| In this paper, fine root, grass root biomass, nutrient and its dynamics in seasons, root system and organ nutrient accumulation, root system and soil nutrient comparison in the compound mode of Betula luminiferra-Hemarthria compressa in Hongya were studied, we discuss growth accumulation of underground part, nutrient competition and use of effectiveness of soil resource in the mode to screen and set up forest-grass mode and to provide a basis for the sustainable development of the mode of Betula luminiferra-Hemarthria compressa.1,In the mode of Betula luminiferra-Hemarthria compressa living fine root ofΦ0～1mm has its total biomass of 0.5828 t/hm~2 in a year, which is 29.73% of fine root total of the group; grass root has 0.4993 t/hm~2, which is 25.47% of the group. So living fine root ofΦ0～1mm has the most part of fine root biomass. Living fine root ofΦ0～1mm of Betula luminiferra is in its vigorous growth period in September and October and its has its minimum: 0.027t/hm~2 in February. However dead fine root ofΦ0～1mm has little up and downs. Its ups are in May and September and dowers in January and March. Living fine root ofΦ1～2mm has two ups in a year: maximum in July. Dead fine root ofΦ1～2mm has growth curves of very small fluctuations in a year, which are between 0.0082～0.0165t/hm~2.The change of grass root in a year is basically consistent with living fine root ofΦ0～1mm and its growth curve takes on "V": its bottom in March, top in October and its vigorous period is from May to October.2,On horizontal distribution, the difference between the fine root of Betula luminiferra and the grass root in every diameter lever is small. The curve of the biomass of living fine root is coincident with that of grass horizontal distribution, which means: 100cm＞150cm＞50cm while on vertical distribution the difference is notable. The biomass of living fine root ofΦ0～1mm on the upper layer takes 63.73% of the total root. Dead fine root on the upper layer owns its total biomass of 0.2402 t/hm~2. Its growth curve takes on many humps, showing the similar change with growing biomass ofΦ0～1mm living fine root. Living and dead fine root ofΦ1～2mm in the upper layer both hare double-apex curves but in the middle and lower layer living fine root takes on "∨" shape and dead fine root takes on "∧"shape on the contrary. Biomass of fine root accounts for 40.02% in the upper layer and 59.98% in the middle and lower layer; while there is 81.27% of Hemarthria compressa in the upper layer. The annual dynamics growing curves of fine root and grass root ofΦ0～1mm and 1～2mm in the same way, showing their growth and reduction in the step with each other. Distribution change in space shows that there is a certain growing competition in 0～10cm soil strata but in the middle and lower layer their competition is weak.3,The non-capillary tube crevice, total crevice, ventilation degree and organic matter show: upper layer＞middle layer＞lower layer, which is the same as the biomass distribution of the fine root ofΦ0～1mm Betula luminiferra and grass root. The alternation strength of the fine root ofΦ1～2mm becomes greater because its diameter level is greater than that ofΦ0～1mm, so it is weakly affected by physical aspect, showing: middle layer＞upper layer＞lower layer. It is shown that the fine root ofΦ0～1mm and grass root are more strongly affected by the soil physical aspect but the fine root ofΦ0～1mm is more weakly affected.4,Betula luminiferra ofΦ0～1mm has moreN, P, K, Ca, Mgthat ofΦ1～2mm.It shows that the greater fine root diameter is, the lower the nutrient concentration is. The monthly change of content of N in every diameter level takes on"V"shape: bottom in January and top in September; content of P,K takes on "W" shape: two bottom in July and December and two tops in March and September; content of Ca and Mg changes just a little and fluctuates marginally in the whole year. There is a small content of P, k in winter and summer and a great one in spring and autumn; while N is connected with the temperature-bottom in January and top in September. On the contrary the monthly change of N of grass root takes on "M" shape; the content of P takes on single-apex shape: maximum of concentration in March; content of K fluctuates in the whole year and minimum in June.5,The nutrient contents in the organs of Betula luminiferra are sorted: leaf＞bark＞branch＞trunk and differences in the performance of the elements in the root system are: N＞K＞Ca＞Mg＞P, which shows more N, K are spent on accumulation of root system biomass. The nutrient contents in the root system of Hemarthria compressa are sorted: K＞N＞Ca＞Mg＞P. There are more elements in the grass than grass root. The rule of the nutrient accumulation of the unit dry matter in the mode is: N＞K＞Ca＞Mg＞P; in the mode the nutrient content in the organ unit weight is: Hemarthria compressa＞leaf＞bark＞grass root＞branch＞tree root＞trunk.6,Considering the monthly dynamics of N in the root system and soil, we think content of N of grass root is greater than fine root, the level of N of the fine root and grass becomes relatively cower during the peak of the nutrient of the fast acting N and its bottom is in February and goes up slowly from June to September. Absorption of P, fast-acting N and all the P of grass have the basic trend line and take on two translational lines but all the P of fine root has the opposite trend to that of grass root. Change of all the K of fine root is in the situation to maintain a steady straight line all the year. Grass root has the similar fluctuation to the fine root all the year and is in the bottom for some time in June. It has more K than fine root overall; the change of soil fast-acting K takes on "W" shape. All the Ca has the similar monthly change to exchange of Ca, content of the grass root is greater than that of the fine root overall but change of the fine root shows the opposite trend to the grass and exchange Ca. The fine root has the opposite monthly dynamics curve trend of Mg to grass root, which shows both of them have the different requires of Mg in time, which don't lead to the lack of exchange of Mg. The content of Mg of the grass root is greater than the fine root and it shows the grass root absorbe more Mg and it plays a major role in the change of Mg in the soil.From the above Betula luminiferra has been collocated with Hemarthria compressa and there is a symbiotic relationship in their biomass accumulating underground. So in the mode the local farmers plant forage under trees to raise cows and they can get much economic benefit from it. We think it the win-win mode in the economy and ecology.
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