高于M植株（使用两种不同方法分别高33%和44%）。因此，即使在感染早期，外生菌根也能非常有效地为其宿主提供磷。此外，有人提出菌根共生体的真菌和宿主之间在磷和碳的最大通量上存在时间上的分离。结合田间生长的木本植物的养分需求和碳经济情况对结果进行了讨论。
