4.4 | Abiotic stress and soil polysaccharide
composition
The saccharides secreted by plant roots are an important source of soil
organic matter, microbial carbon, and energy, mainly hexoses and a small
number of pentoses. This study shows that pentose content tends to
increase under most stress conditions, but it is not synchronized with
the change in hexose. Under N stress, the secretion of polysaccharides
from S. miltiorrhiza roots was down-regulated, confirming that
nitrogen stress significantly reduced the secretion of saccharides from
maize roots (Carvalhais et al., 2010, Zhu et al., 2016). P, DTP, and DT
stress significantly down-regulated polysaccharide secretion in S.
miltiorrhiza roots, unlike phosphorus deficiency, which promoted sugar
secretion in maize roots (Carvalhais et al., 2010), and drought stress,
which promoted polysaccharide secretion in plant roots (Ulrich et al.,
2022). The release of root exudates positively correlates with microbial
growth (Bengtson et al., 2012), suggesting that this result and the
literature results may be related to the lack of microbial involvement
in rhizosphere activities. Further analysis shows that the content of
polysaccharides secreted by roots is positively correlated with plant
yield. Abiotic stress is not conducive to the accumulation of plant
biomass and may also affect the distribution of plant polysaccharides,
resulting in most energy substances, such as carbon source synthetic
sugars, being supplied to plants, reducing the roots secrete
polysaccharides that are not conducive to carbon sequestration in the
soil. Thus, unfavorable environment affects plant growth and also
affects the carbon stored in the soil by the plants.