Abstract
Mixed stands can be more productive if growth facilitation via niche segregation occurs. Dalbergia odorifera T. Chen, a tropical tree species endemic to Hainan Island with great economic values, belongs to the family Leguminosae. However, selecting mixed species with suitable ecological niches to efficiently construct mixed forests of D. odorifera in the context of abiotic stress [drought, nitrogen (N) deposition] remained obscure. In the present study, the target plant D. odorifera was planted with the same species D. odorifera, heterogeneous but the same family Delonix regia and non-Leguminous Family Swietenia mahagoni in the root interaction and isolated models under two watering regimes [100% and 30% field capacity (FC)] and two N applications (application, non-application), respectively. Principle component analysis based on the performances of growth, phenotype, and physiology was performed to identify the main factors affected by the treatments and the most discriminatory effects of water, N level, and species interaction models. Both comprehensive evaluation values and comprehensive index values were calculated to evaluate the influences of different niche neighbors on D. odorifera. Results showed that D. odorifera was benefited from S. mahagoni but inhibited from D. odorifera in all treatments under root system interaction. Drought stress aggravated the inhibitory effects on D. odorifera from D. odorifera. N application stimulated the promoted effects on D. odorifera from S. mahagoni but enhanced competition intensity of D. odorifera from D. regia under the 100% FC condition. N application alleviated the inhibitory effect of drought stress on D. odorifera from D. odorifera and S. mahagoni. Furthermore, the responses of D. odorifera to different niche neighbors were dominated by belowground interaction rather than the negligible aboveground one. Therefore, the feasibility of niche segregation as the criterion for selecting neighbors to construct D. odorifera mixed stands was confirmed. In addition, water level and N application could alter responses of D. odorifera to different niche neighbors under the root system interaction. Appropriate N application could alleviate the inhibitory effect of drought stress on D. odorifera in its mixed forests. A mixture with S. mahagoni under appropriate N application could be the optimal planting model.
Highlights
Interaction among species affects plant growth and community structure (Goisser et al, 2016; Guo et al, 2016)
These findings indicated that the growth of D. odorifera markedly benefited from D. regia and S. mahagoni, whereas they were inhibited by neighboring D. odorifera
The results indicated that D. odorifera modulated traits in photosynthetic capacity according to its neighbors, and the responses of D. odorifera in photosynthetic capacity were associated with its neighbors and their niche differentiation (Burns and Strauss, 2011)
Summary
Interaction among species affects plant growth and community structure (Goisser et al, 2016; Guo et al, 2016). The reduction of competition or facilitation has been proposed to explain the increased productivity from mixed stands (Chomel et al, 2014; Forrester and Bauhus, 2016). Facilitation refers to the fact that a species promotes the growth of its neighboring species by improving the environment [e.g., nitrogen (N) fixation from leguminous species]. Niche segregation is often the basis to select species to reduce competition when constructing mixed stands, such as inter-specific differences in functional traits, resource demand, and absorptive capacity (e.g., shade tolerance, growth rate, root morphology, root structure, nitrogen fixation capacity, nutrient preference) (Forrester and Bauhus, 2016).
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