Shoot Biomass Ratio Research Articles

Overlooking what is underground: Root:shoot ratios and coarse root allometric equations for tropical forests

Coarse roots are a major belowground carbon (C) pool, yet we know little about the factors controlling coarse root distributions in tropical forests, the biome where belowground biomass stocks are largest. We conducted a literature survey to identify potential environmental controls on the root:shoot biomass ratio (R:S) across tropical forests worldwide. Moreover, to aid efforts to extrapolate aboveground biomass measurements to belowground C stocks, we also compiled a list of allometric equations for coarse root biomass.Across our large and geographically comprehensive dataset, we found that R:S is negatively correlated with mean annual precipitation, and positively linked with stand age. However, information on root biomass allocation is still scarce in comparison with the wealth of available data on aboveground plant biomass in tropical forests, and more data will be necessary to understand the drivers of belowground biomass allocation. Moreover, the available root allometric equations show tremendous variation in mathematical form, which is likely related to the many different methods that have been used to quantify root biomass and its distribution with depth. A better understanding of belowground dynamics in tropical forests will require systematic surveys of root biomass along gradients of soil type, climate, and stand age, along with a streamlined protocol for developing root allometric equations.

Tropical montane cloud forest: environmental drivers of vegetation structure and ecosystem function

Abstract:Tropical montane cloud forests (TMCF) are characterized by short trees, often twisted with multiple stems, with many stems per ground area, a large stem diameter to height ratio, and small, often thick leaves. These forests exhibit high root to shoot ratio, with a moderate leaf area index, low above-ground production, low leaf nutrient concentrations and often with luxuriant epiphytic growth. These traits of TMCF are caused by climatic conditions not geological substrate, and are particularly associated with frequent or persistent fog and low cloud. There are several reasons why fog might result in these features. Firstly, the fog and clouds reduce the amount of light received per unit area of ground and as closed-canopy forests absorb most of the light that reaches them the reduction in the total amount of light reduces growth. Secondly, the rate of photosynthesis per leaf area declines in comparison with that in the lowlands, which leads to less carbon fixation. Nitrogen supply limits growth in several of the few TMCFs where it has been investigated experimentally. High root : shoot biomass and production ratios are common in TMCF, and soils are often wet which may contribute to N limitation. Further study is needed to clarify the causes of several key features of TMCF ecosystems including high tree diameter : height ratio.

Influence of Environmental Factors, Cultural Practices, and Herbicide Application on Seed Germination and Emergence Ecology of Ischaemum rugosum Salisb.

Ischaemum rugosum Salisb. (Saramolla grass) is a noxious weed of rice that is difficult to control by chemical or mechanical means once established. A study was conducted to determine the effect of light, temperature, salt, drought, flooding, rice residue mulch, burial depth, and pre-emergence herbicides on seed germination and emergence of I. rugosum. Germination was stimulated by light and inhibited under complete darkness. Optimum temperature for germination was 30/20°C (97.5% germination). Germination reduced from 31 to 3.5% when the osmotic potential of the growing medium decreased from -0.1 to -0.6 MPa and no germination occurred at -0.8 MPa. Germination was 18 and 0.5% at 50 and 100 mM NaCl concentrations, respectively, but was completely inhibited at 150 mM or higher. Residue application at 1–6 t ha-1 reduced weed emergence by 35–88% and shoot biomass by 55–95%. The efficacy of pre-emergence herbicides increased with increasing application rates and decreased with increasing rice residue mulching. The efficacy of herbicides was in the order of oxadiazon> pendimethalin> pretilachlor. At 6 t ha-1, all herbicides, regardless of rates, did not differ from the control treatment. I. rugosum seeds buried at 2 cm or deeper did not emerge; however, they emerged by 4.5 and 0.5% at 0.5 and 1 cm depths, respectively, compared to the 39% germination for soil surface seeding. Flooding at 4 DAS or earlier reduced seedling emergence and shoot biomass while flooding at 8 DAS reduced only seedling emergence. The depth and timing of flooding independently reduced root biomass. Flooding at 4 and 6 cm depths reduced the root biomass. Relative to flooding on the day of sowing, flooding at 8 DAS increased root biomass by 89%. Similarly, flooding on the day of sowing and at 2 DAS reduced the root–shoot biomass ratio. Under the no-flood treatment, increasing rates of pretilachlor from 0.075 to 0.3 kg ai ha-1 reduced weed emergence by 61–79%. At the flooding depth of 2–4 cm, pretilachlor reduced weed emergence and shoot and root biomass, but the differences across rates were non-significant. Information generated in this study will be helpful in developing integrated weed management strategies for managing this weed.

Evaluating the growth of several Mediterranean endemic species in artificial substrates: Are these species suitable for their future use in green roofs?

The study of the growth of several Mediterranean endemic plant species in new artificial substrates is becoming necessary for seeking alternatives in green roof design in Mediterranean regions. In this regard, we evaluated the growth of six native species on three different artificial substrates. These species were Silene vulgaris, Silene secundiflora, Crithmum maritimum, Lagurus ovatus, Asteriscus maritimus, and Lotus creticus. A mixture of a green compost with a clay–loam soil (C+Soil), the same compost mixed with expanded clay (C+Clay), and the compost mixed with crushed bricks (C+Bricks) – all in 1:4 volumetric proportions – were the assayed substrates. Physichochemical and biochemical properties were studied in each mixture at the beginning and end of a three-month assay. Besides, the germination and growth of all plant species in each substrate type were evaluated. The mixtures C+Clay and C+Bricks showed greater porosity than C+Soil, leading to a high root: shoot biomass ratio in all species tested. Conversely, the mixture C+Soil possessed better biochemical properties (higher humic substances content and enzyme activity), but they decreased with experimental time. Contrarily, the humic substances and the dehydrogenase activity increased in the most porous mixtures. Regarding plant behaviour, S. vulgaris and L. ovatus showed greater germination and growth than the other species, especially above C+Clay and C+Bricks mixtures. Accordingly, we strongly recommend the use of lightweight and highly porous substrates as the basis for the growing of Mediterranean native herbaceous species, since they specially enhance their root development. The combined use of perennials and annuals species in that kind of substrates could provide a permanent plant cover in a green roof scenario.

Ecotypic responses to flood and drought in tea tree (Melaleuca alternifolia)

Plantation-grown Melaleuca alternifolia (tea tree) is the principal source of tea tree oil in Australia. Upland and coastal ecotypes of tea tree were grown in a common environment to test responses in root, shoot and developmental attributes to four hydrological conditions. Consistent with its wetland origins, tea tree exhibited morphological adaptations for flood tolerance, with both ecotypes possessing a similar maximal capacity for adventitious roots and aerenchyma. Despite adaptation to flood, growth was reduced under prolonged flood relative to a well-watered control, and to a similar degree in both ecotypes. Coastal plants responded more rapidly to flood, suggesting that upland plants may delay costly morphological modifications until flooding is more protracted. Mild water deficit (drought) had a greater impact on growth and development than flooding, and upon coastal than upland plants. Relatively lower impact of drought on biomass and branch whorl number in upland plants was probably due to a constitutively higher root : shoot biomass ratio buffering against retarded development and growth. This study was the first step in identifying genetically controlled abiotic stress tolerances that may be useful for further domestication of tea tree. The potential to improve drought tolerance appeared most promising; however, further work will require consideration of appropriate breeding strategies given the low-resource-adapted population origins of tolerance alleles, and it should be prefaced by a clear definition of the target deployment environment and include testing of yield variables of economic value in target environments.

Regulation of root morphogenesis in arbuscular mycorrhizae: what role do fungal exudates, phosphate, sugars and hormones play in lateral root formation?

Arbuscular mycorrhizae (AMs) form a widespread root-fungus symbiosis that improves plant phosphate (Pi) acquisition and modifies the physiology and development of host plants. Increased branching is recognized as a general feature of AM roots, and has been interpreted as a means of increasing suitable sites for colonization. Fungal exudates, which are involved in the dialogue between AM fungi and their host during the pre-colonization phase, play a well-documented role in lateral root (LR) formation. In addition, the increased Pi content of AM plants, in relation to Pi-starved controls, as well as changes in the delivery of carbohydrates to the roots and modulation of phytohormone concentration, transport and sensitivity, are probably involved in increasing root system branching. This review discusses the possible causes of increased branching in AM plants. The differential root responses to Pi, sugars and hormones of potential AM host species are also highlighted and discussed in comparison with those of the non-host Arabidopsis thaliana. Fungal exudates are probably the main compounds regulating AM root morphogenesis during the first colonization steps, while a complex network of interactions governs root development in established AMs. Colonization and high Pi act synergistically to increase root branching, and sugar transport towards the arbusculated cells may contribute to LR formation. In addition, AM colonization and high Pi generally increase auxin and cytokinin and decrease ethylene and strigolactone levels. With the exception of cytokinins, which seem to regulate mainly the root:shoot biomass ratio, these hormones play a leading role in governing root morphogenesis, with strigolactones and ethylene blocking LR formation in the non-colonized, Pi-starved plants, and auxin inducing them in colonized plants, or in plants grown under high Pi conditions.

Time of planting and weed suppression abilities of some legumes intercropped with maize in the Guinea savanna zone of Ghana

Field experiments were conducted in the field at Nyankpala in the Northern Region of Ghana to determine the appropriate time of intercropping soybean, cowpea and groundnut with maize for optimum yield; and to compare the weed suppression abilities, vis-a-vis maize yields, of these legumes. The legumes were intercropped with the cereal 0, 2 and 4 weeks after planting (WAP) the maize. The intercrop components were arranged in a 1:1 spatial arrangement. The nonintercropped treatments served as sole crops. The experimental plots were laid out in a randomized complete block design (RCBD) with four replications for each treatment. Results showed that leaf area index, shoot biomass, nodule number, pod number, grain yield and land equivalent ratio (LER) decreased with delay in intercropping. However, LER values indicated that the intercrops had yield advantage over the sole crop maize. The appropriate time of intercropping maize with the legumes for optimum maize yield is very early (before or at 2 WAP maize). Results also showed that cowpea suppressed more weeds in the maize field than groundnut and soybean. Cowpea-maize intercrop gave a maize yield of 2988 kg/ha which was not significantly different from the sole maize yield of 3291 kg/ha at 2 WAP maize.

Tree biomass and soil carbon stocks in indigenous forests in comparison to plantations of exotic species in the Taita Hills of Kenya

Carbon (C) densities of the tree biomass and soil (0–50 cm) in indigenous forest and plantations of eucalyptus, cypress and pine in the Taita Hills, Kenya were determined and compared. The cypress and pine plantations were about 30-years-old and eucalyptus plantations about 50-years-old. Biomass C densities were estimated from breast height diameter and wood density using allometric functions developed for tropical species and an assumed C content of 50%. Belowground biomass C densities were estimated using root:shoot biomass ratios. Soil organic C (SOC) densities were calculated from measured organic carbon contents (0–20 and 20–50 cm layers) and modelled bulk density values. Mean total biomass C and SOC densities for indigenous forest were greater than those of the plantations, and the difference was significant (p < 0.05) in the cases of cypress and pine biomass and pine SOC. The correlation between biomass C and SOC densities was nearly significant in the case of indigenous forest, but negative. Biomass C densities were not significantly correlated with mean annual precipitation, mean annual temperature or potential evapotranspiration, but pine biomass C densities were significantly correlated to actual evapotranspiration. SOC densities were more strongly correlated to mean annual precipitation than biomass C densities, but only significantly so in the case of pine. Neither biomass C nor SOC densities were correlated to plant available water capacity of the soil. Indigenous forest SOC densities were significantly correlated to soil clay contents, but negatively. Indigenous forests sequester more C in biomass and soil than do 30 to 50-year-old plantations of exotics, but it remains unclear if this is an intrinsic difference between indigenous forest and plantations of exotics or because of insufficient time for SOC levels in plantations to recover after clearance of original indigenous forest.

The Nitrogen Adaptation Strategy of the Wild Teosinte Ancestor of Modern Maize, Zea mays subsp. parviglumis

ABSTRACTExamination of wild ancestors can identify which traits have been altered by selection as possible targets for genetic improvement. We investigated the whole plant response to low nitrogen (LN), especially below ground, by the wild ancestor of modern maize (Zea mays L.), Balsas teosinte (Zea mays subsp. parviglumis H. H. Iltis & Doebley). Teosinte responded to LN by reducing the shoot N concentration and increasing the root:shoot biomass ratio. The lengths of individual crown roots and the total lateral root length increased, compensated by reduced crown root number. Low N caused a decrease in total root hair (RH) length and increased expression of high affinity nitrate transporters. To facilitate future mapping studies, these results were compared to a modern inbred (‘W22’) used as the parent in a modern maize × teosinte population and extensively employed in maize domestication studies. The adaptations to LN in teosinte and W22 were surprisingly conserved, but the strategies employed were often different. To reduce total RH length, teosinte reduced RH density whereas W22 reduced average RH length. To achieve reduced shoot biomass in response to LN, teosinte reduced tiller number and hence leaf number whereas W22 reduced average leaf size. Since tiller crown roots initiate from stem tissue, teosinte used tiller plasticity to reduce crown root number whereas modern maize reduced crown root number independently of tillering. We discuss the implications of these results for maize domestication.

The Impacts of Fertilizer and Hexazinone on Sheep Sorrel (Rumex acetosella) Growth Patterns in Lowbush Blueberry Fields

Sheep sorrel is an invasive, creeping perennial weed of lowbush blueberry fields that decreases yields and hinders harvest. Much of the basic phenology of sheep sorrel in blueberry fields is unknown and not documented in peer-reviewed journals. Three levels of fertilizer (0, 20, and 40 kg N ha−1) and two levels of hexazinone (0 and 1.92 kg ai ha−1) were applied to three vegetative-year blueberry fields to determine their effects on root and shoot growth, biomass allocation, and seed production of sheep sorrel plants. Hexazinone efficacy varied widely between sites, but suppressed shoot biomass, achene number and weight, and reproductive biomass, as well as the reproductive : shoot biomass ratio. Fertilizer tended to increase achene number and increased sheep sorrel shoot biomass in the absence of hexazinone, but had no effect on achene weight, root biomass, or reproductive biomass. When fertilizer was applied, sheep sorrel allocated resources to sexual reproduction at the expense of vegetative growth.

Salinity Effects on Germination and Plant Growth of Prairie Cordgrass and Switchgrass

Identifying bioenergy crops that can be produced successfully on marginal lands, such as those affected by salinity, reduces the pressure to produce energy crops on land that would otherwise be used to produce food crops. In this paper, the degree of salinity tolerance of “Red River” prairie cordgrass (Spartina pectinata Link) and “Cave-in-Rock” switchgrass (Panicum virgatum L.) was determined by evaluating seed germination, plant growth, ion uptake, and leaf anatomical feature responses in saline conditions. Red River seeds retained 50% of germination potential under high salinity up to 300 mM NaCl, whereas Cave-in-Rock seed germination was reduced by 80% at 300 mM NaCl. Red River seedlings survived up to 500 mM NaCl, while more than 30% of Cave-in-Rock did not survive above 100 mM NaCl in greenhouse experiments. Red River produced more biomass and second-generation tillers and had a greater root and shoot biomass ratio than Cave-in-Rock under all salinity ranges. Sodium accumulation in shoots of Cave-in-Rock increased with increasing salinity, whereas Red River maintained a low level of sodium in biomass through salt-gland exclusion. The increasing rate of selectivity coefficient for potassium over sodium in Red River was higher than in Cave-in-Rock with increasing salinity. Although seed germination and plant growth decreased as salinity increased, Red River retained its potential of seed germination and to produce new tillers and biomass under salinity stress.

Immature Seedling Growth of Two North American Native Perennial Bunchgrasses and the Invasive Grass Bromus tectorum

Pseudoroegneria spicata (Pursh) A. Löve and Elymus wawawaiensis J. Carlson & Barkworth are two native perennial grasses widely used for restoration in the Intermountain West. However, the rapid establishment and spread of Bromus tectorum L., an invasive annual grass, has led to a decline in the abundance of native perennial grasses. Proliferation of B. tectorum has been attributed to its early germination, superior cold-temperature growth, profuse root production, and high specific leaf area (SLA). To enhance restoration success, we compared B. tectorum to commercially available plant materials of two perennial rangeland bunchgrasses, P. spicata (cv. Whitmar, cv. Goldar, and Anatone Germplasm) and E. wawawaiensis (cv. Secar), for germination, seedling morphological traits, and growth rates at the immature seedling stage. We monitored germination and immature seedling growth in a growth chamber in two separate experiments, one under low (5/10°C) and the other under high (15/20°C) day/night temperatures. Compared to the average of the two perennials, B. tectorum was 93% (77%) greater at high (and low) temperature for root∶shoot length ratio, but only 14% (14%) greater for root∶shoot biomass ratio and 12% (19%) lower for SLA. This suggests that B. tectorum’s substantial investment in surface area of roots, rather than in shoot length, root biomass, or leaf area, may be responsible for the annual’s success at the early seedling stage. Compared to E. wawawaiensis, P. spicata averaged 65% (41%) higher shoot biomass, 39% (88%) higher root biomass, and 70% (10%) higher absolute growth rate, but 25% (15%) lower SLA and 15% (36%) lower specific root length (SRL) at high (and low) temperatures, respectively. Although P. spicata’s greater productivity may initially make for better seedling establishment than E. wawawaiensis, it may also prove disadvantageous in competitive or highly resource-limited environments where high SLA or SRL could be an advantage. Pseudoroegneria spicata (Pursh) A. Löve y Elymus wawawaiensis J. Carlson & Barkworth son dos pastos perennes nativos ampliamente utilizados para la restauración de pastizales naturales de la región comprendida entre las Rocallosas y las Sierras Nevadas del Oeste de los Estados Unidos (Intermountain West). Sin embargo, el rápido establecimiento y dispersión de Bromus tectorum L., una planta invasora anual, ha ocasionado una disminución en la abundancia de pastos perennes nativos. La proliferación de B. tectorum ha sido atribuida a su germinación temprana, su habilidad superior de crecer en condiciones de bajas temperaturas, su elevada producción radicular, y una elevada área foliar específica (AFE). Con la finalidad de mejorar el éxito de los proyectos de restauración, comparamos la germinación, los atributos morfológicos de las plántulas, y las tasas de crecimiento en los estadios previos a la madurez de las plántulas de B. tectorum y germoplasma disponible comercialmente de dos pastos cespitosos perennes, P. spicata (cv. Whitmar, cv. Goldar, y Anatone Germplasm) y E. wawawaiensis (cv. Secar). Monitoreamos la germinación y el crecimiento de plántulas durante los estadios previos a la madurez en una cámara de crecimiento en dos experimentos diferentes, uno en condiciones de baja (5/10°C) y otro en condiciones de alta (15/20°C) temperatura diurna/nocturna. Comparado con el promedio de ambas especies perennes, B. tectorum fue 93% (77%) superior en condiciones de alta (y baja) temperatura en la proporción del largo de raíz∶tallo, pero solamente 14% (14%) mayor en la proporción de biomasa raíz∶tallo y 12% (19%) más bajo en AFE. Esto sugiere que el éxito de esta especie anual durante los estadios tempranos de la plántula podría deberse a la inversión sustantiva en el área de superficie de raíces, en vez de invertir en largo de tallos, biomasa radicular, o área foliar. Comparado con E. wawawaiensis, P. spicata tuvo una biomasa de tallos 65% (41%) más elevada, una biomasa radicular 39% (88%) más elevada y una tasa absoluta de crecimiento 70% (10%) más elevada, pero un AFE 25% (15%) inferior y una longitud específica de raíces (LER) 15% (36%) inferior bajo temperaturas altas (y bajas), respectivamente. Si bien la productividad superior de P. spicata podría inicialmente producir mejor establecimiento de plántulas comparado con E. wawawaiensis, podría también estar en desventaja en situaciones de alta competencia o en ambientes con alta limitación de recursos en los que un elevado AFE o LER podrían ser ventajosos.

Adaptability to elevated temperature and nitrogen addition is greater in a high-elevation population than in a low-elevation population of Hippophae rhamnoides

Hippophae rhamnoides L. is a broadleaf deciduous woody shrub occurring in southwest China, where it has been widely used in ecological restoration. In this study we investigated growth and physiological responses of 2-year-old healthy seedlings to elevated temperature, nitrogen (N) addition and their combination in two contrasting populations from high and low elevations. In closed-top chamber experiments, two populations were subjected to two temperature conditions (ambient temperature and temperature elevated by 2.2 +/- 0.2 degrees C) and two N levels (0 and 25 g N m(-2) a(-1)). Compared with the control, increases in total leaf area (TLA), total chlorophyll content (TC), light-saturated photosynthetic rate (P-max), guaiacol peroxidase activity (POD), catalase activity (CAT) and carbon isotope composition (delta C-13) were greater in the high-elevation population than in the low-elevation population under elevated temperature. On the other hand, decreases in root and shoot biomass ratio (RS), TC, P-max, light saturation point (L-SP), light compensation point (L-CP), superoxide dismutase (SOD), POD, CAT and delta C-13 were lower in the high-elevation population than in the low-elevation population under N addition. Moreover, the combination of elevated temperature and N addition decreased RS, P-max, apparent quantum efficiency (Phi), SOD, POD and delta C-13 significantly more in the low-elevation population than in the high-elevation population. These results demonstrated that there are different adaptive strategies among H. rhamnoides populations, the high-elevation population exhibiting higher adaptability to elevated temperature and N addition than the low-elevation population.

Effect of a phosphonium salt grafted on polymers on cucumber germination and initial growth

The aims of this study were the synthesis, characterization and the testing of vinyldiphenylphosphonium salt phytotoxicity. Phytotoxicity of the synthesised salt was tested on Cucumis sativus L. seed germination and early seedling growth, at five different concentrations, using a standardized toxicity test. Endpoints included the determination of some seedling parameters: root and shoot length, root and shoot biomass, root and shoot dry weight ratio and final germination percentage. The vinyldiphenylphosphonium salt showed moderate to strong root length and root biomass inhibition, which increases progressively with the increasd of the concentration level.

Effects of vegetation and fertilizer on metal and Sb plant uptake in a calcareous shooting range soil

Shooting range soils frequently contain anomalous concentrations of metals (e.g. Pb, Zn, Mn) and Sb coming from bullets which may be released into the environment. In a pot experiment, we investigated metal and Sb uptake by three plant species ( Plantago lanceolata, Lolium perenne and Triticum aestivum) growing on a calcareous shooting range soil (pH 7.8; 500 mg kg −1 Pb, 21 mg kg −1 Sb) and the uptake changes when an acidic fertilizer solution was applied to the soil. Metal and Sb solubility in the soil was determined by extraction with 0.1 M NaNO 3. In addition, we measured pH, electrical conductivity and dissolved organic carbon in drainage samples. The results showed significant increase over time of pH (from 7.8 to 8.3) and decrease of electrical conductivity and dissolved organic carbon (from 230 to ∼130 mg L −1). Fertilizer application increased NaNO 3-extractable Pb and Sb and root:shoot biomass ratio but not plant metal uptake. In T. aestivum spikes accumulated more Zn, Ni and Cu than shoots and grains. Mn and Zb uptake was correlated in L. perenne shoots. P. lanceolata, a Sb-bioindicator, did not accumulate high amounts of Sb (<1 mg kg −1).

Intra-annual changes in biomass, carbon, and nitrogen dynamics at 4-year old switchgrass field trials in west Tennessee, USA

Switchgrass is a potential bioenergy crop that could promote soil C sequestration in some environments. We compared four switchgrass cultivars on a well-drained Alfisol to test for differences in biomass, C, and N dynamics during the fourth growing season. There was no difference ( P > 0.05) among cultivars and no significant cultivar × time interaction in analyses of dry mass, C stocks, or N stocks in aboveground biomass and surface litter. At the end of the growing season, mean (±SE) aboveground biomass was 2.1 ± 0.13 kg m −2, and surface litter dry mass was approximately 50% of aboveground biomass. Prior to harvest, the live root:shoot biomass ratio was 0.77. There was no difference ( P > 0.05) among cultivars for total biomass, C, and N stocks belowground. Total belowground biomass (90 cm soil depth) as well as coarse (≥1 mm diameter) and fine (<1 mm diameter) live root biomass increased from April to October. Dead roots were <10% of live root biomass to a depth of 90 cm. Net production of total belowground biomass (505 ± 132 g m −2) occurred in the last half of the growing season. The increase in total live belowground biomass (426 ± 139 g m −2) was more or less evenly divided among rhizomes, coarse, and fine roots. The N budget for annual switchgrass production was closely balanced with 6.3 g N m −2 removed by harvest of aboveground biomass and 6.7 g N m −2 supplied by fertilization. At the location of our study in west Tennessee, intra-annual changes in biomass, C, and N stocks belowground were potentially important to crop management for soil C sequestration.

Flooding effects on rapid responses of the invasive plant Alternanthera philoxeroides to defoliation

In experiments under controlled growth conditions it was examined how flooding affected the responses of the invasive plant Alternanthera philoxeroides to defoliation. In drained and flooded conditions, plants were subjected to five defoliation levels: 0, 10, 50, 90% removal of leaf tissue and apex removal (90% leaf tissue plus apical bud removal). Plants were harvested weekly for five weeks. In drained conditions, plant biomasses including total biomass, shoot biomass and root biomass after 50% defoliation rapidly recovered to the control plant level. They were significantly lower for the 90% defoliation and apex removal treatments compared to control plants throughout the experiment. In flooded conditions, total biomass and shoot biomass after 50% defoliation, 90% defoliation, and apex removal treatments could return to control plant levels before the end of the experiment. In 90% defoliation and apex removal treatments root to shoot biomass ratios of both drained and flooded plants were initially much higher than in control plants, but the difference disappeared rapidly. The final biomasses decreased with increased defoliation intensity in drained conditions, but no significant difference was generally found in any of the defoliation treatments in flooded conditions. The rapid re-growth of A. philoxeroides plants after defoliation may partly be responsible for its invasion success. However, defoliation capable of removing 90% of the leaf tissue may be desirable in restricting the growth of this invasive species in drained conditions.

Interaction between C 4 barnyard grass and C 3 upland rice under elevated CO 2: Impact of mycorrhizae

Atmospheric CO 2 enrichment may impact arbuscular mycorrhizae (AM) development and function, which could have subsequent effects on host plant species interactions by differentially affecting plant nutrient acquisition. However, direct evidence illustrating this scenario is limited. We examined how elevated CO 2 affects plant growth and whether mycorrhizae mediate interactions between C 4 barnyard grass ( Echinochloa crusgalli (L.) Beauv.) and C 3 upland rice ( Oryza sativa L.) in a low nutrient soil. The monocultures and combinations with or without mycorrhizal inoculation were grown at ambient (400 ± 20 μmol mol −1) and elevated CO 2 (700 ± 20 μmol mol −1) levels. The 15N isotope tracer was introduced to quantify the mycorrhizally mediated N acquisition of plants. Elevated CO 2 stimulated the growth of C 3 upland rice but not that of C 4 barnyard grass under monoculture. Elevated CO 2 also increased mycorrhizal colonization of C 4 barnyard grass but did not affect mycorrhizal colonization of C 3 upland rice. Mycorrhizal inoculation increased the shoot biomass ratio of C 4 barnyard grass to C 3 upland rice under both CO 2 concentrations but had a greater impact under the elevated than ambient CO 2 level. Mycorrhizae decreased relative interaction index (RII) of C 3 plants under both ambient and elevated CO 2, but mycorrhizae increased RII of C 4 plants only under elevated CO 2. Elevated CO 2 and mycorrhizal inoculation enhanced 15N and total N and P uptake of C 4 barnyard grass in mixture but had no effects on N and P acquisition of C 3 upland rice, thus altering the distribution of N and P between the species in mixture. These results implied that CO 2 stimulation of mycorrhizae and their nutrient acquisition may impact competitive interaction of C 4 barnyard grass and C 3 upland rice under future CO 2 scenarios.

Water availability limits tolerance of apical damage in the Chilean tarweed Madia sativa

Plant tolerance is the ability to reduce the negative impact of herbivory on plant fitness. Numerous studies have shown that plant tolerance is affected by nutrient availability, but the effect of soil moisture has received less attention. We evaluated tolerance of apical damage (clipping that mimicked insect damage) under two watering regimes (control watering and drought) in the tarweed Madia sativa (Asteraceae). We recorded number of heads with seeds and total number of heads as traits related to fitness. Net photosynthetic rate, water use efficiency, number of branches, shoot biomass, and the root:shoot biomass ratio were measured as traits potentially related to tolerance via compensatory responses to damage. In the drought treatment, damaged plants showed ≈43% reduction in reproductive fitness components in comparison with undamaged plants. In contrast, there was no significant difference in reproductive fitness between undamaged and damaged plants in the control watering treatment. Shoot biomass was not affected by apical damage. The number of branches increased after damage in both water treatments but this increase was limited by drought stress. Net photosynthetic rate increased in damaged plants only in the control watering treatment. Water use efficiency increased with drought stress and, in plants regularly watered, also increased after damage. Root:shoot ratio was higher in the low water treatment and damaged plants tended to reduce root:shoot ratio only in this water treatment. It is concluded that water availability limits tolerance to apical damage in M. sativa, and that putative compensatory mechanisms are differentially affected by water availability.

Forest biomass and root–shoot allocation in northeast China

Temperate and boreal forests act as major sinks for atmospheric CO 2. To assess the magnitude and distribution of the sinks more precisely, an accurate estimation of forest biomass is required. However, the determinants of large-scale biomass pattern (especially root biomass) are still poorly understood for these forests in China. In this study, we used 515 field measurements of biomass across the northeast part of China, to examine factors affecting large-scale biomass pattern and root–shoot biomass allocation. Our results showed that, Picea & Abies forest and coniferous & broadleaf mixed forest had the highest mean biomass (178–202 Mg/ha), while Pinus sylvestris forest the lowest (78 Mg/ha). The root:shoot (R/S) biomass ratio ranged between 0.09 and 0.67 in northeast China, with an average of 0.27. Forest origin (primary/secondary/planted forest) explained 31–37% of variation in biomass (total, shoot and root), while climate explained only 8–15%, reflecting the strong effect of disturbance on forest biomass. Compared with shoot biomass, root biomass was less limited by precipitation as a result of biomass allocation change. R/S ratio was negatively related to water availability, shoot biomass, stand age, height and volume, suggesting significant effects of climate and ontogeny on biomass allocation. Root–shoot biomass relationships also differed significantly between natural and planted forests, and between broadleaf and coniferous forests. Shoot biomass, climate and forest origin were the most important predictors for root biomass, and together explained 83% of the variation. This model provided a better way for estimating root biomass than the R/S ratio method, which predicted root biomass with a R 2 of 0.71.