Crossing certain aridity thresholds in global drylands can lead to abrupt decays of ecosystem attributes such as plant productivity, potentially causing land degradation and desertification. It is largely unknown, however, whether these thresholds can be altered by other key global change drivers known to affect the water-use efficiency and productivity of vegetation, such as elevated CO2 and nitrogen (N) enrichment.
This study was led by Dr. Jian-Sheng Ye from Lanzhou University, China. In it, researchers gathered over 5,000 field measurements of plant biomass. Their findings revealed that crossing an aridity threshold of ~0.50, which marks the transition from dry sub-humid to semi-arid climates, led to abrupt declines in aboveground biomass (AGB) and progressive increases in the root: shoot ratios. This has a profound impact on carbon storage and its distribution within these ecosystems.
Notably, N enrichment was found to significantly increase aboveground biomass and delay the onset of the aridity threshold from 0.49 to 0.55. However, increased CO2 levels did not alter the observed aridity threshold.
Looking ahead to the year 2100, under a high greenhouse gases emissions scenario, researchers predicted a minor 0.3% net increase in the global land area that surpasses the aridity threshold when considering the effects of N enrichment. In contrast, without factoring in N enrichment, this net increase was projected to reach 2.9%. This suggests that N enrichment can mitigate the negative impacts of rising aridity on plant biomass in drylands.
These findings carry significant implications for our ability to improve forecasts of vegetation responses to change in aridity, nitrogen and CO2. The study is published in the journal National Science Review.
Hailing Li et al, Nitrogen enrichment delays the emergence of an aridity-induced threshold for plant biomass, National Science Review (2023). DOI: 10.1093/nsr/nwad242
Nitrogen enrichment delays the emergence of an aridity-induced threshold for plant biomass (2023, October 16)
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