Root growth and plant biomass in <Emphasis Type="Italic">Lolium perenne</Emphasis> exploring a nutrient-rich patch in soil

We investigated soil exploration by roots and plant growth in a heterogeneous environment to determine whether roots can selectively explore a nutrient-rich patch, and how nutrient heterogeneity affects biomass allocation and total biomass before a patch is reached. Lolium perenne L. plants were grown in a factorial experiment with combinations of fertilization (heterogeneous and homogeneous) and day of harvest (14, 28, 42, or 56 days after transplanting). The plant in the heterogeneous treatment was smaller in its mean total biomass, and allocated more biomass to roots. The distributions of root length and root biomass in the heterogeneous treatment did not favor the nutrient-rich patch, and did not correspond to the patchy distribution of inorganic nitrogen. Specific root length (length/biomass) was higher and root elongation was more extensive both laterally and vertically in the heterogeneous treatment. These characteristics may enable plants to acquire nutrients efficiently and increase the probability of encountering nutrient-rich patches in a heterogeneous soil. However, heterogeneity of soil nutrients would hold back plant growth before a patch was reached. Therefore, although no significant selective root placement in the nutrient-rich patch was observed, plant growth before reaching nutrient-rich patches differed between heterogeneous and homogeneous environments.     

Limited costs of wrong root placement in Rumex palustris in heterogeneous soils

Nutrient hot spots in the soil have a limited life span, but the costs and benefits for root foraging are still underexposed. We assessed short-term costs that may arise when a nutrient-rich patch induces root proliferation, but then rapidly disappears. Rumex palustris plants were grown with a homogeneous or a heterogeneous nutrient application. After root proliferation in a nutrient-rich patch, nutrient supply was switched from homogeneous to heterogeneous, and vice versa, or the patch location was changed. R. palustris proliferated its roots in the rich patch. After switching, the relative growth rates of the roots were adjusted to the novel pattern of nutrient availability. However, the changes in local root biomass lagged behind the rapid shift in nutrient supply, because the root mass realized in specific sectors could not be rapidly relocated. Despite this, R. palustris did not exhibit costs of switching in terms of biomass or nitrogen uptake. Our data suggest that rapid shifts in uptake rate and redistribution of nitrogen within the plant may have lowered the costs of incorrect root placement.     

Root foraging traits and competitive ability in heterogeneous soils

The responses of plant roots to nutrient patches in soil may be an important component of competitive ability. In particular, the scale, precision, and rate of foraging for patchy soil resources may influence competitive ability in heterogeneous soils. In a target–neighbor experiment in the field, per-individual and per-gram competitive effects were measured for six old-field species with known root foraging scale, precision, and rate. The presence and number of nutrient patches were also manipulated in a full factorial design. Number and presence of patches did not influence the outcome of competition. Competitive ability was not related to total plant size, growth rate, or root:shoot allocation, or to root foraging precision. Per-individual competitive effects were marginally correlated with root foraging scale (biomass of roots) and root foraging rate (time required to reach a patch). Therefore, competitive ability was more closely related to ability to quickly fill a soil volume with roots than to ability to preempt resource-rich patches.     

Context dependence in foraging behaviour of Achillea millefolium

Context-dependent foraging behaviour is acknowledged and well documented for a diversity of animals and conditions. The contextual determinants of plant foraging behaviour, however, are poorly understood. Plant roots encounter patchy distributions of nutrients and soil fungi. Both of these features affect root form and function, but how they interact to affect foraging behaviour is unknown. We extend the use of the marginal value theorem to make predictions about the foraging behaviour of roots, and test our predictions by manipulating soil resource distribution and inoculation by soil fungi. We measured plant movement as both distance roots travelled and time taken to grow through nutrient patches of varied quality. To do this, we grew Achillea millefolium in the centers of modified pots with a high-nutrient patch and a low-nutrient patch on either side of the plant (heterogeneous) or patch-free conditions (homogeneous). Fungal inoculation, but not resource distribution, altered the time it took roots to reach nutrient patches. When in nutrient patches, root growth decreased relative to homogeneous soils. However, this change in foraging behaviour was not contingent upon patch quality or fungal inoculation. Root system breadth was larger in homogeneous than in heterogeneous soils, until measures were influenced by pot edges. Overall, we find that root foraging behaviour is modified by resource heterogeneity but not fungal inoculation. We find support for predictions of the marginal value theorem that organisms travel faster through low-quality than through high-quality environments, with the caveat that roots respond to nutrient patches per se rather than the quality of those patches.     

Foraging responses of clonal plants to multi-patch environmental heterogeneity: spatial preference and temporal reversibility

Background and aims

Plant root placement is highly plastic in order to acquire patchily distributed nutrients and to ensure their survival, growth and reproduction. Considering the spatial extension of clonal organs, we selected two clonal plants (Leymus chinensis (Trin.) Tzvel. and Hierochloe glabra Trin.) to determine the spatio-temporal effects of environmental heterogeneity on belowground organs and newly-born ramets.

Methods

Small-scale and multi-patch heterogeneous environments were manipulated by creating four patches filled with different types of soil in a same pot. The four patches were composed of sandy soil, sandy loam, loam soil and humus soil, respectively. Ramet number, bud number, mean spacer length, rhizome length, and biomass allocation within each patch were measured to identify plant foraging responses.

Results

The preferential patch of L. chinensis was humus soil patch which was the highest in nutrient availability, whereas H. glabra preferred to place ramets in sandy loam and loam soil patches. When growing in homogeneous environments, both species randomly rooted their offspring ramets in the four compartments. In heterogeneous environments, foraging responses were detected in ramet placement, aboveground biomass and total rhizome length. However, there were no differences in bud number or belowground biomass among four types of patches in heterogeneous environments, which might suggest that there would be no inter-patch differences in seedling establishment in the next year.

Conclusions

Plants show selective allocation of offspring ramets to preferential patches in the presence of multi-patch environmental heterogeneity. Responses of H. glabra to multi-patch heterogeneity were faster than those of L. chinensis, demonstrating that the foraging patterns are species-specific. Clonal plants can rapidly respond to environmental heterogeneity, whereas foraging responses are potentially reversible over a longer temporal scale.     

Root foraging for patchy resources in eight herbaceous plant species

The root foraging strategy of a plant species can be characterized by measuring foraging scale, precision, and rate. Trade-offs among these traits have been predicted to contribute to coexistence of competitors. We tested for trade-offs among root foraging scale (total root mass and length of structural roots), precision (ln-ratio of root lengths in resource-rich and resource-poor patches), and rate (days required for roots to reach a resource-rich patch, or growth rate of roots within a resource-rich patch) in eight co-occurring species. We found that root foraging scale and precision were positively correlated, as were foraging scale and the rate of reaching patches. High relative growth rate of a species did not contribute to greater scale, precision, or rate of root foraging. Introduced species had greater foraging scale, precision, and rate than native species. The positive correlations between foraging scale and foraging precision and rate may give larger species a disproportionate advantage in competition for patchy soil resources, leading to size asymmetric competition below ground.     

Growth Consequences of Soil Nutrient Heterogeneity for two Old-field Herbs,Ambrosia artemisiifoliaandPhytolacca americana, Grown Individually and in Combination

Plant species can respond to small scale soil nutrient heterogeneityby proliferating roots or increasing nutrient uptake kineticsin nutrient-rich patches. Because root response to heterogeneitydiffers among species, it has been suggested that the distributionof soil resources could influence the outcome of interspecificcompetition. However, studies testing how plants respond toheterogeneity in the presence of neighbours are lacking. Inthis study, individuals of two species,Phytolacca americanaL.andAmbrosia artemisiifoliaL. were grown individually and incombination in soils with either a homogeneous or heterogeneousnutrient distribution. Above-ground biomass of individuallygrown plants of both species was greater when fertilizer waslocated in a single patch than when the same amount of fertilizerwas distributed evenly throughout the soil. Additionally, bothspecies proliferated roots in high-nutrient patches.A. artemisiifoliaexhibitedlarger root:shoot ratios, increased nitrogen depletion fromnutrient patches, and a higher growth rate thanP. americana,suggestingA. artemisiifoliais better suited to find and rapidlyexploit nutrient patches. In contrast to individually grownplants, soil nutrient distribution had no effect on final above-groundplant biomass for either species when grown with neighbours,even though roots were still concentrated in high nutrient patches.This study demonstrates that increased growth of isolated plantsas a consequence of localized soil nutrients is not necessarilyan indication that heterogeneity will affect interspecific encounters.In fact, despite a significant below-ground response, soil nutrientheterogeneity was inconsequential to above-ground performancewhen plants were grown with neighbours.Copyright 1999 Annalsof Botany Company Phytolacca americana, pokeweed,Ambrosia artemisiifolia, ragweed, nutrient heterogeneity, root proliferation, plasticity, foraging, nutrient patches.     

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.     

Invasive clonal plant species have a greater root-foraging plasticity than non-invasive ones

Clonality is frequently positively correlated with plant invasiveness, but which aspects of clonality make some clonal species more invasive than others is not known. Due to their spreading growth form, clonal plants are likely to experience spatial heterogeneity in nutrient availability. Plasticity in allocation of biomass to clonal growth organs and roots may allow these plants to forage for high-nutrient patches. We investigated whether this foraging response is stronger in species that have become invasive than in species that have not. We used six confamilial pairs of native European clonal plant species differing in invasion success in the USA. We grew all species in large pots under homogeneous or heterogeneous nutrient conditions in a greenhouse, and compared their nutrient-foraging response and performance. Neither invasive nor non-invasive species showed significant foraging responses to heterogeneity in clonal growth organ biomass or in aboveground biomass of clonal offspring. Invasive species had, however, a greater positive foraging response in terms of root and belowground biomass than non-invasive species. Invasive species also produced more total biomass. Our results suggest that the ability for strong root foraging is among the characteristics promoting invasiveness in clonal plants.     

Relative Nitrogen Limitation at Steady-state Nutrition as a Determinant of Plasticity in Five Grassland Plant Species

Partitioning of biomass between roots and different shoot partshas often been used to explain the response of plants to variationsin resource availability. There are still many uncertaintiesin the importance of this trait for plant performance, and clearguidelines on how partitioning should be quantified in relationto growth rate and resource supply are of fundamental importancefor such an understanding. This paper reports an attempt toshow how plant nitrogen status relates to root:shoot partitioningand other plastic responses, in a manner that can be used forquantitative predictions. The reactions to nitrogen limitationof five grassland plant species, with different ecological demands,were compared. The species used were the forbs Polygala vulgarisand Crepis praemorsa, and the grasses Danthonia decumbens, Agrostiscapillaris and Dactylis glomerata. The experiment was conductedin a climate chamber where the plants were grown hydroponically(1) under non-limiting nutrient conditions and (2) at a steady-statenitrogen limitation, which enabled the plants to express halfof their growth potential. The relative growth rate (RGR) ofthe species was strongly related to plant nitrogen concentration(PNC) and leaf area ratio (LAR), whereas the effects on netassimilation rate (NAR) were very small. Despite large differencesin maximum relative growth rate, the species showed remarkablesimilarities in dry matter partitioning between root and shoot.It is concluded that root:shoot partitioning can be treatedas a direct function of the relative resource limitation ofthe plant. The difficulty of attaining well-defined levels ofresource limitation in soil, other solid substrates and manyhydroponic systems may be the most important reason for thedivergent results in earlier studies. Better knowledge of soil-rootinteractions, and plant responses to the whole span of resource-supplylevels, is required for a thorough understanding of how nutrientslimit growth. Copyright 1999 Annals of Botany Company Growth rate, plant strategies, plasticity, partitioning, biomass, nitrogen, nutrient limitation, grassland.     

马尾松种源在异质养分环境中的觅养行为差异

选择广东信宜、福建武平、广西岑溪3个不同磷效率特性的马尾松种源,构建同质和异质两种养分环境开展盆栽实验,研究马尾松搜寻利用异质分布养分的获取机制及不同种源觅养行为差异。结果表明,与同质营养环境相比,异质营养环境中马尾松种源具有较高的苗高、地径生长量、较强光合速率和干物质生产能力。研究证实了根系形态可塑性和生理可塑性在马尾松获取异质分布养分中的重要性。马尾松可通过在富养斑块中须侧根的大量增生、对N、P、K等元素的有效吸收提高其觅养能力。马尾松在拓殖富养斑块的初期主要依靠新生侧根的增加和侧根的延长,在拓殖一段时期之后则主要靠新生侧根的生成和须根数量、须根密度的增加来搜寻异质分布养分。异质养分环境中的根系具有较高的养分吸收效率主要缘由在富养斑块中对N、P、K大量的吸收。综合比较分析认为,在3个参试种源中广西岑溪和福建武平种源在异质营养环境中拓殖富养斑块和觅养能力较强,广东信宜种源拓殖和觅养能力相对较弱。     

Differences between resource patches modify root herbivore effects on plants

While soil resource heterogeneity and root herbivory can have significant direct influences on plant growth, soil heterogeneity may also have indirect effects by influencing the foraging behavior of root herbivores. We used sand-filled greenhouse pots to assess root herbivore foraging behavior and potential interactions between patch quality, herbivore foraging, and plant biomass production (yield). Individual pots were divided into four quarters: one fertilized, and three unfertilized, two of which were planted with tree seedlings. Two treatments were used to create fertilized quarters: high-organic manure fertilizer, and slow-release mineral fertilizer. Seedlings of red maple (Acer rubrum L.) and Virginia pine (Pinus virginiana L.) were used to create two single-species and one mixed-species treatments. Root-feeding beetle larvae were added to the pots and allowed to forage freely for ∼8 weeks. At harvest, root herbivores in organic-fertilized pots were strongly attracted to fertilized quarters despite their relatively low-root biomass. Herbivore distribution was significantly different in mineral fertilized pots, where larvae were most abundant in planted quarters, which is also where most of the plant roots occurred. Whole pot plant yield was significantly reduced by larvae; this effect was stronger in the mineral fertilized pots than organic fertilized pots. While one of the plant species appeared more sensitive to herbivory, root herbivores had a greater influence on yield in mixed-species pots than in single-species pots. Overall, these results suggest that patch quality influences on herbivore foraging may indirectly alter yield and plant community composition. Responsible Editor: Angela Hodge.     

Heterogeneity in spatial P-distribution and foraging capability by Zea mays: effects of patch size and barriers to restrict root proliferation within a patch

• Background and Aims Localized proliferation of rootsin nutrient-enriched patches seems to be an adaptive responsein many plants, but its function is still debatable. To understandthe efficiency and limitation of foraging behaviour, the impactof patch size and the presence or absence of a barrier to rootproliferation within phosphorus (P)-enriched patches was examined. • Methods In pots filled with P-poor soil, six treatmentsof heterogeneous P supply were prepared: three patch sizes withor without a root barrier between patches. In addition, a homogeneousP supply treatment was also prepared. Irrespective of thesetreatments, each pot received the same total amount of P. Maize(Zea mays) was grown in each pot for 45 d in a greenhouse. • Key Results P content and biomass were greatest in plantsgrown in the largest patch due to successful root proliferation,and were higher in the presence of a root barrier. Interestingly,plants preferentially developed adventitious nodal roots projectingfrom the stem into the P-enriched soil, particularly in thelargest patch with a root barrier. Removal of the barrier reducedthe P-uptake capacity per unit root surface area or volume inP-enriched patches, revealing that the P-uptake capacity perroot can be suppressed even in P-rich soil if other portionson the root axis encounter P-poor conditions. • Conclusions The results suggest that the efficiency ofroot morphological plasticity is largely determined by the sizeof the P-enriched patch. Furthermore, the results imply a novelaspect of P-uptake physiology that roots in heterogeneous Pcannot demonstrate their potential capacity, as would be observedin roots encountering P continuously; this effect is probablymediated by an internal root factor.     

Contrasting root behaviour in two grass species: a test of functionality in dynamic heterogeneous conditions

Root systems are highly plastic as they express a range of responses to acquire patchily distributed nutrients. However, the ecological significance of placing roots selectively in nutrient hotspots is still unclear. Here, we investigate under what conditions selective root placement may be a significant functional trait that determines belowground competitive ability. We studied two grasses differing in root foraging behaviour, Festuca rubra and Anthoxanthum odoratum. The plants were grown in stable and more dynamic heterogeneous environments, by switching nutrient patches halfway through the experiment. A. odoratum was a factor of two less selective in placing its roots into nutrient-rich patches than F. rubra. A. odoratum produced overall higher root length densities with higher specific root length than F. rubra and acquired more nutrients. A. odoratum appeared to be the superior competitor, irrespective of the nutrient dynamics. Our results suggest that root behaviour consisting of producing high root length densities at relatively low biomass investments can be a more effective foraging strategy than placing roots selectively in nutrient hotspots. When understanding the functionality of root traits among different species, specific root length may play a key role.     

Root morphological plasticity and nutrient acquisition of perennial grass species from habitats of different nutrient availability

We studied the root foraging ability and its consequences for the nutrient acquisition of five grass species that differ in relative growth rate and that occur in habitats that differ widely in nutrient availability. Foraging responses were quantified, based on the performance of the plants in homogeneous and heterogeneous soil environments of the same overall nutrient availability. Although all species tended to produce a significantly higher root length density in a nutrient-rich patch, this response was significant only for the faster-growing species. The increased root length density resulted from small, though not significant, changes in root biomass and specific root length. The effectiveness of root proliferation was determined by quantifying the total amount of nutrients (N and P) accumulated by the plants over the course of the experiment. Plants acquired more N in a heterogeneous environment than in a homogeneous environment, although the total nutrient availability was the same. The ability to acquire nutrients (N or P) in the heterogeneous environment was not related to the ability of species to increase root length density in response to local nutrient enrichment. In contrast to other studies, our results suggest that the role of morphological plasticity of roots in acquiring patchily distributed resources is limited. Possible reasons for this discrepancy are discussed. Received: 11 September 1997 / Accepted: 28 February 1998     

Plant phenotypic plasticity belowground: a phylogenetic perspective on root foraging trade-offs

Many plants proliferate roots in nutrient patches, presumably increasing nutrient uptake and plant fitness. Nutrient heterogeneity has been hypothesized to maintain community diversity because of a trade-off between the spatial extent over which plants forage (foraging scale) and their ability to proliferate roots precisely in nutrient patches (foraging precision). Empirical support for this hypothesis has been mixed, and some authors have suggested that interspecific differences in relative growth rate may be confounded with measurements of foraging precision. We collected previously published data from numerous studies of root foraging ability (foraging precision, scale, response to heterogeneity, and relative growth rate) and phylogenetic relationships for >100 plant species to test these hypotheses using comparative methods. Root foraging precision was phylogenetically and taxonomically conserved. Using a historical and phylogenetically independent contrast correlations, we found no evidence of a root foraging scale-precision trade-off, mixed support for a relative growth rate-precision relationship, and no support for the widespread assumption that foraging precision increases the benefit gained from growth in heterogeneous soil. Our understanding of the impacts of plant foraging precision and soil heterogeneity on plants and communities is less advanced than commonly believed, and we suggest several areas in which further research is needed.     

The dependence of root system properties on root system biomass of 10 North American grassland species

Dependence of the properties of root systems on the size of the root system may alter conclusions about differences in plant growth in different environments and among species. To determine whether important root system properties changed as root systems aged and accumulated biomass, we measured three important properties of fine roots (tissue density, diameter, and C:N) and three biomass ratios (root:shoot, fine:coarse, and shallow:deep) of monocultures of 10 North American grassland species five times during their second and third years of growth. With increasing belowground biomass, root tissue density increased and diameter decreased. This may reflect cortical loss associated with the aging of roots. For non-legumes, fine root C:N decreased with increasing root biomass, associated with decreases in soil solution NO^{3 –} concentrations. No changes in fine root C:N were detected with increasing belowground biomass for the two legumes we studied. Among all 10 species, there were generally no changes in the relative amounts of biomass in coarse and fine roots, root:shoot, or the depth placement of fine roots in the soil profile as belowground biomass increased. Though further research is needed to separate the influence of root system size, age of the roots, and changes in nutrient availability, these factors will need to be considered when comparing root functional traits among species and treatments.     

Foraging for nutrients, responses to changes in light, and competition in tropical deciduous tree seedlings

We evaluated (1) the responses of two co-occurring tropical tree species, Heliocarpuspallidus and Caesalpiniaeriostachys, to changes in light, (2) the ability of these species to search for and exploit a fertilized soil patch, (3) the relationship between the capacity to forage for a fertilized patch and the capacity to respond to changes in light availability and (4) how the relationship between light and nutrient acquisition influenced the competitive interactions between these species. Plants of the two species were exposed to a factorial combination of high (H) and low (L) light intensity and fertilized (+Fp) and unfertilized (−Fp) nutrient patches for 50 days. Half of the plants from H were then transferred to L (HL treatment), and half of the plants from L were transferred to H (LH). The remaining plants were kept in their original light condition and grown for another 50 days. Plants were grown in these light and patch treatments alone (one plant per pot) and in interspecific competition (one plant per species resulting in two plants per pot). Both species exploited fertilized patches by increasing root biomass and length in the patch. This enhanced plant productivity and growth rate mainly under LH and HH conditions for Heliocarpus and the HH condition for Caesalpinia). When plants in the HH light environment were grown with an unfertilized patch, plant biomass and relative growth rates (RGRs) were even lower than␣under the LL light environment [(HH–Fp)<LL]. However, the combined activity of shoot and roots when above- and below-ground resources were temporally and spatially heterogeneous influenced plant productivity and growth rate. The benefit from light increase (LH) was reduced when grown with an unfertilized patch. Larger reductions in root biomass, length and density in the patch, and in plant biomass and RGR, were exhibited by Heliocarpus than by Caesalpinia. These results suggest a close relationship between root foraging and light capture, where the benefit of the exploitation of the patch will be reflected in whole-plant benefit, if enough light is captured above-ground. In addition, the results suggest a change in the expected plant responses to light due to heterogeneity in soil nutrients, even though the fertilized patch was only a small proportion of the total soil volume. Leaf characteristics such as specific leaf area responded only to light conditions and not to patchily distributed nutrients. Root characteristics responded more strongly to nutrient heterogeneity. Competition modified the pattern of foraging under both high- and low-light conditions in Heliocarpus by 50 days, and the ability to forage for a fertilized patch under LL after 100 days of growth for Caesalpinia. Even though plant growth and productivity are greatly reduced under low-light conditions (HL and LL), competition modifies the ability of species to forage for a rich patch (especially for the fast-growing species Heliocarpus). Received: 24 November 1997 / Accepted: 15 June 1998     

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

Background

Plastic 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 Findings

In 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/Significance

Our 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.     

Interactive effects of soil nutrient heterogeneity and belowground herbivory on the growth of plants with different root foraging traits

Aims

Plants with precise root foraging patterns can proliferate roots preferentially in nutrient-rich soil patches. When nutrients are distributed heterogeneously, this trait is often competitively advantageous in pot experiments but not field experiments. We hypothesized that this difference is due to belowground herbivory under field conditions.

Methods

We performed pot experiments using seedlings of Lolium perenne (a more precise root foraging species) and Plantago lanceolata (a less precise root foraging species). The experiment had a two-way factorial randomized block design, with nutrient distribution pattern (homogeneous or heterogeneous) and belowground herbivore (present or absent) as the two factors. Each pot contained one seedling of each species.

Results

With no herbivore present, plant biomass was smaller in the heterogeneous nutrient treatment than in the homogeneous treatment in P. lanceolata, but not in L. perenne. Under homogeneous nutrient distribution, plant biomass was lower in both species with a herbivore present than with no herbivore. Under heterogeneous nutrient distribution, biomass reduction due to herbivory occurred only in L. perenne.

Conclusions

Roots of the precise root foraging species were grazed more under the heterogeneous nutrient distribution, suggesting that the herbivore more efficiently foraged for roots in nutrient-rich soil patches.