Late-season Conditions Research Articles

Auxins differentially affect growth in Scots pine and Norway spruce in spring and autumn

Trees adapt to changing environmental conditions largely by regulating growth processes, and ongoing climate aridization puts pressure on growth processes during spring and summer. However, trees can be limited in their ability to utilize favourable early-season and late-season conditions for growth, and many of these limitations can be due to shortages in auxin transport and/or signalling. We studied whether leaf spraying with auxins in spring and autumn can aid in the growth of Pinus sylvestris and Picea abies saplings. In spring, spruce demonstrated prominent positive effects of auxin supplementation on the growth of current-year shoot and xylem growth, with increased xylem cell formation, whereas a limited effect was observed in pine. Autumnal auxin treatment had prominent positive effects on the growth of the root system and xylem area in pine, activating xylem cell enlargement and increasing carbon deposition in cell walls. In spruce, the effects of auxin spraying on xylem growth were less prominent, and the effects on root growth were absent compared to those in pine. The metabolome analysis of pine organs demonstrated that the activation of growth processes in the xylem and roots was accompanied by a decrease in nonstructural carbohydrates in the cambial zone but an increase in roots, indicating that auxin influenced the link between growth and carbon balance in an organ-specific manner. The major amino acid content was not influenced by auxin treatment. The observed results indicate that changes in the auxin balance during the autumnal period can activate growth processes to increase plant adaptation to changing climate conditions.

Drivers and dynamics of foliar senescence in temperate deciduous forest trees at their southern limit of distribution in Europe

Research on autumn phenology is very important for understanding and simulating the future growth of temperate deciduous forests. This is especially needed at the southern edge of the temperate zone, where climate change impacts are particularly intense. We studied foliar senescence timing for mature stands of Fagus sylvatica L., Populus tremula L., Betula pendula Roth, Quercus petraea (Matt.) Liebl. and Quercus robur L. at the southern edge of European temperate forests. First, we analysed long-term series (1997–2019) of senescence timing in southern France. Then, we compared a more detailed four-year dataset (2017–2020) of senescence dynamics and its correlations to meteorological conditions for stands in northern Spain and Belgium, with the latter area representing the core distribution of the species. In contrast to other temperate regions, no significant delaying trends in the timing of autumn phenology were detected in the long-term in southern temperate forests, which were characterized by high inter-site variability. In the short-term (4 years), species-specific correlations with meteorological conditions were found, with, for example, the senescence of F. sylvatica being affected by temperature while the senescence of Q. petraea was affected by both temperature and precipitation. Autumn dynamics differed between the core and southern areas of distribution of the species in the study period. In particular, while late season conditions affected senescence timing in the southern populations, the senescence dynamics of the core populations was mostly influenced by the legacy of spring – early summer conditions and, overall, more affected by precipitation than southern populations. Our data fill important knowledge gaps on the functioning of temperate deciduous forests at the southern limit of distribution in Europe.

The Best of Both Worlds: Connecting Remote Sensing and Arctic Communities for Safe Sea Ice Travel


 Northern communities are increasingly interested in technology that provides information about the sea ice environment for travel purposes. Synthetic aperture radar (SAR) remote sensing is widely used to observe sea ice independently of sunlight and cloud cover, however, access to SAR in northern communities has been limited. This study 1) defines the sea ice features that influence travel for two communities in the Western Canadian Arctic, 2) identifies the utility of SAR for enhancing mobility and safety while traversing environments with these features, and 3) describes methods for sharing SAR-based maps. Three field seasons (spring and fall 2017 and spring 2018) were used to engage residents in locally guided research, where applied outputs were evaluated by community members. We found that SAR image data inform and improve sea ice safety, trafficability, and education. Information from technology is desired to complement Inuit knowledge-based understanding of sea ice features, including surface roughness, thin sea ice, early and late season conditions, slush and water on sea ice, sea ice encountered by boats, and ice discontinuities. Floe edge information was not a priority. Sea ice surface roughness was identified as the main condition where benefits to trafficability from SAR-based mapping were regarded as substantial. Classified roughness maps are designed using thresholds representing domains of sea ice surface roughness (smooth ice/maniqtuk hiku, moderately rough ice/maniilrulik hiku, rough ice/maniittuq hiku; dialect is Inuinnaqtun). These maps show excellent agreement with local observations. Overall, SAR-based maps tailored for on-ice use are beneficial for and desired by northern community residents, and we recommend that high-resolution products be routinely made available in communities.

Structural Carbon Allocation and Wood Growth Reflect Climate Variation in Stands of Hybrid White Spruce in Central Interior British Columbia, Canada

Research Highlights: This research presents a novel approach for comparing structural carbon allocation to tree growth and to climate in a dendrochronological analysis. Increasing temperatures reduced the carbon proportion of wood in some cases. Background and Objectives: Our goal was to estimate the structural carbon content of wood within hybrid white spruce (Picea glauca (Moench) × engelmannii (Parry) grown in British Columbia, Canada, and compare the percent carbon content to wood properties and climate conditions of the region. Specific objectives included: (i) the determination of average incremental percent carbon, ring widths (RW), earlywood (EW) and latewood (LW) widths, cell wall thickness, and density over time; (ii) the determination of differences between percent carbon in individual forest stands and between regions; and (iii) the evaluation of the relationships between percent carbon and climate variation over time. Methods: Trees were sampled from twelve sites in northern British Columbia. Wood cores were analyzed with standard dendrochronology techniques and SilviScan analysis. Percent structural carbon was determined using acetone extraction and elemental analysis for 5 year increments. Individual chronologies of wood properties and percent carbon, and chronologies grouped by region were compared by difference of means. Temperature and precipitation values from the regions were compared to the carbon chronologies using correlation, regression, and visual interpretation. Results: Significant differences were found between the percent structural carbon of wood in individual natural and planted stands; none in regional aggregates. Some significant relationships were found between percent carbon, RW, EW, LW, and the cell wall thickness and density values. Percent carbon accumulation in planted stands and natural stands was found in some cases to correlate with increasing temperatures. Natural stand percent carbon values truncated to the last 30 years of growth was shown as more sensitive to climate variation compared to the entire time series. Conclusions: Differences between the stands in terms of structural carbon proportion vary by site-specific climate characteristics in areas of central interior British Columbia. Wood properties can be good indicators of variation in sequestered carbon in some stands. Carbon accumulation was reduced with increasing temperatures; however, warmer late-season conditions appear to enhance growth and carbon accumulation.

Some Agronomical Practices for Improving Growth ,Yield and Quality of Pea Growing at Late Seasons. بعض الممارسات الزراعیة لتحسین النمو والمحصول والجودة للبسلة المنزرعة فی العروات المتأخرة

This work was carried out at the Experimental Farm of El-Baramoon Research Station, Horticulture Research Institute, Agricultural Research Center, during the late winter season of 2018 and 2019 to study the effect of two sowing dates (20th January and 20th February), foliar applications, i.e., brassinolide (5 and10 mg/l), mixture of growth regulator (0.5 and 1cm/l), dry yeast extract (5 and 10gm/l) potassium nitrate (1 and 2 gm/l) and potassium silicate (2.5 and 5gm/l) in addition to vernalization practice and their interactions on growth, yield and its components characteristics of pea cv. Master- B.The obtained results revealed that, the first sowing date induced a higher growth values , yield and its components and chemical composition of seeds compared with the second sowing date. Spraying brassinolide at 10 mg/l gave the highest growth, yield and chemical components of pea plants, followed by potassium nitrate at 2gm/l, growth regulators mixture at 1cm/l and yeast extract at 10gm/l. Sowing pea seeds in 20th January and spraying with brassinolide at 10 mg/l introduced the best interaction with respect to growth, yield components and chemical composition of seeds. From the obtained results it could be recommended that sowing pea in 20th January and spraying with brassinolide (10 mg/l) and/or potassium nitrate at 2gm/l, and/or growth regulators mixture at 1cm/l and/or yeast extract at 10 gm/l improved growth, yield and chemical composition of pea growing at late season conditions .

Effects of Temperature and Photoperiod on the Immature Development in Cassida rubiginosa M\xfcll. and C. stigmatica Sffr. (Coleoptera: Chrysomelidae)

Tortoise beetles (Cassida and related genera) are a large cosmopolitan group that includes several pests of agricultural crops and natural enemies of weeds but their biology and ecology remain poorly known. Using a set of environmental chambers, we address simultaneous effects of temperature and photoperiod on immature development and adult body mass in two European species, C. rubiginosa and C. stigmatica. Consistent with its broader distribution range, the former species is less susceptible to low rearing temperatures, develops faster and has a larger body mass than the latter. However, C. rubiginosa seems to be less adapted to late-season conditions as a short-day photoperiod accelerates its immature development to a lesser extent than it does in C. stigmatica, which nevertheless results in greater larval mortality and slightly but significantly smaller adults. By contrast, in C. stigmatica, which is more likely to encounter late-season conditions due to its slower life cycle, short-day acceleration of development is achieved at no cost to survivorship and final body mass. The experiment with C. stigmatica was repeated during two consecutive years with different methods and the main results proved to be well reproducible. In addition, laboratory results for C. rubiginosa agree with field data from literature.

An approach to forecast grain crop yield using multi-layered, multi-farm data sets and machine learning

Many broadacre farmers have a time series of crop yield monitor data for their fields which are often augmented with additional data, such as soil apparent electrical conductivity surveys and soil test results. In addition there are now readily available national and global datasets, such as rainfall and MODIS, which can be used to represent the crop-growing environment. Rather than analysing one field at a time as is typical in precision agriculture research, there is an opportunity to explore the value of combining data over multiple fields/farms and years into one dataset. Using these datasets in conjunction with machine learning approaches allows predictive models of crop yield to be built. In this study, several large farms in Western Australia were used as a case study, and yield monitor data from wheat, barley and canola crops from three different seasons (2013, 2014 and 2015) that covered ~ 11 000 to ~ 17 000 hectares in each year were used. The yield data were processed to a 10 m grid, and for each observation point associated predictor variables in space and time were collated. The data were then aggregated to a 100 m spatial resolution for modelling yield. Random forest models were used to predict crop yield of wheat, barley and canola using this dataset. Three separate models were created based on pre-sowing, mid-season and late-season conditions to explore the changes in the predictive ability of the model as more within-season information became available. These time points also coincide with points in the season when a management decision is made, such as the application of fertiliser. The models were evaluated with cross-validation using both fields and years for data splitting, and this was assessed at the field spatial resolution. Cross-validated results showed the models predicted yield relatively accurately, with a root mean square error of 0.36 to 0.42 t ha−1, and a Lin’s concordance correlation coefficient of 0.89 to 0.92 at the field resolution. The models performed better as the season progressed, largely because more information about within-season data became available (e.g. rainfall). The more years of yield data that were available for a field, the better the predictions were, and future work should use a longer time-series of yield data. The generic nature of this method makes it possible to apply to other agricultural systems where yield monitor data is available. Future work should also explore the integration of more data sources into the models, focus on predicting at finer spatial resolutions within fields, and the possibility of using the yield forecasts to guide management decisions.

Early hatching enhances survival despite beneficial phenotypic effects of late-season developmental environments.

Seasonal shifts in environmental conditions provide predictable cues to which organisms can respond in adaptive ways. For example, seasonal changes in temperature can induce phenotypes at different times of the year that have season-specific fitness benefits. Here, we tested the hypothesis that embryo responses to seasonal changes in thermal environments are adaptively matched to the timing of reproduction (environmental-matching hypothesis). We collected eggs of the brown anole lizard (Anolis sagrei) from early and late seasons, and exposed them to early and late thermal regimes that mimic nest temperatures. After measuring offspring morphology and performance, we quantified their survival in the field. Females had higher fecundity, but produced smaller eggs, early in the season compared with late in the season. Late-season eggs exposed to late thermal regimes had relatively high survival, but early-season eggs exposed to early thermal regimes had similar survival rates to those exposed to mismatched conditions. Late-season nest temperatures and late-season eggs produced offspring that were relatively large and fast runners. However, despite phenotypic benefits of late-season conditions, early-season hatchlings had greater survival in the field. Our results do not fully support the environmental-matching hypothesis but suggest that selection favours seasonal shifts in reproductive investment of mothers (high early-season fecundity) over plastic responses of embryos to seasonal environmental changes.

Simulated Seasonal Photoperiods and Fluctuating Temperatures Have Limited Effects on Blood Feeding and Life History inAedes triseriatus(Diptera: Culicidae)

Biotic and abiotic factors change seasonally and impact life history in temperate-zone ectotherms. Temperature and photoperiod are factors that change in predictable ways. Most studies testing for effects of temperature on vectors use constant temperatures and ignore potential correlated effects of photoperiod. In two experiments, we tested for effects of larval rearing environments creating ecologically relevant temperatures and photoperiods simulating early and late season conditions (June and August), or constant temperatures (cool and warm) with the June or August photoperiods, respectively. We determined effects on survivorship, development, size, and a composite performance index in a temperate-zone population of Aedes triseriatus (Say). We followed cohorts of resulting females, all held under the same environmental conditions, to assess carry-over effects of rearing conditions for larvae on longevity, blood feeding, and egg production. Larval survivorship was affected by treatment in one experiment. Development time was greater in the June and cool treatments, but the constant and fluctuating temperatures did not differ. Significantly larger mosquitoes were produced in fluctuating versus constant temperature treatments. There were no significant treatment effects on the composite performance index. Adult female longevity was lower after rearing at constant versus fluctuating temperature, but there was no difference between June and August, nor did size affect longevity. There was no effect of treatments on blood feeding and a limited effect on egg production. We conclude that seasonal temperatures and photoperiods during development have limited effects on this population of A. triseriatus and find little evidence of strong effects of fluctuating versus constant temperatures.

Application of the photosynthetic light-use efficiency model in a northern Great Plains grassland

Abstract The light-use efficiency (LUE) model of photosynthesis is widely used to estimate ecosystem photosynthesis and net primary production from remote sensing measurements. The fraction of absorbed photosynthetically active radiation ( f APAR ) is a dominant term in this model, and it is fundamentally important for model calculations of ecosystem productivity across large areas. The LUE term is sometimes considered a constant, but may be best represented as a variable scalar under stress conditions. The main objective of this study was to better understand factors influencing f APAR , its relationship with seasonal variation in canopy greenness (Normalized Difference Vegetation Index (NDVI)), and the consequences of potential seasonal changes in the NDVI- f APAR relationship for LUE model calculations of ecosystem photosynthesis in a semi-arid grassland. We used two approaches to determine f APAR , (i) direct incoming and outgoing radiation measurements above and below the canopy, and (ii) an inversion approach based on incident photosynthetically active radiation and the light response curve of net ecosystem productivity measured by eddy covariance at low light levels. The two approaches resulted in f APAR values that were very strongly correlated during the initial development of the canopy until peak leaf area index (LAI) was reached. During this time, a strong linear relationship also occurred between f APAR and NDVI calculated from spectral reflectance measurements of the grassland canopy. After peak LAI, there was hysteresis in the NDVI– f APAR relationship, and the two f APAR estimates diverged. Light-use efficiency model calculations of ecosystem photosynthesis made using f APAR values were strongly correlated with chamber CO 2 exchange measurements during the initial development of the canopy leaf area. After peak LAI, a stress function, based on either soil moisture or vapour pressure deficit (VPD) measurements, was necessary to reduce quantum yield and model calculations of ecosystem photosynthesis during periods of relatively low soil moisture and higher VPD later in the growing season. Both stress functions were similarly effective in improving the correlation between modeled and measured ecosystem photosynthesis values, and indicated reduced LUE under late season conditions. Modulating LUE based on the Photochemical Reflectance Index or the Water Band Index (both proposed as possible indicators of LUE) was not effective to improve the correlation between modeled and measured ecosystem photosynthesis values in this ecosystem.

A combined tracer/evapotranspiration model approach estimates plant water uptake in native and non-native shrub-steppe communities

Here we test an experimental approach that produces estimates of the location, timing and extent of water uptake by individual plant species in the field. A tracer injection experiment was used to estimate the proportion of active roots across soil depths. These proportions were multiplied by species-specific estimates of evapotranspiration. This approach was repeated in early- and late-season conditions in adjacent native- and non-native-dominated shrub-steppe plant communities. Resulting estimates of water uptake by depth were compared to soil water content. Both communities contained a dominant plant that relied on shallow (i.e., 0–10) soil water, a sub-dominant that relied on deep- (i.e., 90 + cm) soil water and a second sub-dominant that used late-season pulses of shallow water. Combining tracer uptake with evapotranspiration estimates indicated that non-natives removed nearly twice the amount of water early in the season as natives, especially from shallow depths. This was consistent with measures of soil moisture. However, modeled estimates of root water uptake were not always consistent with measurements of soil moisture. Despite the intensive sampling conducted in this study, future use of this approach will require more complete tracer sampling of the plant species present and improved estimation of evapotranspiration in sparse, diverse plant canopies.

Identification and distribution of mating‐type idiomorphs in populations of Podosphaera macularis and development of chasmothecia of the fungus

Podosphaera macularis, the causal agent of hop powdery mildew, is known to produce chasmothecia (formerly cleistothecia) in eastern North America and Europe. Ascocarps have not yet been reported from the Pacific Northwestern region of North America. Reasons for the apparent absence of chasmothecia in the Pacific Northwest were unknown. This study established that P. macularis is heterothallic and ascocarp ontogeny, maturation, dehiscence and ascospore infection proceed similarly to other powdery mildew fungi. Genome sequencing of a MAT1‐1 isolate revealed the structure of the MAT1 locus and presence of MAT1‐1‐3, demonstrating further similarities to other powdery mildew fungi. PCR assays with primers designed from conserved domains of the MAT1 idiomorphs were developed to characterize the frequency of idiomorphs in populations of P. macularis. Amongst 317 samples of P. macularis collected during 2012 and 2013 from the Pacific Northwest only the MAT1‐1 idiomorph was found. In contrast, among 56 samples from the eastern United States and Europe, MAT1‐1 and MAT1‐2 idiomorphs were detected at equivalent frequencies. At temperatures representative of late season conditions in the Pacific Northwest, chasmothecia formed readily when a Pacific Northwest MAT1‐1 isolate was paired with a MAT1‐2 isolate collected from outside the region. Although these findings do not encompass all climatic, geographic or temporal barriers that could inhibit the formation of chasmothecia, the current absence of the ascigerious stage of P. macularis in the Pacific Northwest could be explained by the absence of the MAT1‐2 mating type idiomorph.

Warming shows differential effects on late-season growth and competitive capacity of Elodea canadensis and Potamogeton crispus in shallow lakes

Submerged macrophytes are likely to be affected by climate changes through changes in water temperatures and length of growing season. We conducted a lab experiment to examine the influence of a late-season temperature increase on growth, biomass allocation, and acclimation of 2 submerged macrophyte species, Elodea canadensis and Potamogeton crispus. We also ran competitive interaction experiments between the 2 species with mono- and mixed-species cultures in pots placed in outdoor heated mesocosms (5 years at ambient temperature and a higher temperature following the IPCC A2 scenario downscaled to local conditions but enhanced by 50%). In the lab, macrophytes collected in the 2 types of mesocosms were grown at ambient temperatures (12 °C in September and 8 °C in October) and 4 °C higher. Warming had an overall stronger effect on E. candensis than P. crispus, particularly within the low temperature range studied. Hence, the relative growth rate (RGR) of E. canadensis acclimated to ambient mesocosm conditions increased 6-fold from low (8 °C) to high (16 °C) temperature, whereas the RGR of P. crispus increased <2-fold. In the competitive interaction experiment, warming increased the biomass and RGR of E. canadensis in the monoculture. In addition, warming increased shoot elongation of the plant in both the monoculture and mixed culture. P. crispus was generally unaffected by warming when grown in both monoculture and mixed culture, but competition decreased the elongation of shoots pre-adapted to ambient conditions and grown in the warmer mesocosms. The decomposition rate of E. canadensis accelerated with warming but was unaffected in P. crispus. We conclude that E. canadensis is a stronger competitor than P. crispus under warmer late-season conditions; however, it may have a higher demand for oxygen due to the increased decomposition rates at higher temperatures, particularly in the peripheral growing season, with potential profound effects on lake ecosystems. Although acclimatisation was evident, we suggested that temperature changes will affect the growth pattern of the 2 plant species and thereby perhaps induce a switch in macrophyte species dominance.

Genotypic performance, character correlations and path analysis of pod yield in Abelmoschus caillei (A. Chev.) Stevels

Direct selection based on pod yield is often a problem in West African okra (Abelmoschus caillei (A. Chev.) Stevels) breeding programs. Information on inter-relationships among traits to implement indirect selection for pod yield is needed. Objectives of this study were to evaluate the performance of West African okra varieties in two cropping seasons prevailing in Nigeria, and to determine the associations among main agronomic characters and their influence on pod yield. Twenty-five genotypes were grown in two planting seasons at the Research Farm of the Federal University of Agriculture, Abeokuta in 2008-2009 using a randomized complete-block design with three replications. Sixteen plant characters were measured. The data were subjected to variance, correlation and path analyses. Four genotypes, viz., CEN 010, CEN 012, NGAE-96-04 and AGA 97/066-5780 demonstrated potential for high pod yield. CEN 012 and AGA 97/066-5780 in addition, demonstrated early flowering higher number of pods. Character associations varied between planting seasons. The dependence of pod yield on final plant height, number of branches per plant, number of pods per branch, number of pods per plant, number of ridges per pod, weight of 250 seeds, pod length and seed weight per plant was noted in both planting seasons. In both seasons, number of pods per plant exhibited a high positive direct effect on pod yield. In conclusion, the trait of most interest for improving pod yield under early and late-season conditions was number of pods per plant.

Phenotypic plasticity and performance of Taraxacum officinale (dandelion) in habitats of contrasting environmental heterogeneity

Ecological theory predicts a positive association between environmental heterogeneity of a given habitat and the magnitude of phenotypic plasticity exhibited by resident plant populations. Taraxacum officinale (dandelion) is a perennial herb from Europe that has spread worldwide and can be found growing in a wide variety of habitats. We tested whether T. officinale plants from a heterogeneous environment in terms of water availability show greater phenotypic plasticity and better performance in response to experimental water shortage than plants from a less variable environment. This was tested at both low and moderate temperatures in plants from two sites (Corvallis, Oregon, USA, and El Blanco, Balmaceda, Chile) that differ in their pattern of monthly variation in rainfall during the growth season. We compared chlorophyll fluorescence (photosynthetic performance), flowering time, seed output, and total biomass. Plants subjected to drought showed delayed flowering and lower photosynthetic performance. Plants from USA, where rainfall variation during the growth season was greater, exhibited greater plasticity to water shortage in photosynthetic performance and flowering time than plants from Chile. This was true at both low and moderate temperatures, which were similar to early- and late-season conditions, respectively. However, phenotypic plasticity to decreased water availability was seemingly maladaptive because under both experimental temperatures USA plants consistently performed worse than Chile plants in the low water environment, showing lower total biomass and fewer seeds per flower head. We discuss the reliability of environmental clues for plasticity to be adaptive. Further research in the study species should include other plant traits involved in functional responses to drought or potentially associated with invasiveness.

Effect of climatic and sulphur fertilisation conditions, on phenolic compounds and vitamin C, in the inflorescences of eight broccoli cultivars

Flavonoids, hydroxycinnamoyl derivatives (sinapic and ferulic acid derivatives+caffeoyl-quinic acid derivatives) and vitamin C were quantified by HPLC-MS in five commercial and three experimental cultivars from freshly harvested broccoli inflorescences ( Brassica oleracea L. var. italica). In order to identify differences due to genetic and agronomic factors, the broccoli cultivars were grown under different climatic and agronomic conditions, i.e. early (winter) and late (spring) seasons with poor (15 kg/ha) and rich (150 kg/ha) sulphur fertilisation. The predominant sinapic and ferulic acid derivatives in all broccoli cultivars were 1,2-diferuloylgentiobiose, 1,2,2'-trisinapoylgentiobiose and 1,2'-disinapoyl-2-feruloylgentiobiose. In addition, the compounds 1,2-diferuloylgentiobiose, 1-sinapoyl-2,2'-diferuloylgentiobiose and 1,2,2'-triferuloylgentiobiose were identified in broccoli inflorescences for the first time. Extreme agronomic and environmental conditions (late season and rich sulphur fertilisation which could induce different stress situations on the plant) enhanced the phenolic content. Thus, total flavonoids showed the highest content, followed by total sinapic and feruloyl acid derivatives and total caffeoyl-quinic acid derivatives. In general, cultivars grown under rich fertilisation and late season conditions showed higher vitamin C content than those grown under the poor and early ones. Finally, results showed that commercial cultivars rendered higher amounts of phenolic compounds and vitamin C than the experimental ones.

Impact of nitrogen and environmental conditions on corn as detected by hyperspectral reflectance

Indices derived from hyperspectral reflectance spectra have the potential to be used as indicators of environmental stress in crops. This study uses canopy-scale, ground-based measurements of hyperspectral reflectance to demonstrate the temporal patterns in corn development under imposed fertility (N rate) and environmental (water availability) stresses. In 1998, two large areas in a 30-ha corn ( Zea mays, L.) field near Ottawa, Canada (45°18′N, 75°44′W) were supplied with 99 and 17 kg N ha −1, while the balance of the field received the recommended rate of 155 kg N ha −1. Reflectance measurements were taken nine times using a portable spectroradiometer at georeferenced locations within these areas. Individual reflectance-based indices demonstrated the relative differences between application rates and identified both nitrogen and water stresses at various times in the growing season. No single index was able to describe the status of the corn crop throughout the season. Canonical discriminant analysis provided accurate classification of samples by N rate during early, mid, and late season conditions with overall success rates of 70%, 88%, and 93%, respectively. A shift in importance from green-based derivatives to red-based derivatives was noted from mid to late season and attributed to the natural reduction in green pigments as the crop entered senescence. Canopy-scale photochemical reflectance index (PRI) was shown to be correlated with canopy radiation use efficiency (RUE). Mid-season water stress affected the relationship. Multiple years of data are required to demonstrate robust relationships between hyperspectral indices and corn ecophysiological status because of the interaction between environmental and nutrient stresses. Identifying areas of fields sensitive to weather-induced stresses will allow better management of N application. Timing the collection of hyperspectral image data at early and late vegetative phase could enhance precision agriculture by allowing supplemental nutrient application, identifying stress patterns and aid in yield forecasting.

Manipulation of Larval Diapause of the European Corn Borer (Lepidoptera: Pyralidae) as a Potential Mechanism of Integrated Pest Management

Survival of reciprocal populations of European corn borer, Ostrinia nubilalis (Hübner), equaled or was intermediate to natural populations and an introduced low-diapause population (exotic), which survived less well. When peak natural second-generation hatch (31 July–3 August) north of 39°00′ N lat. was approximated, most of seven natural populations approached 100% diapause. However, only 0.25–22.95% of the exotic population diapaused. Diapause by progenies of reciprocal crosses was greatly influenced by this exotic parent. At the most northern locations, Ankeny, Iowa, and St. Paul, Minn., influence of the parental male was particularly evident. When peak natural third-generation hatch (13–16 August) south of 39°00′ N lat. was approximated, five reciprocal populations diapaused similarly to their corresponding natural populations (≈85%). Late-season hatch allowed larval diapause of the exotic population to increase to 46%. Under these late-season conditions, influence of the parental male was evident only at the most southern locations, Portageville, Mo., and Tifton, Ga. This apparent contradition of parental male influence between midsummer and late-summer hatch is because heterogeneity for diapause remains in a low-diapause population. Introductions of a low-diapausing population north of 39°00′ N lat. during late July apparently encourage resultant progeny from reciprocal crosses to avoid larval diapause and to perish in late autumn.

Ecophysiology of Two Solar-Tracking Desert Winter Annuals. I. Photosynthetic Acclimation to Growth Temperature

The ability of two solar-tracking desert winter annuals, Lupinus arizonicus Watson and Malvastrum rotundifolium Gray, to acclimate their photosynthetic characteristics to different growth temperatures was examined. Plants were grown in growth chambers under 25/15°C and 40/30°C thermal regimes. The plants grown at 40/30°C were also subjected to a drying cycle in order to assess whether or not drought affected the photosynthetic acclimation to high temperatures. Both species exhibited shifts in their temperature optima and thermal death points for photosynthesis. The droughted plants showed no further acclimation than did the watered plants grown at 40/30°C. Using representative meteorological conditions measured in Death Valley, California, it was predicted that photosynthetic acclimation plays only a small role in enhancing daily carbon-gaining ability for late-season conditions. However, under conditions of drought stress and high temperatures, the acclimation may prevent thermal death and extend plant life.