Tomonori Tsunoda

Availability and Temporal Heterogeneity of Water Supply Affect the Vertical Distribution and Mortality of a Belowground Herbivore and Consequently Plant Growth

We examined how the volume and temporal heterogeneity of water supply changed the vertical distribution and mortality of a belowground herbivore, and consequently affected plant biomass. Plantago lanceolata (Plantaginaceae) seedlings were grown at one per pot under different combinations of water volume (large or small volume) and heterogeneity (homogeneous water conditions, watered every day; heterogeneous conditions, watered every 4 days) in the presence or absence of a larva of the belowground herbivorous insect, Anomala cuprea (Coleoptera: Scarabaeidae). The larva was confined in different vertical distributions to top feeding zone (top treatment), middle feeding zone (middle treatment), or bottom feeding zone (bottom treatment); alternatively no larva was introduced (control treatment) or larval movement was not confined (free treatment). Three-way interaction between water volume, heterogeneity, and the herbivore significantly affected plant biomass. With a large water volume, plant biomass was lower in free treatment than in control treatment regardless of heterogeneity. Plant biomass in free treatment was as low as in top treatment. With a small water volume and in free treatment, plant biomass was low (similar to that under top treatment) under homogeneous water conditions but high under heterogeneous ones (similar to that under middle or bottom treatment). Therefore, there was little effect of belowground herbivory on plant growth under heterogeneous water conditions. In other watering regimes, herbivores would be distributed in the shallow soil and reduced root biomass. Herbivore mortality was high with homogeneous application of a large volume or heterogeneous application of a small water volume. Under the large water volume, plant biomass was high in pots in which the herbivore had died. Thus, the combinations of water volume and heterogeneity affected plant growth via the change of a belowground herbivore.

Effects of belowground vertical distribution of a herbivore on plant biomass and survival in Lolium perenne

Root herbivory affects plant performance, but the effects are not well understood. We tested the effects of the vertical distribution of a root-feeding beetle larva (Anomala cuprea) by restricting its access to the top, middle, or bottom zone in pots of perennial ryegrass (Lolium perenne) or by allowing unrestricted access. We predicted that plant mortality, biomass, and biomass allocation should change with the zone of root herbivory, because both the magnitude of root loss and the consequences of such loss are specific to the point of damage. Seven of nine plants died in each treatment in which the larvae had access to the top zone. In contrast, no plants died when larvae occupied the middle or bottom zones. Plants were killed when the larvae grazed the root base and severed the shoots from the roots. Moreover, total plant biomass and biomass allocation to roots were significantly lower when the larvae were confined to the top and middle feeding zones. The greatest number of roots were removed when the larvae occupied the top feeding zone. Thus, the vertical distribution of a belowground herbivore is crucially important to plant fate. In nature, most belowground herbivores are concentrated near the soil surface, and thus the effects of belowground herbivory are often more severe than the effects of aboveground herbivory.

Interactive effects of soil nutrient heterogeneity and belowground herbivory on the growth of plants with different root foraging traits

AimsPlants with precise root foraging patterns can proliferate roots preferentially in nutrient-rich soil patches. When nutrients are distributed heterogeneously, this trait is often competitively advantageous in pot experiments but not field experiments. We hypothesized that this difference is due to belowground herbivory under field conditions.MethodsWe performed pot experiments using seedlings of Lolium perenne (a more precise root foraging species) and Plantago lanceolata (a less precise root foraging species). The experiment had a two-way factorial randomized block design, with nutrient distribution pattern (homogeneous or heterogeneous) and belowground herbivore (present or absent) as the two factors. Each pot contained one seedling of each species.ResultsWith no herbivore present, plant biomass was smaller in the heterogeneous nutrient treatment than in the homogeneous treatment in P. lanceolata, but not in L. perenne. Under homogeneous nutrient distribution, plant biomass was lower in both species with a herbivore present than with no herbivore. Under heterogeneous nutrient distribution, biomass reduction due to herbivory occurred only in L. perenne.ConclusionsRoots of the precise root foraging species were grazed more under the heterogeneous nutrient distribution, suggesting that the herbivore more efficiently foraged for roots in nutrient-rich soil patches.

Root and shoot glucosinolate allocation patterns follow optimal defence allocation theory

Summary Optimal defence allocation theory (ODT) is one of the most prominent theoretical frameworks to explain the allocation of defence compounds within plants. It predicts that the most valuable and vulnerable plant organs have the highest levels of chemical defence. The ODT has been well worked out and experimentally tested for shoot defences, but not for root defences. To assess if ODT principles apply similarly to roots and shoots, we examined glucosinolates in above-ground and below-ground organs of nine plant species belonging to two families. In order to evaluate whether ODT equally applies to shoot and root organs, we designed a conceptual model in which above-ground and below-ground organs were assigned to orders of importance to plant performance. We hypothesized that organs constituting the plants core structure are better protected than more distal organs. The nine plant species were cultivated, and their roots and shoots were harvested and divided into three orders for glucosinolate analysis. Using a specialist (Delia radicum) and a generalist (Amphimallon solstitiale) root herbivore, we also experimentally tested the hypothesis that the generalist herbivore prefers to feed on fine roots (FRs) with a low glucosinolate concentration, while the specialist prefers taproots (TRs) with a high glucosinolate concentration. We found that both in roots and shoots, the higher ordered core structural organs (TRs and stems) had the highest levels of glucosinolates. Below-ground, TRs and lateral roots were better protected than the more distal, and less costly, FRs in seven out of nine species tested. The specialist root herbivore preferred feeding on the highly defended TRs, which is in line with what has been found for above-ground specialist herbivores. Moreover, the glucosinolate concentration in roots overall was significantly higher than that in shoots. Synthesis. These results support the hypothesis that Optimal defence allocation theory (ODT) generally applies to glucosinolate allocation in above-ground and below-ground organs and may mainly serve to maintain the integrity of the main plant structure. Moreover, it suggests that above-ground and below-ground insect herbivores independently exert similar selection pressures on defence allocation patterns in roots and shoots.

Effects of Elevated Atmospheric CO2 on Respiratory Rates in Mature Leaves of Two Rice Cultivars Grown at a Free-Air CO2 Enrichment Site and Analyses of the Underlying Mechanisms

Respiratory CO2 efflux and O2 uptake rates in leaves change in response to the growth CO2 concentration ([CO2]). The degrees of change vary depending on the responses of cellular processes such as nitrogen (N) assimilation and accumulation of organic acids to growth [CO2]. However, the underlying mechanisms remain unclear. Here, we examined the respiratory characteristics of mature leaves of two rice varieties with different yield capacities at different growth stages under ambient and elevated [CO2] conditions at a free-air CO2 enrichment site. We also examined the effect of increased water temperature on leaf respiration. We measured the rates of CO2 efflux and O2 uptake, and determined N contents, primary metabolite contents and maximal activities of respiratory enzymes. The leaf CO2 efflux rates decreased in plants grown at elevated [CO2] in both varieties, and were higher in high-yielding Takanari than in Koshihikari. The leaf O2 uptake rates showed little change with respect to growth [CO2] and variety. The increased water temperature did not significantly affect the CO2 efflux and O2 uptake rates. The N and amino acid contents were significantly higher in Takanari than in Koshihikari. The enhanced N assimilation in Takanari may have consumed more respiratory NADH, leading to higher CO2 efflux rates. In Koshihikari, the ratio of tricarboxylic acid (TCA) cycle intermediates changed and maximal activities of enzymes in the TCA cycle decreased at elevated [CO2]. Therefore, the decreased rates of CO2 efflux in Koshihikari may be due to the decreased activities of TCA cycle enzymes at elevated [CO2].

The 30th anniversary of Ecological Research: past, present, and future

In 2016, Ecological Research (ER) celebrated its 30th anniversary. ER’s goal is to be the leading ecological, evolutionary, and biodiversity journal in Asia. This article introduces the development of ER, improvements to its editorial system and their outcomes, and the strategies designed to achieve this goal. ER has already become a leading comprehensive and international publication as shown by statistical evidence and its strong editorial foundation. However, some members of the Ecological Society of Japan (ESJ) retain impressions of an old stereotype about ER. The discrepancy between the current status of the journal and its stereotype may explain why submissions from Japan remain static. A new article category for ER, Biodiversity in Asia, was created to encourage Asian studies. In addition, the Forum category is dedicated to promoting a broad understanding of the ESJ’s various activities. To promote open science, the proportion of open access articles in the journal is increasing. The publication of Data papers has been accelerated to improve the public availability of excellent open data sets. ER symposia and seminars provide good opportunities for members to participate. ER financially supports the invitation of scientists internationally to facilitate research exchanges with other countries and consequently promotes the internationalization of the ESJ. The ESJ is open to the world’s ecologists, and your participation in developing ER is welcome.