Relationship Of Physiological Ecology Between Epiphylls And Host Plants

As the particular feature of tropical and subtropical rainforest, epiphylls occurs on the surface of host leaves in understory shrub commonly. From1960s, the relationship between epiphylls and host plants become the hot topic. Previously studies including:dominant species and groups, distribution, selectivity for substrate, microhabitat and host plants, community succession, influences for host leaves and the function in forest ecosystem. The topic of relationship between them was always the hottest, which is the important precondition for defining the role of epiphylls in forest ecosystem. Focusing on controversial problems or vacant field in this study area, the following contents were conducted. Relationship of spatial distribution between epiphyll and host, material exchange, influence of liverworts and lichens on photosynthesis in same species leaves, and the effect of epiphylls on leaf litter decomposition. Following contents were the main results we can found.(1)Based on their spatial distribution, it was be found that the background number of each host group in the area, the similarity of microenvironment selectivity of them, and the characteristics of the host were affecting the selectivity of epiphyllous liverworts for hosts. Furthermore, epiphyllous liverworts kept consistent with their hosts in species abundance, similarity between sites and phytogeography elements between five sites. These relations in spatial distribution represented the effect of hosts to epiphyllous liverworts in larger scale. The pattern of epiphyllous liverworts distribution on their host leaves would be favored by all of them.(2)Epiphyllous liverworts supplied7%-47%of the nitrogen for host leaves in the treatment period. In addition to the15N treatment, a labeled solution of13C6H12O6was brushed onto the lower surface of host leaves, resulting in an increase in δ13C of host leaves from-35.1‰to11.2‰; δ13C increased even more in liverworts (from-31.5‰to308.0‰) as a result of the treatment. The carbon contribution from host leaves to liverworts ranged from17%to35%. The heavier isotope (15N or13C) increased in organisms which accepted the N or C compound from their neighbor in our short-term treatment, suggesting that the organisms that obtained the external source directly had priority for the lighter isotope over their associated organisms in the nutrient transfer process. In summary, material transports did occur between the epiphyllous liverworts and their host plants, and resulted in a win-win relationship in which resource availability was increased due to resource sharing.(3) By contrast with epiphyllous liverworts, foliicolous lichen had more obvious effects on LMA, WC, Chl a, Chl b, and Chl a:b, and light utilization efficiency of host leaves than epiphyllous liverworts along with the increase of coverage rates. The largest denseness of lichen coverage would lead to a reduced LMA, a increased coverage of lichens would lead to a reduced Chl a:b, Host leaf areas with more than75%coverage rates of lichens would reflect significant more light than uncovered leaf areas, while leaf areas with liverworts represented significant different when the coverage become almost100%. Species of epiphylls had significant effects on characters of host leaf areas, except for LMA. For same species of epiphylls, the coverage rates had significant effects on leaf areas, except for their Chl a:b. When the coverage came to a critical rate, the effect of epiphylls on leaf area may fatal, and the response of their host for this coverage would represent feebly. For the photosynthesis parameters of leaf areas, species of epiphylls had significant effects on LCP and LSP, coverage rates of epiphylls would affect their Pmax and LSP significantly. Effects of epiphylls on host leaves in different stage of colonization were different, the factor of coverage rates should be considered in the study of the relationship between epiphylls and host plants.(4) After shedding from host plants, the existence of epiphylls continued effect the process of leaf litter decomposition. First, because of interactions between epiphylls and host leaves in leaf life time, leaf litter with epiphylls had significant different initial concentration of N (P<0.001), Ca (P<0.001), Mg (P<0.01), Fe (P<0.01), Cu (P=0.001), and the values of C/N (P<0.001) and water content (P<0.05) compared with bare leaf litter. Second, leaf litter with epiphylls had more rapid decline of remaining rate of dry weight in initial period of decomposition. Third, in comparison to bare leaf litter, the time of enrichment for N in leaf litter with epiphylls was advanced, the degree of enrichment had declined, the differences of Na from host species were reduced, and the decline of Cu remaining rate was also limited. By contrast with bare leaf litter, averaged decomposition rate of leaf litter with epiphylls were significant higher (P=0.001) epiphylls fixed on their surface made lower averaged decomposition rate for leaf litter with epiphylls. The time for their estimated complete decomposition were prolonged to1.04-1.36times. Combined with the averaged coverage rate in study district, approximately14.5%of material circulation would be prolonged.