Climatic conditions have changed within the cloud forests of southern Mexico, but the effects of these changes on tree phenology are not well understood. Our study aimed to determine relationships between seasonal patterns of flowering and fruiting and the annual and long-term changes in temperature and rainfall in El Triunfo Biosphere Reserve, Mexico. Flowering and ripe fruiting intensity and fruit number were recorded for 158 trees of 21 zoochorous species during 17 months in 2019–2021. Circular statistics, synchronization calculations, and generalized linear mixed models were used to determine phenological patterns and relationships between phenophases and temperature, rainfall, and solar radiation. Flowering was most closely associated (negatively) with rainfall, whereas ripe fruiting was positively associated with solar radiation. We compared recent fruiting seasonality with phenological data collected in 1991–1993. The mean date of community fruiting in 2019–2020 was earlier (April 4) than in 1992 (May 1) and 1993 (May 13). Community fruit number in 2020–2021 decreased in comparison to 2019–2020. Our results suggest that decadal trends of increasing minimum daily temperature and an earlier and wetter wet season influenced the timing of community fruiting phenology, and fruit numbers varied greatly between years, possibly impacting resource availability for frugivores in El Triunfo.

To exploit the potential of ecological intensification during sunflower cropping, it is crucial to understand the potential synergies between crop management and ecosystem services. We therefore examined the effect of pollination intensification on sunflower yield and productivity under various levels of soil fertilization over two seasons in the eastern Free State, South Africa. We manipulated soil fertility with fertilizer applications and pollination with exclusion bags. We found a synergetic effect between pollination and soil fertilization whereby increasing pollination intensity led to a far higher impact on sunflower yield when the soil had been fertilized. Specifically, the intensification of insect pollination increased seed yield by approximately 0.4 ton/ha on nutrient poor soil and by approximately 1.7 ton/ha on moderately fertilized soil. Our findings suggest that sunflower crops on adequate balanced soil fertility will receive abundant insect pollination and may gain more from both synergies than crops grown in areas with degraded soil fertility.

Comparative transcriptomics can be used to translate an understanding of gene regulatory networks from model systems to less studied species. Here, we use RNA-Seq to determine and compare gene expression dynamics through the floral transition in the model species Arabidopsis thaliana and the closely related crop Brassica rapa. We find that different curve registration functions are required for different genes, indicating that there is no single common ‘developmental time’ between Arabidopsis and B. rapa. A detailed comparison between Arabidopsis and B. rapa and between two B. rapa accessions reveals different modes of regulation of the key floral integrator SOC1, and that the floral transition in the B. rapa accessions is triggered by different pathways. Our study adds to the mechanistic understanding of the regulatory network of flowering time in rapid cycling B. rapa and highlights the importance of registration methods for the comparison of developmental gene expression data.

Temporal and spatial patterns in flowering phenology were assessed for eight tropical African tree species. Specifically, the frequency and seasonality of flowering at seven sites in central Africa were determined using field data, graphical analysis and circular statistics. Additionally, spatial variation in the timing of flowering across species range was investigated using herbarium data, analysing the relative influence of latitude, longitude and timing of the dry season with a Bayesian circular generalized linear model. Annual flowering was found for 20 out of the 25 populations studied. For 21 populations located at the north of the climatic hinge flowering was occurring during the dry season. The analysis of herbarium collections revealed a significant shift in the timing of flowering with latitude for E. suaveolens, and with the timing of the dry season for M. excelsa (and to a lesser extent L. alata), with the coexistence of two flowering peaks near the equator where the distribution of monthly rainfall is bimodal. For the other species, none of latitude, longitude or timing of the dry season had an effect on the timing of flowering. Our study highlights the need to identify the drivers of the flowering phenology of economically important African tree species.

The regrowth of a C3 forage Stylosanthes capitata in a rain-fed field provided the weekly data collection in the southeast of Brazil during a heat event in autumn. A system named Trop-T-FACE simulated the free-air carbon dioxide enrichment and the enhanced temperature in four climatic regimes: current atmospheric conditions (Control), CO2 enrichment (600 ppm, eC), warming (2 °C above ambient canopy temperature, eT), and a combination of eC + eT. The area and biomass of foliage per shoot decreased, and the number of flowers per shoot and flowered ramification increased under single eC treatment besides the increment in palisade parenchyma of leaves. Increased investment in flowering in eC occurred notably when the soil water content was higher than 0.30 m3 m–3. Single eT treatment also impaired the area or biomass of foliage production per shoot, raised the shoot mortality, and promoted the increment of the spongy leaf parenchyma. There was some mitigation of the adverse effects of foliage production of eT or eC in eC + eT, but under this combined treatment, the shoot mortality also increased. Changes in leaf tissues under eC or eT or some mitigation of adverse effects in eC + eT did not offset the constraints on leaf growth per shoot. The harmful impact on foliage production by eC, eT, or eC + eT under rain-fed conditions indicated no advantages for feeding the livestock with the C3 forage S. capitata in expected climate change under field conditions.

Information about weed biology and weed population dynamics is critical for the development of efficient weed management programs. A field experiment was conducted in Fayetteville, AR, during 2014 and 2015 to examine the effects of Palmer amaranth (Amaranthus palmeri S. Watson) establishment time in relation to soybean [Glycine max (L.) Merr.] emergence and the effects of A. palmeri distance from the soybean row on the weed’s height, biomass, seed production, and flowering time and on soybean yield. The establishment time factor, in weeks after crop emergence (WAE), was composed of six treatment levels (0, 1, 2, 4, 6, and 8 WAE), whereas the distance from the crop consisted of three treatment levels (0, 24, and 48 cm). Differences in A. palmeri biomass and seed production averaged across distance from the crop were found at 0 and 1 WAE in both years. Establishment time had a significant effect on A. palmeri seed production through greater biomass production and height increases at earlier dates. Amaranthus palmeri that was established with the crop (0 WAE) overtopped soybean at about 7 and 10 WAE in 2014 and 2015, respectively. Distance from the crop affected A. palmeri height, biomass, and seed production. The greater the distance from the crop, the higher A. palmeri height, biomass, and seed production at 0 and 1 WAE compared with other dates (i.e., 2, 4, 6, and 8 WAE). Amaranthus palmeri establishment time had a significant impact on soybean yield, but distance from the crop did not. The earlier A. palmeri interfered with soybean (0 and 1 WAE), the greater the crop yield reduction; after that period no significant yield reductions were recorded compared with the rest of the weed establishment times. Knowledge of A. palmeri response, especially at early stages of its life cycle, is important for designing efficient weed management strategies and cropping systems that can enhance crop competitiveness. Control of A. palmeri within the first week after crop emergence or reduced distance between crop and weed are important factors for an effective implementation of weed management measures against A. palmeri and reduced soybean yield losses due to weed interference.

Field and container studies were conducted to determine effects of prodiamine on Florida betony and leatherleaf fern. Effects of Florida betony competition on leatherleaf fern frond yield and quality were also determined. Seed germination and growth and flowering of established Florida betony decreased with increasing prodiamine application rates; 4.5 kg ai ha-1 or higher prevented seed germination and eliminated or nearly eradicated established betony one year after treatment. Prodiamine treatments up to 6.7 kg ai ha-1 did not affect leatherleaf fern growth, frond yield (number, fresh weight) or quality (color, size, vase life). When leatherleaf fern and Florida betony were grown together in containers for 7 mo, fern frond yield and quality were reduced.

Seedling vernalization was more effective than seed vernalization in promoting flowering of downy brome (Bromus tectorum L. # BROTE). Vernalizing imbibed downy brome caryopses at 3 C for 0 to 30 days did not induce rapid flowering when the caryopses were planted. Downy brome seedlings were exposed for 30 days to six photoperiod/temperature treatments. After subsequent transfer to long days, plants from the short-day/3 C treatment flowered within 30 days. Flowering was delayed or was absent in treatments with higher temperatures or long days. The shoot apex increased in volume during the short-day/3 C vernalization period. Two days following vernalization, floral initiation had occurred. By day 5, lateral organs had proliferated. Rudimentary glumes and lemmas were visible by day 8.

A survey conducted to determine the distribution of red horned poppy in western Oklahoma identified infestations in 14 Oklahoma and 3 Texas counties. Soil pH from infested fields ranged from 7.0 to 8.5. Red horned poppy grew as an annual, germinating in fall, spring, or summer. Plants that emerged in the fall survived −25 C, flowered in April and produced mature seed in June. Plants that emerged in April, flowered in June and produced mature seed in July. Corolla color varied from red to yellow with time of anthesis.

When velvetleaf plants from Mississippi and Minnesota populations were maintained in growth chambers with day/night temperatures of 29/23 C and photoperiods of 11, 12, 13, 14, and 15 h, flower buds and open flowers appeared first in the 12 h photoperiod. Buds and flowers appeared 2 to 4 d later at photoperiods of 11, 13, or 14 h. Increasing the photoperiod beyond 14 h to 15 h delayed bud appearance an additional 7 d in the MN plants and 12 d in the MS plants. Open flowers appeared four to five nodes higher, 10 d later at 15 than at 14 h in the MN plants and 20 d later in the MS plants. Vegetative shoot weight and fruit weight 73 d after emergence were greater in 13 h or longer photoperiods than at 11 or 12 h. In shorter photoperiods, MN plants produced more vegetative growth than MS plants, but the reverse occurred at longer photoperiods where MS plants were taller than MN plants. These growth differences occurred because earlier shifts in allocation to reproductive growth in MN plants limited their vegetative growth, particularly in the longest photoperiods. Differences in rate of reproductive development between populations were not evident until photoperiod exceeded 13 h. Reciprocal transfer of plants of the MS population between short and long photoperiods revealed the durations of the juvenile (pre-inductive), inductive, and post-inductive phases to be 3 to 5, 7 to 8 (short day) or 30 (long day), and 10 to 11 d, respectively. Differences in competitive ability among latitudinal biotypes of photoperiodically-sensitive weeds may depend on time of emergence in the field and consequent photoperiod exposure. Weed growth simulation models to be used in development of expert systems for weed management should take photoperiodic sensitivity into account.

The reproductive characteristics of natural populations of meadow salsify were monitored between May 1990 and October 1991. Plants in even-aged populations did not produce seeds prior to the second winter and plants in uneven-aged populations died after seed production suggesting that meadow salsify at this site is a monocarpic perennial and not a true biennial. Delayed seed production may enhance abundance of this species by increasing the size of its bud bank. Plants of uneven-aged populations flowered over a range of root crown diameters; the percentage of plants bearing flowers increased with increasing root crown diameters. The minimum root crown diameter at which plants flowered in 1990 and 1991 was 0.2 and 0.6 cm respectively demonstrating that factor(s) other than plant size regulate flowering in this species. Seed production ranged between 100 to 850 seeds per plant. Total number of flower heads per plant and florets per plant were positively correlated with each other and with the root crown diameter. Root crown diameter is, therefore, a good indicator of potential fecundity in meadow salsify. Greater seed production by larger plants may compensate, at least in part, for the high juvenile mortality and longer generation time in this species. The results suggest that prolific seed production and long vegetative survival are important strategies in the maintenance of meadow salsify populations.

Palmer amaranth (Amaranthus palmeri S. Wats. # AMAPA) planted in a field at monthly intervals from March through October at Shafter, CA, began to emerge in March when soil temperatures at a depth of 5 cm reached 18 C. With the exception of March and April plantings, at least 50% of the seed of later plantings produced seedlings within 2 weeks after planting. Although growth of plants was initially slower for early plantings, plantings from March to July reached 2 m or greater in height by fall. Due to longer growing times, plantings from March to June eventually produced more dry matter and a greater number of inflorescences than later plantings. Plants began flowering 5 to 9 weeks after planting in March through June and 3 to 4 weeks after planting in July through October. Some viable seed was produced as early as 2 to 3 weeks after flowering began. Total seed production in the fall ranged from 200 000 to 600 000 seed/plant for the March through June plantings, and 115 to 80 000 seed/plant for the July through September plantings. Killing frosts in November prevented Palmer amaranth planted in October from producing seed.

Morphological and physiological variation among annual bluegrass populations from the green, fairway, and rough were measured to determine the role annual bluegrass infestations outside the green play in maintaining the population in the green. Annual bluegrass populations from the fairway and the rough were similar to each other but differed from that of the green in habit, dry mass production, flowering, seed size, and germination. Seeds from each population established best in the type of turf from which they originated. It is concluded that, since few genotypes were common to the green and its surroundings, the populations in the fairway and rough played little or no role in maintaining the population of the green. The same is likely to be true wherever the management of greens and their surroundings differs sufficiently for marked population differentiation to occur. This finding does not preclude the possibility that some genotypes adapted to the green persist in the surroundings, and that these genotypes serve as sources of seeds for the colonization or reinfestation of annual bluegrass-free greens.

Seed of johnsongrass [Sorghum halepense (L.) Pers.] were planted during 1976 and 1977 at monthly intervals from March through October to study the growth and reproductive habits of this weed at Shafter, California. Plants were grown for 12 weeks and harvested at 3-week intervals. Emergence and development of plants increased with temperature. April through August plantings yielded 10-to 20-fold as much total fresh weight as March and September plantings. After planting, rhizome production normally began in 3 to 6 weeks and seed production in 6 to 9 weeks. From the April through August plantings, rhizomes accounted for averages of 13, 25, and 40% of the total fresh weight of plants 6, 9, and 12 weeks after planting, respectively. This compared, respectively, with 16, 9, and 6% for roots and 70, 66, and 54% for shoots. Seedlings emerging in March produced rhizomes in early June and viable seed in late June. Seedlings emerging as late as September produced rhizomes and some viable seed before killing frosts in November.

Horsenettle was described quantitatively in two grazed bermudagrass pastures for two years. Six times from April through October, plants were counted, phenologically documented, and tops were harvested for estimation of above-ground phytomass. Roots were sampled for carbohydrate, N fraction, and macronutrient analyses. Top growth, flowering, fruiting, and chemical composition were similar between sites within years, but differed between years. Starch and total non-structural carbohydrates in roots increased following reproductive periods both years. Root concentrations of protein and non-protein N increased and concentrations of P decreased in August and September in one year only. Analysis of the relationship between seasonal trends in carbohydrate fluctuation and pasture management practices suggests that systemic herbicide application in mid-summer may lead to more effective control than application in spring.

The effects of 8-, 12-, and 16-h photoperiods on the growth and reproductive biology of purple nutsedge (Cyperus rotundus L.) were investigated over a 3-month period. Plants under the 8-h photoperiod produced the least total, shoot, root, rhizome, and tuber dry weight. Flowering occurred only at the 12-h photoperiod; thus, purple nutsedge is intermediate in flowering response to daylength. Although the total dry weight varied with photoperiod, the relative amount of dry weight (as percent of total weight) partitioned to shoots, roots, rhizomes, and tubers was constant.

Knowledge of Palmer amaranth demographics and biology is essential for the development and implementation of weed management strategies. A field experiment was conducted to investigate the effects of Palmer amaranth density on seedling mortality, flowering initiation, and flowering progress throughout the growing season and biomass production and fecundity in wide-row soybean. The experimental design was a randomized complete block design with three levels of Palmer amaranth density-clusters: high, medium, and low. Palmer amaranth mortality rate was greater at high Palmer amaranth population density-cluster, reaching a peak within 30 to 40 d after Palmer amaranth emergence (DAE) (0.55 and 0.80 for 2014 and 2015, respectively), in comparison with mortality rate at medium and lower density-clusters. Likewise, as Palmer amaranth density increased, biomass and seed production per unit area of the weed also increased. Biomass production at the high density-cluster in 2014 was 664.7 g m−2 compared with 542.9 and 422.1 g m−2 at medium and low density-clusters, respectively. Similarly, biomass production at high density-cluster in 2015 was 100.6 g m−2 compared with 37.3 and 34.2 at medium and low density-clusters, respectively. In addition, seeds produced at high density-cluster were 1.5 million and 245,400 seeds m−2 for 2014 and 2015, respectively. Seed production was reduced by 29% and 54% in 2014 and by 65% and 75% in 2015 at medium and low density-clusters, respectively. Earlier flowering initiation (i.e., between 30 to 40 DAE) occurred in higher Palmer amaranth density-clusters, indicating a trade-off between reproduction and survival at high densities and more stressed environments for species survival. Palmer amaranth male-to-female sex ratio was greater at high densities, 1.3 and 1.9, compared with lower densities of 0.6 to 0.7 and 0.7 to 0.8 in 2014 and 2015, respectively. The plasticity of Palmer amaranth population and population-structure regulation, vegetative growth, and flowering shifts at various levels of intraspecific competition (i.e., high vs. low population density-clusters) and the trade-off between these biological transitions merits further investigation.

Knowledge of Palmer amaranth biology and physiology is essential for the development of effective weed management systems. The aim of this study was to investigate the response of Palmer amaranth gender to nutrient deficiency and light stress. Differential gender responses were observed for all the growth, phenology, and photochemistry parameters measured. Female plants, for example, invested more in height, stem, and total dry weight, whereas male plants invested more in leaf area and leaf dry weight. The growth rate of females was higher than that of male Palmer amaranth plants, although both followed similar declining trends as the experimental period progressed. Initiation of flowering of female plants occurred 6 to 8 d earlier compared with male plants. Nitrogen and to a certain extent phosphorous were the most influential nutrients that affected measured parameters in both Palmer amaranth genders, particularly under high light intensity. Electron transport rate and chlorophyll content of female Palmer amaranth plants compared with male plants was lower at high light intensity in combination with nitrogen and phosphorous deficiencies. There is a potential to manipulate Palmer amaranth population structure by altering microenvironments at the field level.

Methods were developed and tested for mapping the distribution of Scotch broom, an invasive shrub species expanding its range and disrupting native species and habitats in several parts of the world. During spring, the Scotch broom produces yellow flowers. Landsat imagery during the flower bloom period and during summer was acquired for several years for a study area on Vancouver Island, British Columbia, Canada. Ground-based reflectance measurements plus statistical separability tests were conducted to determine the effectiveness for identifying Scotch broom with Landsat spectral bands, band ratios, vegetation indices, and combinations of bloom and nonbloom imagery. Maximum likelihood classifications of three Scotch broom density classes (dense, ≥ 75% cover; moderate, 25 to 75%; low, 10 to 25%) and other land covers were run with various image and band sets and tested against independent reference sites. Accuracies of classifications using the better band combinations for moderate and dense Scotch broom patches combined were on the order of 80%, with unreliable results for sites of low Scotch broom density. Scotch broom patches less than 0.5 ha were often missed. Some commission error occurred (areas erroneously classified as Scotch broom). Suggested improvements are the use of time series of classifications over multiple years, incorporating knowledge of Scotch broom spread mechanisms or temperature and elevation limitations, and use of higher resolution satellites if the expense warrants it. Despite some limitations, a satellite-based remote sensing approach may be useful for aspects of Scotch broom management.

During the past century, common ragweed has spread from its native eastern North America to Europe, where it has become an increasing problem from both an agricultural and a human health perspective. Two field experiments were performed over a 2-yr period in a naturally infested fallow field in northern Italy to evaluate the effects of common ragweed plant density on its growth dynamics and to study its response to clipping. In the first experiment, three plant densities were tested (4, 12.5, and 25 plants m−2) and plant height, aboveground biomass, and leaf area were assessed. Intraspecific competition had a substantial negative effect on leaf area and aboveground biomass on a per plant basis in both years, but did not affect plant height. However, the high-density (25 plants m−2) treatment resulted in the highest total aboveground biomass (1,428 and 4,377 g m−2) and leaf area index (5.6 and 12.6 m2 m−2) in 2006 and 2007, respectively. In the second experiment, common ragweed plants were clipped at reaching 20 cm (four clippings during the season), 50 cm (three clippings), or 80 cm (two clippings) plant height. Number of surviving plants, flowering plants, and aboveground biomass were assessed before each clipping. Clipping resulted in a partial reduction in the surviving plants and did not prevent flowering. Under the most stressing condition (clipping at 20 cm height), more than 67% of plants survived to the last clipping and, among these, more than 97% flowered, whereas before the last clipping at reaching 80 cm height from 50 to 100% of plants survived and 100% of them flowered. These findings in northern Italy confirm that common ragweed is a fast-growing annual species, capable of producing considerable aboveground biomass at various pure stand densities and that plants can still flower from plants clipped at various frequencies.