Allocation of photosynthestically-fixed carbon in plant and soil during growth of reed (Phragmites australis) in two saline soils

Abstract

Aims Terrestrial carbon (C) sequestration is derived mainly from plant photosysthetically-fixed C deposition but soil organic C (SOC) content in saline soils is generally low due to low deposition of C from restricted plant growth. It is important to explore the effects of soil salinity on the allocation of photosynthetically-fixed C to better understand C sequestration in saline wetland soils. Methods We conducted a pot experiment in which reed (Phragmites australis) was grown in a low salinity (LS) soil and a high salinity (HS) soil from the Yellow River Delta under flooded conditions. The allocation of photosynthetically-fixed C into plant tissues, SOC, dissolved organic C (DOC), microbial biomass C (MBC), particulate organic C (POC), and mineral-associated organic C (MAOC) was determined using a C-13 pulselabeling method after four labeling events during the 125-day-long reed growing season and destructive sampling immediately at the end of six hours of pulse labeling (end 6-h) and on the final harvest day (final day). Results In most cases soil salinity, reed growth stage, or reed biomass significantly (P < 0.05) affected the deposition of photosynthetically-fixed C into the plant-soil system. At all four pulses at end 6-h the high salinity soil had significantly (P < 0.05) lower percentage net assimilated C-13 in the roots and significantly higher (P < 0.05) percentage net assimilated C-13 in the soil than did the low salinity soil. At both end 6-h and on the final day the high salinity soil had significantly (P < 0.05) lower (SOC)-C-13, and significantly (P < 0.05) higher (DOC)-C-13/(SOC)-C-13 ratio than the low salinity soil except for pulses 3 and 4 on the final day. The majority of photosynthetically-fixed C in soil was deposited into MAOC pools and > 80 % of deposited (SOC)-C-13 was present as MAOC in the high salinity soil due to its significantly (P < 0.05) higher clay content compared with the low salinity soil. Conclusions Soil salinity affected the allocation of photosynthetically-fixed C in the plant-soil system, and soil texture altered the allocation of rhizodeposition C in different soil particles