Rooting characteristics of two widely distributed woody plant species growing in different karst habitats of southwest China

A series of studies claimed that deep root development of plant established in karst regions was facilitated by fractured bedrock beneath the shallow soils; however, bedrock is not a uniform medium for root proliferation. We hypothesized plant species that survived in different karst habitats had some other rooting characteristics rather than deep penetration. To test the hypothesis, coarse root systems of two widely distributed woody species (one tree and one shrub) growing in three typical rocky karst habitats (shallow soil, loose rocky soil and exposed rock) were excavated in karst region of southwest China. Root systems were investigated based on four parameters: maximum rooting depth, maximum radial extent, root tapering pattern and root curvature. In all the three habitats, maximum rooting depths were no deeper than 120 and 40 cm for the tree and shrub species, respectively. Maximum radial extents were extremely large compared with maximum rooting depth, indicating that rooting characteristics were dominated by horizontal extension rather than deep penetration. Roots of both species growing in shallow soil habitat tapered gradually and curved slightly, which was consistent with the specific characteristics of this habitat. On the contrary, roots of the tree species growing in the other two habitats tapered rapidly but curved slightly, while roots of the shrub species tapered gradually but curved strongly. It was speculated that limited depths and rapid tapering rates of the tree roots were likely compensated by their utmost radial extensions, while the shrub species might benefit from its root curvature as the associated root tropisms may increase the ability of root to encounter more water and contribute to potentially high resource absorption efficiency. Our results highlight the importance of taking shallow-rooted species into account in understanding the distribution of natural plant communities and predicting future vegetation dynamics in karst regions.     

Interspecific interactions and biomass allocation among grassland plant species

Although a handful of studies have shown how interspecific interactions may influence plant shoot to root ratios, the issue of how these interactions influence biomass partitioning among coexisting plant species remains largely unexplored. In this study, we determined whether a given plant species could induce other plant species to allocate relative biomass to each of four zones (aboveground, and three soil depth layers) in a different manner to what they would otherwise, and whether this may influence the nature of competitive or facilitative interactions amongst coexisting plant species. We used a glasshouse study in which mixtures and monocultures of ten grassland plant species were grown in cylindrical pots to determine the effects of plant species mixtures versus monocultures on the production of shoots and of roots of other species for each of three soil depths. Across all experiments, stimulation of production in mixtures was far less common than suppression of production. Different plant species shifted their allocation to shoots or roots at different depths, suggesting that interspecific interactions can either: (1) increase the ratio of deep to shallow roots, perhaps because competition reduces root growth in the uppermost part of the soil profile; or (2) decrease this ratio by reducing plant vigour to such an extent that the plant cannot produce roots that can reach deep enough to exploit resources at lower depths. Further, these results suggest that there are instances in which competition may have the potential to enforce resource partitioning between coexisting plant species by inducing different species to root at different depths to each other.     

Analysis of interactions between the invasive tree-of-heaven (<Emphasis Type="Italic">Ailanthus altissima</Emphasis>) and the native black locust (<Emphasis Type="Italic">Robinia pseudoacacia</Emphasis>)

Invasive exotic plants can persist and successfully spread within ecosystems and negatively affect the recruitment of native species. The exotic invasive Ailanthus altissima and the native Robinia pseudoacacia are frequently found in disturbed sites and exhibit similar growth and reproductive characteristics, yet each has distinct functional roles such as allelopathy and nitrogen fixation, respectively. A four-month full additive series in the greenhouse was used to analyze the intraspecific and interspecific interference between these two species. In the greenhouse experiment, the inverse of the mean total biomass (g) response per plant for each species was regressed on the density of each species and revealed that the performance of the plants was significantly reduced by interspecific interference and not by intraspecific interference (p < 0.05). Other biomass traits such as root dry weight, shoot dry weight, stem dry weight, and leaf dry weight were also negatively affected by interspecific interference. Competition indices such as Relative Yield Total and Relative Crowding Coefficient suggested that A. altissima was the better competitor in mixed plantings. Ailanthus altissima consistently produced a larger above ground and below ground relative yield while R. pseudoacacia generated a larger aboveground relative yield in high density mixed species pots.     

Initial growth of Brazilian pine (Araucaria angustifolia) under equal soil volumes but contrasting rooting depths

Araucaria angustifolia is a critically endangered tall tree species of valuable wood, and field observations led to the suggestion that limitations imposed to the vertical growth of its tap root system greatly restrict the height of mature individuals. However, experimental studies dealing with the effects of soil depth on the species growth are mostly lacking. This study evaluated and compared the growth responses of young plants of A. angustifolia to distinct rooting depths but same soil volumes. Seeds were planted in pots of different heights and diameters, all containing 3 liters of soil mixture. Plants were submitted to four available rooting depths: 65 (T1), 35 (T2), 20 (T3), and 10 (T4) cm. There were eight experimental units in each treatment, arranged in a randomized complete block design, each block containing two units per treatment. Contrary to what was expected, the T3 and T4 plants had accumulated more mass and attained the same height as the other two groups, after a 10-month growth period in a green house. Those plants also had thicker stems, longer shoot branches, and thicker and longer lateral roots, which were interpreted as compensatory responses to increase plant anchorage and stability. The inverse relationship between rooting depth and plant mass was attributed to a down-regulation of shoot growth because or restricted lateral space and/or poor soil aeration of the longer and narrower pots. This experiment allowed us to demonstrate that is not the possibility of the tap root to grow deep into the soil that ensures a better growth to plants of A. angustifolia: provided that the offer of soil volume and resources are the same, the vertical extension of the tap root does not result in greater growth of the plants. In fact, much greater growth impairment is expected from lateral than from vertical restriction to root growth.     

Complementarity among species in horizontal versus vertical rooting space

Aims: Many experiments have shown a positive effect of species richnesson productivity in grassland plant communities. However, itis poorly understood how environmental conditions affect thisrelationship. We aimed to test whether deep soil and limitingnutrient conditions increase the complementarity effect (CE)of species richness due to enhanced potential for resource partitioning. Methods: We grew monocultures and mixtures of four common grassland speciesin pots on shallow and deep soil, factorially combined withtwo nutrient levels. Soil volume was kept constant to avoidconfounding soil depth and volume. Using an additive partitioningmethod, we separated biodiversity effects on plant productivityinto components due to species complementarity and dominance. Important findings: Net biodiversity and complementarity effects were consistentlyhigher in shallow pots, which was unexpected, and at the lownutrient level. These two results suggest that although belowgroundpartitioning of resources was important, especially under lownutrient conditions, it was not due to differences in rootingdepths. We conclude that in our experiment (i) horizontal rootsegregation might have been more important than the partitioningof rooting depths and (ii) that the positive effects of deepsoil found in other studies were due to the combination of deepersoil with larger soil volume.     

Limitations to CO2-induced growth enhancement in pot studies

Recently, it has been suggested that small pots may reduce or eliminate plant responses to enriched CO₂ atmospheres due to root restriction. While smaller pot volumes provide less physical space available for root growth, they also provide less nutrients. Reduced nutrient availability alone may reduce growth enhancement under elevated CO₂. To investigate the relative importance of limited physical rooting space separate from and in conjunction with soil nutrients, we grew plants at ambient and double-ambient CO₂ levels in growth containers of varied volume, shape, nutrient concentration, and total nutrient content. Two species (Abutilon theophrasti, a C₃ dicot with a deep tap root andSetaria faberii, a C₄ monocot with a shallow diffuse root system) were selected for their contrasting physiology and root architecture. Shoot demography was determined weekly and biomass was determined after eight and ten weeks of growth. Increasing total nutrients, either by increasing nutrient concentration or by increasing pot size, increased plant growth. Further, increasing pot size while maintaining equal total nutrients per pot resulted in increased total biomass for both species. CO₂-induced growth and reproductive yield enhancements were greatest in pots with high nutrient concentrations, regardless of total nutrient content or pot size, and were also mediated by the shape of the pot. CO₂-induced growth and reproductive yield enhancements were unaffected by pot size (growth) or were greater in small pots (reproductive yield), regardless of total nutrient content, contrary to predictions based on earlier studies. These results suggest that several aspects of growth conditions within pots may influence the CO₂ responses of plants; pot size, pot shape, the concentration and total amount of nutrient additions to pots may lead to over-or underestimates of the CO₂ responses of real-world plants.     

Experimentally increased nutrient availability at the permafrost thaw front selectively enhances biomass production of deep‐rooting subarctic peatland species

Climate warming increases nitrogen (N) mineralization in superficial soil layers (the dominant rooting zone) of subarctic peatlands. Thawing and subsequent mineralization of permafrost increases plant‐available N around the thaw‐front. Because plant production in these peatlands is N‐limited, such changes may substantially affect net primary production and species composition. We aimed to identify the potential impact of increased N‐availability due to permafrost thawing on subarctic peatland plant production and species performance, relative to the impact of increased N‐availability in superficial organic layers. Therefore, we investigated whether plant roots are present at the thaw‐front (45 cm depth) and whether N‐uptake (¹⁵N‐tracer) at the thaw‐front occurs during maximum thaw‐depth, coinciding with the end of the growing season. Moreover, we performed a unique 3‐year belowground fertilization experiment with fully factorial combinations of deep‐ (thaw‐front) and shallow‐fertilization (10 cm depth) and controls. We found that certain species are present with roots at the thaw‐front (Rubus chamaemorus) and have the capacity (R. chamaemorus, Eriophorum vaginatum) for N‐uptake from the thaw‐front between autumn and spring when aboveground tissue is largely senescent. In response to 3‐year shallow‐belowground fertilization (S) both shallow‐ (Empetrum hermaphroditum) and deep‐rooting species increased aboveground biomass and N‐content, but only deep‐rooting species responded positively to enhanced nutrient supply at the thaw‐front (D). Moreover, the effects of shallow‐fertilization and thaw‐front fertilization on aboveground biomass production of the deep‐rooting species were similar in magnitude (S: 71%; D: 111% increase compared to control) and additive (S + D: 181% increase). Our results show that plant‐available N released from thawing permafrost can form a thus far overlooked additional N‐source for deep‐rooting subarctic plant species and increase their biomass production beyond the already established impact of warming‐driven enhanced shallow N‐mineralization. This may result in shifts in plant community composition and may partially counteract the increased carbon losses from thawing permafrost.     

Resolving the differences in plant burial responses

Burial is one of the major factors influencing plant ecology in deserts and coastal areas. Consequently, many studies have measured the responses of dune plants to sand burial. However, there remains little agreement about the mechanisms and characteristics constituting the burial response of plants. In particular, stimulation of growth has been reported as the most common plant burial response; however, stimulation has not been reported consistently among studies. Here, a literature survey showed that the depth of burial relative to the height of the plant determined whether the growth of a species was stimulated by burial. Growth stimulation was limited to shallow burial depths, while burial depths greater than the height of the plant consistently resulted in reduced growth. As studies used widely differing burial depths or units of growth measurement, the variation in reported stimulation of plant growth can be partly attributed to differences in experimental procedure. The stimulation of growth in many species was accompanied by an increase in photosynthesis over a limited period and by a shift in biomass allocation from root to shoot. Most plants demonstrated stimulated growth (up to 200%) in response to shallow burial indicating that some burial response mechanisms are general to many species. However, a few specialist dune species displayed a much greater ability to respond to burial (up to 700% stimulation of plant mass). Although allocation shifts and increased photosynthesis have been shown to be associated with dune plant burial response, there remains a need for field measurements that focus on the diversity of mechanisms underlying plant response to burial.     

The species richness–biomass relationship in herbaceous plant communities: what difference does the incorporation of root biomass data make?

So far, in all studies on the much-discussed hump-backed relationship between plant community productivity and species richness, productivity has been assessed through plant shoot biomass, i.e. it has been ignored that frequently most of the biomass is produced below ground. We revisited the 27 grassland and forest field-layer communities, studied earlier by Zobel and Liira, to sample root biomass, plant total biomass and root/shoot allocation, and learn how the incorporation of below-ground biomass data would affect the shape of the hump-backed relationship. In order to avoid scaling artefacts we estimated richness as the average count of species per 500 plant ramets (absolute richness). We also included relative richness measures. Relative richness was defined as richness per 500 ramets/size of the actual species pool (the set of species present in the community), relative pool size was defined as size of the actual species pool/size of the regional species pool (the set of species available in the region and capable of growing in the given community).
The biomass-absolute richness relationship was humped, irrespective of the biomass measure used, the hump being most obvious when plant total biomass was used as the independent variable. Evidently, the unimodal richness–productivity curve is not a sampling artefact, as suspected by Oksanen. However, relative richness was not related to community biomass (above-ground, below-ground or total). The hump-backed curve is shaped by the sizes of actual species pools in communities, implying that processes which are responsible for small-scale diversity pattern mainly operate on the community level.
Neither absolute nor relative richness were significantly related to root/shoot allocation. The presumably stronger (asymmetric) shoot competition at greater allocation to shoots appears not to suppress small-scale richness. However, there is a significant relationship between relative pool size and root/shoot allocation. Relatively more species from regional species pools are able to enter and persist in communities with more biomass allocated into roots.     

Understanding plant rooting patterns in semi‐arid systems: an integrated model analysis of climate,soil type and plant biomass

Aim A consistent set of root characteristics for herbaceous plants growing in water‐limited environments has been developed based on compilations of global root databases, but an overall analysis of why these characteristics occur is still missing. The central question in this study is whether an ecohydrological model which assumes that rooting strategies reflect maximization of transpiration can predict the variations in rooting strategies of plants in dry environments. Location Arid ecosystems across the globe. Methods A model was used to explore interactions between plant biomass, root–shoot allocation, root distribution, rainfall, soil type and water use by plants. Results Model analyses showed that the predicted shifts in rooting depth and root–shoot allocation due to changes in rainfall, soil type and plant biomass were quite similar to observed shifts. The model predicted that soil type, annual rainfall and plant biomass each had strong effects on the rooting strategies that optimize transpiration, but also that these factors have strong interactive effects. The process by which plants compete for water availability (soil evaporation or drainage) especially affected the depth distribution of roots in the soil, whereas the availability of rainfall mainly affected the optimal root–shoot allocation strategy. Main conclusions The empirically observed key patterns in rooting characteristics of herbaceous plant species in arid environments could be explained in this theoretical study by using the concept of hydrological optimality, represented here by the maximization of transpiration.     

Effects of density on above and below ground biomass of the native alpine grass Poa fawcettiae and the environmental weed Achillea millefolium

Competition between Poa fawcettiae Vickery, the dominant native snowgrass, and the invasive herbaceous Achillea millefolium L., was examined in three glasshouse experiments. The first experiment investigated the potential for intra-specific competition in plants by growing them in pots with low and high density. The second experiment examined the potential for inter-specific competition at low, medium and high density. In the third experiment plants in pots where either roots or shoots of the species could not compete were compared to those where root and shoot competition was possible.
Achillea millefolium plants produced more than four times the biomass of P. fawcettiae plants. As a result the two species responded differently. In the A. millefolium monocultures both root and shoot biomass per plant declined at high density. By contrast, P. fawcettiae biomass was not affected. In mixed species pots, P. fawcettiae had no effect on the biomass of A . millefolium plants, while P. fawcettiae shoot and root biomass per plant decreased when grown with A. millefolium at all densities tested. Root competition from A. millefolium appears to be the main cause of the decrease in biomass of P. fawcettiae . The results imply that A. millefolium may have a competitive advantage over P. fawcettiae in the Australian Alps.     

A new index of interspecific competition for replacement and additive designs

The literature is reviewed to summarize the major indices of interspecific competition used in De Wit replacement experiments. Of the many indices that have been defined, some are less than clear as to their meaning, so interpretations are often difficult to make. In an effort to explore the performance of individual indices and to permit cross-correlation among indices, a series of hypothetical results in different competition scenarios is created. A standardized notation for all indices is also provided, along with equations and proofs. Nine indices are reviewed and analyzed for their behavior under the hypothetical scenarios and a new index that provides increased clarification and interpretability over other indices is proposed. Relative Yield Total, Aggressivity, and Relative Replacement Rate were shown to be poor measures of competition. Relative Crowding Coefficient has many restrictions to its use. The clearest index that includes two or more species is Relative Yield of Mixture. Indices that describe single species accurately were found to be Relative Yield (RY) and Relative Competition Intensity (RCI), both of which are mathematically convertible. An index introduced here, Change in Contribution (CC), is a single species index that differs from RY and RCI because it takes into account the overall biomass each species contributes.     

Root restriction as a factor in photosynthetic acclimation of cotton seedlings grown in elevated carbon dioxide

Interactive effects of root restriction and atmospheric CO₂ enrichment on plant growth, photosynthetic capacity, and carbohydrate partitioning were studied in cotton seedlings (Gossypium hirsutum L.) grown for 28 days in three atmospheric CO₂ partial pressures (270, 350, and 650 microbars) and two pot sizes (0.38 and 1.75 liters). Some plants were transplanted from small pots into large pots after 20 days. Reduction of root biomass resulting from growth in small pots was accompanied by decreased shoot biomass and leaf area. When root growth was less restricted, plants exposed to higher CO₂ partial pressures produced more shoot and root biomass than plants exposed to lower levels of CO₂. In small pots, whole plant biomass and leaf area of plants grown in 270 and 350 microbars of CO₂ were not significantly different. Plants grown in small pots in 650 microbars of CO₂ produced greater total biomass than plants grown in 350 microbars, but the dry weight gain was found to be primarily an accumulation of leaf starch. Reduced photosynthetic capacity of plants grown at elevated levels of CO₂ was clearly associated with inadequate rooting volume. Reductions in net photosynthesis were not associated with decreased stomatal conductance. Reduced carboxylation efficiency in response to CO₂ enrichment occurred only when root growth was restricted suggesting that ribulose-1,5-bisphosphate carboxylase/oxygenase activity may be responsive to plant source-sink balance rather than to CO₂ concentration as a single factor. When root-restricted plants were transplanted into large pots, carboxylation efficiency and ribulose-1,5-bisphosphate regeneration capacity increased indicating that acclimation of photosynthesis was reversible. Reductions in photosynthetic capacity as root growth was progressively restricted suggest sink-limited feedback inhibition as a possible mechanism for regulating net photosynthesis of plants grown in elevated CO₂.     

Assessment of Root System Dynamics of Species Grown in Mixtures under Field Conditions using Herbicide Injection and 15N Natural Abundance Methods: A Case Study with Pea, Barley and Mustard

Two methods were developed and used to study the root system dynamics of two species grown together or separately under field conditions. The first method, based on herbicide injection at different soil depths, was used to determine the rooting depth penetration rate of each species in pea–barley and pea–mustard mixtures. The roots absorbed the herbicide when they reached the treated zone leading to visible symptoms on the leaves which could be readily monitored. The second method used differences in ¹⁵N natural abundance and N concentration between legume and non-legume species to quantify the contribution of each species to root biomass of a pea–barley mixture. Each contribution was calculated using ¹⁵N abundance and N concentration of root mixtures and of subsamples of roots of individual species within mixtures. Both methods can indeed be used to distinguish roots of species in mixtures and thus to study belowground competition between associated species. The use of these methods demonstrated species differences in root system dynamics between species but also significant effects of interactions between species in mixtures. The rooting depth penetration rate was mainly species specific whereas root biomass was dependant on plant growth, allocation of dry matter between shoot and root components and growth factors such as N fertilization. Root biomass of each species may vary therefore with the level of competition between species.     

Interactions between seed source,planting arrangement,and soil treatment in determining plant size and root allocation in Phlox drummondii

Summary Two varieties of the annual plant Phlox drummondii were grown in pots in the greenhouse. Pots differed in the mixture of varieties, total number of plants, spatial clustering of plants, and soil treatment.The shoot biomass of centrally located target plants was significantly influenced by the varietal composition within a pot, and the pattern of this genetic effect varied with both plant density and soil treatment. Density and soil treatment interacted strongly, with the negative effect of neighbors on shoot growth being significantly greater when soil nutrient concentrations were lower.The varieties differed significantly in their relative allocation of biomass to roots. Relative root allocation was increased in response to both the presence of neighbors and a decrease in soil nutrient availability. These factors did not interact significantly in their effects.Although both plant size and relative allocation to roots were influenced by varietal composition, these genetic effects were small relative to the effects of density and soil treatment.The strong interactions between plant location, plant identity, and soil treatment suggest that relations between neighbors will be very complex in natural populations occupying microgeographically heterogeneous habitats. A more complete understanding of these interactions will be required before realistic dynamic models of natural populations can be constructed.     

Glutamine synthetase activity and free amino acid pools of eelgrass (Zostera marina L.) roots

Activity of the enzyme glutamine synthetase (GS, EC 6.3.1.2) was determined in vitro for roots of the marine angiosperm Zostera marina L. (eelgrass) collected from a population in Great Harbor, Woods Hole, Massachusetts, U.S.A. The GS synthetase activity was lowest in roots of plants collected from the shallow region of the eelgrass bed (12.0 μmol·g⁻¹ (fresh wt)· h⁻¹) and increased in the mid (3.0 m, 40.3 μmol·g⁻¹ (fresh wt)·h⁻¹) and deep (5.0 m, 72.3 μmol·g⁻¹ (fresh wt)·h⁻¹) plant collection depths. GS transferase activity increased with collection depth in a similar manner: shallow, 28.6 μmol·g⁻¹ (fresh wt)·h⁻¹; mid, 52.0 μmol·g⁻¹ (fresh wt)·h⁻¹; deep, 92.8 μmol·g⁻¹ (fresh wt)·h⁻¹. When sediment-embedded plants were held in continuous darkness for 2 days to create extended root anoxia, root GS activities nearly doubled. In contrast, in vivo incorporation of ¹⁴C-glutamate into glutamine and protein residue remained constant or declined under short-term hypoxia and anoxia. During aerobic recovery from anoxia, root labelling of glutamine and protein increased markedly. Free amino acid patterns of eelgrass roots growing in situ were determined over a diurnal cycle. Total free amino acid content was maximal at dawn and decreased 50% by noon. In contrast, the proportion of glutamine was lowest at dawn and maximal at noon for both shallow and deep-growing plants. Despite differences in depth-specific plant sizes, root/rhizome/shoot ratios, and relative growth rates, the daily whole plant nitrogen demand of shallow and deep growing plants were equivalent. When corrected for assay temperature response, the enzyme synthetase activities measured in vitro suggest that all of the plant nitrogen assimilation requirements can be met within daylight hours during the period of peak summer biomass.     

Plant traits enabling survival in Mediterranean badlands in northeastern Spain suffering from soil erosion

Question: This study analysed the effect of severe soil erosion on species composition of plant communities by favouring species showing certain growth forms, root‐sprouting and clonal growth abilities. Location: The study area was located between the middle Ebro Valley and the Pre‐Pyrenees (northeastern Spain). Methods: Root‐sprouting and shoot‐rooting abilities, clonal reproduction and growth form were assessed for the 123 most common plant species from eroded lands in the study area. We obtained 260 vegetation relevés in three different substrata (gypsum outcrops, Miocene clays and Eocene marls) on areas with different degrees of soil erosion. The frequency of every plant trait in each relevé was estimated according to species presence. The effect of soil erosion on the frequency of plant attributes was assessed by correlation analyses. Results: Bipolar, non‐clonal plants and annual species decreased their frequency with increasing soil erosion in the three substrata analyzed, whereas root‐sprouters and woody plants (mostly sub‐shrubs) increased their frequency in most of the substrata analysed. Conclusions: Woody sub‐shrubs, root‐sprouters and clonal species are favoured in eroded lands in NE Spain. Bipolar species and annual plants might not be plastic enough to survive the high stress and frequent disturbances prevailing in such eroded areas.     

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

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

Roles of leaf in regulation of root and shoot growth from single node softwood cuttings of grape (Vitis vinifera)

The role of leaf in regulation of root and shoot growths in single node softwood cuttings of grape (Vitis vinifera) was characterised. Leafy cuttings showed early rooting, vigorous root growth and subsequent shoot development. Defoliation at planting induced early sprouting, but adversely affected rooting and decreased the survival of cuttings irrespective of pre‐planting treatment with 100 μM indole 3‐acetic acid (IAA). Treatment with IAA did not affect the percent rooting of leafy cuttings but increased root and shoot growth. Leaf weight (wt) and leaf area of the cuttings showed a highly significant correlation to root wt of the new plant at 4 wk after planting, while cutting stem + petiole wt was either not or less significantly correlated to root and shoot weights of the subsequent plant. The greater the area or wt of leaf, the better the root and shoot growths, implying that leaf contributed to adventitious root growth. However, retaining the leaf for just 2 days was enough to stimulate rooting in more than 80% of the cuttings, suggesting that leaf tissue could also induce root formation. Root growth increased with the period of leaf retention but leaf removal before 3 wk triggered sprouting leading to high mortality in rooted cuttings. Bringing the leaf closer to the rooting zone by preparing leaf at base (LAB) cuttings delayed rooting and sprouting compared with the standard leaf at top (LAT) cuttings. An inhibitory effect on rooting and sprouting by the exposed upper internode region in LAB cuttings is suggested.     

水淹深度、持续时间及发生频率对扬子狐尾藻早期生长的影响

研究了水淹扰动包括不同的深度(0,10,60 cm)、持续时间(1周、2周)和发生频率(1次、2次)对扬子狐尾藻(Myriophyllum oguraense Miki subsp.yangtzense Wang)早期生长的影响。结果表明,湿生状态下未经过水淹处理的植株的总生物量最大、所产生的分枝数最多、株高最小;在经过水淹处理后,植株的总生物量、植株所产生的分枝数显著减少,而株高则显著增加。随着水淹深度的增大和持续时间的增加,植株的总生物量、分枝数显著减小,而株高则在浅水位处理下(10 cm)随着水淹持续时间的增加而增加,在深水位处理下(60 cm)随着水淹持续时间的增加而减小。总生物量在较长时间持续于浅水位下(2周,10 cm)和较短时间持续于深水位下(1周,60 cm)时随水淹发生频率的增高而增大,分枝数也呈增多趋势。随着水淹发生频率的增高,深水位(60 cm)显著促进株高的增加。此外,水淹处理后,茎生物量比增大,而根生物量比、叶生物量比、分枝生物量比则呈减小趋势。这些研究结果表明水淹扰动是影响扬子狐尾藻早期生长和克隆繁殖的重要因子之一,同时也说明扬子狐尾藻对不同的水淹扰动有不同的生长和克隆繁殖对策。