ABSTRACT
Quercus myrsinifolia is one of the dominant species in the evergreen broad-leaf forest on the southern slope of Shennongjia. The study of spatial distribution pattern and spatial correlation of Q. myrsinifolia population will help to understand population development and potential ecological processes, as well as the structure and biodiversity maintenance mechanism of evergreen broad-leaf forests at the northern edge of the subtropics. Based on forest dynamic monitoring data from one 1 hm2 permanent plot on the southern slope of Shennongjia, we employed pair correlation functions g(r) and marked correlation functions to analyze the diameter structure of the Q. myrsinifolia population, spatial distribution patterns at different diameter classes, and intraspecific and interspecific spatial associations. The results showed that diameter structure of Q. myrsinifolia population exhibited an inverted 'J'-shaped distribution, suggesting a healthy regeneration status and belonging to a growing population type. The spatial distribution showed a decreasing trend in aggregation with increasing diameter. Positive correlations among individuals strengthened with closer diameter classes, while weakening with larger diameter differences. Interspecific spatial associations showed an increasing correlation of Q. myrsinifolia with understory dominant species with increasing spatial scales, but no correlation was observed with canopy-dominant species. Our results suggested that the spatial pattern of Q. myrsinifolia populations on the southern slope of Shennongjia was mainly influenced by habitat filtering, seed dispersal limitation, and intraspecific and interspecific competition. Furthermore, the adaptive strategies of Q. myrsinifolia varied when they coexisted with different species.
Subject(s)
Ecosystem , Population Dynamics , Quercus , Spatial Analysis , China , Quercus/growth & development , Biodiversity , ForestsABSTRACT
Riparian zone, the ecological transition buffer between terrestrial and aquatic ecosystems (rivers, lakes, reservoirs, wetlands, and other specific water bodies) with unique eco-hydrological and biogeochemical processes, is the last ecological barrier to prevent ammonium, nitrate and other non-point nitrogen pollutants from adjacent water bodies. Based on a summary of current progress of related studies, we found there were two major mechanisms underpinning the nitrogen retention/removal by the riparian ecosystems: 1) the relative locations of nitrogen in the soil-plant-atmosphere continuum system could be altered by riparian vegetation; 2) nitrogen could also be denitrified and then removed permanently by microorganisms in riparian soil. However, which process is more critical for the nitrogen removal remains elusive. Due to large variances of hydro-dynamic, vegetation, microbial, and soil substrate properties in nitrogen retention and transformation with various watersheds, it's difficult to identify which factor is the most important one driving nitrogen cycle in the riparian ecosystems. It is also found that the limitation of study methods, paucity of data at large spatial and temporal scale, and no consensus on the riparian width, are the three major reasons leading to large variances of the results among studies. In conclusion, it is suggested that further efforts should be focused on: 1) the detailed analysis on the successive environmental factors with long-term; 2) the application of a comprehensive method combining mathematical models, geographic information system, remote sensing and quantified technique (such as the coupled technique of the isotopic tracer and gas exchange measurement); 3) the implementation of studies at large temporal and spatial scales. It is sure that, these efforts can help to optimize the nitrogen removal pathways in the riparian ecosystems and provide scientific basis for ecosystem management.
Subject(s)
Ecosystem , Nitrogen Cycle , Nitrogen/analysis , Agriculture , Atmosphere , Denitrification , Environmental Monitoring , Geographic Information Systems , Models, Theoretical , Nitrates , Plants , Rivers , Soil , WetlandsABSTRACT
A total of 10 annuals and perennials of herbaceous species were investigated in reservoir riparian region of Three Gorges Reservoir. The correlations between the plants' nutrient release rate and the substrate composition and structural matter were studied under flooding condition. The decomposition rates of different species differed substantially, with the maximum of Alternanthera philoxeroides (decomposition rate constant k = 0.0228 d(-1)) and the minimum of Microstegium vimineum (k = 0.0029 d(-1)). There was no significant difference in k between annuals and perennials. There was no significant difference in nitrogen and phosphorus contents between annuals and perennials. Paspalum paspaloides and Bidens pilosa released more nutrients into the water than the other species. A. philoxeroides had a higher potential to release nitrogen while it had little effect on water phosphorus compared with the other species. Total N, P contents in the water were negatively correlated with the plants' decomposition rate, initial C content, C:N ratio, lignin:N ratio, and positively correlated with initial contents of K, Ca and N in plants.
