Effects of arbuscular mycorrhizal fungi on plant growth and herbivore infestation depend on availability of soil water and nutrients

Abstract

IntroductionFitness of plants is affected by their symbiotic interactions with arbuscular mycorrhizal fungi (AMF), and such effects are highly dependent on the environmental context.MethodsIn the current study, we inoculated the nursery shrub species Artemisia ordosica with AMF species Funneliformis mosseae under contrasting levels of soil water and nutrients (diammonium phosphate fertilization), to assess their effects on plant growth, physiology and natural infestation by herbivores.ResultsOverall, plant biomass was synergistically enhanced by increasing soil water and soil nutrient levels. However, plant height was surprisingly repressed by AMF inoculation, but only under low water conditions. Similarly, plant biomass was also reduced by AMF but only under low water and nutrient conditions. Furthermore, AMF significantly reduced leaf phosphorus levels, that were strongly enhanced under high nutrient conditions, but had only minor effects on leaf chlorophyll and proline levels. Under low water and nutrient conditions, specific root length was enhanced, but average root diameter was decreased by AMF inoculation. The negative effects of AMF on plant growth at low water and nutrient levels may indicate that under these conditions AMF inoculation does not strongly contribute to nutrient and water acquisition. On the contrary, the AMF might have suppressed the direct pathway of water and nutrient absorption by the plant roots themselves despite low levels of mycorrhizal colonization. AMF inoculation reduced the abundance of the foliar herbivore Chrysolina aeruginosa on plants that had been grown on the low nutrient soil, but not on high nutrient soil. Fertilization enhanced the abundance of this herbivore but only in plants that had received the high water treatment. The lower abundance of the herbivore on AMF plants could be related to their decreased leaf P content. In conclusion, our results indicate that AMF negatively affect the growth of Artemisia ordosica but makes them less attractive to a dominant herbivore.DiscussionOur study highlights that plant responses to AMF depend not only on the environmental context, but that the direction of the responses can differ for different components of plant performance (growth vs. defense).

The arbuscular mycorrhizal fungi inoculation affects plant growth and flavonoid content in tomato plant (Lycopersicum esculentum Mill.)

“…This study pointed out that AMF inoculation improved nutrient uptake into the root, especially phosphor and nitrogen, which play a role in plant growth [30]. Nutrient and water availability conditions in soil regulated the effect of AMF on plant growth, which has been reported in some plants, such as apple [31], Artemisia ordosica [32], cherry tomato [33], and Boswellia papyrifera [28]. The positive effect of AMF inoculation occurs when nutrients and soil water are sufficient.…”

Arbuscular Mycorrhizal Fungi and Higher Plants

“…Being an inevitable element for plant functions, P is required by plants during various developmental stages. The utilization of inorganic P (Pi) from the soil is not an easy task for many plant species due to its low mobility and solubility in the soil (Wang et al 2023). Since plants alone cannot absorb sufficient Pi for their utilization, they seek help from the mycorrhizal fungal partner and fulfill their need (Ferrol et al 2019).…”

“…However, Artemisia ordosica plants inoculated with F. mosseae, an AM fungus, lowered the availability of leaf P, indicating that AMF association may not always enhance plant nutrient levels. Moreover, a lowering in leaf P content due to the symbiosis between A. ordosica and F. mosseae negatively regulated the population of a foliar herbivore Chrysolina aeruginosa, emphasizing that AMF-mediated reduction in P concentration of A. ordosica leaves might have a positive role in limiting the damages caused by C. aeruginosa (Wang et al 2023). In addition to the enhancement in plant nutrient uptake, AMF association also contributes to the sequestration of heavy metals (HMs) present in HM-polluted soil (Khan et al 2022), suggesting that AMF interaction may have the potential to alleviate the toxic effect of HM stress.…”

Mutualist-Provided Resources Increase Susceptibility to Parasites

“…Broadly, nitrogen can be utilized for size, photosynthesis, signaling, and defense. The pattern we identified of an intermediate peak may help to explain the wide range of effects of mutualisms on parasitism; while we focused on increasing susceptibility to parasites, many mutualisms do deter parasites (Braquart-Varnier et al 2015, Gonzalez-Teuber et al 2014, Jander 2015, Clay 1988, Wang et al 2023). Nitrogen as a resource could both attract as well as defend against antagonists depending on the resource landscape, availability, and use.…”

“…It has been noted, however, that if plant growth rate is greater than biomass removal by antagonism, increased plant defenses appear not to be necessary (Lou & Baldwin 2004). The peak in size-adjusted parasite load at intermediate nitrogen levels may help to explain the wide range of effects of mutualisms on parasitism; while we focused on increasing susceptibility to parasites, many mutualisms do deter parasites (Braquart-Varnier et al 2015;Clay 1988;González Teuber et al 2014;Jandér 2015;Wang et al 2023). Nitrogen as a resource could both attract as well as defend against antagonists depending on the resource landscape, availability, and use.…”