Natural formation and degradation of chloroacetic acids and volatile organochlorines in forest soil: challenges to understanding

Goal, Scope and Background. The anthropogenic environmental emissions of chloroacetic acids and volatile organochlorines have been under scrutiny in recent years because the two compound groups are suspected to contribute to forest dieback and stratospheric ozone destruction, respectively. The two organochlorine groups are linked because the atmospheric photochemical oxidation of some volatile organochlorine compounds is one source of phytotoxic chloroacetic acids in the environment. Moreover, both groups are produced in higher amounts by natural chlorination of organic matter, e.g. by soil microorganisms, marine macroalgae and salt lake bacteria, and show similar metabolism pathways. Elucidating the origin and fate of these organohalogens is necessary to implement actions to counteract environmental problems caused by these compounds. Main Features. While the anthropogenic sources of chloroacetic acids and volatile organochlorines are relatively well-known and within human control, knowledge of relevant natural processes is scarce and fragmented. This article reviews current knowledge on natural formation and degradation processes of chloroacetic acids and volatile organochlorines in forest soils, with particular emphasis on processes in the rhizosphere, and discusses future studies necessary to understand the role of forest soils in the formation and degradation of these compounds. Results and Discussion. Reviewing the present knowledge of the natural formation and degradation processes of chloroacetic acids and volatile organochlorines in forest soil has revealed gaps in knowledge regarding the actual mechanisms behind these processes. In particular, there remains insufficient quantification of reliable budgets and rates of formation and degradation of chloroacetic acids and volatile organochlorines in forest soil (both biotic and abiotic processes) to evaluate the strength of forest ecosystems regarding the emission and uptake of chloroacetic acids and volatile organochlorines, both on a regional scale and on a global scale. Conclusion. It is concluded that the overall role of forest soil as a source and/or sink for chloroacetic acids and volatile organochlorines is still unclear; the available laboratory and field data reveal only bits of the puzzle. Detailed knowledge of the natural degradation and formation processes in forest soil is important to evaluate the strength of forest ecosystems for the emission and uptake of chloroacetic acids and volatile organochlorines, both on a regional scale and on a global scale. Recommendation and Perspective. As the natural formation and degradation processes of chloroacetic acids and volatile organochlorines in forest soil can be influenced by human activities, evaluation of the extent of this influence will help to identify what future actions are needed to reduce human influences and thus prevent further damage to the environment and to human health caused by these compounds

Water-extractable organic matter and its fluorescence fractions in response to minimum tillage and organic farming in a Cambisol

Abstract Background Minimum tillage (MT) and organic farming (OF) are increasingly conducted in agricultural managements from the interest of optimizing soil conditions and developing sustainable agriculture. Our understanding of their effects on water-extractable organic matter (WEOM) is still insufficient. Methods To study the effects of MT and OF on WEOM, we analyzed soil materials sampled at two depths (0–8-cm-upper soil and 12–25-cm-deeper soil) from long-term field experiments using different farming and tillage methods. The content, composition, and quality of WEOM were examined. Results The results showed organic farming significantly decreased water-extractable organic carbon and nitrogen, but had positive effect on WEOM humic-like components revealed by parallel factor analysis with excitation–emission matrix, soil organic carbon (SOC), total nitrogen (TN), as well as SOC/TN. In addition, organic farming increased the aromaticity and condensation of WEOM as indicated by specific UV absorption and humification index. MT had no effect on WEOM both quantitatively and qualitatively but significantly decreased SOC and TN of the whole investigated soil profile. The depth effect was significant with strong stratification of WEOM, WEOM components as well as SOC and total N in upper soil. Moreover, the WEOM spectroscopic quality showed sharp differences between the upper and deeper soils. Conclusions The results indicated that in the combined presence both tillage management and farming management, farming management imposed more influence on WEOM than tillage, and organic farming may facilitate the transformation of WEOM and lead to formation of WEOM with high stability. MT significantly changed the distribution of SOC and WEOM in soil, profile but did not increase the contents of SOC and WEOM in the site of the present study. However, the presence of larger pool of WEOM in MT + OF treatment at upper soil is likely to fuel possibly greater microbial activity and more rapid nutrient cycling in soil which can be favorable practice with potential in improving soil conditions in view of developing a sustainable ecosystem in the studied site Graphical abstract The impacts of agricultural practices on soil water extractable organic matte

Microbial communities and residues in robinia- and poplarbased alley-cropping systems under organic and integrated management

Organic farming and agroforestry are considered as sustainable alternative agricultural practices for intensive agriculture. In a long-term field trial in Scheyern Germany, we evaluated the effects of 21-year organic farming and 4-year agroforestry (robinia and poplar) on microbial community and microbial residues. Microbial biomass and microbial community were determined by fumigation–extraction method and the analysis of phospholipid fatty acid (PLFA), respectively. Microbial residues were evaluated by the measurement of amino sugars. The results showed that organic farming had significantly positive effect on soil organic carbon (SOC) but that it tended to decrease microbial biomass C (MBC), PLFA functional guilds, muramic acid (MurN), and glucosamine (GlcN). Robinia system, however, significantly increased SOC and had the potential to enhance MBC, PLFA functional guilds especially Gram (?), but it tended to decrease MurN and GlcN, in comparison with poplar system. The hedgerow tree did not show significantly positive effect on SOC and microbial properties except the abundance of fungi and Gram (?) bacterial, after 4-year establishment period. The principal component analysis of the PLFA profile showed that in comparison with other investigated treatments, robinia system under organic farming had significantly a different microbial community structure. It also indicated tree species-specific effect on microbial community in the organic farming was stronger than that in the integrated farming. In summary, the short-term introduction of trees into an existing agricultural system will not substantially change the microbial biomass, but it has certain influence on the abundance of specific microbial groups in the hedgerow. Although organic farming did not show positive effect on overall microbial indices, we still see positive effect on SOC after 21-year organic farming and its additive effect with robinia on SOC in current study. We expect that alley-cropping agroforestry system that combines organic farming and robinia hedgerow has a great potential for sequestering SOC and developing sustainable agroecosystems with time

Soil microbial community and microbial residues respond positively to minimum tillage under organic farming in Southern Germany

In a field trial comprising organic farming and minimum tillage management strategies in Scheyern, Germany, we evaluated the long-term (21-year) effects of organic farming (use of a diverse crop rotation with legume cover crop and without application of synthetic fertilizer or pesticides) and minimum tillage (6–8 cm depth) on the microbial community structure and microbial residues in Cambisols. Organic farming had a positive effect on microbial biomass, total phospho-lipid fatty acids (PLFA), Gram (+) bacteria, Gram (-) bacteria and the arbuscular mycorrhizal fungi (AMF) indicator PLFA 16:1v5 and amino sugars. The increase in presence of Gram (+) bacteria when compared to integrated farming was also reflected by increased content of bacterial muramic acid (MurN), i.e. an increased formation of bacterial residues. Minimum tillage significantly increased microbial biomass N and the fungal PLFA 18:2v6,9, averaging the values of upper (0–8 cm) and deeper (12–25 cm) soil, but had no effects on PLFA 16:1v5. Minimum tillage generally resulted in a negative depth gradient of almost all microbial properties analyzed. The only important exception was fungal galactosamine (GlcN), which led to increases in the fungal C/bacterial C ratio and in the contribution of microbial residue C to SOC in the deeper soil. Significant second order tillage management interactions indicated that minimum tillage effects on microbial biomass and PLFA indices (Gram (+) and (i15:0 + i17:0)/(a15:0 + a17:0)) were much stronger in the organic farming system than in the integrated farming system. Redundancy analysis (RDA) showed SOC and H2O content predominantly affected the microbial community structure in the present study. Minimum tillage in combination with organic farming appears to be an effective agricultural strategy that enhances soil microbial biomass, microbial residues and bacterial and fungal abundances. The results indicate that the positive effects of minimum tillage on microbial community can be enhanced by organic farming. Microbial residues as a fraction of SOC respond faster to farming management than to tillage