1. Introduction
As one of the world’s important economic crops, coffee is mainly produced in countries in tropical and subtropical regions, such as Brazil, Argentina, Ethiopia, Vietnam, etc. It has important economic value owing to representing an annual trade value of $10 billion [1]. It is noteworthy that coffee quality, such as the content of caffeine, chlorogenic acid, and specific flavor substances [2], are usually dependent on the region, altitude, as well as factors such species, cultivar, and a number of important parameters of processing at harvest and after (roasting, grinding, and brewing) [3,4]. However, the impact of planting patterns on coffee quality cannot be ignored. Therefore, the production process of coffee has attracted extensive attention, especially in developing countries in the tropical region, because the yield and quality of coffee determine the value of the coffee industry and income of farmers.
The mulching of agricultural wastes such as straw and coconut has been proved to improve the survival rate, yield, and quality of coffee plants and to generate higher economic returns in the traditional coffee planting process [5]. However, the traditional cultivation methods have encountered challenges in adapting to the changing needs of industrial development with the gradual growth and expansion of the coffee industry. On the one hand, most of the by-products produced during coffee processing, especially coffee cherry pericarp (cascara), are not properly treated, resulting in an alarming waste of recyclable resources [6]. On the other hand, the escalating cost of agricultural mulching materials has precipitated a direct increase in coffee cultivation expenses, and the long-term retention of fertilizers and pesticides in the soil is having a negative feedback effect on the growth of coffee plants [7]. In order to solve these problems in the process of traditional coffee cultivation, the use of coffee litter and cascara instead of traditional mulch has become a promising method of coffee cultivation. This innovation not only reduces the use of mulching materials, fertilizers and other inputs, but also promotes the efficient recycling of coffee waste, thus improving the cost reduction and efficiency improvement in the process of coffee planting.
As an important link between plants and soil, agricultural organic waste plays a crucial role in maintaining the nutrient balance and material cycling in the agroecosystem [8]. Studies have shown that coffee cascara and litter are potential materials for high-quality organic fertilizer due to their rich nitrogen, phosphorus, and potassium content [9]. Coffee cascara and litter mulch not only enhanced soil nutrient content but also improved soil texture and moisture content [9,10]. It is generally believed that the photosynthesis of plants is usually affected by factors such as light and temperature, but soil moisture and nutrient content should not be ignored [11]. Therefore, coffee cascara and litter mulch also contribute to improving the physiological mechanism of coffee plants, especially their photosynthetic properties. The change of soil moisture content will affect leaf water potential, which has a significant impact on photosynthesis [12]. Mineral elements such as nitrogen, phosphorus and potassium play a crucial role in promoting plant photosynthesis. For example, phosphorus and potassium can improve the photosynthetic rate of plants by promoting chlorophyll synthesis and optimizing the photosynthetic utilization of captured light energy [13].
Leaf carbon use efficiency (CUE) is an important indicator of plant carbon balance, which reflects the carbon assimilation ability of thee coffee plant by considering photosynthesis and respiration [14]. Leaf water use efficiency (WUE) reflects the water consumption per unit of carbon, which is one of the important indicators to measure plant drought tolerance [15]. Previous studies indicated that environmental factors, such as precipitation, temperature, light, and soil nutrients, should have significance on photosynthesis, respiration, and transpiration of coffee leaves’ photosynthesis and the respiration and transpiration of coffee leaves [16,17,18] and may result in the complex and variable correlation between these environmental factors and CUE and WUE [19,20]. In summary, coffee cascara and litter mulch also significantly affect photosynthesis, respiration, and transpiration by regulating environmental factors such as soil moisture, temperature, light, and nutrient availability, thereby regulating coffee CUE and WUE. On the one hand, coffee cascara and litter accelerate the migration of its own nutrients into the soil through its decomposition, thereby increasing soil nutrient content and changing the photosynthetic characteristics of coffee leaves. On the other hand, coffee cascara and litter mulch enhances soil moisture and improves soil properties in coffee plantations, thereby regulating the photosynthetic characteristics of coffee. These two regulatory pathways may have a positive impact on the growth and productivity of coffee plants, while the healthy growth of coffee plants may have a positive or negative feedback effect on the microenvironment by changing the nutrient absorption efficiency and agronomic traits of their own roots. Understanding these complex interactions is crucial for optimizing agricultural practices and maintaining sustainable farmland ecosystems.
The impact of coffee cascara and litter mulch on the net photosynthesis rate, stomatal conductance, transpiration rate, CUE, and WUE of coffee leaves remains inconclusive. Therefore, a field experiment concerning coffee cascara and litter mulching was established to monitor the changes of soil properties and photosynthetic indices of coffee leaves in coffee plantations under different coffee waste-mulching methods and to explore the main influencing factors and key regulatory pathways of physiological and photosynthetic indices of coffee seedlings under different mulching modes. The results of this study contribute to a better understanding of the impact of coffee waste mulching on the growth and development of coffee plants and will provide valuable insights into cost-saving measures and efficiency improvements in coffee production.
2. Materials and Methods
2.1. Experimental Site
The experiment was located in the coffee plantations of Xinglong Tropical Botanical Garden, which in the southeast of Hainan Province, China (110°11′ E, 18°44′ N). The annual precipitation was 2100 mm, and the annual sunshine duration exceeds 1750 h. The soil was mainly classified as tidal sand–mud (US Soil Taxonomy classification). Soil pH was 6.15.
2.2. Experimental Materials
One-year-old Robusta coffee seedlings (Coffea Canephora Pierre ex A. Froehner cv. Reyan No.1) were selected for planting in the field, and they began to be mulched with coffee cascara and litter after three months. Coffee litter was collected from the Coffee Germplasm Resource Nursery at the Institute of Spices and Beverages of the Chinese Academy of Tropical Agricultural Sciences (CATAS). The coffee cascara was collected from the coffee viewing plantation of Taiyanghe Coffee Processing Factory located in Xinglong Farm, Hainan, China. It is noteworthy that the coffee cascara, litter, and experimental coffee seedling varieties remain consistent. The main coffee variety in Hainan Island, China, is Robusta coffee, which is mainly divided into four production regions. The Wanning city in the southeast of Hainan Island has a relatively large planting area, and the above-mentioned variety of coffee is the main cultivated variety in this region.
2.3. Experimental Design
A completely randomized block design was performed in the coffee field experiment in June 2020. Two different coffee waste materials, coffee litter and coffee cascara, were used for different mulching treatment combinations. There were 4 types of mulch treatments, including non-mulch coffee waste (C), mulching coffee litter (L), mulching coffee cascara (cherry pericarp, P), and mulching coffee litter and cascara (LP) in this field experiment. Each treatment was repeated 6 times. The average cumulative amounts of coffee litter and cascara in coffee plantations of Hainan Province were 301.39 g·m−2 and 239.05 g·m−2, respectively. The amount of coffee litter and cascara added in this experiment was consistent with the field investigation. The management plan for coffee seedlings under all treatments was to maintain consistency, including the frequency, amount, and duration of fertilization and irrigation.
2.4. Measurement Indicators
Soil moisture content (SM), soil temperature (ST), and soil bulk density (SBD) were measured directly in situ by using the hygrothermograph and ring knife method, respectively; soil samples were sieved through a 2 mm sieve, roots and debris were removed, and pH was measured by pH meter after natural drying for 7–10 d. Soil organic matter (SOM) was measured using a total organic carbon analyzer (Multi N/C 3100); and alkali-hydrolyzed nitrogen (SAN) was measured using the alkaline dissolved diffusion method; soil-available potassium (SOP) was measured using an ultraviolet spectrophotometer; and soil-available potassium (SAK) was measured using a flame photometer.
Coffee plant height was determined using a meter scale, leaf area was determined immediately after leaf collection; specific leaf area (SLA) = leaf dry weight/leaf area; and leaf area index (LAI) = total leaf area/vertical projected area of the plant and other indices. The collected leaves were promptly placed in 105 °C for 1 h and then dried at 75 °C for 48 h and weighed; the relative chlorophyll content (SPAD) was determined at the same time as the determination of the photosynthetic indices using the SPAD-502plus chlorophyll meter.
The leaves for measuring photosynthetic indices were selected from the fourth layer of leaves, and the Li-6400XT (Li-Cor Inc., Lincoln, NE, USA) portable photosynthesizer was used to determine net photosynthesis (Pn), leaf respiration (R), stomatal conductance (Gs), intercellular CO2 concentration (Ci), and transpiration (Tr). The gross photosynthesis (Pg), carbon use efficiency (CUE) and water use efficiency (WUE) of the plant were calculated as Pg = Pn + R, CUE = Pn/Pg, WUEn = Pn/Tr, and WUEg = Pg/Tr. Three leaves were randomly measured for each coffee plant, with a total of 72 leaves measured.
Coffee plant photosynthesis and physiological indices (Pn, R, Gs, Ci, Tr, Pg, CUE, WUEn, WUEg, plant height, and SPAD) and microenvironment (SM, ST, SBD, and pH) were measured once in each season (September and December 2020 and March and mid-June 2021, select sunny days from 10:00 to 11:00), and soil nutrient content (SOM, SAN, SOP and SAK) was measured once after the determination of the photosynthetic indicators (mid-June) in 2021. The functional characteristics of coffee leaves (SLA, LAI) were measured using destructive sampling methods once a year in 2021.
2.5. Statistical Analysis
Two-way analysis of variance (two-way ANOVA) was used to determine the difference between the coffee litter and cascara on soil properties and photosynthetic indices. Before the data analysis, all the data were in accord with the normality test. Data analysis was performed using the Duncan test, and the difference between mean values was determined using the least significant difference (LSD) by using SPSS 23.0 software (SPSS Inc., Chicago, IL, USA). The statistical significance (p < 0.05) was calculated using the Tukey test. Redundancy analysis (RDA) was performed to analyze the relation between soil properties and photosynthetic indices by using the CANOCO 5.0 software package. The model was assessed for 999 iterations based on Monte Carlo permutations. Correlations between soil properties and photosynthetic indices were calculated and analyzed using Spearman correlation matrices. The affiliation function method was used to synthesize each photosynthetic and plant trait index, and the affiliation values of different mulch treatments within each index were calculated to synthesize the coffee plant traits. The affiliation function formula was as follows:
U(Xi) = (Xi − Xmin)/(Xmax − Xmin)
where U(Xi) is the value of the affiliation function, U(Xi) ∈ [0, 1], Xi is the measured value of a particular photosynthetic indicator, and Xmax and Xmin are the maximum and minimum values within the measured value of the indicator, respectively. The graphs were plotted using Origin 2021.3. Results
3.1. The Difference of Soil Properties and Microenvironment under Coffee Litter and Cascara Mulch Treatments
Coffee litter and cascara mulch significantly reduced soil temperature by 0.42 °C (F = 6.66, p < 0.05) and 0.33 °C (F = 10.40, p < 0. 01), respectively (Table 1), but there was no interaction between litter and cascara mulch on soil temperature (Table 2). Coffee litter rather than cascara mulch significantly increased SAK content by 46.28% (F = 4.70, p < 0.05), but there was no interaction effect of different mulch treatments on SAK content. Coffee litter and cascara mulch did not affect SM, pH, SBD, SOM, SOP, and SAN content, and there was no interaction effect between the effects of the two treatments on the above index.
3.2. The Difference of Coffee Plant Agronomic Traits under Coffee Litter and Cascara Mulch Treatments
Coffee cascara rather than litter mulch significantly increased coffee SLA by 45.46% (F = 6.83, p < 0.05), whereas there was no interaction between coffee cascara and litter mulch treatments on SLA (Figure 1a, Table 3). Coffee litter rather than cascara mulch significantly reduced coffee plant height by 12.11% (F = 6.39, p < 0.05, Figure 1a, Table 3), whereas there was no interaction between coffee litter and cascara treatments on coffee plant height (Figure 1c, Table 3). Coffee litter treatments did not affect coffee LAI and SPAD, and there was no interaction between different coffee waste mulch on these two indices (Figure 1b,d, Table 3).
3.3. The Difference of Coffee Plants’ Photosynthetic Indices under Coffee Litter and Cascara Mulch Treatments
Coffee litter and cascara mulch did not affect Gs, Tr, and CUE, but there was an interaction effect between litter and cascara mulch treatments on Gs (F = 8.89, p < 0.01), Tr (F = 7.27, p < 0.01), and CUE (F = 5.19, p < 0.05) (Figure 2a,b,f, Table 4). Coffee cascara mulch significantly increased coffee Pn, R, Pg, WUEn, and WUEg by 78.33% (F = 4.60, p < 0.05), 109.34% (F = 7.11, p < 0.01), 91.72% (F = 10.19, p < 0.001), 80. 54% (F = 9.99, p < 0.01), and 104.95% (F = 4.50, p < 0.05), respectively, whereas coffee litter mulch did not affect the above indices and there was no interaction between different coffee waste mulch on these two indices on the above indices (Figure 2c–e,g,h, Table 4).
3.4. The Correlation among Photosynthetic Indicators, Agronomic Traits, and Microenvironment Index
Redundancy analysis (RDA) was used to analyze the relationship between each coffee photosynthetic physiological index and environmental factors (Figure 3). All environmental variables together explained 56.7% of the variation of photosynthetic indices among samples, and the first two sorting axes of the RDA explained 40.26% and 11.13% of the total variance, respectively (Table 5). The Monte Carlo permutation test showed that ST (F = 4.2, p = 0.01) and SAK (F = 1.7, p = 0.05) significantly affected coffee photosynthetic physiological indices. The SPAD (F = 1.6, p = 0.09) also had a trend in the photosynthetic physiological indicators of coffee. The variance among samples and the order of effect sizes was ST > SAK > SPAD > Height > SM > pH > SOM > SLA > LAI > SBD > SAN > SOP.
Spearman rank correlation analysis showed significant negative correlations between Pg (R = −0.51), Pn (R = −0.42), WUEg (R = −0.43), WUEn (R = −0.42), and ST (p < 0.05). There was a significant negative correlation between R and SOP (R = −0.44, p < 0.05), while height showed a significant positive correlation with R (R = 0.41, p < 0.05). There was a significant negative correlation between Gs and SPAD content (R = −0.47, p < 0.05), and a significant negative correlation between CUE and plant height content (R = −0.41, p < 0.05), whereas there was a significant positive correlation between Tr and LAI (R = 0.41, p < 0.05, Figure 4). Moreover, most of the photosynthetic indices had significant positive correlations with each other (Figure 4).
3.5. Comprehensive Evaluation of the Effect of Coffee Litter and Cascara on Coffee Photosynthetic Physiological Indices
The membership degrees of various indicators under different mulch treatments were calculated in this study and then the advantages and disadvantages of the physiological status of coffee seedlings were comprehensively determined. The average membership degrees of different mulch treatments were ranked from largest to smallest as P > LP > L > CK (Table 6). Therefore, the growth of coffee seedlings was optimal under the coffee cascara mulch treatment.
4. Discussion
4.1. Effect of Coffee Litter and Cascara Mulch on Soil Properties and Microenvironment
Agricultural organic waste is one of the important sources of nutrients in soil. Mulching cultivation with agricultural waste is conducive to maintain soil fertility in plantations and accelerate nutrient cycling in agricultural ecosystems [6,21]. Previous studies have consistently shown that soil nutrient content, such as nitrogen, phosphorus, and potassium, are increased significantly with the accumulation of exogenous organic matter [22]. However, coffee cascara and litter mulch have a few impacts on SAN and SOP, which may be related to the quality of coffee waste [23]. The quality of agricultural waste includes decomposable components (e.g., nitrogen and phosphorus compounds) and non-decomposable components (e.g., lignin, cellulose, and polyphenols) [24]. Nitrogen and phosphorus elements are fully released during the brief rapid decomposition in the early decomposing stage of coffee cascara and litter, while nitrogen and phosphorus elements may be slowly released in the later decomposing stage, during the one-year decomposition process, resulting in the soil nitrogen and phosphorus content under the coffee cascara and litter mulch cultivation conditions not significantly increasing. It is worth noting that the coffee cascara mulch significantly increased the SAK in the coffee plantation, which may be related to the higher potassium content present in coffee cascara compared to other plant organs.
Previous studies have confirmed that adding litter mulch could significantly enhance soil moisture and reduce soil temperature [25]. However, soil moisture did not respond to coffee waste mulch treatment in the current study, which may be related to the perennial high air humidity in the area where the field experiment was conducted. Plant transpiration is the primary mode of water dissipation in agroecosystems, compared to soil evaporation, and higher air humidity is positively correlated with leaf water potential [25,26]. The elevated air humidity may become one of the reasons why coffee cascara and litter does not alter soil moisture content by inhibiting the transpiration rate of coffee leaves [27]. Therefore, the enhanced retention function of soil moisture in farmland was weakened by the mulching of coffee cascara and litter under the sustained high soil moisture conditions of current experiment.
4.2. Effect of Coffee Litter and Cascara Mulch on Coffee Agronomic Traits and Photosynthetic Indexes
A previous study has indicated that the photosynthesis of coffee is influenced by environmental factors, such as soil nutrients content, light intensity, soil temperature, and humidity [28,29,30]. This study confirmed that the changes in photosynthesis under coffee litter and cascara mulch treatment were primarily regulated by soil temperature and soil potassium content. On the one hand, as a shallow-rooted plant, coffee is suitable for growing at 22.0 to 28.4 °C, and it is particularly sensitive to variations in soil temperature [31]. Higher temperatures will inhibit coffee plant photosynthesis by reducing the enzyme activity of plant roots or leaves when the soil temperature is higher than the suitable photosynthetic temperature for coffee plants [32]. This study is located in the transitional zone between subtropical and tropical regions with year-round high temperatures. The stacking of coffee cascara layers has a honeycomb-like structure, which could change the surface airflow dynamics, reduce the soil temperature of the coffee plantation [33], and then promote the photosynthesis of coffee plants under the coffee cascara treatment.
On the other hand, it is generally believed that leaf nitrogen, phosphorus, and potassium could enhance the net photosynthesis by improving photosynthetic activity of mesophyll cells [34]. However, the photosynthetic indicators of coffee were not sensitive to the various soil nitrogen and potassium contents (Figure 4), indicating that soil nutrient content was not the main influencing factor regulating the photosynthetic physiological process of coffee in the current study. The enrichment of soil phosphorus can enhance leaf respiration, thereby reducing the synthesis of photosynthetic products, such as starch and sugar accumulation, leading to early crop senescence [35]. Although the negative correlation between coffee leaf respiration and SAN in this study confirms the above statement, soil phosphorus is also not the main influencing factor in regulating coffee photosynthetic physiological processes. Furthermore, the positive correlation between Tr and LAI is consistent with most previous research findings (Figure 4); that is, the transpiration rate significantly increases with the increase in photosynthetic organs in the coffee canopy [36]. Overall, the photosynthesis of coffee plants remained stable, while plant height under coffee litter mulch was significantly reduced, reflecting their adaptability to environmental variety.
Previous studies have shown that the increased soil nutrient content and improved soil microenvironment under litter mulch conditions stimulate coffee plants to distribute more photosynthetic products to above-ground photosynthetic organs, which is used to enhance plant light competition rather than enhancing plant stress-resistance physiological mechanisms. Previous research indicated that the increased soil nutrient content and improved soil microenvironment conditions under litter mulch treatments stimulate coffee plants to distribute more photosynthetic products to above-ground photosynthetic organs, which is used to enhance plant light competition rather than enhancing plant stress-resistance physiological mechanisms [37]. Coffee plants were not constrained by light competition and were able to distribute more photosynthetic products to their leaves, which was used to improve the leaf area index of coffee plants under coffee litter mulch treatment in this study. Moreover, the improved availability of resources and nutrient status in the soil under coffee litter mulch also contributed to the increased specific leaf area of coffee plants under coffee cascara mulch treatment.
4.3. Effect of Coffee Litter and Cascara Mulch on the Water Use Efficiency of Coffee
Water use efficiency in plants represents the amount of photosynthetic yield produced per unit of water consumed through transpiration [38]. A previous study suggested that the WUE of tropical woody plants under litter mulch treatment is negatively correlated with temperature and is attributed to the accelerated transpiration caused by higher temperatures [16]. However, the findings of the current study are inconsistent with the aforementioned research results, which may be due to the fact that coffee cascara mulch promotes an increase in photosynthesis by reducing soil temperature. The transpiration rate of coffee is not sensitive to the coffee cascara mulch treatment, resulting in the coffee plant significantly promoting its carbon absorption rate while maintaining stable transpiration, thereby increasing leaf WUE. Furthermore, there is a significant positive correlation between soil potassium content and transpiration in this study, indicating that potassium is one of the primary driving factors for accelerating water vapor flux in coffee plants [39]. Although coffee cascara mulch significantly increases the SAK, the transpiration rate of coffee may be influenced by other factors, and its specific regulatory mechanism still needs further research.
Temperature is a crucial climatic factor that greatly influences the CUE of plants, and it has been extensively studied [40]. Previous research has indicated that photosynthesis and respiration have varying sensitivities to temperature changes, leading to significant differences in the impact of temperature on CUE [41]. However, the coffee CUE in this study did not respond to soil temperature changes and may be related to the adaptive response of the coffee plant to long-term temperature variation. Specifically, coffee cascara mulch significantly increased net photosynthesis by reducing soil temperature but also significantly promoted respiration, offsetting the stimulating effect of cascara on the carbon absorption of the coffee plant [42]. Therefore, the photosynthesis and respiration of the coffee plant maintained a relatively constant ratio with temperature, restoring the balance between photosynthesis and respiration, resulting in coffee cascara and litter mulch not altering the CUE of the coffee plant.
4.4. Comprehensive Assessment of Coffee Litter and Cascara Mulch on the Photosynthetic Physiology of Coffee Plant
Individual photosynthetic indices only reflect a single aspect of photosynthetic characteristics of coffee plants, while the coordination and balance of various plant photosynthetic physiological indicators collectively determine the process of photosynthesis. The membership value is calculated using different photosynthetic and physiological indicators to comprehensively evaluate the growth status of plants in this study. The increase in membership value indicates that the photosynthetic physiological process of coffee is stable and the plant growth is vigorous. The membership value of coffee plants was the highest in the treatment of mulch coffee cascara alone, which was consistent with the corresponding plant growth indicators. Thus, it was considered the most suitable coffee waste mulching treatment in this study.
However, the amount of coffee waste used in this study remained fixed and did not investigate the impact of different amounts of coffee cascara and litter on the physiological processes of coffee plants. It is necessary to explore the coverage combination of various amounts of coffee cascara and litter on coffee photosynthetic indicators in order to establish a more scientifically sound mulching approach in further studies. Furthermore, it is an important deficiency that this study is based on single-year data. This study has been planned based on multiple years of experience, and indicators such as climate factors, soil physicochemical properties, agronomic traits of coffee plants, photosynthetic physiology, yield, and quality of coffee cherries will be continuously monitored in future research to clarify the impact of long-term coffee waste mulch on coffee plants.
5. Conclusions
Both cascara cherry and litter mulch do not affect the agronomic traits of coffee seedlings, soil properties, and microenvironment except significantly reducing soil temperature and increasing soil available potassium content in this study. Coffee cascara mulching had a positive impact on the photosynthesis of coffee seedlings by improving the soil microenvironment rather than increasing nutrient content conditions, although the water use efficiency and carbon use efficiency of coffee seedlings are not sensitive to the coffee cascara mulching cultivation. The promotion effect of coffee cascara mulching on the photosynthetic and growth indices of coffee seedlings is significantly higher than that of coffee litter mulching or mixed mulching treatment after comprehensive evaluation in this study. Coffee cascara mulching is conducive to promoting the growth of seedlings, cost savings, and efficiency improvements in the coffee production process, which is beneficial in coffee cultivation practices. However, this study is based on the results of a one-year experiment, and long-term monitoring and analysis need to be further implemented in future research.
A.Z.: conceptualization, funding acquisition, methodology, project administration, resources, supervision, writing—review and editing; S.-S.C.: conceptualization, data curation, formal analysis, software, validation, visualization, writing–original draft, writing—review and editing; L.-H.L.: methodology, writing—review and editing; X.-J.L.: formal analysis, methodology, project administration, supervision, writing—review and editing; L.Y.: formal analysis, supervision, visualization, writing—review and editing; S.-G.Z.: formal analysis, supervision, writing—review and editing; Y.-L.H.: formal analysis, project administration, supervision, writing—review and editing; Y.S.: supervision, writing—review and editing; Q.-Y.Z.: supervision, writing—review and editing; Y.-P.D.: resources; Y.-Z.L.: resources. A.Z. and S.-S.C. contributed to the work equally and should be regarded as co-first authors. All authors have read and agreed to the published version of the manuscript.
The data presented in the study are deposited in the Mendeley Data repository,
We are grateful to Yaoyu Zhang, Zhiqing Lu, Yiming Zhong, Faming Qu, Anlei He, and Shuangyan Qi for the soil sample collection and measurements. Thanks to Xinglong Tropical Botanical Garden for providing experimental materials for the research.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest and The authors declare no conflict of interest.
Footnotes
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Enlarge this image.Figure 1. Effects of coffee litter and cascara of mulch on specific leaf area (SLA, (a)), leaf area index (LAI, (b)), plant height (c), relative chlorophyll content (SPAD, (d)) Plant of coffee plants. Note: Different lowercase letters in the bar chart during the same period indicate significant differences between different treatments (p < 0.05).
Enlarge this image.Figure 2. Effects of coffee litter and cascara mulch on stomatal conductance (Gs, (a)), net photosynthesis (Pn, (b)), gross photosynthesis (Pg, (c)), transpiration (Tr, (d)), leaf respiration (R, (e)), net water use efficiency (WUEn, (f)), gross water use efficiency (WUEg, (g)), carbon use efficiency (CUE, (h)) of coffee plants. Note: Different lowercase letters in the bar chart during the same period indicate significant differences between different treatments (p < 0.05).
Enlarge this image.Figure 3. Redundant analysis (RDA) of coffee photosynthetic indices, coffee physiological indices, and microenvironment factors. See the abbreviations of indicators in Table 1 and Table 3 and Figure 2.
Enlarge this image.Figure 4. Correlation among photosynthetic indices, coffee physiological indices, and microenvironment factors. See the abbreviations of indicators in Table 1 and Table 3 and Figure 2; “*” represents p < 0.1; “**” represents p < 0.05.
Effects of mulching treatments on microclimate and physiochemical properties of soil.
| Mulch Pattern | SM | ST | pH | SBD | SOM | SAK | SOP | SAN |
|---|---|---|---|---|---|---|---|---|
| C | 8.20 ± 0.86 | 27.55 ± 0.06 | 5.65 ± 0.32 | 1.59 ± 0.08 | 21.99 ± 1.56 | 36.28 ± 5.66 | 29.64 ± 6.90 | 86.72 ± 10.41 |
| L | 8.33 ± 0.88 | 27.33 ± 0.05 | 5.57 ± 0.30 | 1.61 ± 0.10 | 22.10 ± 2.77 | 46.42 ± 4.78 | 27.74 ± 4.81 | 90.84 ± 13.97 |
| P | 7.26 ± 0.62 | 27.28 ± 0.07 | 5.55 ± 0.18 | 1.57 ± 0.09 | 21.33 ± 3.36 | 33.01 ± 7.86 | 28.09 ± 8.50 | 91.70 ± 17.45 |
| LP | 8.53 ± 1.23 | 27.18 ± 0.07 | 5.76 ± 0.23 | 1.60 ± 0.09 | 21.28 ± 2.84 | 54.93 ± 10.10 | 33.48 ± 9.76 | 90.15 ± 13.32 |
Note: SM: soil moisture content; ST: soil temperature; SBD: soil bulk density; SOM: soil organic matter; SAK: soil-available potassium; SOP: soil-available phosphorus; SAN: soil alkali-hydrolyzed nitrogen. Data are presented as mean ± standard errors.
Two-way ANOVA on microclimate and physiochemical properties of soil under mulching treatments (F value).
| Mulch Pattern | SM | ST | pH | SBD | SOM | SAK | SOP | SAN |
|---|---|---|---|---|---|---|---|---|
| L | 0.58 | 6.66 * | 0.02 | 0.05 | 0.07 | 4.70 * | 0.07 | 0.02 |
| P | 0.16 | 10.40 ** | 0.07 | 0.08 | 0.00 | 0.13 | 0.05 | 0.01 |
| L × P | 0.38 | 0.82 | 0.31 | 0.00 | 0.00 | 0.64 | 0.22 | 0.04 |
Note: “*” represents p < 0.05; “**” represents p < 0.01.
Two-way ANOVA on physiological indices of coffee plants under mulching treatments (F-value).
| Mulch Pattern | SLA | LAI | Height | SPAD |
|---|---|---|---|---|
| L | 0.63 | 0.08 | 6.39 * | 1.39 |
| P | 6.83 * | 0.16 | 1.64 | 2.15 |
| L × P | 0.63 | 0.23 | 0.09 | 1.06 |
Note: SAL: specific leaf area; LAI: leaf area index; Height: plant height; SPAD: relative chlorophyll content. “*” represents p < 0.05.
Two-way ANOVA on photosynthetic indices of coffee plants under mulching treatments (F value).
| Overlay Mode | Gs | Tr | Pn | R | Pg | CUE | WUEn | WUEg |
|---|---|---|---|---|---|---|---|---|
| L | 0.62 | 0.71 | 1.63 | 0.14 | 0.49 | 2.35 | 0.68 | 0.89 |
| P | 0.02 | 0.20 | 4.60 * | 7.11 ** | 10.19 *** | 0.01 | 9.99 ** | 4.50 * |
| L × P | 8.89 ** | 7.27 ** | 3.01 | 0.49 | 2.86 | 5.19 * | 0.06 | 1.22 |
Note: “*” represents p < 0.05; “**” represents p < 0.01; “***” represents p < 0.001
Contributions and significance of environmental variables to soil microbial community composition.
| Environment and Coffee Properties | Contribution Rate % | F Value | p Value |
|---|---|---|---|
| ST | 16 | 4.2 | 0.01 |
| SAK | 7.3 | 1.7 | 0.05 |
| SPAD | 6.7 | 1.6 | 0.09 |
| Height | 6.0 | 1.4 | 0.11 |
| SM | 4.5 | 1.0 | 0.37 |
| pH | 3.6 | 0.8 | 0.45 |
| SOM | 2.2 | 0.5 | 0.60 |
| SLA | 2.4 | 0.5 | 0.62 |
| LAI | 1.6 | 0.3 | 0.75 |
| SBD | 1.1 | 0.3 | 0.84 |
| SAN | 1.0 | 0.2 | 0.87 |
| SOP | 0.5 | 0.1 | 0.92 |
Effects of coffee waste mulching on photosynthetic indices of coffee plants.
| Mulch Pattern | Height | LAI | SLA | SPAD | Gs | Tr | Pn | R |
| CK | 0.59 | 0.00 | 0.07 | 1.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| L | 0.00 | 1.00 | 0.00 | 0.11 | 1.00 | 1.00 | 0.77 | 0.10 |
| P | 1.00 | 0.24 | 0.56 | 0.32 | 0.90 | 0.63 | 1.00 | 1.00 |
| LP | 0.26 | 0.13 | 1.00 | 0.00 | 0.19 | 0.11 | 0.88 | 0.68 |
| Mulch pattern | Pg | CUE | WUEn | WUEg | Average membership | Ranking | ||
| CK | 0.00 | 0.00 | 0.00 | 0.00 | 0.14 | 4 | ||
| L | 0.49 | 1.00 | 0.62 | 0.25 | 0.53 | 3 | ||
| P | 1.00 | 0.57 | 1.00 | 0.85 | 0.76 | 1 | ||
| LP | 0.80 | 0.62 | 0.95 | 1.00 | 0.55 | 2 | ||
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Details
; Su-Sen, Chen 2 ; Xing-Jun, Lin 1 ; Lin, Yan 1 ; Yan-Li, Huang 3 ; Sun, Yan 1 ; Qing-Yun, Zhao 1 ; Shao-Guan, Zhao 4 ; Li-Hua, Li 5 ; Yu-Zhou, Long 1 ; Yun-Ping, Dong 3 1 Spice and Beverage Research Institute, Chinese Academy of Tropical Agricultural Sciences/Hainan Provincial Key Laboratory of Genetic Improvement and Quality Regulation for Tropical Spice and Beverage Crops/Key Laboratory of Genetic Resource Utilization of Spice and Beverage Crops, Ministry of Agriculture and Rural Affairs/Hainan Engineering Research Center for Coffee, Wanning 571533, China;
2 Spice and Beverage Research Institute, Chinese Academy of Tropical Agricultural Sciences/Hainan Provincial Key Laboratory of Genetic Improvement and Quality Regulation for Tropical Spice and Beverage Crops/Key Laboratory of Genetic Resource Utilization of Spice and Beverage Crops, Ministry of Agriculture and Rural Affairs/Hainan Engineering Research Center for Coffee, Wanning 571533, China;
3 College of Tropical Crops, Yunnan Agricultural University, Pu’er 665099, China;
4 Spice and Beverage Research Institute, Chinese Academy of Tropical Agricultural Sciences/Hainan Provincial Key Laboratory of Genetic Improvement and Quality Regulation for Tropical Spice and Beverage Crops/Key Laboratory of Genetic Resource Utilization of Spice and Beverage Crops, Ministry of Agriculture and Rural Affairs/Hainan Engineering Research Center for Coffee, Wanning 571533, China;
5 College of Agronomy and Biotechnology, Yunnan Agricultural University, Kunming 650201, China;