Background
Grazing is an important human activity and the different grazing managements would affect the carbon allocation diversely in temperate grasslands.
Question
The aim of this study was to quantify the photosynthetic carbon allocation and transfer between different carbon pools of the grasslands, and clarify the response of carbon allocation to different grazing managements.
Methods
An in situ field experiment of pulse 13C labeling was conducted, in July of 2014, in the temperate grasslands (ungrazed, rotational or continuous grazed) of North China.
Results
Grazing managements could alter the photosynthetic carbon allocation from aboveground to belowground. The carbon allocated to aboveground plant tissues declined slowly, which allocated to respiration of aboveground plant and belowground parts rose significantly as sampling days going on. Ungrazed grasslands allocated most of photosynthetic carbon (54.64%) to belowground, while that of rotational (54%) or continuous grazed grasslands (46.3%) allocated to aboveground. Grazing managements altered carbon allocation in the roots and soil organic matter (including microbial biomass carbon, dissolved organic carbon, other soil carbon and soil respiration). The root carbon allocation of 0-15 cm depth in continuous grazed grasslands was 11.8%, while that in rotational and ungrazed grasslands was 3.6% and 4.1%. The carbon allocation of SOM in ungrazed, rotational and continuous grasslands was 17.4%, 12.9%, and 10.9%, respectively; and that in MBC showed as following: ungrazed (3.4%）>rotational（2.1%）>continuous (1.3%), in DOC as following: continuous grazed（1.3%）> ungrazed (1.3%)> rotational grazed（1.1%. Meanwhile, grazing managements had significantly affected carbon allocation in soil respiration (root and microbial respiration). Soil respiration in ungrazed grassland (33.2%) was stronger than that in other two grasslands perhaps for its bigger root biomass, which produced more root exudates in rhizosphere and further stimulated microbial activities. The contribution of microbial respiration to soil respiration was higher than root respiration.
Conclusions
This study revealed more photosynthetic carbon would be allocated to the belowground in the ungrazed grasslands for root growth, and more carbon would be allocated to aboveground in continuous or rotational grazed grasslands for plant growth. The diverse photosynthetic carbon allocations to different carbon pools, in the grasslands of different grazing managements, explained plant and microbes would respond differently to different grazing managements. The carbon allocation between above- and belowground of grasslands would be mostly determined by this response.