Heterogeneous Nutrient Environments Research Articles

Does soil nutrient heterogeneity affect the competition and adaptation of Vernicia montana?

Plants respond to variations in soil nutrient distribution and the presence of neighboring plants, yet consensus is lacking on the impact of naturally heterogeneous soil nutrient environments on plant competition. This study employs pot experiments to simulate homogeneous and heterogeneous forest soil nutrient environments and designs neighbor competition experiments for Vernicia montana, Cunninghamia lanceolata, and Phoebe bournei, to assess the impact of neighbor competition on these seedlings from the perspective of root morphology and foraging ability in different nutrient environments. The results reveal that when faced with heterogeneous nutrient environments or competitive settings, V. montana primarily utilized morphological and physiological plasticity, such as increasing root morphological indicators and concentrating more nutrients in the underground part, to enhance its adaptability and achieve competitive advantages. C. lanceolata and P. bournei mainly depended on physiological plasticity, like increased root nutrient concentration, when they were co-planted with other species. Compared to interspecific competition, intraspecific competition had a significant inhibitory effect on V. montana, especially under heterogeneous nutrient conditions, with notable reductions in root morphological indicators and root N, P concentration in mono-culture. Nutrient heterogeneity also altered the effects of interspecific competition on C. lanceolata and P. bournei. When mixed-planted with C. lanceolata or P. bournei, V. montana exhibited stronger competitive ability in both nutrient environments. The effects of mixed planting on C. lanceolata and P. bournei were significantly different between the two nutrient environments, in that homogeneous nutrient environment favored the growth and nutrient absorption of C. lanceolata, while heterogeneous nutrients generally benefited P. bournei. Most research on seedling competition is conducted under homogenous nutrient environments, and the results may not accurately reflect in-situ competition, potentially obscuring the scientific implementation of forestry management. Taking into account competition under unevenly distributed soil resources will help in optimizing tree species selection and cultivation methods, thereby improving the adaptability and ecological benefits of forests.

Response of the root morphological structure of Fokienia hodginsii seedlings to competition from neighboring plants in a heterogeneous nutrient environment.

Critical changes often occur in Fokienia hodginsii seedlings during the process of growth owing to differences in the surrounding environment. The most common differences are heterogeneous nutrient environments and competition from neighboring plants. In this study, we selected one-year-old, high-quality Fokienia hodginsii seedlings as experimental materials. Three planting patterns were established to simulate different competitive treatments, and seedlings were also exposed to three heterogeneous nutrient environments and a homogeneous nutrient environment (control) to determine their effect on the root morphology and structure of F. hodginsii seedlings. Heterogeneous nutrient environments, compared with a homogeneous environment, significantly increased the dry matter accumulation and root morphology indexes of the root system of F. hodginsii, which proliferated in nutrient-rich patches, and the P heterogeneous environment had the most significant enhancement effect, with dry matter accumulation 70.2%, 7.0%, and 27.0% higher than that in homogeneous and N and K heterogeneous environments, respectively. Homogeneous environments significantly increased the specific root length and root area of the root system; the dry matter mass and morphological structure of the root system of F. hodginsii with a heterospecific neighbor were higher than those under conspecific neighbor and single-plant treatments, and the root area of the root system under the conspecific neighbor treatment was higher than that under the heterospecific neighbor treatment, by 20% and 23%, respectively. Moreover, the root system under heterospecific neighbor treatment had high sensitivity; the heterogeneous nutrient environment increased the mean diameter of the fine roots of the seedlings of F. hodginsii and the diameter of the vascular bundle, and the effect was most significant in the P heterogeneous environment, exceeding that in the N and K heterogeneous environments. The effect was most significant in the P heterogeneous environment, which increased fine root diameter by 20.5% and 10.3%, respectively, compared with the homogeneous environment; in contrast, the fine root vascular ratio was highest in the homogeneous environment, and most of the indicators of the fine root anatomical structure in the nutrient-rich patches were of greater values than those in the nutrient-poor patches in the different heterogeneous environments; competition promoted most of the indicators of the fine root anatomical structure of F. hodginsii seedlings. According a principal component analysis (PCA), the N, Pm and K heterogeneous environments with heterospecific neighbors and the P heterogeneous environment with a conspecific neighbor had higher evaluation in the calculation of eigenvalues of the PCA. The root dry matter accumulation, root morphology, and anatomical structure of F. hodginsii seedlings in the heterogeneous nutrient environment were more developed than those in the homogeneous nutrient environment. The effect of the P heterogeneous environment was the most significant. The heterospecific neighbor treatment was more conducive to the expansion and development of root morphology of F. hodginsii seedlings than were the conspecific neighbor and single-plant treatments.

Effects of Different Heterogeneous Nutrient Environments on the Growth and Activities of Enzymes in the Roots of Fokienia hodginsii Families.

Currently, research on the F. hodginsii asexual lineage primarily focuses on the screening of growth traits and the control of single fertilizer applications. The effects of the heterogeneity of soil nutrients on root growth and activity have not been studied in detail. Therefore, we propose forest management measures to improve the foraging ability of forest trees in conjunction with stand productivity. In this experiment, annual containerized seedlings of 10 free-pollinated F. hodginsii lines from a primary asexual seed orchard were used as test subjects, and three heterogeneous nutrient environments of nitrogen (N), phosphorus (P), and potassium (K) were constructed. In contrast, homogeneous nutrient environments were used as the control to carry out potting experiments, to study the growth of F. hodginsii lines and the differences in the activities of root enzymes under the three heterogeneous nutrient environments, and to carry out the comprehensive evaluation using the principal component and cluster analysis method. The results were as follows: (1) The seedling height of F. hodginsii family lines under a homogeneous nutrient environment was significantly higher than that of all heterogeneous nutrient environments; the diameter of the ground was the highest under N heterogeneous nutrient environment and significantly higher than that of all the other nutrient environments; the biomass of the root system was the highest under P heterogeneous nutrient environment, which was significantly higher than that of homogeneous nutrient environment and K heterogeneous nutrient environment. The catalase (CAT) activity of F. hodginsii roots was higher than that of homogeneous nutrients in all heterogeneous nutrient environments but not significant, and the superoxide dismutase (SOD) activity was slightly higher than that of K heterogeneous and homogeneous nutrient environments in N and P heterogeneous nutrient environments. SOD activity was slightly higher than that of K heterogeneous and homogeneous nutrient environments under N, and P. peroxidase (POD) activity in the F. hodginsii root system was the highest under the P heterogeneous nutrient environment, which was significantly higher than that of the other nutrient environments. Unlike the activities of the enzymes, the content of malondialdehyde (MDA) in the roots of F. hodginsii was higher in the heterogeneous environment than in all the other nutrient environments. (2) Under N and P heterogeneous nutrient environments, lines 552 and 590 had higher seedling height, ground diameter, and root enzyme activity, while root biomass was highest in line 544; and under K heterogeneous nutrient environments, line 591 had higher seedling height, ground diameter, and root enzyme activity while root biomass was highest in line 551. In contrast to the patterns of seedling height, accumulation of root biomass and activities of root enzymes, family No. 590 had the highest ground diameter of all the F. hodginsii families under the heterogeneous nutrient environments. Family No. 547 had the highest MDA content. In conclusion, it can be seen that N heterogeneous and homogeneous nutrient environments can significantly increase the seedling height and diameter of F. hodginsii compared with P and K heterogeneous nutrient environments, and N and P heterogeneous nutrient environments can also increase the root biomass, root enzyme activities and significantly reduce the MDA content of F. hodginsii. According to the principal component analysis and cluster analysis, it can be seen that among the 10 F. hodginsii family lines, family lines 590 and 552 have higher evaluation in growth, root biomass accumulation, and enzyme activity.

Responses of Growth and Root Vitality of Fokienia hodginsii Seedling to the Neighbor Competition in Different Heterogeneous Nutrient Environments

Fokienia hodginsii is characterized by shallow and developed lateral roots with no obvious taproot. It can be used as a pioneer tree species for opening up barren land and as a mixed species for creating plantation forests. During the growth process of F. hodginsii seedlings, they are often exposed to heterogeneous nutrient environments and competition for nutrients, water, and space from neighboring plants, which have significant impacts on the growth of F. hodginsii. These impacts are most directly reflected in the root vitality of F. hodginsii, whose physiological changes embody the plant’s adaptability to different heterogeneous nutrient environments and neighbor competition. Herein, high-quality one-year-old F. hodginsii seedlings were subjected to three planting patterns to simulate different competition patterns. The three planting patterns were also exposed to three heterogeneous nutrient environments and a homogeneous nutrient environment (control) to determine the differences in the F. hodginsii seedling growth and root vitality under different heterogeneous nutrient environments and planting patterns. The F. hodginsii seedling height, ground diameter (root neck diameter), and root biomass under the heterospecific neighbor condition were significantly higher than under the single-plant condition. Across heterogeneous nutrient environments, the average seedling height in the N heterogeneous environments was higher than in the P and K heterogeneous environments. The root biomass in the P heterogeneous environment was slightly higher than in the N heterogeneous environment and significantly higher than in the homogeneous and the K heterogeneous environments. Moreover, the average F. hodginsii seedling root vitality under the heterospecific neighbor was the highest, and the root vitality in the N heterogeneous environment was the highest under each planting pattern. The F. hodginsii root catalase (CAT) and peroxidase (POD) activities under the competition patterns were significantly higher than under the single-plant condition. Additionally, the superoxide dismutase (SOD) activity under single-plant was higher than under the competition patterns. At the same time, the F. hodginsii root malondialdehyde (MDA) content was the highest under the conspecific neighbor. Relative to the homogeneous environment, the root CAT, SOD, and POD activities were increased in the N and P heterogeneous environments. The CAT, SOD, and POD activities were highest in the P heterogeneous environment, while the K heterogeneous environment had the highest average MDA content. From the results of principal component analysis, when F. hodginsii seedlings were in N and P heterogeneous nutrient environments and heterospecific neighbor, their growth, root biomass accumulation, and root activity indexes reached better levels.

Responses of Planting Modes to Photosynthetic Characteristics and Fluorescence Parameters of Fokienia hodginsii Seedlings in a Heterogeneous Nutrient Environment

Fokienia hodginsii seedlings tend to vary significantly in response to differences in the surrounding environment, especially when the nutrient environment is heterogeneous and neighboring plants are in competition. Plant physiological differences occur not only in the root system, but also in the photosynthetic characteristics and fluorescence parameters of the leaves. Therefore, in this experiment, three planting modes (single planting, pure planting of F. hodginsii and mixed planting of F. hodginsii and Cunninghamia lanceolata) were set up to simulate different competition patterns. Three heterogeneous nutrient environments (N, P, K heterogeneous nutrient environment) were planted in this experiment, and the homogeneous environments were used as controls to determine the differences in photosynthetic characteristics, fluorescence parameters and the interaction of different environmental factors on each index in different heterogeneous nutrient and planting environments. The interactions of different environmental factors with various indicators were measured. In addition, all treatment combinations were evaluated and ranked by principal components analysis. The results showed that the net photosynthetic rate (Pn) was on average 28.8% and 22.3% higher under monoculture treatment compared to pure and mixed planting in each nutrient environment. Transpiration rate (Tr) and stomatal conductance (Gs) were the lowest under pure planting mode, and the overall mean of Tr was 27.2% and 5.5% lower than monoculture and mixed planting, respectively, and the overall mean of Gs was 36.5% and 14.7% lower, respectively. Intercellular CO2 concentration (Ci) was higher under mixed and pure planting mode than monoculture, but their overall increments were not significant. Pn, Tr and Gs values of F. hodginsii in the N and P patches were significantly higher than those in the homogeneous patches, whereas the average values of Pn, Tr and Gs in the K patches were slightly higher than those in the homogeneous patches. The average values of leaf Fo, Fv/Fm and qP in each nutrient patch under single planting were higher than those under pure and mixed planting, but most of the differences were not significant. The actual photochemical efficiency (yield), photosynthetic electron transfer rate (ETR) and Fv/Fm in N and P patches were significantly higher than those in the homogeneous patches, whereas qP and NPQ in N and P patches differed due to different planting patterns. Most fluorescence parameters in the K patches were lower than those in the homogeneous patches. Planting patterns and nutrient heterogeneity showed significant interaction effects on Pn, Gs, Yield, ETR, Fv/Fm and NPQ. The highest scores for photosynthetic characteristics and fluorescence parameters of F. hodginsii single planting were in N and P nutrient patches.

Effects of nutrient heterogeneity on root foraging and plant growth at the individual and community level.

Plants enhance nutrient uptake in heterogeneous nutrient environments through selective root placement. Many studies have documented that plants grow better under heterogeneous than under homogeneous nutrient distribution, but comprehensive syntheses are relatively few. In a meta-analysis, we examined the effects of patch scale and contrast on plant responses by synthesizing the effects of nutrient heterogeneity on root foraging and plant growth in 131 comparative studies. Plant responses to nutrient heterogeneity were phylogenetically conserved, and the response in shoot biomass was significantly correlated with the response in root biomass but not with root foraging precision. Root precision depended on the competition regime, and plants had lower precision in interspecific than in conspecific competition. Community-level growth was significantly promoted by nutrient heterogeneity and was less variable than individual-level responses. Along with increasing patch scale, overall shoot and root responses of individuals increased but root foraging precision declined. In addition, moderate patch contrast induced the highest root responses. Our results indicate that plants optimize nutrient acquisition from heterogeneous patches mainly through increasing root growth, and plant communities exploit heterogeneous nutrients more effectively than individuals. Understanding the roles of patch attributes in nutrient-heterogeneity effects may help in designing fertilization practices to promote productivity and conserve biodiversity.

Roots and arbuscular mycorrhizal fungi are independent in nutrient foraging across subtropical tree species

Plant species with thin roots and high root-growth rate are thought to have greater root foraging precision than species with thick roots and low root-growth rate. However, whether root morphological traits (such as root diameter) are correlated with foraging precision of roots and mycorrhizal fungi in heterogeneous nutrient environments across tree species remains unclear. We examined 13 coexisting arbuscular mycorrhizal subtropical tree species, measured functional traits of roots, leaves and mycorrhizal fungi and assessed foraging precision of roots and mycorrhizal fungi in response to different nutrient patches using an in situ root-bag approach. Thin-root species had greater specific root length and root growth rate than thick-root species, but they showed similar root and mycorrhizal hyphae foraging precisions. As root diameter increased, root foraging precision exhibited the U-shape patterns in the nitrogen and phosphorus patches, but hyphal foraging precision showed a slightly increasing trend only in the nitrogen patch. Foraging precisions of roots and hyphae were independent, and were not influenced by plant traits across species. Our findings challenge the notion that thin-root species with high root growth rate have greater foraging precision, suggesting that root morphological traits may not be correlated with the variation in foraging strategies of roots and mycorrhizal hyphae.

异质养分环境下邻株竞争对3个木荷种源干物质积累及氮磷效率的影响

异质养分环境下邻株竞争对3个木荷种源干物质积累及氮磷效率的影响

Effects of neighbor competition on growth, fine root morphology and distribution of Schima superba and Cunninghamia lanceolata in different nutrient environments

Taking Schima superba and Cunninghamia lanceolata as test materials, a pot experiment was conducted to simulate the heterogeneous and homogeneous forest soil nutrient environments, and design three planting modes including single plant, two-strain pure plant and two-strain mixed ones to reason the promotion in mixed S. superba and C. lanceolata plantation and the competitive advantage of S. superba. Results showed that compared with the homogeneous nutrient environment, both S. superba and C. lanceolata had the higher seedling height and dry matter accumulation, when mixed in the heterogeneous nutrient environment, S. superba displayed the obviously competitive advantage, which related to its root plasticity. The fine root of S. superba mixed in each diameter class showed a lot of hyperplasia, and the root total length, surface area and volume of which were 80%-180% higher than that of C. lanceolata. S. superba took the advantage of the compensatory growth strategy of vertical direction in fine roots, namely, they still multiplied to gain greater competitive advantage in low nutrient patches, besides occupying eutrophic surface. The different soil colonization and niche differentiation in fine root of S. superba and C. lanceolata alleviated the strong competition for nutrients of the roots of the two species, and improved the mixed-plantation production. Pure plantation of S. superba harvested the lower yield, which due to the root self-recognition inhibited the growth of root system. Fine roots staggered and evenly distributed on the space might be a reason for stable structure of pure S. superba plantation. So, it was recommended that block surface layer soil preparation and fertilization are used to improve the soil nutrient distribution, and the mixed plantation is constructed to promote the growth of S. superba and C. lanceolata, at the same time, the stand density is regulated to promote tree growth for the pure artificial S. superba plantation which had already been built.

Different responses of growth and root development of Schima superba provenance to the adjacent plant competition in different nutrient conditions

Growth and root development of three Schima superba seedling provenances were influenced by adjacent plant competition in the homogeneous and heterogeneous nutrient environment, which revealed the reasons of S. superba competition differences in the different genotypes. The results indicated that, compared with homogeneous nutrient environment, all three S. superba provenances showed higher seedling height, more dry matter accumulation, and significant root proliferation in heterogeneous nutrient environment. Under heterogeneous nutrient environment, the seedlings of S. superba from Jian'ou of Fujian exhibited higher competitive advantage in growth than that of S. superba from Longquan of Zhejiang and Xinfeng of Jiangxi, especially standing out under mixed cultivation with seedlings of Cunninghamia lanceolata. Under mixed cultivation, the root growth parameters of S. superba such as root length, root surface area and volume increased by 20.4%-69.0% compared with the single plant, which enhanced the foraging ability and growth advantage. To some extent, however, the root development in Longquan of Zhejiang and Xinfeng of Jiangxi was suppressed when subjected to the pattern of mixed cultivation. Besides, the root growth and development of all three S. superba provenances were suppressed, which might be due to their root self-recognition in the pattern of mono cultivation. Therefore, the seedling growth in Jian'ou of Fujian decreased significantly, but seedling growth in Longquan of Zhejiang and Xinfeng of Jiangxi was not suppressed, even increased evidently, as their root physiological plasticity might play the crucial role in seedling growth. Hence the S. superba from Jian'ou of Fujian with high foraging efficiency and competition ability was suggested with the method of mixed forestation to improve the S. superba forest plantation productivity.

Root over-production in heterogeneous nutrient environment has no negative effects on Zea mays shoot growth in the field

Nutrient patches in soil have a limited life-span, but the long-term costs and benefits of root foraging in agro-ecological systems are poorly understood. Maize (Zea mays L) was grown in homogeneous or heterogeneous nutrient (nitrogen and phosphorus) environments in the field. After patch exhaustion, nutrient supply was switched from heterogeneous to homogeneous (Het1-Hom) or remained heterogeneous in the same location (Het1S) or had a new patch location established (Het1-Het2). Heterogeneous nutrient supply induced fine root proliferation and produced more shoot biomass than homogeneous treatments in the early growth stages. However, local roots still proliferated after nutrient patch exhaustion, resulting in temporary root over-production. In the Het1-Het2 treatment, roots still proliferated in the initial (subsequently depleted) patch, and new roots proliferated in the new patch at 15 days after the nutrient supply changed. Maize did not show decreased shoot biomass or nutrient accumulation because of temporary root over-production, which might have been due to low cost:benefit ratio of fine roots, quick redistribution of nutrients within the plant and/or high intrinsic root system redundancy. Our data suggest that temporary root over-production has little negative effects on plant growth, especially if plants have large root morphological plasticity.

Root Foraging Increases Performance of the Clonal Plant Potentilla reptans in Heterogeneous Nutrient Environments

BackgroundPlastic root-foraging responses have been widely recognized as an important strategy for plants to explore heterogeneously distributed resources. However, the benefits and costs of root foraging have received little attention.Methodology/Principal FindingsIn a greenhouse experiment, we grew pairs of connected ramets of 22 genotypes of the stoloniferous plant Potentilla reptans in paired pots, between which the contrast in nutrient availability was set as null, medium and high, but with the total nutrient amount kept the same. We calculated root-foraging intensity of each individual ramet pair as the difference in root mass between paired ramets divided by the total root mass. For each genotype, we then calculated root-foraging ability as the slope of the regression of root-foraging intensity against patch contrast. For all genotypes, root-foraging intensity increased with patch contrast and the total biomass and number of offspring ramets were lowest at high patch contrast. Among genotypes, root-foraging intensity was positively related to production of offspring ramets and biomass in the high patch-contrast treatment, which indicates an evolutionary benefit of root foraging in heterogeneous environments. However, we found no significant evidence that the ability of plastic foraging imposes costs under homogeneous conditions (i.e. when foraging is not needed).Conclusions/SignificanceOur results show that plants of P. reptans adjust their root-foraging intensity according to patch contrast. Moreover, the results show that the root foraging has an evolutionary advantage in heterogeneous environments, while costs of having the ability of plastic root foraging were absent or very small.

The influence of light conditions and interspecific competition on the root foraging traits and seedling growth of two tree species

Enriched nutrient patches within natural soil represent an important source of nutrients for tree growth. In the present study, pot experiments in a heterogeneous nutrient environment were conducted to investigate the influence of light conditions and interspecific competition on the root foraging traits and seedling growth of Pinus massoniana and Schima superba. The root foraging scale and the whole-seedling biomass of both species were decreased by shading. The result of this treatment was a lower sensitivity to nutrient heterogeneity in plants that underwent the shading treatment than in plants that were exposed to full-light conditions. The above-ground biomass and whole-seedling biomass of S. superba were not affected by competition with P. massoniana. In contrast, the above-ground biomass and whole-seedling biomass of P. massoniana were negatively affected by competition with S. superba. The more rapid rate of root extension and the more efficient resource uptake of S.superba appear to explain this effect. The species-specific patterns of the influence of environmental factors on foraging ability and seedling growth should be given thorough consideration and should be applied to afforestation and to the management of tree plantations.

Foraging ability and growth performance of four subtropical tree species in response to heterogeneous nutrient environments

Considering the ubiquitous heterogeneity in spatial distribution of soil nutrients, we conducted a pot experiment to investigate the foraging traits and growth performance of four important subtropical tree species in a heterogeneous nutrient environment. The tested species exhibited large differences in foraging traits as well as growth benefits obtained from root foraging. Pinus massoniana, Schima superba and Liriodendron chinese all showed a higher degree of root morphological plasticity (expressed as relative fine root mass difference; RFRMD) than Cunninghami lanceolata (P < 0.05). P. massoniana exhibited the largest degree of morphological plasticity, followed by L. chinese and S. superba, whereas there were no significant differences in RFRMD among the three species. S. superba was the only species that exhibiting both morphological plasticity and physiological plasticity. Both P. massoniana and S. superba exhibited greater whole-seedling biomass and high sensitivity in response to nutrient heterogeneity, resulting from both types of plasticity. In contrast, both types of root plasticity were poor for C. lanceolata, resulting in poor growth benefit in heterogeneous environments. As for L. chinese, the root proliferation in nutrient-rich patches occurred at the expense of depressed root growth in other parts of the root system, leading to the lack of increment in total root biomass and nutrient absorption in heterogeneous environments. Our results provide insight and practical advice for silviculture and forest management.

Computation of mutual fitness by competing bacteria

Competing populations in shared spaces with nonrenewable resources do not necessarily wage a battle for dominance at the cost of extinction of the less-fit strain if there are fitness advantages to the presence of the other strain. We report on the use of nanofabricated habitat landscapes to study the population dynamics of competing wild type and a growth advantage in stationary phase (GASP) mutant strains of Escherichia coli in a sealed and heterogeneous nutrient environment. Although GASP mutants are competitors with wild-type bacteria, we find that the 2 strains cooperate to maximize fitness (long-term total productivity) via spatial segregation: despite their very close genomic kinship, wild-type populations associate with wild-type populations and GASP populations with GASP populations. Thus, wild-type and GASP strains avoid each other locally, yet fitness is enhanced for both strains globally. This computation of fitness enhancement emerges from the local interaction among cells but maximizes global densities. At present we do not understand how fluctuations in both spatial and temporal dimensions lead to the emergent computation and how multilevel aggregates produce this collective adaptation.

Effects of algal diversity on the production of biomass in homogeneous and heterogeneous nutrient environments: a microcosm experiment.

BackgroundOne of the most common questions addressed by ecologists over the past decade has been-how does species richness impact the production of community biomass? Recent summaries of experiments have shown that species richness tends to enhance the production of biomass across a wide range of trophic groups and ecosystems; however, the biomass of diverse polycultures only rarely exceeds that of the single most productive species in a community (a phenomenon called ‘transgressive overyielding’). Some have hypothesized that the lack of transgressive overyielding is because experiments have generally been performed in overly-simplified, homogeneous environments where species have little opportunity to express the niche differences that lead to ‘complementary’ use of resources that can enhance biomass production. We tested this hypothesis in a laboratory experiment where we manipulated the richness of freshwater algae in homogeneous and heterogeneous nutrient environments.Methodology/Principal FindingsExperimental units were comprised of patches containing either homogeneous nutrient ratios (16∶1 nitrogen to phosphorus (N∶P) in all patches) or heterogeneous nutrient ratios (ranging from 4∶1 to 64∶1 N∶P across patches). After allowing 6–10 generations of algal growth, we found that algal species richness had similar impacts on biomass production in both homo- and heterogeneous environments. Although four of the five algal species showed a strong response to nutrient heterogeneity, a single species dominated algal communities in both types of environments. As a result, a ‘selection effect’–where diversity maximizes the chance that a competitively superior species will be included in, and dominate the biomass of a community–was the primary mechanism by which richness influenced biomass in both homo- and heterogeneous environments.Conclusions/SignificanceOur study suggests that spatial heterogeneity, by itself, is not sufficient to generate strong effects of biodiversity on productivity. Rather, heterogeneity must be coupled with variation in the relative fitness of species across patches in order for spatial niche differentiation to generate complementary resource use.

Influence of root herbivory on plant communities in heterogeneous nutrient environments

While plant species respond differently to nutrient patches, the forces that drive this variability have not been extensively examined. In particular, the role of herbivory in modifying plant-resource interactions has been largely overlooked. We conducted a glasshouse study in which nutrient heterogeneity and root herbivory were manipulated, and used differences in foraging among plant species to predict the influence of root herbivores on these species in competition. We also tracked the influence of neighborhood composition, heterogeneity, and herbivory on whole-pot plant biomass. When herbivores were added to mixed-species neighborhoods, Eupatorium compositifolium, the most precise forager, was the only plant species to display a reduction in shoot biomass. Neighborhood composition had the greatest influence on whole-pot biomass, followed by nutrient heterogeneity; root herbivory had the smallest influence. These results suggest that root herbivory is a potential cost of morphological foraging in roots. Root herbivores reduced standing biomass and influenced the relative growth of species in mixed communities, but their effect was not strong enough at the density examined to overwhelm the bottom-up effects of resource distribution.

Root and shoot plasticity of the stoloniferous herb Ajuga reptans L. planted in a heterogeneous environment

Summary In a greenhouse experiment, single ramets of Ajuga reptans, a stoloniferous herb, were planted on the divider of two halves of trays. The two halves of a tray had the same or different nutrient supply. The aim was to study root and shoot plasticity and the placement of ramets and roots in response to the heterogeneous nutrient environment. Number of primary stolons, number of secondary stolons, stolon internode length, number of leaf ramets, total root length (including fine and coarse roots) and root dry weight were greater, but biomass allocation to fine and coarse roots and specific coarse root length were lower under the homogeneous nutrient-rich (the HH-treatment) than under the homogeneous nutrient-poor (the LL-treatment) conditions. No significant response was observed in specific stolon length and specific fine root length. In the heterogeneous nutrient environment (the HL-treatment), total root length, root dry weight, root biomass allocation and specific root length did not differ between the nutrient-rich and the nutrient-poor halves of the trays for both fine and coarse roots. The same response pattern was found for the number of primary and secondary stolons, the number of leaf ramets, spacer lengths between leaf-ramets (internode length) and specific stolon length. Only the number of shoot ramets was larger in the nutrient-rich than in the nutrient-poor patch. Ajuga reptans responded strongly to the different homogeneous nutrient supplies (the HH-treatment vs. the LL-treatment) in terms of morphology and growth of roots and shoots. In the heterogeneous environment (the HL-treatment), the differences in response to local nutrient conditions seemed to be reduced due to intraclonal physiological integration. Predictions of an increase in root mass in the nutrient-rich patch as compared to root mass in the homogeneous HH-treatment or even in the nutrient-poor patch of the HL-treatment were not confirmed by the results. Apparently, behaviour of clonal plants in a heterogeneous environment cannot be simply predicted from their behaviour in different homogeneous environments.

EFFECTS OF NUTRIENT PATCHES AND ROOT SYSTEMS ON THE CLONAL PLASTICITY OF A RHIZOMATOUS GRASS

Clonal plant foraging has been examined primarily on individual clones exposed to resource-poor and resource-rich environments. We designed an experiment to examine the clonal foraging behavior of the rhizomatous grass Elymus lanceolatus ssp. lanceolatus under the influence of neighboring plant root systems in a heterogeneous nutrient environment. Individual Elymus clones were planted in large bins together with one of three neighboring grass species, Agropyron desertorum, Pseudoroegneria spicata, or Bromus tectorum, which differ in rooting density and growth activity. The position of Elymus clones was manipulated so rhizomes encountered a short-duration nutrient patch and subsequently root systems of the neighboring plants. Unexpectedly, the morphological plasticity of the perennial grass Elymus lanceolatus ssp. lanceolatus was influenced by the presence of the neighboring species much more than by the local nutrient enrichments, although nutrient patches did amplify some of the foraging responses. Elymus rhizomes branched readily and initiated large daughter plants as they encountered the low-density root systems of Pseudoroegneria. When Elymus encountered the fine, dense root systems of the annual Bromus, clonal expansion was initially reduced. Yet, after the short growing season of Bromus, Elymus resumed clonal expansion and produced several daughter plants. Elymus clones were most constrained by the fine, dense root systems of Agropyron desertorum. In this case, a few, long rhizomes avoided the densely rooted soil environment by growing aboveground as stolons crossing over the Agropyron tussocks. Elymus clonal biomass was largest in neighborhoods of Pseudoroegneria, intermediate in neighborhoods with Bromus, and smallest in neighborhoods with Agropyron. The latter were approximately half the size of those in the Pseudoroegneria environments. Elymus growth could not be explained by simple resource competition alone; other mechanisms must have been involved in the apparent differences in interference patterns of neighboring plants with Elymus.

Effects of Nutrient Patches and Root Systems on the Clonal Plasticity of a Rhizomatous Grass

Clonal plant foraging has been examined primarily on individual clones exposed to resource-poor and resource-rich environments. We designed an experiment to examine the clonal foraging behavior of the rhizomatous grass Elymus lanceolatus ssp. lanceolatus under the influence of neighboring plant root systems in a heterogeneous nutrient environment. Individual Elymus clones were planted in large bins together with one of three neighboring grass species, Agropyron desertorum, Pseudoroegneria spicata, or Bromus tectorum, which differ in rooting density and growth activity. The position of Elymus clones was manipulated so rhizomes encountered a short-duration nutrient patch and subsequently root systems of the neighboring plants. Unexpectedly, the morphological plasticity of the perennial grass Elymus lanceolatus ssp. lanceolatus was influenced by the presence of the neighboring species much more than by the local nutrient enrichments, although nutrient patches did amplify some of the foraging responses. Elymus rhizomes branched readily and initiated large daughter plants as they encountered the low-density root systems of Pseudoroegneria. When Elymus encountered the fine, dense root systems of the annual Bromus, clonal expansion was initially reduced. Yet, after the short growing season of Bromus, Elymus resumed clonal expansion and produced several daughter plants. Elymus clones were most constrained by the fine, dense root systems of Agropyron desertorum. In this case, a few, long rhizomes avoided the densely rooted soil environment by growing aboveground as stolons crossing over the Agropyron tussocks. Elymus clonal biomass was largest in neighborhoods of Pseudoroegneria, intermediate in neighborhoods with Bromus, and smallest in neighborhoods with Agropyron. The latter were approximately half the size of those in the Pseudoroegneria environments. Elymus growth could not be explained by simple resource competition alone; other mechanisms must have been involved in the apparent differences in interference patterns of neighboring plants with Elymus.