Heterogeneous light supply affects growth and biomass allocation of the understory fern Diplopterygium glaucum at high patch contrast

Invasive clonal plants possess greater capacity for division of labor than natives in high patch contrast environments

Invasion success of clonal plants is closely related to their unique clonal life history, and clonal division of labor is a crucial clonal trait. However, so far, it is unclear whether invasive alien clonal species generally possess a greater capacity for division of labor than native species and whether this pattern is affected by environmental conditions. To test whether patch contrast affects the differences in the capacity for division of labor between invasive alien and native clonal plants, we selected five pairs of exotic invasive and native clonal plant species that are congeneric and co-occurring in China as experimental materials. We grew the clonal fragment pairs of these invasive and native plants under high, low, or no contrast of reciprocal patchiness of light and nutrient, respectively, with ramet connections either severed (division of labor prevented) or kept intact (division of labor allowed). The results showed that connection significantly decreased the proportion of biomass allocated to roots in distal (younger) ramets, whereas it increased in proximal (older) ramets of all studied plants under high -contrast treatments. This clear pattern strongly indicated the occurrence of division of labor. Furthermore, the connection had a more pronounced effect on the pattern of biomass allocation of invasive alien plants, resulting in a greater increase in biomass for invasive alien plants compared to native plants. These findings suggest that the invasive alien plants possess a greater capacity for division of labor, which may confer a competitive advantage to them over natives, thus facilitating their invasion success in some heterogeneous habitats such as forest edges where light and soil nutrients show a high negative correlation.

Effects of scale and contrast of spatial heterogeneity in plant-soil feedbacks on plant growth

Spatial heterogeneity in plant-soil feedbacks (PSFs) has been evidenced to influence plant growth. However, it is unclear whether patch size and contrast of PSF heterogeneity influence plant growth. We first conditioned a background soil by seven species separately and then grew each of them in a homogeneous soil and three heterogeneous soils. The first heterogeneous soil (large patch and high contrast; LP-HC) consisted of two large patches, of which one was filled with the sterilized background soil and the other with the conditioned soil. The second heterogeneous soil (small patch and high contrast; SP-HC) consisted of four small patches, of which two were filled the sterilized background soil and the other two with the conditioned soil. The third heterogeneous soil (small patch and low contrast; SP-LC) also consisted of four patches, of which two were filled with a 1:3 (w:w) mixture and the other two with a 3:1 mixture of the sterilized background soil and the conditioned soil. In the homogeneous soil, all patches were filled with a 1:1 mixture of the two soils. Both shoot biomass and root biomass were equal in the homogeneous and heterogeneous soils. No significant growth difference was observed between the SP-HC and LP-HC heterogeneous soil. However, shoot biomass and root biomass of the legume Medicago sativa, and root biomass of the grass Lymus dahuricus were greater in the SP-HC heterogeneous soil than in the SP-LC heterogeneous soil, probably due to enhanced root growth in the conditioned soil. Moreover, plant growth in the heterogeneous soils was associated with plant growth but not soil nutrient availability at the end of the conditioning phase. Our results show for the first time that patch contrast of PSF heterogeneity can influence plant growth via changing root placement and highlight the importance of fundamentally different facets of PSF variability.

A bump in the node: The hydraulic implications of rhizomatous growth

PREMISE

Rhizomatous growth characterizes numerous taxa among vascular plants. While abundant information exists on nutrient sharing and demography, the question of how these metameric organisms move water through their bodies remains largely unstudied. Moreover, we lack an understanding of the evolutionary implications of rhizomatous growth across vascular plants. Here, we examined these questions by investigating how rhizomatous growth and vascular construction affect whole-plant hydraulic function.

METHODS

In five terrestrial fern species with diverse vascular construction, we used microcomputed tomography and bright-field microscopy to examine vascular construction across nodes along the rhizome. These data were integrated with measurements of leaf stomatal conductance under rooted and uprooted conditions to relate vascular patterning and hydraulic architecture to leaf water status.

RESULTS

Similar to phytomers of woody seed plants, nodal regions in rhizomatous ferns are areas of hydraulic resistance. While water is shared along the rhizomes of these investigated species, hydraulic conductivity drops at nodes and stomatal conductance declines when nodes were locally uprooted. Together, our data suggest that nodes are chokepoints in axial water movement along the rhizome.

CONCLUSIONS

Nodal chokepoints decrease hydraulic integration between phytomers. At the same time, chokepoints may act as "safety valves", hydraulically localizing each phytomer-potentially decreasing embolism and pathogen spread. This suggests a potential trade-off in the principal construction of the fern rhizome. Moreover, we propose that shoot-borne roots (homorhizy) and the prostrate habit of rhizomatous ferns decrease the hydraulic and structural burdens that upright plants typically incur. The absence of these hydraulic and structural demands may be one reason ferns (and many rhizomatous plants) lack, or have minimally developed, secondary xylem.

Spatial Vegetation Patch Patterns and Their Relation to Environmental Factors in the Alpine Grasslands of the Qilian Mountains

Globally, grasslands are affected by climate change and unsustainable management practices which usually leads to transitions from stable, degraded and then to desertification. Spatial vegetation patch configurations are regarded as key indicators of such transitions. Understanding the relationships between this grass-land vegetation and its environment is key to vegetation restoration projects. Spatial vegetation patch patterns were chosen across different soil and topographic conditions. Patch numbers, perimeter, and cover of each patch were measured along transects of each patch type. Using field surveys and multivariate statistical analysis, we investigated the differences in vegetation biomass and distribution and soil properties of four typical alpine plant species patches along with a range of environmental and topographic conditions. It was found that topographic conditions and soil properties, particularly soil moisture explained most of the variation in spatial patch vegetation characteristics and thus control vegetation restoration in the alpine grassland. The Kobresia humilis, Blysmus sinocompressus and Iris lactea patches under the drylands recorded small patch sizes, large patch numbers, low connectivity, and large total perimeter per unit area. Generally, species within the high moisture sites recorded small patch numbers, a large fraction of vegetation cover and a small total perimeter per m2. Patches in limited soil moisture areas recorded patch configurations indicating they are unstable and undergoing degradation and therefore need urgent restoration attention to forestall their further degradation and its resultant effect of desertification. These results would provide quantitative easy-to-use indicators for vegetation degradation and help in vegetation restoration projects.

Heterogeneous Nitrogen Supply With High Frequency and Ramet Damage Increases the Benefits of Clonal Integration in Invasive Hydrocotyle vulgaris

Nitrogen (N) deposition significantly affects the growth and the function of invasive clonal plants. However, the effects of heterogeneous N supply with different frequencies on the growth and the potential contribution of clonal integration in invasion plants are still unclear, especially in the complex environment considering ramet damage. To address this question, apical and basal ramets of the clonal invader Hydrocotyle vulgaris were connected or disconnected, N was added to the basal ramets with a high frequency, a low frequency, or no supply, and the total N quantity was the same for the different frequency. Furthermore, 8 aphids were placed on the apical ramets, and 30% of each leaf was cut off to cause damage. The connection between ramets significantly increased the biomass, total carbon (C), and total N of the basal and apical ramets. Higher frequency N supply significantly increased the biomass, total C, and total N of the basal ramets and the entire clonal fragment biomass. The damage had no significant effect on the growth of basal and apical ramets. Especially, under the high N frequency and ramet damage condition, the connection between ramets more significantly increased the biomass, total C, and total N of the apical ramets and the entire clonal fragment biomass. In addition, the uptake rates of ¹⁵ NH 4 + and ¹⁵ NO 3 - in H. vulgaris had no significant difference, and N supply increased the uptake rates of ¹⁵ NH 4 + and ¹⁵ NO 3 - of the basal ramets. Our results suggest that both higher frequency N supply and clonal integration are beneficial to the growth of H. vulgaris. Moreover, the heterogeneous N supply with high frequency and ramet damage increases the benefits of clonal integration in H. vulgaris. These findings improve our understanding of the response of clonal invader H. vulgaris to nitrogen deposition and ramet damage.

Clonal integration and phosphorus management under light heterogeneity facilitate the growth and diversity of understory vegetation and soil fungal communities

The spatial heterogeneity of light and nutrient deficiency occurs in many forest understories. Proper fertilization management of unhealthy forests can benefit forest understory diversity and improve the stability of degraded soil; and clonal integration is a major advantage of resource sharing for many forest understory vegetation, such as pteridophytes. In this study, we tested whether understory soil fertilization and clonal integration under light heterogeneity were able to increase the performance and diversity of understory vegetation and soil microbial communities in nature. Field experiments-with or without phosphorus (P) addition, with intact or severed rhizome, and under homogeneous or heterogeneous light environments-were conducted in the understory of a typical evergreen forest in southeast China. Light heterogeneity, P addition and clonal integration promoted the growth, diversity and evenness of ferns and soil microbial biomass C, N and P (MBC, MBN and MBP) at both experimental plot and patch level. They also increased Chao1 richness and Shannon diversity of soil fungal communities at patch level, especially in the high light patches with P addition. The positive effects of P addition and clonal integration on the growth and diversity of ferns and soil microbial biomass were greatly increased under heterogeneous light. The positive effects of clonal integration on the growth were the greatest in the heterogeneous high light patches. Moreover, the interactive effect of P addition and clonal integration increased soil MBN and MBP. Clonal integration promoted the increased growth and diversity of ferns and soil MBC in the heterogeneous light environment (9.35%-35.19%), and enhanced soil MBN and MBP in the P addition treatment (9.03%-12.96%). The interactive effect of P addition and clonal integration largely led to the transition of fungal groups from slow-growing oligotrophic types to fast-growing copiotrophic types. Our results show that the interactions between clonal integration and/or P addition under light heterogeneity increase the benefits of ferns in light-rich patches, and further promote integrative performance of ferns and soil microbial communities.

Light-induced systemic signalling down-regulates photosynthetic performance of soybean leaves with different directional effects

When plants are exposed to a heterogeneous environment, photosynthesis of leaves is not only determined by their local condition, but also by certain signals from other parts of the same plant, termed systemic regulation. Our present study was conducted to investigate the effects of light-dependent systemic regulation on the photosynthetic performance of soybean (Glycine max L. Merr.) under heterogeneous light conditions. Soybean plants were treated with heterogeneous light. Then gas exchange characteristics were measured to evaluate the photosynthetic performance of leaves. Parameters related to photosynthetic pigments, chlorophyll fluorescence, Rubisco and photosynthates were examined to study the mechanisms of light-dependent systemic regulation on photosynthesis. Light-induced systemic signalling by illuminated leaves reduced the Pn of both upper and lower non-illuminated leaves on the same soybean plant. The decrease in gs and increase in Ci in these non-illuminated leaves indicated restriction of carbon assimilation, which was further verified by the decline in content and activity of Rubisco. However, the activation state of Rubisco decreased only in upper non-illuminated leaves. Quantum efficiency of PSII (ΦPSII) and ETR also decreased only in upper non-illuminated leaves. Moreover, the effects of light-induced systemic signalling on carbohydrate content were also detectable only in upper non-illuminated leaves. Light-induced systemic signalling by illuminated leaves restricts carbon assimilation and down-regulates photosynthetic performance of non-illuminated leaves within a soybean plant. However, effects of such systemic regulation differed when regulated in upward or downward direction.

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

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

Trait expression and signatures of adaptation in response to nitrogen addition in the common wetland plant Juncus effusus

Wetland ecosystems are known to mitigate high nutrient loadings and thus can improve water quality and prevent potential biodiversity loss caused by eutrophication. Plant traits affect wetland processes directly through effects on accumulation or metabolization of substances, and indirectly by affecting microbial transformation processes in the soil. Understanding the causes and consequences of intraspecific variation in plant functional traits and associated ecosystem processes can aid applied ecological approaches such as wetland restoration and construction. Here we investigated molecular variation and phenotypic variation in response to three levels of nitrogen availability for a regional set of populations of the common wetland plant Juncus effusus. We asked whether trait expression reveals signatures of adaptive differentiation by comparing genetic differentiation in quantitative traits and neutral molecular markers (Q_ST—F_ST comparisons) and relating trait variation to soil conditions of the plant’s origin. Molecular analyses showed that samples clustered into three very distinct genetic lineages with strong population differentiation within and among lineages. Differentiation for quantitative traits was substantial but did not exceed neutral expectations when compared across treatments or for each treatment and lineage separately. However, variation in trait expression could be explained by local soil environmental conditions of sample origin, e.g. for aboveground carbon-to-nitrogen (C:N) ratios, suggesting adaptive differentiation to contribute to trait expression even at regional level.

Invasive alien plants benefit more from clonal integration in heterogeneous environments than natives

What confers invasive alien plants a competitive advantage over native plants remains open to debate. Many of the world's worst invasive alien plants are clonal and able to share resources within clones (clonal integration), particularly in heterogeneous environments. Here, we tested the hypothesis that clonal integration benefits invasive clonal plants more than natives and thus confers invasives a competitive advantage. We selected five congeneric and naturally co-occurring pairs of invasive alien and native clonal plants in China, and grew pairs of connected and disconnected ramets under heterogeneous light, soil nutrient and water conditions that are commonly encountered by alien plants during their invasion into new areas. Clonal integration increased biomass of all plants in all three heterogeneous resource environments. However, invasive plants benefited more from clonal integration than natives. Consequently, invasive plants produced more biomass than natives. Our results indicate that clonal integration may confer invasive alien clonal plants a competitive advantage over natives. Therefore, differences in the ability of clonal integration could potentially explain, at least partly, the invasion success of alien clonal plants in areas where resources are heterogeneously distributed.

Nitrogen addition and clonal integration alleviate water stress of dependent ramets of Indocalamus decorus under heterogeneous soil water environment

Water and nitrogen are two of the most important factors for plant growth and development. However, little is known about effects of N on water translocation between connected bamboo ramets. We performed experiment connected Indocalamus decorus ramets in adjacent pots with different soil water contents and three N levels. We determined antioxidase activities, concentration of osmotic adjustment products, O₂·⁻, MDA and photosynthetic pigments, and electrolyte leakage rate in paired unit. When N supply to supporting ramets increased, their electrolyte leakage rates and contents of O₂·⁻ and MDA significantly increased, while antioxidase activities and contents of osmotic adjustment products and photosynthetic pigments in connected dependent ramets increased markedly as their electrolyte leakage rates and contents of O₂·⁻ and MDA decreased greatly. When N addition to dependent ramets increased, antioxidant enzyme activity and contents of osmotic adjustment products and photosynthetic pigments decreased in both ramets, but electrolyte leakage rates and O₂·⁻ and MDA contents increased significantly. Therefore, N addition to either supporting or dependent ramets can improve water integration among I. decorus ramets. N addition to supporting ramets promotes water translocation and alleviates water stress of dependent ramets, but N addition to dependent ramets exacerbates drought stress damage to dependent ramets.

Re-establishment of species from synonymies based on DNA barcoding and phylogenetic analysis using Diplopterygium simulans (Gleicheniaceae) as an example

Because synonymy treatment traditionally relies on morphological judgments, it usually causes many problems in species delimitation and in the biodiversity catalogue. For example, Diplopterygium simulans, which belongs to the Gleicheniaceae family, has been considered to be synonymous with D. glaucum or D. giganteum based mainly on the morphology of its pinna rachis and blade. In the absence of molecular evidence, these revisions remain doubtful. DNA barcoding, which is considered to be a powerful method for species-level identification, was employed to assess the genetic distance among 9 members of the Diplopterygium genus. The results indicate that D. simulans is an independent species rather than a synonymy of D. glaucum or D. giganteum. Moreover, phylogenetic analysis uncovered the sisterhood of D. simulans and D. cantonense, which is supported by their geographical distributions and morphological traits. Incorrect synonymy treatment is prevalent in the characterization of biological diversity, and our study proposes a convenient and effective method for validating synonym treatments and discovering cryptic species.

Effects of patch contrast and arrangement on benefits of clonal integration in a rhizomatous clonal plant

The availabilities of light and soil water resources usually spatially co-vary in natural habitats, and the spatial pattern of such co-variation may affect the benefits of physiological integration between connected ramets of clonal plants. In a greenhouse experiment, we grew connected or disconnected ramet pairs [consisting of a proximal (relatively old) and a distal (relative young) ramet] of a rhizomatous herb Iris japonica in four heterogeneous environments differing in patch arrangement (reciprocal vs. parallel patchiness of light and soil water) and patch contrast (high vs. low contrast of light and water). Biomass of the proximal part, distal part and clonal fragment of I. japonica were all significantly greater in the intact than in the severed treatment, in the parallel than in the reciprocal patchiness treatment and in the high than in the low contrast treatment, but the effect of severing the connection between ramet pairs did not depend on patch arrangement or contrast. Severing the connection decreased number of ramets of the distal part and the clonal fragment in the parallel patchiness arrangement, but not in the reciprocal patchiness arrangement. Therefore, the spatial arrangement of resource patches can alter the effects of clonal integration on asexual reproduction in I. japonica.

Effects of Spatial Patch Arrangement and Scale of Covarying Resources on Growth and Intraspecific Competition of a Clonal Plant

Spatial heterogeneity in two co-variable resources such as light and water availability is common and can affect the growth of clonal plants. Several studies have tested effects of spatial heterogeneity in the supply of a single resource on competitive interactions of plants, but none has examined those of heterogeneous distribution of two co-variable resources. In a greenhouse experiment, we grew one (without intraspecific competition) or nine isolated ramets (with competition) of a rhizomatous herb Iris japonica under a homogeneous environment and four heterogeneous environments differing in patch arrangement (reciprocal and parallel patchiness of light and soil water) and patch scale (large and small patches of light and water). Intraspecific competition significantly decreased the growth of I. japonica, but at the whole container level there were no significant interaction effects of competition by spatial heterogeneity or significant effect of heterogeneity on competitive intensity. Irrespective of competition, the growth of I. japonica in the high and the low water patches did not differ significantly in the homogeneous treatments, but it was significantly larger in the high than in the low water patches in the heterogeneous treatments with large patches. For the heterogeneous treatments with small patches, the growth of I. japonica was significantly larger in the high than in the low water patches in the presence of competition, but such an effect was not significant in the absence of competition. Furthermore, patch arrangement and patch scale significantly affected competitive intensity at the patch level. Therefore, spatial heterogeneity in light and water supply can alter intraspecific competition at the patch level and such effects depend on patch arrangement and patch scale.

Effects of heterogeneous competitor distribution and ramet aggregation on the growth and size structure of a clonal plant

Spatially heterogeneous distribution of interspecific competitors and intraspecific aggregation of offspring ramets may affect the growth and size structure of clonal plant populations, but these have been rarely studied. We conducted a greenhouse experiment in which we grew a population of eight offspring ramets (plants) of the stoloniferous clonal plant Hydrocotyle vulgaris aggregately or segregately in two homogeneous treatments with or without a competing grass Festuca elata and a heterogeneous treatment with a patchy distribution of the grass. In patchy grass treatments, H. vulgaris produced markedly more biomass, ramets and stolons in open patches (without grasses) than in grass patches, but displayed lower size variations as measured by coefficient of variation of biomass, ramets and stolons among the eight plants. In open areas, H. vulgaris produced statistically the same amounts of biomass and even more stolons and showed higher size variations in patchy grass treatments than in open (no grass) treatments. In grass areas, H. vulgaris grew much worse and displayed higher size variations in patchy grass treatments than in full grass treatments. Ramet aggregation decreased the growth of H. vulgaris in open treatments and in both open and grass patches in patchy grass treatments, but had little effect in full grass treatments. Ramet aggregation had little effect on size variations. Therefore, heterogeneous distribution of competitors can affect the growth and size structure of clonal plant populations, and ramet aggregation may decrease population growth when they grow in open environments or heterogeneous environments with a patchy distribution of interspecific competitors.

Physiological integration ameliorates negative effects of drought stress in the clonal herb Fragaria orientalis

Clonal growth allows plants to spread horizontally and to establish ramets in sites of contrasting resource status. If ramets remain physiologically integrated, clones in heterogeneous environments can act as cooperative systems--effects of stress on one ramet can be ameliorated by another connected ramet inhabiting benign conditions. But little is known about the effects of patch contrast on physiological integration of clonal plants and no study has addressed its effects on physiological traits like osmolytes, reactive oxygen intermediates and antioxidant enzymes. We examined the effect of physiological integration on survival, growth and stress indicators such as osmolytes, reactive oxygen intermediates (ROIs) and antioxidant enzymes in a clonal plant, Fragaria orientalis, growing in homogenous and heterogeneous environments differing in patch contrast of water availability (1 homogeneous (no contrast) group; 2 low contrast group; 3 high contrast group). Drought stress markedly reduced the survival and growth of the severed ramets of F. orientalis, especially in high contrast treatments. Support from a ramet growing in benign patch considerably reduced drought stress and enhanced growth of ramets in dry patches. The larger the contrast between water availability, the larger the amount of support the depending ramet received from the supporting one. This support strongly affected the growth of the supporting ramet, but not to an extent to cause increase in stress indicators. We also found indication of costs related to maintenance of physiological connection between ramets. Thus, the net benefit of physiological integration depends on the environment and integration between ramets of F. orientalis could be advantageous only in heterogeneous conditions with a high contrast.

Distinguishing the biomass allocation variance resulting from ontogenetic drift or acclimation to soil texture

In resource-poor environments, adjustment in plant biomass allocation implies a complex interplay between environmental signals and plant development rather than a delay in plant development alone. To understand how environmental factors influence biomass allocation or the developing phenotype, it is necessary to distinguish the biomass allocations resulting from environmental gradients or ontogenetic drift. Here, we compared the development trajectories of cotton plants (Gossypium herbaceum L.), which were grown in two contrasting soil textures during a 60-d period. Those results distinguished the biomass allocation pattern resulting from ontogenetic drift and the response to soil texture. The soil texture significantly changed the biomass allocation to leaves and roots, but not to stems. Soil texture also significantly changed the development trajectories of leaf and root traits, but did not change the scaling relationship between basal stem diameter and plant height. Results of nested ANOVAs of consecutive plant-size categories in both soil textures showed that soil gradients explained an average of 63.64-70.49% of the variation of biomass allocation to leaves and roots. Ontogenetic drift explained 77.47% of the variation in biomass allocation to stems. The results suggested that the environmental factors governed the biomass allocation to roots and leaves, and ontogenetic drift governed the biomass allocation to stems. The results demonstrated that biomass allocation to metabolically active organs (e.g., roots and leaves) was mainly governed by environmental factors, and that biomass allocation to metabolically non-active organs (e.g., stems) was mainly governed by ontogenetic drift. We concluded that differentiating the causes of development trajectories of plant traits was important to the understanding of plant response to environmental gradients.

Spatial heterogeneity in light supply affects intraspecific competition of a stoloniferous clonal plant

Spatial heterogeneity in light supply is common in nature. Many studies have examined the effects of heterogeneous light supply on growth, morphology, physiology and biomass allocation of clonal plants, but few have tested those effects on intraspecific competition. In a greenhouse experiment, we grew one (no competition) or nine ramets (with intraspecific competition) of a stoloniferous clonal plant, Duchesnea indica, in three homogeneous light conditions (high, medium and low light intensity) and two heterogeneous ones differing in patch size (large and small patch treatments). The total light in the two heterogeneous treatments was the same as that in the homogeneous medium light treatment. Both decreasing light intensity and intraspecific competition significantly decreased the growth (biomass, number of ramets and total stolon length) of D. indica. As compared with the homogeneous medium light treatment, the large patch treatment significantly increased the growth of D. indica without intraspecific competition. However, the growth of D. indica with competition did not differ among the homogeneous medium light, the large and the small patch treatments. Consequently, light heterogeneity significantly increased intraspecific competition intensity, as measured by the decreased log response ratio. These results suggest that spatial heterogeneity in light supply can alter intraspecific interactions of clonal plants.