Focus issue on plants and their soil communities

The below-ground environment is often viewed with a bipolar eye, being on the one hand a hostile, alien environment where death and decay reside, and on the other a place of life-giving renewal that leads to fertility and verdant luxury. The soil is the hidden half, unseen by surface dwellers, yet rich with a myriad of creatures whose forms and activities are strange and exotic, being more likely to appear in our nightmares than in our dreams. Even within the plant kingdom, the below-ground body of the plant is dark and mysterious, with sinuous roots reaching deep into recesses of organic decay. What cannot be seen is often what can be ignored, and so in their mystery, below-ground environments have become convenient dumping grounds for our refuse, organic and otherwise. Out of sight, out of mind.

Unfortunately, as witnessed throughout history, including today, the soil does not comprise inert layers of dirt and rock in which we can conveniently hide our wastes, but a living and often fragile ecological community whose functions depend upon its inhabitants, however hideous and dangerous they may seem. Kill the inhabitants, and one kills the soil, which in turn will collapse the above-ground ecosystems upon which our vitality depends. This realization is driving a new era of botanical research on community dynamics in below-ground ecosystems, some of which regularly appear in Annals of Botany. Occasionally, we receive multiple papers on below-ground processes which we group together into focus issues, such as the Focus on Plants and Soils presented in the current issue. Here, we group five papers addressing various aspects of plant and soil community dynamics, as well as how these below-ground dynamics affect the above-ground systems that we readily recognize and cherish.

The papers represent an eclectic mix that demonstrates the range of research on the dynamic interactions between soil biota, nutrients and roots, along with their implications for above-ground vegetation. The highlights include Li et al.’s (2023) examination of how soil phosphorus (P) amendments can alleviate negative interactions between microbes and roots in a semi-arid steppe. Notably, they observed that P amendments reduced expression of defence genes in roots, implicating amelioration of competitive and/or parasitic interactions between roots and microbes in a resource-rich environment. In contrast to these postulated antagonisms between plants and microbes, the mutualistic relationships between mycorrhizal fungi and plants are essential to primary production in ecosystems and thus have a major influence over vegetation communities. The nature of this dependency is addressed by López-Angulo et al. (2023), who show that the assembly of below-ground arbuscular–mycorrhizal communities is a reflection of above-ground vegetation composition as well as soil properties. To understand community processes, they hypothesize that it is important to understand the phylogenetic relationships among the mutualistic partners. Similarly, nutrient acquisition and plant growth can reflect the physiology of plant functional types, such as found in relatively fast-growing and high-nutrient-requiring annuals as compared to slow-growing, persistent perennials. Zhang et al. (2023) note that the different strategies can also have a strong phylogenetic basis, with ferns tending to fall into the slower-growing, lower-nutrient-requiring categories while herbaceous angiosperms such as annual grasses fall into the faster-growing, nutrient-demanding categories. The success of angiosperms over ferns in recent geological time could be due in part to a less conservative strategy found in angiosperms than in ferns, while the occurrence of ferns in the modern flora may reflect conservative strategies that confer fitness on oligotrophic soils of low fertility. The size class of forest trees also influences their relationship to soil fertility, as shown by Ren et al. (2023), who noted that small-stature trees in old-growth temperate forests of China respond to increasing levels of soil nitrogen and phosphorus, in contrast to large trees of the forest canopy, which show little response to nutrient status. However, in response to neighbourhood crowding, growth in both large and small trees was reduced with greater effects on large trees. As a highlight of how soils can influence the above-ground features of plants in a surprising way, Yamawo and Tomlinson (2023) describe how spines and phenolic content in the Asian deciduous tree Aralia elata respond to soil nutrient status and light availability. Spines and phenolics are contrasting defence strategies in plants. Both are expensive, so it is reasonable to expect that resource allocation to each reflects a cost–benefit trade-off within the plant. Yamawo and Tomlinson demonstrate that allocation to spines is greatest in high light situations, where herbivory would enhance light availability by consumption of the leaf canopy, and an abundant carbon supply is able to support prolific spine growth. Enhanced soil nutrients, by contrast, reduced allocation to phenolics while having no effect on spine production, suggesting mechanical defence may become more important in competitive situations where the costs of phenolics would slow growth.

With the five papers in this focus issue, we hope the readers of Annals of Botany can gain a better appreciation of the intricacies of below-ground interactions and their consequences for above-ground vegetation. We also invite readers to consider organizing a focus issue to highlight original work within their particular research area. Focus issues normally consist of five to eight articles within a given theme, and which present novel research and insights that provide new perspectives to move the discipline forward. Focus issues should include original research reports, but will often present reviews and/or perspective articles that highlight the state of the art within the specialty. A short preface should also accompany the articles, calling attention to their leading contributions. Focus issues should not require the elaborate preparation of special issues, and will often be suitable for publishing the half-dozen or so reports in a typical conference symposium or workshop. High-resolution cover photos highlighting the theme of the focus issue are also encouraged. Funding support from the Annals of Botany company for symposia or workshops that are written up as a focus issue can also be considered.

To propose a focus issue, please submit a 100- to 300-word summary of the topics and potential authors, including a timeline and statement of suitability for the Annals of Botany. If the focus issue follows a symposium or workshop for which the organizers wish to receive financial support from the Annals of Botany company, the proposal should also have details on the conference and proposed symposium, including dates, budget and expected audience. Please send proposals to the managing editor at Annals of Botany at office@annbot.com.

LITERATURE CITED