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E. Sayad 2010. Nitrogen retranclocation in pure and mixed plantations of Populus deltoides and Alnus subcordata
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may relate to the ecological status of the species (pioneer vs. late successional species, sun vs.
shade tolerant species). Litter chemistry is determined both by the chemistry of green leaves and
by the nutrient resorption. The latter has not been given enough attention despite its major role
in nutrient conservation both at the individual and ecosystem level (Binkley and Menyailo
2005).
Thus in this paper, we focus on N resorption in pure and mixed plantations in order to increase
our understanding of the ecology of these tree species in this region. Therefore our question is:
Are there differences in the degree of internal cycling of N (resorption) of each species in
different proportions And dose it differ between the two species
2. Methodology
2.1 Study site
The study area is located at the Chamestan experiment station, in Mazandaran province, on the
northern parts of Iran (36º29’N, 51º59’E). Experimental plantations were established in 1996
using a randomized complete block design that included four replicate 40 m × 40 m plots of
each of the following treatments: (i) Populus deltoides (100P), (ii) Alnus subcordata (100A),
(iii) 50% P. deltoides + 50% A. subcordata (50P:50A), (iv) 67% P. deltoides + 33% A.
subcordata (67P:33A), (v) 33% P. deltoides + 67% A. subcordata (33P:67A). Tree spacing
within plantations was 4 m × 4 m and tow species were systematicly mixed within rows.
2.3 Leaf
Leaf samples were collected from the stands in September 2003. Leaves were collected from
the bottom one-third of the tree by clipping two small twigs located on opposite sides of the
crown. Six representative trees (two near the center of sub-plot and one in each corner of it) of
each species were sampled for fully expanded leaves. In addition, senescent leaves were
collected from each species in each sub-plot. The samples were dried at 65 o C and ground prior
to analysis. Nitrogen was analyzed using the Kjeldhal.
2.5 Statistical Analyses
The percent of retranslocation efficiency was calculated from the fallowing formula (1):
R =
A − B
× 100
A
(1)
In this formula A is the weight of each nutrient in fully expanded leaf and B is the weight of that
nutrient in leaf litter. The percent of retranslocation between the species and for each species in
different treatments were compared using general linear model analysis of variance (ANOVA)
tests. Normality of the data was checked for analyses. Statistical analyses were done using SAS
9 software.
3. Result
The Nitrogen retranslocations of both species were not significantly differed between the
different proportions. Alnus Nitrogen retranslocation was higher in pure plantations than the
mixtures, but for Populus it was higher under 67%P: 33%A than the other treatments. Nitrogen
retranslocation also was not different between the two species, whereas the retranslocation in
Alnus as Nitrogen fixing tree was lower than Populus (Figure 1).
Forest Landscapes and Global Change-New Frontiers in Management, Conservation and Restoration. Proceedings of the IUFRO Landscape Ecology
Working Group International Conference, September 21-27, 2010, Bragança, Portugal. J.C. Azevedo, M. Feliciano, J. Castro & M.A. Pinto (eds.)
2010, Instituto Politécnico de Bragança, Bragança, Portugal.