The inefficient utilization of nitrogen (N) in soil and
drought
stress seriously threatens agricultural and food production. Herein,
soil application of carbon dots (CDs, 5 mg kg–1)
promoted the growth and nutritional quality of soybeans by improving
N bioavailability, which was beneficial to alleviate the economic
losses caused by drought stress. Soil application of CDs enhanced
the N-fixing ability of nodules, regulated rhizosphere processes,
and ultimately enhanced N and water uptake in soybeans under drought
stress. Compared to control (drought stress), the application of CDs
under drought stress enhanced soybean nitrogenase activity by 8.6%
and increased N content in soybean shoots and roots by 18.5% and 14.8%,
respectively. CDs in soil promoted the secretion of root exudates
(e.g., organic acids, fatty acids, and polyketides) and regulated
beneficial microbial communities (e.g., Proteobacteria, Acidobacteria,
Gemmatimonadetes, and Actinobacteria), thus enhancing the N release
from soil. Besides, compared to control, the expression of GmNRT, GmAMT, GmLB, and GmAQP genes in roots were upregulated by 1.2-, 1.8-, 2.7-,
and 2.3-fold respectively, implying enhanced N transport and water
uptake. Furthermore, the proteins, fatty acids, and amino acids in
soybean grains were improved by 3.4%, 6.9%, and 17.3%, respectively,
as a result of improved N bioavailability. Therefore, CD-enabled agriculture
is promising for improving the drought tolerance and quality of soybeans,
which is of significance for food security in facing the crisis of
global climate change.
