Biomass Investment Research Articles

Leaf area development strategies of cover plants used in banana plantations identified from a set of plant traits

Abstract Cover crops introduced into cropping systems can lead to chemical input reductions and pollution mitigation because they enhance ecological functions. The choice of the best cover crops for a specific cropping system is, however, difficult because of the large range of potential cover species. A promising method involves functional traits as simplified indicators of plant functions. In banana cropping systems, cover crops are used especially to control weeds by development of their leaf area to boost competition for light. The aim of this study was to seek trait-based leaf area development strategies among tropical cover species, based on four plant traits chosen because of their mathematical link with leaf area development: specific leaf area (SLA), aboveground leaf mass fraction (LMFa), seed mass (SM) and aboveground relative growth rate (RGRa). We measured trait values and leaf areas of 17 tropical cover species grown for 1 month in a growth chamber. Strong positive and negative covariations were observed between SM, LMFa and RGRa, revealing a “syndrome” of traits and suggesting trade-offs between traits. Four groups of species were identified based on PCA and cluster analyses and were characterized by significantly different sets of trait values. They showed four leaf area development strategies: species that allocate a large part of biomass to leaf area (G1), species that develop large biomass and leaf area at emergence (G2), species with rapid biomass growth and low biomass investment in leaves (G3) and species with a non-specialized strategy (G4). After 1 month, species of groups G1 and G2 had higher leaf area, although not significantly, than species of groups G3 and G4. Comparisons between this functional classification and the taxonomic monocot/dicot classification showed that the functional classification captured a larger part of the variability in traits involved in leaf area development than the taxonomic monocot/dicot classification. This encourages the use of such a classification to describe plant functioning, to understand plant roles in plant–plant interactions and guide the choice of the best cover species to introduce into cropping systems.

Geographic, environmental and biotic sources of variation in the nutrient relations of tropical montane forests

Abstract:Tropical montane forests (TMF) are associated with a widely observed suite of characteristics encompassing forest structure, plant traits and biogeochemistry. With respect to nutrient relations, montane forests are characterized by slow decomposition of organic matter, high investment in below-ground biomass and poor litter quality, relative to tropical lowland forests. However, within TMF there is considerable variation in substrate age, parent material, disturbance and species composition. Here we emphasize that many TMFs are likely to be co-limited by multiple nutrients, and that feedback among soil properties, species traits, microbial communities and environmental conditions drive forest productivity and soil carbon storage. To date, studies of the biogeochemistry of montane forests have been restricted to a few, mostly neotropical, sites and focused mainly on trees while ignoring mycorrhizas, epiphytes and microbial community structure. Incorporating the geographic, environmental and biotic variability in TMF will lead to a greater recognition of plant–soil feedbacks that are critical to understanding constraints on productivity, both under present conditions and under future climate, nitrogen-deposition and land-use scenarios.

Evaluating general allometric models: interspecific and intraspecific data tell different stories due to interspecific variation in stem tissue density and leaf size.

The ability of general scaling models to capture the central tendency or dispersion in biological data has been questioned. In fact, the appropriate domain of such models has never been clearly articulated and they have been supported and challenged using both interspecific and/or intraspecific data. Here, we evaluate several simplifying assumptions and predictions of two prominent scaling models: West, Brown and Enquist's fractal model (WBE) and a null model of geometric similarity (GEOM). Using data for 53 herbaceous angiosperm species from the Songnen Grasslands of Northern China, we compared both the interspecific and intraspecific scaling relationships for plant geometry and biomass partitioning. Specifically, we considered biomass investment in shoots and leaves as well as related several traits not commonly collected in plant allometric analyses: shoot volume, leaf number, and mean leaf mass. At the interspecific level, we find substantialvariation in regression slopes, and the simplifying assumptions of WBE and predictions of both the WBE and GEOM models do not hold. In contrast, we find substantial support for the WBE model at the intraspecific level, and to a lesser extent for GEOM. The differences between our results at interspecific and intraspecific levels are due to the fact that leaf size and stem tissue density vary considerably across species in contrast to the simplifying assumptions of WBE. These results highlight the domain within which simplifying model assumptions might be most appropriate, and suggest allometric models may be useful points of departure within some species, growth forms or taxonomic groups.

Interactions among cluster-root investment, leaf phosphorus concentration, and relative growth rate in two Lupinus species.

Cluster-root (CR) formation is a desirable trait to improve phosphorus (P) acquisition as global P resources are dwindling. CRs in some lupine species are suppressed at higher P status. Whether increased growth rate enhances CR formation due to a "dilution" of leaf P concentration is unknown. We investigated interactive effects of leaf P status and relative growth rate (RGR) on CR formation in two Lupinus species, which differ in their CR biomass investment. Variation in RGR was imposed by varying day length. Lupinus albus and L. pilosus were grown hydroponically with KH2PO4 at a day length of 6, 10, or 14 h. We used a slightly higher P supply at longer day lengths to avoid a decline in leaf P concentration, which would induce CRs. Cluster-root percentage, leaf P concentrations, and RGR were determined at 22, 38, and 52 d after sowing. Lupinus species grown at similar root P availability, but with a faster growth rate, as dependent on day length, showed a greater CR percentage. Because our aim to achieve exactly the same leaf P concentrations at different day lengths was only partially achieved, we carried out a multiple regression analysis. This analysis showed the CR percentage was strongly and negatively correlated with plant P status and only marginally and positively correlated with RGR. The two Lupinus species invariably formed fewer cluster roots at higher leaf P status, irrespective of RGR. Differences in RGR or leaf P concentration cannot explain the species-specific variation in cluster-root investment.

Assessing the Determinants of Renewable Electricity Acceptance Integrating Meta-Analysis Regression and a Local Comprehensive Survey

In dealing with renewable electricity (RE), individuals are involved both as end-consumers on the demand side and as stakeholders (citizens) in the local production process on the supply side. Empirical evidence shows that in many countries, consumers are willing to pay a significant amount to facilitate adoption of RE. By contrast, environmental externalities are often the cause of strong opposition to RE adoption if local communities are involved as stakeholders in wind, solar or biomass investment projects. Looking at the literature on willingness to pay and on willingness to accept, we have investigated RE acceptance mechanisms. First, we have used the meta-analysis to assess the major determinants of RE acceptance on both demand and supply sides. Meta-analysis has provided some insights useful for managing field research on an onshore wind farm enlargement project located in the Umbria region. Meta-analysis and survey results confirm that the local community plays a central role in local RE acceptance. Furthermore, people who have previous experience with windmills require less compensation, or are willing to pay more, for RE development. Results suggest that these attributes should be included in future research to improve understanding of determinants of RE acceptance.

Impacts of drought and nitrogen addition onCallunaheathlands differ with plant life‐history stage

SummaryClimate change and atmospheric deposition of nitrogen (N) affect the biodiversity patterns and functions of ecosystems world‐wide. While many single‐factor studies have quantified ecosystem responses to single global change drivers, less is known about the interaction effects of these drivers on ecosystem functions.Here, we present the results of a three‐year field and a two‐year glasshouse experiment, in which we assessed responses ofCalluna vulgarisheathlands to the single and combined effects of drought events (D) and N fertilization (D: 25% precipitation reduction in the field experiment and 20–50% soil water content reduction in the glasshouse experiment; N fertilization: 35 kg N ha−1 year−1).We examined the effects of D and N treatments on growth responses of the dominant dwarf shrubCalluna vulgaris(in terms of biomass production and allocation, tissue δ13C signatures and C:N ratios) in relation to two plant life‐history stages and different ‘ecotypes’ (sub‐Atlantic vs. subcontinental heathlands).Plant responses varied strongly with life‐history stage, and the interaction of N and D showed lower effects than would be expected based on additive responses to single factors. While D treatments had no effects onCallunain the building phase (ca. ten‐year‐old plants), seedlings (particularly one‐year‐old plants) were highly susceptible to drought. Differences in response patterns were attributable to the high shoot–root ratios typical of youngCallunaplants. These ratios decreased with progressing life history as a result of increasing below‐ground biomass investments. Below‐ground biomass production and shoot–root ratios differed between plants from the different heathland sites.Tissue δ13C signatures decreased and C:N ratios increased with plant age as a result of decreasing evaporative demands (per unit root biomass). N fertilization increases the shoot–root ratios and thereby the drought susceptibility ofCallunaplants.Synthesis. Our findings suggest that plant responses to global change are difficult to anticipate by means of single‐factor studies or by focusing on a single life‐history stage. This highlights the need for global change research to include multiple factors and life‐history stages when assessing an ecosystem's susceptibility to shifts in environmental conditions.

The underlying basis for the trade‐off between leaf size and leafing intensity

Summary Recent studies have reported a consistent trade‐off between leaf size (mass) and leafing intensity (the number of leaves produced per unit of supporting stem tissue volume); however, a theoretical basis for this trade‐off has not been described. We explore the mechanistic basis for this trade‐off and assess the relationship in the light of other prominent theories for allometric biomass partitioning. We show algebraically how the allocation of mass to leaves versus stems and the density of stem tissue can potentially influence this trade‐off. To assess these possible effects, we compared the relationship between leaf size and leafing intensity, expressed on both mass and volume basis, at the level of a single branch as well as the entire above‐ground plant in 61 forbs over a 3‐year period. Our results support the idea that the trade‐off between leaf size and volume‐based leafing intensity depends on both biomass investment (leaves vs. stems) and stem bulk density (mass vs. volume), whereas the trade‐off between leaf size and mass‐based leafing intensity only depends on the biomass investment. Similar exponents in the scaling of leaf mass vs. stem mass and stem mass vs. stem volume at branch and whole plant levels lead to similar trade‐offs. An isometric trade‐off between leaf size and volume‐based leafing intensity is consistent with a constant biomass partitioning between leaves and stems as well as constant stem tissue density. Conversely, an allometric trade‐off between leaf size and volume‐based leafing intensity arises when biomass allocation is allometric and stem bulk density varies with plant size.

Recurrent Water Level Fluctuation Alleviates the Effects of Submergence Stress on the Invasive Riparian Plant Alternanthera philoxeroides.

Recurrent water level fluctuation and submergence of plants are common in riparian zones. Our study objectives were to test the independent and interactive effects of submergence level and fluctuation frequency on a globally important riparian invasive plant, Alternanthera philoxeroides. To this end, we conducted a greenhouse experiment, in which ramets of the plants, obtained from a wetland in China, were treated with four fluctuation frequencies (0, 3, 6, and 12 cycles over a 96-day experimental period) under three water levels (0, 10, and 30 cm). We found that effects of fluctuation frequency were non-significant, negative, and positive under water levels of 0, 10 and 30 cm, respectively. As fluctuation frequency increased, the effects of increasing water level decreased significantly. When water levels were high, A. philoxeroides allocated greater biomass to shoot production probably in order to elongate and escape from submergence. However, as fluctuation frequency increased, biomass investment in roots and leaves also increased, probably in order to maximize nutrient absorption and photosynthesis, respectively. These results suggest that water level fluctuation may alleviate the effects of submergence on A. philoxeroides. In addition, A. philoxeroides showed significant phenotypic plasticity, adjusting its functional traits, such as number of nodes and leaves per stem, as well as stem diameter and pith cavity diameter, according to recurrent water level fluctuation. We conclude that A. philoxeroides may perform better in shallow water zones under conditions of disturbance that include recurrent water level fluctuation. This ability to adapt to disturbance likely promotes its growth and invasion in disturbed habitats.

Leaf Mass Per Area (LMA) as a Possible Predictor of Adaptive Strategies in Two Species ofSesleria(Poaceae): Analysis of Morphological, Anatomical and Physiological Leaf Traits

Leaf mass per area (LMA) is an important variable in a set of coordinated leaf traits to determine plant species' ecological strategies. We hypothesized that LMA was the main predictor of the adaptive strategies of Sesleria juncifolia and S. nitida (Poaceae), growing on Mount Terminillo (Central Apennines) and cultivated ex situ. We broke LMA down into leaf anatomical components (i.e. leaf tissue density and thickness) and then related them to physiological traits. We found that the different habitats of the two species determine a different control of the anatomical components of the LMA variation. These differences are related to photosynthetic capacity, scaling linearly with leaf biomass investment per unit leaf area. On the whole, our study, taking into account the changes in LMA and its anatomical components, provides a trait framework which could be used to analyze adaptive strategies of other species in dry, mountain grasslands.

Application of micro-computed tomography to microstructure studies of the medicinal fungus Hericium coralloides

The potential of 3-D nondestructive imaging techniques such as micro-computed tomography (micro-CT) was evaluated to study morphological patterns of the potential medicinal fungus Hericium coralloides (Basidiomycota). Micro-CT results were correlated with histological information gained from scanning electron microscopy (SEM) and light microscopy (LM). It is demonstrated that the combination of these imaging methods results in a more distinct picture of the morphology of the edible and potentially medicinal Hericium coralloides basidiomata. In addition we have created 3-D reconstructions and visualizations based on micro-CT imagery from a randomly selected part of the upper region of a fresh H. coralloides basidioma: Analyses for the first time allowed an approximation of the evolutionary effectiveness of this bizarrely formed basidioma type in terms of the investment of tissue biomass and its reproductive output (production of basidiospores).

Analysis of Tanzanian Biomass Consumption Using Artificial Neural Network

The growing biomass consumption in developing countries context is being driven by a mixture of concerns over energy security, sustainable development and the climate change mitigation. The development of the comprehensive, sustainable and efficient biomass energy sector policies, strategies and investments requires proper biomass utilization and planning which in fact has not yet received the attention it deserves in the developing countries policies. This paper aims are twofold; one being to demonstrate the practicability of the application of artificial neural network multilayer perceptron (ANN-MLP) in the analysis of the biomass energy consumption and two, to identify the demographic and economic indicators which works better in the analysis and prediction of biomass consumption in Tanzania. Three models made up of Tanzania rural, Tanzania urban and Tanzania population with the addition of economic indicators were formulated for the analysis. The ANN-MLP has shown promising results with the statistical correlation coefficient of 0.9972 indicating that it can be used for practical analysis and prediction of biomass energy consumption. Furthermore the results show the use of Tanzania population model in the analysis and prediction of biomass consumption gives better results in comparison to the Tanzania rural and Tanzania urban population models individually.

Ecophysiology of four co-occurring lycophyte species: an investigation of functional convergence.

Lycophytes are the most early divergent extant lineage of vascular land plants. The group has a broad global distribution ranging from tundra to tropical forests and can make up an important component of temperate northeast US forests. We know very little about the in situ ecophysiology of this group and apparently no study has evaluated if lycophytes conform to functional patterns expected by the leaf economics spectrum hypothesis. To determine factors influencing photosynthetic capacity (Amax), we analysed several physiological traits related to photosynthesis to include stomatal, nutrient, vascular traits, and patterns of biomass distribution in four coexisting temperate lycophyte species: Lycopodium clavatum, Spinulum annotinum, Diphasiastrum digitatum and Dendrolycopodium dendroideum. We found no difference in maximum photosynthetic rates across species, yet wide variation in other traits. We also found that Amax was not related to leaf nitrogen concentration and is more tied to stomatal conductance, suggestive of a fundamentally different sets of constraints on photosynthesis in these lycophyte taxa compared with ferns and seed plants. These findings complement the hydropassive model of stomatal control in lycophytes and may reflect canalization of function in this group. Our data also demonstrate functional ecological similarities: De. dendroideum and D. digitatum are species that have substantial belowground biomass investment and are consistently more similar to each other across multiple traits than either is to the more surficial S. annotinum and L. clavatum. Such differences may partition environments in ways that allow for the close coexistence of these species.

Cohort-specific tuning of foliage physiology to interacting stresses in evergreens.

Leaf economics spectrum is the basic concept linking leaf carbon gain strategies, fast vs slow turnover, to foliage functional traits (Wright et al. 2004). At the heart of the economics spectrum is the reverse correlation among traits responsible for leaf longevity and physiological activity; thus, high leaf longevity in evergreens is associated with traits improving leaf robustness such as high leaf dry mass per unit area and density reflecting enhanced biomass investment in support biomass (Wright et al. 2004). Increased support investments inevitably result in low photosynthetic capacity per dry mass placing evergreens towards the slow return end of the leaf economics spectrum (Wright et al. 2004, Reich 2014). The economics spectrum describes the basic co-variation patterns among leaf functional traits across plant functional types, but it does not implicitly consider several potentially confounding sources of variation such as leaf age (e.g., Niinemets 2014). Evergreens characteristically support multiple leaf age classes with potentially contrasting structural, chemical and physiological characteristics, but due to practical reasons, often only the leaves from the newest fully mature leaf flush are included in analyses involving evergreens. However, older leaves contribute a major proportion of total canopy leaf area in many evergreens (Whitehead et al. 1994, Niinemets et al. 2005), implying that age-specific differences in foliage performance play a major role in whole canopy carbon gain. While the basic age-dependent modifications in foliage functional traits have been studied in evergreens (Kitajima et al. 1997a, Radoglou and Teskey 1997, Ellsworth 2000, Niinemets and Lukjanova 2003, McGarvey et al. 2004, Niinemets et al. 2005), there is limited information on responses of different-aged leaves to environmental stresses with a few exceptions (e.g., Mulkey et al. 1992, Ogaya and Penuelas 2006). Many evergreen species also have a complex phenology of foliage development characterized by multiple foliage flushes during the same growing season. In this issue of Tree Physiology, the study of Morales et al. (2014) conducted in a Chilean temperate rain forest with the evergreen relatively shade-intolerant species Eucryphia cordifolia Cav. demonstrates that seasonality in environmental conditions can strongly affect foliage growth and development as well as physiological potentials of fully mature leaves. They observed major differences in leaf structural, chemical and physiological traits among leaf flushes produced during a given growing season (Figure 1, Morales et al. 2014). Such flush-specific differences in foliage characteristics have been observed in several warm temperate and subtropical conifers (Whitehead et al. 1994, Teskey 1997, Niinemets et al. 2002, McGarvey et al. 2004) and in evergreen angiosperms in climates with seasonal distribution of precipitation (Mulkey et al. 1992, Kitajima et al. 1997b), and collectively emphasize the importance of the timing of leaf flush in foliage functioning. The study of Morales et al. (2014) further found that differences among leaf cohorts in E. cordifolia were amplified in the low-light environment and under water stress (Figure 1). Although stress led to immediate physiological adjustments such as changes in stomatal conductance, the scaling among foliage physiological potentials (maximum carboxylase activity of Rubisco) and leaf nitrogen content was also altered (Figure 1). Such modifications in foliage functioning to stress during foliage growth suggest that the timing of leaf flush is an important driver altering the leaf economics spectrum in Commentary Tree Physiology Advance Access published November 25, 2014

Invasion of Spartina alterniflora in China is greatly facilitated by increased growth and clonality: a comparative study of native and introduced populations

Different mechanisms have been proposed to explain invasion success of alien species, among which genetic differentiation and phenotypic plasticity are extensively studied. In order to explore whether the invasion of Spartina alterniflora is facilitated by enhanced phenotypes or trait plasticity, we conducted a common garden experiment on this clonal invasive plant, in which three native populations (from the US) and eight introduced populations (from China) were included and grown at two water levels. We measured their plant traits related to growth, reproductive phenology, reproductive output, and their plasticity in response to water availability. No difference in plant height was observed between native and introduced populations of S. alterniflora, but introduced populations had greater total biomass than the native ones at high water level. Reproductive performances facilitating invasion success were also found for introduced populations, indicated by the advanced initiation of phenological events, greater total number of ramets, and more investment of total biomass in rhizomes versus stalk and leaf in both water treatments. Finally, a non-significant difference in inflorescence biomass for flowering individuals and phenotypic plasticity of most measured traits was observed between native and introduced populations. In conclusion, enhanced growth and asexual reproduction make greater contributions to the invasion success of S. alterniflora in China.

Growth, phenology, and biomass allocation of alien Solidago species in central Europe

AbstractPlant invasion is a major threat to the integrity of an ecosystem. Exceptionally successful invaders in Europe are the American species of Solidago genus. In this study we examined growth, reproduction, and phenology of Solidago species, of American origin, growing in central Europe (S. altissima, S. canadensis, S. gigantea, S. graminifolia). These taxa were compared with two native species: Solidago virgaurea and Tanacetum vulgare. We observed high differentiation in height, number of shoots, and biomass production between individuals within taxa. Generally, the invasive species produced substantially (two to five times) more biomass than the native ones, being statistically significant in the comparison of alien Solidago graminifolia and S. gigantea versus native S. virgaurea and T. vulgare. The ratio of biomass of reproductive parts to overall biomass varied considerably among years, but generally the lowest one was for Solidago altissima, and the highest for S. graminifolia. It shows a lack of a clear pattern of differentiation between alien and native species in terms of biomass investment in reproduction. We observed a general tendency of allocation of a major part of biomass in rhizomes by phalanx species (S. graminifolia and S. gigantea), while species with guerrilla strategy (S. altissima and S. canadensis) invested more biomass in stems and leaves. However, because of the high variability there was no clear, stable pattern of statistically significant differences between these two groups. The results suggest that S. graminifolia reveals a strong potential of invasion, in spite of its, so far limited, distribution in Europe.

Divergent functioning of Proteaceae species: the South AmericanEmbothrium coccineumdisplays a combination of adaptive traits to survive in high‐phosphorus soils

SummaryProteaceae species in south‐western Australia thrive on phosphorus‐impoverished soils, employing a phosphorus‐mining strategy involving carboxylate‐releasing cluster roots. Some develop symptoms of phosphorus toxicity at slightly elevated soil phosphorus concentrations, due to their low capacity to down‐regulate phosphorus uptake. In contrast, Proteaceae species in Chile, e.g.Embothrium coccineumJ.R. Forst. & G. Forst., occur on volcanic soils, which contain high levels of total phosphorus, but phosphorus availability is low.We hypothesised that the functioning of cluster roots ofE. coccineumdiffers from that of south‐western Australian Proteaceae species, in accordance with the difference in soil phosphorus status. With more phosphorus to be gained from the soil with high levels of total phosphorus, we expect less investment in biomass and more release of carboxylates. Furthermore, we hypothesised thatE. coccineumregulates its phosphorus‐uptake capacity, avoiding phosphorus toxicity when grown at elevated phosphorus levels. To test these hypotheses,E. coccineumseedlings were grown at a range of phosphorus supplies in nutrient solution.We show thatE. coccineumallocated at least five times less biomass to cluster roots that released at least nine times more carboxylates per unit cluster root weight compared with south‐western Australian species (e.g.Banksia,Hakea). The highest phosphorus supply caused a growth inhibition and high leaf phosphorus concentration, without symptoms of phosphorus toxicity. We accept our hypotheses on the functioning of cluster roots and the high capacity to reduce the net phosphorus uptake in plants grown at a high‐phosphorus supply.This novel combination of traits indicates divergent functioning of Proteaceae species from southern South America, exposed to frequent phosphorus input due to volcanic activity, in contrast with the functioning of south‐western Australian Proteaceae species that thrive on severely phosphorus‐impoverished soils. These traits could explain the functioning ofE. coccineumon soils that are rich in total phosphorus, but with a low concentration of available phosphorus.

Symbiosis with Frankia sp. benefits the establishment of Alnus viridis ssp. crispa and Alnus incana ssp. rugosa in tailings sand from the Canadian oil sands industry

Canada's oil sands reserves found in an area of about 142,000km2 in Northern Alberta are estimated to be about 170 billion barrels. Extraction procedures generates oil sands process-affected materials (OSPM), a high pH, high salt and low nutrient residue which contains phytotoxic hydrocarbons. Efficient methods are needed to revegetate impacted landscapes in line with governmental standards. Actinorhizal alders could be used to provide nitrogen in a reclamation program as they are early successional species that naturally colonize harsh habitats and improve the soil conditions. In order to evaluate the extent to which alders can withstand OSPM-generated stress, the growth and development of both green (Alnus viridis (Chaix) DC. ssp. crispa) and speckled (Alnus incana (L.) Moench ssp. rugosa) alders in varying proportions of OSPM mixed with pristine sand (from 0 to 100 %) was assessed both in the presence and the absence of their symbiont, Frankia sp. Alder survival was not impaired by the presence of OSPM, although symbiosis establishment was less efficient when the alders grew in pure OSPM residue. Actinorhizal alders are very tolerant to OSPM: when grown in pure OSPM (100%), their dry biomass was 15 times greater than that of non-nodulated alders. Moreover, symbiotic alders allocated a higher proportion of their biomass to aerial parts, regardless of the OSPM percentage, whereas non-symbiotic alders showed a greater biomass investment in roots. When symbiosis was present, the alders thrived and produced a large amount of biomass that was highly correlated to the total nodule biomass. The pre-inoculation of alder seedlings in commercial greenhouses prior to their outplanting on OSPM-affected reclamation sites could significantly accelerate their growth and development.

Genotypic differences in deep water extraction associated with drought tolerance in wheat.

The ability of roots to extract soil moisture is critical for maintaining yields during drought. However, the extent of genotypic variation for rooting depth and drought tolerance in Northern European wheat (Triticum aestivum L.) germplasm is not known. The objectives of this study were to measure genotypic differences in root activity, test relationships between water use and yield, examine trade-offs between yield potential and investment of biomass in deep roots, and identify genotypes that contrast in deep root activity. A diverse set of 21 wheat genotypes was evaluated under irrigated and managed drought conditions in the field. Root activity was inferred from patterns of water extraction from the soil profile. Genotypes were equally capable of exploiting soil moisture in the upper layers, but there were significant genotypic differences in rates of water uptake after anthesis in deeper soil layers. For example, across the three years of the study, the variety Xi19 showed consistently deeper root activity than the variety Spark; Xi19 also showed greater drought tolerance than Spark. There were positive correlations between water extraction from depth and droughted yields and drought tolerance, but correlations between deep water use and yield potential were not significant or only weakly negative. With appropriate screening tools, selection for genotypes that can better mine deep soil water should improve yield stability in variable rainfall environments.

Functional trait trade-offs for the tropical montane rain forest species responding to light from simulating experiments.

Differences among tropical tree species in survival and growth to light play a key role in plant competition and community composition. Two canopy species with contrasting functional traits dominating early and late successional stages, respectively, in a tropical montane rain forest of Hainan Island, China, were selected in a pot experiment under 4 levels of light intensity (full, 50%, 30%, and 10%) in order to explore the adaptive strategies of tropical trees to light conditions. Under each light intensity level, the pioneer species, Endospermum chinense (Euphorbiaceae), had higher relative growth rate (RGR), stem mass ratio (SMR), specific leaf area (SLA), and morphological plasticity while the shade tolerant climax species, Parakmeria lotungensis (Magnoliaceae), had higher root mass ratio (RMR) and leaf mass ratio (LMR). RGR of both species was positively related to SMR and SLA under each light level but was negatively correlated with RMR under lower light (30% and 10% full light). The climax species increased its survival by a conservative resource use strategy through increasing leaf defense and root biomass investment at the expense of growth rate in low light. In contrast, the pioneer increased its growth by an exploitative resource use strategy through increasing leaf photosynthetic capacity and stem biomass investment at the expense of survival under low light. There was a trade-off between growth and survival for species under different light conditions. Our study suggests that tree species in the tropical rainforest adopt different strategies in stands of different successional stages. Species in the earlier successional stages have functional traits more advantageous to grow faster in the high light conditions, whereas species in the late successional stages have traits more favorable to survive in the low light conditions.

Adaptation of biomass allocation patterns of wild Fritillaria unibracteata to alpine environ-ment in the eastern Qinghai-Xizang Plateau

Aims Under different selection stresses, alpine plants tend to adjust their biomass investments to different functions and/or organs, and this biomass allocation strategy presents different patterns during different life history stages of plants. Our objective is to address three hypotheses regarding Fritillaria unibracteata: 1) elevation gradients impact individual bulb biomass and individual total biomass; 2) biomass allocation adapts to the elevational change of environmental factors; and 3) biomass allocation at different life history stages show different patterns. Methods We collected wild F. unibracteata at different elevations in the alpine belt of Songpan County in the eastern Tibetan Plateau. The samples were cleaned and divided into different organs, the biomasses of which were then weighed after being dried in the oven. Important finding Elevation significantly affected individual bulb biomass (IBB) and individual total biomass (ITB), both of which decreased gradually with increased elevation. Elevation representing the heat factor was the pivotal factor limiting the growth of alpine plants such as F. unibracteata. For plants with different life history stages, their biomass allocation presented diverse patterns. First, the bulb biomass allocation (BBA) of 2-year-old F. unibracteata significantly decreased with increased elevation, but its leaf biomass allocation (LBA) increased. Second, both BBA and LBA of 3-and 4-year-old F. unibracteata were relatively stable at different elevations, but their stem biomass allocation (SBA) significantly decreased with increased elevation. In contrast, the sexual reproductive (flower) allocation (SRA) significantly increased with increased elevation. Third, at different life history stages, the root biomass allocation (RBA) of F. unibracteata was relatively stable at different elevations. Both RBA and SBA showed an increasing trend with the growth of plants, but BBA and LBA showed a decreasing trend.Three-year-old individuals normally had the maximum IBB.