How the root bacterial community of Ficus tikoua responds to nematode infection: enrichments of nitrogen-fixing and nematode-antagonistic bacteria in the parasitized organs.

Plant-parasitic nematodes (PPNs) are among the most damaging pathogens to host plants. Plants can modulate their associated bacteria to cope with nematode infections. The tritrophic plant-nematode-microbe interactions are highly taxa-dependent, resulting in the effectiveness of nematode agents being variable among different host plants. Ficus tikoua is a versatile plant with high application potential for fruits or medicines. In recent years, a few farmers have attempted to cultivate this species in Sichuan, China, where parasitic nematodes are present. We used 16S rRNA genes to explore the effects of nematode parasitism on root-associated bacteria in this species. Our results revealed that nematode infection had effects on both endophytic bacterial communities and rhizosphere communities in F. tikoua roots, but on different levels. The species richness increased in the rhizosphere bacterial communities of infected individuals, but the community composition remained similar as compared with that of healthy individuals. Nematode infection induces a deterministic assembly process in the endophytic bacterial communities of parasitized organs. Significant taxonomic and functional changes were observed in the endophytic communities of root knots. These changes were characterized by the enrichment of nitrogen-fixing bacteria, including Bradyrhizobium, Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium, and nematode-antagonistic bacteria, such as Pseudonocardia, Pseudomonas, Steroidobacter, Rhizobacter, and Ferrovibrio. Our results would help the understanding of the tritrophic plant-nematode-bacterium interactions in host plants other than dominant crops and vegetables and would provide essential information for successful nematode management when F. tikoua were cultivated on large scales.

Dipterocarpoidae genomics reveal their demography and adaptations to Asian rainforests.

Dipterocarpoideae species form the emergent layer of Asian rainforests. They are the indicator species for Asian rainforest distribution, but they are severely threatened. Here, to understand their adaptation and population decline, we assemble high-quality genomes of seven Dipterocarpoideae species including two autotetraploid species. We estimate the divergence time between Dipterocarpoideae and Malvaceae and within Dipterocarpoideae to be 108.2 (97.8‒118.2) and 88.4 (77.7‒102.9) million years ago, and we identify a whole genome duplication event preceding dipterocarp lineage diversification. We find several genes that showed a signature of selection, likely associated with the adaptation to Asian rainforests. By resequencing of two endangered species, we detect an expansion of effective population size after the last glacial period and a recent sharp decline coinciding with the history of local human activities. Our findings contribute to understanding the diversification and adaptation of dipterocarps and highlight anthropogenic disturbances as a major factor in their endangered status.

Functional trait divergence associated with heteromorphic leaves in a climbing fig.

Introduction: Plants that display heteroblasty possess conspicuous variations in leaf morphology between their juvenile and adult phases, with certain species retaining juvenile-like leaves even in adulthood. Nevertheless, the ecological advantages of maintaining two or more distinct leaf types in heteroblastic plants at the adult stage remain unclear. Method: The aim of this study is to examine the adaptive significance of heteroblastic leaves sampled from branches with divergent functions (sterile and fertile branches) of mature Ficus pumila individuals by comparing their morphological, anatomical, and physiological characteristics. Result: Leaves on sterile branches (LSs) exhibited a significantly larger specific leaf area, thinner palisade and spongy tissues, lower chlorophyll contents, and lower light saturation points than leaves on fertile branches (LFs). These results demonstrate that LSs are better adapted to low light environments, while LFs are well equipped to take advantages of high light conditions. However, both LFs and LSs have a low light compensation point with no significant difference between them, indicating that they start to accumulate photosynthetic products under similar light conditions. Interestingly, significant higher net photosynthetic rate was detected in LFs, showing they have higher photosynthetic capacity. Furthermore, LFs produced significant more nutrients compared to LSs, which may associate to their ability of accumulating more photosynthetic products under full light conditions and higher photosynthetic capacity. Discussion: Overall, we observed a pattern of divergence in morphological features of leaves on two functional branches. Anatomical and physiological features indicate that LFs have an advantage in varied light conditions, providing amounts of photosynthetic products to support the sexual reproduction, while LSs adapt to low light environments. Our findings provide evidence that heteroblasty facilitates F. pumila to utilize varying light environments, likely associated with its growth form as a climbing plant. This strategy allows the plant to allocate resources more effectively and optimize its overall fitness.

Source-sink dynamics assists the maintenance of a pollinating wasp.

Dispersal that unites spatially subdivided populations into a metapopulation with source-sink dynamics is crucial for species persistence in fragmented landscapes. Understanding such dynamics for pollinators is particularly urgent owing to the ongoing global pollination crisis. Here, we investigated the population structure and source-sink dynamics of a pollinating wasp (Wiebesia sp. 3) of Ficus pumila in the Zhoushan Archipelago of China. We found significant asymmetry in the pairwise migrant numbers for 22 of 28 cases on the historical timescale, but only two on the contemporary timescale. Despite a small population size, the sole island not colonized by a superior competitor wasp (Wiebesia sp. 1) consistently behaved as a net exporter of migrants, supplying large sinks. Comparable levels of genetic diversity, with few private alleles and low genetic differentiation (total Fst : 0.03; pairwise Fst : 0.0005-0.0791), were revealed among all the islands. There was a significant isolation-by-distance pattern caused mainly by migration between the competition-free island and other islands, otherwise the pattern was negligible. The clustering analysis failed to detect multiple gene pools for the whole region. Thus, the sinks were most probably organized into a patchy population. Moreover, the estimates of effective population sizes were comparable between the two timescales. Thus the source-sink dynamics embedded within a well-connected population network may allow Wiebesia sp. 3 to persist at a competitive disadvantage. This study provides evidence that metapopulations in the real world may be complicated and changeable over time, highlighting the necessity to study such metapopulations in detail.

Combined effects of nitrogen fertilizer and biochar on greenhouse gas emissions and net ecosystem economic budget from a coastal saline rice field in southeastern China.

Biochar amendment has complex impacts on greenhouse gas emissions, crop production and economic benefit. However, few studies have comprehensively investigated the effects of biochar amendment in coastal saline rice fields. Thus, a biochar amendment field experiment was established in a coastal saline rice field in China to estimate the CH4 and N2O emissions, global warming potential (GWP), greenhouse gas intensity (GHGI), and net ecosystem economic budget (NEEB) of the biochar amendment during the rice growing season in 2017. There were six treatments (N0B0, N0B1, N0B2, N1B0, N1B1, N1B2) with different N fertilizer levels of 0 and 300 kg N ha-1 and biochar rates of 0, 20, and 40 t ha-1. The results showed that the application of N fertilizer increased N2O emissions and rice yield by 128.3% (p < 0.001) and 44.4% (p < 0.001), respectively, while decreased the GHGI by 20.5% (p < 0.01); additionally, there were no significant effects on the CH4 emissions and GWP compared with the treatments without N fertilizer. Although biochar amendment significantly increased the N2O emissions and rice yield by 13.7-38.1% and 31.5-34.9%, respectively, biochar amendment had no significant effects on CH4 emissions, GWP, and GHGI relative to the treatments without biochar amendment. From an economic perspective, N fertilizer significantly increased the NEEB by 135.5%, relative to the treatments without N fertilizer. Due to the high price of biochar and the large quantity applied, biochar amendment significantly reduced the NEEB by 99.8-229.3% compared with the treatments without biochar amendment. Considering the different characters between field-aged biochar and fresh biochar. Thus, long-term observations are needed to evaluate the environmental and economic profits affected by biochar and N fertilizer.

Sky islands as foci for divergence of fig trees and their pollinators in southwest China.

The dynamics of populations and their divergence over time have shaped current levels of biodiversity and in the case of the "sky islands" of mountainous southwest (SW) China have resulted in an area of exceptional botanical diversity. Ficus tikoua is a prostrate fig tree subendemic to the area that displays unique intraspecific diversity, producing figs typical of different pollination modes in different parts of its range. By combining climate models, genetic variation in populations of the tree's obligate fig wasp pollinators and distributions of the different plant phenotypes, we examined how this unusual situation may have developed. We identified three genetically distinct groups of a single Ceratosolen pollinator species that have largely parapatric distributions. The complex topography of the region contributed to genetic divergence among the pollinators by facilitating geographical isolation and providing refugia. Migration along elevations in response to climate oscillations further enhanced genetic differentiation of the three pollinator groups. Their distributions loosely correspond to the distributions of the functionally significant morphological differences in the male figs of their host plants, but postglacial expansion of one group has not been matched by spread of its associated plant phenotype, possibly due to a major river barrier. The results highlight how interplay between the complex topography of the "sky island" complex and climate change has shaped intraspecies differentiation and relationships between the plant and its pollinator. Similar processes may explain the exceptional botanical diversity of SW China.

The combined effects of nitrogen fertilizer, humic acid, and gypsum on yield-scaled greenhouse gas emissions from a coastal saline rice field.

In coastal saline rice fields, rice production shows high greenhouse gas (GHG) emissions but low nitrogen use efficiency (NUE). However, few studies have focused on the combined effects of nitrogen (N) fertilizer and soil ameliorants on GHG emissions. Thus, a field experiment was conducted to study the combined effects of N fertilizer, humic acid, and gypsum on the global warming potential (GWP), yield-scaled greenhouse gas intensity (GHGI), rice grain yield, and NUE in coastal saline rice fields in southeastern China. The experiment was conducted with eight treatments: N0, N1, N0H1, N1H1, N0G1, N1G1, N0H1G1, and N1H1G1. The codes N0, N1, H1, and G1 represented treatments without N (0 kg N ha-1), with N (300 kg N ha-1), with humic acid (0.6 t ha-1), and with gypsum (0.6 t ha-1), respectively. Compared with the treatments without N addition, the application of N fertilizer significantly increased N2O emissions and grain yield by 41.9~130.6% and 32.8~57.5%, respectively, while significantly decreased the yield-scaled GHGI by 9.4~31.9%. Humic acid amendment significantly increased N2O emissions and grain yield as compared with the treatments without humic acid. Gypsum addition had no significant effects on CH4 and N2O emissions, GWP, yield-scaled GHGI, and grain yield in relation to the treatments without gypsum. In addition, compared with the N1 treatment, the N1H1, N1G1, and N1H1G1 treatments increased the grain yield by 18.3% (p < 0.05), 2.3%, and 10.4%, and decreased yield-scaled GHGI by 9.6%, 20.5%, and 31.2% (p < 0.05), despite similar GWPs, respectively. Overall, the N1H1 and N1H1G1 treatments are the appropriate fertilizer management to realize high yield together with low environmental impacts in coastal saline rice fields in China.

Extremely high proportions of male flowers and geographic variation in floral ratios within male figs of Ficus tikoua despite pollinators displaying active pollen collection.

Most plants are pollinated passively, but active pollination has evolved among insects that depend on ovule fertilization for larval development. Anther-to-ovule ratios (A/O ratios, a coarse indicator of pollen-to-ovule ratios) are strong indicators of pollination mode in fig trees and are consistent within most species. However, unusually high values and high variation of A/O ratios (0.096-10.0) were detected among male plants from 41 natural populations of Ficus tikoua in China. Higher proportions of male (staminate) flowers were associated with a change in their distribution within the figs, from circum-ostiolar to scattered. Plants bearing figs with ostiolar or scattered male flowers were geographically separated, with scattered male flowers found mainly on the Yungui Plateau in the southwest of our sample area. The A/O ratios of most F. tikoua figs were indicative of passive pollination, but its Ceratosolen fig wasp pollinator actively loads pollen into its pollen pockets. Additional pollen was also carried on their body surface and pollinators emerging from scattered-flower figs had more surface pollen. Large amounts of pollen grains on the insects' body surface are usually indicative of a passive pollinator. This is the first recorded case of an actively pollinated Ficus species producing large amounts of pollen. Overall high A/O ratios, particularly in some populations, in combination with actively pollinating pollinators, may reflect a response by the plant to insufficient quantities of pollen transported in the wasps' pollen pockets, together with geographic variation in this pollen limitation. This suggests an unstable scenario that could lead to eventual loss of wasp active pollination behavior.