APPLICATION OF N-15-ENRICHMENT METHODOLOGIES TO ESTIMATE NITROGEN-FIXATION IN CASUARINA-EQUISETIFOLIA

Citation
Ja. Parrotta et al., APPLICATION OF N-15-ENRICHMENT METHODOLOGIES TO ESTIMATE NITROGEN-FIXATION IN CASUARINA-EQUISETIFOLIA, Canadian journal of forest research, 24(2), 1994, pp. 201-207
Citations number
15
Categorie Soggetti
Forestry
ISSN journal
00455067
Volume
24
Issue
2
Year of publication
1994
Pages
201 - 207
Database
ISI
SICI code
0045-5067(1994)24:2<201:AONMTE>2.0.ZU;2-X
Abstract
The N-15-enrichment technique for estimating biological nitrogen fixat ion in Casuarina equisetifolia J.R. and G. Forst. was evaluated under field conditions in single-species and mixed-species plantings (with a nonfixing reference species, Eucalyptus Xrobusta J.E. Smith) between ages 6 and 24 months in Puerto Rico. Trenched and untrenched quadrats within the plantations were labelled at 6-month intervals with N-15-en riched ammonium sulfate at a rate of 0.2 g N-15.m(-2).year(-1) (2.0 g N.m(-2).year(-1)). Analyses of foliar and whole-tree (weighted average ) N-isotope ratios, based on periodic nondestructive and whole tree ha rvests, were used to estimate the proportion of nitrogen derived from biological dinitrogen fixation (PNDFA) and total nitrogen derived from fixation (TNDFA) in Casuarina. These results were compared with those obtained using the nitrogen difference method. The N-15-enrichment te chnique yielded consistent estimates of biological nitrogen fixation i n Casuarina when either foliar or whole-tree N-isotopic data were used to calculate PNDFA and TNDFA. Estimates of PNDFA in Casuarina were si milar for trenched monoculture and mixed-species quadrats, and in tren ched and untrenched quadrats where the reference species (Eucalyptus) was interplanted with the N-fixing species. However, the results indic ate that eucalyptus grown in small, untrenched monoculture quadrats is an inappropriate reference for estimating PNDFA in Casuarina. During the first 2 years after plantation establishment, Casuarina obtained f rom 48 to 67% of its nitrogen from the atmosphere based on foliar and whole-tree sampling. This amounted to between 82 and 94 kg.ha(-1).year (-1) in the monoculture treatment and between 39 and 62 kg.ha(-1).year (-1) in the mixed stands with Eucalyptus. These results also were in c lose agreement with estimates made using an N-difference method.