不同树种结构对农田防护林效益的影响机制

Difference in Protective Effects of Farmland Shelterbelts with Different Structures of Tree Species

研究了在小黑杨、落叶松、樟子松防护林带防护范围内,玉米、大豆、向日葵的光合指标及土壤水分。结果表明:对各作物种植区土壤水分的影响,杨树林带最大,樟子松次之,落叶松最小。杨树林带胁地范围1.6H(杨树平均树高H的1.6倍)内,大豆光合指标最优,玉米最弱。1.6H外,向日葵光合指标最优,大豆最弱;落叶松林带胁地范围0.8H(落叶松平均树高H的0.8倍)内,玉米光合指标最优。0.8H外,3种作物的光合指标近似;樟子松林带胁地范围0.8H(樟子松平均树高H的0.8倍)内,3种农作物的光合指标近似。0.8H外,玉米光合指标最优,大豆最弱。对玉米净光合速率的影响,杨树林带最大,落叶松最小;对向日葵的光合的影响,杨树最大,樟子松最小;3种树种对大豆的净光合速率的影响基本相同。

The photosynthetic indexes of corn, soybean, and sunflower as well as soil absolute moisture content were determined and analyzed by selecting croplands within the protected range of farmland shelterbelts of poplar, larch, and Scotch pine. Poplar shelterbelt had the most obvious effect on soil moisture, and then followed by Scotch pine shelterbelt and larch shelterbelt in order. The photosynthetic indexes of soybean were the best and those of corn were the worst when the cropland was within 1.6 times of poplar height away from the poplar sheherbeh, while the photosynthetic indexes of sunflower was the best and those of soybean were the worst when the distance between cropland and poplar shelterbelt was beyond 1.6 times of tree height of poplar. The photosynthetic indexes of corn were the best when the distance between cropland and larch shelterbelt was within 0.8 times of tree height of larch, and those of these three crops were similar when the distance between cropland and larch sheherbelt was beyond 0. 8 times of tree height of larch. The photosynthetic indexes of these three crops were similar when the distance between cropland and Scotch pine shelterbelt was within 0.8 times of tree height of Scotch pine, while the photosynthetic indexes of corn was the best and those of soybean were the worst when the distance between cropland and Scotch pine shelterbelt was beyond 0.8 times of tree height of Scotch pine. Poplar shelterbelt greatly influenced the net photosynthetic rate of corn and larch shelterbelt showed the weakest influence, while poplar shelterbelt had marked influence on the net photosynthetic rate of sunflower and Scotch shelterbelt exerted the slightest influence. The shelterbelts of poplar, larch, and Scotch pine had similar influences on the net photosynthetic rate of soybean.