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Multiple global changes drive grassland productivity and stability: A meta-analysis
No full textTemporal stability of primary productivity is the key to stable provisioning of ecosystem services to human beings. Yet, the effects of various global changes on grassland stability remain ambiguous. Here, we conducted a comprehensive meta-analysis based on 1070 multi-year paired observations from 173 studies, to examine the impacts of various global changes on productivity, community stability and plant diversity of grasslands on a global scale. The global change drivers include nitrogen (N) addition, phosphorus (P) addition, N and P addition, precipitation increase, precipitation decrease, elevated CO2 and warming. Global change drivers generally had stronger impacts on grassland productivity than on temporal stability, except for precipitation changes. Community temporal stability was reduced by N addition, N and P addition and precipitation decrease, but was increased by precipitation increase and remained unchanged under P addition, elevated CO2 and warming. In addition, species richness decreased under N addition, N and P addition and precipitation decrease. At the plant functional group level, N and P addition reduced grasses' stability and precipitation increase enhanced forbs' stability. Nutrient additions decreased community stability via increasing the inter-annual variation more than the mean of primary productivity, while precipitation changes mainly affected community temporal stability via changing mean productivity. The negative impacts of global change drivers (i.e. N and P addition, warming) on community temporal stability increased with the degree of species loss but decreased with increasing stability of grasses. Moreover, the negative impacts of nutrient addition and precipitation decrease on community stability was lessened while the positive effect of precipitation increase on community stability was enhanced in grasslands with higher historical precipitation variability, greater soil fertility and longer experimental duration. Synthesis. Our findings demonstrate that N-based nutrient additions and drought destabilise grassland productivity, while precipitation increase enhances community stability. Impacts of global changes on community productivity and stability are mediated by species richness, plant functional group, site-specific environmental conditions (i.e. climate, soil) and experimental duration, which deserve more attention in grassland management practices under future global change scenarios
Contrasting effects of arbuscular mycorrhizal fungi on nitrogen uptake in Leymus chinensis and Cleistogenes squarrosa grasses, dominants of the Inner Mongolian steppe
No full textBackground and aims The acquisition of nitrogen (N) captured via arbuscular mycorrhizal (AM) hyphal networks is a major pathway in the N uptake of host plants. However, the relative contribution of arbuscular mycorrhizal fungi (AMF) to N uptake in different species has not been well quantified. Methods Two dominant plant species in semiarid steppes, i.e., Leymus chinensis (a C-3 grass) and Cleistogenes squarrosa (a C-4 grass), were selected. We conducted a greenhouse manipulation experiment that involved specifically designed microcosms combined with (15) N labelling techniques to quantify the relative contribution of AMF to plant N uptake under high and low levels of available soil N. Results AMF contributed more to N uptake in L. chinensis than that in C. squarrosa. For L. chinensis, AM symbiosis suppressed plant growth under low soil N conditions but improved plant growth under high soil N conditions, contributing c. 23% and 20% of the total plant N, respectively. For C. squarrosa, AM symbiosis consistently inhibited plant growth under both low and high soil N conditions, contributing only 9% and 7% of the plant N uptake, respectively. Conclusions AMF contributed significantly to N uptake in the C-3 grass of L. chinensis but not in the C-4 grass of C. squarrosa. Our findings indicate that AMF may modify the relative fitness of the two dominant grass species on the Mongolian Plateau through their influence on plant growth and N uptake in the face of increasing global N deposition
Phylogeography of the widespread fern Lemmaphyllum in East Asia: species differentiation and population dynamics in response to change in climate and geography
No full textPast climatic oscillations and complex geodynamic processes had tremendous effects on the current distributions of species in East Asia. Previous studies have revealed that spermatophytes experienced different demographic histories and survived in multiple refuges. However, very few studies involving ferns have been conducted over a large geographical area like East Asia. The monophyletic epiphytic fern genus Lemmaphyllum, which is composed of four species, is widespread in East Asia and offers a good model for exploring how geoclimatic oscillations influence the diversification and demographic history of fern species. We studied the phylogeography of Lemmaphyllum based on 115 populations using plastid sequences and ecological niche modeling. A total of 91 haplotypes were found in Lemmaphyllum. Molecular clock estimation revealed that speciation coincided with the three phases of the Qingzang Movement at beginning of the third uplift of Qinghai-Tibetan Plateau. The Tanaka-Kaiyong Line demarcated lineages within L. carnosum. The split of the mainland and island lineages of L. rostratum and L. carnosum var. microphyllum may have resulted from ancestral isolation whereby land-bridges acted as a barrier rather than as a corridor between mainland and island lineages. Multiple glacial refuges such as Sichuan Basin, Jinggangshan region, YGG region, HDM region, and the islands of the China East Sea during the LGM were revealed. The entities of Lemmaphyllum experienced species-specific demographic histories in response to the Pleistocene climate change. The case study of epiphytic ferns may provide evidences for understanding the migration of evergreen broad-leaf forest under climate oscillation
Deepened snow loosens temporal coupling between plant and microbial N utilization and induces ecosystem N losses
No full textSeasonal differences in plant and microbial nitrogen (N) acquisition are believed to be a major mechanism that maximizes ecosystem N retention. There is also a concern that climate change may interrupt the delicate balance in N allocation between plants and microbes. Yet, convincing experimental evidence is still lacking. Using a N-15 tracer, we assessed how deepened snow affects the temporal coupling between plant and microbial N utilization in a temperate Mongolian grassland. We found that microbial N-15 recovery peaked in winter, accounting for 22% of the total ecosystem N-15 recovery, and then rapidly declined during the spring thaw. By stimulating N loss via N2O emission and leaching, deepened snow reduced the total ecosystem N-15 recovery by 42% during the spring thaw. As the growing season progresses, the N-15 released from microbial biomass was taken up by plants, and the competitive advantage for N shifted from microbes to plants. Plant N-15 recovery reached its peak in August, accounting for 17% of the total ecosystem N-15 recovery. The Granger causality test showed that the temporal dynamics of plant N-15 recovery can be predicted by microbial N-15 recovery under ambient snow but not under deepened snow. In addition, plant N-15 recovery in August was positively correlated with and best explained by microbial N-15 recovery in March. The lower microbial N-15 recovery under deepened snow in March reduced plant N-15 recovery by 73% in August. Together, our results provide direct evidence of seasonal differences in plant and microbial N utilization that are conducive to ecosystem N retention; however, deepened snow disrupted the temporal coupling between plant-microbial N use and turnover. These findings suggest that changes in snowfall patterns may significantly alter ecosystem N cycling and N-based greenhouse gas emissions under future climate change. We highlight the importance of better representing winter processes and their response to winter climate change in biogeochemical models when assessing N cycling under global change
Genomic footprints of sorghum domestication and breeding selection for multiple end uses
No full textDomestication and diversification have had profound effects on crop genomes. Originating in Africa and subsequently spreading to different continents, sorghum (Sorghum bicolor) has experienced multiple onsets of domestication and intensive breeding selection for various end uses. However, how these processes have shaped sorghum genomes is not fully understood. In the present study, population genomics analyses were performed on a worldwide collection of 445 sorghum accessions, covering wild sorghum and four end-use subpopulations with diverse agronomic traits. Frequent genetic exchanges were found among various subpopulations, and strong selective sweeps affected 14.68% (= 107.5 Mb) of the sorghum genome, including 3649, 4287, and 3888 genes during sorghum domestication, improvement of grain sorghum, and improvement of sweet sorghum, respectively. Eight different models of haplotype changes in domestication genes from wild sorghum to landraces and improved sorghum were observed, and Sh1- and SbTB1-type genes were representative of two prominent models, one of soft selection or multiple origins and one of hard selection or an early single domestication event. We also demonstrated that the Dry gene, which regulates stem juiciness, was unconsciously selected during the improvement of grain sorghum. Taken together, these findings provide new genomic insights into sorghum domestication and breeding selection, and will facilitate further dissection of the domestication and molecular breeding of sorghum
Response of four evergreen savanna shrubs to an incidence of extreme drought: high embolism resistance, branch shedding and maintenance of nonstructural carbohydrates
No full textExtreme drought events are becoming frequent globally, resulting in widespread plant mortality and forest dieback. Although savanna vegetation cover similar to 20% of the earth's land area, their responses to extreme drought have been less studied than that of forests. Herein, we quantified branch dieback, individual mortality and the associated physiological responses of four evergreen shrubs (Tarenna depauperate Hutch., Maytenus esquirolii (H. Lev.) C.Y. Cheng, Murraya exotica L., Jasminum nudiflorum Lindl.) in a savanna ecosystem in Southwest China to an incidence of extreme drought during 2019 and 2020. We found that 80-100% of the individuals of these species exhibited branch dieback, whereas individual mortality was only found in T. depauperate (4.5%). All species showed high resistance to stem embolism (P-50, water potential at 50% loss of hydraulic conductivity ranged from -5.62 to -8.6 MPa), whereas the stem minimum water potentials reached -7.6 to ca -10.0 MPa during the drought. The low water potential caused high native embolism levels (percentage loss of hydraulic conductivity (PLC) 23-65%) in terminal branches, and the remaining stems maintained 15-35% PLC at the end of the drought. Large within-individual variations in stem vulnerability to embolism were detected, and shedding of vulnerable branches could be a mechanism for shrubs to reduce water and carbon consumption. Overall, the content of total nonstructural carbohydrates (NSC) and their components in the stem were generally comparable to or higher than those in the rainy season in three of the four species. Because the leaves were turgor-less for most time during the drought, high NSC levels during the drought could be due to recycling of NSC from dead branches or translocation from roots. Our results suggest high tolerance of savanna shrub species to extreme drought, which could be facilitated by high embolism resistance in some stems and shedding of vulnerable branches to maintain individual water and carbon balance
BIOACTIVE POTENTIAL OF CULTIVATED Mentha arvensis L. FOR PRESERVATION AND PRODUCTION OF HEALTH-ORIENTED FOOD
No full textMentha arvensis L. is traditionally used in folk medicine, and pharmacological industry due to presence of active chemical substances. It is also valuable for food industry as additives because of the presence of antioxidant, cytotoxic, antidiabetic and antimicrobial constituents. This study is intended to examine reactive oxygen species (Cvetanovi?? et al.) generation, lipid oxidation, cytotoxicity and antimicrobial effect of aqueous extract from M. arvensis L. prepared in various solvents i.e. fermented methanol extract (FM.E), distilled water extract (DW.E) and methanol extract (M.E). Phytochemical screening of the extract was qualitatively investigated for the isolation of alkaloids, flavonoids, fats and oils, menthol and quinones. To check the potential of extract as preservative, pH, lipid oxidation and Fourier transformed infrared spectroscopy (FT-IR) analysis was performed. Our results showed FM.E induce ROS generation, cytotoxicity and inhibit Staphylococcus aureus (4.20??0.90 mm) and Pseudomonas aeruginosa (3.23??0.32 mm) growth. In addition, in vivo results showed FM. E and M.E efficiently maintained chicken meat pH and reduced lipid oxidation. The presence of essential phytochemicals was responsible for inhibition of biofilm formation. FT-IR analysis revealed the presence of free OH stretching vibrations at 3878.69 cm-1, free NH at 3459.56 cm-1 and H-NH bond stretching 3388.02 cm-1 groups in chicken meat which belong to M. arvensis L. extracts. These results suggest that menthol from M. arvensis L. extract is favorable food additive against resistant pathogens
A Possible Mechanism for Aggregation-Induced Chlorophyll Fluorescence Quenching in Light-Harvesting Complex II from the Marine Green Alga Bryopsis corticulans
No full textThe light-harvesting complex II of a green alga Bryopsis corticulans (B-LHCII) is peculiar in that it contains siphonein and siphonaxathin as carotenoid (Car). Since the S1 state of siphonein and siphonaxathin lies substantially higher than the Qy state of chlorophyll a (Chl a), the Chl a(Qy)-to-Car(S1) excitation energy transfer is unfeasible. To understand the photoprotective mechanism of algal photosynthesis, we investigated the influence of temperature on the excitation dynamics of B-LHCII in trimeric and aggregated forms. At room temperature, the aggregated form showed a 10-fold decrease in fluorescence intensity and lifetime than the trimeric form. Upon lowering the temperature, the characteristic 680 nm fluorescence (F-680) of B-LHCII in both forms exhibited systematic intensity enhancement and spectral narrowing; however, only the aggregated form showed a red emission extending over 690-780 nm (F-RE) with pronounced blueshift, lifetime prolongation, and intensity boost. The remarkable T- dependence of F-RE is ascribed to the Chl-Chl charge transfer (CT) species involved directly in the aggregation-induced Chl deactivation. The CT-quenching mechanism, which is considered to be crucial for B. corticulans photoprotection, draws strong support from the positive correlation of the Chl deactivation rate with the CT state population, as revealed by comparing the fluorescence dynamics of B-LHCII with that of the plant LHCII
Decreased ultraviolet radiation and decomposer biodiversity inhibit litter decomposition under continuous nitrogen inputs
No full text1. Atmospheric nitrogen (N) deposition has altered biogeochemical cycles and ecosystem functioning. As a key process involved in carbon and nutrient cycles in terrestrial ecosystems, litter decomposition is sensitive to external N inputs. However, it remains unclear how the interactions of ultraviolet (UV) radiation, soil biodiversity (bacteria, fungi and invertebrates) and conventional drivers (e.g. litter chemistry and microbial activities) regulate the responses of litter decomposition to continuous N inputs. 2. Based on a multilevel N addition experimental platform, we conducted a 2-year litter decomposition experiment to examine the relative importance of N-induced changes in biotic and abiotic factors in mediating changes in the decomposition rates of four litter types (three representative species and their mixture) along an experimental N gradient in a Tibetan alpine steppe. 3. Our results showed that litter decomposition rates exhibited a consistent decrease in response to N enrichment among all species and their mixture. The slowed decomposition rates with increasing N addition were associated with N-induced reductions in UV radiation and soil bacterial diversity. An additional UV radiation manipulative experiment further confirmed that photodegradation had strong effects on plant litter decomposition at our study site. 4. These results demonstrated that N-induced declines in UV radiation and soil bacterial diversity inhibited litter decomposition, challenging the traditional view that changes in litter chemistry and microbial activities determine the responses of litter decomposition to external N inputs. Read the free Plain Language Summary for this article on the Journal blog