The Interaction Of Understory Vegetation Root Growth And Litter Decomposition In Hilly Red Soil Region

Underground process is the research frontier of forest ecology. It’s a common phenomenon that lots of roots grow into the litter in hilly red soil region. In forest ecosystem, most nutrients in plants returned to the soil through litter decomposition and these soil nutrients are again absorbed by plant roots. The material cycling and energy flowing are linked together in forest ecosystem by the litter decomposition and plant nutrient uptake. However, we are few known how the roots affect the decomposition of litter and how the litter decomposition induce the root growth and development.In this work, leaf litters of Pinus elliottii and Liquidambar formosana were selected as our research objects. We investigated the dynamics of litter mass loss, organic carbon, nitrogen and phosphorus under two treatments with or without the understory plant(Loropetalum chinense) roots using the nylon bag method, in order to explore the mechanism of root growth influence on litter decomposition. In contrast, we selected the understory plant Loropetalum chinense as a research object to study root growth and nutrient dynamics in litter and soil layers under the four treatments of litter doubled + water normal supply, litter doubled + 50% water normal supply, litter removed + water normal supply and litter removed + 50% water normal supply, in order to reveal the effect of litter decomposition on roots growth. Based on these two experiments, we plan to explore the interaction mechanisms between understory plant roots growth and litter decomposition, to provide a scientific basis for understory vegetation and litter management, to promote the development of forest ecology and to improve plantations management.The main results and conclusions are as follows:(1) The participation of Loropetalum chinense root has a significant effect in promoting the decomposition of Liquidambar formosana leaf litter, especially in the early stage, but minimal effect on the later stage. At the early stage, the roots may be as the source of nitrogen to symbiosis microbe, then the microbes with increasing biological activity can accelerated the litter decay rate and the release rate of carbon, nitrogen and phosphorus. The participation of Loropetalum chinense roots has no significant effect on the decomposition of pine leaf litter. The potential reason is that the leaf litter of pine with a lower nitrogen content and higher C/N ratio may not be helpful to improve the activity of root symbiosis microbe. Therefore, the participation of root help slow down the release of litter organic carbon, total phosphorus, but has no significant effect on litter mass loss and nitrogen dynamics.(2) The participation of root may accelerate or slow down the changes of organic carbon, total nitrogen and total phosphorus, but unaffected the dynamic of C: N: P during leaf litter decomposition of Liquidambar formosana and Pinus elliottii. Our results supported the theory of homogeneous with litter decomposition.(3) Litter input significantly promoted the differentiation of the understory vegetation roots in the litter layer, inhibited its differentiate in the soil layer, and the supply of water exacerbated these changes. Compared with the soil, the litter provide more NH4+-N and NO3–-N, and the water supply further help increase the mineral nitrogen content in the litter. Therefore, root layer can induce to grow lots of roots.(4) Litter input promoted the differentiation of absorption root, while inhibited the differentiation of storage root, and the water supply of increased the differentiation and growth of transportation root and storage root. At the situation of simultaneous litter input and water supply, the plant differentiated more absorption root to instead of the transport and storage roots. We deduced that the root growth and differentiation pattern might depend on with exogenous water and nutrient supplies.In summary, various factors regulated the interaction of undergrowth plant root growth and leaf litter decomposition in hilly red soil region plantation. We deduced in general that litter stoichiometric ratio has stronger ability to control the litter decomposition than the root growth of understory vegetation. But the participation of root could alter the dynamic pattern of litter decomposition with increasing the release rate of litter organic carbon, nitrogen, phosphorus. As we known, litter decomposition provides lots of mineral nitrogen and available phosphorus to satisfy plant requirement, and water supply promote the litter decomposition rate. Therefore, the roots would be induced to better grow and more differentiate in litter layer, compared with soil layers, since a better environment with higher water and nutrients content existed in litter layer. Clearly, water would play an important role in the "positive feedback" between litter decomposition and root growth.