Phosphorus (P) is the main limiting factor for forage production in grasslands. It is important to determine levels of available P in soil that optimise production with minimum impact on arbuscular mycorrhizal (AM) symbiosis. We investigated the effects of increasing P availability on biomass production, root morphology, AM symbiosis and P acquisition of a forage legume (Lotus tenuis), a C₃ grass (Schedonorus arundinaceus) and a C₄ grass (Panicum coloratum) growing on a P-deficient soil in pots with P applied at rates of 0–160 mg kg^–1 dry soil. The three forage species responded strongly to addition of P, with 90% of maximum shoot growth reached at available P levels of 24.3 mg kg^–1 for L. tenuis, 14.4 mg kg^–1 for P. coloratum and 11.2 mg kg^–1 for S. arundinaceus. Lotus tenuis and P. coloratum produced higher yields of shoot biomass than S. arundinaceus. Root dry weight was higher in the legume than in the grasses, with the root-mass fraction being lowest in P. coloratum. AM colonisation was higher in L. tenuis roots than in grass roots, and decreased with increased soil P availability, especially in grasses. Low to moderate additions of P did not affect, and could even improve, AM colonisation in L. tenuis roots. For L. tenuis, it is possible to increase forage yield while maintaining high values of AM colonisation at 10–20 mg kg^–1 of available P, but for grasses, especially S. arundinaceus, it is difficult to achieve both objectives. The presence of L. tenuis in grasslands or pastures may contribute to maintaining the native AM inoculum under a wide range of soil P availability in regions such as the Salado River basin of Argentina.

磷是草原牧草生产的主要限制因素。重要的是要确定土壤中的有效磷水平，以使生产最优化，而对丛枝菌根（AM）共生的影响最小。我们研究了增加磷的施用量对生长在磷上的牧草（Lotus tenuis），C ₃草（Schedonorus arundinaceus）和C ₄草（Panicum coloratum）的生物量生产，根形态，AM共生和磷吸收的影响。盆栽土壤中P含量为0–160 mg kg ^–1干燥土壤中的缺土。这三种牧草对磷的添加反应强烈，在24.3 mg / kg的有效磷水平下，最大苗生长达到90％^-1用于L.细叶，14.4毫克千克^-1为P. coloratum和11.2毫克千克^-1为S.茅。莲花tenuis和彩色假单胞菌产生的枝条生物量高于阿鲁氏链球菌。根干重是在豆科植物比草更高，根质量分数是在最低P. coloratum。特异劳斯氏菌根中的AM定植高于草根，并随着土壤磷有效性的增加而减少，尤其是在草中。低至中度添加P不会影响甚至可以改善Tenuis L.AM中AM的定殖根。对于L. tenuis，可以提高牧草产量，同时在10–20 mg kg ^–1的可用磷保持较高的AM菌落值，但是对于草，尤其是沙棘，很难实现两个目标。在阿根廷或萨拉多河流域等地区，土壤和土壤中磷的供应量很大，草地或牧场中存在的ten。L.可能有助于维持天然AM接种物。