The overall decomposition of the spring-lodged litter is faster than the autumn-lodged litter in a steppe ecosystem

In grasslands, a large proportion of senescent plant shoots in autumn pass
the winter period as standing dead materials instead of becoming detached
litter immediately. However, the information is hardly available on the
decomposition of plant standing dead materials during the winter period
and its impacts on the subsequent decomposition of these materials after
littering in the coming spring. We conducted a two-year experiment to
compare the decomposition process of the litters lodged in autumn versus
that lodged in spring of two dominant plant species, Leymus chinensis and
Stipa grandis, in a native steppe ecosystem in Inner
Mongolia. Throughout the whole decomposition period, the
autumn-lodged litter was directly positioned upon the soil surface, while
the spring-lodged litter suspended as standing dead for the first 7 months
in the autumn and winter period before being detached. We found that the
overall decomposition rate of spring-lodged litter was faster than that of
autumn-lodged litter over the experimental period. The decomposition rate
was correlated positively with the N content, but negatively with the C/N
ratio, lignin concentration and lignin/N ratio in litters. The
spring-lodged litter showed a sharp decrease in lignin remaining during
the standing-dead stage, while the autumn-lodged litter did not, which
suggested an important role played by photodegradation in the breakdown of
lignin over the winter period that facilitated the litter decomposition in
subsequent stages. These findings highlight the difference in the
decomposition rates of the litters lodged in autumn versus in spring, and
suggest it important to incorporate the effects of the standing-dead stage
on litter decomposition in calculating or modeling the nutrient turnover
rates in semi-arid steppe ecosystems.