We investigated the influence of availability as well as type of organic substrate on the growth of the cyanolichen Peltigera membranacea. A total of 145 lichen lobes were grown in a plant growth chamber for 28 days. Of these, 73 were kept in permanent darkness and another 72 were exposed to a diurnal light-dark cycle. A third of the lobes from both treatments were grown on pulverized leaf litter, the second third on pulverized bryophytes, and the remainder were grown without an organic substrate to serve as a control group. Growth was quantified via relative growth rate, relative thallus area growth rate, and changes in specific thallus mass. The lobes kept in a diurnal light-dark cycle showed higher growth rates than those kept in darkness, as is expected for an organism that obtains its carbon from its photoautotrophic symbiosis partner. Furthermore, growth rates were higher in lobes growing on organic substrates. The results show that the availability of an organic substrate positively affects lichen growth in a growth cabinet. Leaf litter led to a higher biomass gain in lichen lobes, whereas area gain was unrelated to substrate type.

Harvest weed seed control (HWSC) is a weed management technique that intercepts and destroys weed seeds before they replenish the soil weed seedbank and can be used to control herbicide-resistant weeds in global cropping systems. Wild radish (Raphanus raphanistrum L.) is a problematic, globally distributed weed species that is considered highly susceptible to HWSC, as it retains much of its seed on the plant during grain harvest. However, previous studies have demonstrated that R. raphanistrum is capable of adapting its life cycle, in particular its flowering time, to allow individuals more time to mature and potentially shed seeds before harvest, thereby evading HWSC interception. This study compared the vegetative growth plus physiological and ecological fitness of an early-flowering R. raphanistrum biotype with an unselected genetically related biotype to determine whether physiological costs of early flowering exist when in competition with wheat (Triticum aestivum L.). Early flowering time adaptation in R. raphanistrum did not change the relative growth rate or competitive ability of R. raphanistrum. However, the height of first flower was reduced in the early flowering time–selected population, indicating that this population would retain more pods below the typical harvest cutting height (15 cm) used in HWSC. The presence of wheat competition (160 to 200 plants m−2) increased flowering height in the early flowering time–selected population, which would likely increase the susceptibility of early-flowering R. raphanistrum plants to HWSC. Overall, early-flowering adaption in R. raphanistrum is a possible strategy to escape being captured by the HWSC; however, increasing crop competition is likely to be an effective strategy to maintain the effectiveness of HWSC.

In vascular plants, larger seeds are generally associated with higher germination potential, healthier seedlings and overall higher rates of survivorship. How this relationship holds or what other physiological tradeoffs evolved in plants adapted to high-altitude environments, such as the tropical and subtropical highland Polylepis tree, remain unclear. In this study, we evaluated the relationship between seed mass and seedling performance by testing the reserve effect, the metabolic effect, and the seedling-size effect hypotheses in Polylepis tomentella Weddell (Rosaceae). Since the relationship between fitness and seed size can often depend on maternal plant size, we additionally investigated the association between germination success, seedling performance (survival, relative growth rate (RGR) and height), and size of bearing-seed trees under controlled greenhouse conditions. Our results showed that heavier seeds are more likely to germinate, but we did not find evidence that could support the reserve effect, metabolic effect or seedling-size effect. As seedlings from larger and medium seeds exhibited comparatively similar RGR, survival percentages and final size, maternal plant size was positively associated with improved seed quality and seedling performance. These results demonstrate that seed mass and maternal size during early seedling establishment are critical for Polylepis persistence, demography and conservation.

The effects of chlorimuron as related to application timing were evaluated on sicklepod and soybean in the glasshouse. Plants were sprayed with chlorimuron at 8.8 g ai ha–1 at 14, 21, 28, and 35 days after planting (DAP). Early (14 DAP) chlorimuron application reduced sicklepod dry weight, leaf area, and water use to levels significantly less than those of plants treated at 28 and 35 DAP. Soybean dry weight and leaf area were not affected by chlorimuron. However, soybean water use was initially reduced at application timings of 28 DAP or earlier but recovered by 4 weeks after treatment (WAT). Sicklepod net assimilation rate (NAR) and relative growth rate (RGR) were reduced by chlorimuron regardless of application timing while soybean was not affected.

Rate of seedling emergence, relative growth rate (RGR), and phenological development were compared in several accessions of rigid ryegrass belonging to three distinct resistance classes. The aryloxyphenoxypropionate resistant (AOPP-R) class had a faster and less variable seedling emergence than the sulfonylurea resistant (SU-R) and susceptible (S) classes. However, even the fastest of the AOPP-R accessions was within the range of the S and SU-R classes. No significant differences were detected among the resistant classes in seed dormancy, RGR, and the rate of phenological development. The rate of spike emergence, irrespective of the resistance class, was related to the latitude of the origin of the accessions, suggesting adaptation to the local climates since introduction. Due to considerable variation among weed populations for most biological attributes, the need to include several R and S accessions, in studies similar to the one reported here, is of vital importance. Because of the means and variances of the three resistance classes, at least four accessions from each resistance class would have been required to detect the observed differences between emergence rates of the AOPP-R and S classes with a confidence of 95%.

Triazine-susceptible (S) and -resistant (R) biotypes of smooth pigweed (Amaranthus hybridus L.) were grown in the field under competitive conditions at varying initial proportions of S and R plants. R plants were less competitive than S plants as measured by accumulation of total above-ground dry weight and seed dry weight. S and R plants were also grown in the field under non-competitive conditions at 100, 40, and 10% light. Growth rate at 10% light did not differ between S and R plants. At the two higher light intensities, dry-matter accumulation 11 weeks after seeding was about 40% less in the R plants. At 100% light, relative growth rate and net assimilation rate were lower in the R plants by about 3.5 and 19%, respectively. The light- and CO2-saturated rates of CO2 fixation in intact leaves of glasshouse-grown R plants were 20% less than those in S plants. An apparent 10 and 20% greater number of chlorophyll molecules per photosystem II reaction center in R plants (as compared with S plants) grown in the field at 40 and 100% light, respectively, did not explain differences between the S and R biotypes in photo synthetic capacity. The S and R plants did not differ in specific leaf weight or chlorophyll content on a leaf-area basis. Lower growth rate of R plants may be responsible for inferior competitive ability of R biotypes and could be the result of an impaired photosynthetic capacity.

Growth and morphological characteristics of four weed and two crop species were analyzed to determine how small-seeded weeds can compete with large-seeded crops despite the initial size disadvantage. Small-seeded weeds had higher relative growth rates because of increased percentages of biomass devoted to leaves. This morphological scheme was achieved primarily through a reduction in the percentage of biomass devoted to roots. Yet, small-seeded weeds were able to develop larger mean plant root lengths as a result of having both roots of smaller diameter and higher rates of root length increase.

Two greenhouse experiments were conducted to compare the growth of individual sulfonylurea-resistant and -susceptible kochia under noncompetitive conditions. Aboveground leaf and stem dry weight, and leaf area per plant were measured weekly 14 times, starting 14 d after planting. Data were fitted using the Richards function for shoot dry weight per plant, a polynomial exponential for leaf area per plant and splined function to calculate leaf area ratio, leaf weight ratio, and leaf/stem ratio. Absolute and relative growth rates, and net assimilation rate were derived from these functions. Growth and development of individual sulfonylurea-resistant and -susceptible kochia plants under noncompetitive conditions was the same. Final shoot dry weight and leaf area were unaffected by aceto lactate synthase enzyme differences in the kochia biotypes. However, more resources were partitioned to leaves than stems in resistant than in susceptible kochia. If competitive abilities of sulfonylurea-resistant and -susceptible kochia are different, it is not the consequence of differential growth and ontogeny of the two types of plants.

Repeated use of sulfonylurea herbicides in continuous, no-till winter wheat selected for a herbicide resistant biotype of prickly lettuce in Idaho. Greenhouse experiments were conducted to compare the relative competitiveness and growth rate of sulfonylurea herbicide resistant (R) and susceptible (S) prickly lettuce. The S biotype of prickly lettuce produced 31% more aboveground biomass than the R biotype averaged over all densities. Both biotypes were equally competitive when analyzed for both inter- and intrabiotype competition. In relative growth rate studies, regression analysis showed that the S biotype accumulated biomass 52% faster than the R biotype. The results of this study showed that the S biotype was superior to the R biotype in biomass production and growth rate, but competitiveness appeared to be equal for both biotypes. Other fitness parameters must be measured before fitness differences between biotypes can be determined.

A study was conducted to evaluate the response of common and giant ragweed to postemergence applications of imazethapyr using relative growth rate parameters. The relative growth rate was the same for untreated common and giant ragweed through the 21 d harvest interval. Relative growth rates of treated common and giant ragweed were 50% lower than the relative growth rates of untreated ragweeds 21 d after treatment. Between 21 and 56 d after treatment, the relative growth rate of common ragweed declined an additional 13%, while the relative growth rate of giant ragweed declined an additional 38%. The sharp continued decline in the relative growth rate of giant ragweed indicated plant death. The moderation and slight increase in the relative growth rate of common ragweed between 21 and 56 d corresponded with the initiation of lateral axillary buds and the regeneration of plant growth. Relative growth rate parameters identified differences in the response of common and giant ragweed to imazethapyr as early as 21 d after treatment. Relative growth rate demonstrated utility by objectively measuring differences in the growth response of these two weeds that are moderately susceptible to imazethapyr under laboratory conditions.

Cogongrass is a highly invasive perennial grass that threatens agriculture, forestry, and native plant assemblages in many regions of the world. Cogongrass is a prolific seed producer, but the ecological importance of seeds as a vector of invasion has not been adequately addressed. Propagule pressure plays a key role in many successful invasions and the relative importance of propagule pressure across environmental gradients is an area of research that is quickly becoming important in understanding invasion success. The present study was conducted to test the effects of varying propagule density upon the ability of cogongrass seedlings to grow and establish across experimentally manipulated light and soil gradients. Seedlings growing in high-nutrient soil performed the best regardless of the amount of available light, but overall biomass was always greatest in high-light environments. Cogongrass showed a very strong trend in biomass allocation, with seedlings in reduced light environments partitioning more biomass to aboveground tissue. The data provided no evidence that initial propagule density affected the growth and establishment of cogongrass seedlings, but growth and biomass production were positively correlated with final seedling density.

An experiment was conducted in growth chambers to determine the influence of cold temperature regimes, designed to simulate winter temperature conditions and spring recovery, on the interaction between purple deadnettle and soybean cyst nematode (SCN). The study was a factorial arrangement of treatments with five levels of temperature (20, 15, 10, 5, or 0 C), two levels of exposure time to the temperature (10 or 20 d), and two levels of recovery time at 20 C following exposure (0 or 20 d). In general, purple deadnettle shoot and root growth increased with temperature and time. The ability of purple deadnettle to recover from cold temperatures declined as the length of time that the plant was subjected to the cold temperature increased. SCN juveniles per gram of root at the conclusion of the temperature treatment declined as the temperature increased from 0 to 15 C, likely a result of continued purple deadnettle root growth and the inhibition of SCN hatch, growth, or development at those temperatures. SCN female, cyst, and egg production per gram of root generally increased with temperature and occurred under all temperature regimes. The results of this research indicate that, after hatching, SCN juveniles can survive a period of cold temperature inside the roots of a winter annual and continue development when transferred to warmer temperatures. Therefore, in a field environment, where fall or spring alone may not be sufficient for SCN to complete a reproductive cycle on a winter annual weed, the nematode may be able to reproduce by combining the fall and spring developmental periods.

Anecdotal observations of improved glyphosate efficacy on glyphosate-resistant (GR) tall waterhemp populations in corn production compared with soybean suggested the presence of nitrogen (N) fertilizer may influence the expression of glyphosate resistance. Greenhouse and field experiments were conducted to determine the influence of soil-applied nitrogen fertilizer on the growth rate and sensitivity of glyphosate-susceptible (GS) and GR tall waterhemp and Palmer amaranth. The addition of supplemental fertilizer increased the relative growth rate (plant height and shoot volume), number of nodes, and percentage of shoot nodes with axillary branches on GS and GR biotypes of both weed species. The axillary bud activity was increased 52 and 8% with increasing N for the GR and GS biotypes of tall waterhemp and Palmer amaranth, respectively. The GS populations of tall waterhemp and Palmer amaranth were more sensitive to glyphosate in the greenhouse under increased fertilizer levels compared with no fertilizer. Additionally, GR tall waterhemp was more sensitive to glyphosate under the higher fertilizer treatments, which resulted in a reduction in the calculated resistance factor (RF) from 27.8 under no fertilizer to 4.7 for the high fertilizer treatment. The RF for GR Palmer amaranth was not influenced by the fertilizer treatments in the greenhouse. Field experiments demonstrated that glyphosate efficacy may be greater on GR populations of tall waterhemp and Palmer amaranth under high N conditions, but these results were not consistent and most likely were influenced by soil moisture in 2012, which was more limiting than N supply. This research implies that soil fertility can influence the sensitivity of some GR weed species to glyphosate and the RF. Therefore, the evolution and management of GR weed species in commercial crop production may be influenced by the nutrient status of the soil and the use of supplemental fertilizers.

Bridal creeper has become a serious environmental weed in southern Australia. Historically the invaded areas had low soil nutrient levels. However, our field surveys indicate that soils in bridal creeper–invaded areas have higher phosphorus and iron levels than soils in nearby native reference areas regardless of the proximity to agriculture or other disturbances. A glasshouse experiment was undertaken to determine the influence of increased nutrients on plants that co-occur with bridal creeper in order to (1) assess the impact of changed soil conditions and (2) predict the response of dominant species following the biological control of bridal creeper. The relative growth rate (RGR) of bridal creeper, two native shrubs (narrow-leaved thomasia [Thomasia angustifolia] and bluebell creeper [Billardiera heterophylla]), and an invasive exotic grass (annual veldt grass [Ehrharta longiflora]) were determined in three soil types: soil collected within a bridal creeper stand, soil collected from a nearby reference area, and a potting mix with nutrient levels higher than that recorded in the field. The plant species were chosen due to their association with bridal creeper. For example, the native species narrow-leaved thomasia was identified in a previous survey as the most abundant shrub at the invaded site where the soil was collected. The two other species, bluebell creeper and annual veldt grass, were identified from a previous seedbank trial as being abundant (in the seedbank) and able to readily germinate in invaded areas. When grown in either the bridal creeper–invaded soil or reference soil, bluebell creeper had significantly lower RGRs than narrow-leaved thomasia and annual veldt grass. However, as all these species showed increases in RGRs between reference soil and bridal creeper soil, this study indicates that for at least these three species the impact of increased nutrients may not be a barrier to the recovery of invaded areas following the control of bridal creeper.

The nitrogen (N) response of competing plants may be affected by photosynthetically active radiation (PAR) availability and maximum potential growth rate, which determine N requirements. The responses of two crop (corn and soybean) and six weed species (common lambsquarters, common waterhemp, giant foxtail, velvetleaf, wild mustard, and woolly cupgrass) in low and high (150 and 450 μmol m−2 s−1) PAR levels to daily fertilization with either low or high (0.2 or 7.5 mM) NH4NO3 levels were studied. Leaf area of all species responded positively to N by 8 d after emergence (DAE) when grown in high PAR; in low PAR, most species did not respond until 11 DAE. Dry weight and leaf area of all species at 18 DAE were greater with high than with low N. These responses to high N were also greater in high than in low PAR for all species. Dry weights with high N were up to 100% greater in low PAR and up to 700% greater in high PAR than dry weights with low N. These responses suggest that low PAR reduced the benefit of N to the plants. The regression of relative growth rate (RGR) with high N to RGR with low N had a slope that was less than unity (β = 0.79), indicating that species with a higher RGR with high N experienced greater decreases in RGR with low N. Similarly, the sensitivity (change in RGR) of plants grown with high and low N was positively related to RGR with high N. RGR differences among crop and weed species may be related to differences in N requirement that could be exploited for weed management. RGR and seed size were negatively correlated, which may explain previous observations that small-seeded weeds were more sensitive to environmental stress.

Composted manure produced in deep-bedded hoop structures constitutes a source of nutrients and organic materials that can influence crop and weed emergence, growth, competitive interactions, and soil physical properties. The impact of composted swine manure on corn, soybean, winter wheat, velvetleaf, giant foxtail, and common waterhemp emergence and early growth were compared at compost rates of 0, 8, 16, or 24 Mg C/ha. Compost amendment had no effect on crop emergence but did reduce weed emergence. Inhibition of seedling emergence ranged between 15 and 57% for giant foxtail, 0 and 23% for velvetleaf, and 16 and 76% for common waterhemp. Soil amendment enhanced weed growth but not crop growth. A response surface regression analysis indicated that, while large-seeded crops have constant relative growth rates, small-seeded weed species increase their relative growth rates with compost amendment (P < 0.0001, r2 = 0.5252).

A 2-yr field study was conducted to compare the growth of Amaranthus palmeri, A. rudis, A. retroflexus, and A. albus planted in June and July. Rates of height increase (centimeters per growing degree day) were 0.21 and 0.18 for A. palmeri, 0.16 and 0.11 for A. rudis, 0.12 and 0.09 for A. retroflexus, and 0.08 and 0.09 for A. albus in 1994 and 1995, respectively, when planted in June. A. palmeri had among the highest values for plant volume, dry weight, and leaf area, while A. albus had the lowest. Specific leaf area values (cm2 g−1) ranged from 149 to 261 for A. palmeri, 160 to 205 for A. rudis, 150 to 208 for A. retroflexus, and 127 to 190 for A. albus. Maximum relative growth rates (g g−1 day−1) for any measured period were 0.32 for A. palmeri, 0.31 for A. rudis, 0.30 for A. retroflexus, and 0.26 for A. albus. Recent increases in species range and observed changes in weed community structure may be partially explained by the growth characteristics of A. palmeri and A. rudis. Herbicide rate and timing recommendations for mixed populations of these weeds should be based on A. palmeri because of its high growth rates.

A 2-yr field study was conducted to compare growth characteristics of 24 Palmer amaranth accessions collected from across the indigenous range of the species in the United States. Variation in growth and development of Palmer amaranth was noted among accessions based on leaf area ratio (LAR), specific leaf area (SLA), net assimilation rate (NAR), and stem leaf ratio (SLR), but only SLR varied across harvest intervals among accessions. Accessions collected across the range of Palmer amaranth in the United States displayed variation in growth and development based on differences in LAR, SLA, NAR, and SLR. Observed differences among accessions indicate the existence of Palmer amaranth ecotypes.

Research was initiated to determine the periodicity of emergence, seasonal plant growth and reproductive potential, and response to selected preemergence (PRE) and postemergence (POST) herbicides for burcucumber. Under Indiana conditions, burcucumber germinated from late April to October and was stimulated by periodic rainfall. Relative growth rates of plants were greatest up to 10 wk after establishment and declined when flowering was initiated. Without competition, early spring (May)–established burcucumber plants attained a fresh weight of up to 86 kg and produced almost 80,000 seeds. With later establishment, less biomass and and a smaller number of seeds were produced. Seedlings emerging up to mid-August produced germinable seed prior to frost, thus indicating that season-long control strategies are needed to minimize reproduction. A PRE application of atrazine, metribuzin plus chlorimuron, or linuron plus chlorimuron provided greater than 90% visual control up to 8 wk after treatment (WAT). Greater than 80% visual control was obtained with POST applications of glyphosate or with combinations of glyphosate plus dicamba or glyphosate plus 2,4-D; chlorimuron, metribuzin plus chlorimuron; or paraquat. Both imazaquin and bentazon provided less than 70% control. Results indicate that burcucumber displays rapid development with periodic germination throughout the growing season and is capable of producing large amounts of plant biomass and seed.

Relative growth rates (RGR) and carbon-based secondary compounds (CBSCs) were quantified in four dominant terricolous arctic-alpine mat-forming lichens with different preferences for snow cover. The aim was to evaluate the effects of snow depth, and thus snow cover duration, on lichen growth and performance. The species, Alectoria ochroleuca, Flavocetraria nivalis, Cladonia mitis and Cetrariella delisei, are associated with increasing snow depth, respectively. They were transplanted for one year at five snow depths (0, 60, 120, 160 and 200 cm measured in early May) along each of four natural ridge to snow bed gradient transects in oceanic-alpine sites (western Norway). Snow slightly thicker than in source habitats caused negative RGR in the ridge top-dependent A. ochroleuca and the co-occurring F. nivalis with somewhat higher snow tolerance. Only C. mitis with the broadest ecological niche had positive RGR along most of the gradients (0–160 cm), even outside its natural range. The most snow-tolerant species, C. delisei, tolerant also to temporal inundation in water, had the lowest RGR. Nevertheless, it performed as well in places with little or no snow as in places where it grows naturally. Snow depth significantly affected total concentrations of CBSCs mainly in A. ochroleuca, which experienced substantial mass loss under snow. There was a highly significant increase in usnic acid concentration with increasing mass loss in A. ochroleuca, probably because usnic acid decays more slowly than other components. In conclusion, snow reduced lichen RGR, but in species-specific ways. Therefore, increasing snow depth per se along spatial and/or temporal scales likely reduces abundance and distribution of dominant mat-forming lichens in the alpine ecosystems of Scandinavia.