Dioecious trees are important components of many forest ecosystems. Outcrossing advantage and sexual dimorphism are two major mechanisms that explain the persistence of dioecious plants; however, they have rarely been studied in dioecious trees. In this study, we investigated the influence of gender and genetic distance between parental trees (GDPT) on the growth and functional traits of 229 seedlings of a dioecious tree, Diospyros morrisiana. We found significant positive relationships between GDPT and seedling sizes and tissue density. However, the positive outcrossing effects on seedling growth mainly manifested in female seedlings, but were not prominent in male seedlings. Male seedlings generally had higher biomass and leaf area than female seedlings, but such differences diminished as the GDPT increased. Our research highlights that outcrossing advantage in plants can be sex-specific and sexual dimorphism begins from the seedling stage of dioecious trees.

Most dioecious plants are trees. However, because of the difficulty in determining sex from vegetative morphology, previous investigations of the sex ratios of dioecious trees were limited to flowering individuals, leading to inadequate and potentially unreliable data on patterns of sex ratios and the underlying mechanisms driving their variation. Here, we applied sex-specific molecular markers to investigate the sex ratio of a fully mapped population of the dioecious tree Diospyros morrisiana (Ebenaceae) in a subtropical forest. We also investigated the sexual dimorphism of life-history traits and spatial association between male and female trees to determine potential processes shaping the sex ratio at different life stages. Molecular sexing revealed a female-biased population sex ratio for this D. morrisiana population, contrasting with the male-biased operational (i.e., flowering) sex ratio. The sex ratio of D. morrisiana shifted from female-biased to male-biased over older life stages. We found that reproduction had a larger impact on the growth of female trees, which may account for the ontogenetic shift in sex ratio. There was no evidence of spatial segregation of the sexes beyond a scale of 2 m. Through molecular sexing of all individuals across all life stages, our work revealed for the first time a shift from a female- to a male-biased sex ratio in a huge population of a dioecious tree species. To better understand variation in sex ratios and the underlying mechanisms in dioecious trees, the sex of non-flowering and juvenile individuals should be included in future studies.

Soil carbon (C) cycling plays critical role in regulating global C budget and atmosphere CO2 concentration. The ongoing global warming potentially accelerates soil C loss induced by microbial respiration (MR) and makes soil a large C source to atmosphere. Quantifying the drivers of MR and its response to rising temperature (also called temperature sensitivity, Q10) is a high priority in order to improve the modelling and prediction of terrestrial C cycle under global warming. In this study, we applied a standardized soil sampling along 9 gradients from 400 m to 1100 m in a subtropical forest in South China, and conducted the incubation experiment at the same temperature ranges (from 10 °C to 25 °C) to measure MR and Q10, then the measured MR was adjusted by the field temperature of sampling site. Our objectives were to examine the response of MR and Q10 to the environmental change induced by elevational gradients in the subtropical forest, and then quantify their main drivers. We totally collected 54 abiotic and biotic factors relative to the MR and Q10. Our results showed that the incubated MR increased from low to high elevation. However, significantly elevational trend of the adjusted MR was not examined after adjusted by the field temperature of sampling sites, due to the tradeoff between increasing soil C concentration and declining temperature as elevation increased. We further found that the 9 elevational gradients did not cause significant change of Q10. The variation of Q10 was negatively dominated by soil C quality. Since climate warming is predicted faster at high elevation than that at low elevation, C loss from high elevation might be accelerated in the future and need more attentions in the further studies

Global change affects terrestrial litter inputs with cascading effects on soil respiration (SR). Cellulase and ligninase are dominant carbon-degrading enzymes, targeting the decomposition of readily decomposable and structurally complex carbon pools, respectively. Nevertheless, how litter alterations influence cellulase and ligninase activities and the implications for SR remain unclear. We conducted a meta-analysis to show that litter addition increased cellulase activity by 25.2%, whereas litter removal decreased it by 25.9%. Neither litter addition nor removal influenced ligninase activity. The changes in cellulase activity correlated positively with changes in SR, but not for ligninase activity. The effects of litter addition and removal on cellulase activity decreased with treatment duration. These results indicate that litter alterations affect SR primarily by controlling the microbial decomposition of readily decomposable rather than structurally complex carbon pools. Altogether, we suggest that the total and long-term effects of litter alterations on SR might be smaller than previously thought.

Vertical root segregation can be a key underpinning of species co-existence through below-ground niche partitioning but has rarely been tested in diverse forest communities. We randomly sampled > 4000 root samples from 625 0-30 cm soil profiles in a subtropical forest in China to determine the degree of vertical root segregation among 109 woody species and rooting plasticity in response to edaphic heterogeneity and root neighbours. Over 85% of species were predominantly distributed in the 0-10 cm soil zone, exhibiting low and inconsistent rooting plasticity in response to either edaphic heterogeneity or root neighbours. There was no evidence of vertical root segregation among co-occurring species. Contrastingly, the increase of one species’ root abundance tended to increase, but not reduce other species’ root abundance within soil zones. These findings suggest that interspecific differentiation of resource acquisition strategies might be more important than root segregation in mediating species co-existence in diverse forests.

The widespread observation that rare species have stronger conspecific plant-soil feedback (PSF) than common species raises more questions than answers on how rare species can possibly win the dance with abundant species. Here, we test soil feedback effect of phylogenetically related species on seedlings of contrasting local abundance in a subtropical forest. The results showed that although rare species suffered strong negative PSF in soils of conspecifics or phylogenetically close relatives, no such feedback was found in the soils of distant relatives. In contrast, although common species had weak conspecific PSF, they suffered consistently strong heterospecific soil feedback. These mechanisms ensure that rare species would fare well in the neighborhood of phylogenetically distant heterospecifics but do poorly under their close relatives, while common species perform relatively well in their own neighborhood but poorly in others’. This phylogenetic conservatism in PSF facilitates the persistence of rare species in a community.

Rhizosphere fungi are essential for plant survival and ecosystem functioning, but the processes structuring plant-fungal interactions remain largely unknown. We constructed association networks between 43 plant species and two groups of root-associated fungi (mycorrhizal and pathogenic) using sequence data. We revealed modularity within the association networks using network analysis, and correlated this modular structure with functional traits and phylogenetic history driving plant-fungal interactions. We observed strong modularity in both plant-mycorrhizal fungal and plant-pathogenic fungal association networks. Plant functional traits and fungal phylogeny clustered within modules. Host plants of mycorrhizal fungi differed significantly between modules in terms of their leaf dry matter content, photosynthetic traits and root tissue density. Host plants of pathogenic fungi differed significantly between modules in terms of their dark respiration rate, light compensation point and root morphology. Modularity within fungi was a product of fungal phylogeny, whereas host plant modularity was a product of functional traits (leaf morphology, photosynthetic rate and root morphology). Our study illustrates the link between plant functional traits and fungal assembly, and highlights the importance of niche-based processes in shaping plant-fungus association networks. Our results suggest that plant traits may be instrumental in managing the composition of belowground fungal communities.

How historical and concurrent drought regulate plant diversity-productivity relationships through altering soil microbial communities remains a key knowledge gap. We addressed this gap with plant diversity-productivity relationship experiments under drought and ambient conditions over two phases (Phase I: soil conditioning, and Phase II: plant response). Our results reveal that plant diversity and drought interacted and caused divergent soil microbial communities in Phase I, leading to soil microbial legacies. These soil legacies interacted and caused more pronounced plant diversity-productivity relationships in Phase II, reflecting increased net biodiversity effects over time. Complementarity effects were most positive in plant communities with highest plant richness and in the Drought-Ambient (Phase I-II) treatment, and selection effects were most negative in these communities. Our results highlight the importance of soil microbial communities in driving positive plant diversity effects, and future rainfall changes can cause complicated patterns in the biodiversity-ecosystem functioning relationships through soil microbial legacy.

Plants respond differently to neighbor identity showing plasticity in traits. However, solid experiment evidence on the functional traits of dioecious trees shaped by the recognition of neighbors with different gender and kinship is scarce. Here we examined the sexual and kinship interactions in a dioecious tree species, Diospyros morrisiana, by monoculturing and pair-culturing seedlings in a transparent gel system. Our results showed that sex-specific competition and kin recognition interacted and co-shaped the functional traits of D. morrisiana seedlings, especially root traits, while intra-sexual and non-kin neighbors facilitated the growth of seedlings. This implies kin- and gender-interactions depend on different mechanisms, kin selection and niche partitioning respectively, which is critical to understand how species coexist and traits are shaped in the nature.

1. The reduction of plant diversity following eutrophication threatens many ecosystems worldwide. Yet, the mechanisms by which species are lost following nutrient enrichment are still not completely understood, nor are the details of when such mechanisms act during the growing season, which hampers understanding and the development of mitigation strategies. 2. Using a common garden competition experiment, we found that early-season differences in growth rates among five perennial grass species measured in monoculture predicted short-term competitive dominance in pairwise combinations and that this effect was stronger under a fertilisation treatment. 3. We also examined the role of early-season growth rate in determining the outcome of competition along an experimental nutrient gradient in an alpine meadow. Early differences in growth rate between species predicted short-term competitive dominance under both ambient and fertilized conditions and competitive exclusion under fertilized conditions. 4. The results of these two studies suggests that plant species growing faster during the early stage of the growing season gain a competitive advantage over species that initially grow more slowly, and that this advantage is magnified under fertilisation. This finding is consistent with the theory of asymmetric competition for light in which fast-growing species can intercept incident light and hence outcompete and exclude slower-growing (and hence shorter) species. We predict that the current chronic nutrient inputs into many terrestrial ecosystems worldwide will reduce plant diversity and maintain low biodiversity state by continuously favouring fast-growing species. Biodiversity management strategies should focus on controlling nutrient inputs and reducing the growth of fast-growing species early in the season.