Effects of Biochar Feedstock and Pyrolysis Temperature on Soil Organic Matter Mineralization and Microbial Community Structures of Forest Soils

Biochar has received much attention as a strategy to enhance soil carbon (C) sequestration and mitigate climate change. Previous studies found that the feedstock and pyrolysis temperature can largely determine biochar properties, which in turn, impact the stability of native soil organic matter (SOM) and soil microorganisms. The Schima superba and Cunninghamia lanceolata are two tree species widely distributed in the subtropical region of southern China, but how the biochars from these two species influence the soil C sequestration and microbial communities of plantation remain poorly understood. In this study, we produced biochars from these two different feedstocks (13C-labeled S. superba and C. lanceolata litters) at three pyrolysis temperatures (350°C, 550°C, 750°C), then added them to the soils from C. lanceolata plantation, and maintained the experiments at 25°C for 112 days. We found both C mineralization and soil microbial community structures were strongly, but inconsistent, affected by biochar feedstock and pyrolysis temperature. The C. lanceolata biochar triggered the negative priming effect faster and greater compared with the S. superba biochar amendment. Biochars produced at 550°C showed the most significant negative priming effect during the whole incubation period, regardless of the different feedstocks. The cumulative amount of CO2 derived from biochars was significantly decreased with pyrolysis temperature (p < 0.05), indicating that biochars prepared at higher temperatures were more stable in the soil. Further, the soil microbial community structure was only affected by biochar pyrolysis temperature rather than biochar feedstock and their interaction. Together, our results reveal that biochar feedstock and pyrolysis temperature may play more important roles in dictating the priming effect than the structure of microbial community for C. lanceolata plantation. Overall, we concluded that the biochars prepared at 550°C could rapidly decrease the turnover of native SOM in a short term and biochar amendment has the potential to be a management practice for soil C sequestration in the C. lanceolata plantation.

Priming Effect Induced by the Use of Different Fertilizers on Soil Functional Diversity

Agricultural practices, such as the use of fertilizers, can change the structure and function of soil microbial community. Monitoring and assessing the soil microbiota and its dynamics related to different factors can be a powerful tool for understanding basic and applied ecological contexts. The main objective of this paper was to assess the changes of carbon turnover rate and the microbial metabolic activity, when different types of fertilizers were used, process called priming effect. A microcosm experiment was designed and performed under controlled temperature and humidity and the soil samples were analyzed using the MicroResp technique. Results show that the integration in soil of different carbon sources, such as green manure, can lead to a positive priming effect and integration of mineral fertilizers can lead to negative priming effect. The carbon sources with the highest respiratory activity were α-ketoglutaric acid, malic acid, oxalic acid, citric acid, while the lowest respiratory activity was obtained in case of arginine.

The unidirectionality of semantic changes in grammaticalization: an experimental approach to the asymmetric priming hypothesis

Why is semantic change in grammaticalization typically unidirectional? It is a well-established finding that in grammaticalizing constructions, more concrete meanings tend to evolve into more schematic meanings. Jäger & Rosenbach (2008) appeal to the psychological phenomenon of asymmetric priming in order to explain this tendency. This article aims to evaluate their proposal on the basis of experimental psycholinguistic evidence. Asymmetric priming is a pattern of cognitive association in which one idea strongly evokes another (i.e. paddle strongly evokes water), while that second idea does not evoke the first one with the same force (water only weakly evokes paddle). Asymmetric priming would elegantly explain why semantic change in grammaticalization tends to be unidirectional, as in the case of English be going to, which has evolved out of the lexical verb go. As yet, empirical engagement with Jäger & Rosenbach's hypothesis has been limited. We present experimental evidence from a maze task (Forster et al.2009), in which we test whether asymmetric priming obtains between lexical forms (such as go) and their grammaticalized counterparts (be going to). On the asymmetric priming hypothesis, the former should prime the latter, but not vice versa. Contrary to the hypothesis, we observe a negative priming effect: speakers who have recently been exposed to a lexical element are significantly slower to process its grammaticalized variant. We interpret this observation as a horror aequi phenomenon (Rohdenburg & Mondorf 2003).