Growth, Evapotranspiration, Gas Exchange and Chl a Fluorescence of Ipê-Rosa Seedlings at Different Levels of Water Replacement

Abstract

In general, young plants in the establishment phase demonstrate sensitivity to changes in environmental conditions, especially regarding water availability. The effects of the seasonality of biophysical processes on plant physiology can trigger differential responses, even within the same region, making it necessary to conduct studies that characterize the physiological performance of the species at different spatial and temporal scales, making it possible to understand their needs and growth limits under water stress conditions. This paper aimed to evaluate the growth, gas exchange and Chl a fluorescence in ipê-rosa seedlings subjected to levels of water replacement (LWRs) of 100, 75, 50 and 25% in a greenhouse. The morphometric variables of plant height, diameter at stem height, numbers of leaves and leaflets, root length and volume, plant dry mass and leaf area were evaluated. The potential evapotranspiration of seedlings (ETc) was obtained using direct weighing, considering the water replacement of 100% of the mass variation between subsequent days as a reference; the cultivation coefficients (kc) were obtained using the ratio between ETc and the reference evapotranspiration (ETo) obtained by the Penman-Monteith FAO-56 method. Biomass and evapotranspiration data were combined to determine water sensitivity. Diurnal fluxes of gas exchange (net photosynthesis rate, transpiration rate, stomatal conductance, internal and atmospheric carbon ratio, water use efficiency and leaf temperature) and Chl a fluorescence (Fv/Fm, Φ_PSII, ETR, Fv'/Fm', NPQ and qL) were evaluated. Water restriction caused reductions of 90.9 and 84.7% in the increase in height and diameter of seedlings subjected to 25% water replacement when compared to seedlings with 100% water replacement. In comparison, biomass accumulation was reduced by 96.9%. The kc values increased throughout the seedling production cycle, ranging from 0.59 to 2.86. Maximum water sensitivity occurred at 50% water replacement, with Ky = 1.62. Maximum carbon assimilation rates occurred in the morning, ranging from 6.11 to 12.50 µmol m^-2 s^-1. Ipê-rosa seedlings regulate the physiology of growth, gas exchange and Chl a fluorescence depending on the amount of water available, and only 25% of the water replacement in the substrate allows the seedlings to survive.

Keywords: ipê-rosa - Handroanthus impetiginosus (Mart. ex DC.) Mattos; irrigation management; native tree; photochemical stress; photosynthesis; water sensitivity.

Figure 1

Location map of the collection region of Handroanthus impetiginosus seeds, Sinop, Mato Grosso state, Brazil. (A) plastic greenhouse for producing forestry agricultural seedlings; (B) view of seedlings in pots; (C) adult ipê-rosa tree in bloom; (D) ipê-rosa pods and seeds.

Figure 2

Flowchart of the experimental steps used in the development of the research. All symbols are explained throughout the sub-items of the methodology.

Figure 3

Correlation between maximum and minimum air temperatures and the total average leaf area (A and B, respectively) and total average dry mass (C and D, respectively) per plant to determine upper basal temperature (TB) and lower basal temperature (Tb), in Sinop, Mato Grosso state, Brazil. Prepared from the database assembled by Monteiro [40].

Figure 4

Daily variations in maximum (T_MAX), average (T_M) and minimum (T_MIN) air temperature (A) and maximum (RH_MAX), average (RH_M) and minimum (RH_MIN) relative air humidity (B) outside the greenhouse; global radiation outside and inside the greenhouse (C); and rainfall (D) as a function of the accumulated degree days of the ipê-rosa seedlings, between 28 August 2019 and 13 December 2019, in Sinop, Mato Grosso state, Brazil.

Figure 5

Adjusted regression curves for the non-destructive growth variables height (A), basal stem diameter (B), number of leaves (C) and number of leaflets (D) of ipê-rosa seedlings at 25, 50, 75 and 100% levels of water replacement (LWRs), as a function of the accumulated degree days, in a greenhouse.

Figure 6

Mean values of root length (A), root volume (B), leaf area (C), total dry mass and percentages of dry mass partition of leaves, stems and roots (D) of ipê-rosa seedlings at 25, 50, 75 and 100% levels of water replacement (LWRs), 107 days after transplanting, in a greenhouse. Means followed by the same capital letter between water replacement levels do not differ by Tukey’s test at the 5% probability level.

Figure 7

Daily evapotranspiration (A) and accumulated evapotranspiration (B) for the crop (ET_C: ipê-rosa seedlings, in a greenhouse and potential; ET₀: Penman–Monteith FAO-56 method [34]) as a function of the accumulated degree days of the seedlings, between 28 August 2019 and 13 December 2019, in Sinop, Mato Grosso state, Brazil. Real accumulated crop evapotranspiration (ETr) under 25, 50 and 75% levels of water replacement (LWRs) is represented by ETr_25%, ETr_50% and ETr_75%, respectively.

Figure 8

Crop coefficient as a function of accumulated degree days of the ipê-rosa seedlings, in a greenhouse (p-value < 0.01 indicates the significance of the adjustment at the 1% probability level; the red line represents the line of the fitted linear equation).

Figure 9

Mean values and standard deviation of minimum fluorescence (Fo_predawn) (A), maximum fluorescence (Fm_predawn) (B) and maximum quantum yield of PSII (Fv/Fm_predawn) before dawn (C), in ipê-rosa seedlings as a function of water replacement levels, at 28, 66 and 90 DATs (464, 1046 and 1400 DDAs). The red lines represent the standard deviation values. Means followed by the same capital letter between levels of water replacement (LWRs) and lowercase letter between DDAs do not differ by Tukey’s test at the 5% probability level.