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Article

Characteristics of Dissolved Organic Matter as Affected by Decomposition of Different Organic Materials in Alpine Wetland

by
Yueguang Song
1,2,
Meng Li
1,*,
Yifei Wang
1 and
Weishan Yang
3
1
Wetland Research Center, Institute of Ecological Conservation and Restoration, Chinese Academy of Forestry, Beijing 100091, China
2
School of National Safety and Emergency Management, Beijing Normal University, Beijing 100875, China
3
Center for Ecological and Environmental Accounting, Chinese Academy of Environmental Planning, Beijing 100041, China
*
Author to whom correspondence should be addressed.
Agronomy 2024, 14(9), 1979; https://doi.org/10.3390/agronomy14091979 (registering DOI)
Submission received: 31 July 2024 / Revised: 25 August 2024 / Accepted: 29 August 2024 / Published: 1 September 2024
(This article belongs to the Section Soil and Plant Nutrition)
Browse Figures
Versions Notes

Abstract

:
Dissolved organic matter (DOM) plays a significant role in the nutrient supply, energy flow, and pollutant transportation in the wetland ecosystem. However, little is known about the effect of the decomposition of different organic materials in alpine wetland water on the DOM characteristics. By conducting a 90-day decomposition experiment with the addition of different organic materials (peat soil, yak manure, and plant litter) alone or their combinations into alpine wetland water, we characterized the water DOM using three-dimension excitation-emission matrix spectroscopy. The results showed that the decomposition of organic materials significantly affected the chemical properties, sources, humification degree, and composition of the water DOM. The decomposition increased dissolved organic carbon and dissolved total nitrogen in the water. For most of the water samples, a fluorescence index ranging from 1.4 to 1.7 and a biological index of less than 0.8 may indicate that both autochthonous and allochthonous sources contributed to the water DOM, which may primarily rely on allochthonous sources. UVA (37.55–46.81% of total fluorescent components) and UVC fulvic-like substances (29.91–35.53% of total fluorescent components) dominated the water DOM compositions. Among the treatments, additions of peat soil and yak manure led to the highest and the lowest humification degree of the water DOM, respectively. For the treatment of the combination decomposition of all three organic materials, the yak manure may stimulate microbial activity and facilitate the decomposition of plant litter and peat soil and, therefore, boost the humic-like substances in the water DOM. These findings may help the development of wetland biomass management with the objective of maintaining alpine wetland ecosystem services.

1. Introduction

Dissolved organic matter (DOM) comprises a broad range and a complex mixture of naturally soluble organic compounds [1,2]. DOM in aquatic ecosystems participates in many significant ecological processes, including acting as a chelating agent for metals to affect their solubility and toxicity, functioning as an important carbon pool in the global carbon cycle, and so on [3,4]. Many studies have revealed that chemical properties and compositions of DOM strongly affect its biogeochemical behavior [5,6]. DOM with high molecular weight seemed to have higher stability than that with low molecular weight [5,7]. Studies found that a higher abundance of UVA fulvic and visible humic-like substances in the DOM may be more liable to increase the mobility and toxicity of mercury in pore water of paddy soil. DOM characterization has, therefore, drawn increasing attention to the primary research objectives of carbon management, ecological conservation, and pollution control [8,9].
In wetland ecosystems, DOM bridges the energy flow and elemental cycle between terrestrial and aquatic ecosystems [10,11]. Wetland DOM is mainly the remnant of abiotic actions and biological decomposition of organic matter originally derived from terrestrial and autochthonous sources [1,12]. The origin sources of DOM exhibit a great influence on DOM composition and, consequently, on its environmental chemical processes and its susceptibility to environmental change [13]. DOM is highly correlated with soil organic matter in the wetland ecosystem and shows similarity between them [14,15]. Vascular plant decomposition in wetlands contributes to the DOM with 10% proteins, 30–50% carbohydrates, 15–25% lignin, and some lipids [16,17]. In particular, some subfractions of lignin, which is typically derived from terrestrial sources, may enter DOM and then facilitate the stability and complexity of DOM [18]. In comparison, DOM originated from phytoplankton decay and consists of 25–50% proteins, 40% carbohydrates, and 5–25% lipids [19,20]. In addition, livestock manure is another source of wetland DOM, which principally provides extra protein [21]. In wetland ecosystems, organic materials decomposition simultaneously involves microbial metabolism, which is the primary autochthonous source of DOM, and imports tryptophan-like substances into wetland DOM [3,22].
In China, alpine wetlands mainly concentrate on the Tibetan Plateau, which is commonly known as the “Asian water tower,” has an average elevation of over 4500 m and is the source of major Chinese river systems, including the Yangtze, the Lantsang, and the Yellow River [23]. It is of great significance to identify the DOM characteristics in the alpine wetland with the purpose of understanding the biogeochemical behaviors of DOM in the plateau and downstream ecosystems. Controlled by the unique plateau water cycling and climatic conditions, alpine wetlands are characterized by low temperature, large direct radiations, and strong evapotranspiration when compared to the wetlands of the other regions [24]. It has been reported that UV radiation, temperature, and microhabitat properties affect the decomposition of wetland organic substances, such as lignin, manure, etc. [25]. The strong UV radiation could change the photochemical decomposition process and rate for the DOM in alpine wetland water [24,25]. In addition, low temperatures may limit microbial activity and then inhibit the decomposition of plant residue by microorganisms, which may influence the DOM release rate [26]. However, little is currently known about the characteristics of DOM derived from the decomposition of different organic materials in alpine wetlands.
Thus, the objectives of this study were the following: (1) to investigate the effect of different organic materials decomposition on the chemical properties, sources, and compositions of DOM; and (2) to find the optimal combination of different organic materials decomposition that most promote DOM humification degree.

2. Materials and Methods

2.1. Preparation of Organic Materials

Three organic materials, including typical peat soil, plant litter, and yak manure, were collected from a typical alpine wetland in the Zoige region of the Tibetan plateau. The Zoige wetland is the largest plateau peatland globally, with a mean elevation of 3500 m and a total area of over 16,670 km2. It belongs to a humid monsoon climate in the cold-temperate plateau zone, with a mean annual temperature of 0.96 °C and a summer mean temperature of 10.8 °C. The mean annual precipitation in the region is 600–750 mm and concentrates mostly in the summer [27]. Carex muliensis, Carex meyeriana, Heleocharis uniglumis, Myriophyllum, Halerpestes cymbalaria, and Scirpus validus are widely distributed in the Zoige marsh wetland. The soil in the region is generally classified into peat soil. After the removal of impurities, these collected organic materials were air-dried at room temperature till constant weight. Among them, the peat soil and yak manure were ground and passed through a 2 mm sieve. The pH of peat soil was measured using a pH meter (FE20-FiveEasy plus, Mettler Toledo, Columbus, Switzerland) with a soil/water ratio of 1:2.5. The collected soil had a pH of 8.05, total organic carbon of 129.54 mg g−1, and total nitrogen of 4.37 mg g−1, while the yak manure possessed pH o 8.98, total organic carbon of 267.25 mg g−1, and total nitrogen of 18.39 mg g−1. The plant litter was ground to pass through a 5 mm sieve and had total organic carbon of 469.12 mg g−1 and total nitrogen of 8.63 mg g−1. Overlying marsh water was also collected from the alpine wetland in the region and was passed through a 0.45 μm PTFE filter membrane. The dissolved organic carbon (DOC) and dissolved total nitrogen (DTN) in the water samples were 53.49 mg L−1 and 6.48 mg L−1, respectively.

2.2. Decomposition Experiment and Sampling

A decomposition experiment was conducted by adding different organic materials uniformly containing 10 g of total organic carbon into 300 mL of alpine wetland water in wide-mouth open glass bottles. The experimental trial consisted of six treatments, including the following: (1) addition of peat soil (S), (2) addition of plant litter (P), (3) addition of yak manure (M), (4) combined addition of peat soil and plant litter (SP), (5) combined addition of peat soil and yak manure (SM), and (6) combined addition of peat soil, plant litter and yak manure (SPM) (Table S1). All treatments were conducted in triplicate. The incubation experiment was performed at 10 ± 1 °C in an artificial climate chamber for three months. Six ultraviolet (UV) fluorescent tubes (UVA 340, LongPro, Guangzhou, China) were used as a UV radiation source with a light wavelength range of 315–400 nm and light intensity of approximately 605 Lumen. Ultraviolet irradiation was applied for twelve hours every day. Deionized water was added to the bottle every 2–3 days using the weighting method. On the 90th day, water was sampled and passed through a 0.45 μm PTFE filter membrane. The freshwater samples were directly used for chemical analysis and DOM characterization.

2.3. Measurement of Basic Properties

Water pH was directly measured with a pH meter (FE20-FiveEasy plus, Mettler Toledo, Switzerland). The DOC and DTN were determined using an element analyzer (Elementar, Langenselbold, Germany). The water samples were digested with HNO3-H2O2 at 180 °C in a microwave digestion system for 30 min (Mars 5, CEM, Matthews, NC, USA). Total phosphorus (P), potassium (K), iron (Fe), and calcium (Ca) in the digested solution were then detected using inductively coupled plasma optical emission spectroscopy (ICP-OES, Optima 5300DV, Perkin-Elmer, Waltham, MA, USA), which has a detection limit of 0.003 mg L−1 for P, K, Fe, and Ca.

2.4. Three-Dimensional Excitation-Emission Matrix Fluorescence Spectroscopy (3D-EEM)

The 3D-EEM analysis for the DOM in water samples was performed using the procedure described in previous studies [2,8]. The DOC of all the water samples was uniformly diluted to 5 mg L−1 prior to the 3D-EEM analysis to avoid inner filter effects on the DOM fluorescence [2,28]. The EEM spectra for all the samples were recorded by measuring the fluorescence intensity at emission wavelengths ranging from 200 to 800 nm and at excitation wavelengths ranging from 230 to 700 nm with a resolution of 1 nm. The fluorescence spectra were scanned on a F7000 fluorescence spectrometer (Hitachi, Tokyo, Japan) with a slit width of 5 nm and a scanning speed of 1200 nm min−1. Parallel factor analysis (PARAFAC) was then applied using the DOMFluor toolbox on MATLAB R2014 to identify the outlier, eliminate the Raman scatter effect, and perform residual and split-half analysis for all the EEM spectra. EEM components of the water DOM were finally identified by the PARAFAC and were assigned based on previous studies [5,15,29,30].
Spectral indices for the DOM, including fluorescence index (FI), biological index (BIX), and humification index (FI), were calculated. In brief, FI was calculated by the ratio of fluorescence intensity at emission wavelengths of 470 nm and 520 nm and at an excitation wavelength of 370 nm, which is typically used to distinguish the autochthonous (FI > 1.9) and the allochthonous (FI < 1.4) sources for the DOM [10,18]. BIX was calculated by the ratio of fluorescence intensity at emission wavelengths of 380 nm and 430 nm and at an excitation wavelength of 310 nm, indicating recently produced biological DOM [12,13]. HIX was defined as the inner-filter corrected fluorescence intensity in the 435–480 nm region divided by the sum of fluorescence intensity in the regions of 300–345 nm and 435–480 nm, which is widely used to indicate the humification degree of the DOM [4,31].

2.5. Statistical Analysis

One-way analysis of variance (ANOVA) was conducted using the R software v4.4.1 www.r-project.org (accessed on 14 June 2024) to test the significant differences in basic properties, relative abundance of EEM components, and spectral indices between different treatments. Correlations of the EEM components with spectral indices and basic properties were performed using the R package “staRdom,” and a correlation heatmap was created using the R package “pheatmap.” Principal component analysis (PCA) was conducted using the R package “factoextra R” to detect the multivariate relationships among basic properties, spectral indices, and EEM components.

3. Results

3.1. Basic Properties

The collected water samples were alkaline, with a pH range of 8.39–8.79 (Table 1). The M samples had the highest pH (8.75 ± 0.04). Water DOC ranged from 97.82 mg L−1 to 263.96 mg L−1 with an average of 172.04 mg L−1. The P (213.40 ± 10.93 mg L−1) and SP (254.73 ± 12.26 mg L−1) samples had higher DOC than the other samples (141.03 ± 34.35 mg L−1). The S samples possessed the lowest DOC (128.83 ± 17.89 mg L−1). The water samples had a mean DTN of 12.73 mg L−1, ranging from 10.24 mg L−1 to 15.98 mg L−1. The DTN was higher in the M (15.44 ± 0.67 mg L−1), SM (13.75 ± 0.27 mg L−1), and SMP samples (13.09 ± 0.37 mg L−1) than in the S, P, and SP samples. Therefore, the P (20.23 ± 1.62 mg L−1) and SP samples (21.96 ± 1.46 mg L−1) had the highest DOC/DTN ratios (Table 1). In the collected water samples, 30.49–45.28 mg L−1 of K, 0.070–0.108 mg L−1 of Fe, and 46.26–58.39 mg L−1 of Ca were detected. However, no significant differences in K, Fe, and Ca content were found among the six treatments. In addition, the P content ranged from 0.079 mg L−1 to 0.138 mg L−1 in all the samples and was higher in the M (0.121 ± 0.016 mg L−1), SM (0.122 ± 0.020 mg L−1), and SMP (0.125 ± 0.019 mg L−1) samples (Table 1).

3.2. Spectral Indices of DOM

A range of 1.374–1.643 for the FI was found in all the water samples, with an average of 1.506 (Table 2). FI in most of the collected samples was in the range of 1.4–1.7. Among the treatments, the M (1.612 ± 0.030) and SP (1.440 ± 0.066) samples had the highest and lowest FI values. The BIX values for all the samples ranged from 0.409 to 0.593, with an average of 0.475. The M (0.578 ± 0.016 for the BIX, 1.524 ± 0.053 for HIX) samples had higher BIX values and lower HIX values than the other samples. The range of HIX values was from 1.474 to 2.985, with an average of 2.243 in all the samples. The highest and lowest HIX values were found in the S samples (2.907 ± 0.128) and M samples (1.524 ± 0.053), respectively (Table 2).

3.3. DOM Components by EEM and Parallel Factor Analysis

Four fluorescence components (C1–C4) for the DOM were identified in all the samples by the EEM-FARAFAC, which may be assigned to be as follows: UVA fulvic-like substances with maximum Ex/Em loading at 380/485 nm (C1), UVC fulvic-like substances with maximum Ex/Em loading at 340/430 nm (C2), humic-like substances with maximum Ex/Em loading at 460/540 nm (C3), and tryptophan-like substances with maximum Ex/Em loading at 285/350 nm (C4) (Figure 1 and Figure 2) [2,31,32,33]. Among them, C1 (37.55–46.81% of total fluorescent components) and C2 (29.91–35.53% of total fluorescent components) were the dominant EEM components in the DOM of all the water samples, whilst C4 had the lowest abundance, accounting for 4.42–10.88% (Figure 3). Among the treatments, the S and M samples had the highest and lowest fluorescence intensities, respectively (Figure 3). The M and SMP samples had the highest proportion of C3 (18.08% for the M and 19.61% for the SMP) and the lowest proportions of C1 (37.55–41.64% of total fluorescent components) and C2 (29.91–33.79% of total fluorescent components). Meanwhile, the M samples possessed the highest proportion of C4 (10.35 ± 0.70% of total fluorescent components) (Figure 3).

3.4. Correlation of DOM Components with Basic Properties and Spectral Indices of DOM

The PCA plot showed the multiple variations of DOM components among different treatments (Figure 4). The PC1 and PC2 axes in the PCA plot explained 78.64% and 20.61% of the total variation, respectively. The PCA showed a distinct separation for different treatments except for the SP and P samples. Along the PC1 axis, the SMP and M were separated from the other treatments, being mainly ascribed to the C3 and C4 components. Along the PC2, the C1 and C3 components mainly contributed to a net differentiation of the M samples from the SMP samples (Figure 4). The heatmap plot showed that C3 and C4 abundances were positively correlated with BIX, pH, and DTN and were negatively correlated with HIX (Figure 5). In contrast, C1 showed negative correlations with FI, BIX, pH, and DTN and a positive correlation with HIX. Among the four components, only C2 was correlated with DOC (p < 0.01) (Figure 5).

4. Discussion

4.1. Chemical Characteristics of DOM in Decomposition of Different Organic Materials in Alpine Wetland

The decomposition of all the organic materials was beneficial for the nitrogen release and the increase of DTN in the water (Table 1). Higher total nitrogen and phosphorus in the yak manure than in the peat soil and plant litter led to higher DTN and P content in the M, SM, and SMP samples [18,19]. In the present study, the decomposition of yak manure, plant litter, and peat soil resulted in a significant rise in water pH and showed a weak alkaline environment (Table 1). This is in agreement with many previous studies and may be due to the decarboxylation and excess alkali in the plant litter decomposition process and the high alkalinity of the manure and peat soil [13,29].
The addition of all the organic materials induced a significant increase in the DOC in the water samples (Table 1), which was mainly attributed to organic carbon released from these organic materials [23,33]. The higher DOC and DOC/DTN in the P, SP, and SMP samples than in the other samples may imply that plant litter decomposition seemed to be more liable to release DOC than the yak manure and peat soil. This may be due to the higher concentration of total organic carbon in the plant litter than in the other organic materials. In addition, the higher humification degree of DOM produced from the plant litter decomposition may also contribute to DOC accumulation, which can be proved by the high HIX of DOM in the P samples [16,34]. It is also worth noting that the addition of peat soil brought about the lowest DOC in the S samples (Table 1), which may be because organic matter in the peat soil had endured a long-term decomposition process and was, therefore, not easy to release [29,35,36]. This can also be proved by the highest HIX values for the S samples compared with the other treatments (Table 2).
The FI values for most of the samples fell in the range of 1.4–1.7 (Table 2), indicating that both the autochthonous and the allochthonous sources contributed to the water DOM [21,30]. Meanwhile, the BIX values of all the samples were less than 0.8, indicating that the water DOM in the water samples mainly relied on allochthonous sources along with organic materials amendment [15,16]. This may also hint that the contribution of autochthonous microbial activity and alga to water DOM was limited by low temperature and anaerobic environment in alpine wetlands [10,25,26]. Additionally, the M samples possessed the highest BIX values, indicating that the addition of yak manure promoted biological activity more than the other organic materials in alpine wetlands [4,6,8]. This is partly because the DOM in the M samples had the lowest humification degree and was relatively easy for microbes and alga in alpine wetlands to use [22,33]. When the decomposition process, combined with yak manure, peat soil, and plant litter, occurs in alpine wetlands, the humification degree of DOM in the water may decrease.

4.2. DOM Compositions in Decomposition of Different Organic Materials in Alpine Wetland

The addition of different organic materials greatly affected DOM composition in alpine wetland water (Figure 3 and Figure 4). The relative abundance of C4 fluorescence components in the M water samples was significantly promoted by the addition of yak manure, which corresponds with the previous literature on manure amendment (Figure 3) [18,37]. This may be attributed to the fact that the introduction of protein and amino acids contained in the yak digestive residue into wetland water was beneficial for microbial activity and the increase of tryptophan-like substances in DOM [23,25]. It has been reported that peat soil was rich in UV fulvic-like substances that had gone through a long-term decomposition process under high-intensity UV radiation in the Tibetan Plateau [26,34]. Therefore, the addition of peat soil contributed to the C1 fluorescence component and the highest DOM humification degree, as indicated by the highest HIX in the S samples (Table 2, Figure 3). The PCA plot showed that C2 primarily contributed to the separation of the P and the SP treatments, which may be due to the fact that the plant litter decomposition process may release UVC fulvic-like substances (Figure 4) [15,32]. It is worth noting that DOM composition in the alpine wetland water did not change significantly when compared to the single peat soil decomposition due to its combined decomposition with yak manure or plant litter (Figure 3 and Figure 4). This may be attributed to the lack of either sufficient liable organic substances in the SM treatment, as shown by its low DOC content, or effective microbial activity in the SP treatment, as shown by the low BIX values (Table 1 and Table 2) [19,20,23]. However, in the SMP samples, the promotion of the relative abundance of the C3 component may suggest that stimulating microorganisms by manure addition can facilitate plant litter decomposition and boost humic-like substances in water DOM [27,38].
The positive correlation between the DTN and C4 component can be explained by the fact that these protein-like amino acids contained nitrogen, and their production enhanced the DTN in the water DOM (Figure 5) [16,17]. The higher relative abundance of the C4 component implied more microbial activity in the water and, therefore, matched the positive correlation between the C4 component and FI and BIX (Table 2 and Figure 5) [24,25]. In addition, the negative relationship of the C4 component with HIX was in line with previous studies that reported that tryptophan-like substances had low humification degrees [21,23]. In the present study, the C1 component was negatively correlated with FI and BIX and positively with HIX, which may hint that the C1 component may be mostly derived from allochthonous sources and have a high humification degree (Figure 5) [32,36].

5. Conclusions

Here, we conducted a decomposition experiment to follow the chemical characteristics and composition of DOM as affected by the decomposition of different organic materials in alpine wetland water. The decomposition of organic material significantly affected chemical properties, sources, humification degree, and fluorescence components of the water DOM. Decomposition of all the organic materials increased DOC and DTN in the water. The FI and BIX showed both the autochthonous and the allochthonous sources contributed to the water DOM of all the water samples. The C1 and C2 were primary fluorescence components among the four identified DOM components. The DOM in the S treatment was more derived from allochthonous sources and had a higher humification degree than the other treatments. The enhancement of the C4 component in the M treatment was mainly attributed to the fact that the yak manure contained protein and amino acids, which were beneficial for microbial activity in the alpine wetland water. In addition, the yak manure in the SMP treatment may stimulate microbial activity and facilitate the decomposition of plant litter and peat soil, therefore boosting the C3 components. Our findings may deepen the understanding of the DOM biogeochemical cycling in the alpine wetland ecosystem and have significant implications for the development of wetland biomass management with the objective of maintaining wetland ecosystem services.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/agronomy14091979/s1, Table S1: Quantities of peat soil, plant litter, and yak manure used in different treatments.

Author Contributions

Writing—original draft preparation, Y.S.; Writing—review and editing, M.L.; Visualization, W.Y.; Investigation, Y.W. and W.Y., Funding acquisition, M.L. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Fundamental Research Funds of Chinese Academy of Forestry (CAFYBB2021QB008) and the National Key Research and Development Program (2017YFA0604903).

Data Availability Statement

Data are contained within the article and Supplementary Materials.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. EEM spectra of dissolved organic matter in water for different treatments: S, addition of peat soil, P, addition of plant litter, M, addition of yak manure, SM, combined addition of peat soil and yak manure, SP, combined addition of peat soil and plant litter, SMP, combined addition of peat soil, plant litter, and yak manure.
Figure 1. EEM spectra of dissolved organic matter in water for different treatments: S, addition of peat soil, P, addition of plant litter, M, addition of yak manure, SM, combined addition of peat soil and yak manure, SP, combined addition of peat soil and plant litter, SMP, combined addition of peat soil, plant litter, and yak manure.
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Figure 2. Spectra loading of fluorescence components (C1–C4) of dissolved organic matter in water by the EEM spectroscopy and parallel factor analysis.
Figure 2. Spectra loading of fluorescence components (C1–C4) of dissolved organic matter in water by the EEM spectroscopy and parallel factor analysis.
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Figure 3. Intensity (A) and percent (B) of four fluorescence components (C1–C4) of dissolved organic matter in water under different treatments: S, addition of peat soil, P, addition of plant litter, M, addition of yak manure, SM, combined addition of peat soil and yak manure, SP, combined addition of peat soil and plant litter, SMP, combined addition of peat soil, plant litter, and yak manure.
Figure 3. Intensity (A) and percent (B) of four fluorescence components (C1–C4) of dissolved organic matter in water under different treatments: S, addition of peat soil, P, addition of plant litter, M, addition of yak manure, SM, combined addition of peat soil and yak manure, SP, combined addition of peat soil and plant litter, SMP, combined addition of peat soil, plant litter, and yak manure.
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Figure 4. Principle component analysis plot for the fluorescence components (C1–C4) of dissolved organic matter in water for different treatments: S, addition of peat soil (diamond), P, addition of plant litter (triangle), M, addition of yak manure (plus), SM, combined addition of peat soil and yak manure (square), SP, combined addition of peat soil and plant litter (multiple), SMP, combined addition of peat soil, plant litter, and yak manure (circle).
Figure 4. Principle component analysis plot for the fluorescence components (C1–C4) of dissolved organic matter in water for different treatments: S, addition of peat soil (diamond), P, addition of plant litter (triangle), M, addition of yak manure (plus), SM, combined addition of peat soil and yak manure (square), SP, combined addition of peat soil and plant litter (multiple), SMP, combined addition of peat soil, plant litter, and yak manure (circle).
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Figure 5. Heatmap showed a correlation of fluorescence components (C1-C4) with basic properties and spectral indices of the DOM in collected samples. HIX, humification index, FI, fluorescence index, BIX, biological index. DOC, dissolved organic carbon, DTN, dissolved total nitrogen. * and ** represented significant correlations at p < 0.05 and 0.01.
Figure 5. Heatmap showed a correlation of fluorescence components (C1-C4) with basic properties and spectral indices of the DOM in collected samples. HIX, humification index, FI, fluorescence index, BIX, biological index. DOC, dissolved organic carbon, DTN, dissolved total nitrogen. * and ** represented significant correlations at p < 0.05 and 0.01.
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Table 1. Basic properties of the collected water samples for different treatments.
Table 1. Basic properties of the collected water samples for different treatments.
TreatmentspHDOC/mg L−1DTN/mg L−1DOC/DTNP/mg L−1K/mg L−1Fe/mg L−1Ca/mg L−1
S8.49 ± 0.05 b128.83 ± 17.89 c11.91 ± 0.55 b10.83 ± 0.42 b0.086 ± 0.010 b32.56 ± 4.29 a0.084 ± 0.011 a49.71 ± 7.58 a
M8.75 ± 0.08 a179.66 ± 11.95 b15.44 ± 0.67 a11.64 ± 0.93 b0.121 ± 0.016 a35.96 ± 5.81 a0.089 ± 0.012 a55.68 ± 6.42 a
P8.57 ± 0.09 b213.44 ± 10.93 a10.56 ± 0.31 b20.23 ± 1.62 a0.099 ± 0.014 ab41.85 ± 6.72 a0.079 ± 0.017 a51.82 ± 8.33 a
SP8.43 ± 0.05 c254.73 ± 12.26 a11.61 ± 0.33 b21.96 ± 1.46 a0.092 ± 0.011 b37.82 ± 5.22 a0.091 ± 0.016 a49.69 ± 6.95 a
SM8.51 ± 0.05 c148.36 ± 22.82 bc13.75 ± 0.27 ab10.78 ± 3.10 b0.122 ± 0.020 a34.98 ± 4.96 a0.085 ± 0.014 a48.35 ± 7.86 a
SMP8.58 ± 0.05 b197.33 ± 16.42 b13.09 ± 0.37 ab8.22 ± 1.43 b0.125 ± 0.019 a37.43 ± 4.37 a0.093 ± 0.023 a52.74 ± 6.99 a
S, addition of peat soil, P, addition of plant litter, M, addition of yak manure, SM, combined addition of peat soil and yak manure, SP, combined addition of peat soil and plant litter, SMP, combined addition of peat soil, plant litter, and yak manure. DOC, dissolved organic carbon, DTN, dissolved total nitrogen. Different letters represent significant differences at p < 0.05.
Table 2. Spectral indices of water DOM for different treatments.
Table 2. Spectral indices of water DOM for different treatments.
TreatmentsFIBIXHIX
S1.458 ± 0.039 c0.418 ± 0.011 c2.907 ± 0.128 a
M1.612 ± 0.030 a0.578 ± 0.016 a1.524 ± 0.053 c
P1.524 ± 0.026 ab0.459 ± 0.008 bc2.327 ± 0.125 b
SM1.485 ± 0.007 bc0.430 ± 0.006 c2.770 ± 0.071 ab
SP1.440 ± 0.066 c0.501 ± 0.010 ab2.260 ± 0.046 c
SMP1.514 ± 0.079 bc0.463 ± 0.028 bc2.165 ± 0.293 b
S, addition of peat soil, P, addition of plant litter, M, addition of yak manure, SM, combined addition of peat soil and yak manure, SP, combined addition of peat soil and plant litter, SMP, combined addition of peat soil, plant litter, and yak manure. HIX, humification index, FI, fluorescence index, BIX, biological index. Values are given with mean ± standard error. Different letters represent significant differences at p < 0.05.
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Song, Y.; Li, M.; Wang, Y.; Yang, W. Characteristics of Dissolved Organic Matter as Affected by Decomposition of Different Organic Materials in Alpine Wetland. Agronomy 2024, 14, 1979. https://doi.org/10.3390/agronomy14091979

AMA Style

Song Y, Li M, Wang Y, Yang W. Characteristics of Dissolved Organic Matter as Affected by Decomposition of Different Organic Materials in Alpine Wetland. Agronomy. 2024; 14(9):1979. https://doi.org/10.3390/agronomy14091979

Chicago/Turabian Style

Song, Yueguang, Meng Li, Yifei Wang, and Weishan Yang. 2024. "Characteristics of Dissolved Organic Matter as Affected by Decomposition of Different Organic Materials in Alpine Wetland" Agronomy 14, no. 9: 1979. https://doi.org/10.3390/agronomy14091979

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