The effect of cover crop presence on microbial community structure was also greater in some soil great groups, such as the Xeralfs, indicating that attributes associated with soil development can amplify effects of specific management practices like cover cropping. However, an isolated group of samples from alleys supporting grasses, legumes þ cereals or mustards were clustered together and associated with higher values in soil pH and clay content. All measured soil attributes also explained the most variation in microbial community structure in the variation partitioning analysis . Together, these findings suggest that soil chemical attributes and C and N pools played strong roles in structuring soil microbial communities .Bacterial communities tended to separate weakly, although significantly, with respect to presence and absence of tillage, but when looking within group factors through ADONIS a stronger effect of tillage emerged . For example, within soils with planted cover crops there was a stronger effect of tillage compared to across all soils . This may be due to the pre-plant preparation of soil by disking and rolling as well as incorporation of the cover crop into the soil. Similarly, within organic vineyards, tillage played a stronger role compared to conventional vineyards or across all vineyards , corresponding to lower soil C pools in organic vineyards . In this region, organic growers will till alleys to reduce competition between vines and cover crops and for weed control, and in at least one organic vineyard in this study, alleys had been tilled 4e5 times per vine growing season. Nonetheless, vertical hydroponic nft system vineyard soils in Napa are not intensively tilled in comparison to annual cropping systems with conventional tillage practices. This presents challenges in comparing effects of tilled treatments on taxa among annual and perennial cropping systems.
However, in Australia, a similar effect on Firmicutes was observed, in which no-till soils that had been tilled just once exhibited enrichment in Firmicutes . Furthermore, tillage seemed more important within Xeralfs compared to Fluvents or across all soils . For vineyards in Napa Valley, soil type tends to influence choice of tillage practice, in which Xeralfs and Fluvents are typically tilled while Xerolls and Xerults are not. Also, in Napa Valley, vineyards at higher elevations tend to be no-till due to rocky conditions and steeper slopes. Therefore, the effects of tillage and soil type are linked. Tillage disturbance creates shifts in soil nutrient availability and in aggregate size, composition, and stability, thereby changing the physical environment and resource availability experienced by soil microorganisms . This then can lead to shifts in soil microbial communities and microbially-mediated processes . One soil organic matter pool that re- flects both tillage disturbance and microbially-mediated processes is that associated with the fine soil fraction . As it is not always mineral associated , we will refer to it as ‘fine SOM’ instead of ‘organomineral complexes.’ Typically, fine SOM is thought to reflect residues that have been highly decomposed by soil microorganisms. Therefore, it is likely that fine SOM concentrations and measures of soil microbial activity, like respiration and potentially mineralizable nitrogen , reflect the microbial community structure . In our case, no till soils had distinct microbial community structure and the greatest concentrations of total and fine SOM and PMN compared to tilled soils, regardless of the time since tillage occurred . However, less recently tilled soils had highest diversity and richness, higher than no-till and recently tilled soils . At the same time, taxa that exhibited significant differences with tillage or time since tillage had occurred had greater relative abundances in tilled soils, suggesting that these taxa either had a greater stability in response to tillage disturbance or were selected in response to tillage, as compared to other taxa across all sites.
At the phyla level across all sites, no specific taxa had consistent decreases in relative abundance with tillage, suggesting that taxa most sensitive to tillage were consistent among sites. Interestingly, there was no clear overlap between soil microbial communities supporting specific kinds of cover crops and tillage status, suggesting that these practices had relatively independent effects on soil microbial communities . However, total cover crop biomass was not collected, and so any correlation of cover crop biomass production and its total contributions to labile soil resources with pre-plant tillage in fall, spring incorporation of cover crops by tillage or no-till is indeterminate. Further supporting the idea that soil resources drive diversity, compost addition was associated with an increase in overall bacterial diversity and changes in community composition. Increased diversity and relative abundances of certain taxa under compost application may be a response from increased availability of resources, especially as soils that received compost had lower C pools, or from microbial introductions from compost itself . Compost has varied origins and is derived from diverse materials, which might explain the lack of a consistent effect across all vineyards on particular taxa abundances, despite the consistent increase in phylogenetic diversity. As an example of the hierarchy of effects observed within groups , recency of tillage had a greater impact than tillage presence, in general, on structuring soil bacterial communities, especially when excluding no-till soils . An effect of recency of tillage was even resolved for groups in which tillage in general did not have an effect, such as within conventional vineyards and within Fluvents. Presumably, all vineyards were cultivated during their conversion from previous land-use types. Because tillage is known for its long-lasting impacts, even on soil microbial communities , all vineyards could be considered disturbed ecosystems. Therefore, it might not be a surprise that recency of tillage has a greater influence in structuring soil bacterial communities than the practice of tillage, in general. Tillage also is known for its short-term effects on soil resources and soil microorganisms, as shown in intensively cultivated vegetable crop soils and annual grasslands . In our case, less recently tilled soils had highest diversity and richness, above that of no-till and recently-tilled soils. This lends some support to the ecological concept of adaptive radiation, where an event gives rise to many new species expanding into new habitats or ecological roles in a relatively short time .
Other studies have supported the idea of adaptive radiation of bacteria particularly when species were absent from the medium prior to inoculation with the experimental bacterium , which could be analogous to adaptive radiation following the tillage-associated reduction of microbial biomass, richness, and diversity. However, further research is required to confirm the accuracy and wide applicability of such ecological concepts to microbial ecology.Bacterial community composition and diversity differed with conventional, organic, and bio-dynamic vineyard management. It is commonly known that these systems tend to differ in the types of pesticides and fertilizers used, and that pesticides and fertilizers affect soil microbial communities . However, since fertilizers and herbicides are typically only applied under the vine, and other pesticides are most commonly applied foliarly to vines, we do not expect these factors to play large roles in distinguishing our samples, which were taken from alleyways. Nevertheless, conventional, organic, and bio-dynamic vineyard management systems in our study also differed with respect to tillage, cover crop, compost application and practices specific to bio-dynamic like field sprays of cow manure and quartz silica as well as additives to compost , all factors that influence soil physical environment and resources available to microorganisms. Furthermore, differences in soils, climate, and sub-appellation may influence management decisions, impacting likelihood of a grower to adopt certain designations, whether conventional, organic, or bio-dynamic and observed distinctions among bacterial communities with respect to vineyard management systems. For vineyards, underlying practices embedded within the conventional, organic, nft hydroponic system and bio-dynamic management systems affected bacterial communities both in terms of biodiversity and overall community structure. Growers employ tillage as a water and weed management practice to prevent competition between vines and cover crops or weeds, particularly in organic and dry-farmed vineyards. Conventional systems were more likely to be no-tilldlikely due to the lack of a need for tillage as a water management or weed control practice. As previously discussed, tillage was associated with lower soil bacterial a-diversity and richness compared to no-till. Since organic vineyards were associated with tillage, we attribute the lower a-diversity and richness associated with organic vineyards to the impact of tillage. Studies in annual cropping systems have found the opposite effect or no differences between conventional, organic, and bio-dynamic management . This may be due to the different nature of conventional, organic, and bio-dynamic systems in vineyards compared to annual cropping systems.Soil bacterial communities were structured as a function of vineyard management practices and soil properties. As ranked by the highest ADONIS R2 -value, cover crop mix was the strongest management factor, but hierarchical effects of recency of tillage and compost additions on soil microbial structure were also noted. Our work supports the paradigm that vineyard management practices affect soil microbial communities through their suite of impacts on soil properties, but mechanistic studies will further elucidate the ecological role of specific taxa identified in these vineyard soils. The identification of distinctive soil bacterial communities related to soil resources and vineyard management indicates that soil bacterial community structures can be developed as a biological indicator of soil quality. This may provide a strategy to monitor soil quality or health in vineyard soils. This work also has opened the door for future assessments of interrelationships of vineyard management, microbial biodiversity, and agroecosystem services, especially as they relate to soil quality, soil health, vine health, and berry quality .
In a typical year, debates surrounding the state’s budget are among the most controversial matters addressed by Colorado state lawmakers. Because the current legislature is closely divided along party lines, many expected the budget to take center stage once again in the 2018 legislative session. Before the current session began, the Denver Post outlined some of the major items on the General Assembly’s agenda. Among the most pressing issues facing lawmakers were transportation funding, the opioid crisis, energy development, and the financial stability of the Public Employees’ Retirement Association , in addition to matters surrounding sexual harassment in the legislature . For the fourth consecutive year, divided party control exists in the General Assembly with Democrats holding a 10-seat advantage in the state House, while a slim Republican majority exists in the Senate with 18 Republicans, 16 Democrats, and one unaffiliated senator. At times the partisan differences between the chambers have been substantial. In prior legislative sessions, the issue of guns has been among the most controversial topics addressed by legislators as evidenced by the successful recall elections of two Democratic lawmakers over their votes on gun control bills in 2013 . During the current session, the Republican controlled Senate passed legislation in a party-line vote to allow Coloradans to conceal carry a firearm without a permit . With no Senate Democrats supporting the measure, the bill was dead on arrival in the House where Democrats hold the majority. A bill to ban bump stocks was recently defeated by Republicans in the State, Veterans, and Military Affairs Committee following a party-line vote. While political parties in Colorado remain bitterly divided on the issue of guns, other previously controversial measures witnessed unexpected compromise during this session such as increased funding for the program to provide driver’s licenses for undocumented residents. Beginning in August 2014, an estimated 120,000 undocumented residents could begin applying for driver’s licenses. Although the state issued 32,325 licenses through the program, it was troubled by a lack of staff and funding since demand outpaced the number of appointments offered by the state . Many expected further problems as the licenses first issued were due for renewal, and the program originally required all individuals to procure or renew their licenses in person. However, a bill recently passed in the Republican-controlled Senate provides additional funding to the program and allows existing licenses to be renewed online, among other changes . Following successful passage in the House, Governor Hickenlooper signed the bill in May. The passage of this bill into law demonstrates the possibility for bipartisan compromise in a divided General Assembly on controversial issues as well as debates surrounding spending priorities.