Responses of tree growth and biomass production to nutrient addition in a semi-deciduous tropical forest in Africa
Loading...
Date
2022
Journal Title
Journal ISSN
Volume Title
Publisher
Ecology
Abstract
Experimental evidence of nutrient limitations on primary productivity in
Afrotropical forests is rare and globally underrepresented yet are crucial for
understanding constraints to terrestrial carbon uptake. In an ecosystem-scale
nutrient manipulation experiment, we assessed the early responses of tree
growth rates among different tree sizes, taxonomic species, and at a community
level in a humid tropical forest in Uganda. Following a full factorial
design, we established 32 (eight treatments four replicates) experimental
plots of 40 40 m each. We added nitrogen (N), phosphorus (P), potassium
(K), their combinations (NP, NK, PK, and NPK), and control at the rates of
125 kg N ha 1 year 1, 50 kg P ha 1 year 1 and 50 kg K ha 1 year 1, split into
four equal applications, and measured stem growth of more than 15,000 trees
with diameter at breast height (dbh) ≥1 cm. After 2 years, the response of tree
stem growth to nutrient additions was dependent on tree sizes, species and leaf
habit but not community wide. First, tree stem growth increased under N
additions, primarily among medium-sized trees (10–30 cm dbh), and in
trees of Lasiodiscus mildbraedii in the second year of the experiment. Second,
K limitation was evident in semi-deciduous trees, which increased
stem growth by 46% in +K than –K treatments, following a strong, prolonged
dry season during the first year of the experiment. This highlights
the key role of K in stomatal regulation and maintenance of water balance
in trees, particularly under water-stressed conditions. Third, the role of P in
promoting tree growth and carbon accumulation rates in this forest on
highly weathered soils was rather not pronounced; nonetheless, mortality
among saplings (1–5 cm dbh) was reduced by 30% in +P than in –P treatments.
Although stem growth responses to nutrient interaction effects were
positive or negative (likely depending on nutrient combinations and climate
variability), our results underscore the fact that, in a highly diverse forest ecosystem, multiple nutrients and not one single nutrient regulate
tree growth and aboveground carbon uptake due to varying nutrient
requirements and acquisition strategies of different tree sizes, species, and
leaf habits.
Description
Keywords
Budongo forest, Carbon stock, Fertilization, Nitrogen, Nutrient limitations, Phosphorus, Potassium, Primary productivity, Relative growth rate, Uganda
Citation
Manu, R., Corre, M. D., Aleeje, A., Mwanjalolo, M. J., Babweteera, F., Veldkamp, E., & van Straaten, O. (2022). Responses of tree growth and biomass production to nutrient addition in a semi‐deciduous tropical forest in Africa. Ecology, e3659. DOI: 10.1002/ecy.3659