A study on the root competitive pattern of annual pasture in mixed grassland in alpine region

Competition is a common phenomenon among plant communities, especially among natural communities. It is an important factor in biology and plant–plant interactions has inspired an increasing concern in recent years. The investigation of inter-specific competition is useful to reveal the mechanism in plant growth and reproduction of organisms. Plant root systems play an important role in uptake of water and nutrients from soil for plant growth. However, it is still a divergent topic about the regulating mechanism between root morphological variations and competition. The spatial distribution, morphology of plant roots and above-ground growth can be influenced by inter-specific interactions. Their morphology characteristics and structure distribution were studied to reveal the adaptive mechanism of roots system in the soil environment. The deWit series experiments were conducted to study the relationship between relative competitive ability immixture and monoculture along seven levels of density at the experiment station of Shiyang river in Sunan country of Gansu province in 2010 (latitude 37°58′26′′N, longitude 101°47′ 34′′E). It was carried out to analyze inter-specific interaction between Avena sativa L. and Vicia villosa Roth. Taking the roots both A. sativa L. and V. villosa Roth as the research object, the WinRHZO was used to measure the changes of root length, diameter, surface area and so on. To evaluate the competitive responses and the competitive effects of target plants, the plant combinations with A. sativa L. and V. villosa Roth were established in plots in seven replacement grass–legume combinations (monoculture of A. sativa L. and V. villosa Roth, and mixed culture of A. sativa L. and V. villosa Roth with the ratios: 8:2, 6:4, 5:5, 4:6, 2:8).Four indexes of Relative yield (RY), relative yield total (RYT), Aggressivity (AG) and Relative crowding coefficient (RCC) were used to measure competition performances of inter-specific competition, and inter-superiority during different phonological period. The results showed that RYy, RYm and RYT of each seeding group was less-than 1 from seeding stage to mature stage, the degree of inter-specific competition was stronger than intra-specific, A. sativa L. and V. villosa Roth obviously showed hostile relations, however, the competitive superiority of two species has significant difference. From seeding stage to tillering stage, the RCCy of group B and group E was bigger than 1, RCCm was less-than 1 and the AG was bigger than 0, so the competitive power of A. sativa L. was stronger than V. villosa Roth, A. sativa L. gain advantage in the competition by increasing the root length and advancing the nutrient absorption ability, the competitive power of other groups cannot be judged. From jointing stage to seeding stage, the RCCy of group A, C and D was less-than 1, RCCm was bigger than 1 and the AG was bigger than 0, so the competitive power of V. villosa Roth was stronger than A. sativa L., which was caused by increasing the number of A. sativa L. root, so the advantage in the competition gradually declined. Two species responded the transforming of inter-specific relationship well by adjusting the root morphology plasticity.