Nutrient Heterogeneity Research Articles

Differential carbon allocation to nitrogen-rich patches in Poa annua precedes root proliferation but has no immediate benefit to N uptake

Nutrients are heterogeneously distributed in the soil environment. Plants have evolved a variety of mechanisms to maximise their ability to compete for limited resources, with differential root growth considered among the more important mechanisms. Despite the significant costs of root growth, little data is available regarding carbon (C) allocation to roots growing in heterogeneous conditions. Here, we investigate the allocation of recently assimilated C in Poa annua plants growing in uniform or heterogeneous nutrient conditions. In the first experiment we grew plants in split-root boxes, providing N either equally between the two chambers (0.5 mg/0.5 mg, 8 mg/8 mg) or with one side receiving more N (0.5 mg/8 mg, 8 mg/0.5 mg), and quantified C allocation and N uptake using 13CO2 and K15NO3. Where N was supplied equally to the two chambers, C was allocated equally to the roots irrespective of the total N supply. However, the 13C label was preferentially allocated (60:40) to high-N roots in the unequal treatments. N uptake was a function of local supply and was not affected by N supply to the roots in the other chamber. C allocation had no discernible effect on N uptake. In the second experiment, we tested whether differential N supply would lead to increased root growth in the high-N side. In this experiment, equal amounts of N were supplied to all plants as ammonium, with half receiving an equal distribution to the two root chambers (50/50), while the other half received an unequal supply (94/6). While no difference in root growth was noted in 50/50 plants, a 60:40 mass allocation was noted from day six onwards in plants receiving the 94/6 N supply. Despite increased root growth in the high-N side, the plants receiving the 94/6 treatment could not achieve the same shoot mass or N concentration as the 50/50 plants. No difference in total C allocation to the roots between treatments was noted in the first experiment, and no difference in total root mass between treatments was found in the second experiment, suggesting that root C supply was source-limited, while allocation to specific roots was strongly influenced by sink strength. Differential C allocation appears to be an important pre-requisite for increased root growth in N-rich patches.

Effects of Temporal Heterogeneity of Water Supply and Spatial Heterogeneity of Soil Nutrients on the Growth and Intraspecific Competition of Bolboschoenus yagara Depend on Plant Density.

Clonal plants may face various types of resource heterogeneity in their natural habitats; as such, spatial or temporal resource heterogeneity can affect the growth of clonal plants. Clonal plants can concentrate their organs in a smaller area where resources are high would cause heterogeneity to increase competition between plants. Most studies on resource heterogeneity have investigated the response of plants under a single density or by manipulating a single resource. Few studies have tested the effects of the heterogeneous distribution of two covariable resources on plant growth and intraspecific competition. A greenhouse experiment was therefore conducted to study plant responses to the spatial and temporal heterogeneity of the soil and water supply under a variety of plant densities (one, two, four, or six plants per container). The perennial clonal herb Bolboschoenus yagara was grown under different combinations of water supply patterns, soil nutrient distribution types and plant densities while maintaining the total water and soil nutrient availability per container constant. Compared with that at a relatively high plant density, soil nutrient heterogeneity resulted in significantly less total plant biomass and less-modified morphological traits when the plant density is relative low. At the highest plant density, compared with the homogeneous soil treatments, the heterogeneous soil treatments significantly increased the total biomass and R/S ratio. Water supply patterns also clearly affected plant morphological traits at the highest plant density. Furthermore, soil heterogeneity significantly increased intraspecific competition intensity at low plant densities, but did not significantly affect intraspecific competition intensity at higher plant densities. Water heterogeneity had little impact on intraspecific competition. These results suggest that the growth performance and intraspecific competition of B. yagara are more strongly affected by soil nutrient distribution rather than by water supply patterns and that competition for soil nutrients may increase plant sensitivity to soil heterogeneity.

Forest termites mitigate the effects of drought

Tropical Ecology In many tropical regions, where drought is predicted to become more frequent in the coming years, termites are key components of ecosystem function. Ashton et al. experimentally manipulated termite communities to quantify their role during the 2015–2016 “super El Nino” drought in a Malaysian tropical rainforest. Termite relative abundance more than doubled in control plots during drought, maintaining three major ecosystem processes: decomposition, nutrient heterogeneity, and moisture retention. Seedling mortality increased where termites were suppressed. Science , this issue p. [174][1] [1]: /lookup/doi/10.1126/science.aau9565

Termites mitigate the effects of drought in tropical rainforest.

Termites perform key ecological functions in tropical ecosystems, are strongly affected by variation in rainfall, and respond negatively to habitat disturbance. However, it is not known how the projected increase in frequency and severity of droughts in tropical rainforests will alter termite communities and the maintenance of ecosystem processes. Using a large-scale termite suppression experiment, we found that termite activity and abundance increased during drought in a Bornean forest. This increase resulted in accelerated litter decomposition, elevated soil moisture, greater soil nutrient heterogeneity, and higher seedling survival rates during the extreme El Niño drought of 2015-2016. Our work shows how an invertebrate group enhances ecosystem resistance to drought, providing evidence that the dual stressors of climate change and anthropogenic shifts in biotic communities will have various negative consequences for the maintenance of rainforest ecosystems.

Soil nutrient heterogeneity affects the accumulation and transfer of cadmium in Bermuda grass (Cynodon dactylon (L.) pers.)

There have been no studies demonstrating the correlation between soil nutrient heterogeneity and cadmium (Cd) absorption of Bermudagrass. In this study, a pot experiment was carried out to study the correlation between them. The purpose is to find soil nutrient factors which are conducive to improving the Cd absorption and translocation. The eighth group had the largest total number of surviving plants, the highest Fv/Fo value (3.24) and the best growth characteristics. The fifth group had the lowest total number of surviving plants, Fv/Fo (2.47) and the worst growth. The Cd content of the fifth group (36.11 mg kg−1) was close to the eighth group (35.72 mg kg−1), but the two groups had significant differences in plant height, stem node length and stem node number (P < 0.05). The eighth group showed the highest contents of nitrate nitrogen (NO3−-N), available potassium and urease activity. The fifth group showed the lowest NO3−-N content, but the highest ammonium nitrogen (NH4+-N) and available phosphorus content. There was significant difference of the Cd bioconcentration factors (BCF) and translocation factor (TCF) between the fifth and the eighth group although they had the similar total soil Cd content (P < 0.05). The fifth group had the highest BCF and TCF. RDA analysis indicated the BCF and TCF were positively correlated with soil NH4+-N and available phosphorus and negatively correlated with soil NO3−-N. The results demonstrated that soil NH4+-N and available phosphorus were important soil ecological factors to enhance Cd absorption and translocation of bermudagrass.

Influence of Soil Nutrient Heterogeneity and Competition on Sprouting and Ramets Growth of Alternanthera philoxeroides

Environmental heterogeneity and plant competition influence plant vegetative sprouting and ramets growth. Many major invasive plants reproduce largely or exclusively by vegetative propagation. The terrestrial invasive Alternanthera philoxeroides mainly regenerates from fleshy roots. Here, it is tested whether resource heterogeneity and intraspecific competition influence the fleshy root sprouting and ramet growth of this species. Four or twelve similar‐sized fleshy roots of A. philoxeroides are grown in two soil substrates that are either homogeneous or heterogeneous but have the same total amount of nutrients. After 6 months, the sprouting and ramet growth traits (i.e., ramet number, leaf traits, biomass and biomass allocation) are analyzed. The fleshy root density significantly affects the sprouting and ramet growth traits, but the soil nutrient heterogeneity does not. The sprouting and ramet growth traits decrease in the treatments with high densities of fleshy roots. These results suggest that intraspecific competition has a greater influence on the root sprouting and ramet growth of the invasive terrestrial A. philoxeroides than soil nutrient heterogeneity. Thus, intraspecific competition can limit the establishment of terrestrial A. philoxeroides.

A multi-species comparison of selective placement patterns of ramets in invasive alien and native clonal plants to light, soil nutrient and water heterogeneity

A worth noticing pattern in current invasive biology is the clonal ability of many of the world's worst invasive plants. Selective placement of ramets (i.e. foraging behavior) can intensify ramet performance and allocation, and place more ramets in the more favorable microhabitats, which can maximum utilize resource and share risk in heterogeneous environments. Still little is known about whether invasive alien and native clonal plants differ in the selective placement patterns of ramets in invasive clonal plants or not.We used five congeneric pairs of naturally co-occurring invasive alien and native clonal plant species in China. In a glasshouse, we grew all species in pots under a homogeneous and three heterogeneous conditions (i.e. light, soil nutrients or water) subjected to resource-high or -low patches.All biomass parameters and number of ramets significantly increased in resource-high patches in all three types of heterogeneous environments. Interestingly, growth of invasive alien plants benefited significantly more from resource-high patches than native plants in all heterogeneous environments. Overall, invasive had higher biomass parameters per ramet than natives. Ramet parameters of invasive plants also benefited more from resource-low patches than natives. Three different selective placement patterns of ramets in resource-low patches were exhibited in invasive plants: ramet increasing shoot investment (above pattern), increasing root investment (below pattern) and increasing both investments (complete pattern) in the light, soil water and nutrient heterogeneity, respectively. Investment on less, larger ramet was the adaptive strategy of invasive plants in resource-poor patches.The results suggest that adaptively selective placement patterns of ramets promote a higher morphology plasticity and performance in invasive clonal plants over natives. When alien clonal plants spread new areas with light, soil nutrients or water heterogeneity, selective placement patterns of ramets might play an important role in plant performance and competitive superior by capitalizing more on additional resources.

Physiological integration of growth, carbohydrates, and soluble protein of Zoysia japonica clonal ramets under nutrient heterogeneity

This study was carried out to analyze the changes of growth, the contents of carbohydrates and soluble protein of Zoysia japonica clonal ramets under nutrient heterogeneity, where the connected and disconnected ramets were treated with different nutrient levels. The results indicated that under the nutrient heterogeneity the parent ramets in middle or high nutrient levels improved the aboveground biomass, belowground biomass, and total biomass, with the enhancement of 32.5%, 22.1% and 24.8% at high nutrient level, respectively, reduced the root/shoot ratio, the contents of soluble sugar and non-structural carbohydrates (NSC), with the reduction of 7.7%, 15.2% and 13.1% in high nutrient level, respectively, but had no significant impacts on the contents of starch, cellulous, and soluble protein of the connected daughter ramets. The daughter ramets in middle and high nutrient levels had no significant impacts on the growth and the contents of carbohydrates and soluble protein of the connected parent ramets. There was a significant physiological integration effects from parent to the daughter ramets on the biomass, root/shoot, the contents of soluble sugar and NSC. The intensity of physiological integration was proportional to the nutrient gradient of ramets, but had no significant physiological integration effects on the contents of starch, cellulous and soluble protein. The daughter ramets had no physiological integration for any indicator of the parent ramets. There was a unidirectional physiological integration between parent and daughter ramets of Z. japonica.

Comparing Spatial Heterogeneity of Bioavailable Nutrients and Soil Respiration in Boreal Sites Recovering From Natural and Anthropogenic Disturbance

The mining of oil sands in Alberta, Canada is a large-scale disturbance that requires land reclamation to equivalent land capability. Cover soils used for upland forest reclamation are forest floor mineral-mix (FFM) sourced from upland forest ecosystems and peat mineral-mix (PM) sourced from lowland ecosystems. Spatial heterogeneity and quantity of soil resources, especially nutrient bioavailability, is important because it affects the establishment of native vegetation in forest ecosystems and soil respiration is an indicator for overall soil biologic activity. We studied spatial heterogeneity of soil nutrients as well as seasonal and spatial patterns of soil respiration in two sites reclaimed either with FFM or PM and two reference sites recovering either from harvest or fire. Contrary to our initial hypothesis, we identified spatial heterogeneity in some bioavailable nutrients in FFM and PM cover soil, indicating that standard placement processes can recreate spatial heterogeneity. However, some nutrients such as P, K and S showed no heterogeneity in PM at all. P and K availability was significantly lower and S was significantly higher in PM than in FFM and reference sites. Seasonal pattern of respiration showed variability on natural reference sites and on FFM, indicating that disturbance had not removed belowground function completely. PM reclaimed sites showed no strong seasonal respiration patterns indicating homogeneous belowground function. Surprisingly PM treatments were not characterized by highest rates of soil respiration while having highest amounts of total organic carbon. We conclude that FFM reclaimed sites may be more successfully reclaimed than PM sites because they are more similar to reference sites in terms of nutrient status and seasonal respiration patterns.

Root competition resulting from spatial variation in nutrient distribution elicits decreasing maize yield at high planting density

Nutrient spatial heterogeneity occurs ubiquitously in soil, but its impact on plant growth and competition throughout the whole growth cycle remains unclear. We assessed the effects of different nutrient supply patterns and planting density on maize (Zea mays L.) growth rate, root competitive intensity and grain yield. Maize was grown with homogeneous or heterogeneous nutrient (ammonium and phosphorus) supplies under low and high planting densities in field conditions. Nutrient patches promoted root proliferation and plant growth rate in the short term; however, with nutrient depletion and roots still proliferating in the patch zone, the plant growth rate was surpassed by that of plants in the homogeneous ammonium and phosphorus treatments with time. Consequently, final shoot biomass showed no difference between nutrient supply patterns at a given planting density. Furthermore, the temporal decoupling between root growth and soil nutrient availability induced greater competitive intensity in the heterogeneous than homogeneous treatments between the vegetative stage and anthesis. Under these conditions, heterogeneous ammonium and phosphorus supply markedly decreased grain yield at high planting density. Our results demonstrate that heterogeneous nutrient supply-induced root competition at high planting density modulates the dynamics of plant development and decreases final productivity.

Distribution Characteristics and Seasonal Variation of Soil Nutrients in the Mun River Basin, Thailand.

Based on soil sampling data from the dry season and the rainy season, the spatial heterogeneity and spatial pattern of soil nutrients in the Mun River Basin, Thailand, were studied and the seasonal variation in soil nutrients was analyzed using classical statistical methods and geostatistical methods. The soil nutrient content in the Mun Basin showed moderate and strong variations, and the descending order of soil variability was as follows: available phosphorous (AP) > electric conductivity (EC) > soil organic matter (SOM) > total nitrogen (TN) > pH value in the dry season, with AP showing strong variation, and EC > AP > SOM > TN > pH in the rainy season, with EC showing strong variation. Different soil nutrients and different soil properties had different spatial variation characteristics, and their corresponding best-fitting models were also different. Based on the nugget (C0), sill (C0 + C), and range (A), spatial analysis was performed for the soil nutrients, pH, and EC in the dry season and in the rainy season. Analysis based on kriging spatial interpolation data showed that pH, SOM, TN, and EC had convex or concave distributions, whereas AP had a patchy distribution. Terrain, vegetation, and human disturbance are the main factors that contribute to the differences in the soil nutrient pattern of the Mun River Basin.

A personalized mathematical tool for neuro-oncology: A clinical case study

This work evaluates the predictive ability of a novel personalized computational tool for simulating the growth of brain tumours using the neuroimaging data collected during one clinical case study. The mathematical model consists of an evolutionary fourth-order partial differential equation with degenerate motility, in which the spreading dynamics of the multiphase tumour is coupled with a parabolic equation determining the diffusing oxygen within the brain. The model also includes a reaction term describing the effects of radiotherapy, that is simulated in accordance with the clinical schedule. We collect Magnetic Resonance (MRI) and Diffusion Tensor (DTI) imaging data for one patient at given times of key clinical interest, from the first diagnosis of a giant glioblastoma to its surgical removal and the subsequent radiation therapies. These neuroimaging data allow reconstructing the patient-specific brain geometry in a finite element virtual environment, that is used for simulating the tumour recurrence pattern after the surgical resection. In particular, we characterize the different brain tissues and the tumour location from MRI data, whilst we extrapolate the heterogeneous nutrient diffusion parameters and cellular motility from DTI data.The numerical results of the simulated tumour are found in good qualitative and quantitative agreement with the volume and the boundaries observed in MRI. Moreover, the simulations point out a consistent regression of the tumour mass in correspondence to the application of radiotherapy, with an average growth rate which is of the same order as the one calculated from the neuroimaging data. Remarkably, our results display the highest Jaccard index of the tumour region reported in the biomathematical literature. In conclusion, this work represents an important proof-of-concept of the ability of this mathematical framework to predict the tumour recurrence and its response to therapies in a patient-specific manner.

Competition and facilitation of two wetland macrophytes under different water levels and nutrient-heterogeneous conditions

According to the stress gradient hypothesis, competition intensity decreases or changes to facilitation with increasing environmental stress. However, the role of water level and nutrient heterogeneity in influencing plant-plant competition is far from clear. Relative yield total, relative yield, total N (TN) and total P (TP) contents, and N∶P ratios for Carex brevicuspis and Polygonum hydropiper were investigated in an experiment including 3 sediment types corresponding to different levels of nutrient availability (type Ι: 0–15 cm sand and 15–30 cm clay; type II: 0–30 cm mixture with 1∶1 sand and clay volume; and type III: 0–15 cm clay and 15–30 cm sand) and 2 water levels (0 and 15 cm). Facilitation occurred at 15-cm water level in the type I and type II sediments. The presence of C. brevicuspis facilitated the growth of P. hydropiper at the 15-cm water level in all sediment types. However, growth of C. brevicuspis was promoted only at the 15-cm water level in type Ι sediments. At the 0-cm water level, growth of each species was limited by the other species. TN, TP, and N∶P ratios of P. hydropiper were higher in the type III sediment than in the other 2 sediment types and at the 15- than the 0-cm water level. TN and TP contents of C. brevicuspis were highest in type I and type III sediments, respectively. The N∶P ratio of C. brevicuspis was higher in type I sediment than in the other 2 sediments and at the 15- than the 0-cm water level. Competition between these 2 species shifted to facilitation as the water level increased, and this facilitation might be regulated by sediment nutrient heterogeneity.

Responses of seminal wheat seedling roots to soil water deficits

The aims of this paper are to develop our understanding of the ways by which soil water deficits influence early wheat root growth responses, particularly how seminal roots respond to soil drying and the extent to which information on differences in soil water content are conveyed to the shoot and their impact on shoot behaviour. To achieve this, wheat seedlings have been grown, individually for around 25 days after germination in segmented soil columns within vertical plastic compartments. Roots were exposed to different soil volumetric moisture contents (SVMC) within the two compartments. Experiments where the soil in the lower compartment was allowed to dry to different extents, while the upper was maintained close to field capacity, showed that wheat seedlings allocated proportionally more root dry matter to the lower drier soil compartment. The total production of root, irrespective of the upper or lower SVMC, was similar and there were no detected effects on leaf growth rate or gas exchange. The response of seminal roots to proportionally increase their allocation of dry matter, to the drier soil was unexpected with such plasticity of roots system development traditionally linked to heterogeneous nutrient distribution than accessing soil water. In experiments where the upper soil compartment was allowed to dry, root growth slowed and leaf growth and gas exchange declined. Subsequent experiments used root growth rates to determine when seminal root tips first came into contact with drying soil, with the intentions of determining how the observed root growth rates were maintained as an explanation for the observed changes in root allocation. Measurements of seminal root ABA and ethylene from roots within the drying soil are interpreted with respect to what is known about the physiological control of root growth in drying soil.

Physiological integration of growth and photosynthesis of Zoysia japonica clonal ramets under nutrient heterogeneity

This study was carried out to analyze the changes of growth and photosynthesis of clonal ramets under nutrient heterogeneity, where the connected and disconnected ramets were treated with different nutrient levels. The results showed that under the nutrient heterogeneity the parent ramets in middle or high nutrient levels improved leaf length, leaf width, root mass, leaf mass, net photosynthetic rate, stomatal conductance, transpiration rate and water use efficiency of the connected daughter ramets, with an increase of 16.0%, 8.3%, 24.4%, 58.1%, 30.3%, 54.0%, 9.2% and 21.9% in high nutrient level, respectively, but reduced the root/shoot and intercellular CO2 concentration of the connected daughter ramets, with a decreases of 21.6% and 31.5% in high nutrient level, respectively. In contrast, the daughter ramets in the middle or high nutrient level had no significant impacts on the growth and photosynthesis of the connected parent ramets. There was a physiological integration from the parent ramets to the daughter ramets. The larger the nutrient differences of ramets was, the stronger the intensity of physiological integration was. The daughter ramets were the unidirectional beneficiary from the physiological integration, as the daughter ramets benefited from the parent ramets but had no positive effects on the daughter ramets.

Relationships between Nutrient Heterogeneity, Root Growth, and Hormones: Evidence for Interspecific Variation.

(1) Background: Plant roots respond to nutrients through root architecture that is regulated by hormones. Strong inter-specific variation in root architecture has been well documented, but physiological mechanisms that may control the variation have not. (2) Methods: We examined correlations between root architecture and hormones to seek clues on mechanisms behind root foraging behavior. In the green house at Beijing Normal University, hydroponic culture experiments were used to examine the root responses of four species—Callistephus chinensis, Solidago canadensis, Ailanthus altissima, Oryza sativa—to two nitrogen types (NO3− or NH4+), three nitrogen concentrations (low, medium, and high concentrations of 0.2, 1, and 18 mM, respectively) and two ways of nitrogen application (stable vs. variable). The plants were harvested after 36 days to measure root mass, 1st order root length, seminal root length for O. sativa, density of the 1st order laterals, seminal root number for O. sativa, the inter-node length of the 1st order laterals, and root hormone contents of indole-3-acetic acid, abscisic acid, and cytokinins (zeatin + zeatinriboside). (3) Results: Species differed significantly in their root architecture responses to nitrogen treatments. They also differed significantly in hormone responses to the nitrogen treatments. Additionally, the correlations between root architecture and hormone responses were quite variable across the species. Each hormone had highly species-specific relationships with root responses. (4) Conclusions: Our finding implies that a particular root foraging behavior is probably not controlled by the same biochemical pathway in all species.

Fine root responses to temporal nutrient heterogeneity and competition in seedlings of two tree species with different rooting strategies.

There is little direct evidence for effects of soil heterogeneity and root plasticity on the competitive interactions among plants. In this study, we experimentally examined the impacts of temporal nutrient heterogeneity on root growth and interactions between two plant species with very different rooting strategies: Liquidambar styraciflua (sweet gum), which shows high root plasticity in response to soil nutrient heterogeneity, and Pinus taeda (loblolly pine), a species with less plastic roots. Seedlings of the two species were grown in sandboxes in inter‐ and intraspecific combinations. Nutrients were applied in a patch either in a stable (slow‐release) or in a variable (pulse) manner. Plant aboveground biomass, fine root mass, root allocation between nutrient patch and outside the patch, and root vertical distribution were measured. L. styraciflua grew more aboveground (40% and 27% in stable and variable nutrient treatment, respectively) and fine roots (41% and 8% in stable and variable nutrient treatment, respectively) when competing with P. taeda than when competing with a conspecific individual, but the growth of P. taeda was not changed by competition from L. styraciflua. Temporal variation in patch nutrient level had little effect on the species’ competitive interactions. The more flexible L. styraciflua changed its vertical distribution of fine roots in response to competition from P. taeda, growing more roots in deeper soil layers compared to its roots in conspecific competition, leading to niche differentiation between the species, while the fine root distribution of P. taeda remained unchanged across all treatments. Synthesis. L. styraciflua showed greater flexibility in root growth by changing its root vertical distribution and occupying space of not occupied by P. taeda. This flexibility gave L. styraciflua an advantage in interspecific competition.

Seasonal trophic variation of yellow perch exceeds spatial variation in a large lake basin

Abstract Trophic structuring of complex food webs may vary at multiple spatial and temporal scales, both in terms of direct trophic connections and underlying energy pathways that support production. In large freshwater systems, the prey and primary producers that support individual higher-order consumers may vary across seasons and habitats due to differences in food availability, predator consumption patterns, seasonal succession of organisms at lower trophic levels, and heterogeneous nutrient inputs. We examined spatial and temporal variation in stomach contents, fatty acids, and stable isotopes of yellow perch (Perca flavescens) across seasons and across sites spanning approximately 200 km in Lake Erie's Central Basin (LECB). Stomach contents provided a short-term index of trophic patterns, while biochemical markers (fatty acids and stable isotopes) provided a more temporally integrated description of underlying energy pathways and trophic links. We found limited spatial variation of biochemical indicators and documented seasonal variation for all three trophic indicators, especially fatty acid profiles. Differences in stomach contents were driven by relative chironomid consumption, the most abundant prey resource, while fatty acid profiles were predominantly influenced by seasonal fluctuations in C22:6n-3 (DHA). Seasonal trends were evident in δ13C and δ15N; however, they varied within a narrow range of values. Our findings suggest that adult yellow perch in LECB showed little differentiation in resource use across space in 2014, but their diets and biochemical compositions varied seasonally.

Intraspecific aggregation and soil heterogeneity: competitive interactions of two clonal plants with contrasting spatial architecture

Intraspecific aggregation of plant individuals can promote species coexistence by delaying competitive exclusions. However, such impacts may differ among species with contrasting spatial architecture and rely on the spatial distribution of resources. We grew a phalanx clonal plant Carex neurocarpa (with aggregated ramets) and a guerilla one Bolboschoenus planiculmis (with diffused ramets) in monocultures or in 1:1 mixtures with an even or a clustered distribution pattern of the two species in homogeneous or heterogeneous soils. After 16 months, shoot biomass and ramet number were greater in mixtures than in monocultures in C. neurocarpa, but smaller in B. planiculmis. However, the growth of neither C. neurocarpa nor B. planiculmis differed between even and clustered mixtures. Soil nutrient heterogeneity did not significantly affect the growth of either species, but increased relative yield of B. planiculmis and decreased that of C. neurocarpa. The relative importance of intra- vs. interspecific competition depends on the spatial architecture of plants, and soil nutrient heterogeneity slows down competitive exclusion by decreasing differences in competitive ability between plants. However, our results do not support the idea that intraspecific aggregation of individuals alters competitive interactions between species.

Nutrient foraging by mycorrhizas: From species functional traits to ecosystem processes

Abstract Plant roots and the associated mycorrhizal fungal hyphae often selectively proliferate into patchily distributed soil nutrient hotspots, but interactions between these two components of a mycorrhizal root system are usually ignored or experimentally isolated in nutrient foraging studies. From studies in which both roots and mycorrhizal hyphae had access to nutrient hotspots, we compiled data on root foraging precision (increase in roots in nutrient hotspots relative to outside hotspots) of plant species from different ecosystems, ranging from temperate grasslands to subtropical forests. We found that root foraging precision across the wide range of plant species was strongly influenced by root morphology and mycorrhizal type. The precision of root nutrient foraging, as a plant functional trait, may coordinate with other root traits that are related to the economics of nutrient acquisition. High foraging precision is expected to associate with the strategy of fast return on the investment in roots, such as low construction cost, high metabolic rate and rapid turnover. Nutrient foraging by mycorrhizal fungi alone may be influenced by functional traits such as hyphal exploration distance, hyphal turnover, and hyphal uptake capacity and efficiency, but such data are limited to a small portion of mycorrhizal fungal species. We propose a conceptual framework in which to simulate nitrogen and phosphorus acquisition from both nutrient hotspots and outside hotspots in mixed‐species plant communities. Simulation outputs suggest that plant species with varying root morphology and mycorrhizal type can be adaptive to a range of nutrient heterogeneity. Although there are still knowledge gaps related to nutrient foraging, as well as many unexplored plant and fungal species, we suggest that scaling nutrient foraging from individual plants to communities would advance understanding of plant species interactions and below‐ground ecosystem function. A plain language summary is available for this article.