Extraradical hyphae exhibit more plastic nutrient-acquisition strategies than roots under nitrogen enrichment in ectomycorrhiza-dominated forests

Ectomycorrhizal (ECM) functional traits related to nutrient acquisition are impacted by nitrogen (N) deposition. However, less is known about whether these nutrient-acquisition traits associated with roots and hyphae differentially respond to increased N deposition in ECM-dominated forests with different initial N status. We conducted a chronic N addition experiment (25 kg N ha⁻¹ year⁻¹) in two ECM-dominated forests with contrasting initial N status, that is, a Pinus armandii forest (with relatively low N availability) and a Picea asperata forest (with relatively high N availability), to assess nutrient-mining and nutrient-foraging strategies associated with roots and hyphae under N addition. We show that nutrient-acquisition strategies of roots and hyphae differently respond to increased N addition. Root nutrient-acquisition strategies showed a consistent response to N addition, regardless of initial forest nutrient status, shifting from organic N mining toward inorganic N foraging. In contrast, the hyphal nutrient-acquisition strategy showed diverse responses to N addition depending on initial forest N status. In the Pinus armandii forest, trees increased belowground carbon (C) allocation to ECM fungi thus enhancing hyphal N-mining capacity under increased N availability. By comparison, in the Picea asperata forest, ECM fungi enhanced both capacities of P foraging and P mining in response to N-induced P limitation. In conclusion, our results demonstrate that ECM fungal hyphae exhibit greater plasticity in nutrient-mining and nutrient-foraging strategies than roots do in response to changes of nutrient status induced by N deposition. This study highlights the importance of ECM associations in tree acclimation and forest function stability under changing environments.     

Competition between near and far dispersers in spatially structured habitats

Competitive interactions and invasibility between short- and long-distance dispersal was investigated in a population on a heterogeneous landscape with spatial correlations in habitat types, and where the driving interaction between individuals is competition for space. Stochastic spatially explicit simulations were used, along with differential equation models based on pair approximations. Conditions under which either dispersal strategy can successfully invade the other were determined, as a function of the amount and clustering of suitable habitat and the relative costs involved in the two dispersal strategies. Long-distance dispersal, which reduces intraspecific competition, is sometimes advantageous even where aggregation of suitable habitat would otherwise favor short-distance dispersal, although certain habitat distributions can lead to either strategy being dominant. Coexistence is also possible on some landscapes, where the spatial structure of the populations partitions suitable sites according to the number of suitable neighboring sites. Mutual competitive exclusion, where whichever strategy is established first cannot be invaded, is also possible. All of these results are observed even when there is no intrinsic difference in the two strategies' costs, such as mortality or competitive abilities.     

Soil‐dwelling insect pests of tree crops in Sub‐Saharan Africa,problems and management strategies—A review

This review aims to draw the attention of researchers, ecologists and farmers to the threats of soil‐dwelling insect pests on important tree crops in sub‐Saharan Africa, with a special focus on termites. It synthesizes the information on the effects of various factors affecting soil pest occurrence and damage, suggesting that the resultant undesirable effects of soil pests in this region are largely as a result of indiscriminate tree cutting, slash‐and‐burn agriculture and indiscriminate use of pesticides. Major insect orders, their host ranges and the nature of damage on selected tree crops are described. This study further critiques existing soil pest management practices, showing that majority of soil pest management practices are ineffective. Thus, management strategies like “attract and kill” approach based on entomopathogenic fungi need to be studied, developed and emphasized for the management of soil insect pests in sub‐Saharan Africa. A conclusion section attempts to offer suggestions for ways in which future work on soil pests in sub‐Saharan Africa could proceed.     

Transfer of Pterosiphonia pumila Yendo to the genus Symphyocladia (Rhodomelaceae, Rhodophyta)

The red alga Pterosiphonia pumila Yendo (Rhodomelaceae, Ceramiales) has flattened thalli in which there is complete lateral fusion between branches and their parental axes during early stages of development, the laterals only becoming distally free in reproduc-tively mature plants. This results in a leaf-like organization distinct from that displayed by all other species of the genus Pterosiphonia, the members of which have terete to compressed axes that are congenitally fused along only a few (<4.5) proximal segments of the laterals. The organization of P. pumila is, thus, similar to that of species of the genus Symphyocladia, to which it is here transferred as Symphyoctadia pumila (Yendo) Uwai et Masuda, comb. nov. Symphyoctadia pumila is restricted to Japan and Korea and is distinguished from the other three described species of Symphyocladia by its small (<3 cm long) ecorticate thalli and complete lack of vegetative trichoblasts. Symphyoctadia pennata Okamura has a similar suite of characteristics, has been successfully cross-bred with S. pumila in laboratory culture and is, thus, placed in synonymy with S. pumila.     

On the ecological and evolutionary significance of storage in clonal plants

Environmental heterogeneity has received wide attention in clonal plant research over the last decade. Most studies have focussed on the effects of spatial variation in environmental conditions on the performance of ramets and genets, while the effects of temporal heterogeneity have only occasionally been studied. As a consequence, our current knowledge about functional responses of clonal plants to habitat patchiness is biased towards spatial aspects of environmental heterogeneity. Nevertheless, temporal changes in biotic and abiotic conditions do occur in most natural habitats, and they are very likely to affect plant growth and performance, and to create positive selection pressures on traits that can buffer plants against unfavorable consequences of this variability. Storage of resources is a widespread phenomenon in clonal plant species. Typical clonal structures such as stolons, rhizomes and hibernacles serve as storage organs. However, the ecologic significance of storage in clonal plant structures remains partly unclear. We suggest that the lack of understanding with respect to resource storage in clonal plants be related to our poor knowledge of ecologic implications of temporal habitat heterogeneity in natural environments. Resource storage can be understood as a safety measure against temporal changes in the growing conditions of plants. This paper summarizes existing information about the ecologic relevance of storage in clonal plants and it tries to develop a framework for further investigation of resource storage as a strategy to enhance the performance of clonal plants in temporally variable environments.     

Genetic and physiological bases for phenological responses to current and predicted climates

We are now reaching the stage at which specific genetic factors with known physiological effects can be tied directly and quantitatively to variation in phenology. With such a mechanistic understanding, scientists can better predict phenological responses to novel seasonal climates. Using the widespread model species Arabidopsis thaliana, we explore how variation in different genetic pathways can be linked to phenology and life-history variation across geographical regions and seasons. We show that the expression of phenological traits including flowering depends critically on the growth season, and we outline an integrated life-history approach to phenology in which the timing of later life-history events can be contingent on the environmental cues regulating earlier life stages. As flowering time in many plants is determined by the integration of multiple environmentally sensitive gene pathways, the novel combinations of important seasonal cues in projected future climates will alter how phenology responds to variation in the flowering time gene network with important consequences for plant life history. We discuss how phenology models in other systems—both natural and agricultural—could employ a similar framework to explore the potential contribution of genetic variation to the physiological integration of cues determining phenology.     

The use of optimal foraging theory in the understanding of fishing strategies: A case from Sepetiba Bay (Rio de Janeiro State,Brazil)

The community of Gamboa is located on Itacuruçá Island, Sepetiba Bay (State of Rio de Janeiro, Brazil) and includes 26 families, mostly of artisanal fishermen who use paddled or motor canoes, and encircling nets for fishing. In this study, predictions from optimal foraging theory (patch model), in particular of patch residence time, are compared to the observed behavior of fishermen on fishing trips. Fishermen's strategies differ depending on their intended prey. They spend more time in patches and use fewer patches for shrimp than for fish. Gamboa's fishermen tend to leave a patch later than predicted by the model. The difficulty in evaluating stock availability, the comparatively few patches available for shrimp, and the competitive aspects of fishing contribute to the explanation of this behavior.     

Regional environments, life-history patterns, and habitat use of spirostreptid millipedes in arid regions

Among diplopods with desert populations, only three species of Spirostreptida have been studied in an ecological context. The present review compares regional environments, life-history patterns, and uses of habitat by Orlhoporus ornatus (Girard) from southwestern North America, Archispirostreptus tumuliporus judaicus (Attems) from the eastern Mediterranean seaboard, and Harpagophora nigra (Attems) from southwestern Africa. Published and unpublished studies are used to explore evidence for convergence among these species, as opposed to traits adapting them to physical aspects of given regions or habitats. Unlike A. t. judaicus, O. ornatus and H. nigra are relatively restricted to arid habitats, although populations of all three species experience a variety of rainfall regimes and regional topographies. Where studied, O. ornatus and H. nigra hibernate during the long, often cool or cold dry season; they forage following warm-season rains. A. t. judaicus , in contrast, forages during its long, warm dry season and hibernates in the cool, wet winter. Populations from the Judaean and Negev deserts differ from those inhabiting a mesic habitat (Megiddo) closer to the coast in regard to rates of development, seasonal activity and seasonal water balance. Convergence in the form of well-developed desiccation resistance characterizes the two strictly desert species. All three species, together with other subtropical millipedes exposed to long dry seasons, are convergent with respect to patterns of diel surface activity and use of shelter. However species- and habitat-specific life-history features such as the seasonal timing of dormancy and emergence tend to mask convergence at the habitat level. Hence, the independent evolution of the three species with desert populations has resulted in life histories and habitat use that combine a moderate amount of convergence with considerable opportunistic adaptation to regional and local conditions.     

Plant functional types broadly describe water use strategies in the Caatinga,a seasonally dry tropical forest in northeast Brazil

1. In seasonally dry tropical forests, plant functional type can be classified as deciduous low wood density, deciduous high wood density, or evergreen high wood density species. While deciduousness is often associated with drought‐avoidance and low wood density is often associated with tissue water storage, the degree to which these functional types may correspond to diverging and unique water use strategies has not been extensively tested.
2. We examined (a) tolerance to water stress, measured by predawn and mid‐day leaf water potential; (b) water use efficiency, measured via foliar δ¹³C; and (c) access to soil water, measured via stem water δ¹⁸O.
3. We found that deciduous low wood density species maintain high leaf water potential and low water use efficiency. Deciduous high wood density species have lower leaf water potential and variable water use efficiency. Both groups rely on shallow soil water. Evergreen high wood density species have low leaf water potential, higher water use efficiency, and access alternative water sources. These findings indicate that deciduous low wood density species are drought avoiders, with a specialized strategy for storing root and stem water. Deciduous high wood density species are moderately drought tolerant, and evergreen high wood density species are the most drought tolerant group.
4. Synthesis. Our results broadly support the plant functional type framework as a way to understand water use strategies, but also highlight species‐level differences.