Measured and modeled interactive effects of potassium deficiency and water deficit on gross primary productivity and light‐use efficiency in Eucalyptus grandis plantations

Abstract

Global climate change is expected to increase the length of drought periods in many tropical regions. Although large amounts of potassium (K) are applied in tropical crops and planted forests, little is known about the interaction between K nutrition and water deficit on the physiological mechanisms governing plant growth. A process-based model (MAESPA) parameterized in a split-plot experiment in Brazil was used to gain insight into the combined effects of K deficiency and water deficit on absorbed radiation (aPAR), gross primary productivity (GPP), and light-use efficiency for carbon assimilation and stem biomass production (LUEC and LUEs ) in Eucalyptus grandis plantations. The main-plot factor was the water supply (undisturbed rainfall vs. 37% of throughfall excluded) and the subplot factor was the K supply (with or without 0.45 mol K m(-2 ) K addition). Mean GPP was 28% lower without K addition over the first 3 years after planting whether throughfall was partly excluded or not. K deficiency reduced aPAR by 20% and LUEC by 10% over the whole period of growth. With K addition, throughfall exclusion decreased GPP by 25%, resulting from a 21% decrease in LUEC at the end of the study period. The effect of the combination of K deficiency and water deficit was less severe than the sum of the effects of K deficiency and water deficit individually, leading to a reduction in stem biomass production, gross primary productivity and LUE similar to K deficiency on its own. The modeling approach showed that K nutrition and water deficit influenced absorbed radiation essentially through changes in leaf area index and tree height. The changes in gross primary productivity and light-use efficiency were, however, driven by a more complex set of tree parameters, especially those controlling water uptake by roots and leaf photosynthetic capacities.

Seedling Growth and Physiological Responses of Sixteen Eucalypt Taxa under Controlled Water Regime

“…Christina et al [27] studied, under field conditions, the response of 37% of rainfall exclusion in three year old E. grandis Hill ex Maiden clonal stands. They found significant decrease in growth (53% in leaf area and 30% in total height) and in physiological characteristics.…”

Sensitivity and uncertainty analysis of the carbon and water fluxes at the tree scale inEucalyptusplantations using a metamodeling approach

“…Grassi et al 2002;Whitehead and Beadle 2004;Medlyn et al 2007;Wullschleger 1993;Christina et al 2015; this study V CMAX Maximum rate of Rubisco carboxylase activity at 25°C (mol·m −2 ·s −1 ) 40 to 126 " R d…”

“…This second site was located 15 km from the Eucflux study site. The structure of this second plantation was comparable with the Eucflux site in terms of tree density and tree age (Christina et al 2015). Sap flow was measured for 10 trees representing the whole range of DBH from January to December 2012.…”

“…Dark respiration at 25°C (mol·m −2 ·s −1 ) 0.3 to 3 Grassi et al 2002;Medlyn et al 2007;Alcorn et al 2008;Christina et al 2015; this study ␣ Quantum yield of electron transport (mol·mol −1 ) 0.2 to 0.4 Grassi et al 2002;Medlyn et al 2007;Christina et al 2015; this study Curvature parameter of the light response of photosynthesis (unitless) 0.2 to 1 Grassi et al 2002;Christina et al 2015 Marsden et al 2013;Christina et al 2015; this study…”

“…Vertical leaf area density distribution was calculated using the leaf area in the bottom, medium, and upper third of the crown using destructive sampling. The horizontal leaf area distribution was measured as part of another experiment with the same Eucalyptus species (Christina et al 2015). Photosynthesis parameters used in the MAESPA model were measured for six trees (photosynthesis -internal leaf CO 2 concentra-tion (A-C i ) curves for estimating J MAX , V CMAX , R d , as defined in Table 1) or three trees (photosynthesis-irradiance (A-PAR) curves for estimating ␣ and , as defined in Table 1) of different heights, using a portable gas exchange system (LI-COR 6400, LI-COR Inc., Lincoln, Nebraska, USA).…”