Preamble

ARID ZONE RESEARCH Vol. 42 No. 7 Jul. 2025

Effects of Meteorological Factors on Litter Decomposition of the Fungal Endophyte Stipa purpurea Symbiont in Alpine Grassland

GUO Qiang¹, WANG Yuqin², SONG Meiling²
¹Xinghai County Meteorological Bureau, Xinghai 813300, Qinghai, China
²Academy of Animal and Veterinary Science of Qinghai University, Xining 810016, Qinghai, China

Abstract

Litter decomposition plays a crucial role in carbon and nutrient cycling within terrestrial ecosystems, with climate conditions serving as the primary determinant of decomposition rates. However, research on litter decomposition in alpine grassland ecosystems remains limited. To investigate how meteorological factors influence the decomposition and nutrient release processes of Stipa purpurea litter under climate change scenarios, this study examined endophyte-infected (E⁺) and endophyte-free (E⁻) S. purpurea plants from alpine grasslands using the litterbag method. We analyzed decomposition characteristics, litter component changes, and the impact of meteorological factors on the endophytic symbiont's litter decomposition. The results demonstrated that E⁺ litter decomposed at a significantly higher rate with a shorter decomposition cycle compared to E⁻ litter. Over time, the total nitrogen content in S. purpurea litter showed an increasing trend, while lignin content shifted from being significantly higher in E⁺ to showing no significant difference between treatments, and cellulose content transitioned from being significantly lower in E⁺ to no significant difference (P < 0.05). Regardless of endophyte status, litter weight and mass loss rate were significantly correlated with monthly mean air temperature and monthly mean ground temperature (P < 0.05). Precipitation was positively correlated with the decomposition rate of S. purpurea litter, while total nitrogen content showed significant positive correlations with temperature and precipitation (P < 0.05). Lignin and cellulose contents were negatively correlated with temperature and precipitation. Sunshine duration also significantly influenced decomposition, showing strong correlations with lignin, cellulose, and litter weight. Overall, endophytic fungi accelerated the decomposition process of S. purpurea litter, and meteorological factors exerted consistent effects on both E⁺ and E⁻ litter decomposition.

Keywords: Stipa purpurea; endophytic fungi; litter decomposition; meteorological factors; alpine grassland

Introduction

Litter constitutes a vital component of grassland ecosystems, connecting producers, decomposers, and consumers through ecological processes of material cycling, energy flow, and information transfer. Litter also regulates surface microenvironments by forming buffer layers. As the core stage of organic matter degradation, litter decomposition represents a critical process for mineral nutrient turnover and cycling in ecosystems. This process enhances soil nutrient inputs by releasing nitrogen (N), phosphorus (P), potassium (K), and other essential elements, thereby increasing plant-available nutrients and promoting productivity. The decomposition rate is jointly determined by intrinsic factors—including litter chemistry such as N, lignin, and cellulose contents—and extrinsic factors such as soil microorganisms, soil fauna, and climatic conditions. At global and regional scales, climate factors, particularly temperature and precipitation, predominantly control litter decomposition, while at smaller spatial scales or under stable climatic conditions, litter chemical composition and soil biota become more influential.

Recent research has increasingly focused on how climate factors affect litter decomposition in the context of global warming and altered precipitation patterns. Studies have revealed that elevation effects on litter decomposition may be temperature-driven, seasonal litter quantity variations may relate to precipitation regimes, and decomposition rates correlate positively with ultraviolet radiation. However, litter components exhibit heterogeneous sensitivity to meteorological factors, resulting in differential impacts on various litter constituents. While most decomposition studies have focused on forest ecosystems, the unique environmental conditions of alpine grasslands—high altitude, intense radiation, and aridity—suggest that climate may play a particularly important role in litter decomposition and nutrient cycling. Therefore, investigating meteorological influences on litter decomposition in these ecosystems is essential for understanding how future climate change will affect alpine grassland processes.

Stipa purpurea, a cold- and drought-tolerant species, represents the most widely distributed and characteristic community type in the alpine grasslands of the Qinghai-Tibet Plateau, playing crucial roles in sand fixation, soil conservation, and providing foundational resources for pastoralism. Recent research on S. purpurea has primarily examined community structure, grazing responses, soil nutrients, and microbial communities, yet few studies have investigated how meteorological factors influence its litter decomposition. Notably, S. purpurea exhibits significant endophytic fungal symbiosis, which can alter host plant metabolism and affect litter decomposition, while climate factors simultaneously regulate decomposition processes. To elucidate the roles of both meteorological factors and endophytic fungi in S. purpurea litter decomposition and identify key climatic drivers, this study examined the endophytic symbiont to provide theoretical insights into how climate change affects material cycling in alpine grassland ecosystems.

Materials and Methods

1.1 Litter Collection

Following the methods of Li et al. [reference], we detected endophytic fungi in S. purpurea inflorescences collected from the field. Endophyte-infected seeds were obtained, and endophyte-free seeds were produced through high-temperature and high-humidity treatment to remove fungal symbionts. Both E⁺ and E⁻ seeds were planted in sterilized soil in greenhouse conditions with 50 cm spacing between pots to prevent cross-contamination. During the late growth stage, aboveground senesced tissues were collected, air-dried, and stored as experimental litter material.

1.2 Experimental Design

The field experiment was conducted in Guinan County, Qinghai Province (35°34′11″N, 100°46′51″E), a typical alpine meadow region. Senesced plant tissues were cut into 5–10 cm segments, and 5.00 g of litter was placed in 10 cm × 10 cm nylon mesh bags (1 mm mesh size). In mid-September, litterbags were randomly placed at the experimental site after removing aboveground vegetation to ensure direct contact with the soil surface. Bags were secured with nails, spaced >10 cm apart. At 1, 2, 3, 4, 5, 6, 8, 10, and 12 months after placement, five litterbags per treatment were randomly collected, air-dried, and analyzed for litter weight, total N, lignin, and cellulose content.

1.3 Measurements and Calculations

All collected samples were analyzed for total nitrogen, lignin, and cellulose content. Total nitrogen was determined using an automatic Kjeldahl nitrogen analyzer [reference]. Lignin and cellulose contents were measured using the acid detergent fiber method [reference]. Meteorological data were obtained from the Guinan National Basic Meteorological Station (35°35′12″N, 100°44′24″E, 3107 m elevation).

Litter mass loss rate (Mc) was calculated as:
$$Mc = \frac{W_0 - W_t}{W_0} \times 100\%$$

A modified Olson exponential model was used to calculate decomposition rate (k):
$$W_t = W_0 \times e^{-kt}$$

The time required for 50% and 95% decomposition was calculated as:
$$T_{50\%} = \frac{-\ln(1-0.50)}{k}$$
$$T_{95\%} = \frac{-\ln(1-0.95)}{k}$$

where $W_t$ is the weight at time $t$, $W_0$ is the initial weight, $k$ is the decomposition rate constant, and $t$ is decomposition time.

1.4 Data Analysis

Data were organized and plotted using Microsoft Excel. SPSS 27.0 software was used for one-way ANOVA to examine temporal changes in litter parameters, independent samples t-tests to analyze differences between E⁺ and E⁻ treatments for litter weight, total N, lignin, and cellulose, and Pearson correlation analysis to assess relationships between decomposition characteristics and meteorological factors (significance defined as P < 0.05). Redundancy analysis (RDA) was performed to examine relationships between environmental variables (meteorological factors) and litter decomposition characteristics.

Results

2.1 Decomposition Characteristics of S. purpurea Litter

Changes in litter weight and mass loss rate are shown in [FIGURE:1]. Over time, litter weight decreased substantially in both E⁺ and E⁻ treatments, with the decline slowing after June. Litter weight in E⁺ was significantly lower than in E⁻ after 6 months (P < 0.05). Mass loss rate increased with decomposition time, being rapid before March and slower thereafter. The mass loss rate of E⁺ litter was significantly higher than that of E⁻ (P < 0.05). Exponential regression equations showed good fit (R² > 0.80, P < 0.01), with decomposition rates of 1.1024 yr⁻¹ for E⁺ and 0.69698 yr⁻¹ for E⁻. Estimated half-decomposition times were 0.80 and 1.05 years, and 95% decomposition times were 3.45 and 4.54 years, respectively, indicating E⁺ decomposed faster with a shorter cycle.

2.2 Litter Composition Analysis

Total nitrogen content in S. purpurea litter increased over time, with E⁺ showing higher N content than E⁻ (P < 0.05) [FIGURE:2]. Lignin content decreased overall, with E⁺ having significantly higher lignin than E⁻ initially (P < 0.05), but differences became non-significant after 6 months. Cellulose content showed an initial increase followed by decrease, with E⁺ having significantly lower cellulose than E⁻ at 1 month (P < 0.05). Both treatments showed initial increases, but cellulose content decreased significantly over time, stabilizing after 8 months. Overall, E⁺ litter had lower cellulose content throughout decomposition.

2.3 Meteorological Factor Variation

Monthly mean air temperature and precipitation showed unimodal distributions [FIGURE:3]. Mean temperature peaked in July then declined to approximately -10°C. Precipitation peaked in July–August, with July values significantly higher than other months. Mean ground temperature followed a similar pattern, peaking in July then dropping to around -10°C. Sunshine duration showed no clear annual pattern, reaching maximum values in May and minimum values in December–January.

2.4 Relationships Between Decomposition and Meteorological Factors

Correlation analysis revealed that E⁺ litter weight was significantly negatively correlated with monthly mean air and ground temperatures (P < 0.01), while mass loss rate was significantly positively correlated with these temperatures (P < 0.01) [TABLE:2]. Total N content was significantly positively correlated with temperature and precipitation (P < 0.05), while lignin and cellulose contents were significantly negatively correlated with temperature (P < 0.01). For E⁻ litter, total N content was significantly positively correlated with temperature (P < 0.01), while lignin and cellulose were significantly negatively correlated (P < 0.05). Litter weight and mass loss rate were significantly correlated with precipitation (P < 0.05), but not with sunshine duration.

RDA analysis showed that for E⁺, the first and second axes explained 42.9% and 18.1% of variation, respectively (cumulative 61.0%) [FIGURE:4]. Lignin, cellulose, and litter weight were positively correlated with sunshine duration, while total N was negatively correlated with meteorological factors. For E⁻, the first and second axes explained 51.4% and 26.1% of variation (cumulative 77.5%). Cellulose, lignin, and litter weight were positively correlated with sunshine duration, while total N was negatively correlated with temperature, ground temperature, and precipitation. These results indicate that meteorological factors significantly influence S. purpurea litter decomposition, with stronger correlations observed for E⁺.

Discussion

3.1 Decomposition Rate and Substrate Quality Dynamics

Litter decomposition involves mineral element and nutrient release, with substrate quality—including N, lignin, and cellulose contents—being a key intrinsic factor. Microorganisms are the primary drivers of decomposition, regulating decomposition rates. Recent studies have documented widespread symbiosis between grasses and endophytic fungi, which can indirectly affect decomposition by competing with soil saprotrophs. In this study, both E⁺ and E⁻ litter showed rapid initial weight loss that slowed after 6 months, consistent with typical decomposition patterns. The exponential model revealed that E⁺ decomposed approximately 1.5 times faster than E⁻, with a substantially shorter decomposition cycle, confirming that endophytic fungi accelerate S. purpurea litter decomposition. This aligns with Dereske et al.'s findings that endophyte infection enhanced decomposition of Ammophila breviligulata litter, likely by altering soil microbial community structure and abundance.

Nutrient content changes during decomposition directly reflect element transformation processes and influence decomposition rates. Three nutrient dynamics patterns have been identified: direct release, leaching-immobilization-release, and immobilization-release. Total N content, a critical quality factor affecting decomposition rate, showed a fluctuating pattern of initial decrease followed by increase in both treatments, similar to the leaching-immobilization-release pattern. The overall higher N content in E⁺ litter suggests that endophyte presence increases nutrient demand during decomposition. Lignin and cellulose, the main litter components whose degradation rates affect carbon balance, decreased significantly over time. E⁺ litter showed faster lignin degradation than E⁻, while cellulose content was consistently lower in E⁺, indicating that endophytic fungi accelerate cellulose degradation, possibly by increasing cellulase activity.

3.2 Effects of Meteorological Factors on Endophytic Symbiont Decomposition

Beyond litter quality and soil biota, environmental conditions critically influence decomposition, with climate (temperature, moisture) considered the most important factor. In this study, both E⁺ and E⁻ litter showed consistent responses to meteorological factors, though correlations were stronger for E⁺. Litter weight and mass loss rate were significantly correlated with monthly mean air and ground temperatures, indicating that temperature controls microbial activity and metabolism, thereby regulating decomposition. This supports Kravchenko et al.'s findings that decomposition rates increase with ground temperature. Precipitation was positively correlated with decomposition rate, as high-intensity rainfall can accelerate surface litter decomposition and leaching of water-soluble compounds. However, some studies have found no significant precipitation effects, suggesting that impacts depend on precipitation magnitude, surface moisture, and litter characteristics.

Sunshine duration also significantly affected decomposition, showing strong correlations with lignin, cellulose, and litter weight. In arid and semi-arid ecosystems, solar radiation and ultraviolet light are important decomposition drivers that can preferentially degrade lignin. The high radiation, aridity, and altitude of alpine grasslands create conditions where microbial activity is relatively low, making photodegradation particularly important. The stronger correlations between meteorological factors and E⁺ decomposition suggest that climate may enhance the endophyte-mediated acceleration of decomposition. While this study examined overall meteorological effects, future research should simulate different temperature, light, and precipitation conditions to clarify the relative contributions and mechanisms of individual meteorological factors, providing scientific basis for understanding litter decomposition responses to climate change.

Conclusion

This study of Stipa purpurea endophytic fungal symbiont litter decomposition revealed two key findings: (1) Endophytic fungi positively enhanced the decomposition rate and shortened the decomposition cycle of host plant litter, promoting degradation of N, lignin, and cellulose over time. (2) Air temperature, ground temperature, and precipitation were key meteorological factors influencing decomposition, with sunshine duration also playing a significant role. Meteorological factors affected both E⁺ and E⁻ litter decomposition consistently, though correlations were stronger for E⁺ litter.

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