• Energy Research

AbstractLand use is a key factor driving changes in soil carbon (C) cycle and contents worldwide. The priming effect (PE)—CO2 emissions from changed soil organic matter decomposition in response to fresh C inputs—is one of the most unpredictable phenomena associated with C cycling and related nutrient mobilization. Yet, we know very little about the influence of land use on soil PE across contrasting environments. Here, we conducted a continental‐scale study to (i) determine the PE induced by 13C‐glucose additions to 126 cropland and seminatural (forests and grasslands) soils from 22 European countries; (ii) compare PE magnitude in soils under various crop types (i.e., cereals, nonpermanent industrial crops, and orchards); and (iii) model the environmental factors influencing PE. On average, PEs were negative in seminatural (with values ranging between −60 and 26 µg C g−1 soil after 35 days of incubation; median = −11) and cropland (from −55 to 27 µC g−1 soil; median = −4.3) soils, meaning that microbial communities preferentially switched from soil organic C decomposition to glucose mineralization. PE was significantly less negative in croplands compared with seminatural ecosystems and not influenced by the crop type. PE was driven by soil basal respiration (reflecting microbial activity), microbial biomass C, and soil organic C, which were all higher in seminatural ecosystems compared with croplands. This cross European experimental and modeling study elucidated that PE intensity is dependent on land use and allowed to clarify the factors regulating this important C cycling process.

Changing climatic conditions (warming and decreasing precipitation) have been found to be a threat to the agricultural sustainability of Mediterranean croplands. From the climate change perspective, biochar amendment may interact with the effects of warming and drought stresses on soil ecosystems. However, the responses of soil microbial communities to the joint effects of climate change and biochar in Mediterranean croplands are not sufficiently known. To help fill this knowledge gap, in this work we used a field experiment to determine the effects of partial rain exclusion alone or combined with a soil temperature increase in biochar-amended (20 t ha) and unamended plots under crop rotation on soil chemical properties, enzyme activities, and the microbial community activity, structure, composition, abundance, and functions. The biomass, composition, and activity of the soil bacterial and fungal communities were more responsive to biochar addition than to climate manipulation. Thus, soil chemical parameters, enzyme activities and the relative abundances of bacterial populations were not responsive to the interaction of biochar and climate manipulation, while the predicted functionality of the bacterial community was modified by both factors. Soil β-glucosidase activity significantly decreased in response to biochar addition and climate manipulation, while urease activity was significantly increased by biochar, and protease activity was significantly decreased by climate manipulation. Gram negative and fungal biomasses were significantly affected by the interaction of biochar with climate manipulation. Climate manipulation produced changes in the composition of the soil fungal community without loss of diversity. This study illustrates how the interactions between biochar amendment and future climate change scenarios influence microbially-driven ecosystem services related to the maintenance of nutrient cycles and biodiversity in a Mediterranean agroecosystem. This research was financially supported by the Spanish MICINN MINECO, AEI, FEDER, EU), through the research projects CGL2015-65162-R and AGL2016-75752-R. The authors are also grateful for the AEPP CSIC funds (2020AEP004). We also thank the Spanish Ministry and FEDER funds for the project AGL2017–85755-R (AEI/FEDER, UE), the i-LINK + 2018 (LINKA20069) from CSIC.