Root and leaf senescence of maize subject to spatial differentiation of soil water and CO2 in sandy fields with plastic film mulching
摘要: 干旱区新垦绿洲沙地灌溉强度大, 农田覆膜后往往出现春玉米早衰现象。为探讨土壤水分和通气性是否是引发早衰的原因, 本研究在河西走廊绿洲春玉米农田设置不覆膜(NM)和覆膜(PFM)处理, 探求覆膜条件下土壤水分和CO2分压(pCO2)对玉米根系生长、绿叶面积衰减、光合生理以及籽粒产量与品质的影响。相比不覆膜处理, 覆膜区域的土壤pCO2较未覆膜区域高40%以上; 覆膜区域过高的土壤pCO2 (0.93%~1.27%)使玉米花期根系活力下降19.7%, 但非覆膜区根长密度和根系活力分别增加22.7%和9.6%。覆膜提高了春玉米拔节期叶片光合速率(20.0%)和蒸腾速率(8.5%), 但抑制了花后叶片光合速率(−40.0%)和蒸腾速率(−18.0%); 覆膜处理相对绿叶面积衰减启动时间和衰减最大速率时间分别提前1.7 d和7.1 d, 而平均衰减速率和最大衰减速率分别增加6.7%和21.7%。覆膜的上述效应未显著影响玉米籽粒产量, 但使籽粒淀粉含量和蛋白质含量分别降低20.1%和22.1%。以上结果表明, 在干旱区新垦绿洲沙地, 覆膜根区土壤pCO2过高可能是导致玉米花后早衰和籽粒品质下降的重要原因, 后期建议开展适时揭膜、控制灌溉(如亏缺灌溉、分根交替灌溉)或加气灌溉对覆膜新垦绿洲农田土壤通气性的改善研究。Abstract: High intensive irrigation is commonly found in newly reclaimed oasis sandy land in arid area, which easily causes plant senescence of spring maize in farmland with plastic film mulching. The previous studies have found that land cover significantly affected soil moisture and soil aeration, but the data of spatial differentiation of soil moisture and soil aeration under mulching condition was lacking. In order to explore whether soil moisture and aeration causes plant senescence, an experiment was conducted to investigate the effects of plastic film mulching on spatial differentiation of soil water and partial pressure of soil CO2 (pCO2) in root zone, root growth, green leaf duration, leaf photosynthetic physiology, grain yield and grain quality of spring maize in a sandy farmland in the Hexi Corridor (100°12′E, 39°20′N, 1370 m above sea level). Two treatments [plastic film mulching (PFM) and no mulching (NM)] were set up in this experiment. In the current study, oven drying method was used to determine soil water content. Soil gas was collected by gas well method, which was composed of collecting pipe, transmission pipe and a sampler. The CO2 concentration of gas samples was analysed by a gas chromatograph (Agilent 7890A, Agilent, Palo Alto, USA). Plant roots were sampled using a steel drilling, washed into a nylon mesh bag, scanned with root a scanner (EPSON Perfection V700) and then obtained root length density (RLD) using WinRHIZOPro software. Crop evapotranspiration was determined using water balance method. Soil moisture showed no significant difference in horizontal direction in NM treatment, whereas, the average soil moisture of mulched soil (narrow row and wide row at 5 cm distance from plants) was 28.1% (P<0.05), 15.2% (P<0.05) and 21.7% (P<0.05) higher than that under non-mulched soil (wide row at 25 cm distance from plants) before, 6-days after, and 9-days after irrigation. In contrast, soil pCO2 in mulched zone was 40% higher than that in the in non-mulched zone. Compared with NM treatment, the excessively high soil pCO2 (0.93%−1.27%) under mulched zone decreased the maize root activity by 19.7% at flower stage, but the root distribution and activity in the non-mulch zone increased by 15.8% and 9.6%, respectively. Compared with the NM, the leaf photosynthetic rate and transpiration rate in PFM were increased by 20.0% and 8.5% at the jointing stage, respectively, but the corresponding value were −40.0% and −18.0% respectively. In addition, compared with the NM, the senescence-start time and senescence-maximum time of green-leaves were 1.7 d and 7.1 d earlier in PFM, respectively, while the average and maximum green-leaves senescence rates were increased by 6.7% and 21.7% in PFM, respectively. The above effects of mulching did not significantly affect the yield of corn grain, but reduced the starch content and protein content of grain by 20.1% and 22.1%, respectively. The above results show that the excessively high soil pCO2 after maize flowering in the newly reclaimed oasis sandy land in the arid area may be an important reason of plant senescence and grain quality degradation, and it is recommended to take timely film-uncovering, controlled irrigation (e.g., deficit irrigation, root alternating irrigation) or aerated irrigation to improve soil aeration.
图 4 覆膜(PFM)和不覆膜(NM)处理下灌水前后春玉米根区土壤(0~60 cm)含水率
−10为窄行在水平方向距植株10 cm处, 5、15和25分别为宽行在水平方向距植株5 cm、15 cm 和25 cm处; PFM处理中, −10和5为覆膜区域, 15为覆膜区域边缘, 25为不覆膜区域。不同小写字母表示同一处理不同水平距离间差异显著(P<0.05), 不同大写字母表示同一水平距离不同处理间差异显著(P<0.05)。−10 is the sampling point at 10 cm distance from the plant in narrow row in the horizontal direction, and 5, 15 and 25 are the sampling points at 5 cm, 15 cm and 25 cm distance from the plant in wide row in the horizontal direction, respectively. Under PFM treatment, −10 and 5 refer to the mulching area, 15 refers to the edge of mulching area, and 25 refers to uncovered area. Different lowercase letters indicate significant differences at P<0.05 level among different horizontal distances of the same treatment, and different capital letters indicate significant differences at P<0.05 level among different treatments at the same horizontal distance.
Figure 4. Soil water content in root zone (0−60 cm) of spring maize before and after irrigation under no mulching (NM) and plastic film mulching (PFM) treatments
图 5 覆膜(PFM)和不覆膜(NM)处理下灌水前后春玉米生育期根区(0~60 cm)土壤CO2分压
−10为窄行在水平方向距植株10 cm处, 5、15和25分别为宽行在水平方向距植株5 cm、15 cm和25 cm处; PFM处理中, −10和5为覆膜区域, 15为覆膜区域边缘, 25为不覆膜区域。不同小写字母表示同一处理不同水平距离间差异显著(P<0.05), 不同大写字母表示同一水平距离不同处理间差异显著(P<0.05)。−10 is the sampling point at 10 cm distance from the plant in narrow row in the horizontal direction, and the 5, 15, and 25 are the sampling points at 5 cm, 15 cm, and 25 cm distance from the plant in wide row in the horizontal direction. Under PFM treatment, −10 and 5 refer to the mulching area, 15 refers to the edge of mulching area, and 25 refers to uncovered area. Different lowercase letters indicate significant differences at P<0.05 level among different horizontal distances at the same treatment, and different capital letters indicate significant differences at P<0.05 level among different treatments at the same horizontal distance.
Figure 5. Partial pressure of soil CO2 (pCO2) in root zone (0−60 cm) of spring maize before and after irrigation under no mulching (NM) and plastic film mulching (PFM) treatments
图 7 覆膜(PFM)和不覆膜(NM)处理下春玉米花期根长密度分布及根系活力
不同小写字母表示同一指标在同一垂直深度(左图)或水平距离(右图)不同处理间差异显著(P<0.05)。右图中, −10 cm 为窄行在水平方向距植株10 cm处, 5 cm、15 cm 和25 cm分别为宽行在水平方向距植株5 cm、15 cm 和25 cm处l; PFM处理中, −10和5为覆膜区域, 15为覆膜区域边缘, 25为不覆膜区域; 柱子和带散点的折线分别为平均根长密度和根系活力。
Figure 7. Root length density and activity of spring maize at flower stage at different soil depth and horizontal distance from plant under no mulching (NM) and plastic film mulching (PFM) treatments
Different lowercase letters indicate significant differences at P<0.05 level of the same indicator among different treatments at the same depth (left figure) or horizontal distance (right figure). In the right figure, −10 cm is the sampling point at 10 cm distance from the plant in narrow row in the horizontal direction; 5 cm, 15 cm and 25 cm are the sampling points at 5 cm, 15 cm and 25 cm distance from the plant in wide row in the horizontal direction, respectively; Under PFM treatment, −10 and 5 refer to the mulching area, 15 refers to the edge of mulching area, and 25 refers to uncovered area; bar and line with dots in the right figure refer to average root length density and root activity, respectively.
图 9 覆膜(PFM)和不覆膜(NM)处理下春玉米不同生长阶段叶片光合与蒸腾速率
Figure 9. Leaf photosynthetic rate and transpiration rate of spring maize under no mulching (NM) and plastic film mulching (PFM) treatments at different growth stage
Different lowercase letters indicate significant differences at P<0.05 level between different treatments at the same time at elongation stage, and different capital letters indicate significant differences at P<0.05 level between different treatments at the same time at grainfilling stage.
表 1 试验地0~120 cm土层土壤基本理化性质
Table 1. Basic soil physical and chemical properties (0−120 cm depth) at the experimental site
Field capacity (%)
Soil particle size distribution (%)
0~20 1.43 33.2 7.81 18.5 13.2 16.2 18.3 65.5 20~40 1.49 31.9 3.73 12.3 21.8 13.1 18.3 68.6 40~60 1.52 28.6 2.78 9.8 13.4 11.2 14.2 74.6 60~90 1.56 26.5 2.22 6.7 7.3 9.6 9.8 80.6 90~120 1.58 24.3 1.57 5.8 6.2 7.8 6.4 85.8
表 3 春玉米籽粒产量和品质以及土壤和作物的其他指标的相关矩阵
Table 3. Correlation matrix containing grain yield and quality and other indexes of soil and crop of spring maize
Partial pressure of CO2 in soil
Leaf senescence start time
Average leaf senescence
1.00 0.53* −0.21 −0.14 0.19 0.28 0.25 −0.27 −0.18 土壤CO2分压
of CO2 in soil
1.00 −0.66* −0.57* 0.73** 0.66* 0.32 −0.61* −0.59* 根系活力
1.00 0.62* −0.51* −0.57* 0.21 0.35 0.62* 光合速率
1.00 −0.78** −0.82** 0.28 0.52* 0.48 绿叶衰减启动时间
Leaf senescence start time
1.00 0.73** 0.16 −0.69* −0.52* 绿叶平均衰减速率
Average leaf senescence rate
1.00 0.41 −0.75** −0.64* 产量 Grain yield 1.00 0.17 −0.22 淀粉含量
1.00 −0.30 蛋白质含量
1.00 *和**分别表示在P<0.05和P<0.01水平显著相关。* and ** indicate significant correlations at P<0.05 and P<0.01 level, respectively.
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