The addition of Biochar (BC) into the soil is expected to improve soil physicochemical properties and plant growth. However, few studies have verified such an effect on the growth and physiological characteristics of conifers. The current study aims to assess the efficacy of novel physiological parameters as an indicator for assessing the impact of hardwood biochar (BH) on the development of
Soil fertility is a key factor of forest productivity and its long-term maintenance without harming the environment is a crucial and challenging goal. A comprehensive understanding is required to evaluate the soil’s ability to ensure plant growth. Recently, the use of biochar (BC) as an organic amendment has become an alternative to returning biomass into the soil to address numerous agronomic and environmental problems (
Large areas in tropical and subtropical regions of southern China are characterized by acidic soils, which hinders plant growth by affecting many physiological processes (
Several investigations have been focused on the impact of BC as an amendment on plant growth and soil, mostly on crops rather than forest tree species. For instance,
To date, there are limited BC studies that support such an influence on the physiology and biochemical of woody plants in forest soils. For example,
Most of the above BC studies focused on the analysis of biomass production. However, to understand how plant growth can be affected by BC, further parameters related to plant physiological status need to be explored. In view of this, the current study aims to assess the efficacy of physiological parameters as an indicator of the impact of BC amended soil on
The main goals of this study were to investigate the influence of varying levels (0, 5, 20, and 80 g Kg-1 of soil) of BH amendment to red soil on: (i) photosynthetic pigments, biochemicals, and gas exchange attributes of
The present work was carried out at the Bamboo Institute of Fujian Agriculture and Forestry University, Fuzhou, China. Hardwood biochar (BH) was produced from
Before the experiment, both soil and BC were assessed for basic physicochemical properties (see Tab. S2 in Supplementary material). In addition, soil samples were taken from each replicate at the final harvest to assess the physicochemical properties of the soil, including pH, total nitrogen (N), total carbon (C), total and available phosphorus (P), and available potassium (K). The soil samples were air-dried and then passed through a 2/0.149 mm sieve and the fractions were analyzed for selected physicochemical properties. The soil pH (1:2.5 soil/water suspensions) was recorded using a portable pH meter (INESA Science Instrument Co., Ltd., Shanghai, China) as described by
During each season (June 2017 to March 2018), upper-middle healthy leaves from each replicate were selected for recording gas exchange attributes and constructing light-response curves of Pn. All the measurements were conducted between 09:00 and 11:30 a.m. Before each measurement, photo-induction of 30 mins at 800 µmol m-2 s-1 was ensured as suggested by
In each season, healthy leaves from seedlings were collected, washed, and dried on filter paper to assess the concentrations of biochemicals. The photosynthetic pigments were determined immediately after the collection of the samples by retaining leaves in 80% acetone for 48-72 h in darkness at 4 °C until their color changed completely to white. Further absorbance of extractions for chlorophylls (a, b), total, and carotenoids were determined at 663, 645, and 470 nm, respectively, and calculated by using the equations of
The total soluble protein (TSP) at absor-bance 595 nm and amino acids at 650 nm was determined following the procedures of
Before the final harvest, the height and diameter of seedlings were determined using a diameter tape and a vernier caliper, respectively. To determine biomass, all the seedlings were uprooted, washed with care, dried on filter paper, and fresh weight was examined. These seedlings were then tagged and oven-dried at 80 °C for 48 h to record dry weight.
All the data are expressed as means and standard errors. Analysis of variance (ANOVA) was performed using SPSS® ver. 17.0 (SPSS Inc., Chicago, IL, USA) to determine the effect of soil BH treatments, and Tukey-HSD test was used to identify significant differences between mean treatments. The softwares Origin® v. 8.5 (OriginLab Corp., Northampton, MS, USA) and Prism v. 8.0.1 (GraphPad, San Diego, CA, USA) were used to fit the light response curves and produce graphs, respectively.
The increase in BC application rates resulted in a significant (p < 0.05) rise in soil pH under BH20 and BH80 treatments compared with B0 and BH5. Total nitrogen (TN), total carbon (TC), and organic matter (OM) content increased significantly (p < 0.05) in all BH amended soils over B0 (
Overall, seedlings treated with BH80 showed a significant impact on total chlorophyll (TC) concentrations throughout the year as compared to B0 (
The values of photosynthetic parameters such as initial slope (α), maximum photosynthetic rate (Pn-max), light saturation point (LSP), light compensation point (LCP), rate of dark respiration (Rd), and adjusted R2 are depicted in
The effect of BC as soil amendment on the biochemical attributes of
In terms of morphological attributes, seedlings of
The amendment of BC has been suggested to enhance soil nutrients dynamics, quality, and plant productivity (
Biochemical leaf traits and photosynthetic pigments are the key indicators of plant metabolism that are mainly influenced by the availability of resources (nutrients) and environmental conditions. BC increases the absorption of nutrients by enhancing the physiological state of the entire plant (
The variations in concentration of soluble sugars and ascorbic acids were also due to temperature fluctuations in various seasons. Ascorbic acid is an antioxidant molecule which plays a key role in the mechanisms of defense against environmental stress due to temperature variations (Fig. S4 in Supplementary material). The most effective function of ascorbic acid is to protect lipids and proteins against salinity or oxidative adverse reactions caused by drought (
Based on biochemical and molecular research, soluble sugars play a key role in controlling plant metabolism. In our experiment, BC amended seedlings accumulated more soluble sugars at first and third season compared to B0. Increased concentrations of soluble sugars enable plants to cope with cold stress in winters (
Several environmental factors affect Pn, including light, temperature, air CO2 concentration, water supply, the vapor pressure differential between leaves and air, soil fertility, salinity, toxins, applied chemicals, insects, diseases, and various interactions between them. Among them, light and temperature are the most influential factors involved in species survival, development, and reproduction. Their responses usually cause physiological changes, which are decisive for assimilating CO2 and optimizing gas exchange (
The above mentioned beneficial effects of soil BC amendments together lead to a significant increase in plant physiological and biochemical efficiency. The use of BC in vineyards enhanced the soil water content and then improved the plant supply of water and Pn activity in the leaves of
During the third and fourth seasons, suppression in Pn-max in plants was caused by the combined effects of daylight and temperature (Fig. S4 in Supplementary material). As reported in previous studies, low temperature inhibits Pn by reducing the activity of Calvin cycle enzymes (
The process of acclimatization to high-irradiance environments is very complex, involving both water and nutrient availability (
In the short term (days to weeks) the environmental conditions affect Pn by controlling stomatal conductance and photosynthetic ability of mesophylls. We found great differences in Cond and Trmmol among BC applications in diverse seasons except for Ci (Fig. S1, Fig. S2, Fig. S3 in Supplementary material). The increase in Ci indicates a reduction in the activity of CO2 assimilation, with limited carboxylation efficiency (
Numerous BC studies have demonstrated beneficial effects on biomass increase (
The findings of the present research suggest that BH amendments can be recommended as soil ameliorants into acidic soil. The addition of BH20 and BH80 to red soil had a significantly positive impact on the biomass (21% and 25%, respectively) of
This work was supported by Science and Technology Major Projects of Fujian Province [2018NZ0001-1] and Fujian Seedling Science and Technology Research Project, P. R. China.
Physicochemical properties of soil treated with different levels of hardwood biochar (BH). (B0): control soil without hardwood biochar amendment; (BH5): hardwood biochar-amended soil at 5 g kg-1; (BH20): hardwood biochar-amended soil at 20 g kg-1; (BH80): hardwood biochar-amended soil at 80 g kg-1, respectively. (TN): total nitrogen; (TP): total phosphorous; (AP): available phosphorous; (AK): available potassium; (OM): organic matter; (TC): total carbon. Significant differences (p < 0.05) among various treatments are shown by various letters. Vertical bars represent the standard error of the mean (n=4).
Photosynthetic pigments concentrations in four seasons under various level of hardwood biochar. TC and CARO indicate total chlorophyll and carotenoid, respectively. (B0): control soil without hardwood biochar amendment; (BH5): hardwood biochar-amended soil at 5 g kg-1; (BH20): hardwood biochar-amended soil at 20 g kg-1; (BH80): hardwood biochar-amended soil at 80 g kg-1, respectively. (a): 1st season (June 2017); (b): 2nd season (September 2017); (c): 3rd season (December 2017); (d): 4th season (March 2018). Different letters indicate significant differences (p < 0.05) among treatments. Vertical bars represent the standard error of the mean (n=4).
Response of net photosynthetic rate at different photosynthetic photon flux density levels (PPFD) under different BH levels. (B0): control soil without hardwood biochar amendment; (BH5): hardwood biochar-amended soil at 5 g kg-1; (BH20): hardwood biochar-amended soil at 20 g kg-1; (BH80): hardwood biochar-amended soil at 80 g kg-1, respectively. (a): 1st season (June 2017); (b): 2nd season (September 2017); (c): 3rd season (December 2017); (d): 4th season (March 2018). Vertical bars represent the standard error of the mean (n=3).
(a) Height and diameter (b) biomass and dry weight of seedlings treated with different levels of hardwood biochar. (B0): control soil without hardwood biochar amendment; (BH5): hardwood biochar-amended soil at 5 g kg-1; (BH20): hardwood biochar-amended soil at 20 g kg-1; (BH80): hardwood biochar-amended soil at 80 g kg-1, respectively. A significant difference (p < 0.05) among treatments is indicated by different letters. Vertical bars represent the standard error of the mean (n=4).
Season-wise comparison in photosynthetic parameters of seedlings treated with varying levels of hardwood biochar (BH). (α): initial slope; (Pn-max): maximum photosynthetic rate; (LSP): light saturation point; (LCP): light compensation point; (Rd): rate of dark respiration; (R2): adjusted R2; (B0): control soil without hardwood biochar amendment; (BH5): hardwood biochar-amended soil at 5 g kg-1; (BH20): hardwood biochar-amended soil at 20 g kg-1; (BH80): hardwood biochar-amended soil at 80 g kg-1. Significant differences (p < 0.05) among treatments are indicated by different letters. Values are means ± standard errors (n=3).
Date | Treatments | α | Pn-max (CO2 µmol m-2 s-1) | LSP(µmol m-2s-1) | LCP(µmol m-2s-1) | Rd(CO2 µmol m-2 s-1) | R2 |
---|---|---|---|---|---|---|---|
Jun-17 | B0 | 0.06 ± 0.01 a | 3.48 ± 0.38 a | 745.17 ± 79.82 a | 16.01 ± 4.88 b | 0.81 ± 0.07 a | 0.98 ± 0.07 a |
BH5 | 0.10 ± 0.01 ab | 5.42 ± 0.34 b | 948.51 ± 6.86 ab | 8.57 ± 2.55 b | 0.89 ± 0.28 a | 0.98 ± 0.01 a | |
BH20 | 0.09 ± 0.01 ab | 6.32 ± 0.08 bc | 856.35 ± 22.38 ab | 3.61 ± 1.36 a | 0.35 ± 0.13 a | 0.99 ± 0.01 a | |
BH80 | 0.10 ± 0.01 b | 6.72 ± 0.34 c | 1111.30 ± 131.27 b | 5.025 ± 0.95 a | 0.53 ± 0.12 a | 0.99 ± 0.01 a | |
Sep-17 | B0 | 0.08 ± 0.03 a | 5.12 ± 0.15 a | 729.30 ± 31.42 a | 5.46 ± 1.77 a | 0.47 ± 0.16 a | 0.98 ± 0.02 a |
BH5 | 0.08 ± 0.04 a | 5.53 ± 0.49 a | 853.07 ± 88.36 ab | 4.873 ± 1.91 a | 0.42 ± 0.17 a | 0.99 ± 0.04 a | |
BH20 | 0.09 ± 0.04 a | 6.94 ± 0.32 b | 1030.46 ± 62.91 bc | 3.97 ± 1.31 a | 0.35 ± 0.12 a | 0.99 ± 0.02 a | |
BH80 | 0.08 ± 0.04 a | 7.24 ± 0.25 b | 1102.68 ± 92.00 c | 3.21 ± 0.61 a | 0.28 ± 0.04 a | 0.99 ± 0.01 a | |
Dec-17 | B0 | 0.06 ± 0.01 a | 3.01 ± 0.24 a | 733.42 ± 30.58 a | 15.05 ± 0.09 a | 0.93 ± 0.13 a | 0.98 ± 0.03 a |
BH5 | 0.07 ± 0.02 a | 3.30 ± 0.18 ab | 780.39 ± 69.98 a | 12.60 ± 0.80 a | 0.95 ± 0.03 a | 0.98 ± 0.04 a | |
BH20 | 0.08 ± 0.01 a | 3.86 ± 0.27 b | 819.21 ± 122.80 a | 12.16 ± 2.36 a | 0.92 ± 0.08 a | 0.98 ± 0.05 a | |
BH80 | 0.08 ± 0.01 a | 4.04 ± 0.19 b | 805.57 ± 129.43 a | 11.66 ± 2.46 a | 0.90 ± 0.09 a | 0.99 ± 0.01 a | |
Mar-18 | B0 | 0.08 ± 0.01 a | 3.95 ± 0.36 a | 711.93 ± 63.01 a | 11.87 ± 1.41 a | 0.94 ± 0.07 b | 0.99 ± 0.06 a |
BH5 | 0.06 ± 0.01 a | 4.32 ± 0.069 a | 752.32 ± 65.55 a | 12.25 ± 0.76 a | 0.85 ± 0.02 b | 0.99 ± 0.01 a | |
BH20 | 0.08 ± 0.01 a | 4.37 ± 0.13 a | 809.25 ± 108.94 a | 7.34 ± 3.05 a | 0.56 ± 0.17 ab | 0.99 ± 0.01 a | |
BH80 | 0.08 ± 0.01 a | 4.43 ± 0.37 a | 975.94 ± 74.84 a | 6.16 ± 1.81 a | 0.51 ± 0.15 a | 0.99 ± 0.02 a |
Season-wise biochemical attributes in seedlings treated with different levels of biochar (BC). (B0): control soil without hardwood biochar amendment; (BH5): hardwood biochar-amended soil at 5 g kg-1; (BH20): hardwood biochar-amended soil at 20 g kg-1; (BH80): hardwood biochar-amended soil at 80 g kg-1. Significant differences (p < 0.05) among treatments are shown by different letters. Values are means ± standard errors (n=4).
Date | Treatments | Amino acid(µg g-1) | Ascorbic acid (µg g-1) | Soluble sugar(µg g-1) | Total Soluble Protein(g L-1) |
---|---|---|---|---|---|
Jun-17 | B0 | 4.04 ± 0.38 a | 19.58 ± 1.22 b | 11040.97 ± 495.12 a | 0.23 ± 0.02 ab |
BH5 | 5.17 ± 0.26 ab | 19.01 ± 0.90 b | 12458.47 ± 134.26 b | 0.20 ± 0.03 a | |
BH20 | 7.01 ± 0.26 b | 14.57 ± 2.28 b | 12558.13 ± 76.72 b | 0.28 ± 0.04 b | |
BH80 | 8.76 ± 1.00 b | 9.52 ± 1.06 a | 15049.83 ± 191.81 c | 0.40 ± 0.02 c | |
Sep-17 | B0 | 1.00 ± 0.29 a | 186.16 ± 17.36 b | 24316.80 ± 3953.43 a | 0.42 ± 0.01 a |
BH5 | 2.29 ± 0.15 b | 124.36 ± 20.30 a | 35241.51 ± 3130.46 a | 0.64 ± 0.01 b | |
BH20 | 2.70 ± 0.23 b | 113.50 ± 4.45 a | 35561.35 ± 6541.47 a | 0.69 ± 0.02 b | |
BH80 | 2.96 ± 0.28 b | 130.31 ± 13.90 a | 34843.34 ± 2321.57 a | 0.83 ± 0.01 c | |
Dec-17 | B0 | 1.44 ± 0.35 a | 76.84 ± 6.55 c | 34623.27 ± 392.65 a | 0.16 ± 0.06 a |
BH5 | 2.83 ± 0.52 a | 41.31 ± 0.99 b | 36870.68 ± 1845.46 a | 0.16 ± 0.05 a | |
BH20 | 2.89 ± 0.67 a | 7.93 ± 0.95 a | 47086.20 ± 1037.59 b | 0.17 ± 0.04 a | |
BH80 | 2.64 ± 0.52 a | 6.17 ± 0.24 a | 51801.72 ± 2485.96 b | 0.17 ± 0.03 a | |
Mar-18 | B0 | 1.32 ± 0.47 a | 37.74 ± 0.50 c | 36000.00 ± 1076.49 a | 0.17 ± 0.04 a |
BH5 | 1.32 ± 0.47 a | 17.02 ± 1.12 b | 37028.45 ± 486.15 a | 0.17 ± 0.03 a | |
BH20 | 1.51 ± 0.38 a | 5.08 ± 0.14 a | 37045.97 ± 521.88 a | 0.18 ± 0.04 a | |
BH80 | 2.02 ± 0.45 a | 4.61 ± 0.16 a | 37568.96 ± 180.55 a | 0.20 ± 0.02 a |
Appendix 1 - Equations used for calculation of leaf biochemical traits and photosynthetic pigments.
Appendix 2 - Light-response curves of photosynthesis fitting.
Tab. S1 - Physiochemical properties of soil and hardwood biochar.
Fig. S1 - Seasonal comparison in conductance to H2O of seedling at different photosynthetic photon flux density levels (PPFD) under different hardwood biochar (BH) levels.
Fig. S2 - Seasonal comparison in intercellular CO2 concentration of seedling at different photosynthetic photon flux density levels (PPFD) under different hardwood biochar (BH) levels.
Fig. S3 - Seasonal comparison in transpiration rate of seedling at different photosynthetic photon flux density levels (PPFD) treated with different hardwood biochar (BH) levels.
Fig. S4 - Metrological information of study area, during the entire experiment period