Grazing exclusion had greater effects than nitrogen addition on soil and plant community in a desert steppe, Northwest of China

Responses of soil fertility indicators and fungi community diversity to fertilization strategies in legume-grass mixtures

Introduction

Alfalfa-grass binary mixtures outperformed monocultures in nutrient use, soil nutrient content, and biomass yield. Nonetheless, the impact of fertilization strategies on fungal community composition and ecological functions in legume-Grass mixtures remains under-researched. This study aimed to explore the effects of different fertilization strategies on soil fungal community distribution and soil environmental characteristics.

Methods

A field experiment in Gansu, China, has been conducted to explore the effects of five different fertilization strategies-no fertilization (CK), three partial fertilization methods (+PK, +NK, +NP), and balanced fertilization (+NPK)-on fungal population richness, community composition, and soil environmental drivers. Rhizosphere soils from the five treatments were sampled and investigated using high-throughput ITS sequencing.

Results

Compared to CK, +NPK led to higher soil capabilities (P< 0.05), soil organic matter (SOM), available nitrogen (AN), available phosphorus (AP), and available potassium (AK) increased by an average of 29.7 %, 42.3 %, 101.2 %, and 24.3 %, respectively; alkaline phosphatase (APA), catalase (CAT), and sucrase (SA) increased by an average of 56.6 %, 31.8 %, and 46.7 %, respectively; soil microbial biomass carbon (SMBC), soil microbial biomass nitrogen (SMBN), and soil microbial biomass phosphorus (SMBP) increased by an average of 64.8 %, 65.1 %, and 60.4 %, respectively. The dominant fungi in the rhizosphere soil were Mortierellomycota and Ascomycota, accounting for 82.2%-92.3%. The fungal species richness was the highest in the +PK treatment. From the NMDS and RDA analysis, it can be discerned that SA, AK, and CAT were the key environmental factors influencing the structure of the inter-root soil fungal community in alfalfa; CAT and SOM were the key environmental factors influencing the structure of the inter-root soil fungal community in awnless brome.

Discussion

Our findings investigated the optimal fertilizer strategy for legume-Grass mixtures. Results provided a technical basis for scientific fertilizer application and development of local mixed grassland ecosystems.

Combining different species in restoration is not always the right decision: Monocultures can provide higher ecological functions than intercropping in a desert ecosystem

Vegetation restoration in deserts is challenging due to these ecosystems' inherent fragility and harsh environmental conditions. One approach for active restoration involves planting native species, which can accelerate the recovery of ecosystem functions. To ensure the effectiveness of this process, carefully selecting species for planting is crucial. Generally, it is expected that a more diverse mix of species in the plantation will lead to the recovery of a greater number of ecosystem functions, especially when the selected species have complementary niche traits that facilitate maximum cooperation and minimize competition among them. In this study, we evaluated the planting of two native species from the hyper-desert of Taklamakan, China, which exhibit marked morpho-physiological differences: a phreatophytic legume (Alhagi sparsifolia) and a halophytic non-legume (Karelinia caspia). These species were grown in both monoculture and intercrop communities. Monoculture of the legume resulted in the highest biomass accumulation. Intercropping improved several ecosystem functions in the 50 cm-upper soil, particularly those related to phosphorus (P), carbon (C), and sulfur (S) concentrations, as well as soil enzyme activities. However, it also increased soil sodium (Na+) concentration and pH. Halophyte monocultures enhanced ecological functions associated with nitrogen concentrations in the upper soil and with P, S, C, and cation concentrations (K+, Ca2+, Mg2+, Cu2+, Fe2+, Zn2+, Co2+, Ni2+), along with enzyme activities in the deep soil. It also maximized Na+ accumulation in plant biomass. In summary, we recommend legume monoculture when the primary goal is to optimize biomass accumulation. Conversely, halophyte monoculture is advisable when the objective is to extract sodium from the soil or enhance ecosystem functions in the deep soil. Intercropping the two species is recommended to maximize the ecosystem functions of the upper soil, provided there is no salinization risk. When planning restoration efforts in desert regions, it is essential to understand the impact of each species on ecosystem function and how complementary species behave when intercropped. However, these interactions are likely species- and system-specific, highlighting the need for more work to optimize solutions for different arid ecosystems.