Journal of Sustainable Agriculture and Environment最新文献

Predatory protists are widely recognized as critical biotic forces driving soil microbial communities, but their top-down controls on ammonia-oxidizing microorganisms (AOMs), the major players in nitrification, are largely unresolved. Here, we investigated the communities of predatory protists and their associations with AOMs using high-throughput sequencing and network analysis in soil aggregates following various long-term organic substitutions. We found that organic substitutions increased while soil aggregation decreased the alpha diversity of predatory protists. Predatory protistan communities were significantly associated with AOMs. Variosea, an important group of Amoebozoa, were the keystone predatory protists associated with the AOMs. Collectively, our findings highlight the importance of predatory protists, especially Variosea, in regulating the communities of AOMs in an acidic Ultsisol, with implications for managing nitrification by predatory protists in agricultural soils.

Crop production depends on input of nitrogen (N) but because N-use efficiency is low in current conventional cropping systems, farmers fertilize much more than the plants need. More than 50% of added fertilizer N is lost to the environment, mainly as nitrate and gaseous N, that is, dinitrogen, nitrous oxide (N₂O), and ammonia (Lassaletta et al., 2014). Apart from deteriorating water quality and negatively impacting biodiversity, a main concern is the emissions of the greenhouse gas N₂O. Nitrous oxide exhibits a global warming potential approximately 300 times higher than that of CO₂, and the N₂O concentration in the atmosphere is increasing at an accelerating rate (Thompson et al., 2019). Anthropogenic sources contribute ca. 45% to global N₂O emissions, with direct and indirect emissions from N additions in agriculture accounting for ca. 50% (Tian et al., 2020). The negative consequences of N fertilisation therefore make the global food system a key target to limit climate change (Clark et al., 2020) and allow humanity to remain within a safe operating space of the Earth system.

A main challenge for sustainable agriculture is to increase N-use efficiency in cropping systems without compromising yields. One possibility is to improve the retention of soil N by increasing the time N stays in the form of ammonium, as ammonium adsorbs clay particles and soil organic matter. This can be done by using nitrification inhibitors that hinder the microbially mediated oxidation of ammonium to nitrate (Coskun et al., 2017) or by supporting nitrate ammonification, an overlooked process in the N cycle in which nitrate is reduced via nitrite to ammonium (a process also known as dissimilatory nitrate reduction to ammonium [DNRA]). Similar to the competing process of denitrification, nitrate ammonification is performed by phylogenetically diverse microorganisms, which couple the oxidation of various electron donors, most often organic carbon compounds, to the reduction of nitrate under anoxic conditions. Nitrate ammonification creates a short-circuit in the N cycle, bypassing denitrification and N-fixation, and can thereby contribute to primary production (Figure 1). There is, however, a possible risk of ammonia volatilization in alkaline soils. By contrast, the reduction of nitrate to gaseous N oxides through denitrification always results in ecosystem N losses, with a substantial amount emitted as N₂O. Thus, the predominant nitrate reduction pathway affects the fate of nitrate and may have major consequences for N-use efficiency in cropping systems and possibly also climate change.

In this commentary, we highlight challenges and key research questions that need to be addressed to be able to evaluate the promises of nitrate ammonification and the feasibility of exploiting this process in sustainable agriculture. These in

Drylands cover almost half of the planet and support >25% the global population. In this era of global warming, they are expected to continue expanding by the end of the century as a consequence of predicted increases in aridity, which will affect multiple global locations that are already characterised by extreme temperatures, low and variable rainfall, and low soil fertility. In these fragile ecosystems, where microorganisms are integral to maintain functioning and primary productivity, endoliths (i.e., rock-inhabiting microorganisms) play a key role in soil formation and dynamics and are and critical drivers of ecological succession. Here, we posit that endolithic microbes could also function as early alarm warning indicators for environmental changes in the most arid ecosystems. Nevertheless, studies on endoliths are still rather fragmentary and mainly focused in a few specific dry areas such as the Antarctic or Atacama deserts. A global appraisal of the structure and function of the endolithic microbiome is needed for the assessment of the current state of dryland biodiversity worldwide, and to identify the regions that are more vulnerable to global changes. Such an effort will provide new knowledge and will implement official and international initiatives to track and conserve biodiversity on global drylands.