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

Open Access
Publisher Website
Google Scholar
Abstract
Tree carbon (C) uptake (net primary productivity excluding fine root turnover, NPP′) in a New Zealand Pinus radiata D. Don plantation (42°52′ S, 172°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.

This publication has 0 references indexed in Scilit: