Predominant frameworks for understanding plant ecology have an aboveground bias that neglects soil micro-organisms. This is inconsistent with recent work illustrating the importance of soil microbes in terrestrial ecology. Microbial effects have been incorporated into plant community dynamics using ideas of niche modification and plant–soil community feedbacks. Here, we expand and integrate qualitative conceptual models of plant niche and feedback to explore implications of microbial interactions for understanding plant community ecology. At the same time we review the empirical evidence for these processes. We also consider common mycorrhizal networks, and propose that these are best interpreted within the feedback framework. Finally, we apply our integrated model of niche and feedback to understanding plant coexistence, monodominance and invasion ecology.

http://europepmc.org/articles/PMC2921684?pdf=render

Rooting theories of plant community ecology in microbial interactions

Plant litter represents a major basal resource in streams, where its decomposition is partly regulated by litter traits. Litter-trait variation may determine the latitudinal gradient in decomposition in streams, which is mainly microbial in the tropics and detritivore-mediated at high latitudes. However, this hypothesis remains untested, as we lack information on large-scale trait variation for riparian litter. Variation cannot easily be inferred from existing leaf-trait databases, since nutrient resorption can cause traits of litter and green leaves to diverge. Here we present the first global-scale assessment of riparian litter quality by determining latitudinal variation (spanning 107°) in litter traits (nutrient concentrations; physical and chemical defences) of 151 species from 24 regions and their relationships with environmental factors and phylogeny. We hypothesized that litter quality would increase with latitude (despite variation within regions) and traits would be correlated to produce ‘syndromes’ resulting from phylogeny and environmental variation. We found lower litter quality and higher nitrogen:phosphorus ratios in the tropics. Traits were linked but showed no phylogenetic signal, suggesting that syndromes were environmentally determined. Poorer litter quality and greater phosphorus limitation towards the equator may restrict detritivore-mediated decomposition, contributing to the predominance of microbial decomposers in tropical streams.

http://ecite.utas.edu.au/123684/1/123684%20-%20Riparian%20plant%20litter%20quality%20increases%20with%20latitude.pdf

Riparian plant litter quality increases with latitude

Understanding, modeling, and predicting the impact of global change on ecosystem functioning across biogeographical gradients can benefit from enhanced capacity to represent biota as a continuous distribution of traits. However, this is a challenge for the field of biogeography historically grounded on the species concept. Here we focus on the newly emergent field of functional biogeography: the study of the geographic distribution of trait diversity across organizational levels. We show how functional biogeography bridges species-based biogeography and earth science to provide ideas and tools to help explain gradients in multifaceted diversity (including species, functional, and phylogenetic diversities), predict ecosystem functioning and services worldwide, and infuse regional and global conservation programs with a functional basis. Although much recent progress has been made possible because of the rising of multiple data streams, new developments in ecoinformatics, and new methodological advances, future directions should provide a theoretical and comprehensive framework for the scaling of biotic interactions across trophic levels and its ecological implications.

https://www.pnas.org/content/pnas/111/38/13690.full.pdf

The emergence and promise of functional biogeography

Macroclimatic variation along latitudinal gradients provides an excellent natural laboratory to investigate the role of temperature and the potential impacts of climate warming on terrestrial organisms. Here, we review the use of latitudinal gradients for ecological climate change research, in comparison with altitudinal gradients and experimental warming, and illustrate their use and caveats with a meta-analysis of latitudinal intraspecific variation in important life-history traits of vascular plants. We first provide an overview of latitudinal patterns in temperature and other abiotic and biotic environmental variables in terrestrial ecosystems. We then assess the latitudinal intraspecific variation present in five key life-history traits [plant height, specific leaf area (SLA), foliar nitrogen:phosphorus (N:P) stoichiometry, seed mass and root:shoot (R:S) ratio] in natural populations or common garden experiments across a total of 98 plant species. Intraspecific leaf N:P ratio and seed mass significantly decreased with latitude in natural populations. Conversely, the plant height decreased and SLA increased significantly with latitude of population origin in common garden experiments. However, less than a third of the investigated latitudinal transect studies also formally disentangled the effects of temperature from other environmental drivers which potentially hampers the translation from latitudinal effects into a temperature signal. Synthesis. Latitudinal gradients provide a methodological set-up to overcome the drawbacks of other observational and experimental warming methods. Our synthesis indicates that many life-history traits of plants vary with latitude but the translation of latitudinal clines into responses to temperature is a crucial step. Therefore, especially adaptive differentiation of populations and confounding environmental factors other than temperature need to be considered. More generally, integrated approaches of observational studies along temperature gradients, experimental methods and common garden experiments increasingly emerge as the way forward to further our understanding of species and community responses to climate warming.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/1365-2745.12074

Latitudinal gradients as natural laboratories to infer species' responses to temperature

Question: Are plant traits more closely correlated with mean annual temperature, or with mean annual precipitation? Location: Global. Methods: We quantified the strength of the relationships between temperature and precipitation and 21 plant traits from 447,961 species-site combinations worldwide. We used meta-analysis to provide an overall answer to our question.

/pdf/which-is-a-better-predictor-of-plant-traits-temperature-or-4ci4es0swl.pdf

Which is a better predictor of plant traits: temperature or precipitation?

• It has long been believed that plant species from the tropics have higher levels of traits associated with resistance to herbivores than do species from higher latitudes. A meta-analysis recently showed that the published literature does not support this theory. However, the idea has never been tested using data gathered with consistent methods from a wide range of latitudes. • We quantified the relationship between latitude and a broad range of chemical and physical traits across 301 species from 75 sites world-wide. • Six putative resistance traits, including tannins, the concentration of lipids (an indicator of oils, waxes and resins), and leaf toughness were greater in high-latitude species. Six traits, including cyanide production and the presence of spines, were unrelated to latitude. Only ash content (an indicator of inorganic substances such as calcium oxalates and phytoliths) and the properties of species with delayed greening were higher in the tropics. • Our results do not support the hypothesis that tropical plants have higher levels of resistance traits than do plants from higher latitudes. If anything, plants have higher resistance toward the poles. The greater resistance traits of high-latitude species might be explained by the greater cost of losing a given amount of leaf tissue in low-productivity environments.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.2011.03732.x

Putting plant resistance traits on the map: a test of the idea that plants are better defended at lower latitudes

Summary 1. The coexistence of leguminous trees and C4 grasses in many African savannas forces competition between these two distinct plant life-forms. The nature of tree–grass coexistence and the consequent competition for resources remains poorly understood. 2. We hypothesized that grass suppression of tree seedling growth was due to competition for N in plants not capable of fixing N2 and due to the costs of N2 fixation in those capable of nodulation. 3. Growth and N2 fixation of nodulating (Acacia karroo, Acacia nilotica, Acacia tortilis and Acacia nigrescens) and non-nodulating (Acacia ataxacantha Acacia brevispica and Acacia schweinfurthii) Acacia spp. in response to soil characteristics and fertilizer variations in irrigated field experiments were compared. The extent of N2 fixation was determined fromd 15 Nv alues. 4. Grass suppressed the growth of all species, but particularly of the non-nodulating species. The N2-fixing tree seedlings had high tissue N and high water-use efficiencies (WUE, based on d 13 C) relative to non-nodulating legumes, making the N2-fixing species strong competitors with C4 grasses, which have low tissue N contents and high WUE. The suppression of seedling growth by grass was smaller for plants grown in a soil with 66 mg kg )1 than in a soil with 9 mg kg )1 of Bray II P. The tissue N : P ratios (15.1) indicated that P-limitation constrained growth of seedlings in soils with low Bray II P when grass was present, rather than the energetic costs of N2 fixation. 5. Synthesis .I nAcacia savannas and in the absence of water limitation, competition for N is the main constraint imposed by grass on growth of Acacia seedlings and that the ability to fix N2 overcomes this limitation. However, the growth of N2 fixing Acacias may be additionally limited by grass competition for P.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2745.2009.01594.x

An van Cauter

Papers

Putting plant resistance traits on the map: a test of the idea that plants are better defended at lower latitudes

Growth of N2‐fixing African savanna Acacia species is constrained by below‐ground competition with grass