image: Aridity thresholds for measured (a) aboveground biomass (n = 1353) and (d) root-shoot ratio (n = 3093). Solid red lines represent the linear fits on both sides of each threshold. The red numbers and vertical dashed lines represent the identified aridity thresholds. Plant biomass data were log-transformed to conform to normality. The violin diagrams in panels b and e show bootstrapped slopes of the predicted fitted trend at the threshold of the two regressions existing at each side of the threshold (purple before the threshold, red after the threshold). The violin diagrams in panels c and f show bootstrapped intercepts. The asterisks represent a significant difference before and after the aridity threshold at p < 0.001 using the Mann-Whitney U test.
Credit: ©Science China Press
This study is led by Dr. Jian-Sheng Ye from Lanzhou University, China.
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.
In this study, researchers gathered over 5000 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.
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See the article: https://doi.org/10.1093/nsr/nwad242
Journal
National Science Review