Brazil nut tree increases photosynthetic activity and stem diameter growth after thinning

Bertholletia excelsa Bonpl. is widely planted in the Amazon and information about thinning effects is poorly documented. Here, we investigate thinning effects on the ecophysiology of B. excelsa plantations. The thinning trial was set up as a randomized complete block design (RCBD) with two treatments (unthinned and thinned to 50% basal area removal). The canopy openness of plots thinned was two times higher than the unthinned treatment (control). B. excelsa under thinning growed three times in relation to trees of control. One week after thinning, we observed increase of 25% photosynthesis (P_N), 100% respiration (R_d), 35% stomatal conductance (g_s), and 25% transpiration (E). After thinning, we verified reduction of the maximum photochemical efficiency of photosystem II (F_V/F_M), with subsequent recovery. At the end of 5 months after thinning, the trees on thinned plots achieved values of leaf mass per area (LMA), nitrogen (N_a), phosphorus (P_a), and potassium (K_a) about 27% higher than trees of unthinned plots. Thinning did not affect the midday leaf water potential (Ψw). Thinning increased the growth of B. excelsa influenced by photosynthetic performance and regulated by the g_s, LMA, leaf N_a, and P_a concentrations. Our findings demonstrated that thinning can be recommended for timber production under the dense planting of Brazil nut trees cultivated in degraded Amazonian areas.

Graphical abstract