Are photosynthetic leaf traits related to the first-year growth of tropical tree seedlings? A light-induced plasticity test in a secondary forest enrichment planting

Understanding light-induced plasticity of growth and its relationship with photosynthetic trait plasticity is central to the identification of the mechanisms associated with tropical tree seedling establishment in enrichment plantings. In a secondary forest submitted to silvicultural treatments - that manipulate light environment - and enriched with six tropical tree species we tested three main hypothesis. First, the growth of the six species are related to photosynthetic leaf traits; second, there is a relationship between the light-induced plasticity of growth and photosynthetic leaf traits and, finally, that growth plasticity is a subjacent mechanism of the growth-survival trade-off. Growth was analyzed as a biomass index that combines collar and height growth. Photosynthetic leaf traits were selected considering their significance in the photosynthetic process: light interception (specific leaf area, SLA), light absorption (chlorophyll a and b ratio, Chl(a/b)), light use (fluorescence parameters, F-v/F-m; PIabs, PItotal) biochemical limitations (light-saturated CO2 assimilation, A(sat)) and diffusive limitations (stomatal conductance, g(s)). The plasticity was represented by the slope of the relationship between the canopy light transmittance and growth and the photosynthetic leaf traits. At the end of the first year after planting, growth was related to almost all photosynthetic leaf traits, and the strongest relationships (high slope and R-2) were observed with A(sat), SLA and PItotal. Light-induced growth plasticity varied three times between species. The interspecific growth plasticity was related to SLA and F-v/F-m plasticity, which varied 4.9 and 2.4 times between species, respectively. Seedling mortality in the shaded understory and the growth in a high light environment were associated with growth plasticity. Photosynthetic leaf traits effectively represent the growth response mechanisms to silvicultural treatments that manipulate the light environment in enrichment plantings, and the subjacent mechanism of growth plasticity has an intrinsic effect on the growth-survival trade-off.