Soil respiration after forest conversion to tea gardens: A chronosequence study

Documenting the influences of land-use change and time after conversion on soil respiration is fundamental to understanding the interplay between soil carbon sequestration and greenhouse gas emissions. We conducted fortnightly in situ measurements of soil respiration (considered herein as both total respiration [R-total] and "root-free" basal respiration [R-basal]) along a land-use chronosequence: a native broad-leaf evergreen forest and three tea gardens (10, 40, and 100 years old) with similar characteristics of soil type and site management. Compared to the forest, soil organic carbon decreased by 7% in the 10-year-old tea garden, whereas it was similar in the 40-year-old tea garden and 18% higher in the 100-year-old tea garden; total N content increased by 35%, 44%, and 50% in the 10-, 40-, and 100-year-old tea gardens, respectively. The seasonal variation in R-total and R-basal could be 62-83% and 39-69% explained by the mixed model of soil temperature and water content, respectively. The temperature sensitivity (Q 10 ) of R-total increased from 1.67 in the forest to 1.98 and 1.93 in the 10- and 40-year-old tea gardens, respectively, but decreased to 1.64 in the 100-year-old tea garden. The Q(10) of R-basal increased from 1.26 in the forest to 1.58-1.95 in the tea gardens. Annual CO2 efflux of R-basal increased similar to 1.5 times, but the SOC-normalized R-basal was similar between the forest and the 100-year-old tea garden. We suggest that the loss of soil carbon storage would be compensated over a period of 40 years after the conversion of forests to tea gardens, and the time after conversion to tea gardens is an important ecological factor in mitigating the effects of land-use change.