Dormant Season Research Articles

A Review of Landscape Water Requirements Using a Multicomponent Landscape Coefficient

HighlightsA multi-component decoupling method for the landscape coefficient is described that provides a thorough means to estimate the water requirements of landscapes.The decoupling method considers differences in vegetation type, density, local climate, and soil water management.Methods for incorporating managed stress and frequency of irrigation are described.Winter or dormant season ET is described.The procedure in ASABE Standard S623 is a simpler form of the multi-component procedure and is complementary.Abstract. Water requirements of landscapes are highly variable due to the heterogeneous natures of landscapes, vegetation types, influence of buildings, and nutrient and water management. Objectives for water management of landscapes are for general appearance and health rather than for maximum biomass production. A multi-component method developed for the Irrigation Association (IA) and extended from the California WUCOLS procedure is demonstrated in which the landscape coefficient (KL, equivalent to a crop coefficient) is broken down into four components: vegetation type, vegetation density, microclimate, and managed stress. Each of these components can be estimated using readily made descriptions of a landscaped area and management objectives. One form of the KL equation is used to determine target KL that incorporates a target amount of soil water stress to support water conservation and to support water planning studies. A second form of the KL equation can be used to estimate the actual KL occurring under actual water management. The second form is used in studies of water balances and actual water conservation. The general decoupled equation is further expanded to optionally incorporate impacts of evaporation from exposed soil to assess impacts of irrigation frequency on total water consumption. The mathematics for the approach can be incorporated into software applications and smart irrigation controllers to produce improved water consumption estimates for landscape water requirements for use in irrigation scheduling, water requirement planning, and water depletion studies. The simplified procedure for estimating landscape water requirements in ASABE Standard S623 that is complementary to the IA procedure is discussed and compared. Both methods use a vegetation type and density system as the basis for efficiently estimating scientifically accurate landscape water requirements. Keywords: . Evapotranspiration, Irrigation requirements, Landscape coefficients, Landscape water requirements, Managed Stress, Microclimates, NAIP areal imagery.

Aboveground traits define differences in biomass allocation among 16 prairie species

Agrosystems, Geosciences & EnvironmentVolume 3, Issue 1 e220117 COVER IMAGE Aboveground traits define differences in biomass allocation among 16 prairie species First published: 08 October 2020 https://doi.org/10.1002/agg2.20117AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinked InRedditWechat Abstract On the cover: Surface energy fluxes play a crucial role in quantifying the dynamics of water and energy use efficiencies of agroecosystems. This image shows operation of flux towers to measure surface energy fluxes during the non-growing (dormant) season. These flux towers are 2 of the 10 towers that operate as a part of the Nebraska Water and Energy Flux Measurement, Modeling and Research Network (NEBFLUX) that was established by Suat Irmak. All these flux towers have been operating on an hourly basis since 2004 for various vegetation surfaces. See Kukal and Irmak: https://doi.org/10.1002/agg2.20110. Photo by Suat Irmak. Volume3, Issue12020e220117 RelatedInformation

Saline Experimental Range Dormant Season Wildfire: Short-Term Effect on Forage Production and Plant Composition

Saline Experimental Range Dormant Season Wildfire: Short-Term Effect on Forage Production and Plant Composition

Bud cold-hardiness of some Vitis vinifera L. cultivars during the dormant season of 2018/2019

Bud cold-hardiness of some Vitis vinifera L. cultivars during the dormant season of 2018/2019

Analysis of fire frequency on the Talladega National Forest, USA, 1998-2018

Fire is an essential ecological process and management tool for many forested landscapes, particularly the pine (Pinus spp.) forests of the southern USA. Within the Talladega National Forest in Alabama, where restoration and maintenance of pine ecosystems is a priority, fire frequency (both wild and prescribed) was assessed using a geographical process applied to a fire history database. Two methods for assessing fire frequency were employed: (1) a simple method that utilised the entire range of years acknowledged in the database and (2) a conservative method that was applied only the date of the first and last fires recorded at each location. Analyses were further separated by (a) method of mean fire return interval calculation (weighted by area or Weibull) and (b) fire season interval with analyses conducted on growing season and dormant season fires. Analyses of fire frequency for national forest planning purposes may help determine whether a prescribed fire program mimics ecological and historical fire frequencies and meets intended objectives. The estimated fire return interval was between ~5 and 6.5 years using common, straightforward (simple) methods. About one-third of the forest receives no fire management and about half of the balance has sufficiently managed fuels.

Effects of simulated nitrogen deposition on soil microbial biomass and community function in subtropical evergreen broad-leaved forest

Aim of the study: The aim of this study was to examine the effects of a 5-year simulated nitrogen (N) deposition on soil microbial biomass carbon (MBC), nitrogen (MBN), microbial community activity and diversity in subtropical old-growth forest ecosystems.Area of study: The study was conducted in forest located at subtropical forest in Anhui, east China.Material and methods: Three blocks with three fully randomized plots of 20 m × 20 m with similar forest community and soil conditions were established. The site applied ammonium nitrate (NH4NO3) to simulate N deposition (50 and 100 kg N ha−1 year −1). From three depths (0–10, 10–20 and 20–30 cm), were collected over four seasons (December, March, June and September), and then measured by community-level physiological profiles (CLPPs).Main results: N addition had no significant effect on MBC and MBN. The spatiotemporal variations in MBC and MBN were controlled by seasonality and soil depth. Soil microbial activities and diversity in the growing season (June and September) were apparently higher than the dormant season (March and December), there were significantly lower diversity indices found following N addition in September. However, N addition enhanced microbial activities and increased diversity indices in the dormant season. Redundancy analysis showed that pH, soil moisture, NO3--N and total phosphorus were the most important factors controlling the spatial pattern of microbial metabolic activity.Research highlights: These results suggest that soil microbial community function is more easily influenced than microbial biomass. The site has a trend of P-limited or near-N saturation, and will threaten the whole forest ecosystem with the increasing duration of N addition.Keywords: Nitrogen deposition; Seasonality; Soil microbial biomass; Microbial community; Subtropical old-growth forest.

Diel discharge variations in dormant and growing seasons in a headwater catchment suggest potential sources of an evapotranspiration signal

AbstractDiel fluctuations in discharge not associated with precipitation have been identified in streams around the world and attributed to evapotranspiration of both hillslope and near‐stream vegetation. Several mechanisms have been hypothesized to explain the generation of these signals, but a consensus has not been reached. In order to investigate the origin of these daily discharge fluctuations, we measured discharge and groundwater levels in a 43‐ha headwater catchment near Cullowhee, NC, USA. The catchment was logged at least twice in the past 120 years, allowing the evergreen invasive Chinese privet (Ligustrum sinense) to become established in near‐stream areas. Stream discharge was measured at the outlet, and stream stage and near‐stream groundwater level were measured at a second location higher in the catchment. Daily fluctuations in discharge were quantified and found to increase in magnitude with daily mean discharge. Interestingly, daily discharge fluctuations were observed in the dormant season, and our analysis suggests that their magnitude may increase more with discharge than during the growing season. Two previously hypothesized processes may explain our observations. A decrease in signal dampening due to faster transmission of an evapotranspiration signal at elevated flows may explain the increased diel fluctuation magnitude at higher flows. Additionally, because the primary active vegetation in our catchment in the dormant season is in near‐stream areas, we suggest that this indicates most of the evapotranspiration signal in stream discharge is derived from near‐stream vegetation, not hillslopes.

152 Effects of mineral supplementation on performance and serum mineral status in beef steers grazing annual ryegrass

Abstract Thirty six crossbred (predominantly English with some Bos indicus influence) beef steers (initial BW 264.8 + 35.8 kg) were blocked by BW and used in a completely random design to examine the effects of mineral supplementation on performance and serum mineral status in beef cattle grazing annual ryegrass pastures for 84 d. All cattle were withheld from mineral for approximately 60 d prior to the initiation of the study and were allowed to graze dormant bahiagrass pastures (Paspalum notatum), and also had access to bahiagrass hay. On d -1, cattle were weighed and stratified by BW into Light (n = 6 pastures) and Heavy (n = 4 pastures) blocks and returned to their dormant warm season pasture. On d 0, cattle were weighed, a 10 mL blood sample was collected for serum mineral status and cattle were moved to their respective 1.2 ha annual ryegrass treatment pastures. Treatments were randomly assigned to pasture and consisted of CON (no complete mineral supplementation), or MIN (free choice access to a complete beef mineral.) Cattle grazed annual ryegrass for 84 d, after which a final BW was collected as well as a second 10 mL blood sample. Data were analyzed as a mixed model with weight block a random effect and treatment a fixed effect and pasture was the experimental unit. Supplementing MIN tended (P = 0.06) to increase total weight gain at d 84 and increased (P = 0.01) ADG (1.61 vs. 1.67 kg/d for CON and MIN, respectively). Additionally, feeding MIN resulted in increased serum Co, Zn, and Se (P = 0.01) but resulted in no differences in serum Fe and Cu (P > 0.10). Feeding MIN resulted in greater performance and increased some serum mineral levels, however the lack of response in serum Cu to MIN bears further examination.

Effects of Mowing and Prescribed Fire on Plant Community Structure and Function in Rare Coastal Sandplains, Nantucket Island, MA, USA.

Coastal sandplains provide habitat for a suite of rare and endangered plant and wildlife species in the northeastern United States. These early successional plant communities were maintained by natural and anthropogenic disturbances including salt spray, fire, and livestock grazing, but over the last 150 years, a decrease in anthropogenic disturbance frequency and intensity has resulted in a shift towards woody shrub dominance at the expense of herbaceous taxa. This study quantified the effects of more than a decade of dormant season disturbance-based vegetation management (mowing and prescribed fire) on coastal sandplain plant community composition on Nantucket Island, Massachusetts, USA. We used time-series plant cover data from two similar sites to evaluate the effectiveness of disturbance management for restoring herbaceous species cover and reducing woody shrub dominance. Our results indicate that applying management outside of the peak of the growing season has not been effective in maintaining or increasing the cover of herbaceous species. While management activities resulted in significant (P < 0.01) increases in herbaceous species immediately after treatment, woody species recolonized and dominated treated sites within 3-years post treatment at the expense of graminoids and forbs. These results highlight the difficulties associated with directing ecological succession using disturbance-based management to maintain rare, herbaceous species in coastal sandplain systems that were once a prevalent landscape component under historically chronic anthropogenic disturbance. Further experimentation with growing season disturbance-based management and different combinations of management techniques could provide insights into management alternatives for maintaining herbaceous conservation targets in coastal sandplains.

Phenology and Winter Hardiness of Cold-climate Grape Cultivars and Advanced Selections in Iowa Climate

The popularity of grape (Vitis sp.) and wine production in the upper midwest region of the United States is increasing steadily. The development of several cold-climate, interspecific-hybrid grape cultivars (northern hybrids) since the 1980s has improved the probability of success for both new and established vineyards in this area of the country, but long-term data describing the performance of these cultivars in midwestern U.S. climates are needed to both aid growers in their choice of cultivars and to provide them with information about factors important in their management. We characterized the long-term winterhardiness and annual phenology of 12 cold-climate northern hybrid grape cultivars (two established cultivars, five newer cultivars, and five advanced selections) grown in a randomized and replicated field plot in central Iowa, an area that offers a warm growing season and very cold dormant season for grape culture. The established cultivars included in the study were Frontenac and St. Croix. The newer cultivars evaluated were Arandell, Corot noir, La Crescent, Marquette, and Petit Ami, and the advanced selections were MN 1189, MN 1200, MN 1220, MN 1235, and MN 1258. The grape trial was established in 2008, and vines were evaluated from 2011 through 2017 for annual timing of budbreak, bloom, veraison, and harvest, as well as winter survival of vines and primary buds. As a group, the northern hybrids in our trial showed good winterhardiness of vines but variable hardiness of primary buds across the six winters, which ranged from warmer than average to much colder than average. In Iowa climate, buds of northern hybrids were generally most vulnerable to cold temperature damage from late-winter (March) low-temperature events or from extreme midwinter low-temperature events. The bud hardiness of individual cultivars ranged from very hardy (Frontenac, Marquette, and MN 1235) to poor hardiness (Arandell, Corot noir, Petit Ami, and MN 1189), with all 12 cultivars showing good bud survival during Iowa winters that were warmer than average, but the less-hardy cultivars showing poor bud survival during winters that were colder than average. Evaluations of phenology revealed that heat accumulation measured in growing degree days with a threshold of 50 °F was not a reliable index for predicting the timing of annual developmental stages for the cultivars we tested. Our results indicate that northern hybrids rely on other factors in addition to heat accumulation for guiding annual development, and that factors such as photoperiod likely have a strong influence on phenological timing during seasons with unusual weather patterns. We determined that none of the cultivars were vulnerable to cold temperature damage to fruit before harvest in Iowa’s climate, but that three of the cultivars (Arandell, Marquette, and MN 1235) were highly vulnerable to shoot damage from spring freeze events, and four others (Corot noir, La Crescent, MN 1200, and MN 1220) were moderately vulnerable to cold damage to shoots in spring. An itemized summary of the relative hardiness, vulnerabilities, and timing of phenological stages of the 12 cultivars is provided to aid growers in selection and management of grape cultivars for Iowa climate. Based on hardiness and phenology, four of these cultivars (Frontenac, MN 1258, MN 1220, and MN 1200) have the lowest risk of issues related to cold temperatures.

Spatial variability of historical fires across a red pine–oak landscape, Pennsylvania,USA

AbstractLong‐term, ecosystem‐specific fire regime information improves natural community restoration and management by providing a basis for scientifically reasoned fire management prescriptions. Historical fire regimes can be reconstructed to sub‐annual resolution using fire‐scarred trees, and while such reconstructions have become increasingly prevalent across the easternUSA, little information regarding how they vary at landscape scale is available. Most studies report fire regime characteristics (i.e., frequency, seasonality) at site‐composite levels, commonly at ≤1 km2spatial resolution. In this study, we analyzed the historical spatial variation of fire regime characteristics over the past four centuries (1620CEto present) in a red pine/oak landscape (30.75 km2) in north‐central Pennsylvania,USA. Fire event data were reconstructed based on fire scars and locations of 192 living and dead red pines. The spatial and temporal distributions of fire scars revealed a historical fire regime dominated by frequent, dormant season fires most often detected at relatively small spatial extents and by relatively few trees. There was, however, evidence of less frequent, relatively large fires that scarred high percentages of trees. These fire regime characteristics likely resulted in a spatially and temporally transient patchwork of varying vegetation age and structures resulting in a heterogeneous landscape. At the landscape scale, fire frequency changed with human cultures, while fire spatial extent and scarring patterns appeared to be modulated by drought conditions. Results from this study show historical precedence for landscape‐scale burning across a broad range of drought conditions and spatial extents, which should be considered when designing fire‐management and ecosystem restoration objectives.

Winter Injury to Grapevine Secondary Phloem and Cambium Impairs Budbreak, Cambium Activity, and Yield Formation

Vitis vinifera is a species of temperate origin that reactivates the dormant secondary phloem from the previous year at the resumption of growth in spring. Following harsh winters, grapevines may display a set of symptoms including delayed and heterogeneous budbreak, dieback with shoot renewal from the trunk base or sudden death of the plant. Although it was suggested that these symptoms may be associated with freeze damage to the secondary phloem, there is no experimental evidence that quantifies tissue responses to freezing and their consequences for the plant. This work evaluated how different severities of cold damage to the secondary phloem during the dormant season impacted the anatomical, physiological, and agronomic responses of grapevines during the subsequent growing season. Single-node cane sections were subjected to a range of freezing temperatures that damaged only the phloem, and changes in anatomy and physiology were monitored. In addition, the consequences of natural winter freezes for yield formation of field-grown plants were evaluated. Our results suggest that the more severe a freeze event is, the greater will be the degree of secondary phloem disorganization, leading to delays in budbreak and subsequent phenological stages, and in cambial activity. Winter freezes also led to a loss of plant vigor and a reduction in cluster number, berries per cluster, and fruit sugar content. We conclude that winter freeze events can produce hidden damage in grapevine perennial tissues, which may compromise subsequent growth and productivity depending on the severity of the damage.

Seasonal control of seed germination.

This article is a Commentary on Footitt et al. (2020), 225: 2035–2047.

Moisture stimulates galler emergence from dry season dormancy in the leaf litter

In tropical regions, a great proportion of trees and shrubs shed their leaves over the dry season. Since gall-inducing insects are generally host species-specific, where do they go when their hosts have no leaves? There is practically no research into dormancy strategies of tropical galling insects. We hypothesised that the galling insect Eurytoma sp. (Chalcidoidea, Eurytomidae) undergo dormancy inside their galls on shed leaves of the host plant Caryocar brasiliense Camb. (Caryocaraceae). The insects would emerge from the galls in synchrony with the sprouting of new leaves, at the beginning of the wet season, stimulated by increased moisture after the first rain of the wet season. In order to test that, we collected leaves from the leaf litter in the last month of the dry season and gently showered half of them in a sink to simulate rain. In the two weeks before the first rainfall, the watered leaves presented an over trifold higher gall eclosion rate than the ones in the control group. There is no previous account of a tropical galling insect undergoing dormancy inside galls in the leaf litter. We contrast this evidence with the possibility that, at least in the tropics, galls may also have had an adaptive value as dormancy structures during their evolutionary history, and evolved in response to the deciduousness of plants growing in harsh environments.

Predicting Ailanthus altissima presence across a managed forest landscape in southeast Ohio

BackgroundThe negative impacts of the exotic tree, Ailanthus altissima (tree-of-heaven, stink tree), is spreading throughout much of the Eastern United States. When forests are disturbed, it can invade and expand quickly if seed sources are nearby.MethodsWe conducted studies at the highly dissected Tar Hollow State Forest (THSF) in southeastern Ohio USA, where Ailanthus is widely distributed within the forest, harvests have been ongoing for decades, and prescribed fire had been applied to about a quarter of the study area. Our intention was to develop models to evaluate the relationship of Ailanthus presence to prescribed fire, harvesting activity, and other landscape characteristics, using this Ohio location as a case study. Field assessments of the demography of Ailanthus and other stand attributes (e.g., fire, harvesting, stand structure) were conducted on 267 sample plots on a 400-m grid throughout THSF, supplemented by identification of Ailanthus seed-sources via digital aerial sketch mapping during the dormant season. Statistical modeling tools Random Forest (RF), Classification and Regression Trees (CART), and Maxent were used to assess relationships among attributes, then model habitats suitable for Ailanthus presence.ResultsIn all, 41 variables were considered in the models, including variables related to management activities, soil characteristics, topography, and vegetation structure (derived from LiDAR). The most important predictor of Ailanthus presence was some measure of recent timber harvest, either mapped harvest history (CART) or LiDAR-derived canopy height (Maxent). Importantly, neither prescribed fire or soil variables appeared as important predictors of Ailanthus presence or absence in any of the models of the THSF.ConclusionsThese modeling techniques provide tools and methodologies for assessing landscapes for Ailanthus invasion, as well as those areas with higher potentials for invasion should seed sources become available. Though a case study on an Ohio forest, these tools can be modified for use anywhere Ailanthus is invading.

Restoring Fire-Grazer Interactions to Pursue Heterogeneity in Sandhills Prairie

Heterogeneity has emerged as a fundamental principle for rangeland management and the importance of environmental heterogeneity for biological diversity has raised questions about the appropriateness of rangeland practices that seek to promote uniform grassland structure and composition. Principles of uniformity in rangeland management reflect a utilitarian target of “managing for the middle” by minimizing both overgrazing and underutilization while avoiding or preventing fire and other disturbances that consume aboveground biomass. We implemented a study to evaluate pioneering efforts to restore historical fire-grazer interactions via patch burning in an effort to increase spatial heterogeneity in the Nebraska Sandhills, a sandy soil, mixed-grass ecoregion with a long history of “management for the middle”. The application of patch burning did not increase landscape heterogeneity of vegetation structure or composition in the Nebraska Sandhills. Instead, grassland structure exhibited greater temporal variability than spatial variability in growing and dormant seasons. The low stocking rate and the rapid regrowth of live herbaceous vegetation following fire likely constrained the degree of spatial heterogeneity observed in our study and highlights the challenges of balancing forage supply and demand in semi-arid grasslands.

Historical fire in the Appalachian Plateau of Ohio and Kentucky, USA, from remnant yellow pines

BackgroundKnowledge of historical fire regimes informs the restoration of woodland communities. In the Appalachian Plateau of Ohio and Kentucky, USA, little is known about the long-term history of fire in oak–pine communities, which are declining in the region. To address this knowledge gap, two sites with remnant fire-scarred yellow pines, Hatton Ridge in Kentucky and McAtee Run in Ohio, were studied to document aspects of the historical fire regime. Cross-sections from fire-scarred yellow pines were collected. Fire chronologies were constructed and fire intervals were calculated using standard dendrochronological methods.ResultsFires, the great majority of which occurred in the dormant season, were frequent at both sites from circa 1750 at Hatton and 1800 at McAtee, until the suppression period (1930 to present); only one fire was recorded after 1930. Mean fire intervals (MFI) for the entire period were nearly identical, 4.7 and 4.4 years at Hatton and McAtee, respectively. At both sites, MFIs were lowest in the industrial period (1850 to 1930). At Hatton, the MFI was 6.6 years before 1850 and 3.5 years from 1850 to 1930, while at McAtee, the MFI was 8.4 years before 1850 and 2.7 years from 1850 to 1930. At both sites, the occurrence of fire was not more frequent than expected in years associated with a drought. At McAtee, the majority of pine establishment occurred in pulses during two periods, 1770 to 1781 and 1853 to 1867, suggesting stand-scale canopy disturbances; the second pulse was associated with frequent burning. In contrast, large pulses of pine establishment were not found at Hatton.ConclusionsYellow pines were a component of these communities, which experienced frequent fire for at least 130 to 160 years. After more than 70 years with little or no fire, yellow pines are now a minor component of the overstory and pine regeneration is essentially absent. Although intensive management with partial harvesting and frequent fire would be required to restore oak–pine woodlands on appropriate sites, it would serve to sustain these increasingly uncommon communities.

Hormonal Orchestration of Bud Dormancy Cycle in Deciduous Woody Perennials.

Woody perennials enter seasonal dormancy to avoid unfavorable environmental conditions. Plant hormones are the critical mediators regulating this complex process, which is subject to the influence of many internal and external factors. Over the last two decades, our knowledge of hormone-mediated dormancy has increased considerably, primarily due to advancements in molecular biology, omics, and bioinformatics. These advancements have enabled the elucidation of several aspects of hormonal regulation associated with bud dormancy in various deciduous tree species. Plant hormones interact with each other extensively in a context-dependent manner. The dormancy-associated MADS (DAM) transcription factors appear to enable hormones and other internal signals associated with the transition between different phases of bud dormancy. These proteins likely hold a great potential in deciphering the underlying mechanisms of dormancy initiation, maintenance, and release. In this review, a recent understanding of the roles of plant hormones, their cross talks, and their potential interactions with DAM proteins during dormancy is discussed.

Annual dynamics of soil gross nitrogen turnover and nitrous oxide emissions in an alpine shrub meadow

Soil nitrogen (N) transformations play a vital role in maintaining grassland productivity and influence nitrous oxide (N2O) emissions. To evaluate annual dynamics of soil gross N turnover and its effects on N2O emissions in typical grasslands, we conducted year-round measurements of soil gross N turnover rates, inorganic N pool sizes and N2O fluxes in an alpine shrub meadow of the Qinghai–Tibet Plateau. Gross ammonium (NH4+) and nitrate (NO3−) immobilization rates were calculated by the “isotope dilution method” (i.e., based on the consumption rates) and the “reformed difference method” (i.e., based on the differences between gross and net turnover rates). The “reformed difference method” avoids additional measurements of net N turnover rates in unlabeled soils compared to the traditional “difference method”, and provides more reliable estimates of NH4+ immobilization in soils with low ambient NH4+ pool sizes than the “isotope dilution method”. The annual gross rates of mineralization, nitrification, NH4+ and NO3− immobilization amounted to 606 ± 43, 236 ± 27, 389 ± 24 and 82 ± 19 mg N kg−1 dry soil yr−1, respectively, in a topsoil of 10 cm. The soil gross N turnover rates during freezing and freeze–thaw periods contributed considerably to the annual totals (22–44%). Thus, the freezing and freeze–thaw periods were not dormant seasons for microbial N transformations, even under a frigid alpine climate. The annual N2O emission was 0.20 ± 0.03 kg N ha−1 yr−1, 35% of which originated from a short-lived emission pulse during the freeze–thaw period (52 d). The promotion of gross mineralization increased soil NH4+ pool sizes, whereas the increase in gross nitrification did not enhance soil NO3− pool sizes during the freeze–thaw period. Coupled nitrification–denitrification dominated NO3− consumption and freeze–thaw related N2O production and hence, the low NO3− pool sizes were not indicative of the potential of pulsed N2O emissions. Year-round measurements with intensive observations during both the non-freezing and freeze–thaw periods are indispensable to fully understand soil N cycling and its response to climate change in alpine ecosystems.

Intraspecific seasonal variation of dormancy and mortality of Phelipanche ramosa seeds

SummaryPhelipanche ramosa (Branched broomrape) is an obligate root parasitic plant that is a major pest of oilseed rape in France. Knowledge on seed viability and dormancy under field conditions is crucial to understand how to control P. ramosa, but is as yet unknown. Our study aimed to quantify these processes with a 2‐year seed burial experiment. Two genetically distinct populations of P. ramosa were studied, collected on winter oilseed rape (population O) and hemp (population H). Seed mortality was very low in both populations (4–7% per year). Although obligate parasitic seeds are assumed to germinate only after exposure to germination stimulants from host root exudates, a high proportion of population H seeds germinated spontaneously (up to 90%). Seeds of both populations displayed seasonal dormancy, with timing and magnitude depending on the population. Dormancy was low at the time each native host crop is usually sown. Populations differed in germination dynamics, with seeds of population H germinating faster. The difference in behaviour that we observed between populations is consistent with reported adaptations of pathovars to their preferred hosts. The results indicate that the parasitic plant management requires targeting at the populations concerned. For example, delayed sowing is more promising against population O than against population H.