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The anatomical structures, i.e., the cortex and stele, are fundamental for the absorptive function of plant roots. Unraveling how the allometric structures are assembled in absorptive roots is essential for our understanding the plant ecology, physiology and responses to global environmental changes. In this review study, we first compile a globally largest dataset on key root structural traits, i.e., root diameter, cortex thickness and stele radius across 512 species. Using this largest dataset, we confirm an allometric relationship of absorptive root structures in a previous study using a much smaller species pool, i.e., the cortex thickness increased much faster than the stele radius with increasing root diameter. The allometric relationship is further validated within and across different plant growth forms (woody, grass, and liana species), mycorrhiza types (arbuscular mycorrhiza, ectomycorrhiza, and orchid mycorrhizas), phylogenetic gradients (from ferns to Orchidaceae of primitive angiosperms), and environmental change scenarios (e.g., the elevation of atmospheric CO2 concentration and nitrogen fertilization), supporting the universal allometric relationship in plant roots. We then summarized recent proceedings as well as possible issues on mechanisms underlying the root allometric relationship. The ecological and evolutionary implications for this allometric relationship in roots are also discussed. Finally, we propose several directions that should be stressed in future studies regarding the allometric relationship in plant roots.

Interactions among root and leaf traits (in particular, leaf hydraulic and leaf economics traits) are fundamental in generating diverse strategies in land plants, yet it remains a knowledge gap in mangrove plants that experiences saline stress distinct from most other vascular plants. Here, we tested the trait relationships in mangrove plants and compared them with typical land plants (non-mangrove). Consistent with non-mangrove plants, leaf hydraulic and economics traits were decoupled in mangrove plants. However, mangrove leaf economics traits correlated strongly with root hydraulic traits, which are normally decoupled in non-mangrove plants. Moreover, we observed a unique scaling relationship between leaf dry mass per area and root hydraulic traits in mangroves. The novel coordination between leaves and roots arises from the wide-presence of leaf water storage tissues in mangroves, and this potentially represents a new paradigm with which we look into the ecology, physiology and evolution of this important vegetation.

AimsGenerally, deciduous and evergreen trees coexist in subtropical forests, and both types of leaves are attacked by numerous insect herbivores. However, trees respond to and defend themselves from herbivores in different ways, and these responses may vary between evergreen and deciduous species. To understand tree responses to leaf herbivore attack under varying intensities of herbivory.MethodsWe examined both the percentage of leaf area removed by herbivores as well as the percentage of leaves attacked by herbivores to evaluate leaf herbivore damage across 15 subtropical deciduous and evergreen trees, quantified plant responses to varying intensities of herbivory and analyzed both leaf herbivore attack and leaf traits among species.ResultsWe have found that there was a higher intensity of herbivory on deciduous species than evergreen species, both as percentage of leaf area removed and the percentage of leaves attacked. In addition, leaf herbivory was positively correlated with defensive traits (concentrations of tannin and lignin), and negatively correlated with nutrient content (ratios of NSC:lignin and NSC:cellulose), which may be largely attributed to long-term and frequent insect herbivore stress and potentially evolutionary arms races between plants and insects.ConclusionsThis study highlights that leaf responses to varying intensities of herbivory differed widely among subtropical plant species and there was a stronger defensive response for deciduous trees to leaf herbivore attack than that of evergreen trees. These results have implications for better understanding plant responses and defenses to varying intensities of herbivory, and reveal several underlying relationships between leaf traits and herbivory.