DNA metabarcoding dietary analyses of the wood mouse Apodemus speciosus on Innoshima Island, Japan, and implications for primer choice

We used DNA metabarcoding to assess the seasonal diets of the large Japanese wood mouse, Apodemus speciosus (Muridae, Rodentia), in forest edges adjacent to citrus orchards on Innoshima Island, Japan. We used one chloroplast and three mitochondrial DNA barcoding markers to determine mouse diets. Among the various plant and invertebrate diets, A. speciosus typically consumed Chinese cork oak (Quercus variabilis) in early spring (likely acorns preserved during winter) and gypsy moths (Lymantria dispar, a forest pest) in late spring and summer. In addition, we found that A. speciosus also preyed on orchard pests, including the gutta stink bug and other potentially harmful invertebrates. The season during which A. speciosus preyed on stink bugs corresponded with the harvest of orchard products. This study revealed several of the ecological roles of A. speciosus within the boundary zone between forest and human ecosystems. Furthermore, based on the performance of various mitochondrial markers in dietary profiling of invertebrate food items, we recommend the multi-locus DNA metabarcoding method to comprehensively assess the diet of A. speciosus.

Water Storage of Plants Cannot Be Ignored During The Process of Water Movement

Water migration and use are important processes in trees. However, it is possible to overestimate transpiration by equating the water absorbed by plant roots with that diffused back to the atmosphere via the stomata. The δ2H/δ18O technique and heat ratio method were used to explore the patterns of water use of coniferous and broad-leaved tree species to determine the proportions of water used for transpiration and water storage. Our results indicate that both species showed strong plasticity in their use of water sources. The species Platycladus orientalis (Oriental arbor-vitae) and Quercus variabilis (Chinese cork oak) primarily absorbed water from groundwater and the 60–100 cm soil layer, and Q. variabilis also absorbed water from the 0–20 cm and 20–40 cm soil layers during the dry season. Only P. orientalis was sensitive to precipitation and used water from the 0–20 cm layers. Q. variabilis did not change its water source but increased its uptake of groundwater during the rainy season. We observed reverse flow and hydraulic redistribution in P. orientalis, which alleviated the spatial heterogeneity of soil water and provided water for neighboring trees. Nocturnal sap flow in P. orientalis and Q. variabilis facilitated the storage of water in the trunk. The water used for storage in both species comprised 6–7% of the total quantity and therefore, should be considered in water balance models.

Across-trophic variation of potassium, calcium and magnesium stoichiometric traits in a parasitism food chain across temperate and subtropical biomes

Potassium (K), calcium (Ca) and magnesium (Mg) are three macro-elements essential for plants and animals. The ratios K : Mg or K : (Ca + Mg) are viewed as indices of physiological status in livestock animals. In plants, Ca, Mg and K concentrations can vary with climate in terrestrial ecosystems. Here, with a widespread tree species (Chinese cork oak, Quercus variabilis Blume) and an acorn predator (the weevil Curculio davidi Fairmaire), we investigate how K, Ca and Mg vary in soils, plant tissues (leaves and acorns) and a consumer (herbivore insects) with climatic variables induced by latitude (LAT) across the temperate–subtropical areas of eastern China. Concentrations of K, Ca and Mg in soils, leaves, acorns and weevil larvae showed different degrees of variation across the study area, but only Mg concentration increased significantly with rising LAT across all four trophic levels, albeit with varying slopes. With rising mean annual temperature (MAT) and precipitation (MAP), soil Ca significantly decreased, as did leaf and acorn K concentrations, whereas all four tropic levels showed significant decreases in Mg content with both MAT and MAP (P < 0.05–0.001). Leaf and acorn Ca : Mg showed significant relationships with LAT and MAT (P < 0.05–0.01). The K : (Mg + Ca) ratio in soils and weevil larvae increased linearly with MAP (P < 0.05), and acorn K : (Mg + Ca) ratio varied in a concave manner (P < 0.001). Our results suggest that variations of Ca, Mg and K in plant tissues and weevil larva across a study area of 20° LAT range were largely driven by climatic factors, and that Mg concentration changes in all four trophic levels with climate (and LAT) largely drive changes in soil, plant and consumer ratios between Mg, Ca and/or K. These results provide information on possible effects of climate change on nutrient dynamics in terrestrial ecosystems.