The “Regulator” Function of Viruses on Ecosystem Carbon Cycling in the Anthropocene

Viruses act as “regulators” of the global carbon cycle because they impact the material cycles and energy flows of food webs and the microbial loop. The average contribution of viruses to the Earth ecosystem carbon cycle is 8.6‰, of which its contribution to marine ecosystems (1.4‰) is less than its contribution to terrestrial (6.7‰) and freshwater (17.8‰) ecosystems. Over the past 2,000 years, anthropogenic activities and climate change have gradually altered the regulatory role of viruses in ecosystem carbon cycling processes. This has been particularly conspicuous over the past 200 years due to rapid industrialization and attendant population growth. The progressive acceleration of the spread and reproduction of viruses may subsequently accelerate the global C cycle

Bringing Social Science Into Critical Zone Science:Exploring Smallholder Farmers' Learning Preferences in Chinese Human-Modified Critical Zones

There is a growing global emphasis on sustainable agriculture to reduce human impacts and improve delivery of Sustainable Development Goals (SDGs). With increasing investment in critical zone observatories (CZOs), it becomes important to understand how sustainable agricultural knowledge is produced, shared and used between different groups including farmers, scientists and government. To explore these issues, scientists leading the knowledge exchange (KE) component of a China-UK CZO program studied three farming regions with contrasting geologies and varying economic levels, using a practice-based research method. We demonstrate how additional funding for social science research allowed us to understand how farmers access and share farming knowledge through bonding, bridging and linking networks, and how this varies spatially, using interviews and survey questionnaires. Knowledge flows, barriers and opportunities for designing locally suited two-way KE activities were identified. First, we highlight the need for a more locally, socially embedded and reflexive approach to build trust and better address pressing local environmental challenges. Second, we show how social science can usefully inform KE for collaborative, international development science, to draw on local knowledge, promote research impacts and capacity building while avoiding knowledge mismatches. Lastly, a blueprint for the design and funding of future CZOs, social-ecological and planetary health research agendas that combine science, social science, local knowledge and KE is presented, including the need for substantive social science research to take place in addition to science research in human-modified landscapes—enabling the CZ science to be better grounded in, informed by and useful to local communities

Base cations and micronutrients in soil aggregates as affected by enhanced nitrogen and water inputs in a semi-arid steppe grassland

The intensification of grassland management by nitrogen (N) fertilization and irrigation may threaten the future integrity of fragile semi-arid steppe ecosystems by affecting the concentrations of base cation and micronutrient in soils. We extracted base cations of exchangeable calcium (Ca), magnesium (Mg), potassium (K), and sodium (Na) and extractable micronutrients of iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) from three soil aggregate sizes classes (microaggregates, 2 mm) from a 9-year N and water field manipulation study. There were significantly more base cations (but not micronutrients) in microaggregates compared to macroaggregates which was related to greater soil organic matter and clay contents. Nitrogen addition significantly decreased exchangeable Ca by up to 33% in large and small macroaggregates and exchangeable Mg by up to 27% in three aggregates but significantly increased extractable Fe, Mn and Cu concentrations (by up to 262%, 150%, and 55%, respectively) in all aggregate size classes. However, water addition only increased exchangeable Na, while available Fe and Mn were decreased by water addition when averaging across all N treatments and aggregate classes. The loss of exchangeable Ca and Mg under N addition and extractable Fe and Mn in soil aggregates under water addition might potentially constrain the productivity of this semi-arid grassland ecosystem

Mechanisms of nitrogen transfer in a model clover-ryegrass pasture: a 15N-tracer approach

Purpose Nitrogen (N) transfer from white clover (Trifolium repens cv.) to ryegrass (Lolium perenne cv.) has the potential to meet ryegrass N requirements. This study aimed to quantify N transfer in a mixed pasture and investigate the influence of the microbial community and land management on N transfer. Methods Split root 15N-labelling of clover quantified N transfer to ryegrass via exudation, microbial assimilation, decomposition, defoliation and soil biota. Incorporation into the microbial protein pool was determined using compound-specific 15N-stable isotope probing approaches. Results N transfer to ryegrass and soil microbial protein in the model system was relatively smallwith one-third arising from root exudation. N transfer to ryegrass increased with no microbial competition but soil microbes also increased N transfer via shoot decomposition. Addition of mycorrhizal fungi did not alter N transfer, due to the source-sink nature of this pathway, whilst weevil grazing on roots decreased microbial N transfer. N transfer was bidirectional, and comparable on a short-term scale. Conclusions N transfer was low in a model young pasture established from soil from a permanent grassland with long-term N fertilisation. Root exudation and decomposition were major N transfer pathways. N transfer was influenced by soil biota (weevils, mycorrhizae) and land management (e.g. grazing). Previous land management and the role of the microbial community in N transfer must be considered when determining the potential for N transfer to ryegras

Towards environmentally sound intensification pathways for dairy development in the Tanga region of Tanzania

The gap between milk demand and domestic supply in Tanzania is large and projected to widen. Meeting such demand through local production of affordable milk presents an opportunity to improve the welfare of producers and market agents through the income and employment generated along the value chain (VC). Efforts to maximize milk yields, production and profitability need to be balanced with long-term sustainability. We combined environmental and economic ex-ante impact assessments of four intervention scenarios for two production systems in the Tanzanian dairy VC using the CLEANED model and an economic feasibility analysis. Intervention scenarios propose increases in milk production through (i) animal genetic improvement, (ii) improved feed, (iii) improved animal health and (iv) a package combining all interventions. Results show that economically feasible farm-level productivity increases of up to 140% go hand-in-hand with increased resource-use efficiency and up to 50% reduction in greenhouse gas (GHG) emission intensities. Absolute increases in water, land and nitrogen requirements in mixed crop-livestock systems call for careful management of stocks and quality of these resources. An overall rise in GHG emissions is expected, with a maximum of 53% increase associated with an 89% increase in milk supply at VC level. The CLEANED tool proved effective to evaluate livestock interventions that improve incomes and food security with minimal environmental footprint. Here, our simulations suggest that due to current low productivity, the greatest efficiency gains in combination with relatively low increases in total GHG emissions can be made in the extensive agro-pastoral dairy systems, which represent the majority of herds

Soil functions and ecosystem services research in the Chinese karst Critical Zone

Covering extensive parts of China, karst is a critically important landscape that has experienced rapid and intensive land use change and associated ecosystem degradation within only the last 50 years. In the natural state, key ecosystem services delivered by these landscapes include regulation of the hydrological cycle, nutrient cycling and supply, carbon storage in soils and biomass, biodiversity and food production. Intensification of agriculture since the late-20th century has led to a rapid deterioration in Critical Zone (CZ) state, evidenced by reduced crop production and rapid loss of soil. In many areas, an ecological ‘tipping point’ appears to have been passed as basement rock is exposed and ‘rocky desertification’ dominates. This paper reviews contemporary research of soil processes and ecosystems service delivery in Chinese karst ecosystems, with an emphasis on soil degradation and the potential for ecosystem recovery through sustainable management. It is clear that currently there is limited understanding of the geological, hydrological and ecological processes that control soil functions in these landscapes, which is critical for developing management strategies to optimise ecosystem service delivery. This knowledge gap presents a classic CZ scientific challenge because an integrated multi-disciplinary approach is essential to quantify the responses of soils in the Chinese karst CZ to extreme anthropogenic perturbation, to develop a mechanistic understanding of their resilience to environmental stressors, and thereby to inform strategies to recover and maintain sustainable soil function. © 2019 Elsevier B.V