Despite their ubiquitous distribution and significant ecological roles, soil microorganisms have long been neglected in investigations addressing parasitic plant-host interactions. Because nutrient deprivation is a primary cause of host damage by parasitic plants, we hypothesized that beneficial soil microorganisms conferring nutrient benefits to parasitized hosts may play important roles in alleviating damage. We conducted a pot cultivation experiment to test the inoculation effect of an arbuscular mycorrhizal fungus (Glomus mosseae), a rhizobium (Rhizobium leguminosarum) and their interactive effects, on alleviation of damage to a legume host (Trifolium repens) by two root hemiparasitic plants with different nutrient requirements (N-demanding Pedicularis rex and P-demanding P. tricolor). Strong interactive effects between inoculation regimes and hemiparasite identity were observed. The relative benefits of microbial inoculation were related to hemiparasite nutrient requirements. Dual inoculation with the rhizobium strongly enhanced promotional arbuscular mycorrhizal effects on hosts parasitized by P. rex, but reduced the arbuscular mycorrhizal promotion on hosts parasitized by P. tricolor. Our results demonstrate substantial contribution of arbuscular mycorrhizal and rhizobial symbioses to alleviating damage to the legume host by root hemiparasites, and suggest that soil microorganisms are critical factors regulating host-parasite interactions and should be taken into account in future studies.

Spatial expansion of root hemiparasitic Pedicularis kansuensis in Bayanbulak Grassland of Xinjiang Uygur Autonomous Region (China) has caused great loss of herbage yield and has threatened the local livestock industry. Current management practices using manual eradication and chemical control have been proved problematic. Arbuscular mycorrhizal (AM) fungi have been suggested to be potential biocontrol agents against a number of plant pests, but experimental evidence is lacking against weedy P. kansuensis. In this study, we tested the hypothesis that inoculation with AM fungi will cause growth depression in P. kansuensis and reduce its damage to host plants. Based on the confirmation of AM status and host community of the hemiparasite in the field, a pot cultivation experiment was conducted to test the influence of an AM fungus (Glomus mosseae) on growth of P. kansuensis and the parasitized host (Elymus nutans). AM colonization was observed in roots of P. kansuensis, but the levels were much lower than those of its adjacent host species. A negative correlation between AM levels and the numbers of haustoria was detected for the field samples of the hemiparasite. Strong suppression of haustorium formation, a significant reduction in plant dry weight (DW), as well as marked reduction in the survival rate of P. kansuensis after inoculation with AM fungi was observed. In contrast, inoculation with G. mosseae increased root DW and whole plant DW of parasitized host plants. Our findings demonstrated significantly repressive effects of AM fungi on growth performance of P. kansuensis with and without the presence of a host. The potential of AM fungi as biocontrol agents against the damaging hemiparasite was confirmed.

Eff ective options for reducing P losses from P-enriched soils remain a major challenge, particularly in intensive agricultural areas. While diff erent strategies have been shown to control P mobility (e.g., Ca-and Al-based soil amendments and riparian buff ers), they provide no means to reduce in situ soil P concentrations. Th e objectives of this study were to: (i) investigate the potential P-removal capacity of four bioenergy crops (elephantgrass [Pennisetum purpureum Schumach.], sugarcane [Saccharum spp.], switchgrass [Panicum virgatum L.], and stargrass [Cynodon nlemfuensis Vanderyst]) grown on a manure-enriched soil, and (ii) examine the impacts of crop P uptake on soil P concentrations and surface groundwater quality. Treatments were distributed in a completely randomized design with four replicates. Th e greatest dry matter yields were observed for elephantgrass (average of 46 Mg ha -1 yr -1 ) followed by sugarcane (average of 40 Mg ha -1 yr -1 ). Tissue P concentrations were greater for stargrass (~4 g kg -1 ) than elephantgrass (3.2 g kg -1 ) or sugarcane (1.9 g kg -1 ). Elephantgrass showed the greatest cumulative P removal (420 kg P ha -1 during the 3-yr period). Soil P concentrations in the Ap horizon decreased with time, while an increase in soil P concentration was observed in the Bh horizon. Elephantgrass resulted in the lowest leachate P concentrations (~0.5 mg P L -1 ) at the 60-cm depth. Crop species had no eff ect on leachate P at the 90-cm depth. Growth of elephantgrass as a biofuel feedstock appears to be an eff ective approach for remediation of excess soil P.