Community Supported Agriculture appeals to an increasing number of people. In recent decades, CSA farm and member numbers have grown rapidly in the United States and in California’s Central Valley and foothills. CSA numbers in our study area grew from a few in the early 1990s to 74 in 2010. The loss of 28 CSAs found in our initial online search, which were actually defunct when contacted, merits further research. Membership growth has similarly exploded: CSA membership in our sample increased from less than 700 in 1990 to almost 33,000 expected members in 2010. CSA membership characteristics also deserve further study. The CSA expansion has been accompanied by innovation in CSA types. The CSA concept appears to be both robust and flexible, and different CSA operations are using it to address different challenges. The motivations of farmers for creating CSAs are diverse; ideological predispositions vary greatly, as do farmer attitudes around CSAs as a business and their practices for paying themselves. The diversity of CSA types, and the loose adherence to many of the features of the original concept of CSA, brings into question whether the original model met the needs of the California population. Expanding market opportunities for CSA farmers could involve further adaptations to reach consumers not commonly involved, such as participants in USDA’s nutritional assistance programs,vertical farming companies including the Special Supplemental Nutrition Program for Women, Infants and Children . Despite the diversity of types we identified, CSAs in our study retained a number of core characteristics.
Namely, the vast majority of CSA farmers in the Central Valley cultivated high levels of agrobiodiversity, were committed to agroecological practices and embodied an ethic of reducing off-farm resource use. CSA farmers in our study were also dedicated to enhancing the environment on and off their farms and to providing healthy food to their communities. Our study also revealed that CSAs in the Central Valley and surrounding foothills share characteristics with CSAs nationwide: Smaller-scale CSA farmers are more dependent upon the CSA as a market outlet; CSAs are less dependent upon off-farm work than U.S. agriculture generally; CSA farmers are younger, less diverse ethnically, more likely to be women and more formally educated than the general farming population; and CSA farming practices demonstrate strong commitments to environmental ethics . CSAs are an increasingly important form of direct marketing, crucial for smaller farms. The gross sales per acre of CSAs were considerably higher in our study than of almost all other agricultural endeavors, even in California where gross sales per acre are high. Although most CSAs are profitable, CSAs are like other forms of U.S. farming in often requiring farm partners to work off farm. Even though a CSA is hard work, farmers tend to fi nd it rewarding. The vast majority were happy with their work and continued to view the CSA as a viable option for small- and medium-scale farmers. Overall, CSAs provide an increasingly important marketing option for Central Valley and foothill farmers. However, the extent to which existing and new CSAs will be able to expand the movement and collectively increase their market share, rather than increasingly compete with one another for a limited number of members, remains to be seen. With the numerous economic, social and environmental benefits of the CSA model and its growing popularity, it would seem wise to explore the creation of policy instruments, informational clearinghouses, and additional UC Cooperative Extension efforts to support the needs of CSA farmers and members.
Microorganisms inhabiting the rhizosphere play a key role in plant health and defense , stress response , nutrition and promoting plant growth . The rhizosphere is considered a dynamic ‘hotspot’ of microbial diversity and ecological interactions across the plant–soil system. It comprises a thin layer of soil surrounding and sometimes adhered to the roots of superior vascular plants . The roots release a variety of exudates, mucilage and other compounds to the rhizosphere, via rhizodeposition , serving as source of carbon and energy to microorganisms, as well as chemotaxis signals that lead members of microbial communities in the surrounding soil, called bulk soil, to recognize and occupy niches in this region . Thus, microbial diversity and abundance in the rhizosphere zone can be largely higher compared with its main source in free-roots surrounding soil . Moreover, the microbial community structure in the rhizosphere soil can be largely different from that in the bulk soil, resulting in a potential functional differentiation . Except for some endophytes that come to soil adhered to or even colonizing the seeds of cultivated plants, the main source of microbial diversity in the rhizosphere is the bulk soil . Niche occupancy in the rhizosphere is believed to be dependent on the source and quantity of those substrates released by the roots , root architecture , plant species or genotype and development stage . In some cases, authors have found that the influence of the plant root system can surpass the effect of soil type or management for both assembly and functional potential . Forest-to-agriculture conversion is often found to be detrimental to microbial diversity . However, literature is controversial when linking taxa trade-offs with the consequences to functional potential and ecosystem services . Furthermore, the low number of environmental variables generally measured leads to the assumption that the same set of soil factors, markedly pH , rule microbial shifts when converting forest to agriculture systems.
A multidimensional approach, linking taxonomy, functions and a broader set of environmental variables, could enable researchers to depict correlations among diversity and niche occupancy, as well as to define the real factors modulating ecological patterns in agriculture soils . Thus, it is possible for microbial ecologists to depict those combinations, resulting in a better understanding of changes in microbial community assembly related to disturbances such as deforestation , changes in soils management or even natural ecosystems transitions over time . In this study, we hypothesize that soybean roots act as filters, selecting microbial communities via taxa trade-offs according to niche, to maintain functional resilience. Thus, we aimed to identify the microbial community patterns, in bulk soil and soybean rhizosphere, in a long-term forest-to-agriculture conversion chronosequence, in Eastern Amazon.Sampling fields are located into the Amazon Rainforest Biome, within the ‘Alto Xing ´u’ water basin, which is currently recognized as ‘the last agricultural border’ in the Southeastern Brazilian Amazon. Bulk soil samples were collected in January 2013, in agricultural fields, located in the municipality of Quer ˆencia , Mato Grosso State, Brazil . The climate of the region is Am ,vertical garden indoor with annual average temperature of 27◦C and annual precipitation of 1400 mm in 2013, composed of well defined periods of wet and drought . In order to evaluate long-term microbial dynamics we established a chronosequence varying from 1-year cultivation after deforestation, to 10- and 20-year cultivation in a no-till cropping system, with successive rotation of cultures. All areas were deforested via slash-and-burn, followed by cultivation with common rice for one season, in order to prepare the soil for further cropping. Since that, the selected areas have been cultivated in a no-till cropping system, with successive rotation, including: millet , ryegrass and black oat in the winter season, as cover plants, and maize and soybean in the summer season, as main crops. After deforestation, both areas received liming in the first year and each fifth year to increase and keep pH around 6. Fertilizers and pesticides had been regularly applied over time, according to cultivation demand and technical recommendation. We collected soil samples from the 0–20 cm profile, between lines of soybean plants at V6 stage, in a cartesian-geogrid scheme . Eight samples were mixed to form one composite sample × six replicates × three areas, totalling 18 composite soil samples. The straw layer was removed from topsoil and used as cover in the further greenhouse experiment, in order to keep soil cover conditions. All samples were transported to the laboratory within 48 h after sampling for implementation of the mesocosms experiment.Soil samples collected in the field were used to grow soybean plants in mesocosms at CENA-University of S˜ao Paulo, Brazil. The experiment was carried out in greenhouse in order to normalize the influence of environmental parameters, such as temperature and moisture. The vases were filed with 5 kg of soil from each composite sample. Then, six soybean seeds were sown in each vase. The straw collected in each chronosequence area was distributed in the vases according to the quantity found in each sampling point in the field. The experiment was carried out with 36 vases, consisting of 18 vases with plants, to evaluate the rhizosphere effect, and 18 vases with no plant, to evaluate the bulk soil effect, totalling 36 vases . The soil moisture in all vases was corrected for 60% of water holding capacity in the beginning of the experiment, and maintained via irrigation with deionized water . Soybean seeds were germinated at 28/20◦C and 12-h photoperiod. Ten days after germination, seeds with lower vigor were removed from the vases, keeping three plants per vase. The experiment was conducted until stage R1 , 65 days after sowing, from January to March 2013.Immediately, roots were briefly shaken to separate bulk from rhizosphere soil.
The soil that remained attached to the roots was defined as rhizosphere soil and extracted from the roots with the aid of a sterile brush. Soil samples from the control vases, with no plant, were collected and considered as bulk soil.A total of 10.7 million sequences were obtained by high throughput shotgun metagenomics, for 36 soil samples. Shannon’s α-diversity did not vary across bulk soil and rhizosphere, but did across the chronosequence, with samples from 1-year being less diverse than samples from 10- and 20-year, with no differences between 10- and 20-year no-till . Regardless of time, α-diversity was higher in bulk soil compared with the rhizosphere. Whittaker’s global β-diversity decreased along the chronosequence, in both bulk soil and rhizosphere, indicating that the communities in the same fraction became more similar in both sides of the interface. Despite that, regardless of time, β-diversity was always higher in rhizosphere compared with bulk soil. Based on results that showed a clear reduction of β-diversity, in both bulk soil and the rhizosphere over time, we asked whether community structure presented distinct patterns across time and soil fractions. Taxonomic NMDS plot revealed a separation of microbial communities from bulk soil and rhizosphere. Microbial community structure changed over time of no-till cropping, with separation of 1-year bulk soil samples from 10- and 20-year samples , the same as found for 1-yearrhizosphere samples, which differed from 10- and 20-year samples , with no differences between 10- and 20-year, in both bulk soil and rhizosphere . The taxonomic variation from the whole set of samples was 41%. We investigated possible shifts in microbial community composition through relative abundance of taxonomic profiles. From a total of 32 observed bacterial and archaeal phyla, 15 presented significant abundance differences between bulk soil and rhizosphere in 1-year, 19 in 10-year and 10 in 20-year no-till cropping . In almost all cases, relative abundances were higher in bulk soil than in rhizosphere, except for Proteobacteria and Bacteroidetes in 1-year, which presented higher abundance in rhizosphere. We also evaluated the microbial dynamics along the chronosequence. In bulk soil, 19 out of 30 bacterial phyla had significant changes in abundances after 20-year no-till cropping . Acidobacteria and Actinobacteria abundances decreased after 20-year no-till cropping, while 17 other phyla increased in abundance, markedly Proteobacteria , Planctomycetes , Gemmatimonadetes , Bacteroidetes , and both archaeal Euryarchaeota and Crenarchaeota . Yet for rhizosphere, from 1- to 20-year no-till cropping, 16 bacterial phyla had changes in abundance . Proteobacteria and Acidobacteria decreased their abundances, while 14 other phyla increased, with emphasis on Planctomycetes , Nitrospirae , Gemmatimonadetes , Firmicutes , Cyanobacteria , Aquifcae and both archaeal Euryarchaeota and Crenarchaeota . Owing the fact that Proteobacteria increased in bulk soil and decreased in rhizosphere after 20-year no-till cropping, we depicted its variability at class level . α– and β-Proteobacteria presented higher abundances in rhizosphere, while δ– and γ -Proteobacteria had higher abundances in bulk soil.