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.     

Hierarchical Reproductive Allocation and Allometry within a Perennial Bunchgrass after 11 Years of Nutrient Addition

Bunchgrasses are one of the most important plant functional groups in grassland ecosystems. Reproductive allocation (RA) for a bunchgrass is a hierarchical process; however, how bunchgrasses adjust their RAs along hierarchical levels in response to nutrient addition has never been addressed. Here, utilizing an 11-year nutrient addition experiment, we examined the patterns and variations in RA of Agropyron cristatum at the individual, tiller and spike levels. We evaluated the reproductive allometric relationship at each level by type II regression analysis to determine size-dependent and size-independent effects on plant RA variations. Our results indicate that the proportion of reproductive individuals in A. cristatum increased significantly after 11 years of nutrient addition. Adjustments in RA in A. cristatum were mainly occurred at the individual and tiller levels but not at the spike level. A size-dependent effect was a dominant mechanism underlying the changes in plant RA at both individual and tiller levels. Likewise, the distribution of plant size was markedly changed with large individuals increasing after nutrient addition. Tiller-level RA may be a limiting factor for the adjustment of RA in A. cristatum. To the best of our knowledge, this study is the first to examine plant responses in terms of reproductive allocation and allometry to nutrient enrichment within a bunchgrass population from a hierarchical view. Our findings have important implications for understanding the mechanisms underlying bunchgrass responses in RA to future eutrophication due to human activities. In addition, we developed a hierarchical analysis method for disentangling the mechanisms that lead to variation in RA for perennial bunchgrasses.     

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.     

荒漠植物白刺属4个物种的生殖分配比较

选定乌兰布和沙漠地区白刺属4种植物为研究对象,通过对其样株在花期的各生殖构件的数量特征及生物量调查,系统研究了唐古特白刺(Nitraria tangutorum Bobr.)、西伯利亚白刺(Nitraria sibirica Pall.)、大白刺(Nitraria roborowskii Kom.)和泡泡刺(Nitraria sphaerocarpa Maxim.)4种白刺属植物在生殖枝水平上的生殖分配。结果表明:不同白刺属植物在分株高度、生殖枝长、生殖枝基径、单枝花数、花序干重、枝叶干重等生殖构件的数量性状方面均有显著差异,其中泡泡刺的各生殖构件的数量均最小;除了西伯利亚白刺的生殖分配值达到44.51%外,其余3种白刺的生殖分配值均没有超过20%。经统计分析,4种白刺种群的生殖枝长分别与分株高度呈显著(P<0.05)的直线性正相关关系;生殖枝花序干重与分株高显著正相关;4种白刺的生殖分配随着分株生殖枝生物量的增加而减少,即白刺的个体大小与生殖分配之间呈现负相关关系。这种生殖分配特点反映了不同白刺植物对生长环境的资源利用、与克隆繁殖的权衡及对生态适应的策略。     

松嫩平原碱化草甸星星草种群分蘖株延长生殖生长的表型可塑性调节

在松嫩平原碱化草甸,采用大样本随机取样的方法,研究了不同时间到达抽穗初期、抽穗期、开花期和乳熟期的星星草种群生殖分蘖株数量性状的可塑性及其调节规律.结果表明：除在开花期存在一定的波动外,在每5 d的时间里,随着生殖生长时间的延长, 星星草种群在抽穗初期、抽穗期和乳熟期的生殖分蘖株高、分蘖株生物量、花序长和花序生物量均依次显著增加.各生育期的星星草种群生殖分蘖株高与花序生物量呈显著正相关,而与生殖分配呈显著负相关.随着生殖生长时间的延长,抽穗初期、开花期和乳熟期的星星草花序生物量随着分蘖株高增加,其幂函数的增长速率均呈增大趋势.生殖生长时间延长10 d,其抽穗初期和抽穗期的生殖分配直线下降速率分别降低了43.2%和44.31%;延长5 d,乳熟期的下降速率降低了130%.表明星星草种群分蘖株生殖生长的表型可塑性调节遵循着一定的规律.     

紫翅猪毛菜、钠猪毛菜不同个体大小繁殖分配差异及随海拔的变化

以新疆准噶尔盆地藜科猪毛菜属植物紫翅猪毛菜(Salsola affinis C.A.Mey)、钠猪毛菜(Salsola nitraria Pall)为研究对象,用繁殖分配比例的方法对比分析了两种猪毛菜不同海拔同一种群内不同个体大小繁殖分配的特点,并用异速生长模型分析了不同海拔繁殖生物量与营养生物量之间分配与个体大小的依赖关系。结果发现:1)不同海拔繁殖生物量(R)与营养生物量(V)呈不同程度的异速生长。紫翅猪毛菜随海拔的升高R-V的异速生长斜率显著升高,截距随海拔的升高没有显著增加;而钠猪毛菜的斜率随海拔升高显著降低,截距则显著升高。2)紫翅猪毛菜在较低海拔个体大小与繁殖分配呈负相关,在较高海拔呈正相关;钠猪毛菜在较低海拔个体大小与繁殖分配呈正相关,在较高海拔呈负相关;两种猪毛菜繁殖分配的适应对策相反。3)将同一种群个体大小分成大、中、小3种类型,多重比较发现紫翅猪毛菜在较低海拔,中小个体的繁殖分配显著高于大个体的繁殖分配;在较高海拔,大个体的繁殖分配显著高于中小个体的繁殖分配。钠猪毛菜在较低海拔,大个体的繁殖分配显著高于中、小个体的繁殖分配;在较高海拔,小个体的繁殖分配显著高于大、中个体的繁殖分配。综合分析认为:两个物种随海拔变化产生不同的繁殖分配策略,除遗传效应外,环境和个体大小对钠猪毛菜繁殖分配的变化均产生重要影响,而紫翅猪毛菜繁殖分配的变化主要由海拔差异导致。由于微生境对同一种群的个体大小产生影响,进而产生不同的繁殖分配模式,所以在干旱区更应重视个体大小对繁殖分配的影响。     

黄龙钙化滩流地物种-面积关系

黄龙沟钙化滩流地由于溪流的作用,在滩流地之间形成面积大小不一的植物群落斑块。这些小尺度斑块面积的大小对植物物种数量的影响尚不清楚。应用回归分析法和幂函数方程对黄龙沟钙化滩流地内的物种-面积关系进行了研究。结果表明黄龙沟钙化滩流地中斑块的大小对物种数(含兰科植物)具有强烈的影响,而调查的其他因子对总的植物物种数量的影响不显著。在所调查的环境因子中,斑块面积对物种数量的影响达到79.5%,即斑块越大,所包含的物种数量越多。兰科植物种类数量除了受斑块面积的影响外,还与距离林缘的距离有关(负相关)。物种-面积关系符合幂函数方程S=cA^Z的规律。不同的尺度下,z值略有差异,在中等尺度下 (1-10 m²)最大,为0.2616,较大尺度下(10-100 m²)的最小,z值为0.2050,小尺度下(<1 m²),z值为0.2382。表明中等尺度的斑块(1-10 m²)包含的物种数(含兰科植物)的增长速度最快,而在斑块面积大于10 m²时,物种数增长速度最小。     

松嫩平原贝加尔针茅无性系构件的结构及生长规律

采用整个分蘖丛挖掘的取样方法,对松嫩平原栽培条件下贝加尔针茅无性系构件的结构,以及生长与生产规律进行了定量分析.结果表明,在9月末停止生长期,经过2个生长季的营养繁殖,贝加尔针茅无性系的丛径为9.4±3.24 cm.无性系的全体构件数为161.±8.2个.其中,生殖分蘖株为14.6±11.48个,占9.2%;营养分蘖株为146.9±78.70个,占90.7%.全体构件总生物量为3.8±34.22 g,其中生殖分蘖株生物量为2.0±20.34 g,占43.7%;营养分蘖株为28.8±19.43 g,占6.2%.随着丛径的增加,不同构件的数量均具有线性同速生长规律,而不同构件的生物量均具有幂函数异速增长规律.不同构件生物量与无性系全体构件的数量和生物量之间均呈显著(P<0.0)或极显著(P<0.01)的幂函数正相关关系.平均单个生殖分蘖株的生产力约为营养分蘖株的10倍.生殖分蘖株的数量和生物量的表型可塑性普遍大于营养分蘖株.     

Contrasting Effects of Long-Term Grazing and Clipping on Plant Morphological Plasticity: Evidence from a Rhizomatous Grass

Understanding the mechanism of plant morphological plasticity in response to grazing and clipping of semiarid grassland can provide insight into the process of disturbance-induced decline in grassland productivity. In recent studies there has been controversy regarding two hypotheses: 1) grazing avoidance; and 2) growth limiting mechanisms of morphological plasticity in response to defoliation. However, the experimental evidence presented for the memory response to grazing and clipping of plants has been poorly reported. This paper reports on two experiments that tested these hypotheses in field and in a controlled environment, respectively. We examined the effects of long-term clipping and grazing on the functional traits and their plasticity for Leymus chinensis (Trin.) Tzvelev (the dominate species) in the typical-steppe grassland of Inner Mongolia, China. There were four main findings from these experiments. (i) The majority of phenotypic traits of L. chinensis tended to significantly miniaturize in response to long-term field clipping and grazing. (ii) The significant response of morphological plasticity with and without grazing was maintained in a hydroponic experiment designed to remove environmental variability, but there was no significant difference in L. chinensis individual size traits for the clipping comparison. (iii) Plasticity indexes of L. chinensis traits in a controlled environment were significantly lower than under field conditions indicating that plants had partial and slight memory effect to long-term grazing. (iv) The allometry of various phenotypic traits, indicated significant trade-offs between leaf and stem allocation with variations in plant size induced by defoliation, which were maintained only under grazing in the hydroponic controlled environment experiment. Taken together, our findings suggest that the morphological plasticity of L. chinensis induced by artificial clipping was different with that by livestock grazing. The miniaturization of plant size in long-term grazed grassland may reflect retained characteristics of dwarf memory for adaptation to long-term grazing by large herbivores.     

Increased spatial dominance in high nitrogen, saturated soil due to clonal architecture plasticity of the invasive wetland plant, Phalaris arundinacea

Clonality as a plant growth strategy has been a successful adaptation contributing to clonal plants being the dominant vegetation in many ecosystems and has been implicated as a significant factor contributing to invasiveness. The objective of this study was to determine if Phalaris arundinacea, an invasive wetland plant, modifies its clonal growth behavior when grown in high resource conditions. When grown in ideal conditions (high soil-N and moisture), we hypothesized that along with an increase in tiller production and robustness (biomass per tiller), P. arundinacea would increase the spatial spread of tiller placement (distance from parent and daughters). To test this we conducted a greenhouse study in which we grew P. arundinacea seedlings under two soil-N levels (no nitrate addition or 40 g N m^?2 year^?1) at two soil moisture levels (dry or saturated) for 10 weeks and recorded the placement (angle and distance from the parent plant) of each tiller produced. Total aboveground and belowground biomass, shoot/root ratio, and biomass per tiller were measured at the conclusion of the experiment. Plants grown in saturated conditions produced significantly more tillers that were more widely dispersed. Surprisingly, soil-N did not significantly affect most characteristics of spatial pattern, though soil-N did affect biomass production, shoot/root ratio, and biomass per tiller. These results indicate soil moisture and soil-N affect different aspects of the clonal growth behavior of P. arundinacea in the early stage of colonization. This new information provides a mechanism to explain how P. arundinacea aggressively competes for space in wetland habitats.     

Changes in soil biochemical properties associated with Ligularia virgaurea spreading in grazed alpine meadows

Ligularia virgaurea, a toxic perennial weed, has become a dominant species in the heavily-grazed alpine meadows of the eastern Qinghai?CTibetan Plateau over recent decades. We investigated changes in soil biochemical properties associated with L. virgaurea spreading in grazed alpine meadows at three sites. Soil and root biomass samples were taken at depths of 0?C8?cm, 8?C16?cm and 16?C24?cm from patches where L. virgaurea was dominant and from areas between L. virgaurea patches, with only other native species. Across sites, root biomass, acid-extracted carbohydrate C, organic C and N mineralization, and microbial biomass C and N concentrations in the top 8-cm layer were significantly higher while nitrate N concentration was significantly lower in L. virgaurea patches than in areas between L. virgaurea patches. The increased activities of dehydrogenase, ???Cglucosidase, urease and phosphatase in the top 8-cm layer under L. virgaurea were associated with enhanced soil microbial biomass. Our results indicate a close association between changes in soil biochemical properties in the top 8-cm layer and the spread of L. virgaurea in grazed alpine meadows of the eastern Qinghai?CTibetan Plateau.     

松嫩平原碱化草甸朝鲜碱茅(Puccinellia chinampoensis)种群生殖分蘖株的生长规律

朝鲜碱茅(Puccinellia chinampoensis)是一种耐盐碱丛生型禾草,广泛分布于松嫩平原碱化草甸.采用每隔3d对朝鲜碱茅种群中处于抽穗初期的生殖分蘖株随机挂一次标签,于籽实蜡熟期同时进行大样本取样与测定的方法,定量分析了5次所标记的生殖分蘖株的数量性状的变化规律及生殖分蘖株的生长规律.结果表明,在朝鲜碱茅种群中,虽然抽穗时间只相隔3d,但生殖分蘖株的各数量性状均具有较大的表型可塑性,总的变化趋势是抽穗时间相隔越长,差异越大.其中,5次样本中的相邻平均花序生物量之间的差异均达到了显著水平.延长生殖生长16d,平均分蘖株高增加了23.16%,花序长增加了25.70%,分蘖株生物量增加了74.99%,花序生物量增加到2.63倍,生殖分配增加了93.25%.随着生殖生长时间的延长,朝鲜碱茅种群生殖分蘖株高、分蘖株生物量和花序生物量均呈指数增加,花序长和生殖分配呈直线增加,生殖生长比率呈先增加后降低的抛物线变化.不同时间进入生殖生长阶段的生殖分蘖株均具有相同的生长规律.其中,花序长均随分蘖株高的增加呈指数异速增长,花序生物量均随分蘖株生物量的增加呈直线同速增长.分蘖株的生殖生长越延长,对现实种群的贡献就越大,对未来种群的贡献更大.     

Influence of sediment fertility on morphological variability of Vallisneria spiralis L.

One homogeneous and three heterogeneous nutrient enrichment treatments were imposed to investigate the growth responses of Vallisneria spiralis L. Morphological features of V. spiralis differed significantly between different nutrient patches. Roots elongated in nutrient-poor patches, and the specific root length (SRL) also increased significantly. Stolon length, diameter and leaf length and width increased significantly in nutrient-rich patches. Total plant biomass of V. spiralis grown in the homogeneous and three heterogeneous treatments on average were 2.9, 3.0, 3.9 and 2.3 fold higher than that grown in the control treatment. Number of ramets per clone was significantly higher in the heterogeneous treatments than in the homogeneous treatment. In three varying heterogeneous treatments, ramet biomass in nutrient-rich patches was 2.7, 4.3 and 3.0 fold higher than in nutrient-poor patches; however, ramet number was not affected by sediment nutrients, resulting in bigger ramets in nutrient-rich patches. The biomass allocation established adaptive plasticity to heterogeneous environments. The maximum value of biomass allocation to underground parts reached 16% in nutrient-rich patches, whereas the minimum value of underground parts reached 20% in nutrient-poor patches. Results demonstrate that clonal V. spiralis can maintain itself preferentially in favourable nutrient-rich sediments, whereas nutrient-poor conditions could be escaped by plastic biomass allocation.     

The effect of allometric partitioning on herbivory tolerance in four species in South China

Herbivory tolerance can offset the negative effects of herbivory on plants and plays an important role in both immigration and population establishment. Biomass reallocation is an important potential mechanism of herbivory tolerance. To understand how biomass allocation affects plant herbivory tolerance, it is necessary to distinguish the biomass allocations resulting from environmental gradients or plant growth. There is generally a tight balance between the amounts of biomass invested in different organs, which must be analyzed by means of an allometric model. The allometric exponent is not affected by individual growth and can reflect the changes in biomass allocation patterns of different parts. Therefore, the allometric exponent was chosen to study the relationship between biomass allocation pattern and herbivory tolerance. We selected four species (Wedelia chinensis, Wedelia trilobata, Merremia hederacea, and Mikania micrantha), two of which are invasive species and two of which are accompanying native species, and established three herbivory levels (0%, 25% and 50%) to compare differences in allometry. The biomass allocation in stems was negatively correlated with herbivory tolerance, while that in leaves was positively correlated with herbivory tolerance. Furthermore, the stability of the allometric exponent was related to tolerance, indicating that plants with the ability to maintain their biomass allocation patterns are more tolerant than those without this ability, and the tendency to allocate biomass to leaves rather than to stems or roots helps increase this tolerance. The allometric exponent was used to remove the effects of individual development on allocation pattern, allowing the relationship between biomass allocation and herbivory tolerance to be more accurately explored. This research used an allometric model to fit the nonlinear process of biomass partitioning during the growth and development of plants and provides a new understanding of the relationship between biomass allocation and herbivory tolerance.     

The effects of clonal integration on morphological plasticity and placement of daughter ramets in black locust (Robinia pseudoacacia)

We studied the field response of Robinia pseudoacacia L. to light, total soil nitrogen, available soil phosphorus and soil pH. Results indicated that there was very strong clonal integration between mother and daughter ramets. Mother ramets can provide nitrogen and phosphorus to daughter ramets sufficient for their continued growth through strong clonal integration, but cannot provide enough photosynthate. With clonal integration, soil nitrogen and phosphorus availability had no effect on biomass allocation to roots, number of ramets and length of connection roots. Biomass allocation to roots increased markedly and responded to nitrogen and phosphorus availability, when the connections were severed. Light had a significant effect on the percent of biomass allocation to leaves and number of ramets, but no effect on the length of connection roots. Daughter ramets allocated more resources to leaves, and clones placed more daughter ramets in high light patches than in low light patches. Soil pH had a significant effect on ramet number and connection root length. Clones concentrated in alkaline patches and escaped from acid patches through selective placement of daughter ramets and changing the length of connection roots. We suggest that the clonal integration may be very strong and provide sufficient soil resources to daughter ramets, then affect the daughter ramets’ morphology and placement, if the size of a specific ramet is significantly larger than the other ramets in an arbor clone.     

An alternative mechanism for shade adaptation: implication of allometric responses of three submersed macrophytes to water depth

Allometric scaling models describing size-dependent biological relationships are important for understanding the adaptive responses of plants to environmental variation. In this study, allometric analysis was used to investigate the biomass allocation and morphology of three submerged macrophytes (Potamogeton maackianus, Potamogeton malaianus and Vallisneria natans) in response to water depth (1.0 and 2.5?m) in an in situ experiment. The three macrophytes exhibited different allometric strategies associated with distinct adjustments in morphology and biomass allocation in response to varying water depths. In deeper water, after accounting for the effects of plant size, P. maackianus and P. malaianus tended to enhance light harvesting by allocating more biomass to the stem, increasing shoot height and specific leaf area. V. natans tended to allocate more biomass to the leaf than to the basal stem (rosette), showing a higher leaf mass ratio and shoot height in deeper water. The three species decreased biomass allocation to roots as water depth increased. The main effect of water depth treatments was reduced light availability, which induced plastic shoot or leaf elongation. This shows that macrophytes have evolved responses to light limitation similar to those of terrestrial plants.     

Nonlinear processes in seagrass colonisation explained by simple clonal growth rules

The development of single clones of the seagrass Cymodocea nodosa was analysed using a growth model based on the formation of structures limited by diffusive aggregation. The model implemented the measured clonal growth rules (i.e. rhizome elongation and branching rates, branching angle, and spacer length between consecutive shoots) and shoot mortality rate for C. nodosa at Alfacs Bay (Spain). The simulated patches increased their size nonlinearly with time displaying two different domains of growth. Young patches showed a rapid increase with time of the length of rhizome network and the number of living shoots, which depended on rhizome branching rate, and increased the radial patch size (R_g) algebraically with the number of living shoots as R_g ∝ N_s^1/Df, being D_f the fractal dimension of the patch structure. Patches older than 4 years increased the production of rhizome network and the number of living shoots much more slowly, while their radial patch size behaved as R_g ∝ N_s^0.5 resulting from an internal patch compactation. Moreover, the linear growth rate of the simulated patches changed up to 30 fold during patch development, increasing with increasing patch size until patches reached an intermediate size. The modelled patch development was found to closely reproduce the observed patch structure for the species at the Alfacs Bay (Spain). Hence, the growth of C. nodosa patches initially proceeds with a growth mode controlled by the branching pattern (branching frequency and angle) of the species, producing sparse and elongated patches. Once patches exceed 4–5 years of age and contained >500 shoots, becoming dense and circular, they shifts to a growth model typical of compact structures. These results explain previously unaccounted evidence of the emergence of nonlinear patch growth from simple clonal growth rules, and highlight the importance of branching frequency and angles as critical determinants of the space occupation rate of seagrasses and probably other clonal plants.     

How plant allometry influences bud phenology and fruit yield in two Vaccinium species

Background and AimsUnderstanding how plant allometry, plant architecture and phenology contribute to fruit production can identify those plant traits that maximize fruit yield. In this study, we compared these variables and fruit yield for two shrub species, Vaccinium angustifolium and Vaccinium myrtilloides, to test the hypothesis that phenology is linked to the plants’ allometric traits, which are predictors of fruit production.MethodsWe measured leaf and flower phenology and the above-ground biomass of both Vaccinium species in a commercial wild lowbush blueberry field (Quebec, Canada) over a 2-year crop cycle; 1 year of pruning followed by 1 year of harvest. Leaf and flower phenology were measured, and the allometric traits of shoots and buds were monitored over the crop cycle. We hand-collected the fruits of each plant to determine fruit attributes and biomass.Key ResultsDuring the harvesting year, the leafing and flowering of V. angustifolium occurred earlier than that of V. myrtilloides. This difference was related to the allometric characteristics of the buds due to differences in carbon partitioning by the plants during the pruning year. Through structural equation modelling, we identified that the earlier leafing in V. angustifolium was related to a lower leaf bud number, while earlier flowering was linked to a lower number of flowers per bud. Despite differences in reproductive allometric traits, vegetative biomass still determined reproductive biomass in a log–log scale model.ConclusionsGrowing buds are competing sinks for non-structural carbohydrates. Their differences in both number and characteristics (e.g. number of flowers per bud) influence levels of fruit production and explain some of the phenological differences observed between the two Vaccinium species. For similar above-ground biomass, both Vaccinium species had similar reproductive outputs in terms of fruit biomass, despite differences in reproductive traits such as fruit size and number.     

Soil temperature drives elevational patterns of reproductive allometry in a biodiversity hotspot

Understanding the geographic patterns of reproductive allocation helps in clarifying the selective forces that shape the reproductive strategies of plants. However, studies on the elevational patterns of reproductive allocation remain limited. Moreover, although soil attributes have long been suspected to drive elevational patterns of reproductive allocation, few studies have explored this relationship. Delaying reproduction and allocating a high proportion of biomass to vegetative organs may be risky for plants living under high-elevation habitats, as these two processes can potentially lead to plant reproductive failure due to the low temperatures and short growing seasons at high elevations. Thus, we hypothesize that reproductive effort will increase with elevation and the elevational pattern of reproductive allocation will be largely driven by soil attributes, given their covariation with elevation. To test these hypotheses, we determined the vegetative and reproductive biomass of individual Impatiens arguta (Balsaminaceae) plants across 12 populations in the Gaoligong Mountains (China), and collected data on soil temperature, nutrients, moisture, and pH for each population. Based on standard major axis regression and linear regression models, we found that (1) both vegetative and reproductive biomass decreased with elevation; (2) all populations demonstrated significant allometric slopes (i.e., linear coefficients of log[reproductive biomass]???log[vegetative biomass] regressions)?>?1; (3) allometric slopes decreased with elevation; and (4) soil temperature was a better predictor of the allometric slope than elevation, i.e., the allometric slope decreased with soil temperature. These results suggest that plant species growing at high elevation invest proportionately more resources to reproduction as an adaptation to low-temperature environments, and reproductive output is heavily dependent on vegetative growth. This study provides the first evidence of soil temperature driving reproductive allocation patterns, which suggests that plant species will favor allocation to growth under increasing soil temperatures with climate warming.

     

Allometric growth, disturbance regime, and dilemmas of controlling invasive plants: a model analysis

Disturbed communities are observed to be more susceptible to invasion by exotic species, suggesting that some attributes of the invaders may interact with disturbance regime to facilitate invasion success. Alternanthera philoxeroides, endemic to South America, is an amphibious clonal weed invading worldwide. It tends to colonize disturbed habitats such as riparian zones, floodplain wetlands and agricultural areas. We developed an analytical model to explore the interactive effects of two types of physical disturbances, shoot mowing and root fragmentation, on biomass production dynamics of A. philoxeroides. The model is based on two major biological assumptions: (1) allometric growth of root (belowground) vs. shoot (aboveground) biomass and (2) exponential regrowth of shoot biomass after mowing. The model analysis revealed that the interaction among allometric growth pattern, shoot mowing frequency and root fragmentation intensity might lead to diverse plant ‘fates’. For A. philoxeroides whose root allocation decreases with growing plant size, control by shoot mowing was faced with two dilemmas. (1) Shoot regrowth can be effectively suppressed by frequent mowing. However, frequent shoot mowing led to higher biomass allocation to thick storage roots, which enhanced the potential for faster future plant growth. (2) In the context of periodic shoot mowing, individual shoot biomass converged to a stable equilibrium value which was independent of the root fragmentation intensity. However, root fragmentation resulted in higher equilibrium population shoot biomass and higher frequency of shoot mowing required for effective control. In conclusion, the interaction between allometric growth and physical disturbances may partially account for the successful invasion of A. philoxeroides; improper mechanical control practices could function as disturbances and result in exacerbated invasion.