Effects on rhizospheric and heterotrophic respiration of conversion from primary forest to secondary forest and plantations in northeast China

To evaluate the effects of forest transition (conversion of primary temperate forest into secondary forest and plantations) on rhizospheric (R-R) and heterotrophic respiration (R-H), we used the trenching-plot and infrared gas exchange analyzer approaches to partition soil respiration (R-S) for four temperate forest types in northeast China, including the primary mixed broadleaved-Korean pine (Pinus koraiensis) forest, secondary birch (Betula platyphylla) forest, Dahurian larch (Lath gmelinii) plantation and Korean pine plantation, throughout the growing season (May October) in 2011 and 2012. The results showed that R-S and its components displayed obvious seasonal dynamics and were mainly controlled by soil temperature. Furthermore, incorporating soil moisture into the pure R-S (R-H)-tempetature model improved the prediction of R-S and R-H in most forest types (R-S, R-2 = 0.687-0.799; R-H, R-2 = 0.721-0.849). The apparent temperature sensitivity (Q(10)) of R-R (2.69-5.16) was higher than that of R-H (2.34-2.56) in all forest types. The average R-H was increased by 35% following the conversion of primary forest to secondary birch forest, 31% to larch plantation and 19% to pine plantation. Such increment of R-H could be explained by the increase of soil organic carbon storage in the top soil. When the primary forest was converted to secondary birch forest, the average R-R significantly increased (P < 0.05), but no significant differences in R-R between primary forest and two plantations were detected (P > 0.05). The differences in R-R between secondary birch forest and primary forest and two plantations may reflect differences in small root biomass (<5 mm in diameter) at a depth of 0-40 cm and with soil microbial biomass carbon in the top soil. Our results suggest that mechanisms controlling R-H and R-R are probably different and that partitioning soil respiration when evaluating the effect of forest conversion on soil respiration is important. (C) 2014 Elsevier Masson SAS. All rights reserved.