Relationship between leaf phosphorus concentration and soil phosphorus availability across Inner Mongolia grassland

Nutrient budgets drive the changes in shoot N and P concentrations of plants in Inner Mongolia's grasslands over the past 40 years

The nutrient budgets of grassland ecosystems have been extensively disturbed by human activity. The aims of this study were to quantify nitrogen (N) and phosphorus (P) budgets, and evaluate their contributions to changes in shoot nutrient concentrations of dominant plants in Inner Mongolia's grasslands over the past 40 years. N and P budgets were assessed using a nutrient budget model based on flowing intensity of nutrients in and out of the grassland. Meta-analysis was then conducted to quantify changes in shoot nutrient concentrations. The N budget remained positive and continued to increase throughout the study period, while enhanced N deposition and increased supplementary feeding dominated N input (76% of the total in 2017). In contrast, the P budget was negative until 2003, and became positive thereafter. The P input was mainly attributed to supplementary feeding (88% of the total in 2017). The mean shoot N concentration in 1979-1986 was 2.25%, while an increase to 2.53% was observed in 2006-2016. In contrast, the mean shoot P concentration was 0.17% in 1979-1991, subsequently leveling off at 0.17% in 2006-2016. The mean shoot N: P ratio basically remain unchanged over time from 16.72 to 15.85. The N surplus caused major increases in the shoot N concentration of the grassland plants; also, the increased P budget to compensate for past P deficiency resulted in no significant change of shoot P concentrations. Consequently, the grassland system had been in the joint N and P co-limitation over the past 40 years.

Seasonal Variation Characteristics of C, N, and P Stoichiometry and Water Use Efficiency of Messerschmidia sibirica and Its Relationship With Soil Nutrients

The seasonal dynamic characteristics of C, N, and P stoichiometry and water use efficiency (WUE) of Messerschmidia sibirica and the soil in the Yellow River Delta (YRD) were studied. The correlations of stoichiometric characteristics and WUE between organs of M. sibirica and soil were analyzed. The results showed that: (1) the contents of C, N, and P and their stoichiometric ratios in various organs of M. sibirica varied with seasons. The seasonal dynamics of leaf N:P showed that the degree of nutrient restriction by N decreased in July and increased in September. (2) The contents of C, N, and P, as well as their stoichiometric ratio, showed a high correlation throughout the growing season, with N:P showing a significantly positive correlation among organs and the lowest stoichiometric correlation between leaf and root. (3) C13 stable isotope analysis showed that the WUE of M. sibirica in May was significantly higher than that of other months (July and September). The WUE had a significantly positive correlation with leaf C and N content and a significantly negative correlation with leaf C:N, indicating that M. sibirica can compensate for the decline in N use efficiency through the improvement of WUE. The structural equation model (SEM) showed that the leaf N and P contents were affected by the joint effect of season and WUE, and the leaf C content was mainly directly affected by WUE. (4) Redundancy analysis (RDA) analysis showed that soil P content and soil N:P were the main factors affecting the variation of stoichiometry and WUE in various organs of M. sibirica. This study is helpful to deeply understand the adaptive mechanism of plant nutrient and water use, which provides a theoretical basis for vegetation protection and restoration in the study area.

A direct comparison of the effects and mechanisms between species richness and genotype richness in a dominant species on multiple ecosystem functions

Both species (interspecific) richness and genotype (intraspecific) richness of dominant species have significant effects on ecosystem functioning directly or indirectly by regulating plant community functional structure. However, the similarities and differences of the effects between inter- and intraspecific levels are poorly understood. In this study, we selected the main species in the semi-arid Eurasian typical steppe as study objects and simultaneously carried out a species richness experiment and a genotype richness experiment of Stipa grandis which is one of the dominant species in this region. We investigated how plants at each of the two richness levels affected multiple ecosystem functions (biomass, soil C, N and P cycles) directly and indirectly by regulating community functional structure, including community-weighted mean trait values (CWM) and functional dispersion (FDis). Both species richness and genotype richness showed significant direct effects on soil P cycle, and FDis significantly mediated the responses of aboveground biomass and soil N cycle to the changes of species richness and the response of belowground biomass to the changes of genotype richness in S. grandis. CWM showed significant effects on biomass in the species richness experiment and soil nutrient cycles in the genotype richness experiment, independently of the levels of plant richness. These findings provide experimental insights of intraspecific richness effects into the relationships between biodiversity and ecosystem functioning, and highlight the importance of conserving the intraspecific diversity of dominant species in the semi-arid steppe regions.

Ionomic Responses of Local Plant Species to Natural Edaphic Mineral Variations

Leaf ionome indicates plant phylogenetic evolution and responses to environmental stress, which is a critical influential factor to the structure of species populations in local edaphic sites. However, little is known about leaf ionomic responses of local plant species to natural edaphic mineral variations. In the present study, all plant species and soil samples from a total of 80 soil sites in Shiozuka Highland were collected for multi-elemental analysis. Ioniomic data of species were used for statistical analysis, representing 24 species and 10 families. Specific preferences to ionomic accumulation in plants were obviously affected by the phylogeny, whereas edaphic impacts were also strong but limited within the phylogenetic preset. Correlations among elements resulted from not only elemental synergy and competition but also the adaptive evolution to withstand environmental stresses. Furthermore, ionomic differences of plant families were mainly derived from non-essential elements. The majority of variations in leaf ionome is undoubtedly regulated by evolutionary factors, but externalities, especially environmental stresses also have an important regulating function for landscape formation, determining that the contributions of each factor to ionomic variations of plant species for adaptation to environmental stress provides a new insight for further research on ionomic responses of ecological speciation to environmental perturbations and their corresponding adaptive evolutions.

Biomass and nutrient allocation strategies in a desert ecosystem in the Hexi Corridor, northwest China

The allocation of biomass and nutrients in plants is a crucial factor in understanding the process of plant structures and dynamics to different environmental conditions. In this study, we present a comprehensive scaling analysis of data from a desert ecosystem to determine biomass and nutrient (carbon (C), nitrogen (N), and phosphorus (P)) allocation strategies of desert plants from 40 sites in the Hexi Corridor. We found that the biomass and levels of C, N, and P storage were higher in shoots than in roots. Roots biomass and nutrient storage were concentrated at a soil depth of 0-30 cm. Scaling relationships of biomass, C storage, and P storage between shoots and roots were isometric, but that of N storage was allometric. Results of a redundancy analysis (RDA) showed that soil nutrient densities were the primary factors influencing biomass and nutrient allocation, accounting for 94.5% of the explained proportion. However, mean annual precipitation was the primary factor influencing the roots biomass/shoots biomass (R/S) ratio. Furthermore, Pearson's correlations and regression analyses demonstrated that although the biomass and nutrients that associated with functional traits primarily depended on soil conditions, mean annual precipitation and mean annual temperature had greater effects on roots biomass and nutrient storage.

Scaling of nitrogen and phosphorus across plant organs in shrubland biomes across Northern China

Allocation of limiting resources, such as nutrients, is an important adaptation strategy for plants. Plants may allocate different nutrients within a specific organ or the same nutrient among different organs. In this study, we investigated the allocation strategies of nitrogen (N) and phosphorus (P) in leaves, stems and roots of 126 shrub species from 172 shrubland communities in Northern China using scaling analyses. Results showed that N and P have different scaling relationships among plant organs. The scaling relationships of N concentration across different plant organs tended to be allometric between leaves and non-leaf organs, and isometric between non-leaf organs. Whilst the scaling relationships of P concentration tended to be allometric between roots and non-root organs, and isometric between non-root organs. In arid environments, plant tend to have higher nutrient concentration in leaves at given root or stem nutrient concentration. Evolutionary history affected the scaling relationships of N concentration slightly, but not affected those of P concentration. Despite fairly consistent nutrients allocation strategies existed in independently evolving lineages, evolutionary history and environments still led to variations on these strategies.