| World famous geochemically phosphorus-enriched zone is located in southwestern China, and central Yunnan has the most expressive phosphorus-enriched mountainous region. Large amounts of phosphorus from geochemically phosphorus-enriched soils (GPES) get lost in the runoffs, causing significant impact on lakes, e.g. Dianchi and Fuxianhu, and rivers, e.g. Yangtze and Pearl rivers. Vegetation recovery is deemed to be an effective and sustainable method to solve those problems. Using ecological stoichiometry theory to understand the relationships among plants, nutrients and hydrological processes is helpful in ecological restoration. During four years research, this paper mainly focuses on three parts:first, typical plant community structure in GPES mountainous region in central Yunnan; second, leaf stoichiometry of dominant plant communities; third, community dynamics and runoff characteristics. Finally, the relationships among plant-soil-runoff were studied basing ecological stoichiometry theory. Results in GPES of central Yunnan are showed as follows.(1) Shrub, and herbosa communities were the most widely distributed community type, yet tree community was limited. For woody communities, deciduous broad leaf community of Coriaria nepalensis, Buddleja asiatica, Coriaria nepalensis-Buddleja asiatica, Alnus nepalensis-Coriaria nepalensis were the most widely distributed community types. For herbosa communities, Eupatorium adenophorum, Chenopodium ambrosioides, and Artemisia princeps were the dominant species. The diversity index and species richness index of GPES were low; those dominant species have the capacity to face infertility and stress. Also several invasive species were found in our study area, e.g. Eupatorium adenophorum and Chenopodium ambrosioides. Nitrogen fixing plants, e.g. Betulaceae, Coriariaceae, Rosaceae etc. were key species in succession in GPES. Plantations in GPES were not merely observed as low diversity and productivity, but it also limited in planting area.(2) The-recovery pathway was preferentially from the pioneer Coriaria nepalensis-Buddleja asiatica community to Alnus nepalensis-Coriaria nepalensis community, then to serai mixed broad-leaved and coniferous community of Alnus nepalensis-pinus yunnanensis community, and finally to the late-successional evergreen broad-leaved Castanopsis orthacantha community. After 15-18 years’ naturally restoration the upward trends of species diversity and the Shannon-Wiener index decreased. The limited factor for community development changed from N-limited to light-limited. And Nitrogen fixing plants were key type for those restoration process.(3) We found that plants in GPES had higher mean leaf P (4.07mg/g) and lower N: P ratios (4.94) than average plant values that have been recorded. Due to extreme soil P level, the allometric relationships between leaf N and P have been changed, leaf N:P pattern been altered as well. While the responses across species and plant types are different, community leaf P and N:P was primarily determined by soil P availability because of the stability of Leaf N and a large amount of P could accumulate in leaves as inorganic forms responding to elevated soil P availability. And greater accumulation of inorganic P relative to organic P in leaf was the direct driving factor for community leaf P and N:P ratio patterns in GPES.(4) The effects of soil total N to leaf N and P contents of community occurs both directly on leaf contents of individual plants and through changing community composition. Leaf N:P ratios of community are principally controlled by soil total P. Between 54.0% and 73.2% of variation in leaf N, P traits was explained by co-variatipn in soil total N and P, compositional turnover and natural recovery time, by regression analysis. Leaf N was principally explained by composition alone (50.5%) and soil total N (36.0%) respectively. Leaf P was principally explained by soil total P alone (29.8%) and composition alone (25.8%). Leaf N:P ratio was principally explained by soil total P (43.0%) in the GPES. The effects of natural recovery time to leaf N, P stoichiometric trait were not significant.(5) Rainfall lasts from May to October, the fastigium of runoff yield and sediment yield was in August (>25%). Runoffs generally have a high P content (mean=1.56 mg/L) and low N:P ratio (mean=1.1); the mean annual P output was 331.5 g/ha.a-1, N output was 373.1g/ha.a-1.Precipitation, plant community functional diversity, and soil nutrients together explained 41.0%-55.8% of gross N and P output and N:P ratio in the runoffs. Although, as a single factor, less effect was found between plant community functional diversity and runoff patterns, the synergistic effect of plant community functional diversity and other parameters was a fundamental factor of runoff characteristics in phosphorus-enriched region.(6) Soil N were closely related to plant distribution, and thus determined the community composition. The dominant species from communities with higher stability and functional diversity usually had higher stoichiometric homeostasis. Nitrogen fixing plants, e.g. Coriaria nepalensis, had high stoichiometric homeostasis. And the introduction of them could increase soil C and N, could enhance community functional diversity, furthermore, cause P output to decrease and N:P ratio to increase in runoffs in GPES. However, the impact of some nitrogen-fixing plant was not significant, such as Acacia mearnsii.Those results indicated that understanding the relationships among plants, nutrients and hydrological processes is useful for ecological restoration, and improving the balance between nitrogen and phosphorus is effective in reducing risk of eutrophication in GPES mountainous region in central Yunnan.. Additionally, further studies are needed for designing restoration programs in terms of selecting the best species and restoration practices for specific site conditions. |
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