Evidence for facultative protocarnivory in Capsella bursa-pastoris seeds

Hattie R Roberts,Jim Provan,John M Warren

doi:10.1038/s41598-018-28564-x

Hattie R Roberts, Jim Provan + Show 1 more

Open Access

https://doi.org/10.1038/s41598-018-28564-x

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Abstract

Many plants derive nutrients by attracting, ensnaring and killing invertebrates, a process that is described as “protocarnivory”. This has been observed in seeds of the weed Capsella bursa-pastoris, but it is unclear as to whether it confers any material benefit in terms of germination, establishment and development. In the present study, seeds were germinated in zero, low, medium and high nutrient soils in both the presence and absence of nematodes (Steinernema feltiae). Nematodes were attracted to the seeds, with many dying within three days. Germination rates and seedling fresh masses were higher at all nutrient levels, and seedling fresh lengths were higher in all but the zero nutrient treatment, in the presence of nematodes. After transplantation, young plant fresh root lengths and dried leaf and root masses were generally higher in plants that had been germinated in the presence of nematodes across all nutrient levels, with the majority of significant differences being observed in the low-nutrient treatment. Our findings suggest that protocarnivory may play a role in the germination, establishment and early development of C. bursa-pastoris, and that this process may be facultative, since differences between nematode and non-nematode treatments were generally more pronounced in soils with low nutrient levels.

Highlights

Since the Gothic era, scientists, explorers and horticulturalists have formed a morbid fascination with carnivorous plants
It was hypothesised that (a) germination rate and seedling mass and length of C. bursa-pastoris would significantly increase in the presence of soil invertebrates; (b) seedlings established in the presence of nematodes would exhibit significantly greater development of leaves and roots compared to those that were not exposed to nematodes, and (c) these increases would be most pronounced in seedlings germinated in low nutrient soils
The findings of the present study suggest that protocarnivory may play a role in the germination, establishment and early development of Capsella bursa-pastoris

Summary

Introduction

Since the Gothic era, scientists, explorers and horticulturalists have formed a morbid fascination with carnivorous plants. There is a significant lack of evidence to suggest that C. bursa-pastoris seeds fulfil either criteria for carnivory described by Simons or Givnish et al.[3,4], and “protocarnivorous” may be a more suitable term to describe C. bursa-pastoris[2] Whether this mechanism truly acts to the plant’s advantage, i.e. whether C. bursa-pastoris gains a material benefit, has not been determined. The aim of the present study was to determine whether the protocarnivorous traits of C. bursa-pastoris seeds help them to establish, in low-nutrient soils, since it has been suggested previously that the mechanism of attraction, capture and death of small invertebrates may be advantageous to C. bursa-pastoris in such conditions[2]. It was hypothesised that (a) germination rate and seedling mass and length of C. bursa-pastoris would significantly increase in the presence of soil invertebrates; (b) seedlings established in the presence of nematodes would exhibit significantly greater development of leaves and roots compared to those that were not exposed to nematodes, and (c) these increases would be most pronounced in seedlings germinated in low nutrient soils

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