Leaf flushing and shedding,bud and flower production,and stem elongation in tall birch trees subjected to increases in aboveground temperature

Key message

Tall birch trees allocate extra resource due to aboveground temperature elevation to bud and male flower production rather than to plant growth. Saplings increased only plant growth under warming. Size-dependent response should be considered.

Abstract

We experimentally heated canopy organs of tall birch trees (Betula ermanii Cham.; 18–20 m high) growing at a high latitude to determine how leaf phenology, plant growth, and bud and male flower production might shift in response to increases in aboveground temperature during global climate change. We warmed the canopies with infrared heat lamps fixed to steel pipe scaffolds built around the trees. The temperature of the warmed canopies increased by approximately 1 °C. Warming extended the length of the growing season of canopy leaves (by accelerating leaf flush and delaying leaf fall), and significantly increased the numbers of buds and male flowers per shoot. Bud production and shoot length were positively correlated in both warmed and control branches. However, warming did not increase canopy shoot lengths. The intercept value of the positive regression slope between bud production and shoot length for warmed branches was higher than that for control branches. Thus, canopy warming had a direct positive effect on the bud production but had no indirect effect via increases in shoot length. Our experiment showed that tall birch trees allocated extra resources made available by increased aboveground temperature to bud and male flower production rather than to plant growth.

     

Linking above- and belowground phenology of hybrid walnut growing along a climatic gradient in temperate agroforestry systems

Background and aims

Plant phenology is a sensitive indicator of plant response to climate change. Observations of phenological events belowground for most ecosystems are difficult to obtain and very little is known about the relationship between tree shoot and root phenology. We examined the influence of environmental factors on fine root production and mortality in relation with shoot phenology in hybrid walnut trees (Juglans sp.) growing in three different climates (oceanic, continental and Mediterranean) along a latitudinal gradient in France.

Methods

Eight rhizotrons were installed at each site for 21 months to monitor tree root dynamics. Root elongation rate (RER), root initiation quantity (RIQ) and root mortality quantity (RMQ) were recorded frequently using a scanner and time-lapse camera. Leaf phenology and stem radial growth were also measured. Fine roots were classified by topological order and 0–1 mm, 1–2 mm and 2–5 mm diameter classes and fine root longevity and risk of mortality were calculated during different periods over the year.

Results

Root growth was not synchronous with leaf phenology in any climate or either year, but was synchronous with stem growth during the late growing season. A distinct bimodal pattern of root growth was observed during the aerial growing season. Mean RER was driven by soil temperature measured in the month preceding root growth in the oceanic climate site only. However, mean RER was significantly correlated with mean soil water potential measured in the month preceding root growth at both Mediterranean (positive relationship) and oceanic (negative relationship) sites. Mean RIQ was significantly higher at both continental and Mediterranean sites compared to the oceanic site. Soil temperature was a driver of mean RIQ during the late growing season at continental and Mediterranean sites only. Mean RMQ increased significantly with decreasing soil water potential during the late aerial growing season at the continental site only. Mean root longevity at the continental site was significantly greater than for roots at the oceanic and Mediterranean sites. Roots in the 0–1 mm and 1–2 mm diameter classes lived for significantly shorter periods compared to those in the 2–5 mm diameter class. First order roots (i.e. the primary or parents roots) lived longer than lateral branch roots at the Mediterranean site only and first order roots in the 0–1 mm diameter class had 44.5% less risk of mortality than that of lateral roots for the same class of diameter.

Conclusions

We conclude that factors driving root RER were not the same between climates. Soil temperature was the best predictor of root initiation at continental and Mediterranean sites only, but drivers of root mortality remained largely undetermined.

     

Root-favoured biomass allocation improves growth and yield of field-grown rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) plants only when the shoot sink is expandable

We tested the hypothesis that high root/shoot (R/S) in rice improves plant growth and yield when the shoot sink is expandable, and that in a genotype with exaggerated R/S ratio, the shoot growth is not limited by root resources. This study involved the three rice genotypes, Giza 178, PM12, and Moroberekan with a range of R/S ratios and shoot sink sizes. Root regrowth after trimming or high- and low-nitrogen treatments revealed that Moroberekan has consistently high root-favoured biomass partitioning than Giza 178 or PM12. Increasing the R/S ratios by detillering improved the culm growth in Giza 178 and PM12 (by 43.4 and 17.7% of control, respectively) but not Moroberekan, indicating that PM12 was closer to achieving its growth potential than Giza 178 but Moroberekan was operating at maximal shoot growth potential because of high R/S ratio and small sink size. Under drought, shoot growth, gas exchange, and grain yield correlated strongly with R/S ratio and root length density (RLD) in the droughted but not the well-watered plants. We further hypothesized that R/S ratio of Moroberekan was in excess of shoot requirement for optimum growth. Crossing Moroberekan to PM12 generated three F1 hybrids with intermediate R/S ratios but higher growth, gas exchange, and yield than either parent. We conclude that increasing the R/S ratio improved growth and yield in PM12 but not Moroberekan, because the shoot sink size was expandable in PM12. Moreover, lower R/S ratios than that of Moroberekan could support higher shoot growth if shoot sink is expandable.     

Partitioning of belowground C in young sugar maple forest

Background and aims

Trees allocate a high proportion of assimilated carbon belowground, but the partitioning of that C among ecosystem components is poorly understood thereby limiting our ability to predict responses of forest C dynamics to global change drivers.

Methods

We labeled sugar maple saplings in natural forest with a pulse of photosynthetic ¹³C in late summer and traced the pulse over the following 3 years. We quantified the fate of belowground carbon by measuring ¹³C enrichment of roots, rhizosphere soil, soil respiration, soil aggregates and microbial biomass.

Results

The pulse of ¹³C contributed strongly to root and rhizosphere respiration for over a year, and respiration comprised about 75 % of total belowground C allocation (TBCA) in the first year. We estimate that rhizosphere carbon flux (RCF) during the dormant season comprises at least 6 % of TBCA. After 3 years, 3.8 % of the C allocated belowground was recovered in soil organic matter, mostly in water-stable aggregates.

Conclusions

A pulse of carbon allocated belowground in temperate forest supplies root respiration, root growth and RCF throughout the following year and a small proportion becomes stabilized in soil aggregates.     

Biocontrolled soil nutrient distribution under the influence of an oxalogenic-oxalotrophic ecosystem

Background and aims

Root phenology is important in controlling carbon and nutrient fluxes in terrestrial ecosystems, yet, remains largely unexplored, especially in the Arctic. We compared below- and aboveground phenology and ending of the growing season in two contrasting vegetation types of subarctic tundra: heath and meadow, and their response to experimental warming in autumn.

Methods

Root phenology was measured in-situ with minirhizotrons and compared with aboveground phenology assessed with repeat digital photography.

Results

The end of the growing season, both below- and aboveground, was similar in meadow and heath and the belowground growing season ended later than aboveground in the two vegetation types. Root growth was higher and less equally distributed over time in meadow compared to heath. The warming treatment increased air and soil temperature by 0.5 °C and slightly increased aboveground greenness, but did not affect root growth or prolong the below- and aboveground growing season in either of the vegetation types.

Conclusions

These results imply that vegetation types differ in root dynamics and suggest that other factors than temperature control autumnal root growth in these ecosystems. Further investigations of root phenology will help to identify those drivers, in which including responses of functionally contrasting vegetation types will help to estimate how climate change affects belowground processes and their roles in ecosystem function.

     

Native and exotic foundation grasses differ in traits and responses to belowground tri-trophic interactions

A plant’s growth and fitness are influenced by species interactions, including those belowground. In primary successional systems, belowground organisms are known to have particularly important control over plant growth. Exotic plant invasions in these and other habitats may in part be explained by altered associations with belowground organisms compared to native plants. We investigated the growth responses of two foundation grasses on Great Lakes sand dunes, the native grass Ammophila breviligulata and the exotic grass Leymus arenarius, to two groups of soil organisms with important roles in dune succession: arbuscular mycorrhizal fungi (AMF) and plant-parasitic nematodes (PPN). We manipulated the presence/absence of two generalist belowground species known to occur in Great Lakes dunes, Rhizophagus intraradices (AMF) and Pratylenchus penetrans (PPN) in a factorial greenhouse experiment and assessed the biomass production and root architectural traits of the plants. There were clear differences in growth and above- and belowground architecture between Ammophila and Leymus, with Leymus plants being bigger, taller, and having longer roots than Ammophila. Inoculation with Rhizophagus increased above- and belowground biomass production by ~32% for both plant species. Inoculation with Pratylenchus decreased aboveground biomass production by ~36% for both plant species. However belowground, the exotic Leymus was significantly more resistant to PPN than the native Ammophila, and gained more benefits from AMF in belowground tri-trophic interactions than Ammophila. Overall, our results indicate that differences in plant architecture coupled with altered belowground interactions with AMF and PPN have the potential to promote exotic plant invasion.     

Spatial explicit distribution of individual fine root biomass of <Emphasis Type="Italic">Rhizophora mangle</Emphasis> L. (Red Mangrove) in South Florida

Fine roots are of major importance for belowground processes in mangrove ecosystems. Little is known about individual mangrove root systems, particularly the fine root component. We measured fine root biomass distribution of solitary standing Rhizophora mangle L. individuals with the dual aim of (a) deepening our understanding of the belowground ecology and allometric relations of this species; and (b) gaining further information about its climatic relevance. Twelve trees of variable height (45–240 cm) were measured on three reforested sites in south-east Florida, USA. Soil cores were collected from individual trees at transects by means of auger sampling. Fine roots were extracted, sorted, dried and weighed. Mean fine root biomass varied between 20.56–253.12 g/m². Two separate mixed-effects models led to statistically sound predictions of spatial fine root biomass distribution. The first model was based on distance function and tree height (Model 1, \(R^2 = 0.77\), p value ≤ 0.001), and the second on prop root density (Model 2, \(R^2 = 0.56\), p value ≤ 0.001). Besides the aforementioned fixed effects, the results of both models indicated random, site-specific variation with regards to fine root biomass distribution. Nevertheless, we were able to explain individual fine root biomass distribution with reference to aboveground characteristics alone. These findings may help to improve the modelling of belowground plant interaction and carbon storage in mangroves, both of which are intrinsically linked to fine roots.     

Plant production and nitrogen accumulation above- and belowground in low and tall birch tundra communities: the influence of snow and litter

Background and Aim

A vegetation transition to taller and denser deciduous shrub tundra is currently occurring in many locations across the low Arctic, and is associated with climate change. Here, we investigated if deeper snow is a mechanism for enhanced shrub growth.

Methods

To determine if a moderate and climatically realistic increase in snow depth can enhance shrub productivity, we compared growth responses between ambient and experimentally deepened snow plots in low birch hummock tundra. To determine the potential influence of factors other than deepened snow that are associated with taller, denser shrubs, we also compared shrub growth between low birch hummock and tall birch-dominated tundra.

Results

Neither deciduous shrub above- nor belowground production nor nitrogen accumulation was enhanced by deepened snow. However, deciduous birch shrub new shoot production was 23× larger and total vascular shoot to belowground biomass ratios were higher in the tall birch tundra than the birch hummock (~0.7 and ~0.4, respectively), indicating that the combination of deeper snow together with other internal feedbacks greatly enhanced birch growth.

Conclusions

Together, our results strongly suggest that the much larger litter production in tall birch ecosystems is an important internal feedback that may or may not interact with deeper snow to promote birch growth in tall shrub tundra.

     

Soil nutrient patchiness and plant genotypes interact on the production potential and decomposition of root and shoot litter: evidence from short-term laboratory experiments with Triticum aestivum

Aims

The purpose of this study was to test the hypotheses that soil nutrient patchiness can differentially benefit the decomposition of root and shoot litters and that this facilitation depends on plant genotypes.

Methods

We grew 15 cultivars (i.e. genotypes) of winter wheat (Triticum aestivum L.) under uniform and patchy soil nutrients, and contrasted their biomass and the subsequent mass, carbon (C) and nitrogen (N) dynamics of their root and shoot litters.

Results

Under equal amounts of nutrients, patchy distribution increased root biomass and had no effects on shoot biomass and C:N ratios of roots and shoots. Roots and shoots decomposed more rapidly in patchy nutrients than in uniform nutrients, and reductions in root and shoot C:N ratios with decomposition were greater in patchy nutrients than uniform nutrients. Soil nutrient patchiness facilitated shoot decomposition more than root decomposition. The changes in C:N ratios with decomposition were correlated with initial C:N ratios of litter, regardless of roots or shoots. Litter potential yield, quality and decomposition were also affected by T. aestivum cultivars and their interactions with nutrient patchiness.

Conclusions

Soil nutrient patchiness can enhance C and N cycling and this effect depends strongly on genotypes of T. aestivum. Soil nutrient heterogeneity in plant communities also can enhance diversity in litter decomposition and associated biochemical and biological dynamics in the soil.     

A soil-free root observation system for the study of root-microorganism interactions in maize

Background and aims

The root surface of a plant usually exceeds the leaf area and is constantly exposed to a variety of soil-borne microorganisms. Root pathogens and pests, as well as belowground interactions with beneficial microbes, can significantly influence a plants' performance. Unfortunately, the analysis of these interactions is often limited because of the arduous task of accessing roots growing in soil. Here, we present a soil-free root observation system (SF-ROBS) designed to grow maize (Zea mays) plants and to study root interactions with either beneficial or pathogenic microbes.

Methods

The SF-ROBS consists of pouches lined with wet filter paper supplying nutrient solution.

Results

The aspect of maize grown in the SF-ROBS was similar to soil-grown maize; the plant growth was similar for the shoot but different for the roots (biomass and length increased in the SF-ROBS). SF-ROBS-grown roots were successfully inoculated with the hemi-biotrophic maize fungal pathogen Colletotrichum graminicola and the beneficial rhizobacteria Pseudomonas putida KT2440. Thus, the SF-ROBS is a system suitable to study two major belowground phenomena, namely root fungal defense reactions and interactions of roots with beneficial soil-borne bacteria.

Conclusions

This system contributes to a better understanding of belowground plant microbe interactions in maize and most likely also in other crops.     

Fast seedling root growth leads to competitive superiority of invasive plants

The competitive superiority of invasive plants plays a key role in the process of plant invasions, enabling invasive plants to overcome the resistance of local plant communities. Fast aboveground growth and high densities lead to the competitive superiority of invasive species in the competition for light. However, little is understood of the role belowground root competition may play in invasion. We conducted an experiment to test the effect of root growth on the performance of an invasive shrub Cassia alata, a naturalized, non-invasive shrub Corchorus capsularis, and a native shrub Desmodium reticulatum. We compared seedling growth of the three species and their competitive ability in situ. The roots of the C. alata seedlings grew much faster than those of C. capsularis and D. reticulatum during the entire growth period although C. alata had shorter shoots than D. reticulatum. Furthermore, C. alata showed an apparent competition advantage compared to the other two species as evidenced by less biomass reduction in intraspecific competition and higher competitive effects in interspecific competition. Our study reveals that fast seedling root growth may be important in explaining the competitive advantages of invasive plants. Future studies should pay more attention to the belowground traits of invasive plants, the trade-off between shoot and root growth, and the role of root competition in affecting the population dynamics of invasive plants and the structures of invaded communities.     

Seasonality and phenology alter functional leaf traits

In plant ecophysiology, functional leaf traits are generally not assessed in relation to phenological phase of the canopy. Leaf traits measured in deciduous perennial species are known to vary between spring and summer seasons, but there is a knowledge gap relating to the late-summer phase marked by growth cessation and bud set occurring well before fall leaf senescence. The effects of phenology on canopy physiology were tested using a common garden of over 2,000 black cottonwood (Populus trichocarpa) individuals originating from a wide geographical range (44–60ºN). Annual phenological events and 12 leaf-based functional trait measurements were collected spanning the entire summer season prior to, and following, bud set. Patterns of seasonal trait change emerged by synchronizing trees using their date of bud set. In particular, photosynthetic, mass, and N-based traits increased substantially following bud set. Most traits were significantly different between pre-bud set and post-bud set phase trees, with many traits showing at least 25 % alteration in mean value. Post-bud set, both the significance and direction of trait–trait relationships could be modified, with many relating directly to changes in leaf mass. In Populus, these dynamics in leaf traits throughout the summer season reflected a shift in whole plant physiology, but occurred long before the onset of leaf senescence. The marked shifts in measured trait values following bud set underscores the necessity to include phenology in trait-based ecological studies or large-scale phenotyping efforts, both at the local level and larger geographical scale.     

The Impacts of Above- and Belowground Plant Input on Soil Microbiota: Invasive <Emphasis Type="Italic">Spartina alterniflora</Emphasis> Versus Native <Emphasis Type="Italic">Phragmites australis</Emphasis>

Invasive plants affect soil food webs through various resource inputs including shoot litter, root litter and living root input. The net impact of invasive plants on soil biota has been recognized; however, the relative contributions of different resource input pathways have not been quantified. Through a 2 × 2 × 2 factorial field experiment, a pair of invasive and native plant species (Spartina alterniflora vs. Phragmites australis) was compared to determine the relative impacts of their living roots or shoots and root litter on soil microbial and nematode communities. Living root identity affected bacteria-to-fungi PLFA ratios, abundance of total nematodes, plant-feeding nematodes and omnivorous nematodes. Specifically, the plant-feeding nematodes were 627% less abundant when living roots of invasive S. alterniflora were present than those of native P. australis. Likewise, shoot and root biomass (within soil at 0–10 cm depth) of S. alterniflora was, respectively, 300 and 100% greater than those of P. australis. These findings support the enemy release hypothesis of plant invasion. Root litter identity affected other components of soil microbiota (that is, bacterial-feeding nematodes), which were 34% more abundant in the presence of root litter of P. australis than S. alterniflora. Overall, more variation associated with nematode community structure and function was explained by differences in living roots than root or shoot litter for this pair of plant species sharing a common habitat but contrasting invasion degrees. We conclude that belowground resource input is an important mechanism used by invasive plants to affect ecosystem structure and function.     

Mechanical stimuli regulate the allocation of biomass in trees: demonstration with young Prunus avium trees

Background and Aims

Plastic tree-shelters are increasingly used to protect tree seedlings against browsing animals and herbicide drifts. The biomass allocation in young seedlings of deciduous trees is highly disturbed by common plastic tree-shelters, resulting in poor root systems and reduced diameter growth of the trunk. The shelters have been improved by creating chimney-effect ventilation with holes drilled at the bottom, resulting in stimulated trunk diameter growth, but the root deficit has remained unchanged. An experiment was set up to elucidate the mechanisms behind the poor root growth of sheltered Prunus avium trees.

Methods

Tree seedlings were grown either in natural windy conditions or in tree-shelters. Mechanical wind stimuli were suppressed in ten unsheltered trees by staking. Mechanical stimuli (bending) of the stem were applied in ten sheltered trees using an original mechanical device.

Key Results

Sheltered trees suffered from poor root growth, but sheltered bent trees largely recovered, showing that mechano-sensing is an important mechanism governing C allocation and the shoot–root balance. The use of a few artificial mechanical stimuli increased the biomass allocation towards the roots, as did natural wind sway. It was demonstrated that there was an acclimation of plants to the imposed strain.

Conclusions

This study suggests that if mechanical stimuli are used to control plant growth, they should be applied at low frequency in order to be most effective. The impact on the functional equilibrium hypothesis that is used in many tree growth models is discussed. The consequence of the lack of mechanical stimuli should be incorporated in tree growth models when applied to environments protected from the wind (e.g. greenhouses, dense forests).Key words: Prunus avium, growth, mechanical stress, bending, biomass, shoot/root ratio, wind, shelter     

Timing of photoperiodic competency causes phenological mismatch in balsam poplar (Populus balsamifera L.)

Plant phenology is expected to be sensitive to climate warming. In boreal trees, spring flush is primarily temperature driven, whereas height growth cessation and autumn leaf senescence are predominantly controlled by photoperiod. Cuttings of 525 genotypes from the full range of balsam poplar were planted into two common gardens (Vancouver and Indian Head, Canada) at similar latitudes, but with differing winter temperatures and growing seasons. There was clinal variation in spring and, particularly, summer and fall phenology. Bud flush and, despite milder climate, bud set and leaf drop were earlier at Vancouver than at Indian Head by 44, 28 and 7 d, respectively. Although newly flushed growth is insensitive to photoperiod, many genotypes at both sites became competent before the summer solstice. At Vancouver, high‐latitude genotypes set dormant terminal buds in mid‐spring. Most other genotypes grew until midsummer or set bud temporarily and then experienced a second flush. In both gardens and in a growth chamber experiment, earlier bud set was associated with reduced height growth and higher root/shoot ratios. Shoots attained competency ～5 weeks after flushing, which would normally prevent dormancy induction before the solstice, but may be insufficient if spring advances by more than a few weeks.     

Asynchronicity in root and shoot phenology in grasses and woody plants

Phenology is central to understanding vegetation response to climate change, as well as vegetation effects on plant resources, but most temporal production data is based on shoots, especially those of trees. In contrast, most production in temperate and colder regions is belowground, and is frequently dominated by grasses. We report root and shoot phenology in 7‐year old monocultures of 10 dominant species (five woody species, five grasses) in southern Canada. Woody shoot production was greatest about 8 weeks before the peak of root production, whereas grass shoot maxima preceded root maxima by 2–4 weeks. Over the growing season, woody root, and grass root and shoot production increased significantly with soil temperature. In contrast, the timing of woody shoot production was not related to soil temperature (r=0.01). The duration of root production was significantly greater than that of shoot production (grasses: 22%, woody species: 54%). Woody species produced cooler and moister soils than grasses, but growth forms did not affect seasonal patterns of soil conditions. Although woody shoots are the current benchmark for phenology studies, the other three components examined here (woody plant roots, grass shoots and roots) differed greatly in peak production time, as well as production duration. These results highlight that shoot and root phenology is not coincident, and further, that major plant growth forms differ in their timing of above‐ and belowground production. Thus, considering total plant phenology instead of only tree shoot phenology should provide a better understanding of ecosystem response to climate change.     

Winter cereal root growth and aboveground–belowground biomass ratios as affected by site and tillage system in dryland Mediterranean conditions

Background and aims

Understanding the interaction between crop roots and management and environmental factors can improve crop management and agricultural carbon sequestration. The objectives of this study were to determine the response of winter cereal root growth and aboveground–belowground biomass ratios to tillage and environmental factors in the Mediterranean region and to test an alternative approach to determine root surface area.

Methods

Winter cereal root growth and biomass ratios were studied in three sites with different yield potential according to their water deficit (high yield potential, HYP; medium yield potential, MYP; low yield potential, LYP) in the Ebro Valley (NE Spain). At all sites, three tillage systems were compared (conventional tillage, minimum tillage, no-tillage (NT)). Root surface density (RSD), soil water content, yield components, and grain yield were quantified and shoot-to-root and grain-to-root ratios were calculated. RSD was measured with the use of image analysis software comparing its performance to a more common intersection method.

Results

Significant differences on RSD between sites with different yield potential were found being the greatest at the HYP site and the lowest at the LYP one. Shoot-to-root ratio was 2.7 and 4.6 times greater at the HYP site than at the MYP and LYP sites, respectively. Moreover, the grain-to-root ratio was significantly affected by site, with a ratio that increased with yield potential. Tillage had no significant effects on RSD at any of the sites studied; however, tillage did affect grain yield, with NT having the greatest yields.

Conclusions

This study shows that in the Mediterranean dryland agroecosystems, winter cereals relative above- and belowground biomass growth is strongly affected by the yield potential of each area. NT in the Mediterranean areas does not limit cereal root growth and leads to greater grain yields. A highly significant linear relationship (P?<?0.001; r ² 0.77) was observed between the root surface values obtained with the free-software image analysis method and the most common intersection method, showing it to be a reliable method for quantifying root density.     

Contrasting effects of warming on pioneer and fibrous roots growth in <Emphasis Type="Italic">Abies faxoniana</Emphasis> seedlings at low and high planting density

Key message

Distinct differences in pioneer and fibrous roots acclimation to climate warming.

Abstract

This study was conducted to determine whether belowground parts of plants at different planting density differ in their responses to elevated temperature (ET). We investigated plant growth, pioneer and fibrous roots growth, root nonstructural carbohydrates, and root colonization of Abies faxoniana seedlings grown in environment-controlled chambers with two different planting densities. Warming has more pronounced positive effects at low density. Although ET did not affect total root biomass, fibrous roots biomass increased under ET at low planting density while pioneer roots biomass was unaffected by ET, indicating that this species may maintain the main framework of the root system with a high capability for water and N absorption under ET. ET increased root nonstructural carbohydrates concentration and ectomycorrhiza colonization in fibrous roots. Increased root nonstructural carbohydrates in response to ET might be associated with the increased roots ectomycorrhizal infection under ET. The present study provided experimental evidence of distinct differences in pioneer and fibrous roots acclimation to climate change.

     

Light energy partitioning,photosynthetic efficiency and biomass allocation in invasive <Emphasis Type="Italic">Prunus serotina</Emphasis> and native <Emphasis Type="Italic">Quercus petraea</Emphasis> in relation to light environment,competition and allelopathy

This study addressed whether competition under different light environments was reflected by changes in leaf absorbed light energy partitioning, photosynthetic efficiency, relative growth rate and biomass allocation in invasive and native competitors. Additionally, a potential allelopathic effect of mulching with invasive Prunus serotina leaves on native Quercus petraea growth and photosynthesis was tested. The effect of light environment on leaf absorbed light energy partitioning and photosynthetic characteristics was more pronounced than the effects of interspecific competition and allelopathy. The quantum yield of PSII of invasive P. serotina increased in the presence of a competitor, indicating a higher plasticity in energy partitioning for the invasive over the native Q. petraea, giving it a competitive advantage. The most striking difference between the two study species was the higher crown-level net CO₂ assimilation rates (A_crown) of P. serotina compared with Q. petraea. At the juvenile life stage, higher relative growth rate and higher biomass allocation to foliage allowed P. serotina to absorb and use light energy for photosynthesis more efficiently than Q. petraea. Species-specific strategies of growth, biomass allocation, light energy partitioning and photosynthetic efficiency varied with the light environment and gave an advantage to the invader over its native competitor in competition for light. However, higher biomass allocation to roots in Q. petraea allows for greater belowground competition for water and nutrients as compared to P. serotina. This niche differentiation may compensate for the lower aboveground competitiveness of the native species and explain its ability to co-occur with the invasive competitor in natural forest settings.