Impact of K2SiO3 and Luminosity in the Nutrition and Growth of Genipa americana

doi:10.21203/rs.3.rs-4816632/v1

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Impact of K2SiO3 and Luminosity in the Nutrition and Growth of Genipa americana

https://doi.org/10.21203/rs.3.rs-4816632/v1

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Considering the classification of Genipa americana L. in the ecological succession, excessive exposure to light can be stressful condition, and promotes changes on mineral metabolism and morphophysiology. Foliar application of potassium silicate (K₂SiO₃) has demonstrated to be a promising alternative for induced tolerance. We aimed to evaluate the effect of applying K₂SiO₃ on nutrition and growth of G. americana seedlings under two luminous ambiences. Four doses of K₂SiO₃ via foliar spray were tested: 0.0, 2.5, 5.0, and 10.0 mL L^–1, and cultivation under full sun or shade. Assessments of nutritional status, growth and quality of seedlings were carried at 45 and 90 days after 1st application of K₂SiO₃. We observed higher N content in seedlings under full sun at 45 days, and decreased with increased K₂SiO₃ doses in same ambience at 90 days, while P, K, Ca, and Mg were higher in shaded seedlings and with 10.0 mL L^–1 K₂SiO₃ at 45 and 90 days. The order of nutritional requirements for most seedlings, regardless of cultivation conditions, was K > N > Ca, with inversion of Mg to P requirement with 10.0 mL L^–1 K₂SiO₃. Shaded seedlings showed better growth characteristics at 45 and 90 days, but K₂SiO₃ contributed to photoassimilates accumulation under full sun. Foliar application 5.0 mL L^–1 K₂SiO₃ contributed to greater stem diameter, leaf area, and Dickson quality index. Foliar application of K₂SiO₃ alleviated the stressful effects of full sun and favored the nutrition and quality of G. americana seedlings.

ecophysiology. nutritional requirement. potassium. quality index. shade. silicon

Genipa americana L. (“jenipapeiro”, Rubiaceae) is a native fruit tree commonly found in Central and South America. In Brazil, G. americana is most prevalent in the Amazon, followed by the Atlantic Forest and the Cerrado, and has a lower distribution in the Caatinga (Cola et al. 2022). The leaves extract has antiplatelet, anticoagulant, and antithrombotic activity (Assis et al. 2023), and furthermore, these authors and Neri-Numa et al. (2020) reported that fruit extract has antiparasitic and antidiabetic potential.

The composition of the green fruits contains genipin, which is a source of natural coloring and contributes to antibacterial, anti-inflammatory, and antioxidant properties (Neves et al. 2021; Ahmed et al. 2024). Barbosa et al. (2022) reported that the species is recommended for the recovery of degraded areas and those close to watercourses, requiring ex situ cultivation. In ecological succession, G. americana presents slow to moderate growth and long cycle, being classified as late secondary (Jesus et al. 2019), i.e., it develops better in a shaded ambience.

Due to the importance of G. americana, studies are needed on production of seedlings and factors that can influence their quality. In forestry or reforestation areas, light directly affects the physiology, nutrition and growth of plants (Reis et al. 2023; Santos et al. 2023a). Reinforcing the fact that it is late secondary (Jesus et al. 2019), G. americana should preferably be inserted in dense forests, as it requires a higher shading level for better establishment. Under excess light, leaf temperature and evapotranspiration increase, in addition to photoinhibition (Roach and Krieger-Liszkay 2014) and the overproduction of reactive oxygen species (ROS), promoting damage to photosynthetic apparatus (Pospíšil et al. 2022; Kesawat et al. 2023), and changes on growth as adjustment response.

In stress physiology, the use of stress-relieving agents in agriculture and forestry increase, and potassium silicate (K₂SiO₃) has been promising for regulating leaf metabolism, consisting of two mineral elements: silicon (Si) and potassium (K). In plant nutrition, Si is considered beneficial to plants and confers tolerance (Nielsen 2014; Santos et al. 2023b). Si forms a double layer over the stomatal pore (Ma and Yamaji 2006), providing less water loss, photosynthetic rate and protective metabolism more efficient (Santos et al. 2023b; Teixeira et al., 2022; Foresti et al. 2024). However, mechanisms of action of Si for many species are still uncertain and little evidenced.

K is an essential macronutrient, which in addition to participating in the plant development cycle, it also promotes greater tolerance to isolated or multiple stresses, as it acts on osmotic adjustment, improving intracellular water efficiency (Ávila et al. 2022; Mostofa et al. 2022). In addition, it acts on the integrity of membranes (Demidchik et al. 2014), enzyme activation and stomatal control (Hou et al. 2019).

However, there are not studies associating luminous ambiences × K₂SiO₃, and their effects on G. americana seedlings. Considering that species is late secondary, we hypothesized that (i) cultivation in full sun can be stressful and impaired to initial growth of G. americana seedlings, but that (ii) foliar application of K₂SiO₃ can alleviate the effect of full sun, and contribute to the tolerance of seedlings. We aimed to evaluate the effect of applying K₂SiO₃ on nutrition and growth of G. americana seedlings under two luminous ambiences.

2.1 Study Place

The experiment was carried out from October 2022 to March 2023, at the Vale do Teles Pires University Campus (10°49’08.0”S 55°26’52.2”W, 318 m, a.m.s.), Universidade do Estado do Mato Grosso (UNEMAT), municipality Colíder-MT, Brazil. The region's climate is classified as hot and humid equatorial, with a climate classification of Am, according to Köppen-Geiger. (Alvares et al., 2013), with annual average precipitation and temperature of 2,500 mm and 24°C, respectively according to information from the city hall.

2.2 Plant Propagation

Ripe fruits of G. americana were randomly collected from ten mother plants located in the Municipal Forest Park “Jaracatiá” (10°49'08.5"S 55°26’37.0”W, 316 m a.m.s.), being processed manually, and the seeds sanitized in 2% sodium hypochlorite for 5 minutes. Subsequently, sowing was carried out in polyethylene bags (18 cm x 30 cm) previously filled with 2.1 dm³ substrate consisting of cattle manure, sand and Oxisols (Dystrophic Red-Yellow Latosol) in proportion 3:2:3 (v v^–1), presenting the following granulometry: 663.62, 62.75 and 273.25 g kg^–1 of sand, silt and clay, respectively.

The seedlings were maintained under nursery conditions with 50% shading and irrigation carried out at 70% water retention capacity (WRC) according to Souza et al. (2000), and subsequent acclimatization in each luminous ambience (full sun or shade) for 30 days.

2.3 Application of K₂SiO₃ and Luminous Ambiences

Thirty days after emergence, when the seedlings had an average height of 20 cm, they received four doses of potassium silicate – K₂SiO₃ (12% Si, 15% K₂O, and density: 1.40 g L^–1) via foliar: 0.0, 2.5, 5.0 e 10.0 mL L water^–1, corresponding at 0.00, 0.42, 0.84, and 1.68 g L^–1 Si, and 0.00, 0.525, 1.05, and 2.10 g L^− 1 K₂O. The K₂SiO₃ doses were based on work with another native species (data not published). The application of K₂SiO₃ was carried out via foliar on the abaxial and adaxial face, using spraying with a spray bottle, until the dripping point (15.0 mL plant^–1, based pre-test) in two periods: zero time (before submitting the seedlings to different ambiences) and 60 days after the 1st application; in each period, the total dose corresponding to each treatment was applied.

Subsequently, 24 hours after the first application of K₂SiO₃, seedlings were placed in two luminous ambiences: i) full sun, and ii) shade. Shading was simulated using a black nylon screen with 50% luminosity retention (Sombrite®). Using a thermo-hygrometer, temperatures were determined during the experiment, with average in weekly intervals (Fig. 1), varyng 28.5 to 32.5°C, and 29.7 to 37.0°C in shade and full sun, respectively. During the experiment, irrigation was carried out maintain 70% WRC according to the methodology of Souza et al. (2000).

2.4 Experimental Design

The experimental design used was randomized blocks, in a 2 x 4 scheme, with treatments arranged in a subplot scheme, in which the luminous ambiences were allocated to the plots, and the K₂SiO₃ doses in the subplots, with four replications. Each experimental unit consisted of two containers with one seedling each. The evaluation periods (45 and 90 days) were considered as subdivided plots in time, in which the analyzes were carried out individually, that is, not statistically comparing the periods.

2.5 Assessments

At 45 and 90 days after the first application of K₂SiO₃ the following characteristics were evaluated:

Survival and General Appearance

The number of live seedlings was counted, using as criteria the presence of fully expanded green leaves or those with shoots > 2.0 cm, results expressed in %. We carried out visual foliar and root observations of seedlings through photographic records for later description.

Relative Water Content (RWC)

The RWC of leaves was calculated according to the methodology of Turner et al. (1981), results expressed in %.

Plant Growth

Plant height (H, cm) was measured with a ruler, using distance from the stem to the apical bud as a reference standard, stem diameter (D, mm) with a caliper, and manually counting the leaves number. From the division of H and D data, the etiolation indicator (HDR) was calculated. Seedlings were removed whole from the containers, the roots were washed to remove excess substrate, and root length (RL, cm) was measured with a ruler, and the leaf area was determined (LA, cm²) using ImageJ software.

Biomass and Quality Index

The shoot and root were dried in a drying oven with forced air circulation at 60 ± 5°C for 72 h, and weighed on a precision scale. Using data of total dry mass, HDR, and shoot dry mass/root ratio (SRR) the Dickson quality index (DQI) was calculated according to by Dickson et al. (1960).

Soil Chemical Attributes

At end of the experimental test (90 days), soil samples were collected according to the K₂SiO₃ doses and luminous ambiences, in which, using composite samples, chemical attributes and organic matter (O.M.) were determined, presented in the Table 1, for characterization.

Table 1

Chemical attributes of the Oxisols used in the growth of *Genipa americana* L. seedlings cultivated with potassium silicate (K₂SiO₃) doses and luminous ambiences at 90 days
Attributes	Full sun
	K₂SiO₃ (mL L^–1)
	0.0	2.5	5.0	10.0	0.0	2.5	5.0	10.0
pH H₂O	6.7	6.6	6.7	6.1	6.4	6.8	6.2	6.6
pH CaCl₂	6.0	5.9	6.0	5.6	5.8	6.2	5.6	5.9
P _{Melich 1} (mg dm^–3)	14.6	13.0	20.2	13.8	30.2	20.0	14.0	11.4
K (cmol_c dm^–3)	0.12	0.11	0.12	0.15	0.12	0.14	0.09	0.17
Ca (cmol_c dm^–3)	3.17	3.03	3.25	3.34	3.02	3.44	3.60	3.34
Mg (cmol_c dm^–3)	2.43	2.57	2.87	2.10	2.02	2.35	2.39	2.49
Al (cmol_c dm^–3)	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0
H + Al (cmol_c dm^–3)	1.8	1.6	0.6	1.4	0.8	0.0	1.7	0.7
S (mg dm^–3)	4.1	3.5	5.3	7.3	6.2	8.3	5.8	5.0
B (mg dm^–3)	0.14	0.13	0.14	0.14	0.13	0.14	0.17	0.14
O.M. (g dm^–3)	28	28	26	37	29	28	27	29
CEC (cmol_c dm^–3)	7.5	7.3	6.8	7.0	6.0	5.9	7.8	6.7
BS (cmol_c dm^–3)	5.7	5.7	6.2	5.6	5.2	5.9	6.1	6.0
V (%)	76.3	77.7	91.9	79.6	86.0	100.0	78.4	89.9

Plant Nutrition

The total dry material (shoot + roots) of the seedlings was ground in a “Willey” knife mill and the total content of nitrogen, phosphorus, potassium, calcium and magnesium was determined, according to the methodology proposed to by Malavolta et al. (1997). From the total values of each mineral element, the order of nutritional requirement of G. americana.

2.6 Data analysis

For each evaluation period, separately, the data were subjected to analysis of variance (ANOVA), and when significant, the F test (p ≤ 0.10), the average of the isolated effects and the interaction were compared using the Bonferroni t test for luminous ambiences (p ≤ 0.10), and regression analysis for K₂SiO₃ doses, testing linear and quadratic mathematical models (p ≤ 0.10), using SISVAR software. The order of nutritional requirements was presented in a descriptive manner, i.e., without applying statistical analysis.

3.1 Survival and General Appearance

In general, all G. americana seedlings had 100% survival, regardless of luminous ambiences and K₂SiO₃ doses. The seedlings grown in full sun showed greater root volume, in addition to leaves with a less intense green color and some necrotic spots (Fig. 2), typical symptoms of excessive exposure to light.

3.2 Plant Nutrition

We observed that at 45 days the N, P and K contents were influenced by light environments and K₂SiO₃ doses individually, while Ca was influenced by interaction between the factors under study, and Mg by luminous ambiences (Table 2). At 90 days, N, P, K and Mg were influenced by the interaction of luminous ambiences × K₂SiO₃, and Ca was influenced by the factors under study alone.

Table 2

Results of ANOVA (p-value) of isolated and interaction effects of luminous ambiences and application of potassium silicate (K₂SiO₃) doses on content of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) in *Genipa americana* L. seedlings evaluated at 45 and 90 days
	Evaluations periods
	45 days			90 days
Element	Ambience (A)	K₂SiO₃	A × K₂SiO₃	Ambience (A)	K₂SiO₃	A × K₂SiO₃
N	0.0927	0.0857	0.8218	< 0.0001	0.0717	0.0262
P	0.0086	0.0213	0.2876	0.0322	0.0006	< 0.0001
K	0.0004	0.0684	0.4066	< 0.0001	0.1197	0.0717
Ca	0.0096	0.7782	0.0275	< 0.0001	0.0311	0.1291
Mg	0.0601	0.3067	0.1299	0.0002	0.3838	0.0179

At 45 days, highest N content occurred in seedlings under full sun and without significant effect to K₂SiO₃. At 90 days, under full sun occur decreased linear with increasing K₂SiO₃ doses, while in the shade without significant effect of K₂SiO₃ doses; in splitting, the highest value was observed with the application of 10.0 mL L^–1 K₂SiO₃ (Table 3). With regard to P and K, at 45 days, the highest values (2.34 and 16.31 g kg^–1) occurred in seedlings 10.0 mL L^–1 K₂SiO₃ and shaded, respectively. At 90 days, although observed interaction, under full sun there was not significant effect to K₂SiO₃ doses, with the same tendency response at 45 days.

Table 3

Total content of nitrogen, phosphorus, potassium, calcium and magnesium in *Genipa americana* L. seedlings grown under different luminous ambiences and application of potassium silicate (K₂SiO₃) doses at 45 and 90 days
Nitrogen (g kg^− 1)
45 days
Regression equation						Full sun	Shade
Not significant						8.06 a	7.51 b
90 days
Ambience	0.0 mL	2.5 mL	5.0 mL	10.0 mL		Regression equations		R²
Full sun	10.85 a	12.07 a	9.45 a	8.82 a		ŷ = 11.4650–0.2662*x		0.61
Shade	7.10 b	7.25 b	7.30 b	7.52 a		Not significant		---
Phosphorus (g kg^− 1)
45 days
Regression equation						Full sun	Shade
ŷ = 1.2900 + 0.1058*x; R² = 0.96						1.41 b	2.08 a
90 days
Ambience	0.0 mL	2.5 mL	5.0 mL	10.0 mL		Regression equations		R²
Full sun	1.37 a	1.57 b	1.40 b	1.55 b		Not significant		---
Shade	1.42 a	2.27 a	2.62 a	3.22 a		ŷ = 1.6450 + 0.1697*x		0.93
Potassium (g kg^− 1)
45 days
Regression equation						Full sun	Shade
ŷ = 12.6200 + 0.3968*x; R² = 0.69						11.77 b	16.93 b
90 days
Ambience	0.0 mL	2.5 mL	5.0 mL	10.0 mL		Regression equations		R²
Full sun	12.57 b	12.15 b	11.87 b	11.77 b		Not significant		---
Shade	21.05 a	17.37 a	24.27 a	27.30 a		ŷ = 18.9750 + 0.8057*x		0.65
Calcium (g kg^− 1)
45 days
Ambience	0.0 mL	2.5 mL	5.0 mL	10.0 mL		Regression equations		R²
Full sun	3.02 b	3.15 a	3.20 a	3.02 b	Not significant			---
Shade	5.40 a	4.40 a	4.32 a	5.42 a	ŷ = 5.5425–0.8065x + 0.0709x²			0.92
90 days
Regression equation						Full sun	Shade
ŷ = 3.3400 + 0.2130*x; R² = 0.82						2.72 b	5.81 a
Magnesium (g kg^− 1)
45 days
Full sun						Shade
1.98 b						2.40 a
90 days
Ambience	0.0 mL	2.5 mL	5.0 mL	10.0 mL		Regression equations		R²
Full sun	1.77 a	2.32 a	1.77 b	1.50 b		Not significant		---
Shade	2.32 a	2.25 a	3.37 a	3.20 a		ŷ = 2.3300 + 0.1045*x		0.59
Lowercase letters compare the effect of different luminous ambiences in each dose of K₂SiO₃ by Bonferroni t-test at p ≤ 0.10. * significant at p ≤ 0.10

For Ca, at 45 days the highest content (3.24 g kg^–1) was observed in seedlings shaded with 5.68 mL L^–1 K₂SiO₃, and without significant effect K₂SiO3 doses under full sun, while at 90 days, highest Ca content occurred in shaded seedlings, and with 10.0 mL L^–1 K₂SiO₃. We observed higher Mg content in shaded seedlings and with 10.0 mL L^–1 K₂SiO₃ at 45 and 90 days.

In general, at 45 and 90 days the decreasing order of nutritional requirements in the most G. americana seedlings was K > N > Ca > Mg > P, regardless of K₂SiO₃ doses and luminous ambiences. However, the order was K > N > Ca > P > Mg in seedlings shaded with 5.0, and 10.0 mL L^–1 K₂SiO₃ at 45 days, and at 90 days with 10 mL L^–1 K₂SiO₃, regardless of luminous ambiences.

3.3 Plant Growth and Relative Water Content

We observed in ANOVA results that plant height, number of leaves and root length of G. americana seedlings were not influenced by factors under study in two evaluation periods (p > 0.10) (Table 4).

Table 4

Results of ANOVA (p-value) of isolated and interaction effects of luminous ambiences and application of potassium silicate (K₂SiO₃) doses on growth and quality of *Genipa americana* L. seedlings evaluated at 45 and 90 days
	Evaluation periods
	45 days			90 days
Characteristic	Ambience (A)	K₂SiO₃	A × K₂SiO₃	Ambience (A)	K₂SiO₃	A × K₂SiO₃
H	0.1203	0.4852	0.1773	0.9094	0.2068	0.9992
LN	0.1533	0.8025	0.1372	0.4187	0.3955	0.5244
D	0.8438	0.409	0.0723	0.3676	0.0040	0.5635
HDR	0.0722	0.0123	0.0169	0.3841	0.3269	0.7752
RL	0.7147	0.9174	0.9367	0.3366	0.4639	0.4109
LA	0.0003	0.0224	0.1737	0.0003	0.0224	0.0064
RWC	0.1767	0.0207	0.2308	0.6708	0.0201	0.3376
SDM	0.1677	0.0006	0.0006	0.1734	0.1200	0.6016
RDM	0.8178	0.0507	0.0145	0.2029	0.0235	0.3588
SRR	0.0722	0.0123	0.2123	0.9164	0.4712	0.5213
DQI	0.983	0.3142	0.1157	0.5847	0.0001	0.984
H – plant height, LN – leaves number, D – stem diameter, HDR – height-diameter ratio, RL – root length, LA – leaf area, RWC – relative water content, SRR – shoot-root ratio, SDM – shoot dry mass, RDM – root dry mass, DQI – Dickson quality index

Stem diameter (D) was influenced by interaction between luminous ambiences × K₂SiO₃ doses at 45 days, with quadratic adjustment under full sun, with maximum value (0.68 mm) with application of 6.51 mL L^–1 K₂SiO₃, while in the shade the adjustment was linearly decreasing with a higher value (0.78 mm) without application of K₂SiO₃ (Table 5). At 90 days, D was influenced only by K₂SiO₃ doses, in which the maximum value was 0.98 mm with application of 5.28 mL L^–1 K₂SiO₃. HDR was influenced by interaction between factors under study at 45 days, in which the lowest HDR values were 30.42 and 38.22, with 5.63 mL L^–1 and without application of K₂SiO₃ under full sun and shade, respectively.

Table 5

Stem diameter, height-diameter ratio – HDR, relative water content in leaves – RWC and leaf area of *Genipa americana* L. seedlings grown under different luminous ambiences and application of potassium silicate (K₂SiO₃) doses at 45 and 90 days
Stem diameter (mm)
45 days
Ambience	0.0 mL	2.5 mL	5.0 mL	10.0 mL			Regression equations		R²
Full sun	0.50 b	0.70 a	0.62 a	0.65 a			ŷ = 0.5272 + 0.0495x – 0.0038x²		0.96
Shade	0.77 a	0.67 a	0.65 a	0.42 b			ŷ = 0.7800–0.0034*x		0.71
90 days
ŷ = 0.7848 + 0.0750x – 0.0071x²; R² = 0.99
HDR
45 days
Ambience	0.0 mL	2.5 mL	5.0 mL	10.0 mL			Regression equations		R²
Full sun	45.35 a	41.64 a	26.07 b	41.46 b			ŷ = 47.5932–6.1279x + 0.5440x²		0.72
Shade	38.22 a	44.46 a	43.21 a	65.43 a			ŷ = 36.2744 + 2.6423*x		0.88
RWC (%)
45 days					90 days
ŷ = 80.8395–2.9631x + 0.2552x² R² = 0.66					ŷ = 85.4983–2.3184x + 0.1990x² R² = 0.56
Leaf area (cm²)
45 days
Regression equation						Full sun		Shade
ŷ = 179.5365 + 22.5606x – 2.0736x²; R² = 0.67						174.23 b		246.15 a
90 days
Ambience	0.0 mL	2.5 mL	5.0 mL	10.0 mL			Regression equation		R²
Full sun	216.07 a	207.04 b	234.02 b	272.12 a			Not adjustment		---
Shade	287.81 a	320.54 a	457.56 a	246.90 a			ŷ = 266.0635 + 60.3909x – 6.1581x²; R² = 0.66		0.77
Lowercase letters compare the effect of different luminous ambiences in each dose of K₂SiO₃ by Bonferroni t-test at p ≤ 0.10. * significant at p ≤ 0.10

Relative water content (RWC) and leaf area (LA) were influenced in the two evaluation periods, in which RWC was influenced by K₂SiO₃ doses, both with quadratic adjustment, with minimum values (72.23 and 79.00%) with application of 5.80, and 6.07 mL L^–1 K₂SiO₃ at 45 and 90 days, respectively (Table 5). For LA, at 45 days was observed isolated effect of factors under study, with higher values (246.15 and 240.90 cm²) in the shade and with 5.43 mL L^–1 K₂SiO₃, respectively.

At 90 days, we observed the effect of the interaction between luminous ambiences and K₂SiO₃ doses, in which under full sun LA values did not adjust to the mathematical models, presenting an average of 232.32 cm². Conversely, we observed quadratic adjustment in the shade, with a maximum value (414.12 cm²) in the seedlings that received 4.90 mL L^–1 K₂SiO₃.

3.4 Biomass and Quality Index

We verified that shoot dry mass (SDM) was influenced by interaction between factors under study at 45 days, while for root dry mass (RDM) there was also an interaction at 45 days, and the effect of K₂SiO₃ doses at 90 days (Table 6). The maximum SDM were with 5.71 and 4.05 mL L^–1 K₂SiO₃ under full sun and shade, respectively, at 45 days; in the unfolding of the interaction, the highest value was observed with 2.5 and 5.0 mL L^–1 K₂SiO₃ in the shade and full sun, respectively.

Table 6

Shoot and root dry mass, shoot-root ratio – SRR, and Dickson Quality Index – DQI of *Genipa americana* L. seedlings grown under different luminous ambiences and application of potassium silicate (K₂SiO₃) doses at 45 and 90 days
Shoot dry mass (g plant^− 1)
45 days
Ambience	0.0 mL	2.5 mL	5.0 mL	10.0 mL			Regression equations		R²
Full sun	5.39 a	6.85 b	9.99 a	6.72 a		ŷ = 4.9996 + 1.4933x – 0.1307x²			0.83
Shade	6.84 a	11.43 a	7.39 b	6.24 a		ŷ = 7.7383 + 0.7576*x – 0.0934x²			0.51
Root dry mass (g plant^− 1)
45 days
Ambience	0.0 mL	2.5 mL	5.0 mL	10.0 mL			Regression equations		R²
Full sun	6.64 b	7.72 a	12.07 a	7.47 a		ŷ = 6.0108 + 1.7538x – 0.1586x²			0.73
Shade	12.14 a	5.44 a	8.96 a	8.51 a		ŷ = 11.1444–1.5476x + 0.1318x²			0.50
90 days
ŷ = 9.2669 + 1.9568x – 0.1907x²; R² = 0.95
SRR
45 days
Regression equation					Full sun			Shade
ŷ = 0.8367 + 0.1779x – 0.0181x²; R² = 0.59					0.86 b			1.18 a
DQI
90 days
ŷ = 0.4374 + 0.1232x – 0.0124x²; R² = 0.99
Lowercase letters compare the effect of different luminous ambiences in each dose of K₂SiO₃ by Bonferroni t-test at p ≤ 0.10. * significant at p ≤ 0.10

Regarding RDM at 45 days, maximum values were observed in seedlings that received 5.52 and 5.87 mL L^–1 K₂SiO₃ in full sun and shade, respectively. The only statistical difference observed in the unfolding of the interaction occurred in seedlings without application of K₂SiO₃ with a higher value in the shade. At 90 days, the maximum value was observed in seedlings with application of 5.13 mL L^–1 K₂SiO₃.

The SRR was influenced by the factors under study alone, with higher values (1.17 and 1.27) in shade and with 4.91 mL L^–1 K₂SiO₃, respectively, at 45 days. The DQI was influenced by the effect of K₂SiO₃ doses at 90 days, with a maximum calculated value (0.74) in seedlings that received application of 4.96 mL L^–1 K₂SiO₃.

G. americana seedlings show different responses to contrasting luminous ambiences and in function of K₂SiO₃ doses, suggesting phenotypic plasticity owing to morphophysiological adjustments. We observed that in both ambiences, regardless of K₂SiO₃ doses, seedlings showed restricted root growth owing the limitation of the container during the experimental period. Based on the results, we asked the question: G. americana seedlings are sensitive to cultivation in full sun because it is a species classified as late secondary?

Yes! Cultivation of G. americana under full sun can be considered stressful in the seedlings stage. Shaded seedlings had better morphophysiological performance, reinforcing the species' sensitivity to full sun, especially at 45 days, but foliar application of K₂SiO₃ contributes to the growth and nutritional status of seedlings. We accept our initial hypothesis that Si and K act as relieving agents of this stressor for this species, inducing tolerance.

The less intense green color and necrotic spots on the leaves of seedlings grown in full sun may possibly be associated with lower chlorophyll content, although not quantified in this study. Excess light promotes degradation this photosynthetic pigment, damage to chloroplasts, and photo-inhibitory photochemical activities in the reaction centers of photosystem II – PSII (Oguchi et al. 2021; Shevela et al. 2023), indicating sensitivity to this cultivation condition. Similarly, Campomanesia xanthocarpa O. Berg. also had lower photochemical yields under exposure to full sun conditions (Bartieres et al. 2023), and the authors associate these responses to photo-oxidation.

In addition, under high irradiance, in our study represented by full sun cultivation, the light saturation point occurs, i.e., the plant cannot absorb and use all the light and chemical energy, respectively, and then part of the electrons that are dissipated in the reaction centers during photochemical activities in PSII unite with molecular oxygen and H⁺ in the chloroplast lumen, forming ROS (Lu et al. 2021; Pospíšil et al. 2022). These compounds are harmful to the photosynthetic apparatus, as they cause damage to the integrity of the membranes, leaking electrolytes (Sachdev et al. 2021; Kesawat et al. 2023), in addition to oxidation of photosynthetic pigments, especially chlorophylls, decreasing leaf metabolism and carbohydrate production.

In this sense, K₂SiO₃ plays important roles on metabolic regulation of antioxidant defense system. Si contributes to increasing the activity of enzymes such as catalase, peroxidase, and amino acid proline, in addition to activating aquaporins, improving water uptake, and hydraulic conductivity (Abbas et al. 2015; Avila et al. 2021; Teixeira et al. 2022). Eugenia myrcianthes Nied. seedlings treated with 2 mmol of Si had better photosynthetic and tolerance responses (Foresti et al. 2024), demonstrating its stress-relieving effect, similar to our study with G. americana. In most studies, the mechanisms action of Si in mitigating the water deficit are described, but do not report its role in alleviates the effects of light stress, and our study points to these new discoveries.

It is notable that the application of K₂SiO₃ promoted changes in the dynamics of other mineral elements, suggesting an antagonistic or synergistic interaction. The reduction in N can be explained by increase in K in seedlings with increased of K₂SiO₃. This is because cycling occurs in the plasma membrane and depletion of excessive rates of unidirectional influx and efflux between these elements (Britto et al. 2014; Hou et al. 2018). Similar to our study with G. americana seedlings, Hou et al. (2019) reported an antagonistic relationship between N and K in Oryza sativa L., interaction reinforced by Coskun et al. (2015).

The increase N in seedlings under full sun may be associated with the activation mechanism of the most efficient protection system in this stressful condition. From N assimilation pathway, the biosynthesis of amino acids such as glutamine and glutamate occur (Bredemeier and Mundstock 2000; Reitzer 2003; Harper et al. 2010), that in addition to preventing damage from ROS (Liao et al. 2022; Müller et al. 2024), contributes to protein synthesis and carbohydrate accumulation (Gonnet and Díaz 2000; Cooper and Jeitner 2016).

However, although seedlings under full sun had higher N content than those in the shade, showed lower Mg contents, and possibly reflected in the content of chloroplast pigments. Mg is part of the structure of the chlorophyll molecule and its reduction or deficiency in plant tissue impairs the synthesis of this pigment (Papadakis et al. 2023), as observed in our study with G. americana seedlings under full sun, a fact reinforced in the visual appearance of leaves with less intensity of green color.

The increase in K in the G. americana seedlings with K₂SiO₃ doses is explained by the fact that the product contains K in its composition (15% K₂O), in addition to being applied foliar, which may have facilitated its translocation route to other organs. This is because, according to Chérel et al. (2014), it is believed that much of the K in the plant does not come only from root absorption, but also from recirculation in the phloem; therefore, when applied via foliar, it becomes a supplementary source, in addition to its availability in the soil, which possibly contributes to its better distribution and use efficiency.

We believe that reduction of K in seedlings under full sun with linear increase in K₂SiO₃ doses at 90 days may indicate the use and targeting of this nutrient for metabolic adjustments and protective pathways in order to alleviate this stressful condition. From the point of view of mineral and physiological metabolism, K in high concentrations in the cytosol favors protein activity and homeostasis cellular functioning (Johnson et al. 2022), improving the performance of photosynthetic apparatus.

In addition, K plays a role in osmotic adjustment and maintenance of cellular water status. (Mostofa et al. 2022), in which there is regulation of stomatal opening and closing signaled by ABA and mediated by K through its efflux in guard cells (Humble and Hsiao 1970; Andrés et al. 2014), alleviating water loss from excessive leaf transpiration owing to rising temperatures, especially in full sun. Conversely, in the shade as the condition is not considered stressful and did not require investment in protection mechanisms, seedlings accumulated more K in the tissue.

The increase in P in seedlings with 10.0 mL L^–1 K₂SiO₃ indicates greater efficiency in the use of this nutrient, since in the soil the levels were lower as the K₂SiO₃ doses increased, reverse answer, suggesting better uptake, and translocation to seedlings. In the literature, there are descriptions that the Si–P relationship is synergistic, which favors its availability to plants (Schaller et al. 2019; Barman et al. 2023), as observed in our study. According to Hu et al. (2020) plants treated with Si show greater exudation of malate and citrate in the roots related to the P content in soil and plant, and promotes metabolic stability.

When P is converted to Pi, it is transported into the tissue, in which it is converted into ATP, energy molecule, favoring activity ATP synthase, production of NADPH, regeneration of Rubisco, and the photosynthetic process (Carstensen et al. 2018; Khan et al. 2023; Kayoumu et al. 2023), reflecting in growth and biomass production of G. americana seedlings. The inversion of Mg to P requirement with 10.0 mL L^–1 K₂SiO₃ indicates energetic investment in production of carbohydrates rather than in cellular structuring in this condition.

Increased Ca stimulates signaling in plants through several stress proteins and genes (Gupta et al. 2023), in addition to promoting membrane stability and cell tissue rigidity (Hepler 2005; Wang et al. 2023), especially under full sun at 45 and 90 days, similar to K and P.

With regard to luminosity, the classification in the ecological succession varies depending of species and its age, as generally in the initial phase of seedlings or young plants they tend to present a certain light, water and even nutritional requirement, while in adulthood it can reestablish itself, adjusting to others requirement. Therefore, potential for phenotypic plasticity and ecological resilience is important, as plants naturally adjust for survival, but generally with lower performance. In our study with G. americana, although seedlings are sensitive to full sun due to being late secondary at this stage, foliar application of K₂SiO₃ alleviated stressful effect this condition. This information is necessary in forestry planning, both in nursery and in the field, because if the classification of the species is not taken into account, high mortality rate, and seedling replanting can occur, which makes forestry activities costly.

The increase in diameter favors the survival of the seedlings, in which the values of this characteristic are lower in the shade, as the evaporation of water from the soil is lower, favoring the maintenance of water status in the soil and in the plant, characterizing more favorable condition for its morphophysiology, not need to invest in adjustment strategies. Conversely, under full sun the increase of D is desirable, as it ensures the translocation of organic and inorganic solutes in this condition more efficiently, and the application of K₂SiO₃, especially in 5.13 mL L^–1, favored this increase. The role of Si on stem diameter is still uncertain and little discussed in literature, but increases were observed in Zea mays L. (Amin et al. 2016), and Cucurbita pepo L. (Salim et al. 2021), similar response in G. americana.

However, we emphasize that the growth of the shoot must be proportional, that is, in height and diameter, so that there is morphometric stability. In the shade, greater HDR compared to full sun can be explained by hormonal relationship. This is because in an environment with low light exposure, auxin is preserved, and then vegetative growth occurs more accentuated as a result of the elongation of the internodes (Xie et al. 2022), which indicates possible etiolation depending on height and varies between species.

Conversely, under full sun when applying 6.51 mL L^–1 K₂SiO₃, HDR was lower as a result of the increase in D when using a similar dose in this light condition, indicating greater balance in the distribution of photoassimilates, in addition to being more robust and avoiding the possibility of tipping over both in the nursery and in the field after transplanting. In our study, HDR is more associated to D than directly H, since H values did not vary depending on cultivation conditions, possibly owing to container restrictions.

The presence of K in K₂SiO₃ plays a role in osmoregulation through osmotic adjustment. According to Asensio et al. (2020) and Ávila et al. (2022), K acts in the control of transpiration and intracellular water content, and in our study this response is essential especially in full sun conditions. This action is due to, in addition to osmotic adjustment, its participation in protein synthesis, enzymatic activation of H⁺-ATPase, and antioxidant defense system (Marschner 1997; Johnson et al. 2022), which maintains high photosynthetic rate and water use efficiency.

In general, better growth responses in shaded seedlings are associated with more favorable climatic conditions. In nursery, black screen (Sombrite®) reduces temperatures and improves relative air humidity, reducing damage caused by multiple stresses (thermal and water) modulated by excess light. When seedlings are produced or grown in the shade, the evapotranspiration rate is lower compared to full sun and this keeps leaf metabolism more stable (Bartieres et al. 2023). In the field, shading can be achieved by inserting G. americana close to pioneer and initial secondary species in the area.

Another mechanism of action of Si is to improve the architecture of the leaves, leaving them more erect, which favors the capture light energy, better photochemical yield and photosynthetic efficiency (Sume et al. 2023), which ensured the leaf area of G. americana seedlings with application of K₂SiO₃. Furthermore, generally shaded plants tend to increase LA as a compensation strategy, i.e., to maximize the capture of light energy per unit area owing to lower active photosynthetic radiation incident in that ambience (Bartieres et al. 2023), while under full sun reduction may be justified to minimize excessive water loss (Reis et al. 2023).

Plants adjust to different conditions as a mechanism to escape stress, and lower SRR under full sun indicates that seedlings are investing more in the root system than in shoot, since there is possibly greater evaporation of water in the soil. As for K₂SiO₃, seedlings that received its application showed better shoot characteristics, as in LA and SDM, which explains the higher SRR.

Analyzing the effect of each dose in the two luminous ambiences at 45 days, it is clear that seedlings under full sun and which received application of K₂SiO₃ showed better production of biomass in shoot, and root system compared to those not treated with K₂SiO₃, reinforcing the beneficial role of this fertilizer on carbohydrates accumulation, reflecting better mineral and photosynthetic metabolism. At 90 days, with the second application of K₂SiO₃, we found not statistical difference between seedlings in two luminous ambiences, and we therefore suggested that they present the same pattern of biomass production, a fact proven in the DQI.

The better DQI was a reflection of greater characteristics of LA and biomass production with a dose close to 5.0 mL L^–1 K₂SiO₃, regardless of luminous ambiences, reinforcing the effect of K₂SiO₃ on rustification-acclimatization of seedlings. The DQI represents the balanced relationship between the dry matter factors between the different organs, and growth in shoot, indicating better distribution of water, nutrients, and photoassimilates in the seedlings (Santos et al. 2023b). The higher the DQI indicates better vigor of the seedlings in the nursery and the possibility of better establishment in the field, but according to Santos et al. (2023a) complementary post-transplantation studies are needed in forested or reforested areas.

From the growth results, we emphasize that although G. americana seedlings showed linear increase to K, P, Ca, and Mg with the application of K₂SiO₃, we suggest that for maximum gene expression and production of photoassimilates, doses close to 5.0 mL L^–1 K₂SiO₃ were sufficient to meet nutritional needs of the species, indicating that K₂SiO₃ plays a beneficial role in mineral metabolism and physiology.

We accept our hypothesis that K₂SiO₃ has the potential to alleviate the stressful effect of full sun, but we also found that its application enhanced growth in shaded seedlings. In this sense, if the species is produced or inserted in areas with greater exposure to light, such as borders or without vegetation, foliar application of K₂SiO₃ acts to induced tolerance. In future perspectives, we suggest understanding the protective metabolism by determining the activity of antioxidant enzymes, amino acids and other non-enzymatic compounds in seedlings under these cultivation conditions.

Genipa americana L. seedlings are sensitive to cultivation under full sun, but foliar application of K₂SiO₃, especially at dose close to 5.0 mL L^− 1, alleviates impacts of stressful effects, contributing in tolerance induction. Foliar application of K₂SiO₃ contributes to the nutrition, growth, and quality of G. americana seedlings, regardless of luminous ambience.

Conflict of interest

Not applicable

Author Contribution

[Marcos Aurélio de Oliveira] and [Cleberton Correia Santos]: Conceptualization, reviewing and editing; [Cleberton Correia Santos] and [Marcos Aurélio de Oliveira]: Methodology and Fieldwork; [Marcos Aurélio de Oliveira] and [Rafaela Gomes Jardim]: Data Collection and Data Analysis; [Cleberton Correia Santos], [Marcos Aurélio de Oliveira], [Leonardo Meotti Ribeiro], and [José Ricardo Palácio Caldeira Dias]: Writing—Original Draft; All authors Writing— Reviewing and Editing

Acknowledgements

The authors thank the CAPES and CNPq for scholarship, and the FUNDECT and UNEMAT, for financial support.

Data availability statement

Data are available under reasonable request to the corresponding author.

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You are reading this latest preprint version

Impact of K2SiO3 and Luminosity in the Nutrition and Growth of Genipa americana

Status:

Version 1

Abstract

Figures

1 Introduction

2 Materials and Methods

2.1 Study Place

2.2 Plant Propagation

2.3 Application of K₂SiO₃ and Luminous Ambiences

2.4 Experimental Design

2.5 Assessments

2.6 Data analysis

3 Results

3.1 Survival and General Appearance

3.2 Plant Nutrition

3.3 Plant Growth and Relative Water Content

3.4 Biomass and Quality Index

4 Discussion

Conclusion

Declarations

Conflict of interest

Author Contribution

Acknowledgements

Data availability statement

References

Additional Declarations

Status:

Version 1

Impact of K2SiO3 and Luminosity in the Nutrition and Growth of Genipa americana

Status:

Version 1

Abstract

Figures

1 Introduction

2 Materials and Methods

2.1 Study Place

2.2 Plant Propagation

2.3 Application of K2SiO3 and Luminous Ambiences

2.4 Experimental Design

2.5 Assessments

2.6 Data analysis

3 Results

3.1 Survival and General Appearance

3.2 Plant Nutrition

3.3 Plant Growth and Relative Water Content

3.4 Biomass and Quality Index

4 Discussion

Conclusion

Declarations

Conflict of interest

Author Contribution

Acknowledgements

Data availability statement

References

Additional Declarations

Status:

Version 1

2.3 Application of K₂SiO₃ and Luminous Ambiences