Main environmental drivers of abundance,diversity and community structure of comammox Nitrospira in paddy soils

The recently discovered complete ammonia oxidizers comammox Nitrospira contain clades A and B that can establish an independent one-step nitrification process;however,little is known about their environmental drivers or habitat distributions in agricultural soils.Previous studies on comammox Nitrospira in paddy soils have mainly focused on small-scale samples,and there is a lack of multisite research on comammox Nitrospira in paddy soils.In this study,we conducted a survey of 36 paddy soils to understand the community structure,abundance,and diversity of comammox Nitrospira and the degree to which they are affected by environmental factors at a large scale.Comammox Nitrospira were found to be widely distributed among the paddy soils.The abundance of comammox Nitrospira clade A was mostly lower than that of clade B,whereas its diversity was mostly higher than that of clade B.Correlation analysis showed that multiple factors affected(P<0.05)the abundance of comammox Nitrospira,including soil pH,organic matter,total carbon,and total nitrogen,latitude,mean annual temperature,and mean annual precipitation.Moreover,there was a clear relationship between the comammox Nitrospira community and habitat,indicating that some amplicon sequence variants(ASVs)had a unique dominant position in specific habitats.Phylogenetic analysis showed that the ASVs of comammox Nitrospira clade A clustered with the known sequences in the paddy soils and were significantly different from the known sequences in other habitats,which may be related to the unique paddy field habitat.In contrast,comammox Nitrospira clade B showed no clear habitat dependence.These results support the wide distribution and high abundance of comammox Nitrospira in paddy soils and provide novel insights into nitrogen cycling and nutrient management in agricultural ecosystems.

Long chain n-alkanes and their carbon isotopes in lichen species from western Hubei Province： implication for geological records

Five coticolous lichen samples were collected from western Hubei Province of China to analyze the long chain n-alkanes and their carbon isotope compositions. The n-alkanes range in carbon number from C17 to C33 with strong odd-over-even predominance between C21 and C33. Lichens are dominated by n-C29 in the samples of Dajiuhu, Shennongjia Mountain, but by both n-C23 and n- C29 at Qizimei Mountain. This difference may result from the different environmental conditions in these two sites. The δ13C values of long chain n-alkanes in lichen samples show the signature of C3 plants. Based on compound- specific carbon isotopic values and previous results, we state that alkane homologs 〉 C23 mainly originate from the symbiotic fungi, while symbiotic algae only contribute trace amount of long chain alkanes. Of great interesting is the occurrence of long chain 3-methylalkanes in the Qizimei samples. These anteiso compounds range from C24 to C32, displaying obvious even-over-odd predomi- nance. This study reveals that the association of long chain 3-methylalkanes with n-C23 alkane might be used as proxies to reconstruct the paleoecological implications of lichens in Earth history.

Seasonal variations of leaf wax n-alkane distributions and δ^(2) H values in peat-forming vascular plants from the Dajiuhu peatland, central China

Leaf wax n-alkane compositions have been widely applied to reconstruct paleoclimate histories in peat deposits,yet understanding of how the n-alkanes vary during seasonal plant growth remains limited.Here we report variations in the molecular and wax-derived nalkane hydrogen isotope(δ^(2) Halk)in the three dominant vascular plant species(Sanguisorba officinalis,Carex argyi,Euphorbia esula)and surface peat deposits nearby from the Dajiuhu peatland over a growing season.All three species show a relatively high carbon preference index(CPI)in the beginning of the growing season,with the CPI values reaching as high as 50 in two of the three species.Two species(S.officinalis,E.esula)display relatively stable average chain length(ACL)values over the four sampling intervals,with standard derivations of 0.2-0.3.In contrast,C.argyi exhibits a significant fluctuation of ACL values(averaging 28.11.4)over the growing season.Theδ^(2) Halk in all three species decreased during leaf growth.In the final stage of growth,theδ^(2) Halk values of the three species are similar to those in the surface peats collected from the peatland.Combining the results of our measurements of alkane concentration andδ^(2) H values,it is likely that de novo synthesis of leaf wax n-alkanes in the peatforming plant species is mainly at the early stage of leaf development.In the following months,the removal process exceeds renewal,resulting in a general decrease of the concentration of the total n-alkanes and the integratedδ^(2) Halk values.Thus theδ^(2) Halk values probably integrate the environmental variations at the end of the plant growth period rather than the whole period or the early growth period.These results are significant and have the potential to improve the utility ofδ^(2) Halk values in paleoenvironmental reconstructions.