Aridity thresholds in global drylands have long been associated with sudden declines in ecosystem attributes, particularly plant productivity. These shifts have the potential to trigger land degradation and desertification, imposing significant challenges for ecosystems and societies. However, a recent study led by Dr. Jian-Sheng Ye from Lanzhou University in China investigates the intriguing possibility that these aridity thresholds can be influenced by other key global change drivers, including elevated CO2 and nitrogen (N) enrichment.
Drawing from an extensive dataset of over 5,000 field measurements of plant biomass, the researchers uncovered critical insights. The data indicated that crossing an aridity threshold of approximately 0.50, marking the transition from dry sub-humid to semi-arid climates, resulted in abrupt declines in aboveground biomass (AGB) while progressively increasing the root: shoot ratios. These shifts have profound implications for carbon storage and its distribution within these ecosystems.
Intriguingly, the study unveiled that N enrichment played a significant role in countering the decline in aboveground biomass and extending the onset of the aridity threshold from 0.49 to 0.55. However, elevated CO2 levels did not exhibit a discernible impact on altering the observed aridity threshold.
Considering future projections, particularly for the year 2100 under a high greenhouse gas emissions scenario, researchers anticipate a minor 0.3% net increase in the global land area surpassing the aridity threshold when accounting for the effects of N enrichment. Notably, without factoring in N enrichment, this net increase was projected to rise to 2.9%. This suggests that N enrichment has the potential to act as a mitigating force, reducing the adverse impacts of escalating aridity on plant biomass in drylands. These findings shed light on the complex interplay of global change drivers and aridity thresholds, offering insights that are crucial for the conservation and sustainable management of dryland ecosystems.