Plant Biomass Allocation Research Articles

Growth, biomass allocation, and autofragmentation responses to root and shoot competition in Myriophyllum spicatum as a function of sediment nutrient supply

Plant growth, biomass allocation and autofragmentation were investigated in response to root and shoot competition in the submersed macrophyte Myriophyllum spicatum L. growing in two sediment environments. Biomass accumulation and allocation were significantly affected by sediment fertility, with a higher total biomass observed in fertile sediment (average: 4.69 g per plant vs. 1.12 g per plant in infertile sediment). Root-to-shoot ratios were 0.34 and 0.06 in the infertile and fertile sediments, respectively, reflecting the high investment placed on roots under infertile conditions. In the presence of root, shoot, and full competition, whole plant biomass decreased by 18%, 12% and 24% in the infertile sediments, and 23%, 25% and 33% in the fertile sediments, respectively. Root weight ratios (RWRs) increased with root competition by 38% ( P < 0.001) and 12% ( P = 0.002), while leaf weight ratios (LWRs) decreased with shoot competition by 6% ( P = 0.042) and 5% ( P = 0.001) in the infertile and fertile sediments, respectively. A total of 406 autofragments were harvested in the fertile sediments, but none were obtained from the infertile sediments. In the control, autofragment number and biomass was 166% and 175% higher compared to the competition treatment. Root and shoot competition resulted in a 21% ( P = 0.043) and 18% ( P = 0.098) decrease in the autofragment biomass, respectively. These results indicated that M. spicatum responds to different sediment fertility by changing its allocation patterns. Moreover, both root and shoot competition influenced plant growth and autofragmentation, while sediment nutrient availability played an important role in M. spicatum autofragmentation.

Resposta estomática e produção de matéria seca em plantas jovens de aroeira submetidas a diferentes regimes hídricos

Este trabalho objetivou avaliar a transpiração, resistência difusiva do vapor d'água, a produção de matéria seca e alocação de biomassa em plantas jovens de aroeira submetidas a déficit hídrico. Foram utilizadas mudas de Schinus terebinthifolius Raddi com três meses de idade, cultivadas em vasos de polietileno contendo 5,5 kg de terriço vegetal. O delineamento experimental foi inteiramente casualizado com quatro tratamentos hídricos (100% da capacidade de campo (CC), 75% CC, 50% CC e 25% CC) e quatro repetições. Avaliaram-se a transpiração e a resistência difusiva às 12 h em intervalos de seis dias, durante 72 dias de déficit hídrico. No final do experimento, determinaram-se a matéria seca das folhas (MSF), caules (MSC) e raízes (MSR), a alocação de biomassa de diversos órgãos e a razão raiz/parte aérea (R/Pa). O fechamento estomático ocorreu nas plantas submetidas a 25% CC, aos 11 dias depois da aplicação dos tratamentos. Nessa ocasião, essas mesmas plantas foram regadas até 100% CC. As regas foram suspensas até as plantas atingirem novamente 25% CC e serem mantidas nesse tratamento até o final do período experimental, não havendo mais fechamento estomático no horário estudado. A produção de matéria seca aumentou nas plantas cultivadas com 75% CC, em comparação com os demais tratamentos hídricos. Não houve diferença significativa entre os tratamentos para alocação de biomassa nos diversos órgãos. Os resultados indicam que a aroeira é moderadamente tolerante ao déficit hídrico na fase inicial do desenvolvimento.

Hydraulic and mechanical stem properties affect leaf–stem allometry in mango cultivars

Leaf size-stem size allometric relationships are important features of biomass allocation in plants and are affected by biological functions linking the two organs. They have been studied at specific and supraspecific levels, but not at the infraspecific level. It was hypothesized that allometric relationships link leaf size and stem size at the cultivar level, and are cultivar-specific in relation to distinctive functional stem traits: hydraulic conductivity and mechanical strength. Allometric relationships between leaf size and stem size were established for 3 yr, using the standardized major axis method, on current-year branches, composed of one to 16 growth units, for four mango (Mangifera indica) cultivars characterized by contrasting growth habits. The hydraulic and mechanical stem properties of these cultivars were also measured. The slopes of the relationships were similar among cultivars, but not the y-intercepts. Different y-intercepts in the stem mass vs branch cross-sectional area relationship and in the leaf mass vs stem mass relationship were related to mechanical and to hydraulic stem properties, respectively. These results showed that leaf-stem allometry in mango cultivars was shaped by hydraulic and mechanical stem properties, supporting a functional interpretation of the relationship between leaf and stem dimensions.

The role of biomass allocation strategy in diversity loss due to fertilization

Summary Proposed mechanisms for explaining biodiversity loss due to fertilization include interspecific competition and assemblage-level thinning. The interspecific competition hypothesis (ICH) assumes a link between population changes and species competitive ability, which is related to functional traits such as biomass allocation patterns. Based on a 2-year fertilization experiment in an alpine meadow on the Tibetan Plateau, we attempted to explore the relationships between individual and population responses. Individual response was measured by changes in plant biomass and biomass allocation, and population response was estimated by changes in species abundance. The results suggested that following fertilization (1) changes in individual biomass differ among species and functional groups, (2) reproductive allocation tends to decrease for all species whereas leaf allocation generally increases for grasses but decreases for forbs, (3) a strong positive correlation exists between species relative abundance change and individual biomass response, and (4) species relative abundance change has a positive correlation with leaf allocation response, a negative correlation with stem allocation response, and no significant correlation with reproductive allocation response. We conclude that the individual biomass responses and biomass allocation strategy can partly explain diversity loss due to fertilization, a result consistent with the ICH.

Effect of growth media and fertilizer application on biomass allocation and survival of Uapaca kirkiana Müell Arg seedlings

Uapaca kirkiana Muell Arg is one of the few recognized African fruit trees earmarked forconservation and domestication in southern Africa. However, efforts to raise seedlings of this species have been frustrated by the slow growth and high seedling mortality. Therefore, the objective of this study was to assess the effect of potting mixture, soil and foliar fertilizer application on plant growth, biomass allocation and survival of U. kirkiana seedlings in the nursery. Growth in height and diameter was best in plants with root to shoot ratio of <1 or 2.5-4. Growth in height and diameter significantly differed (P<0.01) with treatment main effects and interactions. The best growth was recorded in the treatment combination consisting of unsterilized forest soil + soil and foliar application fertilizer. The probability of plant mortality was significantly higher (P<0.01) in the potting mixture where saw dust was added (mean 0.47) than in the mixture without saw dust (mean 0.12). Mortality was also significantly higher (P<0.05) in unsterilized soil (mean 0.30) than sterilized soil (mean 0.13). Potting mixtures amended with soil-applied fertilizer had lower probability of plant mortality compared to those without. Disease incidence and seedling survival were related to biomass allocation in a curvilinear manner. It is concluded that survival of U. kirkiana seedlings in the nursery is a function of disease incidence, plant growth and biomass allocation, which in turn are functions of the growth medium and nutrient availability. Key words: Biomass allocation, growth, miombo, mortality, Uapaca kirkiana.

Consistency between an allometric approach and optimal partitioning theory in global patterns of plant biomass allocation

Summary Optimal partitioning theory (OPT) suggests that plants should allocate biomass to the organ that acquires the most limiting resource. An implied assumption of this is that there are trade‐offs in allocation between leaf, stem and root functions. Recently, an alternative approach, allometric biomass partitioning theory (APT), was developed to predict how plants should divide their metabolic production between leaves, stems and roots, based on the constraints of body size. APT predicts that, for an allometrically ideal plant, leaf mass should scale to the 3/4th power of body size, and stem and root mass should scale isometrically to body size. In this study, we combine OPT with APT by investigating biomass partitioning not accounted for by allometric constraints across broad environmental gradients. Intraspecific variability in biomass allocation shows correlations with environmental factors that would be predicted by OPT. However, interspecifically, these patterns either do not appear or are greatly reduced. Our study suggests that, after size is accounted for, intraspecific residual variation in biomass allocation may be partially explained by environmental factors in a manner consistent with OPT. However, the particular patterns vary between species, obscuring large‐scale patterns. In summary, differences due to environmental variability can be incorporated with allocation patterns related to total mass to help understand how plants should allocate biomass in response to changes in both size and environment.

Growth and root distribution of Vallisneria natans in heterogeneous sediment environments

Plant growth, biomass allocation and root distribution were investigated in the submerged macrophyte Vallisneria natans growing in heterogeneous sediments. Experimentally heterogeneous sediment environments were constructed by randomly placing 4 cm of clay or sandy loam into the top (0–4 cm) or bottom (4–8 cm) layer within an experimental tray, providing two homogeneous and two heterogeneous treatments. Biomass accumulation was significantly affected by the experimental treatments: higher in the homogeneous sediment of clay (32 mg per plant) and the two heterogeneous treatments (about 27 mg per plant), but lower in the homogeneous sediment of sandy loam (15 mg per plant). Root: shoot ratio was also different among the four treatments. Compared with the treatments of clay in the top layer, plants allocated more biomass to roots at the treatments of sandy loam in the top layer. Heterogeneous sediments significantly affected root distribution pattern. Compared with the treatments of sandy loam in the bottom layer, root number (7–8 versus 13–14) and total root length (3.6–4.0 cm versus 29.5–40.0 cm) in the bottom layer were significantly higher in the treatments with clay in the bottom layer. These results indicate that both sediment structure and nutrient availability influence growth and root system distribution of V. natans.

Plasticity and ontogenetic drift of biomass allocation in response to above‐ and below‐ground resource availabilities in perennial herbs: a case study of Alternanthera philoxeroides

AbstractChanges in plant biomass allocation in response to varying resource availabilities may result from ontogenetic drift caused by allometric growth (i.e., apparent plasticity), a true adjustment of ontogenetic trajectories (true plasticity) or both (complex plasticity). Given that the root allocation of annual species usually decreases during the growth, the developmentally explicit model predicts that annual herbs will exhibit true plasticity in root allocation under above‐ground resource limitation and apparent plasticity for moderate stress of below‐ground resource. For perennial species, the root allocation of which increases during growth, the reverse patterns would be expected. In this study, we tested the developmentally explicit model with a perennial weed, Alternanthera philoxeroides (Mart.) Griseb. We report its adaptive changes and ontogenetic drift of root allocation in response to different resource levels (i.e., light, water and nutrient availability) by comparing root allocation on both an age and a size basis. The root allocation of A. philoxeroides increased with the size (i.e., ontogenetic drift) during the growth, and exhibited significant changes in response to different resource availabilities. Furthermore, the root allocation in response to water or nutrient availability exhibited typical complex plasticity, while the light stress only slowed down the growth, with the ontogenetic trajectory unchanged (apparent plasticity). The contrasting responses to above‐ground and below‐ground stresses were consistent with the prediction of the developmentally explicit model.

Integrated long-term responses of an arctic–alpine willow and associated ectomycorrhizal fungi to an altered environment

We evaluated ectomycorrhizal (ECM) colonization and morphotype community composition together with growth response and biomass distribution in the arctic–alpine, prostrate willow Salix herbacea L. × Salix polaris Wahlenb. after 11 seasons of shading, warming, and fertilization at a fellfield in subarctic Sweden. The aim was to assess responses of the integrated plant–fungal system to long-term field experiments simulating expected environmental changes. Warming more than doubled aboveground S. herbacea × S. polaris biomass and shoot growth, whereas shading and nutrient addition had less influence on these variables. In shaded plants, adjustments at leaf level probably buffered major changes in plant biomass allocation. Fertilization increased the root mass fraction and changed root system morphology by decreasing the number of root tips per unit root mass. While no long-term changes in total ECM colonization (%ECM root tips) in response to the treatments were identified, ECM colonization in June just after snowmelt was positively correlated with root density. Changes in densities of potential host plants may therefore be of great importance for ECM colonization intensity in this ecosystem type. The ECM morphotype community changed through the season, and frequencies of some ECM morphotypes ( Cortinarius saturninus and Clavulina spp.) changed more with season than with the treatments. Warming only slightly affected ECM morphotype frequencies, which implies a balanced increase in root tip numbers of most ECM morphotypes in warmed plants. Fertilization changed ECM morphotype community composition mainly because of a decrease in Cenococcum geophilum frequency and an increase in Tomentella stuposa frequency. We hypothesize that a shift from drought stress-tolerant fungi towards a dominance of minerogenic fungi may take place if nutrient availability increases substantially because of anthropogenic disturbances.

Previous land use alters plant allocation and growth in forest herbs

Summary Former human practices can persistently influence forest ecosystems, particularly by altering the distribution and abundance of vegetation. Previous research has focused on the role of colonization success in governing plant community patterns in abandoned forests, but few studies have explored how changes in the performance of adult plants may contribute to changes in plant populations. We examined patterns of biomass allocation and growth of 12 herbaceous plant species in southern Appalachian forest stands that have developed after agricultural abandonment or logging at least 55 years ago, to determine whether plant performance varied with land‐use history. Soil nutrient availability and canopy closure were also investigated. Adult plant biomass allocation varied appreciably among stands with different histories. Herbs in farmed stands generally allocated the most to leaves and the least to stems, while reference stands showed the opposite pattern. Plants in previously farmed sites had the highest rate of growth, although we observed considerable interspecific variation in plant performance. Stem allocation and relative growth rate were positively correlated in reference stands, but not in farmed or logged stands. Similarly, the growth of plants was clearly associated with soil nutrient concentration in reference stands but not in farmed or logged stands. Differences in understorey density and soil nutrient availability may account for the observed patterns. Total herbaceous cover was appreciably lower in farmed and logged stands (58% and 51%) than in reference stands (78%), and soil phosphorus was higher in farmed stands than in logged and reference stands. Thus, competition for light and nutrients may be lower in farmed and logged stands than in reference stands, despite there being no difference in canopy closure with land‐use history. Overall, these results suggest that land‐use history may influence environmental variables in ways that can enhance the performance of some herbaceous species. However, not all species may respond similarly to these changes.

Effect of year and irrigation on the yield and quantity of different potato varieties

In Hungary, the growing area of potato area dropped dramatically in the last few decades; moreover, we lag behind Western European countries as regards yields. The ecological and climatic conditions of Hungary are not suitable for potato growing everywhere (SSrvdri, 2001), but the low yields also have other causes: the use of not suitable seeds, the low level of irrigation, nutrient supply and old-fashioned machines. The competitiveness of production is further decreased by the great alternation in yields from year to year, unpredictable market conditions, poor consumption habits and often the lack of quality products. For potato growing, considering its original place, humid areas are the most suitable, where the weather is slightly cool, and summer is moderately warm (Mdszdros, 1979). High temperature reduces the allocation of plant biomass to tubers and will result in smaller leaves, more nodes per stem, longer intemodes, taller plants, higher leaf areas and lower rations of leaf/stem leaf (Khedher Ewing, 1985.). Water stress causes yield loss by reducing the growth of crop canopy and biomass. Water at 3-5 mm per day is necessary for evapotranspiration (ET) and the maintenance of optimal soil moisture tension (10-50 kPa) in growing potatoes (Marutani and Cruz, 1989, Kruppa et al., 2003.). In order to maintain at least our domestic market positions we should improve the level of production. To achieve this, quality should improve besides the enhancement of yield per hectare and the simultaneous reduction of production costs. (Kruppa Zsom, 2003). The higher average of yield and tuber quality could be achieved by improving technological elements in the production chain. Ecological limits could be overcome by irrigation and tuber yields of 40-50 t ha , or even higher could be attained (Horvdth, 2002.).

Phylogenetic and Growth Form Variation in the Scaling of Nitrogen and Phosphorus in the Seed Plants

Plant biomass and nutrient allocation explicitly links the evolved strategies of plant species to the material and energy cycles of ecosystems. Allocation of nitrogen (N) and phosphorus (P) is of particular interest because N and P play pivotal roles in many aspects of plant biology, and their availability frequently limits plant growth. Here we present a comparative scaling analysis of a global data compilation detailing the N and P contents of leaves, stems, roots, and reproductive structures of 1,287 species in 152 seed plant families. We find that P and N contents (as well as N : P) are generally highly correlated both within and across organs and that differences exist between woody and herbaceous taxa. Between plant organs, the quantitative form of the scaling relationship changes systematically, depending on whether the organs considered are primarily structural (i.e., stems, roots) or metabolically active (i.e., leaves, reproductive structures). While we find significant phylogenetic signals in the data, similar scaling relationships occur in independently evolving plant lineages, which implies that both the contingencies of evolutionary history and some degree of environmental convergence have led to a common set of rules that constrain the partitioning of nutrients among plant organs.

Foliar Spraying of Vermicornpost Extracts: Effects on Fruit Quality and Indications of Late-Blight Suppression of Field-Grown Tomatoes

ABSTRACT The effect of foliar sprays with aqueous vermicompost extracts on growth, yields, morphological and chemical fruit quality and natural infection with late blight disease (Phytophthora infestons (Mont.) de Bary)) on three tomato varieties (Lycopersicon esculentnm Mill., cv. Diplom Fl, cv. Malina, cv. Rheinlands Ruhm) was investigated in a field experiment. Extracts were prepared of vermicompost produced from fruit, vegetable and cotton waste by redworms (Eisenia fetida Sav., Lumbricidae); tap water served as control treatment. Foliar application (spraying) of vermicompost extracts did not affect plant growth, biomass or nutrient allocation, or yields and number of fruits of the three tomato varieties; however, for several dates it significantly reduced the number of flowers produced. Foliar vermicompost spraying cither increased or decreased peel firmness dependent on tomato variety and increased fruit circumference consistently as well as contents of nitrogen but decreased L-ascorbic acid compared with water sprayed fruits. All other measured parameters of fruit quality (dry matter, C, N, P, K, Ca, Mg, glucose and fructose content) were similar for vermicompost and water sprayed plants. Natural infection of leaves, stems and fruits by P. infestans was generally very low under the experimental conditions; however, across varieties, only half as many vermicompost sprayed plants showed clear signs of P. infestans infection as water sprayed plants; the severity of the infection was unaffected by the two spraying treatments. In conclusion, these results suggest that the use of vermicompost might be considered more in organic farming not only as a substitute for peat in potting media but also as foliar sprays for fertilization and biological disease prevention.

Nutrient availability induces contrasting allocation and starch formation in resprouting and obligate seeding shrubs

Summary Woody plant responses to crown removal in fire‐prone vegetation are of two types: resprouting (resprouters) or killed (obligate seeders). Obligate seeders maximize their fitness by ensuring they are reproductively mature before the next fire; resprouters invest in structures that increase their chance of surviving the next fire. We tested whether seven congeneric pairs of resprouter and obligate seeder shrubs differ in plant size, leaf traits, water relations, biomass allocation and root starch formation in response to resource availability. This was tested by examining the interactive effects of water and nutrient availability in a factorial experiment. Plant size (dry mass and shoot length), leaf area and stomatal conductance did not differ consistently among resprouters and obligate seeders, but were affected by water and nutrient availability. Leaf‐area ratio and specific leaf area were not affected consistently by nutrient or water availability, and did not differ among obligate seeders and resprouters. Biomass allocation responded to resource availability and differed between resprouter and obligate seeder pairs. Nutrient addition reduced allocation to root mass, and resprouters consistently allocated more than obligate seeders to root mass. Leaf mass ratios were higher in obligate seeders, and were maintained at the expense of stem mass when nutrients limited growth. Starch concentrations in the roots of resprouters were higher than in obligate seeders. Resprouters increased the concentration of starch in their roots when growth was limited by nutrients, but obligate seeders did not. Resprouters appear to develop a starch‐storage capacity through both reserve formation and accumulation mediated by nutrient availability. Allocation, rather than growth differences, provide some insight into why resprouters are often more common than obligate seeders, especially on fertile sites. Seedlings of resprouters may be advantaged at fertile sites because allocation to roots and starch reserve formation enable them to be better competitors after fire. We predict that the interplay of biomass allocation, reproduction, starch storage and disturbance frequency provide a framework for patterns of coexistence in shrubs in fire‐prone ecosystems.

Differences in plant‐size structure and biomass allocation in plants between exposed and shaded Plantago asiatica populations at a mid‐elevated habitat in the cool‐temperate region of Japan

Abstract Plantago asiatica L. (Plantaginaceae) is a perennial herb that is distributed over a wide range of habitats from exposed to shaded sites in lowlands to the subalpine zone in Japan. We investigated the patterns of biomass allocation and population structures based on the frequency distribution of individual plants in order to clarify the extent of plasticity in significant life‐history traits and also population dynamics of this plantain species, which occurs under two contrasting light regimes—in exposed and shaded habitats—at Numappara, 1230 m a.s.l., Tochigi Prefecture, central Honshu. The plants at the shaded site allocated more biomass to leaves, but less to rhizomes than those at the exposed site. Increasing the biomass of the reproductive organs resulted in a reduction of the leaf and rhizome fractions. This trend is clearer in the shaded plants than in the exposed plants. In both exposed and shaded populations, the number of seedlings was greater in the first year, but the population structure was skewed more negatively in the second year during two consecutive study years. The possible effects of allocation traits of individuals on the population structures and regeneration mechanisms of P. asiatica at elevated habitats are discussed in terms of cyclic changes in population structure with the fluctuations of seeding activity over some years.

Alterações morfológicas e alocação de biomassa em plantas jovens de espécies florestais sob diferentes condições de sombreamento

A seleção de espécies nativas e/ou exóticas para recuperação de ambientes degradados ou alterados pode ser baseada no potencial de aclimatação das espécies a diferentes níveis de luminosidade. Nesse contexto, o objetivo deste estudo foi avaliar o efeito do sombreamento (0%, 30% e 50% de interceptação da radiação solar incidente) no crescimento, na alocação de biomassa e nos teores de clorofila total de plantas jovens de quatro espécies florestais de diferentes grupos ecológicos: Maclura tinctoria (L.) D. Don ex Steud. (moreira), Senna macranthera (Collad.) Irwin et Barn. (fedegoso), Hymenaea courbaril L. var. stilbocarpa (Hayne) Lee et Lang. (jatobá) e Acacia mangium Willd. (acácia). Os maiores teores de clorofila total foram observados em condições sombreadas, para todas as espécies. A espécie clímax exigente em luz (moreira), apresentou os maiores resultados de crescimento. Em condições de pleno sol, a espécie pioneira (acácia) alocou mais biomassa em folhas enquanto que a espécie clímax exigente em luz (moreira) produziu mais raízes. Estas observações evidenciam o potencial de aclimatação a diferentes condições de disponibilidade de irradiação, que deve ser considerado em programas de recuperação de ambientes degradados e manejo de áreas naturais.

COMPARATIVE STUDY OF TWO KINDS OF AMOMUM VILLOSUM CULTIVATION MODELS IN XISHUANGBANNA

Amomum villosum is a perennial herb that occurs in the understory of tropical and subtropical forests and is an important medicinal plant. A. villosum, native to Guangdong Province, was introduced intentionally to Xishuangbanna, Yunnan in 1963 and was planted under tropical rainforests. Farmers often thin out some of the canopy trees (5%-85%) when they grow this plant for commercial purposes in these primary forests, resulting in a loss of biodiversity in these forests. A. villosum fruit yield is low and varies greatly among fields and years due to the crude cultivation method. The area of primary rainforest is much smaller than secondary forests in Xishuangbanna. The influence of A. villosum cultivation on rainforest biodiversity, biomass, and net productivity was significant, but the influence on secondary forests was negligible. To improve A. villosum yield and to protect rainforest biodiversity, we explored the possibility of cultivating A. villosum in secondary forests. Plant density, biomass, biomass allocation, and fruit yield were measured in A. villosum cultivated in tropical wet seasonal rainforests and secondary forests in Xishuangbanna. The density and biomass of vigorous plants were 72.60% and 85.29% of the total plants in the secondary forest and 71.27% and 86.69% in the rainforest and was significantly higher than those of other plant types. The density of shoots, seedlings, and senescent plants were not significantly different within the same forest types, but the biomass of senescent plants was significantly higher than that of shoots and seedlings. The sum of shoots and seedlings in secondary forest and rainforest were 1.45 and 2.18 times of senescent plants, respectively, indicating that A. villosum populations could be maintained. In the rainforest, many A. villosum seedlings were old and most of them grew poorly and could not develop into normal, healthy and vigorous plants. It is worthwhile to note that the A. villosum yield was very low, stem biomass ratio was very high (above 0.58), and fruit biomass ratio was extremely low (about 0.01). This suggests that increasing the yield potential of A. villosum could be achieved by improving biomass partitioning between the fruit and stem. In one of the experimental plots in the secondary forest, soil water conditions were improved by a rivulet, and fruit yield production was 211.1490 kg•hm~(-2), much higher than that of other fields. Apparently, A. villosum cannot tolerate dry conditions and moderate dry periods might influence A. villosum yield. These yields were related to its low root biomass ratio and shallow root system. Leaf area index, biomass of both vigorous plants and other plants were significantly and positively correlated with fruit yield in A. villosum. Fruit yield and leaf area index were 105.0345 kg•hm~(-2) and 2.9082 in the secondary forest, and 60.9319 kg•hm~(-2) and 2.5600 in the rainforest, respectively. The density and biomass of the same plant types were not significantly different between the secondary forest and the rainforest. These results suggest that A. villosum can be cultivated in secondary forests.

Crescimento de plantas jovens de Myracrodruon urundeuva Allemão (Anacardiaceae) sob diferentes regimes hídricos

Objetivou-se avaliar o crescimento das plantas jovens cultivadas em casa de vegetação submetidas a três regimes hídricos: 25, 50 e 75% da capacidade de campo (cc) em duas épocas de avaliação (30 e 60 dias). As variáveis observadas foram: altura de planta, massa seca, alocação de biomassa e densidade estomática. Os três regimes hídricos não exerceram influência no comprimento da raiz. A razão de comprimento (cm) raiz/parte aérea a 25% cc, foi aproximadamente de 2:1 e sob 50 e 75% cc manteve-se na ordem de 1:1. O déficit hídrico reduziu a altura das plantas sob 25% cc aos 30 dias. Aos 60 dias os valores variaram de 22, 60; 22,70 e 28,76cm em 25%, 50% e 75% cc, respectivamente. Houve redução significativa na área foliar, produção da massa seca sob o regime hídrico de 25% aos 30 e 60 dias, quando comparados a 50 e 75% cc. Maior alocação de biomassa foi para as raízes sob 25% aos 30 e 60 dias. M. urundeuva é hipoestomática, com estômatos do tipo anomocítico e densidade estomática variando de 372 a 524 estômatos por mm².

Antagonistic interactions between competition and insect herbivory on plant growth

Summary 1 Although substantial theoretical work suggests that competition and herbivory should exhibit a wide variety of interactions in their effects on plant growth, empirical studies have shown that the predominant interactions are simply multiplicative. 2 To determine both the relative strengths of, and interactions between, competition and herbivory, we conducted a field experimental study in a native grassland using four focal species: Koeleria macrantha , Coreopsis tinctoria , Linum lewisii and Helianthus petiolaris . 3 The effects of competition and herbivory on plant growth, biomass allocation and survival varied among species. When effects were present, neighbouring vegetation reduced plant growth and survival, and insect herbivores decreased relative biomass allocation to roots and increased plant mortality. 4 Although reduced herbivory caused by insecticide application had little direct effects on plant biomass, it did interact with competition to affect growth for three of the four species. Herbivory reduced the strength of competition experienced by Coreopsis , but increased it in Linum . For both Coreopsis and Helianthus , the combined effects of herbivory and competition on plant growth were less than expected from a simple multiplicative response. 5 We suggest that interactions were found because we used an experimental design that modified insect densities on both neighbours and the focal plant, allowing for determination of both direct and indirect effects. 6 We suggest that the antagonistic interactions between competition and herbivory may have occurred because herbivores altered the competitive environment by harming the neighbouring plants, or because the presence of neighbours facilitated focal plant growth by distributing herbivore loads over the greater amount of plant biomass available. 7 Although as an isolated factor competition is more intense in this system than insect herbivory, herbivory can alter the strength of competitive interactions and thus its importance cannot be determined by measuring intensity alone. This result emphasizes that these two ecological processes are not truly discrete, and further suggests that studies that simultaneously manipulate multiple ecological processes are needed.

Short-term effects of defoliation on the soil microbial community associated with two contrasting Lolium perenne cultivars

Intra-species variation in response to defoliation and soil amendment has been largely neglected in terms of the soil microbial community (SMC). The influence of defoliation and soil fertiliser amendment on the structure of the SMC was assessed with two Lolium perenne cultivars contrasting in ability to accumulate storage reserves. Plant response to defoliation was cultivar specific and depended on the nutrient amendment of the soil. Results suggested a greater ability to alter plant biomass allocation in the low carbohydrate accumulating cultivar (S23) compared to the high carbohydrate cultivar (AberDove) when grown in improved (IMP), but not in unimproved (UNI), soil. Although differences in plant growth parameters were evident, no treatment effects were detected in the size of the active microbial biomass (total phospholipid fatty acid (PLFA) 313.8 nmol g −1 soil±33.9) or proportions of PLFA signature groups. A lower average well colour development (AWCD) of Biolog sole carbon source utilisation profiles (SCSUPs) in defoliated (D) compared to non-defoliated (ND) treatments may be indicative of lower root exudation 1 week following defoliation, as a consequence of lower root non-structural carbohydrate (NSC) concentrations. Within the bacterial community the lower cyclopropyl-to-precursor ratio of PLFAs, and the trans/ cis ratio of 16:1w7, in UNI relative to IMP soil treatments indicates lower physiological stress in UNI soils regardless of L. perenne cultivar. Discrimination of broad scale SMC structure, measured by PLFA analysis, revealed that soil treatment interacted strongly with cultivar and defoliation. In IMP soils the SMCs discriminated between cultivars while defoliation had little effect. Conversely, in UNI soils defoliation caused a common shift in the SMC associated with both cultivars, causing convergence of overall community structure. Separation of SMC structure along the primary canonical axis correlated most strongly ( P<0.001) with root:shoot ratio (47.6%), confirming that differences in cultivar C-partitioning between treatments were influential in defining the rhizosphere microbial community.