Production and quality of eucalyptus mini-cuttings using kaolin-based particle f ilms

Maria de Fátima de Castro Oliveira · Diego Pereira Santos · Karolline Sena Figueredo · Fabrício de

Oliveira Reis 3 · Tiago Massi Ferraz 3 · Heder Braun 3 · Eliemar Campostrini 4 · Fábio Afonso Mazzei Moura de

Assis Figueiredo 3

Abstract Considering the expansion of forest plantations over the Brazilian territory and the imminent increase in air temperatures due to global warming, the search for technologies that ensure high levels of productivity and high quality plants in clonal nurseries is essential. Applying kaolin-based particle f ilms (KBPF) has been used as a physical barrier to reduce the negative Effects of excessive solar radiation and adverse temperatures. The Effects of KBPF on production and physiological quality of eucalyptus mini-cuttings were evaluated during two diff erent seasons. A randomized block design was used, consisting of f ive treatments and four replications. Five concentrations (0, 3%, 5%, 7%, and 10%) were tested here and six weekly replicates of each concentration was applied. The diff erent kaolin concentrations and seasonal variations resulted in a quadratic response of the leaf SPAD reading during both daily evaluation periods. KBPF applications resulted in a quadratic response of photochemical effi ciency in the morning period, and an increasing specif ic leaf weight linear response, and during the dry season,the diff erent kaolin concentrations resulted in a bud length quadratic response. The results indicated that the kaolin application maintained the production and yield index statistically equal between weekly KBPF applications, improving photochemical effi ciency, leaf thickness, SPAD reading,and bud length. The use of KBPF could reduce the intervals between collections of mini-cuttings and increase nursery yields in environments that present high temperatures.

Keywords Photoprotector · Ecophysiology · Forestry ·Clonal propagation

Introduction

Plantations of eucalyptus trees represent 73% of the reforested areas that are used for commercial purposes in Brazil.These reforested areas cover approximately 5.7 million of hectares, of which the trees are mainly used for the production of paper and cellulose, carpentry, steel mill industries, and charcoal production. Forestry contributes 1.1% of Brazilian GDP and 6.2% of the countries’ industrial GDP(IBÁ 2017).

The use of eucalyptus clones has been consolidated, and the production of clonal plantlets has expanded throughout Brazil. Thus, research that contributes to the application of technologies for plantlet production in nurseries, increasing plantlet yield and quality, is essential for improving the morphophysiological characteristics and possible reductions in production cycle time.

Large-scale plantlet production is usually performed by vegetative propagation using the mini-cutting technique,which includes stages of mini-cuttings production, rooting,and acclimation to shade, growth and rustication (Alfenas et al. 2009). Buds production and rooting stages require more attention because of the need for mini-stumps with high vegetative vigor and turgidity to provide buds that can overcome their vulnerability to water stress during the rooting stage, since mini-cuttings do not have a root system that can hydrate the aerial parts (Xavier et al. 2013).

Plants store a minimum quantity of endogenous auxin to induce rooting when they are exposed to adequate intensity and quality of solar radiation. However, intense solar radiation can cause photodestruction of this hormone (Hartmann et al. 2011). Air and substrate temperatures, intensity and quality of solar radiation in the clonal mini-garden are important factors for the increase of carbon photosynthetic assimilation and production of reserves (photoassimilates),as well as substances that induce rooting (Alfenas et al.2009). Negative correlations between rooting of eucalyptus mini-cuttings and air temperature in a clonal mini-garden were observed by Cunha et al. ( 2009), who reported the importance of managing environmental factors to obtain maximum biomass production, optimize rooting and, thus,improve the quality of the plantlets produced.

The application of kaolin-based particle f ilms (KBPF)calcinate and purif ied has been used as a protector barrier against negative Effects of excess solar radiation and water stress (Glenn and Puterka 2005). This technology can improve crop yield in supra optimal stress conditions of air temperature and solar radiation on the surface of the plant.The application of KBPF improved the morphological and physiological characteristics ofJuglans regiaL. trees grown in regions with a history of damage caused by hot and dry summer conditions (Gharaghani et al. 2018).

KBPF is composed of an aluminum silicate mineral that has a white color and low content of abrasive compounds,and it is chemically inert, disperses easily in water and the use of adjuvants facilitates and preserves the adhesion of particles to the applied surface (Glenn et al. 2010). Under conditions of soil and air water def icit and supra optimal solar radiation, application of adequate quantities of KBPF to the leaf surface can decrease leaf temperature by increasing the reflection of excess radiation, thus optimizing photochemical effi ciency and photosynthetic assimilation(Sharma et al. 2015). An increase in net photosynthetic rate can contribute to an increase in plant growth and yield. A high stomatal conductance is expected after a decrease in leaf temperature, resulting in signif icant increases in carbon photosynthetic assimilation.

Decreases in photoinhibition and leaf temperature were related to high sucrose levels in leaves of Touriga grapes treated with KBPF, by providing more favorable conditions for the activity of the sucrose-phosphate synthase enzyme(Conde et al. 2018). Moreover, this product reduces the incidence of pests and diseases (Sharma et al. 2020) and is recommended for organic food production by the Organic Materials Review Institute (OMRI 2019).

Considering the benef icial Effects of KBPF application:decreased leaf temperature, increased water use effi ciency(Glenn et al. 2010, Boari et al. 2015), decreased damage caused by excess solar radiation on photosystem II (PSII)(Dinis et al. 2018), and increased plant yield (Gharaghani et al. 2018), the aim of the present study was to evaluate the Effects of application of processed kaolin-based particle f ilms (KBPF) on eucalyptus mini-stumps cultivated in a clonal mini-garden, considering the parameters of biomass production and quality of the mini-cuttings.

Materials and methods

Experimental area

The experiment was conducted at a commercial clonal eucalyptus plantlet nursery in Açailândia, western state of Maranhão, Brazil (04°56ʹ48″ S; 47° 30′17″ W). The nursery plantation area was covered with transparent plastic (100 μm) from March to April due to the rainy season.The cover was removed from May to July. The climate of the region is hot and humid (Aw), according to the Köppen and Geiger classif ication, presenting temperatures of 21.7-32.2 °C, and mean annual rainfall of 1635 mm (Correia Filho 2011). Daily air temperature and relative humidity measurements were recorded inside the nursery during the experiment (March-July, 2018) using a Datallogger(WatchDog; Spectrum Technologies, Aurora, USA). The vapor pressure def icit (VPDair) was calculated from this data(Fig. 1 a-c). The local daily rainfall and global solar radiation data were obtained from the Geoenvironmental Center at the State University of Maranhão (Fig. 1 b, d).

Experimental implementation

Fig. 1 Diagrams of a temperature, b relative air humidity and rainfall, c vapor pressure def icit, and d total solar radiation during the period of evaluation of eucalyptus mini-stumps in the clonal mini-garden (March to July, 2018)

The experiment was conducted in a clonal mini-garden with 12-month old hybrid eucalyptus plants (Eucalyptus grandis×Eucalyptus urophylla). In the clonal mini-garden, the mini-stumps were planted with spacing of 10 m × 10 cm, grown in 16 m length channels × 1 m width with a washed sand layer in the bottom. A drip fertigation system was used to apply the nutrients N, P, K, Ca, Mg, S,B, Mo, Zn, Mn, Fe and Cu, at rates of 41.43, 25.28, 25.72,34.88, 1.32, 2.92, 0.18, 0.04, 0.31, 0.31, 0.37, and 0.09 mg L −1 , respectively. The system was turned on four times a day for 15 min with a f low of 1.5 L h −1 . The electrical conductivity of the solution applied to the mini-stump rhizosphere was adjusted daily to 1.2-1.5 m S cm −1 .

The experiment was conducted during two seasons: the rainy season (March to April) and the dry season (June to July). The treatments were arranged in split-plots, using a randomized block design with four replications. The replications consisted of four channels. The plots were composed of 100 mini-stumps and the distance between plots was 1 m. The plots were treated with f ive KBPF concentrations (0%, 3%, 5%, 7%, and 10% of the applied volume)and the subplots consisted of six weekly replications of each concentration. The control plots were treated with water applications only. The applications were carried out to the adaxial part of the leaves of mini-stumps at the end of the day, after the evaluation and collection of the minicuttings, with a 7-day interval between applications.

The KBPF used here was manufactured from calcinate purif ied kaolin (Surround WP®; TK Inc., Phoenix, Arizona, USA), which is a mineral composed of aluminum silicate (Al4Si4O10 (OH) 8 ) of white color and with a low abrasive compound content; it is chemically inert and disperses easily in water (Glenn et al. 2010). The KBPF was applied using a 1.25 L manual sprayer of previous compression. The rod of the pump was pressurized continuously until f ind resistance at each application. The application was carried out for 40 s in each plots, which was enough to cover all of the area necessary. The spatially distributed of the plots, at a minimum distance of 1 m,was used to avoid drift of the product and contamination between treatments.

The amount of product applied per area (m 2 ) was estimated by applying the product during 40 s in an area of 1 m 2 with 5 randomly distributed Petri dishes that had been weighed prior to the evaluation. After drying, the Petri dishes were again weighed to obtain the amount of product applied in g m −2 . The values obtained were 4.2, 8.0, 8.5, and 11.8 g m −2 , corresponding to application of 3%, 5%, 7%, and 10% KBPF, respectively.

In the rooting stage, which lasted for 21 days, the minicuttings were placed in 53 cm 3 polyethylene tubes containing a substrate composed of carbonized rice husks and coconut f iber (1:1 v v −1 ), 1.5 kg of simple superphosphate (19%P2O5) and 3 kg of 13-06-16 NPK formulation (Basacote®mini 3 M) per m 3 of substrate. The KBPF application cycle,maintaining the leaves with the product for 7 days, followed by the removal of mini-cuttings and conduction for rooting,was done six times (6 KBPF applications) during both seasons (dry and rainy).

Buds growth and production of eucalyptus mini-cuttings

Five mini-cuttings were randomly chosen from each of the f ive treatment plots during each season to evaluate length(cm) (using a ruler) and diameter (mm) (using digital Vernier calipers).

Five leaf discs of known area (26.42 mm 2 each) were collected from f ive mini-cuttings in each plot of the six evaluations for each season for determination of specif ic leaf weight. The f ive mini-cuttings and leaf discs were placed in an oven at 60 °C for 48 h and then weighed to obtain dry weight. The specif ic leaf weight was obtained by the ratio between the disc dry weight and the respective area of the discs. The discs and mini-cuttings were previously washed in running water to remove the KBPF.

The production of mini-cuttings (maximum 8 cm in length) was evaluated per plot. The yield of mini-cuttings was calculated from the ratio between the number of minicuttings produced in the plot and the number of mini-stumps per plot. The yield index was the ratio between the number of rooted mini-cuttings per plot and the number of ministumps per plot.

The percentage of live, rooted mini-cuttings was evaluated from 10 mini-cuttings per plot for each treatment and season 21 d after the beginning of rooting of the mini-cuttings.

Thermal imaging, gas exchange and photochemical effi ciency of eucalyptus mini-stumps

Gas exchange, maximum quantum yield of photosystem II (Fv/Fm), SPAD reading, and leaf temperature were evaluated during each season and before the collection of mini-cuttings, using healthy completely expanded and not shaded leaves. These variables were evaluated during two periods of the day: 7:00 to 9:00, with a mean light intensity on the leaves of 380 μmol m −2 s −1 ; and 12:00 to 14:00,with a mean light intensity on the leaves of 680 μmol m −2 s −1 . Eight replications were used for each treatment for these variables during each season evaluated.

Net photosynthetic CO2assimilation rate (A), stomatal conductance (g s), instantaneous transpiration (E), and ratio between mesophyll internal CO2concentration rate and leaf external CO2concentration rate (C i /C a) were evaluated using an infrared gas analyzer (IRGA, modelo LI-6400®, LI-COR, Lincoln, NE, USA) with an external source of photosynthetic photon f lux of 1500 μmol m −2 s −1 . The water use effi ciency (WUE) was calculated from the ratio between net photosynthetic CO2assimilation rate and leaf transpiration (A/E), and the intrinsic water use effi ciency (IWUE) was determined from the ratio between net photosynthetic CO2assimilation rate and stomatal conductance (A/gs).

The leaf temperature was obtained by thermal imaging captured at 30 cm approximately from the leaves using an infrared thermograph (Flir i50; Flir Systems, Wilsonville,USA). The images were analyzed using Flir QuickReport 1.2 software.

TheFv /Fm was obtained from the same leaf used for gas exchange analysis, using a pocket portable f luorimeter(PEA; Hansatech, King’s Lynn, UK). Before measuring chlorophyll f luorescence emission, the leaves were adapted to the dark for 30 min, using leaf clips, thus, the reaction centers were completely opened with minimum loss of heat (Bolhar-Nordenkamp et al. 1989; Strasser et al. 2000),and Quinone-awas completely oxidized.

The SPAD reading was evaluated by using a portable chlorophyll meter (SPAD-502 Plus, Konica Minolta) for f ive leaves of f ive mini-stumps randomly chosen to represent the mean of each plot. The KBPF was not removed from the leaves during this evaluation.

Statistical analysis

A cross-season analysis (ANOVA) was carried out to compare the two seasons for mini-cutting growth data, SPAD reading, production of mini-cuttings, and physiological evaluations of mini-stumps. The KBPF concentration were subjected to regression analysis, using linear and quadratic models. The models were chosen based on the biological occurrence of the response and signif icance of the coeff icients of regression using attest with up to 10% probability, and evaluation of the coeffi cient of determination.The F-test was used to compare the means of variables aff ected by season, and the Tukey test (P< 0.05) was used to compare the means of variables aff ected by collection time. The statistical analyses were carried out using the ExpDes.pt package (Ferreira et al. 2013) of the R program(R Core Team 2019).

Results

Analysis of variance (ANOVA)

The signif icance levels of the variation for bud growth, production of mini-cuttings, and SPAD reading are shown in Table 1, considering subplots composed of six KBPF applications. Table 2 shows the signif icance levels of the variation for the physiological parameters.

Bud growth and production of eucalyptus mini-cuttings

The interactions season × KBPF number of applications and season × KBPF concentrations aff ected bud length(Table 1). In the dry season, the KBPF concentration tested affected bud length, which showed a quadratic response (Fig. 2 a), with the KBPF concentration of 7%resulting in 10.5% increase in bud length when compared to the controls. In the rainy season, the bud lengths were similar, presenting a mean of 9.4 cm. In the rainy season,the KBPF applications positively aff ected bud length; and during the dry season, the opposite Effect was observed(Fig. 2 b). Bud length was always higher in the dry season when compared to the rainy season (Fig. 2 b), regardless of the period of the day in which the evaluation was made.

The bud diameter data f itted a decreasing linear model,presenting a decrease of 0.0059 mm per each unity of KBPF concentration (Fig. 3 a). Mini-cutting dry weight was not inf luenced by the concentrations of KBPF tested here, presenting means of 0.08 and 0.11 g for the rainy and dry season, respectively. However, these variables were aff ected by the interaction season × number of application(Table 1). During the rainy season, bud diameter presented results which varied when comparing frequency of applications; in the dry season, the bud diameter increased following the fourth application (Fig. 3 b). In the dry season,mini-cutting dry weight showed a decreasing response,presenting the lowest result at the f ifth application, with a reduction of 40.1% in relation to the f irst application(Fig. 3 c). This result was expected because the same response was seen for bud length (Fig. 2 b).

The specif ic leaf weight data in relation to the KBPF concentration f itted an increasing linear model, presenting the increases of 0.36 g m −2 per unit of KBPF (Fig. 4 a).The specif ic leaf weight expresses the relation betweenweight and area and this variable have a good and positive relationship with leaf thickness.

Table 1 Signif icance levels of the Effect of seasons (E), kaolin-based particle f ilm concentrations (D), KBPF applications (A), and interactions between these factors on bud length (BL), bud diameter (BD),mini-cutting dry weight (MDW), specif ic leaf weight (SLW), production of mini-cuttings (P), yield of mini-cuttings (Y), yield index of mini-cuttings (YI), rooting of mini-cuttings (R%), and SPAD reading of eucalyptus mini-stumps evaluated in the morning (SPADm) and afternoon (SPADa) periods

Table 2 Signif icance levels of the Effect of seasons (E), kaolin-based particle f ilm concentrations (D), and interactions between these factors on photosynthetic CO 2 assimilation ( A), stomatal conductance( g s ), transpiration ( E), water use effi ciency (WUE), intrinsic water use effi ciency (IWUE), leaf temperature (LT), maximum quantum yield of the photosystem II ( F v/ F m) , and ratio between mesophyll internal CO 2 concentration and leaf external CO 2 concentration ( C i/ C a) of eucalyptus mini-stumps evaluated in the morning and afternoon periods

Fig. 2 Effects of kaolin-based particle f ilm concentrations, during the rainy and dry seasons, on eucalyptus mini-stumps bud length ( a);and the Effects of number of KBPF applications, during the rainy and dry seasons, on eucalyptus mini-stump bud length ( b). Regressions were performed within each season. * and ** = signif icant at 5% and 1% probability using the t test, respectively. Means were compared within each season using Tukey’s test at 5% probability. Vertical bars indicate the standard error of the mean

The interaction season × application positively aff ected specif ic leaf weight during the dry season and for the last applications, it presented equal and higher means than in the previous applications. The opposite was found in the rainy season (Fig. 4 b).

KBPF concentration had no Effect on the production or yield index of the eucalyptus mini-cuttings evaluated.Season × application interaction showed similar production and yield levels of mini-cuttings when comparing applications in the rainy season (Fig. 5 a, b); and the yield index results, which considers the rooting of mini-cuttings,were similar over the applications. In the dry season, these variables were diff erent when comparing applications(Fig. 5 a-c).

In the f irst KBPF application, the interaction KBPF concentration × application aff ected the yield of the eucalyptus mini-cuttings, which presented a quadratic response with a maximum estimate of 3.12 mini-cuttings at a KBPF concentration of 6.3% (Fig. 5 d). Therefore, 7% KBPF was optimal for initial yield of mini-cuttings.

KBPF concentration aff ected rooting percentage of the mini-cuttings (Table 1), but this data did not f it to any of the models. The control treatment, without the application of KBPF, had an increase of 3.2% and a mean rooting of 67.5%.

The interaction season × application aff ected the rooting of eucalyptus mini-cuttings. In the rainy season, the low initial rooting rate was overcome, presenting similar results for most of the applications (2, 4, 5, and 6). A similar result was also found in the dry season, when recovery and the higher rooting percentage were seen in for half of the applications(2, 3, and 6) (Fig. 6).

Evaluations of photosynthesis and water status of eucalyptus mini-stumps

Gas exchange and leaf temperature

The diff erent KBPF concentrations tested here had no Effect on leaves of eucalyptus mini-stumps when considering gas exchange [net photosynthetic CO2assimilation rate(A), stomatal conductance (g s), instantaneous transpiration(E), and ratio between mesophyll internal CO2concentration and leaf external CO 2 concentration (C i /C a)], water use effi ciency (WUE), and intrinsic water use effi ciency(IWUE) (Table 2).

The net photosynthetic CO2assimilation rate (A) evaluated in the morning period was similar for both seasons.Awas signif icantly higher in the afternoon period in the rainy season. This higherAwas related to the higher stomatal conductance and transpiration. IWUE in the afternoon period was similar between seasons, but in the morning period, it was signif icantly higher in the rainy season.This higher IWUE was related to lowerg s. A similar response was obtained for WUE.

The seasons aff ected theC i /C aratio in the morning period, with the dry season presenting a mean ratio 8.3%higher than that of the rainy season.

KBPF concentration had no Effect on leaf temperature of the eucalyptus mini-stumps. The leaf temperature was higher in the morning period in the rainy season, presenting a mean of 24.1 °C; and it was higher in the afternoon period in the dry season, presenting a mean of 29.4 °C.

Fig. 3 a Effects of kaolin-based particle f ilm concentrations on bud diameter; and KBPF applications Effects, on b bud diameter, and c mini-cutting dry weight of eucalyptus mini-stumps during the rainy and dry season. * = signif icant at 5% probability by the t test. Means were compared within each season using Tukey’s test at 5% probability. Vertical bars indicate the standard error of the mean

SPAD reading

The interaction season × KBPF concentrations aff ected the SPAD reading for the period 07:00 to 09:00; the increasing KBPF concentrations contributed to an intense leaf green color for both seasons. The maximum estimated SPAD reading was 41.8 and 38.6 for KBPF concentrations of 7.5% and 7.4% in the rainy and dry season, respectively(Fig. 7 a). Thus, the application of 7% KBPF resulted in an increase in the SPAD reading during both seasons evaluated.

The interaction season × application aff ected the SPAD reading at 07:00 to 09:00, which presented similar results in the rainy season; the means were signif icantly lower only for the fourth evaluation of mini-cuttings. The SPAD reading varied between KBPF applications in the dry season,presenting the best result in the last evaluation (Fig. 7 b).

In the afternoon period, the interaction KBPF concentrations × application (Fig. 7 c) resulted in signif icant diff erences in all KBPF applications. The KBPF concentration resulted in a quadratic response of the SPAD reading in the afternoon period in all applications, with maximum estimates of 6.5-9.0%. The 7% KBPF resulted in the best SPAD reading, even for weekly applications. The interaction season × application also aff ected the SPAD reading (Fig. 7 d),which presented increases in the dry season.

Chlorophyll a f luorescence

The KBPF concentration aff ectedF v/F min the evaluations made at the morning, which showed a quadratic response,presenting a maximum estimate of 0.83 for 3.3% KBPF(Fig. 8). The means were between 0.75 and 0.85, indicating that the activity of the photosystem II of the plants was not compromised. This relation denotes the effi ciency of light energy in reducing Quinoneaand decreases in this ratio are related to photoinhibition (Araújo and Deminicis 2009).

KBPF concentration aff ected theF v/F min the evaluations made during the afternoon period, which showed a quadratic response (Fig. 8). The meanF v/F mwas 0.77 for this period, remaining within the adequate range (0.75-0.85).The season aff ected theF v/F mevaluated at the afternoon period (Table 2); in the rainy season, theF v/F mratio was higher than that found in the dry season, presenting mean of 0.72, which indicates moderate damages to the photosynthetic apparatus.

Discussion

The application of KBPF in the dry season can be a strategy to increase the yield of the nurseries. Increases in eucalyptus bud growth (Fig. 2) can decrease the interval between collection/harvesting of mini-cuttings and, thus, the total yield can increase. Continuous collection and maintenance of cut height of mini-stumps between 6 and 10 cm are recommended for commercial nurseries, because at this height the plants displayed higher rooting potential (Alfenas et al.2009).

Fig. 4 a Effects of kaolin-based particle f ilm concentrations on specif ic leaf weight of eucalyptus mini-stumps; b The Effects of KBPF applications, during the rainy and dry seasons on specif ic leaf weight of eucalyptus mini-stumps. The regression was performed for the whole experiment. *** = signif icant diff erences at 0.1% probability level using the t test. Means were compared within each season using Tukey’s test at the 5% probability level. Vertical bars indicate the standard error of the mean

This study was carried out during two diff erent seasons,the rainy season and dry season. The clonal mini-gardens had mean air temperatures of 26.6 °C and 25.8 °C, with a minimum of 21.8 °C and 17.3 °C, and a maximum of 36.1 °C and 35.1 °C; mean relative air humidity of 83.0%and 74.0%; and mean vapor pressure def icit of 0.73 and 1.06 kPa in the rainy and dry seasons, respectively. The higher intensity of collections of mini-cuttings in the dry season may have stressed the mini-stumps, and decreased bud growth. Moreover, mini-stumps can undergo temporary exhaustion due to environmental variations (Brondani 2012),explaining the decrease in bud growth in the dry season.

The specif ic leaf weight (SLW) showed an increasing linear response to KBPF concentration. SLW is aff ected by exposure of leaves to high light intensity, i.e., high photosynthetically active radiation can result in high SLW (Santiago et al. 2009). This result indicates that the application of KBPF did not hinder light reaching the leaf surface.

An increase of 23.7% in global solar radiation when comparing the rainy to the dry season, increased the mean SLW in 24.4%, denoting greater leaf thickness. Increases in SLW of leaves exposed to high levels of solar radiation characterize a morphological adaptation, i.e., a thickening of the palisade leaf layer in response to light (Sanches et al. 2009).

KBPF maintained similar production levels and yield indexes of mini-cuttings when comparing KBPF applications. Variations in production of mini-cuttings are common for eucalyptus mini-stumps (Brondani 2012; Lopes et al. 2016), since the pruning of mini-cuttings causes emergence of new buds that will not reach a minimum size to be taken in the following harvesting. This reduces the production of the second collection mini-cuttings, which will recover by the following collection with the removal of remaining mini-cuttings, and so on. In the dry season,the production, yield and yield index of the eucalyptus mini-cuttings showed signif icant diff erences between collections, probably because of temporary exhaustion of the mini-stumps (Titon et al. 2003), which can explain the decrease in bud length in this season.

The Effect of KBPF concentration on the rooting percentage could be related to the lower lignif ication of the mini-cuttings (Borges et al. 2011), as demonstrated by the decrease in the diameter of mini-cuttings seen as the KBPF concentrations was increased (Fig. 3 a). The increase in rooting during the KBPF applications (Fig. 6) was to be expected because of the continuous collection of minicuttings which maintained the juvenility of propagules and favors rooting (Ferriani et al. 2010).

The gas exchanges were not aff ected by application of KBPF. Similarly, Campostrini et al. ( 2010) evaluatedCarica papayaL. plants and found that gas exchanges of individual leaves were not aff ected by the application of KBPF, as was also the case for grapevine leaves(Lobos et al. 2015). Rosati et al. ( 2007) evaluated the use of KBPF of almond (Prunus dulcis) and walnut (Juglans regia) canopies, found that net photosynthetic CO2assimilation rate of individual leaves may not express the total photosynthetic activity of the whole plant, mainly the canopy, which allows for intense auto shading. When the net photosynthetic CO2assimilation rate was evaluated in the whole plant, the use of KBPF resulted in a positive Effect on carbon photosynthetic assimilation due to improved light distribution inside the canopy, which is aided by the presence of KBPF. Contrastingly, decreases in net photosynthetic CO 2 assimilation rate by individual leaves treated with KBPF can result in higher total plant yield. Thus, the positive Effects of KBPF application on gas exchange are normally observed when the whole plant is evaluated.

Fig. 5 Effects of KBPF applications during the rainy and dry seasons on a production, b yield, and c yield index (IP) of mini-cuttings;and d Effects of kaolin-based particle f ilm concentrations on the f irst application of KBPF in relation to mini-cuttings yield in eucalyptus mini-stumps. Yield = (mini-cuttings produced in the plot) −1 (ministumps per plot). Yield index = (rooted mini-cuttings per plot) −1(mini-stumps per plot). Means were compared within each season using Tukey’s test at 5% probability. Vertical bars indicate the standard error of the mean

The application of the diff erent KBPF concentrations had no Effect on leaf temperature of the eucalyptus ministumps, although decreases in leaf, fruit, and canopy temperatures are seen following application of KBPF in tomato (Cantore et al. 2009; Boari et al. 2015), apple(Glenn 2009, 2016), grape (Glenn et al. 2010; Coniberti et al. 2013), papaya (Campostrini et al. 2010) and in rose plantations (Cuitiva et al. 2011).

The lack of KBPF application Effects on gas exchanges may have been due to the adequate irrigation of the ministumps. Similar results were found by Lombardini et al.( 2005) and Boari et al. ( 2015). Moreover, the Effect of KBPF was reported to be diff erent between species and cultivars (Denaxa et al. 2012), as well as under diff erent environmental conditions.

The KBPF concentrations tested here had no Effect onC i /C a, net photosynthetic CO2assimilation rate, and stomatal conductance.C i /C ais used to measure the carbon f ixation effi ciency reaction, and here it varied from 0 to 1.The closer to 1, the less effi cient is the process of removing CO2from the leaf mesophyll, indicating that the photosynthetic apparatus has lower CO2assimilation capacity(Guerra et al. 2017). Stomatal conductance varied in relation to seasonal evaluation with increases of 15.2% in the morning period during the dry season. Considering that CO2concentration are constant in the environment,C i /C ais the result of variations in the internal CO2concentration caused by variations in the CO2inf lux in the leaf, which are controlled by variations in stomatal conductance and net photosynthetic CO2assimilation rate. Thus, an increase in this concentration means that more CO2is reaching the substomatal cavity or that this gas is not being f ixed by the photosynthetic apparatus.

Fig. 6 Effects of KBPF applications on rooting of mini-cuttings in the rainy and dry seasons. Means were compared within each season by Tukey’s test at 5% probability. Vertical bars indicate the standard error of the mean

The increase in SPAD reading in relation to KBPF concentration (Figs. 7 a, c) is explained by the increase in light ref lectance due to the physical barrier generated by this product. SPAD cannot diff erentiate whether the light quantity that reaches the sensor is due to an increase in absorption or ref lectance of light, and a high leaf ref lectance tends to increase the SPAD reading (Silva et al.2011). This Effect was also found in the leaves of pecan nut trees (Lombardini et al. 2005; Gharaghani et al. 2018)and inPhysalis peruvianaL. plants (Segura-Monroy et al.2015) treated with KBPF.

In the dry season, the increase in SPAD reading(Fig. 7 d) conf irmed the results of SLW (Fig. 4) and a correlation has been found between these variables (Marenco et al. 2009). KBPF was effi cient in maintaining photochemical effi ciency within the ideal range, possibly due to a higher ref lection of ultraviolet rays, which is commonly associated with inhibition of PSII activity (Sharma et al.2015). Similar results were found for grapevines by Dinis et al. ( 2018), who reported that the application of KBPF increased the maximum quantum photochemical effi ciency of the PSII; and inCitrus paradisiL., presented reduction of 30% in the photoinhibition process at noon (Jifon and Syvertsen 2003).

The vapor pressure def icit found in the dry season during the physiological evaluations in the afternoon period was 2.4 kPa, which was 30.6% higher than that found in the same evaluation period in the rainy season. This was probably due to photoinhibition (Araújo and Deminicis 2009) in the dry season during this evaluation period.

Conclusion

The protective layer formed by the application of the KBPF increased the photochemical effi ciency, SPAD reading and specif ic leaf weight of mini-stumps, and maintained similar production levels and yield indexes of eucalyptus mini-cuttings over the evaluation times. In the dry season, the application of the product increased mini-cutting length, which indicates that the application of kaolin-based particle f ilm on clonal mini-gardens under high-temperature environments can be a strategy to reduce the intervals between collections of mini-cuttings, increasing nursery yield.

Fig. 7 Effects of kaolin-based particle f ilm concentrations on SPAD reading of eucalyptus mini-stumps evaluated at the morning (a) and afternoon ( c) during the rainy and dry seasons; Effects of KBPF applications, within the seasons, on SPAD reading of eucalyptus mini-stumps evaluated in the morning ( b) and afternoon ( d). Regressions were performed within each season. ***, **, and * = signif icant at 0.1%, 1%, and 5% probability using the t-test, respectively. Means were compared within each season using Tukey’s test at 5% probability. Vertical bars indicate the standard error of the mean

Fig. 8 Effects of kaolin-based particle f ilm concentrations on the maximum quantum yield of photosystem II ( F v / F m ) of eucalyptus mini-stumps evaluated in the morning and afternoon. The regression was performed for the whole experiment. * = signif icant at 5% probability using the t test. ns = not signif icant at 5% probability. Vertical bars indicate the standard error of the mean

Publisher’s NoteSpringer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affi liations.