Close Encounters

A parasitic plant can cause an invasive plant’s allies to switch sides

Scaldweed, Cuscuta grovonii, can prevent an invasive plant from using soil microbes to help invade territory - and the parasite can even become more vicious by using those same microbes against its invasive host.

Readers of AoB PLANTS will know that invasive plants can benefit from local microbes when moving into an area, attracting more fungi to search for nutrients than native species. There has also been a lot of work in China recently looking for natural defences against such plants. In particular, they’re looking at parasitic plants, the idea that if the invaders do so well, they’d be excellent targets for hungry parasites. Now, Chaonan Cai and colleagues at Taizhou University, China, have found that parasitic plants like Scaldweed can tap into the benefits of these microbes through the invaders. Getting the extra help makes the Scaldweed more harmful, increasing its power to control invasive plants.

A thin yellow string entwined around a green leafy plant. The yellow stem appears to have ensnared the leafier plant. There are no leaves at all on the yellow stem.
Cuscuta gronovii – scaldweed – at the Skaneateles Conservation Area, Onondaga County, New York, USA. Image: R. A. Nonenmacher / Wikimedia Commons.

The botanists made the discovery by growing the invasive plant Alligator weed, Alternanthera philoxeroides, a severe problem in China. First, they grew the Alligator weed in microbe-laden soil. They found that the native microbes only increased the biomass of the Alligator weed if there was no parasite.

Next, they grew the plants in microbe-free soil. Now the Alligator weed grew without harm, despite supporting a parasite. But add the soil microbes and the Scaldweed reduced the biomass of the invasive plant.

Our results showed that parasitism can suppress the effects of native soil microbes on the growth of invasive plants. Such a suppression effect may result from the reduced benefit from soil microbes due to changes in microbial communities, or the fact that part of the benefit was transferred to the parasitic plants. Although direct contact between parasitic plants and the soil ecosystem through roots may be minimal or nonexistent, parasitic plants can have considerable effects on soil organisms. On one hand, parasitism can affect the community of rhizosphere soil microbes by changing the root exudate or by changing the mutualism between the host and soil microbes; on the other hand, parasitic plants may affect the community of soil microbes through the inputs of their particularly nutrient-rich litter.

In our study, we speculated that the enhanced deleterious effect of parasites on A. philoxeroides might have resulted from the fact that native soil microbes promote the growth of host plants, and C. grovonii can acquire more resources from the host plant, thereby causing a more deleterious effect on A. philoxeroides. Therefore, we encourage exploration of the potential of parasitic plants to suppress invasive species and develop methods for practical applications in ecological restoration and nature conservation.

Cai et al. 2023.

READ THE ARTICLE

Cai, C., Zhao, Y., Yuan, Y. and Li, J. (2023) “Parasitism shifts the effects of native soil microbes on the growth of the invasive plant Alternanthera philoxeroides,” Life (Basel, Switzerland), 13(1), p. 150. Available at: https://doi.org/10.3390/life13010150.

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