Negative conspecific interactions have been shown to promote diversity in plant communities, as have some heterospecific interactions such as intransitive competition and facilitation. However, it is ...unclear whether combinations of conspecific and other heterospecific interactions can also promote diversity in plant communities. We therefore investigated the effects of heterospecific plant interaction network architecture with and without conspecific interactions on alpha diversity, beta diversity and long‐term diversity.
We simulated long‐term plant community dynamics for theoretical plant interaction scenarios with modular, ring and nested networks of positive or negative heterospecific interactions and conspecific interactions, using a spatially explicit cellular automaton model that accounted for stochastic effects. Throughout the simulations several measures of diversity were recorded.
The way that heterospecific interactions affected diversity depended strongly on various characteristics of the architecture of the interaction network. Negative conspecific interactions generally promoted alpha diversity and reduced beta diversity, with a few key exceptions. Positive heterospecific ring interactions that resulted in cyclic appearance and disappearance of species groups led to the greatest long‐term diversity (a measure of the total diversity over time).
This study provides new theoretical insights into how the network architecture of heterospecific plant interactions can affect the diversity of plant communities over time and provides the first evidence that heterospecific plant interactions can increase long‐term diversity more than negative conspecific interactions alone.
A free Plain Language Summary can be found within the Supporting Information of this article.
A free Plain Language Summary can be found within the Supporting Information of this article.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Mycorrhizal networks, defined as a common mycorrhizal mycelium linking the roots of at least two plants, occur in all major terrestrial ecosystems. This review discusses the recent progress and ...challenges in our understanding of the characteristics, functions, ecology and models of mycorrhizal networks, with the goal of encouraging future research to improve our understanding of their ecology, adaptability and evolution. We focus on four themes in the recent literature: (1) the physical, physiological and molecular evidence for the existence of mycorrhizal networks, as well as the genetic characteristics and topology of networks in natural ecosystems; (2) the types, amounts and mechanisms of interplant material transfer (including carbon, nutrients, water, defence signals and allelochemicals) in autotrophic, mycoheterotrophic or partial mycoheterotrophic plants, with particular focus on carbon transfer; (3) the influence of mycorrhizal networks on plant establishment, survival and growth, and the implications for community diversity or stability in response to environmental stress; and (4) insights into emerging methods for modelling the spatial configuration and temporal dynamics of mycorrhizal networks, including the inclusion of mycorrhizal networks in conceptual models of complex adaptive systems. We suggest that mycorrhizal networks are fundamental agents of complex adaptive systems (ecosystems) because they provide avenues for feedbacks and cross-scale interactions that lead to self-organization and emergent properties in ecosystems. We have found that research in the genetics of mycorrhizal networks has accelerated rapidly in the past 5 y with increasing resolution and throughput of molecular tools, but there still remains a large gap between understanding genes and understanding the physiology, ecology and evolution of mycorrhizal networks in our changing environment. There is now enormous and exciting potential for mycorrhizal researchers to address these higher level questions and thus inform ecosystem and evolutionary research more broadly.
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► Mycorrhizal networks have a scale-free spatial pattern in natural ecosystems. ► Carbon flux through networks increases with shade and mycoheterotrophy. ► Networks can facilitate early plant survival, growth and defence responses. ► Feedbacks through networks may affect ecosystem diversity and stability. ► Network patterns and processes are consistent with complex adaptive system models.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
South-western Australia harbours a biodiversity hotspot on severely phosphorus-impoverished soils. Threats include eutrophication due to phosphorus enrichment, due to increased fire frequency and ...spraying with phosphite to reduce the impacts of the introduced pathogen Phytophthora cinnamomi. We propose a strategy to work towards alternatives to phosphite for pathogen management.
South-western Australia harbours a global biodiversity hotspot on the world's most phosphorus (P)-impoverished soils. The greatest biodiversity occurs on the most severely nutrient-impoverished soils, where non-mycorrhizal species are a prominent component of the flora. Mycorrhizal species dominate where soils contain slightly more phosphorus. In addition to habitat loss and dryland salinity, a major threat to plant biodiversity in this region is eutrophication due to enrichment with P. Many plant species in the south-western Australian biodiversity hotspot are extremely sensitive to P, due to a low capability to down-regulate their phosphate-uptake capacity. Species from the most P-impoverished soils are also very poor competitors at higher P availability, giving way to more competitive species when soil P concentrations are increased. Sources of increased soil P concentrations include increased fire frequency, run-off from agricultural land, and urban activities. Another P source is the P-fertilizing effect of spraying natural environments on a landscape scale with phosphite to reduce the impacts of the introduced plant pathogen Phytophthora cinnamomi, which itself is a serious threat to biodiversity. We argue that alternatives to phosphite for P. cinnamomi management are needed urgently, and propose a strategy to work towards such alternatives, based on a sound understanding of the physiological and molecular mechanisms of the action of phosphite in plants that are susceptible to P. cinnamomi. The threats we describe for the south-western Australian biodiversity hotspot are likely to be very similar for other P-impoverished environments, including the fynbos in South Africa and the cerrado in Brazil.
1. Mycorrhizal pathways are comprised of fungal hyphae that facilitate carbon transfer between plants. We determined whether net carbon transfer occurred between conspecific conifer seedlings in the ...field, and whether soil disturbance or access to mycorrhizal pathways affected transfer. 2. We established two soil disturbances and planted pairs of different sized Pseudotsuga menziesii var. glauca seedlings (naturally regenerated or planted) into one of four mesh treatments (0.5, 35, 250 μm or directly into soil) restricting mycorrhizal pathways. We pulse-labelled both seedlings, one with ¹³CO₂ and the other with ¹⁴CO₂, to quantify net carbon transfer. Ectomycorrhizas were identified using morphological and molecular techniques. 3. Net carbon transfers were detected and were not due to re-fixation of respired carbon. More transferred carbon accumulated in shoots than roots. In disturbed soil, there was greater net carbon transfer to natural seedlings than planted seedlings; the reverse pattern was observed in undisturbed soil. For planted seedlings only, the magnitude of net carbon gain was positively related to seedling size and height growth rate. Greater net accumulation of carbon occurred in Rhizopogon vinicolor, a long-distance ectomycorrhizal fungi exploration type (morphological character), than the two other most abundant ectomycorrhizal fungi with contact- and short-distance exploration types. Long-distance exploration types have the potential to form long-distance hyphal connections between plant roots, whereas contact- and short-distance are restricted to short-distance (c. 0-0.25 μm) connections. 4. Synthesis. These results confirm that net carbon transfer occurs through mycorrhizal pathways; however, the amount transferred was very small. Mycorrhizal pathways were facilitating net transfer of carbon to large, vigorous natural seedlings in disturbed soils, whereas smaller planted seedlings received more net carbon gain in undisturbed soils. The size variation within these planted seedlings was great enough to elicit a positive relationship between net carbon gain and seedling size and growth rate. These findings are relevant to regeneration of forests characterized by mixed severity disturbance regimes, which leave a suite of environmental conditions that may result in a greater magnitude of transfer.
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BFBNIB, FZAB, GIS, IJS, INZLJ, KILJ, NLZOH, NMLJ, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZRSKP
Background and Aims Carbon and nutrient cycling are influenced by ectomycorrhizal (EM) fungi in forests. Factors altering carbon allocation in trees are likely to alter EM fungal community ...composition. We aimed to determine the effects of high fertilization, thinning, and their interaction on EM fungal communities and fine roots. Methods Roots and EM fungi were sampled three years after establishment of fertilization and thinning plots in Pinus contorta forests of Canada. Ectomycorrhizas were identified using morphological and molecular techniques and changes to EM composition were detected by multivariate analyses. Results We recovered 77 EM fungal taxa with colonization levels up to 99 % in untreated plots; a 30 % decrease in colonization levels and similar declines in EM richness and diversity was found after fertilization. Thinning interacted with fertilization by decreasing the magnitude of shifts in EM abundance. Thinning tended to alleviatiate the effects of fertilization, suggesting there was sustained allocation of carbon to EM communities and greater root exploration. The fertilization treatment highlights an intimate and mechanistic relationship between tree and soil fungi and suggests that a reduced carbon allocation controls fungal proliferation and alters community composition. Conclusions Intensive forest management treatments shift soil communities to an altered state, possibly impacting nutrient cycling in the interim.
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BFBNIB, DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NMLJ, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Changes in soil nutrient availability during long‐term ecosystem development influence the relative abundances of plant species with different nutrient‐acquisition strategies. These changes in ...strategies are observed at the community level, but whether they also occur within individual species remains unknown. Plant species forming multiple root symbioses with arbuscular mycorrhizal (AM) fungi, ectomycorrhizal (ECM) fungi, and nitrogen‐(N) fixing microorganisms provide valuable model systems to examine edaphic controls on symbioses related to nutrient acquisition, while simultaneously controlling for plant host identity. We grew two co‐occurring species, Acacia rostellifera (N2‐fixing and dual AM and ECM symbioses) and Melaleuca systena (AM and ECM dual symbioses), in three soils of contrasting ages (c. 0.1, 1, and 120 ka) collected along a long‐term dune chronosequence in southwestern Australia. The soils differ in the type and strength of nutrient limitation, with primary productivity being limited by N (0.1 ka), co‐limited by N and phosphorus (P) (1 ka), and by P (120 ka). We hypothesized that (i) within‐species root colonization shifts from AM to ECM with increasing soil age, and that (ii) nodulation declines with increasing soil age, reflecting the shift from N to P limitation along the chronosequence. In both species, we observed a shift from AM to ECM root colonization with increasing soil age. In addition, nodulation in A. rostellifera declined with increasing soil age, consistent with a shift from N to P limitation. Shifts from AM to ECM root colonization reflect strengthening P limitation and an increasing proportion of total soil P in organic forms in older soils. This might occur because ECM fungi can access organic P via extracellular phosphatases, while AM fungi do not use organic P. Our results show that plants can shift their resource allocation to different root symbionts depending on nutrient availability during ecosystem development.
Changes in soil nutrient availability during long‐term ecosystem development influence the relative abundances of plant species with different nutrient‐acquisition strategies. We grew two co‐occurring mycorrhizal plant species in three soils of contrasting ages (c. 0.1, 1, and 120 ka). In both species, we observed a shift from AM to ECM root colonization with increasing soil age, consistent with a shift from N to P limitation. Here, we show that plants shift their resource allocation to different root symbionts depending on nutrient availability during ecosystem development.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Pine tree invasions threaten many natural ecosystems of the Southern Hemisphere, modifying their structure and functioning through shifts in fire regimes, water balance, and biodiversity. The ...magnitude of such impacts depends on how much of the landscape has been invaded, thus a better understanding of the dispersal ability of pines and predictions of their future invasions are needed. Here we depict the spatio-temporal patterns of
Pinus elliottii
and
Pinus taeda
invading a new environment away from planted plots (i.e., invasion front), and discuss the underlying mechanisms that lead to a very concerning, yet poorly documented, pine invasion in central Argentina. Combining high-resolution imagery, allometric field data, and dendrochronology, we reconstructed the pine invasion into mountain grasslands from its onset in 1990. We found that even though the maximum density of invading pines (80 trees ha
−1
) was very low compared to adjacent plantation (1000 trees ha
−1
), density decreases exponentially with distance from the plantation edge. Remarkably, invading pines were found throughout the sampling plots showing high dispersal capacity, with no differences in age with increasing distance. The observed low density and spatially widespread exotic pine establishment, create a stealth type of invasion that is difficult to perceive in its early stages and challenging to manage once large areas are compromised. As invasion continues, long-distance dispersal will possibly become a major agent of landscape transformation and may lead to large pine-dominated neo-ecosystems, such as the savanna-like formation described here that replaced native grasslands in only three decades.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
There are concerns that large-scale stand mortality due to mountain pine beetle (MPB) could greatly reduce natural regeneration of serotinous Rocky Mountain (RM) lodgepole pine (
Pinus contorta
var.
...latifolia
) because the closed cones are held in place without the fire cue for cone opening. We selected 20 stands (five stands each of live control, 3 years since MPB 3-yr-MPB, 6 years since MPB 6-yr-MPB, and 9 years since MPB 9-yr-MPB mortality) in north central British Columbia, Canada. The goal was to determine partial loss of serotiny due to fall of crown-stored cones via breakage of branches and in situ opening of canopy cones throughout the 2008 and 2009 growing seasons. We also quantified seed release by the opening of forest-floor cones, loss of seed from rodent predation, and cone burial. Trees killed by MPB three years earlier dropped ∼∼3.5 times more cones via branch breakage compared to live stands. After six years, MPB-killed stands had released 45%% of their canopy seed bank through cone opening, cone fall due to breakage, and squirrel predation. Further losses of canopy seed banks are expected with time since we found 9-yr-MPB stands had 38%% more open canopy cones. This was countered by the development of a modest forest-floor seed bank (6%% of the original canopy seed bank) from burial of cones; this seed bank may be ecologically important if a fire or anthropogenic disturbance reexposes these cones. If adequate levels of regeneration are to occur, disturbances to create seedbeds must occur shortly after tree mortality, before the seed banks are lost. Our findings also suggest that the sustained seed rain (over at least nine years) after MPB outbreak may be beneficial for population growth of ground-foraging vertebrates. Our study adds insight to the seed ecology of serotinous pines under a potentially continental-wide insect outbreak, threatening vast forests adapted to regeneration after fire.
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BFBNIB, FZAB, GIS, IJS, INZLJ, KILJ, NLZOH, NMLJ, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZRSKP
Ecological restoration of species‐rich grasslands remains a priority for conservation of biodiversity. Torrez et al. (Applied Vegetation Science, this issue) determined if plant species ...recolonization of degraded nutrient‐poor grasslands could be increased by adding a local source of arbuscular mycorrhizal fungal (AMF) inoculum at different distances from intact remnant grasslands. They highlight the important role of below‐ground processes on restoration success.
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NMLJ, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
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