不同草本层三倍体毛白杨细根及草根的空间分布及季节变化

以退耕还林后2种不同草本层(自然草、黑麦草)模式下的4年生三倍体毛白杨幼林为研究对象,利用土柱法对林地细根和草根按照0~10 cm(上层)、10~20 cm(中层)、20~30 cm(下层)3个土壤层次,2个径级(0~1 mm,1~2 mm)进行每月1次、为期1 a的草根和细根生长及死亡的生物量研究。结果表明:2种模式林地内,2个径级活细根的生物量,基本为上层中层下层,黑麦草林地在上、中、下层变化趋势均比自然草林地明显,0~1 mm细根上层有明显的年变化趋势,峰值出现在5月和9月,谷值分别出现在8月和7月;2个径级死细根的生物量,0~1 mm径级为上层中层下层,1~2 mm径级则全年均为中层下层上层,黑麦草林地变化同样比自然草林地明显。2种模式内3层0~1 mm、1~2 mm活细根与死细根生物量的比值为5∶1。2种模式草根的生物量上层峰值也都出现在5月和9月,与0~1 mm细根上层相同,谷值则出现在8月。草根的年平均生物量,黑麦草仅在上层和中层分布,每层的自然草根系生物量都比黑麦草根系生物量大得多,上层是黑麦草的3.6倍,中层是黑麦草根系的4.6倍。人工种植的黑麦草林地细根生物量(0.614 t/hm~2)较自然草林地生物量(0.465 t/hm~2)高,但细根和草根合在一起后,自然草林地比黑麦草林地高。在自然草林地内,草根占据了0~2 mm根系生物量的53.4%,可见,就0~1 mm的根系来说,在造林初期,生物量在自然条件下要比人为干扰环境下大得多。

Spatial Distribution and Seasonal Variations of Fine Root and Grass Root in Different Herbaceous Layer of Triploid Populus tomentosa Woodland

According the soil depth:the upper layer(0—10 cm soil layer) ,the middle layer(10—20 cm soil layer) and the lower layer (20—30 cm soil layer) ,and the diameter of fine root:0—1 mm and 1—2 mm,the biomass dynamics of live and dead fine root and grass root in different herbaceous layer ( the natural grass which growed in natural conditions and the ryegrass which were planted by person) of the 4-year old triploid Populus tomentosa woodland were studied every month for one year with the monoliths approach . The results showed that the live fine root biomass in the diameter of 0—1 mm and 1—2 mm all showed upper layer > middle layer > lower layer, and the fine root biomass change trend of ryegrass woodland was obvious compared with that of the natural grass. The biomass of live fine root in the diameter of 0—1 mm of the two forests showed significant annual variations,and the maximum values ofthe two types both appeared in May and September,while the minimum values appeared in August and July respectively. The change trend of dead fine root biomass in the diameter of 0—1 mm and 1—2 mm of ryegrass woodland was obvious compared with that of the natural grass,the dead fine root biomass in the diameter of 0—1 mm showed upper layer>middle layer>lower layer,and the dead fine root biomass in the diameter of 1—2 mm showed middle layer>lower layer>upper layer. Not only in ryegrass woodland but also in grass woodland,the ratio of live fine root and died fine root was 5:1. The root biomass of ryegrass only distributed in upper layer and middle layer. The biggest grass root biomass was found in May and September,and the smallest one occurred in August both in the two types. The grass root biomass in the natural grass forest was far more than that in the ryegrass forest,which were more than 3. 6 times and 4. 6 times respectively in 0—10 cm soil layer and 10—20 cm soil layer. There was a difference in annual average fine root(≤2 mm) biomass between the ryegrass woodland and the grass woodland,which were 0. 614 t/ha and 0. 465 t/ha respectively. But the root biomass of grass woodland was higher than that of ryegrass woodland after grass root was added. In grass woodland,grass root account for more than half of 0—2 mm root biomass(53. 4%),this fully testifies to the biomass of fine root,especially the diameter less than 1mm,which in natural conditions was much larger than in interfered environment by human in the early triploid Populus tomentosa woodland.