Host range varies widely among species of parasitic plants. Parasitic plants realize host selection through induction by chemical molecular signals, including germination stimulants and haustoria‐inducing factors (HIFs). Research on parasitic plant biology has provided information on germination, haustorium induction, invasion, and haustorial structures and functions. To date, some molecular mechanisms have been suggested to explain how germination stimulants work, involving a chemical change caused by addition of a nucleophilic protein receptor, and direct or indirect stimulation of ethylene generation. Haustorium initiation is induced by HIFs that are generated by HIF‐releasing enzymes from the parasite or triggered by redox cycling between electrochemical states of the inducers. Haustorium attachment is non‐specific, however, the attachment to a host is facilitated by mucilaginous substances produced by haustorial hairs. Following the attachment, the intrusive cells of parasites penetrate host cells or push their way through the host epidermis and cortex between host cells, and some types of cell wall‐degrading enzymes may assist in the penetration process. After the establishment of host‐parasite associations, parasitic plants develop special morphological structures (haustoria) and physiological characteristics, such as high transpiration rates, high leaf conductance, and low water potentials in hemiparasites, for nutrient transfer and resource acquisition from their hosts. Therefore, they negatively affect the growth and development and even cause death of their hosts.

Background: Phyllosphere microbes play important roles in host plant performance and fitness. Recent studies have suggested that tropical and temperate forests harbor diverse phyllosphere bacterial and fungal communities and their assembly is driven by host species identity and plant traits. However, no study has yet examined how seasonality (e.g. dry vs. wet seasons) influences phyllosphere microbial community assembly in natural forests. In addition, in subtropical forests characterized as the transitional zonal vegetation type from tropical to temperate forests, how tree phyllosphere microbial communities are assembled remains unknown. In this study, we quantified bacterial and fungal community structure and diversity on the leaves of 45 tree species with varying phylogenetic identities and importance values within a 20-ha lower subtropical evergreen broad-leaved forest plot in dry and wet seasons. We explored if and how the microbial community assembly varies with host species identity, plant traits and seasonality.Results: Phyllosphere microbial communities in the subtropical forest are more abundant and diverse than those in tropical and temperate forests, and the tree species share a “core microbiome” in either bacteria or fungi. Variations in phyllosphere bacterial and fungal community assembly are explained more by host species identity than by seasonality. There is a strong clustering of the phyllosphere microbial assemblage amongst trees by seasonality, and the seasonality effects are more pronounced on bacterial than fungal community assembly. Host traits have different effects on community compositions and diversities of both bacteria and fungi, and among them calcium concentration and importance value are the most powerful explaining variables for bacteria and fungi, respectively. There are significant evolutionary associations between host species and phyllosphere microbiome.Conclusions: Our results suggest that subtropical tree phyllosphere microbial communities vary with host species identity, plant traits and seasonality. Host species identity, compared to seasonality, has greater effects on phyllosphere microbial community assembly, and such effects differ between bacterial and fungal communities. These findings advance our understanding of the patterns and drivers of phyllosphere microbial community assembly in zonal forests at a global scale.

Elucidating the ecological mechanisms underlying community assembly in subtropical forests remains a central challenge for ecologists. The assembly of species into communities can be due to interspecific differences in habitat associations, and there is increasing evidence that these associations may have an underlying phylogenetic structure in contemporary terrestrial communities. In other words, by examining the degree to which closely related species prefer similar habitats and the degree to which they co-occur, ecologists are able to infer the mechanisms underlying community assembly. Here we implement this approach in a diverse subtropical tree community in China using a long-term forest dynamics plot and a molecular phylogeny generated from three DNA barcode loci. We find that there is phylogenetic signal in plant-habitat associations (i.e. closely related species tend to prefer similar habitats) and that patterns of co-occurrence within habitats are typically non-random with respect to phylogeny. In particular, we found phylogenetic clustering in valley and low-slope habitats in this forest, indicating a filtering of lineages plays a dominant role in structuring communities in these habitats and we found evidence of phylogenetic overdispersion in high-slope, ridge-top and high-gully habitats, indicating that distantly related species tended to co-occur in these high elevation habitats and that lineage filtering is less important in structuring these communities. Thus we infer that non-neutral niche-based processes acting upon evolutionarily conserved habitat preferences explain the assembly of local scale communities in the forest studied.

The influence of the holoparasite Cuscuta campestris Yuncker on the growth and photosynthesis of Mikania micrantha H.B.K. was studied. The results indicate that C. campestris infection significantly reduced the light use efficiency and light saturation point of the host. It significantly reduced the net photosynthetic rate (P_n) of the 1st and 8th mature leaves of M. micrantha at light saturation point, the apparent quantum yield of the 1st mature leaves, the carboxylation efficiency and CO₂ saturated P_n of the 8th mature leaves, but increased the light compensation point of the 1st mature leaves. Diurnally, it significantly reduced P_n between 08.00 h and 16.00 h and stomatal conductance and transpiration from 10.00 h to 16.00 h for the 8th mature leaves. Moreover, the significantly adverse effects of C. campestris infection on P_n were observed 18 d after parasitization (DAP) for the 4th, 8th and 12th, and 25 DAP for the 1st mature leaves of M. micrantha, and they became greater with infection time. The infection also significantly reduced the number of leaves, leaf area, stem length, and biomass, and prevented flowering of M. micrantha in the growing season, and caused almost complete death of the aerial parts of the host about 70 DAP, but the uninfected plants grew and developed normally. Furthermore, the total biomass of the infected host and the parasite was significantly less than that of the uninfected plants. Therefore, besides resource capture by C. campestris, the reduced growth of the infected plants must also be due to the negative effects of the parasite on host photosynthesis.

As a means of biologically controlling Mikania micrantha H.B.K. in South China, the influence of the obligate parasite Cuscuta campestris Yuncker on its growth and biomass allocation was studied using pot trials. The effect of C. campestris on M. micrantha became greater with time, such that the host biomass was only 1.8% of the control after 60 d of parasitism and by day 72 almost all the aerial parts of the host plants had died. Afterwards, the hosts and the remnant parasite shoots re-grew but the total biomass of the hosts was still significantly lower than that of the controls. The infection by C. campestris greatly increased the shoot:root dry weight ratio and the allocation to stems of the infected plants from 40 to 50 d after parasitization, but decreased their relative growth rate and unit leaf rate starting from 20 d after parasitization and their leaf area ratio from 30 to 60 d after parasitization. Cuscuta campestris significantly reduced the total biomass, changed the biomass allocation patterns, and completely inhibited the flowering of the infected M. micrantha plants. These results indicate that the use of C. campestris could be a potentially effective way of controlling M. micrantha.

Structure and demographics in many tropical forests is changing, but the causes of these changes remain unclear. We studied 5 y (2005–2010) of species turnover, recruitment, mortality and population change data from a 20-ha subtropical forest plot in Dinghushan, China, to identify trends in forest change, and to test whether tree mortality is associated with intraspecific or interspecific competition. We found the Dinghushan forest to be more dynamic than one temperate and two tropical forests in a comparison of large, long-term forest dynamics plots. Within Dinghushan, size-class distributions were bell-shaped only for the three most dominant species and reverse J-shaped for other species. Bell-shaped population distributions can indicate a population in decline, but our data suggest that these large and long-lived species are not in decline because the pattern is driven by increasing probabilities of transition to larger size class with increasing size and fast growth in saplings. Spatially aggregated tree species distributions were common for surviving and dead individuals. Competitive associations were more frequently intraspecific than interspecific. The competition that induced tree mortality was more associated with intraspecific than interspecific interactions. Intraspecific competitive exclusion and density-dependence appear to play important roles in tree mortality in this subtropical forest.