【作者】 张成霞；

【导师】 南志标；

【作者基本信息】 兰州大学 ， 生态学， 2008， 博士

【摘要】 放牧是草地利用的主要方式之一,家畜通过采食、践踏和排泄粪便等3种主要形式影响草地,特别是草地的土壤状况。本论文于2004-2006年,以陕、甘、宁交界的甘肃省环县、陇东黄土高原不同放牧率的天然草地为对象,系统探讨了放牧对草地土壤物理与化学性质、土壤微生物群落构成及其数量和土壤微生物生物量的影响。主要研究结果如下:1、土壤粘粒、粉(砂)粒、细砂和粗砂的含量百分比在不同放牧率的轮牧分区显著不同。其中粘粒和粉(砂)粒的含量在不放牧的(0只羊/hm~2)轮牧分区显著高于其他各放牧分区,而不同放牧率的轮牧分区间无显著差异。细砂的含量在5.3只羊/hm~2轮牧分区最高,在0只羊/hm~2的最低。粗砂的含量在8.70只羊/hm~2的轮牧分区最高,在0只羊/hm~2和2.7只羊/hm~2的轮牧分区最低。一年中,土壤粘粒、粉(砂)粒、粗砂含量百分比均是9月最高,其在0-30cm土层内的垂直分布特征为粗砂在0-10cm的表层最高,而粘粒、粉(砂)粒、细砂等则是随土层加深而增加。2、连续两年7次对4个放牧强度轮牧分区取样测定土壤有机质和营养成分含量。结果表明,多数情况下,各处理间的有机质和全氮含量无显著差异,而全磷和铵态氮含量在0只羊/hm~2的轮牧分区显著高于2.7只羊/hm~2,硝态氮含量在8.7只羊/hm~2的轮牧分区显著高于0只羊/hm~2的轮牧分区;速效磷含量在2.7只羊/hm~2或0只羊/hm~2轮牧分区显著高于8.7只羊/hm~2的处理。一年中,土壤有机质、全氮、硝态氮含量、pH值均表现为9月最高,全磷和速效磷在11月最高,铵态氮在5月或6月最高。在空间分布上,土壤有机质、全氮、全磷和硝态氮表现为随土层的加深而增加,而土壤铵态氮、速效磷和pH值则表现为随土层的加深而降低。3、各轮牧分区内土壤微生物数量中,以真菌最少,仅占微生物总数的0.10-1.29%,其次为放线菌,占微生物总数的17.37-59.63%,细菌数量最高,占微生物总数的40.27-82.23%。就不同放牧率而言,土壤微生物总数在放牧率为8.7只羊/hm~2的轮牧分区最高,在5.3只羊/hm~2的轮牧分区最低。土壤真菌数量则是在2.7只羊/hm~2轮牧分区最高,其次为5.3只羊/hm~2和8.7只羊/hm~2,在0只羊/hm~2的轮牧分区最低。细菌数量亦是在8.7只羊/hm~2的轮牧分区最高,5.3只羊/hm~2轮牧分区最低,0只羊/hm~2和2.7只羊/hm~2介于其间。放线菌数量在2.7只羊/hm~2的轮牧分区最高,其次为5.3只羊/hm~2和8.7只羊/hm~2的轮牧分区,0只羊/hm~2的轮牧分区最低。一年中,真菌和细菌数量的最高值均出现在9月,最低值在4月或11月;而放线菌的最高值在11月,最低值在4月或6月。在空间分布上,土壤真菌、细菌和放线菌表现为随土层的加深而显著降低。土壤真菌和细菌、真菌和放线菌、细菌和放线菌数量之间呈显著的正相关,相关系数分别为0.3362-0.4626、0.2087-0.4535和0.6434-0.6456。土壤真菌、细菌数量分别与土壤中铵态氮、硝态氮含量呈显著正相关(p＜0.05),放线菌数量与土壤中全磷含量呈显著正相关(p＜0.05),土壤pH值与细菌、放线菌数量均分别呈显著正相关(p＜0.05)。4、不同放牧强度下,0-10cm、10-20cm和20-30cm土层,土壤微生物量碳均是在8.7只羊/hm~2的轮牧分区内最低,而微生物量氮在8.7只羊/hm~2的轮牧分区内的最高,其他3个放牧率分区间微生物量碳和氮含量差异不显著。土壤微生物量磷在0只羊/hm~2的轮牧分区内最低,其他3个放牧率分区间2.7只羊/hm~2或5.3只羊/hm~2的轮牧分区内的磷含量显著高于8.7只羊/hm~2的分区。不同取样期,土壤微生物量碳和磷在9月份达到最高,微生物量氮在11月份最高。连续两年测定结果同时表明,放牧的累加效应十分明显。2005年各期各区的微生物量碳和氮明显低于2004年相同时期。土壤微生物量碳、氮和磷在空间分布上均表现为随土层的加深而显著降低,且含量在各层次间均差异显著(p＜0.05)。土壤微生物量碳和氮、氮和磷、碳和磷均呈显著正相关(p＜0.05),相关系数分别为0.3649、0.2195和0.3390。回归方程式分别为y=0.036x+7.2752、y=0.0562x+5.5049和y=0.0064x+5.1656,决定系数分别为0.3649、0.2195和0.3390。土壤微生物量碳分别与粘粒、粉(砂)粒含量显著正相关(p＜0.05),而与细砂含量显著负相关。微生物量氮与速效磷呈显著正相关。微生物量磷与土壤pH值显著正相关。根据上述结果,似可认为试验草地条件下,适宜放牧率为2.7-5.3只羊/hm~2。更多还原

【Abstract】 Grazing is one of the main uses of grassland. Livestock interacts with grassland by its activities of feeding, trampling and excreting. Effects of grazing on soil physical and chemical properties, and soil microbes in semi-arid grassland were studied during the period of 2004 to 2006 at Huanxian County, eastern Gansu Province, which belongs to the Loess Plateau. The stocking rates of sheep used in the experiments were 0 sheep unit/ha, 2.7 sheep unit/ha, 5.3 sheep/ha and 8.7 sheep unit/ha. Soil samples were taken for seven times at various growing stages of grassland plants at the depth of 0-30cm from paddocks with different stocking rates. The soil samples were studied for the contents of soil particles at various size, nutrient components, and soil microbial components. The main results are summarized as the follows:1、The contents of clay, silt, fine sand and coarse sand were significantly different among the soils taken from paddocks with various stocking rates. The contents of clay and silt at paddocks with 0 sheep unit/ha were significantly higher than the paddocks with other stocking rates. Whereas the contents of coarse sand were the highest at paddock grazed at 8.7 sheep unit/ha , and were the lowest at the paddocks grazed at both 0 sheep unit/ha and 2.7 sheep unit/ha. The highest contents of clay, silt and coarse sand were all obtained on September during the year. In the 0-30 cm soil layers, content of coarse sand was the highest at the 0-10cm depth, while the contents of clay, silt and fine sand were increasing with soil depth.2、The contents of soil organic matter and total N were no significant at different treatments. However, the contents of total P and NH₄⁺-N at the paddocks with 0 sheep unit/ha were significantly higher than those at the paddocks with 2.7 sheep unit /ha. NO₃^-- N content at paddocks with 8.7 sheep unit /ha was significantly higher than that obtained at the paddocks grazed at 0 sheep unit/ha. Contents of available P at paddocks with at 0 sheep unit /ha and 2.7 sheep unit /ha were significantly higher than that at paddocks with 8.7 sheep unit/ha. Contents of soil organic matter, total N, NOV - N and pH were highest on September during the year regardless the stocking rates and soil depth, while contents of total P and available P were highest on November. NH₄⁺- N was highest on May or June. In terms of spatial distribution contents of soil organic matter, total N, total P and NO₃^-- N were all increasing with soil depth. However, contents of NH₄⁺- N, available P and pH were decreasing with soil depth. 3、Among the soil organisms isolated from various paddocks the number of soil fungi was the lowest, which was followed by the number of actinomycete, and the number of bacteria was the highest. They account for 0.10-1.29 %, 17.37-59.63 % and 40.27- 82.23 %, of the total number of microorganism isolated, respectively. The total numbers of soil microorganisms and the number of bacteria were both the highest at paddocks with 8.7 sheep unit/ha and were the lowest at the paddocks with 5.3 sheep unit/ha. Whereas the number of soil fungi was the highest at the paddocks with 2.7 sheep unit/ha, followed by the paddocks with 5.3 sheep unit/ha and 8.7 sheep unit/ha, and the lowest number obtained from the paddocks with 0 sheep unit/ha. The number of actinomycete was highest at the paddocks with 2.7 sheep unit/ha, followed by the stocking rates of 5.3 and 8.7 sheep unit/ha and lowest number was obtained at the paddocks with 0 sheep unit/ha. Both the numbers of fungi and bacteria were the highest on September and the lowest on April and November, while the highest number of actinomycete was on November. The numbers of soil fungi, bacteria and actinomycete were all significantly decreasing with soil depth. The significant positive correlations were found between the numbers of fungi and bacteria, of fungi and actinomycete, of bacteria and actinomycete, the correlation coefficience were 0.3362-0.4626, 0.2087-0.4535 and 0.6434-0.6456, respectively. Soil fungi, bacteria and soil NH₄⁺- N, NO₃^-- N was also correlated significantly and positively （p <0.05）. Actinomycete number and total P was also significantly and positively correlated （p<0.05）. Another significant correlation was found between soil pH and the number of bacteria, the number of actinomycetes, respectively （p<0.05）.4、Soil microbial biomass C the was lowest at the paddocks with 8.7 sheep unit/ha. However, microbial N was the highest under the same stocking rate. Microbial biomass C and N was not differed significantly among other stocking rates. Soil microbial biomass P was the lowest at paddocks with 0 sheep unit/ha, it was significantly higher at paddocks with 2.7 sheep unit/ha or 5.3 sheep unit/ha than the 8.7 sheep unit/ha treatment. At different sampling dates, soil microbial C and P were the highest on September, microbial N was the highest on November. Two years results showed that the cumulative effect of grazing was very obviously. Microbial biomass C and N in 2005 was significantly lower than those obtained at the same period of 2004. Soil microbial biomass C, N and P were significantly decreasing with soil depth and a significant difference was also found among the soil depths of 0 - 10 cm, 10 - 20 cm and 20 - 30 cm. （p<0.05）. A significant and positive correlation was existed between soil microbial biomass C and N, N and P, C and P （p<0.05）, the correlation coefficient was 0.3649, 0.2195 and 0.3390, respectively. The corresponding regression equation was y = 0.036x +7.2752, y = 0.0562x + 5.5049 and y = 0.0064x + 5.1656, respectively. Soil microbial biomass C and the content of clay and silt was correlated with each other positively （p<0.05）. Microbial C and fine sand content was correlated negatively.Based on the results mentioned above it may be conclude that the stocking rates of 2.7 sheep unit /ha and 5.3 sheep unit /ha were more appropriated for the grassland studied.更多还原