Plants had 5-10 cm new vegetative growth several weeks after transplanting, and treatments were applied May 20, 2021 and June 22, 2021 in the first and second replicates, respectively. Non-treated plants were left undisturbed, clipped plants had all above ground tissues removed, and tilled plants had the top 10 cm of soil in each pot stirred with a trowel. The tillage treatment involved a standardized stirring and flipping motion that inverted soils and resulted in the burying, uncovering, and cutting of some plant tissues. However, we had to exclude one repetition of the non-treated-Corning orchard combination in the second replicate, because not enough plant material was available. Plants were grown for 10 weeks following treatment application. During this time, drip irrigation was continued on a daily schedule, and entire replicates were given supplemental hand watering as needed. Plants were monitored weekly for flowering. Plants were harvested at the end of the 10-week window, which occurred on July 28, 2021 and September 1, 2021 in respective replicates. Above ground and below ground tissues were collected separately, and root washing occurred at collection. Plant tissues were bagged and placed into a forced air drier before weighing. Dry biomass was used to calculate root:shoot biomass ratios for each plant. Statistical analysis. All analyses were performed in R 3.0.3 .
We took the general approach of selecting the best, ecologically-relevant statistical models with Akaike information criterion , hydroponic rack system using ANOVA for global analysis, and finally using Fisher’s LSD for multiple comparisons For the field experiment, we tested various logical combinations of ecologically-relevant predictors with the aictab function from the AICcmodavg package . For both flowering timing and above ground biomass, the best model used just treatment and replicate as predictors, with no interactions. Then, we inspected ANOVA assumptions with qqPlot from the car package . One sample with extremely high biomass was removed as an outlier from the biomass dataset based on visual inspection of Q-Q plots. We proceeded with using the Anova function from the car package and the LSD.test function from agricolae .For the greenhouse experiment, we used the same general approach of using AIC to select models, ANOVA to compare predictors, and Fisher’s LSD for multiple comparisons. Some modifications were required to accommodate the factorial design and the structure of the dataset. The flowering timing data required a generalized linear model using a Poisson distribution with a log link function. Model comparison with AIC led us to select treatment, population, and replicate as predictors.
Relevant multiple comparisons were made with Fisher’s LSD using the glht functrion from the multcomp package . For the root:shoot biomass ratio data, we chose a multiway ANOVA that included treatment, population, replicate, and their interactions. Upon visual inspection of with Q-Q plots, three samples with very high root:shoot ratios were removed. Additionally, we removed 13 samples with indeterminate values . Multiple comparisons were made with emmeans and cld from multcomp. All figures were created with ggplot2 . We chose different kinds of figures for the field and potted plant experiments, due to the relative size and complexity of the potted plant experiment datasets.In the field experiment, weed management treatment did not affect field bindweed above ground biomass after 10 weeks of regrowth . The second replicate resulted in overall higher field bindweed biomass than the first and third replicates . However, time to flowering was affected by treatment . Broadcast glyphosate and tillage significantly increased time to flowering by one to two weeks on average compared to other treatments. Conversely, string trimming, glufosinate, glyphosate strips, and mowing resulted in shorter time to flowering, about five weeks on average after treatment application.
These four treatments delayed flowering one week compared to non-treated plots, suggesting that field bindweed flowering phenology is less sensitive to follow up treatment compared to the initial weed management treatment. Time to flowering is a critical trait for agricultural management which affects the ability of field bindweed to contribute to a persistent soil seedbank. Flowering delays of one to two weeks could be relevant for orchard weed management which is frequently constrained by logistical challenges, such as the availability of application equipment or prioritization of irrigation and other pest management operations. Furthermore, flowering timing could contribute to population-level shifts in field bindweed reproduction that affect fitness and lead to more clonal reproduction. These results indicate that disturbance through weed management can have complex effects on field bindweed even when above ground biomass is unaffected. Broadcast glyphosate application appears to be a useful management tool for delaying field bindweed regrowth and affecting the phenology of additions to the soil seedbank. However, we assume that sexual reproduction is positively correlated with above ground biomass, so this study does not support a link between these orchard weed management programs and the magnitude of soil seed bank additions . Future research should evaluate whether certain weed management practices, namely systemic herbicides, affect the relationship between biomass and seed production or viability. Additionally, future research should evaluate the intensity of longer sequential orchard management programs that are required to eliminate soil seed bank additions. The relative contribution of sexual and asexual reproduction to overall fitness remains an open question, and better general understanding of reproductive resource allocation could help us understand how various management programs might select for different reproductive and life history strategies over time.In the potted plant experiment, treatment , population , and replicate were all important predictors of root:shoot biomass ratio . Additionally, there were significant interactions between treatment and replicate and all three variables . In general, differences were subtle and effect sizes were small. However, the clipping treatment resulted in higher root:shoot ratios than the other treatments, which is logical given that shoot tissues had been removed from that treatment 10 weeks before plant tissues were collected. The field bindweed population sourced from an annual crop field generally produced higher root:shoot ratios than other populations, suggesting that this population produces relatively larger root reserves or less above ground biomass than the other populations from perennial and non-agricultural systems. Orchard managers should be aware of the possibility that field bindweed has the potential to reproduce differently between annual and perennial cropping systems or in the early stages following an environmental transition, such as during orchard establishment. Future research could evaluate the reliability of such differentiations and their potential contributions to field bindweed population change over time or changes in resource allocation that affect regrowth. Time to flowering in the potted plant experiment was affected by treatment and replicate and not significantly affected by population . In general, clipping and simulated tillage were similar to one another, and both delayed flowering compared to non-treated plants. The potted plants had different flowering phenology compared to the field experiment, with more variation in flowering timing. We attribute some of these differences to the controlled nature of potted plants, growing plants from transplants, and the subsampling design of the field experiment. Despite these differences, weed management disturbance in the potted plant experiment resulted in average flowering delays of one to two weeks, cannabis vertical grow system which is similar to the field experiment. Again, we argue that these delays can be practically important for orchard growers making decisions about management timing. Knowledge of weed reproduction and population ecology is essential for the implementation of integrated pest management programs. Furthermore, improved knowledge of the diverse and prolific reproductive methods of pernicious weeds like field bindweed can help us understand how weedy plants respond to various kinds of agricultural disturbance. These experiments demonstrate that flowering can be effectively delayed through common management practices.
Management practices that affect both root and shoot tissues, such as glyphosate and tillage, are especially effective at delaying field bindweed flowering under field conditions. This information could support integrated management of field bindweed that includes better scheduling of repeated management applications based on the development of field bindweed. Current orchard weed management programs in California frequently address field bindweed with repeated applications of glyphosate, and optimization of these applications could have sustainability benefits for agricultural landscapes in California and crop safety benefits in young orchards. Additionally, we present information that indicates differential reproductive characteristics between field bindweed collected from different home environments, suggesting the potential for an adaptive response to long term agricultural management programs. Weed populations that change in response to repeated management are a critical threat to agricultural productivity. This research reinforces the importance of planning and repeated management for developing integrated pest management programs that address the unique changes that affect orchards that are situated in complex California landscapes. Future research could account for the24hapiro24ve multi-year effects of disturbance on field bindweed reproduction, including consideration of perennial roots and asexual reproduction of established plants in controlled environments like potted plants or in different stages of the orchard life cycle.Cover cropping is a management strategy which adds potentially beneficial biodiversity to agroecosystems. Cover crops are non-harvested crop plants that cover soil that would typically be left bare under conventional agricultural management. Depending on specific cover crop management practices , farmers may leverage planned agrobiodiversity to enhance regulating ecosystem services , increase cropping system resilience , reduce agricultural externalities, and support sustainable intensification . Research has mainly addressed ecological impacts of annual cover crops grown in the fallow period between two annual cash crops but much remains to be known about impacts and potential in perennial systems where cover crops are grown on the ground beneath orchard trees with spatial separation from the main crop. Cover crops have known impacts on abiotic factors such as those related to soil structure or water use but more research is needed to understand broader biotic functions of horticultural importance. Aside from being practically important for orchard growers, weed suppression can indicate the absence of unfilled ecological niches within the orchard system . Whereas conventional orchards have significant unused resource pools that lead to the need for intensive vegetation control, cropping systems with diverse ground covers lead to regulation of water, light, nutrients, and safe germination sites so that these resources are less available for weed proliferation . An ideal orchard cover crop displaces weed plants with predictable, domesticated species that also provide additional sustainability benefits . Previous studies have demonstrated that cover crops can be useful in the unique environment of irrigated, perennial cropping systems in Mediterranean climates . In these systems, winter annual cover crops have a life cycle coincidental with winter rains as well as the dormant period of deciduous orchard crops. This phenology allows winter annual plants to have significant niche differentiation compared to the orchard crop while having niche overlap with important weedy species. Exploitative competition between cover crops and orchard weeds may be especially relevant given the long winter cover crop season and the cumulative effects of growing cover crops over multiple years. In contrast, other forms of interference, such as allelopathy or suppression of summer weed germination with cover crop residues , may be more important in annual cropping systems, where rapid changes in resource availability and fast life histories change the phenology of competition . Winter annual cover crops are therefore a practical way to use biodiversity in support of vegetation management in orchard systems, but it remains important to understand potential tradeoffs between ease of management and multifunctionality . Studies in unmanaged ecosystems highlight the potential role of diverse, multifunctional plant communities in increasing ecological functions and reducing weed invasability through niche differentiation and variation in developmental biology and phenotypic plasticity . However these patterns might not be reproducible in highly managed agricultural systems at scales relevant to populations, communities, and fields given increased disturbance and decreased species richness. . This study aims to fill a critical knowledge gap in understanding the potential of various multi-species cover crops for integrated pest management goals such as reductions in herbicide use in large-scale, intensified, and highly productive irrigated orchard systems in a unique, Mediterranean climate. We evaluated plant communities under two multi-species cover crop mixes, one that is functionally diverse and one that is functionally uniform, over two seasons in three commercial almond D.A. Webb) orchards in the Central Valley of California.