Root morphological and physiological plasticity of perennial grass species and the exploitation of spatial and temporal heterogeneous nutrient patches

Root morphological and physiological characteristics of four perennial grass species were investigated in response to spatial and temporal heterogeneous nutrient patches. Two species from nutrient-rich habitats (i.e. Holcus lanatus and Lolium perenne) and two species from nutrient-poor habitats (i.e. Festuca rubra and Anthoxanthum odoratum) were included in the study. Patches were created by injecting equal amounts of nutrient solution into the soil either on one location (i.e. spatial heterogeneity) or on several, alternating locations (i.e. temporal heterogeneity) within the pot. The consequences of changes in root morphology and the implications for the exploitation of the nutrient patches by individual plants were quantified by the amount of ¹⁵N captured from the enriched patches. The effects of nutrient heterogeneity on the acquisition of nutrients by species were determined by comparing the total nitrogen and phosphorus acquisition of the species in the two heterogeneous habitats with the total nitrogen and phosphorus acquisition in a homogeneous treatment. In this homogeneous treatment the same amount of nutrient solution was supplied homogeneously over the soil surface. The experiment lasted for 27 days and comprised one harvest. In response to the spatial enrichment treatment, all species produced significantly more root biomass within the enriched patch. The magnitude of the response was similar for species from nutrient-rich and nutrient-poor habitats. In contrast to this response of root biomass, root morphology, including specific root length, branching frequency and mean lateral root length was not affected by the treatments. In response to the temporal enrichment treatment, all species were able to increase the nitrogen uptake rate per unit of root biomass. The species from nutrient-poor habitats had, on average, higher uptake rates per unit root biomass than the species from nutrient-rich habitats, but the magnitude of the response did not differ between the species. These results question the general validity of the assumptions that root foraging characteristics differ among species from nutrient-rich and nutrient-poor habitats. As a result of these root responses, all species captured an equal amount of ¹⁵N from the spatial and temporal enriched nutrient patches and all species acquired significantly more nitrogen in the heterogeneous treatments than in homogeneous treatment. Hence, the ability to exploit local and temporal nutrient heterogeneity does not appear to differ between species from nutrient-rich and nutrient-poor habitats, but is achieved by these species in different ways. The ecological implications of these differences are discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

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。     

Effects of soil nutrient heterogeneity on intraspecific competition in the invasive, clonal plant Alternanthera philoxeroides

Background and Aims

Fine-scale, spatial heterogeneity in soil nutrient availability can increase the growth of individual plants, the productivity of plant communities and interspecific competition. If this is due to the ability of plants to concentrate their roots where nutrient levels are high, then nutrient heterogeneity should have little effect on intraspecific competition, especially when there are no genotypic differences between individuals in root plasticity. We tested this hypothesis in a widespread, clonal species in which individual plants are known to respond to nutrient heterogeneity.

Methods

Plants derived from a single clone of Alternanthera philoxeroides were grown in the greenhouse at low or high density (four or 16 plants per 27·5 × 27·5-cm container) with homogeneous or heterogeneous availability of soil nutrients, keeping total nutrient availability per container constant. After 9 weeks, measurements of size, dry mass and morphology were taken.

Key Results

Plants grew more in the heterogeneous than in the homogeneous treatment, showing that heterogeneity promoted performance; they grew less in the high- than in the low-density treatment, showing that plants competed. There was no interactive effect of nutrient heterogeneity and plant density, supporting the hypothesis that heterogeneity does not affect intraspecific competition in the absence of genotypic differences in plasticity. Treatments did not affect morphological characteristics such as specific leaf area or root/shoot ratio.

Conclusions

Results indicate that fine-scale, spatial heterogeneity in the availability of soil nutrients does not increase competition when plants are genetically identical, consistent with the suggestion that effects of heterogeneity on competition depend upon differences in plasticity between individuals. Heterogeneity is only likely to increase the spread of monoclonal, invasive populations such as that of A. philoxeroides in China.     

土壤养分空间异质性与植物根系的觅食反应

植物在长期进化过程中,为了最大限度地获取土壤资源,对养分的空间异质性产生各种可塑性反应．包括形态可塑性、生理可塑性、菌根可塑性等．许多植物种的根系在养分丰富的斑块中大量增生,增生程度种间差异较大,并受斑块属性(斑块大小、养分浓度)、营养元素种类和养分总体供应状况的影响．植物还通过调整富养斑块中细根的直径、分枝角、节问距以及空间构型来实现斑块养分的高效利用．根系的生理可塑性及菌根可塑性可能在一定程度上影响其形态可塑性．生理可塑性表现为处于不同养分斑块上的根系迅速调整其养分吸收速率,从而增加单位根系的养分吸收,对在时间上和空间上变化频繁的空间异质性土壤养分的利用具有重要意义,可在一定程度上弥补根系增生反应的不足．菌根可塑性目前研究较少,一些植物种的菌根代替细根实现在富养斑块中的增生．菌根增生的碳投入养分吸收效率较高、根系增生对增加养分吸收的作用较复杂,取决于养分离子在土壤中的移动性能以及是否存在竞争植物;对植物生长(竞争能力)的作用因种而异,一些敏感种由此获得生长效益,而其它一些植物种受影响较小．植物个体对土壤养分空间异质性反应能力和生长差异,影响其在群落中的地位和命运,最终影响群落组成及其结构．     

Improving crop nutrient efficiency through root architecture modifications

Improving crop nutrient ef ficiency becomes an essential consideration for environmentally friendly and sustainable agriculture. Plant growth and development is dependent on 17 essential nutrient elements,among them,nitrogen(N) and phosphorus(P) are the two most important mineral nutrients. Hence it is not surprising that low N and/or low P availability in soils severely constrains crop growth and productivity,and thereby have become high priority targets for improving nutrient ef ficiency in crops. Root exploration largely determines the ability of plants to acquire mineral nutrients from soils. Therefore,root architecture,the 3-dimensional con figuration of the plant's root system in the soil,is of great importance for improving crop nutrient ef ficiency. Furthermore,the symbiotic associations between host plants and arbuscular mycorrhiza fungi/rhizobial bacteria,are additional important strategies to enhance nutrient acquisition. In this review,we summarize the recent advances in the current understanding of crop species control of root architecture alterations in response to nutrient availability and root/microbe symbioses,through gene or QTL regulation,which results in enhanced nutrient acquisition.     

Responses to mineral nutrient availability and heterogeneity in physiologically integrated sedges from contrasting habitats

Clonal plants from poor habitats benefit less from morphologically plastic responses to heterogeneity than plants from more productive sites. In addition, physiological integration has been suggested to either increase or decrease the foraging efficiency of clonal plants. We tested the capacity for biomass production and morphological response in two closely related, rhizomatous species from habitats that differ in resource availability, Carex arenaria (from poor sand dunes) and C. disticha (from nutrient-richer, moister habitats). We expected lower total biomass production and reduced morphological plasticity in C. arenaria, and that both species would produce more ramets in high nutrient patches, either in response to signals transported through physiological integration, or by locally determined responses to nutrient availability. To investigate mineral nutrient heterogeneity, plants were grown in boxes divided into two compartments with homogeneous or heterogeneous supply of high (H) or low (L) nutrient levels, resulting in four treatments, H-H, H-L, L-H and L-L. Both C. arenaria and C. disticha produced similar biomass in high nutrient treatments. C. disticha responded to high nutrients by increased biomass production and branching of the young parts and by altering root:shoot ratio and rhizome lengths, while C. arenaria showed localised responses to high nutrients in terms of local biomass and branch production in high nutrient patches. The results demonstrated that although it has a conservative morphology, C. arenaria responded to nutrient heterogeneity through morphological plasticity. An analysis of costs and benefits of integration on biomass production showed that young ramets of both species benefited significantly from physiological integration, but no corresponding costs were found. This suggests that plants from resource-poor but dynamic habitats like sand dunes respond morphologically to high nutrient patches. The two species responded to nutrient heterogeneity in different traits, and this is discussed in terms of local and distant signalling of plant status.     

植物根系养分捕获塑性与根竞争

为了更有效地从土壤中获取养分, 植物根系在长期的进化与适应中产生了一系列塑性反应, 以响应自然界中广泛存在的时空异质性。同时, 植物根系的养分吸收也要面对来自种内和种间的竞争。多种因素都会影响植物根竞争的结果, 包括养分条件、养分异质性的程度、根系塑性的表达等。竞争会改变植物根系的塑性反应, 比如影响植物根系的空间分布; 植物根系塑性程度差异也会影响竞争。已有研究发现根系具有高形态塑性和高生理塑性的植物在长期竞争过程中会占据优势。由于不同物种根系塑性的差异, 固定的对待竞争的反应模式在植物根系中可能并不存在, 其响应随竞争物种以及土壤环境因素的变化而变化。此外, 随着时间变化, 根系塑性的反应及其重要性也会随之改变。植物对竞争的反应可能与竞争个体之间的亲缘关系有关, 有研究表明亲缘关系近的植物可能倾向于减小彼此之间的竞争。根竞争对植物的生存非常重要, 但目前还没有研究综合考虑植物的各种塑性在根竞争中的作用。另外根竞争对群落结构的影响尚待深入的研究。     

Soil nutrient heterogeneity interacts with elevated CO2 and nutrient availability to determine species and assemblage responses in a model grassland community

Interactive effects of atmospheric CO(2) concentration ([CO(2)]), soil nutrient availability and soil nutrient spatial distribution on the structure and function of plant assemblages remain largely unexplored. Here we conducted a microcosm experiment to evaluate these interactions using a grassland assemblage formed by Lolium perenne, Plantago lanceolata, Trifolium repens, Anthoxanthum odoratum and Holcus lanatus. Assemblages exhibited precise root foraging patterns, had higher total and below-ground biomass, and captured more nitrogen when nutrients were supplied heterogeneously. Root foraging responses were modified by nutrient availability, and the patterns of N capture by interactions between nutrient distribution, availability and [CO(2)]. Greater above-ground biomass was observed under elevated CO(2) only under homogeneous conditions of nutrient supply and at the highest availability level. CO(2) interacted with nutrient distribution and availability to determine foliar percentage N and below : above-ground biomass ratios, respectively. Interactions between nutrient distribution and CO(2) determined the relative contribution to above-ground biomass of four of the species. The responses of dominant and subordinate species to [CO(2)] were dependent on the availability and distribution of nutrients. Our results suggest that soil nutrient distribution has the potential to influence the response of plant species and assemblages to changes in [CO(2)] and nutrient availability.     

竞争对马尾松和木荷觅取异质分布养分行为的影响

为了研究邻株竞争对马尾松(Pinus massoniana)和木荷(Schima superba)觅取异质分布养分机理和行为的影响, 我们设计单植、双株纯栽和两株混植3种栽植方式, 构建了同质和异质养分环境开展盆栽实验。结果表明: 单植时, 马尾松和木荷苗木生长对斑块养分反应敏感, 与同质养分环境相比, 两树种在异质养分环境中具有苗高生长量大、干物质积累量高、根系在富养斑块中大量增生, 根系N、P含量和吸收效率高等特点。在异质养分环境中, 木荷与马尾松邻株竞争时的生长表现优于双株纯栽模式而与单植处理相近, 根系形态可塑性和生理可塑性在其觅取斑块养分中的作用显著增强; 与木荷邻株竞争时, 马尾松苗高生长也表现出较单植和双株纯栽模式一定的优势, 这与其根系的广布性、觅养精确性和反应敏感度变化较小及富养斑块中根系P素含量和吸收效率较高等有关。相反, 同种邻株竞争则使得异质养分环境中马尾松和木荷的根系广布性减小, 反应敏感度减弱, 富养斑块中根系N、P含量降低, 苗高生长量和干物质积累量减小。与马尾松相比, 同种邻株竞争对异质养分环境中木荷生长的负向影响更为强烈。建议在生产中采用混交造林的方式促进马尾松和木荷生长。若要营造人工纯林, 可通过适当降低初植密度或及时调控林分密度促进林木生长。     

Nutrient foraging traits in 10 co-occurring plant species of contrasting life forms

1 Responses to spatial heterogeneity of soil nutrients were tested in 10 plant species that differ in life form and successional status, but which co-occur in the South Carolina coastal plain. The morphological responses of the root system were tested by assessing scale (represented by root mass and root length densities), precision (preferential proliferation of roots in nutrient-rich patches compared with less fertile patches) and discrimination (ability to detect and proliferate within the richest patches when patches vary in nutrient concentration). We also investigated sensitivity (growth benefits gained as spatial heterogeneity of nutrients increases, measured as total biomass).
2 Ten individuals of each species were grown in pots under four treatments that had differing nutrient distribution but the same overall nutrient addition. Plants were harvested when roots reached pot edge.
3 We observed high variation between species in scale, precision and sensitivity. No significant discrimination responses were observed, although greatest root mass density occurred at intermediate fertility levels for all species.
4 We rejected the hypothesis that scale and precision are negatively correlated. Indeed, in herbaceous species alone, scale and precision were positively correlated.
5 Sensitivity was not closely related to precision, indicating that proliferation of roots in fertile patches does not always yield growth benefits in heterogeneous soils. Further, some sensitive species had very low precision, suggesting that a positive growth response in heterogeneous environments may be related to plasticity in physiology or root life span, rather than morphology.
6 Plant life form was not correlated with precision or sensitivity. However, scale of response was greater in herbs than in woody plants, possibly because the two life forms develop root systems at different rates.     

杉木不同家系对异质养分环境的适应性反应差异

 构建异质和同质两种养分环境,选择3个杉木(Cunninghamia lanceolata)优良家系作试验材料,并以马尾松(Pinus massoniana)为参照,通过 量化分析不同养分环境中植株生长量、干物质积累和分配、根系形态、养分吸收和利用效率等,研究杉木家系对异质养分环境的适应性反应差 异。结果表明,3个杉木参试家系对不同养分环境的生长反应差异显著,‘锦屏45’家系在异质养分环境中苗高生长量大、干物质积累量多、根 系发达,而‘龙15’和‘靖398’两个家系则在同质养分环境中表现较好。 杉木不同家系的根系均主要在异质养分环境之贫养斑块中大量增生 ,根系形态可塑性与觅养精确性较低。作为参照的马尾松,对异质养分环境反应敏感,根系广布性大、觅养精确性高。在3个参试杉木家系中, ‘龙15’和‘靖398’对异质养分环境的生长反应敏感度低,根系生理可塑性一般,而‘锦屏45’对异质养分环境的生长反应敏感度较高,根系 生理可塑性较高。试验观测到不同杉木家系在异质养分环境中根系N、P、K吸收效率通常低于同质养分环境。在富养斑块中的根系养分吸收效率 明显低于贫养斑块,这与马尾松在富养斑块中根系养分吸收效率较高有很大的差异。然而杉木家系在富养斑块中根系的养分含量却不同程度地 高于贫养斑块或与之相 近。‘锦屏45’家系在异质环境中生长表现显著地优于同质养分环境,除因其具有较高的根系生理可塑性外,还与较多 比例的干物质和营养元素分配至地上部分、根冠比较少有关。     

The effects of shading and N status on root proliferation in nutrient patches by the perennial grass Agropyron desertorum in the field

Competition for light can affect exploitation of spatially heterogeneous soil resources. To evaluate the influence of shoot status on root growth responses in nutrient-rich soil patches, we studied the effects of shading and whole-plant nitrogen status on root growth in N-enriched and nonenriched patches by mature Agropyron desertorum plants growing in the field with below-ground competition. Roots in enriched patches had greater length to weight ratios (specific root length, SRL), indicating increased absorptive surface areas, compared with roots in control patches. Increased SRL was due to increased production and length of higher order laterals rather than morphological changes in roots of the same branching order. Although the pattern of root growth rates in patches was the same for shaded and unshaded plants, the magnitude of this response to enriched patches was damped by shading. Root relative growth rates (RGR) in N-enriched patches were reduced by more than 50% by short-term shading treatments (60% reduction in photosynthetic flux density), while root RGR in unenriched patches was unaffected by shading. Unexpectedly, plants with higher nitrogen status had greater root RGR in enriched patches than plants that had not received nitrogen supplement, again with no detectable effect on root RGR in the unenriched patches. Therefore, while both shading and plant N status affected the ability of roots to exploit enriched patches by proliferation, there was no stimulation or suppression of root growth in the unenriched, control patches. Thus, plants already under competitive pressure above ground for light and below ground for nutrients should be less able to rapidly respond to opportunities presented in nutrient patches and pulses.     

Shading reduces exploitation of soil nitrate and phosphate by Agropyron desertorum and Artemisia tridentata from soils with patchy and uniform nutrient distributions

 Shading may both lessen the demand for soil nutrients and also the energy supply for nutrient acquisition. Since root foraging for nutrients in patchy environments can be energy-costly, especially for an immobile nutrient such as phosphate (P), the effects of shading may be most expected in heterogeneous soils. Plant acquisition of nitrate (N) and phosphate from soils with patchy and uniform nutrient distributions was determined in a field study under open sunlight and with shading for two common perennial Great Basin shrub steppe species, Agropyron desertorum and Artemisia tridentata. Partial shading in a pattern which can occur in shrub steppe vegetation significantly decreased plant N and P acquisition from soils both in the patchy and the uniform nutrient treatments. Artemisia was more affected by the shading than was Agropyron. Exploitation of the rather immobile P ion by both species was reduced to a much greater degree by the shading in the patchy distribution treatment than in the uniform nutrient treatment. As expected, plant acquisition of the more mobile N varied little with nutrient distribution treatment for both species and the depression of N acquisition by shading was the same in both nutrient distributions. The effects of shading appeared to have had its primary influence on different components of root foraging in the two species, especially in the nutrient-rich patches. For Agropyron shading primarily affected root proliferation, as indicated by reduced root density in patches. For Artemisia, shading most influenced root physiological uptake capacity and this was most pronounced in the nutrient-rich patches. While aboveground competition for light may generally reduce nutrient acquisition, the effects appear to be most pronounced if root systems of these steppe species are foraging for nutrients such as P in spatially heterogeneous soils. Received: 29 February 1996 / Accepted: 16 July 1996     

Biomass allocation in a clonal vine: Effects of intraspecific competition and nutrient availability

Biomass allocation to roots, rhizomes, runners and climbing stems (i.e. twining axis and attached leaves) was studied inCalystegia sepium L., a clonal vine. In an experiment which took 2 months, nutrient availability (low and high) and intraspecific competition (none, shoot root and both shoot and root) were manipulated. Under low nutrients the highest biomass of climbing stems was found in plants with shoot competition; the lowest was found in plants with both shoot and root competition. Total biomass under high nutrients was also greatest in plants with shoot competition. Thus, plants benefited from climbing up a shared stake rather than separate stakes. Larger plants allocated a higher proportion of biomass to runners in the nutrient-poor environment than in the nutrient-rich environment. This behaviour may increase the chance of finding nutrient-rich patches in the neighbourhood of the mother plant in a heterogeneous environment.     

Community-aggregated plant traits interact with soil nutrient heterogeneity to determine ecosystem functioning

Background and aims

Spatial distribution of soil nutrients (soil heterogeneity) and availability have strong effects on above- and belowground plant functional traits. Although there is ample evidence on the tight links between functional traits and ecosystem functioning, the role played by soil heterogeneity and availability as modulators of such relationship is poorly known.

Methods

We conducted a factorial experiment in microcosms containing grasses, legumes and non-legume forbs communities differing in composition to evaluate how soil heterogeneity and availability (50 and 100 mg N) affect the links between traits and ecosystem functioning. Community-aggregated specific leaf area (SLA_agg) and specific root length (SRL_agg) were measured as both relevant response traits to soil heterogeneity and availability, and significant effect traits affecting ecosystem functioning (i.e., belowground biomass, β-glucosidase and acid phosphatase activities, and in situ N availability rate).

Results

SRL_agg was negatively and significantly associated to β-glucosidase, phosphatase and N availability rate in the high nutrient availability and heterogeneous distribution scenario. We found a significant negative relationship between SLA_agg and availability rate of mineral-N under low nutrient availability conditions.

Conclusions

Soil heterogeneity modulated the effects of both traits and nutrient availability on ecosystem functioning. Specific root length was the key trait associated with soil nutrient cycling and belowground biomass in contrasted heterogeneous soil conditions. The inclusion of soil heterogeneity into the trait-based response-effect framework may help to scale from plant communities to the ecosystem level.     

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.     

Root system size determines plant performance following short-term soil nutrient pulses

Heterogeneity in soil resources is common in natural communities, in both space and time. In contrast to substantial research into plant responses to spatial nutrient heterogeneity, little is known about the factors that influence plants responses to temporally heterogeneous nutrient supplies. We examine (1) the effects of nutrient pulse length on plant biomass allocation patterns, (2) whether a plant??s root system prior to a nutrient pulse influences the benefit a plant can gain from that pulse, and (3) how competition and nutrient pulses interact to influence plant biomass. To address these issues, we used a pot experiment with varying initial conditions (nutrient levels and competition) designed to produce a range of root system sizes in the grass Poa pratensis. We then subjected the plants to short-term (3 and 10?days long) nutrient pulses where the same total nutrients were delivered at varying rates per unit time (intensity). Plant biomass and tissue nitrogen concentration were lowest when pulses were short relative to either long pulses or continuous supply. Plants with larger root systems at the start of the nutrient pulse gained more benefit than smaller plants because final plant size relative to initial root system size decreased as pulse intensity (nutrients delivered per unit time) increased. This study has two important implications. First, since larger plants benefit disproportionately more from a nutrient pulse than smaller plants, pre-pulse conditions such as the competitive environment and resource supply are likely key determinants of a plant??s ability to capture nutrients from a pulse. Second, the importance of pre-pulse size provides a belowground mechanism to enhance the size variability among plants in a community.     

Soil nutrient heterogeneity and competitive ability of three grass species (<Emphasis Type="Italic">Festuca ovina,Arrhenatherum elatius</Emphasis> and <Emphasis Type="Italic">Calamagrostis epigejos</Emphasis>) in experimental conditions

We studied the effects of differences in root growth and nutrient pool on the competitive ability of Festuca ovina (short grass), Arrhenatherum elatius and Calamagrostis epigejos (tall grasses) grown in monocultures and in mixtures of homogeneous and heterogeneous environments during two growing seasons. Analysis of variance revealed a significant effect of plant species on nutrient concentrations in above-ground biomass and of substrate type on contents of N, K, Ca, Mg in biomass. The ANOVA also confirmed the significant effect of competitive environment on the concentration of N, K in above-ground biomass. In heterogeneous environments, both tall grasses (in competition with F. ovina) were able to produce more roots in the nutrient-rich patches and to accumulate more nitrogen in plant tissues, which was associated with higher yield of their above-ground biomass. Thus, the relative competitive ability for nutrients of both tall grasses was higher than that of F. ovina. This competitive ability of A. elatius to C. epigejos increased in heterogeneous treatments.     

Heterogeneous nutrient supply promotes maize growth and phosphorus acquisition: additive and compensatory effects of lateral roots and root hairs

Background and AimsRoot proliferation is a response to a heterogeneous nutrient distribution. However, the growth of root hairs in response to heterogeneous nutrients and the relationship between root hairs and lateral roots remain unclear. This study aims to understand the effects of heterogeneous nutrients on root hair growth and the trade-off between root hairs and lateral roots in phosphorus (P) acquisition.MethodsNear-isogenic maize lines, the B73 wild type (WT) and the rth3 root hairless mutant, were grown in rhizoboxes with uniform or localized supply of 40 (low) or 140 (high) mg P kg⁻¹ soil.ResultsBoth WT and rth3 had nearly two-fold greater shoot biomass and P content under local than uniform treatment at low P. Significant root proliferation was observed in both WT and rth3 in the nutrient patch, with the WT accompanied by an obvious increase (from 0.7 to 1.2 mm) in root hair length. The root response ratio of rth3 was greater than that of WT at low P, but could not completely compensate for the loss of root hairs. This suggests that plants enhanced P acquisition through complementarity between lateral roots and root hairs, and thus regulated nutrient foraging and shoot growth. The disappearance of WT and rth3 root response differences at high P indicated that the P application reduced the dependence of the plants on specific root traits to obtain nutrients.ConclusionsIn addition to root proliferation, the root response to a nutrient-rich patch was also accompanied by root hair elongation. The genotypes without root hairs increased their investment in lateral roots in a nutrient-rich patch to compensate for the absence of root hairs, suggesting that plants enhanced nutrient acquisition by regulating the trade-off of complementary root traits.     

Effects of Spatial Scale of Soil Heterogeneity on the Growth of a Clonal Plant Producing Both Spreading and Clumping Ramets

Soil nutrients are commonly heterogeneously distributed at different spatial scales. Although numerous studies have tested the effects of soil nutrient heterogeneity on growth of clonal plants producing either spreading ramets or clumping ramets, no study has examined the effects on the growth of clonal plants producing both spreading and clumping ramets and how spatial scale affects such effects. To test these effects, clones of Buchloe dactyloides, a stoloniferous clonal plant that produces both clumping and spreading ramets, were grown in six heterogeneous environments with different patch sizes and one homogeneous environment containing the same quantity of nutrients. Total biomass, total number of ramets, number of clumping ramets, number of spreading ramets, spacer length, or root:shoot ratio of the whole plants did not differ significantly among the seven treatments. However, at the patch level there were significant effects of patch size by nutrient level on biomass, number of ramets, number of spreading ramets, and number of clumping ramets, and these four variables were significantly larger in the nutrient-rich patches than in the nutrient-poor patches in the heterogeneous treatment with the largest patch size, but not in the other five heterogeneous treatments with smaller patch sizes. Neither nutrient level nor patch size significantly affected spacer length or root:shoot ratio. Based on our results, we propose that B. dactyloides can efficiently exploit nutrient-rich patches by a plastic response of clumping ramets and spreading ramets at larger spatial scales of soil heterogeneity but not at smaller ones.