Biomass allocation and nitrogen limitation in a<i>Cryptomeria japonica</i>plantation chronosequence

Abstract

AbstractWe investigated soil net nitrogen mineralization rate, above- and belowground biomass allocation, and nitrogen use in a Cryptomeria japonica plantation chronosequence. Total biomass accumulation showed an asymptotic accretion pattern, and the peak total biomass accumulation rate occurred approximately 30 years after afforestation. Soil net nitrogen mineralization rate was lowest 30 years after afforestation. Between years 30 and 88, net nitrogen mineralization increased again. These results indicate that an imbalance in soil nitrogen supply and plant nitrogen demand occurred approximately 30 years after afforestation. Furthermore, leaf nitrogen concentration, which was used as an index of plant nitrogen status, was lower in mature forest than in young forest, suggesting that mature stands did not take up nitrogen as successfully. If soil resources such as nitrogen limit plant growth, plants may increase biomass allocation to fine root structure; however, fine root biomass was not higher in 30- and 88-year-old stands than in younger stands, suggesting that changes in biomass allocation may not be effective against nitrogen deficiency in a C. japonica plantation chronosequence.Keywords: AgeFine rootNet nitrogen mineralizationStable isotope AcknowledgmentsWe would like to thank technical staffs of Wakayama Forest Research Station, Field Science Education and Research Center, Kyoto University for support of fieldworks. We owe thanks to Sei-ichi Oohata for arranging for us to participate in this study. We wish to thank Muneto Hirobe and Keisuke Koba, Takuo Hishi, Miki Ueda, and Ken-ichiro Osaki for suggestions and for assistance with field and laboratory work. This study was financially supported by Research Program (No. 5–2) of Research Institute for Humanity and Nature (RIHN). This study was also partly supported by a grant of (17710019 and 20780120) from the Ministry of Education, Science, Sports and Culture of Japan.