Higher Specific Leaf Research Articles

Trait-based responses to cessation of nutrient enrichment in a tundra plant community

Plant communities worldwide show varied responses to nutrient enrichment—including shifts in species identity, decreased diversity, and changes in functional trait composition—but the factors determining community recovery after the cessation of nutrient addition remain uncertain. We manipulated nutrient levels in a tundra community for 6 years of nutrient addition followed by 8 years of recovery. We examined how community recovery was mediated by traits related to plant resource-use strategy and plant ability to modify their environment. Overall, we observed persistent effects of fertilization on plant communities. We found that plants with fast-growing traits, including higher specific leaf area, taller stature and lower foliar C:N, were more likely to show a persistent increase in fertilized plots than control plots, maintaining significantly higher cover in fertilized plots 8 years after cessation of fertilization. Additionally, although graminoids responded most strongly to the initial fertilization treatment, forb species were more vulnerable to fertilization effects in the long-term, showing persistent decline and no recovery in 8 years. Finally, these persistent fertilization effects were accompanied by modified environmental conditions, including persistent increases in litter depth and soil phosphorous and lower soil C:N. Our results demonstrate the potential for lasting effects of nutrient enrichment in nutrient-limited systems and identify species traits related to rapid growth and nutrient-use efficiency as the main predictors of the persistence of nutrient enrichment effects. These findings highlight the usefulness of trait-based approach for understanding the persistent feedbacks of nutrient enrichment, plant dynamics, and niche construction via litter and nutrient build-up.

Nitrogen/potassium interactions increase rice yield by improving canopy performance

AbstractThe interactions between nitrogen (N) and potassium (K) are important determinants of rice yield, but the mechanisms involved remain poorly understood. For example, N/K interactions may influence light utilization and N distribution in the canopy. Field experiments were therefore performed to resolve this issue, using factorial combination of N and K. The interaction between N and K had a significant effect on the grain yield, N uptake, and the NUE of grain production (NUEg), and biomass production (NUEb). The application of either N or K alone resulted in lower yields than the combined application of these nutrients. The combined application of N and K increased rice yields by 54.5% in 2018 and by 76.1% in 2019, compared with N0K0. Similarly, N uptake, NUEg, and NUEb were higher when N was supplied with K than with N application alone. The higher grain yields, N uptake rates, and NUEs observed with the combined N and K treatment were attributed to the following: (1) a higher leaf area index that resulted in better light interception; (2) improved the coordination of light and N distribution within the canopy. Evidence for improved light use by photosynthesis is provided by the observed lower light extinction coefficient (KL), the higher specific leaf N in the top leaves (SLNo), higher extinction coefficients for effective leaf N (KN) and KN/KL values. We conclude that the interactions between N and K support higher yields by improving canopy performance even at lower N rates.

Induced mutagenesis for improving water stress tolerance in durum wheat (Triticumturgidum L. subsp. durum)

Over the Water deficit is considered to be one of the most important limiting factors for crop productivity worldwide. Thus, it is important to use water resources more efficiently. One of the ways to conserve water and respond to the climate change is by using appropriate crop species and cultivars, notably which have low requirements for water.Chemical mutagens have contributed immensely to the development of a wide range of genetic variability and the improvement of several crop plants, including durum wheat. This study has the aim of understanding the effect of water stress on some morpho-physiological parameters and identifying tolerant lines to water stress from an EMS-mutated population in durum wheat. The results, under moderate (T1) and severe (T2) conditions of water stress,show the positive effect of mutagenesis on the population resulting in tolerantmutated linesto water deficit. Compared to the non-mutated, 32.15% of lines have a higher specific leaf weight; 57.14% of lines have a better ability to maintain a high water content and 75% of all lines demonstrate a very high intensity of chlorophyll fluorescence .In sum, this study has revealed the improvement of water stress tolerance in some induced durum wheat mutants.

Efecto de bacterias emulsificantes en la atenuación de la fitotoxicidad de suelos contaminados con petróleo intemperizado

Introduction: Plants and microorganisms have been used as bioindicators to evaluate the toxicity of hydrocarbons in soils. Objective: This study evaluates the toxicity of a chronically-contaminated Gleysol with several concentrations of weathered petroleum hydrocarbons (WPH), collected from La Venta, Tabasco (Mexico), on the growth of Clitoria ternatea and the phytoxicity attenuation due to inoculation of emulsifying bacteria. Methods: Soils with 50 and 150 g WPH kg-1, and control soil with 0.15 g WPH kg-1 (biogenic origin) were utilized, as well as the inoculation of six emulsifying bacteria and their combination (consortium). The WPH-phytotoxicity was evaluated by considering plant height, dry biomass production (root, shoot, and total), leaf area, specific leaf area, and the efficiency of photosystem II (EPSII), after 30 days. Results: WPH did not affect plant height, but soil with 50 g WPH kg-1 diminished root and total dry weight, and leaf area, when compared to both control soil and soil with 150 g WPH kg-1. The strain Sml (Stenotrophomonas maltophilia C10S1) significantly increased shoot and total dry weight, while the strain Ro (Raoultella ornithinolytica C5S3) produced higher specific leaf area relative to uninoculated plants. In control soil, the bacterial consortium stimulated plant height. The strains Sm (Serratia marcescens C11S1) and Sm2 (S. marcescens C7S3) improved plant height and specific leaf area when compared to uninoculated plants in soil with 50 g WPH kg-1. In soil with 150 g WPH kg-1, strains Spa (Stenotrophomonas pavanii C5S3F) and Cfr (Citrobacter freundii C4S3) enhanced root and shoot dry weight, respectively. The EPSII was unaffected by soil contamination. Emulsifying bacteria reduced the phytotoxic effects of WP, but depending on the content of WPH in soils. Conclusions: Soil with 50 g WPH kg-1 showed the greatest phytotoxic effects on plant growth. Bacterial inoculation favored growth, biomass production and leaf area in soil with 150 g WPH kg-1. The EPSII was not affected by WPH in soils.

Shifts in Phenology and Plant Architecture across Genus Rhododendron Highlight Different Ways to Become More Acquisitive despite Universally Conservative Xylem Anatomy

Premise of research. Across the leaf economics spectrum, leaves with higher specific leaf area (SLA) have higher transpiration rates, so xylem water transport capacity should be higher for species ...

Dry matter partitioning and K distribution of vegetable soybean genotypes with higher potassium efficiency

ABSTRACTField and pot experiments were conducted to select and identify the characteristics of potassium (K) high efficiency vegetable soybean genotypes. Forty genotypes under two potassium application levels (0, 120 kg ha−1 K2SO4) showed variations in K concentration, K accumulation, K internal use efficiency (KIUE) and K harvest index (KHI) in field experiment conducted in 2016. According to the distinct KIUE for yield (KIUE-Y) and KHI, two K high efficiency (KHE) genotypes (T117, L113) and two K low efficiency (KLE) genotypes (DZ1, ZX8) were used in pot experiment with two K levels (0, 120 kg ha−1 K2SO4) in 2017 for further investigation. Results indicated that KIUE-Y was significantly correlated with harvest index (HI) and KHI. Both K and dry matter (DW) were optimally distributed in the seed of KHE genotypes. In contrast, more DW and K were accumulated in vegetative organs of KLE genotypes, which was the main reason limiting K efficiency. Under K deficiency, KHE genotypes better regulate their DW and K distribution, and have higher specific leaf weight with unaffected leaf area.

Short‐term responses in a secondary tropical forest after a severe windstorm event

AbstractQuestionsHow do abiotic conditions, forest structure, as well as taxonomic and functional diversities and composition recover after wind‐generated treefalls? Do young and old‐growth secondary forests differ in their responses?LocationMandai region of the Central Catchment Nature Reserve, Singapore, where extensive treefalls occurred during an unusually powerful windstorm in 2011. Southeast Asia.MethodsSoil nitrogen, phosphorous, potassium, canopy cover, leaf litter depth, coarse woody debris, and woody stems ≥1‐cm diameter were measured and identified in 10 × 10 m plots. Twenty‐six plots were located in treefall areas and 14 plots were located in relatively unaffected areas, with equal numbers in young and old‐growth secondary forest types. The first round of surveys took place within 3–6 months of the windstorm event and yearly re‐surveys were conducted until 2015. Specific leaf area, leaf dry matter content, leaf thickness, woody density, maximum plant height, and seed dry mass were measured or derived from various sources.ResultsThere was a pulse of soil nutrient availability in both affected and unaffected areas 1 year after the wind event. Canopy cover and basal area in the affected areas recovered to similar levels as unaffected areas by the second year, and coarse woody debris by the fourth year. In affected plots, taxonomic and functional diversities increased and overshot that of—and taxonomic composition diverged from—unaffected plots after the second year. Young and old‐growth secondary forest types mainly differed in the taxonomic composition of new recruits. However, there was no evidence of changes in functional composition towards resource‐acquisitive strategies such as lower wood density or higher specific leaf area.ConclusionsAbiotic conditions and basal area recovered rapidly within 2–4 years after the windstorm. Taxonomic composition in young and old‐growth affected forests both diverged from unaffected forests but also from each other over time.

PESO ESPECÍFICO DE HOJA Y CONCENTRACIÓN DE NITRÓGENO DURANTE LA FENOLOGÍA DEL CIRUELO JAPONÉS CV. METHLEY

Objetivo: Conocer las tendencias y efectos del Peso Específico de Hoja y Concentración de Nitrógeno en Hojas en la fenología del ciruelo japonés cv. Methley.Diseño/metodología/aproximación: A través de un muestreo por cuotas fueron seleccionados veinte árboles sanos con íntegra estructura general. Se determinaron las fechas de inicio y fin de las fases fenológicas. Se realizaron correlaciones estadísticas del Peso Específico de Hoja y Concentración de Nitrógeno en Hojas con fases fenológicas que supusieron una lógica relación entre variables y una distribución bivariada. El grado y tipo de asociación entre variables fue analizado a través de coeficientes de correlación de Spearman mediante el procedimiento SAS|CORR en SAS_studio UniversityVersion 2016 para Windows.Resultados: El mayor Peso Específico de Hoja en 2015 y 2016 ocurrió durante madurez de cosecha, y en ambos años disminuyó durante el último periodo del crecimiento vegetativo; este índice está significativamente correlacionado con el crecimiento vegetativo y de frutos. En 2015 y 2016, la mayor Concentración de Nitrógeno en Hojas ocurrió durante madurez de cosecha; en ambos años la menorConcentración de Nitrógeno en Hojas ocurrió durante la última etapa del crecimiento y desarrollo de frutos; este índice tiene una significativa correlación negativa con el crecimiento vegetativo y de frutos.Limitaciones del estudio/implicaciones: Tanto el Peso Específico de Hoja como la Concentración de Nitrógeno en Hoja disminuyeron durante el crecimiento y desarrollo de frutos, afectando el porcentajede amarre de estos.Hallazgos/conclusiones: La acumulación radical influye en la disminución del Peso Específico de Hoja y Concentración de Nitrógeno en Hojas en ciruelo japonés cv. Methley.

Stomatal aperture rather than nitrogen nutrition determined water use efficiency of tomato plants under nitrogen fertigation

Fertigation can improve water use efficiency (WUE) compared with conventional separate supply of water and fertilizers to plants. Yet the mechanisms underlying the improved WUE under fertigation remain largely elusive. Therefore, the impact of water and nitrogen (N) on leaf gas exchange, plant water relations, ABA signaling and WUE as well as leaf δ13C and δ18O were investigated in order to unravel how water and N modulate plant WUE. Results showed that reduced soil water regimes under N fertigation caused partial closure of stomata via decreased plant water status and intensified root-to-shoot ABA signaling, resulting in improved intrinsic WUE (WUEi). Decreased soil water regimes increased plant WUE (WUEp) and leaf δ13C, and the increased leaf δ13C was due to reduced gs and/or higher specific leaf N content enhanced photosynthetic capacity. Leaf δ18O and δ13C further indicated that the significant increase in leaf δ13C under the reduced water regimes was caused primarily by reductions in gs compared with N nutrition. Therefore, gs rather than N nutrition predominated regulation of plant WUE under fertigation. Moderate soil water regimes with sufficient N supply are recommended for fertigation in terms of achieving high fresh fruit yield, WUE and nutrient uptake.

Photosynthetic acclimation of Grammatophyllum speciosum to growth irradiance under natural conditions in Singapore

Grammatophyllum speciosum, a native species to Singapore, have become extinct mainly due to habitat loss. Recently, Singapore has reintroduced G. speciosum into the natural environment under the orchid conservation programme. In this study, leaves of G. speciosum grown under low light (LL) under natural conditions had faster expansion rate and higher specific leaf area than leaves grown under intermediate light (IL) and high light (HL). All leaves had more than 95% midday relative water content. Although midday Fv/Fm ratios were lower in HL leaves than in IL and LL leaves, none of them exhibited chronic photoinhibition. HL leaves had upregulated their light utilization through higher photochemical quantum yield (ΔF/Fm′) and greater electron transport rate. HL leaves also had higher non-photochemical quenching, indicating that they had higher capability to dissipate excess light as heat, which was supported by their lower chlorophyll but higher carotenoids content. Although there was a linear correction between leaf temperature and photosynthetic photon flux density (PPFD), no correlations were found between stomatal conductance (gs) and PPFD, gs and leaf temperature. Light-saturated photosynthetic CO2 assimilation rate (Asat) was significantly higher in HL leaves than those of IL and LL leaves. However, all leaves had similar light-saturated stomatal conductance. Although LL leaves had higher leaf total reduced nitrogen that those of IL and HL leaves, none of them seemed to suffer from nitrogen deficiency during the experimental period. To conclude, G. speciosum is able to survive under different growth irradiances without watering and adding fertilizers.

Seedling Growth and Recovery in Response to Waterlogging of Wheat Cultivars Grown in the Yangtze River Basin of China from Three Different Decades

Waterlogging is a major constraint on wheat (Triticum aestivum L.) production, especially in the Yangtze River Basin of China (YR). A container experiment was designed to investigate wheat-seedling growth and short-term recoveryin response to waterlogging. Cultivars commonly grown in theYR from three different decades, namely, Yangmai 1 (1970s), Yangmai 158 (1990s), and Yangfumai 4 (2010s), were selected. Seedling waterlogging significantly postponed leaf development, as well as decreased the number of tillers and adventitious roots per plant, seedling height, leaf area, specific leaf dry weight, shoot dry weight, root dry weight, and root/shoot ratio. After a 20-day recovery phase, the leaf stage, seedling height, and root/shoot ratio recovered to the control level, whereas the adverse effects of waterlogging on the number of tillers per plant, leaf area, and shoot dry weight intensified. Significant differences were found in seedling growth among the three wheat cultivars. Yangfumai 4 showed the highest number of adventitious rootsper plant and the highest specific leaf dry weightbut the lowest seedling height, leaf area, and dry weights of shoots and roots. However, Yangfumai 4 showed the lowest percentage decrease in all growth parameters after both waterlogging and recovery. These results suggested thatimprovement inadventitious root numberper plant and specific leaf dry weight may be indicators ofresistance to waterlogging in wheat.

Meso- or xeromorphic? Foliar characters of Asteraceae in a xeric scrub of Mexico

BackgroundThe anatomical traits associated with water deficit are also observed in plants growing in poor soils. The species may resist water deficit through three main strategies: escape, avoid or tolerate. The Pedregal de San Ángel Ecological Reserve (REPSA), Mexico, is an environment with low nutrient soil and low water availability. It is set on the basalt formation derived from the Xitle volcano eruption. The main vegetation type is characterized as xerophytic shrub. Thus we expect that species growing in this community will show leaf xeromorphic traits and may have any of the three response strategies. We analyzed the foliar anatomy of 52 species of the Asteraceae family at the REPSA because it is the most abundant angiosperm family in the site, showing a wide variety of growth forms and anatomical variation.ResultsThe foliar anatomies of the studied Asteraceae were highly variable as well as their quantitative traits as revealed by principal component analysis. This agrees with previous studies that found great anatomical variation within the family. Leaves have multiple layered palisade parenchyma and parenchyma bundle sheaths and could not be categorized as xeromorphic because they possess mesomorphic leaf features as simple lamina, single-layered epidermis, and soft large-size glabrous leaves with high specific leaf area.ConclusionsThe combination of mesomorphic and few xeromorphic foliar traits with other characters at the genus and tribal level probably has been essential in Asteraceae to colonize various environments, including those with low water and nutrient availability.

Plastic Responses in Tree Architecture to Different Light Intensity Habitats: A Case of Chinese Cork Oak

ABSTRACT The capacity of plants to occupy different habitats is made possible by the plastic responses of their presenting in heterogeneous habitats. Light directly influences the plastic responses of plant architectural traits. We measured five years-old saplings of Chinese cork oak growing in different light intensity habitats (forest edge, forest gap and understory). A suite of architectural and leaf morphological attributes indicated a pronounced ability of Chinese cork oak to adapt to shade. Under low light intensity habitats, Chinese cork oak had a significant tendency to invest more in crown growth, characterized by the highest crown area, the lowest crown length ratio and the largest angle of the inclination of the main stem to the vertical. It expressed marked plagiotropic growth in shade indicating a horizontal light-foraging strategy. In addition, Chinese cork oak significantly exhibited the highest specific leaf area and the lowest total leaf area under low light intensity habitats. In shade, ...

Tree species traits but not diversity mitigate stem breakage in a subtropical forest following a rare and extreme ice storm.

Future climates are likely to include extreme events, which in turn have great impacts on ecological systems. In this study, we investigated possible effects that could mitigate stem breakage caused by a rare and extreme ice storm in a Chinese subtropical forest across a gradient of forest diversity. We used Bayesian modeling to correct stem breakage for tree size and variance components analysis to quantify the influence of taxon, leaf and wood functional traits, and stand level properties on the probability of stem breakage. We show that the taxon explained four times more variance in individual stem breakage than did stand level properties; trees with higher specific leaf area (SLA) were less susceptible to breakage. However, a large part of the variation at the taxon scale remained unexplained, implying that unmeasured or undefined traits could be used to predict damage caused by ice storms. When aggregated at the plot level, functional diversity and wood density increased after the ice storm. We suggest that for the adaption of forest management to climate change, much can still be learned from looking at functional traits at the taxon level.

Nitrogen content in fine roots and the structural and functional adaptations of alpine plants

A difference in the adaptation of plants to rich and poor soils is observed at the intraregional level. The nitrogen and carbon content in fine roots and its relation to the taxonomic position and ecologo-morphological traits of a plant has been studied in 92 alpine plant species of the northwestern Caucasus. The nitrogen content varies from 0.43% (Bromus variegates) to 3.75% (Corydalis conorhiza), with the mean value equal to 1.3%. The carbon content varies from 40.3% (Corydalis conorhiza) to 51.7% (Empetrum nigrum), with the mean value equal to 43.4%. The average C: N ratio in fine roots is 34: 1, which is higher than the same value observed in other regions. Roots of dicotyledons have a higher nitrogen content than those of monocotyledons. The highest and lowest values of this parameter are observed in Fabaceae (2.1%) and Poaceae (1.3%), respectively. The highest and lowest carbon concentrations were observed in roots of Ericaceae (47.2%) and Ranunculaceae (42.1%), respectively. Among the species studied, the carbon content in roots increases in the following order: geophytes < hemicryptophytes < chamephytes. The specific root length positively and negatively correlates with the nitrogen and carbon content in roots, respectively. Large-leaved species, which have a higher specific leaf area, are characterized by higher nitrogen and lower carbon content in their roots. The content of nitrogen and carbon in fine roots positively correlates with their content in leaves. This fact confirms the association between the ecologo-morphological traits of plants and the chemical composition of their fine roots. Plant species with a higher growth rate are characterized by a higher nitrogen and lower carbon content in their roots; they are also characterized by the arbuscular mycorrhyza, a higher seed production, and larger leaves with a higher water content and a higher specific leaf area. These traits correspond to the plants of the competitive and ruderal strategies. On the other hand, stress-tolerant (patient) plants with adaptations to low nutrient levels and low growth rate are characterized by higher carbon and lower nitrogen content in fine roots, smaller leaves with a low specific leaf area, and a low seed production.

Interactive effects of elevated temperature and CO2 on two phylogeographically distinct clones of common reed (Phragmites australis)

The aboveground growth, physiological and biochemical parameters of two clones of the cosmopolitan wetland grass Phragmites australis, grown at four treatment combinations of temperature and CO2, were investigated to elucidate whether their climate response differed due to inherent differences in their ecological adaptation. The two phylogeographically distinct P. australis clones (DK clone, European genetic background; ALG clone, Mediterranean genetic background) were grown for 151 days in phytotrons at 19/12 °C (day/night temperature) and 390 ppm CO2, and at elevated temperature (+5 °C) and CO2 (700 ppm) with treatment factors alone or in combination. The ALG clone had 2–4 times higher aboveground biomass, higher light-saturated rates of photosynthesis (Pmax), maximum electron transport rates (ETRmax) and Rubisco activity, and higher photosynthetic nitrogen-use efficiency than the DK clone. The DK clone, however, produced more shoots, leaves and side-shoots, and had 9–51 % higher specific leaf area and 15–39 % higher leaf nitrogen concentration than the ALG clone. Although elevated atmospheric CO2 alone barely affected the aboveground growth of the two P. australis clones, simultaneously elevated temperature and CO2 stimulated growth and aboveground biomass. Overall, elevated CO2 stimulated photosynthesis, but the clones responded differently to a concomitant increase in CO2 and temperature, depending on the phylogeographic background of the plant. The DK clone showed overall stronger responses, and can be considered the more plastic of the two clones with respect to CO2 and temperature. Thus, the DK clone may be better adapted to climate change than the ALG clone, at least in the short term.

Growth-unit structure in trees: effects of branch category and position on Nothofagus nervosa, N. obliqua and their hybrids (Nothofagaceae)

In plants with rhythmic growth, a branch segment extended in one event is known as growth unit (GU). GU structure, resulting from the resources allocated to stem length, volume and mass, and to leaf area and mass, is relevant for understanding branch functioning in the context of plant development. This study compares GU structure between main branches and short branches positioned at low and high positions on nursery-grown trees of three closely related genetic entities: Nothofagusnervosa, N. obliqua and natural hybrids between these species. GUs of short branches, compared to those of main branches, had lower length, diameter and number of leaves, and higher specific leaf area (SLA), stem density and proportional mass in leaves than in stems. GUs at high position on the trees had a higher proportion of their mass in stem than in leaves and a lower SLA than those at low position. Stem density was higher for N. nervosa and the hybrid trees than for N. obliqua. Most other GU traits did not differ statistically between the considered genetic entities. The three genetic entities exhibited distinct patterns of variation in leaf size with leaf position along main-branch GUs. The individual tree had a significant effect on most variables. GU structure would have a major ontogenetic component and would play a relevant role in the architecture of Nothofagus species and their adaptation to different environmental conditions.

Leaf area of common bean genotypes during early pod filling as related to plant adaptation to limited phosphorus supply

Low phosphorus supply markedly limits leaf growth and genotypes able to maintain adequate leaf area at low P could adapt better to limited-P conditions. This work aimed to investigate the relationship between leaf area production of common bean (Phaseolus vulgaris) genotypes during early pod filling and plant adaptation to limited P supply. Twenty-four genotypes, comprised of the four growth habits in the species and two weedy accessions, were grown at two P level applied to the soil (20 and 80 mg kg-1) in 4 kg pots and harvested at two growth stages (pod setting and early pod filling). High P level markedly increased the leaf number and leaf size (leaf area per leaf), slightly increased specific leaf area but did not affect the net assimilation rate. At low P level most genotypic variation for plant dry mass was associated with leaf size, whereas at high P level this variation was associated primarily with the number of leaves and secondarily with leaf size, specific leaf area playing a minor role at both P level. Determinate bush genotypes presented a smaller leaf area, fewer but larger leaves with higher specific leaf area and lower net assimilation rate. Climbing genotypes showed numerous leaves, smaller and thicker leaves with a higher net assimilation rate. Indeterminate bush and indeterminate prostrate genotypes presented the highest leaf area, achieved through intermediate leaf number, leaf size and specific leaf area. The latter groups were better adapted to limited P. It is concluded that improved growth at low P during early pod filling was associated with common bean genotypes able to maintain leaf expansion through leaves with greater individual leaf area.

Vegetative traits predict grass species' invasiveness and the invasibility of restored grassland

Understanding how grass species' traits relate to their invasiveness and the invasibility of their monocultures can inform restoration of diverse grassland. We measured vegetative traits for 18 bunch grass species local to Pietermaritzburg (KwaZulu-Natal, South Africa) and measured their competitive effect on a phytometer. Using 3 m × 3 m plots planted as monocultures 12 years earlier, we related principal components of these traits to how species had invaded other species' plots (invasiveness), and how their monocultures had been invaded (invasibility). Species with high total leaf mass, many tillers and low specific leaf area (SLA) were most invasive and most resistant to invasion by other grasses. Short, slow-growing grasses were most invasible by forbs. This was partly explained by linking traits to invasion through competitive effect: grasses with high total leaf mass, many tillers and low SLA showed the strongest competitive effect, which appears to be necessary but not sufficient for invasiveness. Thus, traits can predict species' ecological performance and provide insight into the processes structuring plant communities. Restoring grasses with short stature, slow growth, low leaf mass, few tillers, and high SLA may facilitate invasion by other native species, thereby increasing species richness.

Morpho-physiological response of durum wheat genotypes to drought stress

The impact of moisture stress on phenology and growth varies for genotypes and the growth stages at which stress is encountered. The aim of this study was to determine the effect of moisture stress on some morpho-physiological traits of durum wheat genotypes under optimum and stress moisture conditions. Genotypes differing in their responses to moisture stress were grown under differing water regimes, one at 70% and the other at 35% available soil moisture. Differences in days to heading, anthesis and physiological maturity were highly significant among genotypes at the two moisture levels. Drought stress delayed the major growth stages. Although this was not expected, it has been reported previously in durum wheat. Variability in relative growth rate, components of relative growth rate, net assimilation rate and leaf area ratio was significant. Drought tolerant genotypes had fast early growth. Variation in relative growth rate was associated with both the net assimilation rate and leaf area ratio. The variation in leaf area ratio under control conditions was both due to specific leaf area and leaf weight ratio. However, under stress conditions, ability to maintain higher leaf area ratio was mainly due to higher specific leaf area.