Relationship Between Root Distribution And Soil Nutrients In Three Forest Stands In Hilly Area Of Central Hainan

In order to clarify the root distribution characteristics and soil nutrient characteristics of tropical natural Secondary forests and plantations,as well as the relationship between them,and explore the relevant management theory and technology,so as to provide technical and theoretical support for scientific and rational management of tropical natural Secondary forests and plantations,and better play to their ecological benefits and productivity,this paper takes tropical natural Secondary forest(Secondary forest),Hevea brasiliensis plantation and Acacia mangium plantation in hilly areas of central Hainan as the research objects.The small sample excavation method was used to study the distribution characteristics of root biomass,root length distribution and soil nutrient characteristics of the three forests,and the relationship between root and soil nutrient.The results shows that:to improve the soil fertility of Secondary forest,Hevea brasiliensis plantation and Acacia mangium plantation in hilly areas of central Hainan,it is the key to improve the soil total phosphorus,available phosphorus and alkali-hydrolyzable nitrogen content.The soil surface layer at 0–20 cm depth is the key area for water and fertilizer management of each stand.For plantation,in order to promote stand growth better,water and fertilizer management can be considered in deeper soil layers,and slow-release fertilizer is recommended.The main conclusions:(1)Root distribution characteristics of Secondary forest,Hevea brasiliensis plantation and Acacia mangium plantation were similar in general.The root biomass and root length of the three stands showed obvious stratification distribution.Root biomass density and root length density decreased significantly with the increase of root diameter and soil depth,and the decreasing trend slowed down layer by layer.Root biomass and root length of each stand were mainly distributed in soil surface layer(0-20 cm),biomass accounted for 63.71%(Secondary forest),55.51%(Hevea brasiliensis plantation),60.57%(Acacia mangium plantation),root length accounted for 65.73%(Secondary forest),44.88%(Hevea brasiliensis plantation)and 41.38%(Acacia mangium plantation).Fine root biomass and root length accounted for the main part of total biomass and root length,fine root biomass accounted for 48.41%(Secondary forest),49.53%(Hevea brasiliensis plantation),45.88%(Acacia mangium plantation).The proportion of fine root length was 91.98%(Secondary forest),92.27%(Hevea brasiliensis plantation),and 89.82%(Acacia mangium plantation),respectively.Root biomass density,Secondary forest(913.42±77.31 g/m~3)>Hevea brasiliensis plantation(633.57±58.09 g/m~3)>Acacia mangium plantation(529.08±23.00 g/m~3).Fine root biomass density,Secondary forest(442.19±62.03 g/m~3)>Hevea brasiliensis plantation(313.81±16.77 g/m~3)>Acacia mangium plantation(242.72±13.85 g/m~3).Root length density of Secondary forest(1023.21±127.90 m/m~3)was the highest,followed by Hevea brasiliensis plantation(998.57±66.38 m/m~3)and Acacia mangium plantation(463.86±45.64 m/m~3).The fine root length density of Secondary forest was the highest(941.16±115.90 m/m~3),followed by Hevea brasiliensis plantation(921.43±61.74 m/m~3)and Acacia mangium plantation(416.63±52.97 m/m~3).(2)The root distribution characteristics of three stands were different in different diameter roots.The adaptability of roots with different diameters in Secondary forest to soil depth was basically the same.The adaptability of roots with different diameters in Secondary forest to soil depth was basically the same.The vertical distribution of different diameter roots is basically the same.In the plantation(Hevea brasiliensis plantation and Acacia mangium plantation),the biomass allocation rules of roots with different diameters in different soil layers were different.The horizontal proportion of fine roots increased with the deepening of soil layer,the horizontal proportion of coarse roots decreased with the deepening of soil layer,and the vertical proportion of roots increased with the increase of root diameter.(3)The soil nutrient contents of the three stands generally decreased with the deepening of soil layer,but they had different characteristics in specific soil nutrients.The main nutrients of each stand were mainly distributed in the soil at 0–40 cm depth,and the soil surface at 0–20 cm depth was the most abundant.In contrast,the contents of soil organic matter,total nitrogen,available phosphorus and nitrate nitrogen in Secondary forest were rich.The contents of total nitrogen,total phosphorus and total potassium in Hevea brasiliensis plantation were abundant.The contents of total potassium,available potassium and ammonium nitrogen in Acacia mangium plantation were abundant.(4)In order to improve the soil fertility of Secondary forest,Hevea brasiliensis plantation and Acacia mangium plantation in hilly areas of central Hainan,the key is to increase the contents of total phosphorus,available phosphorus and alkali-hydrolyzable nitrogen in soil.Affected by climate and leaching effects,the soil of the three forests is relatively barren.Soil comprehensive fertility coefficient Hevea brasiliensis plantation(1.69)>Secondary forest(1.59)>Acacia mangium plantation(1.45).Total phosphorus,available phosphorus and alkali-hydrolyzable nitrogen in Secondary forest and Acacia mangium plantation were the main indexes affecting soil comprehensive fertility coefficient.Available phosphorus,available potassium and alkali-hydrolyzable nitrogen in Hevea brasiliensis plantation are the main indicators affecting soil comprehensive fertility coefficient.(5)The root biomass distribution,root length distribution and soil nutrient distribution of the three forest stands were significantly correlated in general,and all showed obvious surface aggregation.However,the correlation between different diameter roots and soil nutrient indexes was different.The stepwise regression analysis of root biomass density on nutrient factors showed that organic matter and nitrate nitrogen had a significant positive effect on root biomass density of Secondary forest,while total phosphorus had no effect.The regression model was'total root=-16.182+222.501×organic matter-12972.049×total phosphorus+498.840×nitrate nitrogen'.Total nitrogen,total potassium and available phosphorus had significant positive effects on total root biomass density of Hevea brasiliensis plantation.The regression model was'total root=-973.048+764.889×total nitrogen+15.101×total potassium+230.593×available phosphorus'.Total nitrogen had a significant positive effect on total root biomass density of Acacia mangium plantation,and the regression model was'total root=-1735.055+3212.007×total nitrogen'.