Biogeographic Patterns of Leaf Stoichiometry and Adaption Strategy of Stellera Chamaejasme L. in Degraded Grasslands Across Northern China

Background: Plant leaf stoichiometry reflect its adaptations to environments. Leaf stoichiometry variations across different environments have been extensively studied among grassland plants, but little is known about intraspecific leaf stoichiometry, especially for widely distributed species, such as Stellera chamaejasme L. We present the first study on the leaf stoichiometry of S. chamaejasme, and evaluate their relationships with environmental variables by collecting S. chamaejasme leaf and soil samples from 29 invaded sites in the two plateaus of distinct environments [the Inner Mongolian Plateau (IM) and Qinghai-Tibet Plateau (QT)] in Northern China. Leaf C, N, P, and K and their stoichiometric ratios, and soil physicochemical properties were determined, together with climate information from each sampling sites. Results: Results showed that mean leaf C, N, P, and K concentrations were 498.60, 19.95, 2.15, and 6.57 g · kg-1, respectively; the C/N, C/P, and N/P ratios were 25.46, 246.22, and 9.84, respectively. Soil physicochemical properties of S. chamaejasme invaded area varied wildly, and few significant correlations between S. chamaejasme leaf ecological stoichiometry and soil physicochemical properties were observed. Except for C and N in leaves, the P and K had higher homeostasis than 1, between 4.17 and 13.21. Moreover, C and N content of S. chamaejasme leaves were unaffected by any climate factors. However, the correlation between leaf P and climate factors was significant in IM only, while leaf K in QT. Finally, partial least squares path modeling suggested that leaf P or leaf K were affected by different mechanisms in QT and IM regions. Conclusions: Our results indicated that S. chamaejasme tend to be insensitive to variation in soil nutrient availability, resulting in their broad distributions in China grasslands. Moreover, S. chamaejasme adapt to changing environments by adjusting its relationships with climate or soil factors to improve their chances of survival and spread in degraded grasslands.

Grazing intensity changed the activities of nitrogen assimilation related enzymes in desert Steppe Plants

Background Nitrogen, as a limiting factor for net primary productivity in grassland ecosystems, is an important link in material cycles in grassland ecosystems. However, the nitrogen assimilation efficiency and mechanisms of grassland plants under grazing disturbance are still unclear. This study investigated Stipa breviflora desert steppe which had been grazed for 17 years and sampled the root system and leaf of the constructive species Stipa breviflora during the peak growing season under no grazing, light grazing, moderate grazing and heavy grazing treatments. The activities of enzymes related to nitrogen assimilation in roots and leaves were measured. Results Compared with no grazing, light grazing and moderate grazing significantly increased the activities of nitrate reductase (NR), glutamine synthetase (GS), glutamic oxaloacetic transaminase (GOT) and glutamic pyruvate transaminase (GPT) in leaves, and GS, GOT and GPT in roots of Stipa breviflora, while heavy grazing significantly decreased the activities of GS in leaves and NR in roots of Stipa breviflora. NR, GOT and GPT activities in leaves and roots of Stipa breviflora were positively correlated with nitrogen content, soluble protein, free amino acid and nitrate content. Conclusions Grazing disturbance changed the activities of nitrogen assimilation related enzymes of grassland plants, and emphasized that light grazing and moderate grazing were beneficial for nitrogen assimilation by grassland plants. Therefore, establishing appropriate stocking rates is of great significance for material flows in this grassland ecosystem and for the stability and sustainable utilization of grassland resources.

Shoot–Root Interplay Mediates Defoliation-Induced Plant Legacy Effect

Shoot defoliation by grazers or mowing can affect root traits of grassland species, which may subsequently affect its aboveground traits and ecosystem functioning (e.g., aboveground primary production). However, experimental evidence for such reciprocal feedback between shoots and roots is limited. We grew the perennial grass Leymus chinensis–common across the eastern Eurasian steppe–as model species in a controlled-hydroponics experiment, and then removed half of its shoots, half of its roots, or a combination of both. We measured a range of plant aboveground and belowground traits (e.g., phenotypic characteristics, photosynthetic traits, root architecture) in response to the shoot and/or root removal treatments. We found the regenerated biomass was less than the lost biomass under both shoot defoliation and root severance, generating a under-compensatory growth. Root biomass was reduced by 60.11% in the defoliation treatment, while root severance indirectly reduced shoot biomass by 40.49%, indicating a feedback loop between shoot and root growth. This defoliation-induced shoot–root feedback was mediated by the disproportionate response and allometry of plant traits. Further, the effect of shoot defoliation and root severance on trait plasticity of L. chinensis was sub-additive. That is, the combined effects of the two treatments were less than the sum of their independent effects, resulting in a buffering effect on the existing negative influences on plant persistence by increased photosynthesis. Our results highlight the key role of trait plasticity in driving shoot–root reciprocal feedbacks and growth persistence in grassland plants, especially perennial species. This knowledge adds to earlier findings of legacy effects and can be used to determine the resilience of grasslands.

A multispecies amplicon sequencing approach for genetic diversity assessment in grassland plant species

Grasslands are widespread and economically relevant ecosystems at the basis of sustainable roughage production. Plant genetic diversity (PGD; i.e., within-species diversity) is related to many beneficial effects to the ecosystem functioning of grasslands. The monitoring of PGD in temperate grasslands is complicated by the multiplicity of species present and by a shortage of methods for large-scale assessment. However, the continuous advancement of high-throughput DNA sequencing approaches have improved the prospects of broad, multispecies PGD monitoring. Among them, amplicon sequencing stands out as a robust and cost-effective method. Here we report a set of twelve multispecies primer pairs that can be used for high-throughput PGD assessment in multiple grassland plant species. The loci targeted by the amplicons were selected and tested in two phases: a "discovery phase" based on a sequence capture assay (611 target nuclear loci assessed in 16 grassland plant species), which resulted in the selection of eleven loci; and a "validation phase", in which the selected loci were targeted and sequenced using twelve multispecies primers in test populations of Dactylis glomerata L., Lolium perenne L., Festuca pratensis Huds., Trifolium pratense L. and T. repens L. The resulting multispecies amplicons had overall nucleotide diversities per species ranging from 5.19 × 10-3 to 1.29 × 10-2, which is in the range of flowering-related genes but slightly lower than pathogen resistance genes. We conclude that the methodology, the DNA sequence resources, and the amplicon-specific primer pairs reported in this study provide the basis for large-scale, multispecies PGD monitoring in grassland plants.