P22 - Biogeochemical Gradients

Spatiotemporal patterns and controls of rhizosphere biogeochemistry of maize

The aim of this project is to give new insights in rhizosphere self-organization and help to understand soil carbon (C) inputs. Due to the lack of techniques which can analyse C dispersal in an undisturbed environment, it is until now not clear to which extent the spatial arrangement of roots, pores and solid soil matter control C dispersal, turnover and storage. We hypothesize that i) rhizodeposits have different spatial dispersibility depending on their chemistry as well as root morphology, age and soil texture, ii) root morphology, soil texture and moisture control residence times of rhizodeposits, and that iii) microbes feed differently on rhizodeposits depending on the spatial arrangements in soil.
Therefore, we want to identify spatiotemporal patterns of the rhizosphere biogeochemistry by studying radial gradients of deposits of both root and microbial origin, and determine to which degree they result from self-organization (root age and developmental stage) or are controlled by external factors (genotype and soil texture). Through the determination of C concentration, C turnover and biomarker gradients on a wide range of spatial scales (μm to cm), we are going to study and analyze the influence of root, pore and aggregate architecture on C dispersal and turnover as well as the spatial component of microbial response to differences in rhizodeposition. The previous statements will be carried out covering spatial scales from μm to cm and temporal scales from weeks to months.

Outcome

To investigate the effects of the external factors, plant genotype (wildtype and rth3 mutant of Zea mays) and soil texture (loamy and sandy), on spatiotemporal biochemical patterns in the rhizosphere, we developed a new sampling approach to collect soil samples at different radial gradients (at 2, 4, 6, and 8 mm radius) around root sections at the field site in Bad Lauchstädt (Gocke et al., under review). Using this sampling approach in combination with biomarker analyses (PLFA, fatty acids, and neutral sugar) we found that the carbon (C) together with the nitrogen (N) dispersal and turnover was mostly influenced by soil texture rather than the plant genotype (Gocke et al., in prep.). We also found that the organic carbon (Corg) as well as the organic and inorganic phosphorus (Po/I; measured with ICP-OES) content under field conditions were also rather influenced by soil texture than genotype over a period of 6 years. Interestingly, the microbial necromass contribution to the Corg composition was higher in sandy soil than in loamy soil and relatively stable over time (Scheibe et al. in prep.).
In the framework of the SPP rhizosphere experiment we were able to demonstrate a new measurement approach to analyze C dynamics at a micro-scale in environmental samples. By analyzing the δ13C values in- and outside of soil aggregates from a C3/C4 vegetation change experiment at different time points (4, 10 and 19 years) with the laser ablation isotope ratio mass spectrometry (LA-IRMS) and a new embedding method (water glass), we were able to reveal a large micro-scale heterogeneity within aggregates Vergara-Sosa et al., 2021 ). Surprisingly, 15 years after the C3/C4 vegetation change experiment the fresh C4 material was still preferentially found at the aggregate surfaces rather than the interior of the soil aggregates indicating the slow aggregate turnover. The LA-IRMS analysis was also applied to directly visualize the C release into the rhizosphere by measuring root-soil-transects on in situ samples ( Lippold et al., 2023 ).


Link to English scientific abstract

Link to German scientific abstract