|English Abstract: |
Soil is the largest organic carbon pool in the terrestrial ecosystem, therefore, little
variation of soil organic carbon (SOC) efflux will have a significant impact on global
carbon cycle. Forest SOC efflux plays an important role on regional and global carbon
cycle, so it has important meaning to investigate the response of forest SOC efflux to
soil warming under global warming.
In present study, values of soil respiration and its components’ contributions in the
forest were quantified, according to treatments of control (CK), litter removal (NL) and
trenching (NR) treatments, and warming treatment was done based on trenching
treatment (NRW) by infrared radiator to understand the response of heterotrophic
respiration to soil warming in the forest, based on multichannel automated chamber
system for continuous measurement of soil respiration. Based on artificial measurement,
the interaction effect of litter decomposition and rhizosphere activities was investigated,
according to a two-factor plus two-level experiment design of litter and root, with four
treatments of control, litter removal, trenching and trenching together with litter
removal (NRNL) treatments. Priming effect of rhizosphere activity on litter
decomposition was also investigated according to litter decomposition experiments
under CK and NR treatments, respectively, and thereby soil respiration was
repartitioned combined above two researches. In order to known responses of SOC
basic respiration of the forest to different soil warming ranges, soil cores were
transplanted into middle and low elevations based on warming effect of elevation.
The main results are as follows:
(1) In this forest, soil respiration had significant seasonal variation with a large mean
value of 13.80 tC∙ha–1∙yr–1, and the most part (72.1 % of the annual mean) of soil
respiration occurred in rainy seasons (May to October). Model regressions and stepwise
regression (forward method) analyses showed that soil respiration was controlled by
soil temperature and regulated by soil water content. Those suggest climate change will
bring variation of soil respiration and thereby will have a significant impact on carbon
cycle in the forest.
(2) When partition soil respiration into surface litter respiration (RAL) and
belowground respiration (RNL), RNL > RNL; when partition soil respiration into
autotrophic respiration (RA) and heterotrophic respiration (RH), RH > RA. RNL and RH
are conducted by soil organic carbon efflux, which suggest soil organic carbon efflux
play an important role on soil respiration.
(3) Heterotrophic respiration accounted a large proportion in soil respiration. It
accounted for 74.4 % without considering soil water content change due to trenching
treatment, and accounted for 70.2 % after corrected from regression model considering
soil water content change. This suggests treatments for soil respiration partition will
bring changes of soil microenvironment and thereby causes bias on soil respiration
partition, therefore, it is need to correct data by model regression.
(4) After soil warming treatment, soil temperature increased by 2.2 ℃, which
induced an increasing of heterotrophic respiration by 17.1 %. Heterotrophic respiration
fluxed more carbon by 7.02 tC∙ha–1, with an average of 1.76 tC∙ha–1∙yr–1 in the fouryear
(2011 ~ 2014) measurement period. This suggests global warming will accelerate
soil organic carbon efflux. After soil warming treatment, soil water content decreased
by 5.1 % (m3/m3), according to correction by regression model considering the
decreasing of soil water content due soil warming, heterotrophic respiration increased
by 20.7 %. In the four-year measurement period, heterotrophic respiration fluxed more
carbon by 7.98 tC∙ha–1, and the decreasing of soil water content compensated carbon
efflux by 0.96 tC∙ha–1. Warming effect on heterotrophic respiration was controlled by a
range of increased soil temperature and SOC basic respiration (RSOC) had a suitable
range of increased soil temperature by 0 ~ 5.1 ℃ concluded from soil transplantation
experiments. Those suggest global warming and rainfall change will affect soil organic
carbon efflux corporately in the future.
(5) There existed significant interaction between litter decomposition and
rhizosphere activities on soil respiration in the forest. Soil respiration was partitioned
into SOC basic respiration (RSOC), litter respiration (RL), root respiration (RR) and the
interaction (RINT), which accounted for 46 %, 9 %, 15 % and 30 %, respectively. Soil
temperature and soil water content both can affect the interaction, and soil water content
had a larger effect. Rhizosphere activities had significant priming effect on litter
decomposition, increased litter decomposition by 92 %. Soil respiration was
repartitioned into SOC efflux (RSOC-total), litter decomposition (RL-total), root respiration
(RR), which accounted for 68 %, 17 % and 15 %, respectively. Therefore, soil organic
carbon efflux accounts a larger proportion on soil respiration and plays an important
role on forest carbon cycle.
The results above suggest that global warming will accelerate soil carbon efflux and
future warming in subtropical forests can accelerate release of soil organic carbon to
the atmosphere. This study can afford theoretical basis on the effect of global change
such as climate warming on soil respiration components, especially on SOC efflux, in
the future studies.
Key words: soil respiration components, soil organic carbon efflux, soil warming,
soil transplantation, interaction effect, priming effect, global warming.