Award-winning combinatorial technology for cell culture

In this study we leveraged field experimental data accumulated in recent decades with artificial intelligence techniques to quantify the amount of nitrogen (N) plants in natural environments are actually taking yearly from the soil at a global scale. We are providing a global map and disentangling its drivers in a climate change context. We considered the N needed to grow new foliar, woody and root tissue as well as the reabsorbed N before leaves senescence.

Since plants compete with soil microbes for nutrients, the total amount of N in soils does not directly relate to the amount that is readily available for plants. A global quantification of how much N can be taken up by plants is thus missing, limiting estimates of the flexibility of plants for further growth. Current evidence indicates that plants actively acquire N through the association with microbial symbionts, allowing plants to obtain N from the atmosphere (via N-fixation) and from organic sources of N (via mycorrhizal fungi) going through the soil. The amount of N that can be absorbed by plants globally through N-fixation and mycorrhizal fungi has not been accurately quantified globally, and most models do not equip plants with these mechanisms to actively acquire N in exchange for C with their microbial partners. Thus, there is an entire dimension of N soil associations that has been neglected, which can change the entire scale of the N cycle in plants. Such information at a global scale would most likely improve the accuracy of C-cycle models, soil-plant models and climate projections, as well as to better understand the drivers of plant N uptake.

Increases in soil organic carbon (SOC) during secondary succession in Mediterranean and semi-arid climates, global hot-spots for agricultural land abandonment, have been notoriously difficult to predict and are subject to multiple environmental and land management factors. Field studies have reported positive, negative and no change varying over extended periods of time. To better evaluate the potential carbon sink capacity of regenerating semi-natural landscapes in these climates requires an improved understanding of the rates of SOC gains and losses. We compiled a global database of Mediterranean and semi-arid chronosequences and paired plots to investigate the effects of past land use, restoration intensity, and various environmental factors on SOC stocks during post-agricultural succession. Based on a preliminary synthesis of the western Mediterranean basin, we expect significant long-term accumulation rates globally although with high variability and the potential for net losses (compared to cropland control sites) even after several decades. Losses or minimal change are likely due to high initial SOC stock at the time of abandonment (e.g. from anthropogenic organic matter inputs) and too high or too low mean annual precipitation (e.g. < 450 or > 1000 mm), among other factors. A consolidated SOC accumulation rate for both Mediterranean and semi-arid soils undergoing post-agricultural succession is provided to better inform decision-makers on the benefits and challenges of agricultural land abandonment.

Regional cycles of agricultural land expansion and abandonment have been common throughout history in many countries of the world. Following the cessation of agricultural practice, landscapes undergo the spontaneous process of ecological succession resulting in significant above and belowground changes over time. As agricultural lands are often severely depleted of soil carbon, they represent one of the land types with the highest potential to act as carbon sinks through the process of soil carbon sequestration. While best management practices for increasing soil carbon stocks through sustainable agriculture are understandably a key focus point in climate change research today, the lasting effect of the abandonment of agriculture on soil organic carbon has received relatively less attention. However, significant amounts of farmland have been abandoned across the globe in both developed and developing countries, especially over the last several decades. To better understand the ability of old agricultural lands to act as carbon sinks through time, this study compiles field and published data to perform a comprehensive meta-analysis on the impacts of this land use change on soil organic carbon dynamics.

Using a chronosequence approach, three study sites in Catalonia, Spain, each with four fields representing different stages of ecological succession post-abandonment spanning roughly 60 years, were sampled at soil depths of 10, 20, and 30 cm. To determine soil carbon stocks at each site, bulk density samples were also collected. Samples were analyzed for organic carbon, nitrogen and pH. Additionally, published chrononsequence and paired-plot data from abandoned agricultural lands throughout the Mediterranean region were also compiled into a database to perform multiple regression analysis. Our findings are not only meant to test the hypothesis that abandoned fields can act as carbon sinks over time, but to also determine the rate of soil carbon stock increase and projected vulnerability in relation to a variety of environmental and land management variables, thereby highlighting the climate change mitigation value of an as of yet understudied global land use change.

Nitrogen (N) limitation of plant growth and carbon (C) sequestration appears to be widespread in terrestrial ecosystems, yet a substantial global sink of photosynthesis-derived C has persisted in recent decades where CO2 has continuously increased. This appears paradoxical in view of Liebig's conceptual model of the Law of the Minimum, which posits that plant growth is ultimately limited by the most limiting resource. It also poses a challenge for process-based Dynamic Vegetation Models (DVMs) that simulate a strong N limitation of the land C sink. The interpretation of phenomena observed in field studies and the formulation of DVMs commonly conceptualise N limitation as a mismatch between supply (from the soil) and demand (by the plant) of reactive N. However, C allocation is highly flexible and plants thereby control mechanisms by which a shortage of N supply may be relieved. Mechanisms include symbiotic N fixation, plant-soil interactions stimulating N availability to plants, and the aversion of N losses from the ecosystem through effective scavenging of available N. Here, we propose a resource economics paradigm to account for the energetic (C) cost of these adaptations and contend that eco-evolutionary optimality of plant functioning leads supply and demand to ultimately balance. A parsimonious model of optimal root and shoot allocation to balance C and N acquisition predicts that a leaf-level enhancement of photosynthesis under elevated CO2 leads to a shift towards relatively more belowground C allocation. This shift may set in motion a cascade of feedbacks that ultimately accelerates the rate of N cycling, increases net primary productivity and reduces the openness of the N cycle, albeit at an increasing C cost of N acquisition. We investigate observations from CO2 manipulation experiments to test the predicted shift towards relatively more belowground C allocation and the existence of a feedback cascade that counters progressive N limitation and tends to relieve N limitation at longer time scales.This provides key mechanistic insights to reveal whether tight N constraints on CO2 fertilisation and the land C sink may be overestimated when flexible allocation and its effects on C-N cycling are ignored in models. We argue that process-based DVMs should be re-formulated to account for C-N tradeoffs and plant adjustments to balance N supply and demand.