A stronger advance of urban spring vegetation phenology narrows vegetation productivity difference between urban settings and natural environments

The Interaction Among Rhizosphere Soil Nutrients, Metabolites, and Microbes Determines the Productivity of Perennial Cultivated Grassland in Qinghai-Tibet Plateau

The rhizosphere, as the primary site of plant-soil -microbe interactions, plays an important role in plant productivity. The influence of plant species on rhizosphere soil properties and how this influence shapes the productivity of grassland ecosystems remains poorly understood. Therefore, this study analyzed the changes in bacterial community structure and metabolites in the rhizosphere soil of perennial cultivated grassland. The aim was to elucidate the pathways and underlying mechanisms by which soil physicochemical properties, bacterial community structure, and rhizosphere metabolites influence productivity. Taking perennial monocropping grasslands established with three common grass species from the Qinghai -Tibet Plateau as the research objects, a comprehensive study was conducted using replicated field trials. Rhizosphere soil samples were collected from Elymus breviaristatus, Festuca sinensis, and Poa pratensis. The results indicated significant differences in productivity, soil physicochemical properties, bacterial diversity, and community structure among the monocropping grasslands. Among them, ANPP (589.17 g·m-2), root biomass (3601.67 g·m-2), moisture (18.15%) and Verrucomicrobiota (3.60%) of Elymus breviaristatus are higher than those of Festuca sinensis and Poa pratensis, while the relative abundance of Firmicutes (0.82%) is lower than that of Festuca sinensis and Poa pratensis. The topological characteristics of soil bacterial networks varied among the different grass species. The abundances of metabolites consisting of phenylalanine, proline, raffinose, maltotriose, uridine, and 2-methylbenzaldehyde differed among different treatments. Pathway analysis highlighted the upregulation of ABC transporters and pyrimidine metabolism pathways in Elymus breviaristatus compared to Festuca sinensis and Poa pratensis. Moreover, Elymus breviaristatus secreted more uridine, which prevents the recruitment of pathogenic bacteria (such as Firmicutes) and promotes the recruitment of Verrucomicrobiota, thus improving grassland productivity. These findings show that the productivity of perennial monocropping grasslands around Qinghai Lake is the result of the interaction among rhizosphere soil nutrients, metabolites, and microorganisms. From the ecological point of view, Elymus breviaristatus is more conducive to the improvement of forage yield and the restoration of degraded grassland.

Long-term species-level observations indicate the critical role of soil moisture in regulating China's grassland productivity relative to phenological and climatic factors

As a sensitive indicator of climate change and a key variable in ecosystem surface-atmosphere interaction, vegetation phenology, and the growing season length, as well as climatic factors (i.e., temperature, precipitation, and sunshine duration) are widely recognized as key factors influencing vegetation productivity. Recent studies have highlighted the importance of soil moisture in regulating grassland productivity. However, the relative importance of phenology, climatic factors, and soil moisture to plant species-level productivity across China's grasslands remains poorly understood. Here, we use nearly four decades (1981 to 2018) of in situ species-level observations from 17 stations distributed across grasslands in China to examine the key mechanisms that control grassland productivity. The results reveal that soil moisture is the strongest determinant of the interannual variability in grassland productivity. In contrast, the spring/autumn phenology, the length of vegetation growing season, and climate factors have relatively minor impacts. Generally, annual aboveground biomass increases by 3.9 to 25.3 g∙m2 (dry weight) with a 1 % increase in growing season mean soil moisture across the stations. Specifically, the sensitivity of productivity to moisture in wetter and colder environments (e.g., alpine meadows) is significantly higher than that in drier and warmer environments (e.g., temperate desert steppes). In contrast, the sensitivity to the precipitation of the latter is greater than the former. The effect of soil moisture is the most pronounced during summer. Dominant herb productivity is more sensitive to soil moisture than the others. Moreover, multivariate regression analyses show that the primary climatic factors and their attributions to variations in soil moisture differ among the stations, indicating the interaction between climate and soil moisture is very complex. Our study highlights the interspecific difference in the soil moisture dependence of grassland productivity and provides guidance to climate change impact assessments in grassland ecosystems.