Net ecosystem productivity, net primary productivity and ecosystem carbon sequestration in a Pinus radiata plantation subject to soil water deficit

• Published in: Tree physiology 1998-12, Vol.18 (12), p.785-793
• Main Authors: Arneth, A, Kelliher, F.M, McSeveny, T.M, Byers, J.N
• Format: Article
• Language: English
• Subjects: biomass production; canopy; carbon; ecosystems; mathematical models; net assimilation rate; photosynthesis; Pinus radiata; respiration; seasonal variation; soil water; stress response; uptake; water stress
• ISSN: 0829-318X; 1758-4469
• DOI: 10.1093/treephys/18.12.785

Tree carbon uptake (net primary productivity excluding fine root turnover, NPP') in a New Zealand Pinus radiata D. Don plantation (42 degrees 52' S, 172 degrees 45' E) growing in a region subject to summer soil water deficit was investigated jointly with canopy assimilation (Ac) and ecosystem-atmosphere C exchange rate (net ecosystem productivity, NEP). Net primary productivity was derived from biweekly stem diameter growth measurements using allometric relations, established after selective tree harvesting, and a litterfall model. Estimates of Ac and NEP were used to drive a biochemically based and environmentally constrained model validated by seasonal eddy covariance measurements. Over three years with variable rainfall, NPP' varied between 8.8 and 10.6 Mg C ha-1 year-1, whereas Ac and NEP were 16.9 to 18.4 Mg C ha-1 year-1 and 5.0-7.2 Mg C ha-1 year-1, respectively. At the end of the growing season, C was mostly allocated to wood, with nearly half (47%) to stems and 27% to coarse roots. On an annual basis, the ratio of NEP to stand stem volume growth rate was 0.24 +/- 0.02 Mg C m-3. The conservative nature of this ratio suggests that annual NEP can be estimated from forest yield tables. On a biweekly basis, NPP' repeatedly lagged Ac, suggesting the occurrence of intermediate C storage. Seasonal NPP'/Ac thus varied between nearly zero and one. On an annual basis, however, NPP'/Ac was 0.54 +/- 0.03, indicating a conservative allocation of C to autotrophic respiration. In the water-limited environment, variation in C sequestration rate was largely accounted for by a parameter integrative for changes in soil water content. The combination of mensurational data with canopy and ecosystem C fluxes yielded an estimate of heterotrophic respiration (NPP'-NEP) approximately 30% of NPP' and approximately 50% of NEP. The estimation of fine-root turnover rate is discussed.