Obtaining phosphorus is a major driver of the stranglehold host of banyan trees

Banyan trees are keystone species in tropical ecosystems
.
Of the approximately 750 species of banyan trees worldwide, more than 300 species belong to semi-epiphytic banyan trees
.
Under complex tropical environmental conditions, many semi-epiphytic banyan trees have undergone epiphytic, semi-epiphytic and independent tree growth stages (Figure 1), with habitats changing from canopy to land and growth substrates from canopy humus to soil, giving semi-epiphytic banyan trees a unique life history
.
The unique phenomenon of "stranding" of some semi-epiphytic banyan trees has formed a peculiar ecological landscape, among which Ficus tinctoria is one of the most common semi-epiphytic plants in the tropics that cause "stranglement", which plays an important role
in the formation and maintenance of biodiversity and material circulation of tropical forest ecosystems.

For a long time, people have been very curious about the phenomenon of "strangleholding" of semi-epiphytic banyan trees in the tropics, and scientists have conducted more research on the behavior and causes of their stranglehold
.
However, what are the characteristics of nutrient dynamics and functional traits at different stages of growth of banyan trees? How do banyan trees benefit from killing their hosts? How can you adapt to changing habitats? These issues are still poorly
understood.

In order to explore the above problems, the authors conducted a comprehensive study: first, collecting, collating and analyzing the leaf phosphorus content data of banyan trees and palms worldwide from published literature and data, and second, selecting both heptoepiphytic and non-hepteroepiphytic F.
tinctoria as the research object to study the heteroepiphytic plant of Ficus obliquely and its host oil palm (Elaeis guineensis) under homogeneous garden conditions As well as the nutrient content and functional traits of the leaves of non-semi-epiphytic banyan trees at different growth stages, and the nutrient dynamics of the growth matrix were tested
.
The results showed that from the global to the homogeneous garden scale, the leaves of banyan trees and palms had high phosphorus content, and they all belonged to plants with high phosphorus demand.
The phosphorus content of leaves in semi-epiphytic banyan trees at interspecific and intra-species scales is lower than that of non-semi-epiphytic fig trees
.
With the growth of semi-epiphytic banyan trees, the effectiveness of both canopy humus and phosphorus in the soil decreased significantly
.
When competing for soil resources at the hemi-epiphytic stage, the phosphorus content of the leaves of both the banyan tree and its host palm was significantly reduced; After the death of the host palm tree, the phosphorus content of the leaves of the semi-epiphytic fig tree rebounded
.
Banyan trees adapt to changing environments by weighing leaf functional traits and reduce interspecific phosphorus competition by killing hosts to obtain more limited phosphorus resources in the tropics (Figure 2).

The results show that the high phosphorus demand of banyan trees, the lack of phosphorus in tropical soils, and the zero distance between banyan trees and hosts have led to fierce phosphorus competition between them, confirming that in addition to mechanical damage and shielding host trees, the acquisition of phosphorus is a driving factor for banyan trees to kill hosts, and clarifying that the unique life history of banyan trees is a survival strategy evolved to adapt to the complex environmental conditions and interspecies competition in tropical rainforests (Figure 3).

。 These findings provide a new perspective on the behavior and evolution of hemiepiphytes killing hosts, and link the stranglehold of hemiepiphytic banyan trees to the widespread phosphorus restriction in tropical soils, and provide new insights
in revealing nutrient utilization strategies and ecological adaptation mechanisms of hemiepiphytes in tropical regions.

The research results are titled "Hemiepiphytic figs kill their host trees: Acquiring phosphorus is a driving factor" in the international classic journal of plant science, New Phytologist (2022, 236(2): 714-728) was officially published, with Mo Yuxuan, a doctoral candidate in the Restoration Ecology Research Group of Banna Botanical Garden, as the first author of the paper, and researcher Liu Wenyao as the corresponding author
.
The research was supported
by the National Natural Science Foundation of China, the Biodiversity Conservation Strategy Project of the Chinese Academy of Sciences, and the "135" Project of the Chinese Academy of Sciences.

Figure 1.
Plants of semi-epiphytic banyan trees at different stages of growth

Fig.
2: Changes in phosphorus-related leaf functional traits at different growth stages of Hemiepiphytic, Non-Hemiepiphytic Ficus tinctoria and host palm (Elaeis guineensis).

Figure 3: Life history and ecological adaptation strategies of semi-attached banyan trees