Evaluation of currently registered herbicides for fall bearing year red sorrel (Rumex acetosella L.) management in lowbush blueberry (Vaccinium angustifolium Ait.)

Red sorrel is a common creeping herbaceous perennial weed species in lowbush blueberry fields and reproduces asexually via ramets from creeping roots. Ramets emerge throughout the season but remain vegetative due to a vernalisation requirement for flowering. This weed may therefore be managed with fall herbicide applications, but few currently registered herbicides have been evaluated for fall red sorrel management in lowbush blueberry. The objectives of this research were to 1) determine the effect of various herbicide treatments on red sorrel shoot and root biomass in the greenhouse, 2) determine the effect of fall bearing year herbicide applications on overwintered red sorrel ramet density in the field, 3) determine if reduced overwintered ramet density reduces flowering ramet density in the field, and 4) estimate the potential for red sorrel to recover from fall bearing year herbicide applications. Dicamba, tribenuron-methyl, and glufosinate reduced red sorrel shoot and root biomass in the greenhouse and reduced overwintered ramet density in the field. Clopyralid, sulfentrazone, and flumioxazin reduced shoot and root biomass in the greenhouse but exhibited limited efficacy in the field. Nicosulfuron+rimsulfuron and glyphosate were ineffective in both the greenhouse and field. Dichlobenil and pronamide reduced overwintered ramet density in the field. Reduction of overwintered ramet density did not consistently reduce flowering ramet density. Dichlobenil reduced seedling density at two sites, but no herbicide consistently reduced summer non-bearing year ramet density. Fall herbicide applications alone therefore do not appear to maintain red sorrel suppression in lowbush blueberry fields.

The clonal grass Leymus chinensis overcomes salt stress by over-compensatory growth of individual ramets

Soil salinisation and overgrazing are two important factors limiting plant growth in the Songnen Grassland, Northeast China. Leymus chinensis, a dominant rhizomatous grass, resists grazing and tolerates saline–alkali stress. However, its adaptive mechanisms to the dual effects of grazing and saline–alkali stress remain largely unknown. A two-factorial field experiment was conducted in two consecutive years in the natural L. chinensis community, combining the addition of mixed saline–alkali solution (NaCl:NaHCO3:Na2CO3 1:1:1, amount 559.13 g m–2 year–1) with clipping (removal of 60% of aboveground biomass, AGB). Saline–alkali addition significantly increased AGB and total biomass in the no clipping but not in the clipping treatment. Irrespective of clipping, ramet density was significantly decreased, and individual ramet biomass was significantly increased under salt stress. The significant increase in AGB was due to a high K+:Na+ ratio, high water-use efficiency, and an increase in leaf area index and net photosynthesis rate of individual ramets under salt–alkali stress. Clipping significantly decreased AGB and total biomass regardless of saline–alkali addition, possibly because of decreased sugar content of rhizomes. Saline–alkali and clipping had an interactive effect on AGB and total biomass of L. chinensis. The significant reduction in AGB and total biomass were mainly caused by reduced proline and water-soluble carbohydrate content under dual stress. A modified and simplified graphic model of the limiting resource model was proposed based on our results. Leymus chinensis can grow well under saline–alkali stress via ramet biomass compensation, in which the significant decrease in ramet density is compensated by the significant increase in individual ramet biomass. Ramet compensation and clonal integration were identified to be main mechanisms of herbivory and saline–alkali tolerance.

Distribution and Biomass Allocation in Relation to Depth of Flowering Rush (Butomus umbellatus) in the Detroit Lakes, Minnesota

The Detroit Lakes chain of lakes consists of five basins in northwest Minnesota adjacent to the town of Detroit Lakes. Flowering rush has been established in these basins since the 1960s. We evaluated the distribution of flowering rush in the five basins using a point intercept method, with 830 points distributed in a grid with points 150 m apart. These data were analyzed to determine whether invasive and native species frequencies were different between 2010 and 2011. We also assessed co-occurrence of flowering rush with native hardstem bulrush. The distribution of both flowering rush and hardstem bulrush was unchanged from 2010 to 2011. Flowering rush is invading areas with native plants and not establishing in unvegetated areas. Although flowering rush is found as deep as 4.5 m, it is most frequent at a depth of 1.3 m. We also examined the distribution of biomass and growth across a depth gradient from 0.3 to 3.0 m in 0.3-m intervals. At each 0.3-m interval, three biomass samples were collected at each of 10 transects for a total of 30 samples per depth interval or 300 biomass samples. At each point, leaf height, emergent leaf height, water depth, number of ramets, and number of rhizome buds were counted. Biomass samples were collected in a 0.018-m2 core sampler, sorted to shoots and belowground biomass. We found that flowering rush height and biomass peaked at 1.3 m and declined with greater depth. Bud density was negatively related to water depth. Bud density averaged 300 buds m–2, which was three times the average ramet density (100 ramets m–2).

Understory alder in three boreal forests of Alaska: local distribution and effects on soil fertility

The distribution and effects on soil chemistry of shrub alders (Alnus spp.) occurring in the understory of the boreal forest of Alaska were examined. Understory alder ramet distribution was mapped on three sites; ramet density ranged from 150 to 5280 ramets/ha. Allometric biomass models were developed for alder ramets; maps of the spatial distribution of ramets and of estimated aboveground alder biomass are presented. Biomass of alders in the understory ranged from 20 to 690 g•m−2. The total nitrogen of soils collected beneath alder and from areas without alder differed among the three sites and between two sampling episodes. In undisturbed forest, alder soils tended to have more nitrogen than nonalder soils. On the two sites where background soil fertility was low, a greenhouse bioassay matched these results: alder soils had greater nutrient-supplying capacity than nonalder soils. In soil collected after the sites were harvested, however, results varied. Areas that had supported dense alder before harvesting had more soil nitrogen than areas with no alder at only one site, and at another site, alder soils had significantly less total nitrogen. This study suggests that the effect of understory alders on the boreal forest soil mosaic is a function of site characteristics such as canopy openness and soil background fertility.