生态学报  2015, Vol. 35 Issue (14): 4754-4762

文章信息

刘春伟, 康绍忠
LIU Chunwei, KANG Shaozhong
基于茎干直径微变化制定苹果灌溉制度
Assessment of trunk diameter fluctuation for irrigation schedule in apple trees
生态学报, 2015, 35(14): 4754-4762
Acta Ecologica Sinica, 2015, 35(14): 4754-4762
http://dx.doi.org/10.5846/stxb201311132724

文章历史

收稿日期:2013-11-13
修订日期:2014-09-09
基于茎干直径微变化制定苹果灌溉制度
刘春伟1, 2, 康绍忠2     
1. 南京信息工程大学应用气象学院, 江苏省农业气象重点实验室, 南京 210044;
2. 中国农业大学中国农业水问题研究中心, 北京 100083
摘要:茎干直径的动态微变化是研究植物体水分和生长状况的重要指标。利用测树器监测西北旱区盛果期苹果树茎干直径微变化规律,根据监测记录获得茎干直径日最大值(MXTD)、茎干直径日最大收缩量(MDS)数据,并探讨茎干直径微变化规律及其对环境因素的响应,为茎干直径微变化用于指导精确灌溉提供科学依据。实验结果表明,晴天或多云天气下,苹果树茎干直径在每天的7:00或8:00时刻达到一天最大值,在16:00左右达到一天的最小值,茎干直径年增长量与果实产量成反比例关系。整个生育期MXTD呈先快速增加后平稳的变化特征。2010年MDS与茎干水势(φstem)呈显著负相关关系(r2=0.76* * *, n=14),这表明MDS可以反映苹果树的水势状况。生育后期的MDS对环境因素响应比生育前期敏感,全生育期MDS与气象因素的决定系数大小顺序为日最大水汽压差(VPDmax)>日最高温度(Tmax)>净辐射(Rn)。茎干直径微变化规律可以反映西北旱区盛果期果树的水分状况,可以为果园灌溉制度的确定提供科学依据。
关键词茎干直径微变化    茎干直径日最大收缩量    苹果树    环境因子    灌溉制度    
Assessment of trunk diameter fluctuation for irrigation schedule in apple trees
LIU Chunwei1, 2, KANG Shaozhong2     
1. Jiangsu Provincial Key Laboratory of Agricultural Meteorology, College of Applied Meteorology, Nanjing University of Information Science and Technology, Nanjing 210044, China;
2. Center for Agricultural Water Research in China, China Agricultural University, Beijing 100083, China
Abstract:Research on agricultural water consumption in northwest China is crucial to relieve problems associated with the water crisis. Apples are a typical crop in China that have been used in agriculture for centuries. As production increases for economic growth, it is essential to analyze water transport mechanisms and water accessibility to mature apple orchards in arid regions. Trunk diameter fluctuation is an effective indicator of the water condition of plants. Its role as an indicator of plant water conditions thus emphasizes that it is crucial to design an irrigation schedule. The changes in the trunk diameter of mature apple trees (Malus domestica Borkh. cv Golden Delicious) was monitored using dendrometers at the Shiyanghe Experimental Station for Water-saving in Agriculture and Ecology of China Agricultural University (37°52'N, 102°51'E, altitude 1581 m). Stem water potential was measured using a pressure chamber. Wind speed, net radiation, relative humidity, and air temperature were monitored by an automatic meteorological station, and soil moisture was measured every 5 days using Time-Domain Reflectometry (TDR) methods based on the previously described data analysis. Change in the maximum daily trunk diameter (MXTD) and maximum daily diameter shrinkage (MDS), as well as their response to environmental factors were also monitored. The results showed that MXTD occurred at 7:00 to 8:00 in the morning and minimum of daily trunk diameter (MNTD) occurred at approximately 16:00 during sunny or cloudy days in 2008 on a daily scale. The trunk diameter increased at night and decreased during the day, which was meanly depended on reference evapotranspiration. MXTD increased during bud development, flowering, and leaf expansion periods (stage I) and remained constant during the fruit expanding and maturing periods (stage II), which was closely related to the MDS of the apple tree. Higher fruit yields were associated with smaller fruit stem diameter growth. MDS increased at the beginning and then gradually decreased during the entire growing stage. The relationship between MDS and stem water potential was linear and the determination coefficient was 0.76* * *. Consequently, MDS indicated the water status of the mature apple trees. However, MDS was more responsive to net radiation, reference evapotranspiration, vapor pressure deficit, and air temperature at stage II than at stage I because the canopy structure was not developed, and the water stored in the apple trees less frequently fluctuated during stage I. The order of determination coefficient over the whole growing stage was as follows: maximum vapor pressure deficit > maximum air temperature > net radiation. Multiple regression relationships among MDS and environmental factors can be used to calculate the MDS for well water supplied to apple trees, which could be considered as a reference value when the tree requires irrigation. Thus, the fluctuation regularities of tree trunk diameter could reflect the water status of the entire fruit period of fruit trees situated in arid areas of Northwest China and help improve orchard water management, as well as ensure the normal growth of fruit trees.
Key words: trunk diameter fluctuation    maximum daily diameter shrinkage    apple tree    environmental factor    irrigation schedule    

果树茎干直径微变化是指茎干直径每日膨胀和收缩的循环过程,是表征果树生长状况的重要指标,它与土壤含水量、植物水分状况和气象因素关系密切[1, 2]。植物水分参数如茎干水势、叶水势和土壤水分等测定耗时耗力,而茎干直径微变化监测简单易行,因此茎干直径微变化监测有望被用作诊断植物水分状况的手段[3, 4]。测树器是目前测量茎干直径微变化的主要仪器之一[5],其基本原理是利用滑动电阻将茎干变化产生的位移转换为电阻值的变化,通过对电阻值变化的自动记录实现对茎干直径微变化的连续监测。茎干直径微变化可以表征果树生长及其体内水分状况[6, 7]

从果树茎干直径微变化资料中可以得到多个参数,它们与植物体的生长和水分状况的关系是当前研究的热点。日最大茎干直径(MXTD)在生育后期可以很好的反映果树水分状况,且与土壤含水量关系密切[8];茎干生长速率(TGR)是果树营养生长发育的体现,成熟期果树的根系深,植物体调节水分亏缺能力较强,在果树坐果量较大时,TGR与环境因子的相关性较弱,不能用于指导灌溉[9]。茎干直径日最大收缩量(MDS)与茎干水势呈稳定的负相关关系,MDS受水势控制,不受随年际变化的产量影响[10, 11],其大小可反映果树的水分亏缺状况[12]。TGR和MDS可作为梨枣水分亏缺的诊断指标[13],而在不同生长阶段的棉花宜采用不同参数作为水分诊断指标[14]。西北旱区果树茎干直径变化规律如何,由茎干直径微变化监测数据得到的相关参数是否与苹果树水分状况密切相关,有待进一步验证。

本研究采用测树器监测2007—2010西北干旱区盛果期苹果树的茎干直径微变化,在分析茎干直径微变化规律的基础上得到茎干直径微变化与作物水分状况的关系。本文的目的是:(1)研究西北旱区特殊生长条件下盛果期苹果树的茎干直径微变化规律及其影响因素;(2)探讨茎干直径微变化过程中相关参数指导盛果期苹果树灌溉的可行性。

1 材料与方法 1.1 试验区概况

试验于2007—2010年在中国农业大学石羊河流域农业与生态节水试验站(甘肃武威)进行。试验站位于北纬37°52′,东径102°51′,海拔高程1581 m,属武威市平川灌区。年平均气温8 ℃,年积温(>0 ℃)3550 ℃,年平均降雨量164.4 mm,年平均水面蒸发量2000 mm,干旱系数在15—25之间,年平均日照时数3000 h,无霜期150 d左右,为典型温带干旱大陆性气候。地下水位为40—50 m。土壤质地为沙壤土,平均土壤干容重为1.46 g/cm3,平均土壤田间持水量为0.30 cm3/cm3

1.2 不同年份的灌溉制度

试验对象苹果树为元帅系列红香蕉品种,砧木为山丁子(Malus domestica Borkh. cv Golden Delicious),树龄为29a(2010)。苹果树分布呈东西走向,行距为6 m,株距为4 m。试验苹果树生育期有发芽开花、展叶幼果、果实膨大、果实成熟四个生育期。依据多年平均耗水量计算灌水定额;采用小区畦灌的灌溉方式,用水表控制水量,依据果园实际管理情况和环境条件确定灌水时间。灌溉水源为地下水。每年施肥量相同。2007—2010年的灌溉制度及降雨量见表 1

表1 不同年份灌溉制度 Table 1 Irrigation schedule in different years
生育期Stages2007 2008 2009 2010
WNIDOY WNIDOY WNIDOY WNIDOY
发芽开花期 Bud development and flowering120.236-114.836113114.833103168.537122
展叶幼果期 Leaf expansion152.035165151.935161151.936145125.235167
果实膨大期 Fruit expanding149.097197149.078204149.070184149.074203
成熟采收期 Fruit maturing62.51624462.53024862.53623686.327240
全生育期 Whole growth stage483.7184478.2179478.2175528.9173
IDOY: 灌溉时间在一年中的天数the day of year for the irrigation time, N: 生育期天数the number of days for growing season, W: 灌水量the irrigation amount (mm)
1.3 测定指标

本试验采用植物生长测量仪(Diameter Dendrometer,Ecomatik GmbH,Germany)连续自动监测果树茎干直径变化。两个生长测量仪DD1、DD2分别安装在地面以上50 cm处的东西方向和100 cm处的南北方向树干上,用锡箔纸进行防晒处理。生长测量仪与植物生理监测系统(Meteorological monitoring system; Jauntering,Taiwan)的数据自动采集器(HL20 Data Logger)相连接,每隔1 h自动记录生长测量仪滑动电阻的电阻值。植物生理监测系统监测数据还包括净辐射、温湿度、风速和土壤热通量等气象因素。水汽压差由空气温度和相对湿度计算。

相对茎干直径(D):

式中,ohm为生长测量仪监测的滑动电阻值(KΩ),k为电阻、位移转换系数。生长测量仪DD1和DD2的k值分别为0.204和0.223。i时刻茎干直径的变化量Δi由两个相邻时刻的相对茎干直径计算得到:

若以监测起始时间作为茎干直径相对零点,则可以求得监测时段内茎干直径的微变化量。MDS为茎干直径早晨某时刻日最大值和傍晚某时刻日最小值的差[1]。当受大风、降雨等影响时,树干直径可能并非在以上两个特定时刻出现最大和最小值,此时MDS不能反映植物体内的水分状况,应将此时的MDS数据剔除。

根区土壤体积含水率采用管式时域反射仪(Tube-TDR; IMKO Micromodultechink,Germany)监测。试验选取3株果树,每株树布置4根测管,测管深度180 cm,每5 d测定1次,测点垂向间距为10 cm。每隔30 d用烘干称重法对TDR进行校正。

茎干水势的测定方法如下:选取3株样树,测定前3 h,在接近果树树干处选取2片叶柄粗壮的成熟叶片,用锡箔纸覆盖的不透光密封塑料袋将叶片包裹好,在中午将叶片离体后立即测定。采用压力室(SKPM 1400,Skye,United Kingdom)测定中午遮盖叶片水势,并认为中午遮盖叶片水势与茎干水势相等[15]

采用FAO-56中的Penman-Monteith公式计算参考作物蒸发蒸腾量[16]

式中,Rn为冠层表面的净辐射(MJ m-2 h-1),G为土壤热通量(MJ m-2 h-1),T为2 m高度处的平均温度(℃),esea分别为平均温度对应的饱和水汽压和平均实际水汽压(kPa),u2为2 m处平均风速(m/s),Δ为温度水汽压斜率(kPa/℃),γ为湿度计常数(kPa/℃)。

2 结果分析 2.1 茎干直径日变化规律

2 008年不同生育期茎干直径和参考作物蒸发蒸腾量的变化如图 1所示。每个生育期选取3 d进行茎干直径微变化分析,以所选日期初始的0:00时刻为茎干直径相对0点,记录茎干直径的波动状况。从图中可以发现,晴天或多云天气条件下,7:00—8:00的平均ET0接近0 mm/h,这一时刻果树茎干直径达到最大值;在8:00—16:00范围内,树干直径不断减小;在16:00到次日8:00时段内树干直径不断增大。

图1 2008年西北旱区苹果园茎干直径微变化 Fig.1 The trunk diameter fluctuation of apple tree (2008) 注解
2.2 茎干直径日最大值变化规律

茎干直径日最大值(MXTD)的生育期变化反映果树不同生育阶段的生长速率[2]。从图 2中可以看出,灌水及降雨之后1—2 d,MXTD值会增大200 μm—300 μm,降雨后3—4 d,MXTD值减小50 μm—100 μm,果树茎干变化恢复到降雨前的增长趋势。当降雨或灌溉发生时,茎干生长速率增大,之后1—3 d茎干生长速率为负值。

图2 2007—2010年茎干直径日最大值MXTD (以果树发芽为0点) Fig.2 The season vairiation of maximum of stem daily diamter during 2007—2010 (MXTD,which increased from budding)

DOY 94—120 d属于发芽开花期,此时苹果树叶面积指数小,叶片未伸展,果树茎干直径生长不明显;DOY 120—186 d属于展叶幼果期,此时生长速率较大,茎干直径不断增加,MXTD与DOY关系图的斜率为30—50;DOY 200 d后,进入果实膨大和成熟期,枝条和叶片生长显著减慢,果实迅速膨大,此期间MXTD比较稳定。

2.3 茎干直径日最大收缩量的变化规律

众多学者认为茎干直径日最大收缩量(MDS)与植物茎干水势关系密切,最能反映植物体内水分状况,并认为MDS主要受气象因素、土壤含水量影响[17, 18, 19]图 3为MDS与参考作物蒸发蒸腾量的季节变化规律。图 3表明,各年份整个生育期MDS均呈现先增大后减小的季节变化趋势,且变化幅度较大,这可能与果园畦灌灌溉方式有关。4—5月MDS开始增加,6—7月达到最大(400—500 μm)。2007年MDS从7月的500 μm逐渐减小至9月底的300 μm;2008年MDS在6月初达到400 μm逐渐减小到9月底300 μm;2009和2010年MDS从4月的50 μm逐步增加至5月底的300 μm,6月分别达到最大值400 μm和500 μm,然后逐步减小。图 3还表明,除发芽开花期外,ET0增加时,苹果树MDS增大。

图3 茎干直径日最大收缩量MDS (μm) Fig.3 Season variation of maximum daily stem shrinkage (MDS)

苹果树MDS与茎干水势(φstem)呈显著负相关关系(r2=0.76* * *,n=14),随着φstem减小,MDS增大(图 4)。以往研究也表明,MDS与φstem呈线性关系[7, 18, 20, 21]。苹果树MDS与茎干水势关系密切,表明MDS可以反映成年苹果树体内水分状况[11]

图4 晴天天气条件下旱区苹果园茎干直径日最大收缩量(MDS)与茎干水势(φstem)的关系 Fig.4 Relationship between maximum daily stem shrinkage (MDS) and stem water potential (φstem)

通过多年试验资料,分析得到MDS与气象因子间的关系(表 2)。从表 2中可以发现,除2007年外,果实膨大和成熟期MDS对净辐射、日最高空气温度(Tmax)、日最大水汽压差响应明显高于发芽开花和展叶幼果期。果实膨大和成熟期MDS与日平均净辐射(Rn)、日最大水汽压饱和差(VPDmax)的相关系数均超过0.5;2009年果实膨大和成熟期MDS与VPDmax相关系数最高达到0.948。全生育期MDS与气象因素的决定系数大小顺序为VPDmax>Tmax>Rn

表2 不同生育阶段MDS对环境因子的响应 Table 2 Relationship between MDS and environmental factors in different stages
年份 YearX发芽开花和展叶幼果期 Bud development,flowering and leaf expansion 果实膨大和成熟期 Fruit expanding and maturing
abr2nabr2n
2007Rn/(W/m2)3.04-58.420.733* * *431.7480.040.519* * *69
Ta/℃47.38-534.770.633* * *4323.09-164.150.294* * *69
Tmax/℃28.47-405.330.741* * *4322.94-323.710.655* * *69
Tmid13/℃27.67-334.700.761* * *4322.71-274.460.643* * *69
T8—16/℃33.67-403.140.789* * *4325.24-270.330.588* * *69
VPD(KPa)165.55225.240.200* *43207.79103.990.306* * *69
VPDmax/KPa132.20-86.260.775* * *43100.48-31.820.709* * *69
ET0/(mm/d)71.20146.050.322* * *4369.8371.260.499* * *69
多元模型 MDS=-207.82+105.60VPD-25.03Ta+2.00Rn +33.30T8—16+47.38ET0,r2=0.913MDS=332.25-27.07Tmax+213.11VPDmax, r2=0.731
2008Rn/(W/m2)0.7198.460.132* *961.2420.900.677* * *71
Ta/℃2.93156.840.0209613.76-43.450.326* * *71
Tmax/℃3.02123.220.042*9611.49-119.500.560* * *71
Tmid13/℃3.54117.110.061*9611.40-97.040.537* * *71
T8—16/℃3.79123.070.051*9613.45-99.210.511* * *71
VPD/KPa15.20191.500.00396152.4182.090.357* * *71
VPDmax/KPa20.00149.350.046*9663.4629.650.602* * *71
ET0/(mm/d)16.93140.680.041*9650.4119.620.680* * *71
多元模型MDS=141.55+2.20Rn-69.08ET0,r2=0.239MDS=19.62+50.41ET0,r2=0.680
2009Rn/(W/m2)1.57-76.960.420* * *951.91-44.180.791* * *66
Ta/℃22.36-213.530.460* * *9525.52-223.180.402* * *66
Tmax/℃16.32-274.070.439* * *9523.24-403.950.862* * *66
Tmid13/℃14.75-194.470.388* * *9523.80-365.430.820* * *66
T8—16/℃19.87-259.260.491* * *9527.52-371.190.726* * *66
VPD/KPa52.55113.460.02095326.0617.220.617* * *66
VPDmax/KPa86.83-65.810.374* * *95113.03-44.440.948* * *66
ET0/(mm/d)62.81-67.860.408* * *9577.35-21.010.846* * *66
多元模型MDS=101.60-275.26VPD+175.80VPDmax+ 41.92T-37.66Tmax+47.38ET0,r2=0.807MDS=-53.57+0.32Rn+97.65VPDmax,r2=0.953
2010Rn/(W/m2)1.87-80.790.480* * *791.80-26.770.716* * *80
Ta/℃19.58-110.570.575* * *7916.82-90.650.337* * *80
Tmax/℃16.24-214.270.664* * *7916.53-243.770.692* * *80
Tmid13/℃16.39-181.590.654* * *7916.85-217.110.697* * *80
T8—16/℃17.73-158.890.641* * *7918.09-191.510.586* * *80
VPD/KPa217.23-10.510.333* * *79225.1732.810.509* * *80
VPDmax/KPa121.42-112.630.756* * *7991.08-30.560.794* * *80
ET0/(mm/d)77.02-91.470.517* * *7967.44-13.810.700* * *80
多元模型MDS=-86.61-130.28VPD+160.30VPDmax, r2=0.799MDS=36.41-23.03Ta+15.29T8—16+95.38VPDmax, r2=0.864
 以DOY 186—200将生育期划分为两个阶段; 表达式MDS=aX+b,式中X表示不同的环境因子,a,b为系数,r2为相关系数平方;Rn表示净辐射,TaTmaxTmid13T8—16分别为日平均、日最大、中午13:00、和8:00—16:00的空气温度,VPD和VPDmax分别为日平均和日最大水汽压差(KPa),ET0表示参考作物蒸发蒸腾量(mm/d);r2没有标记表示显著性因子高于0.05,不显著,*、* *、* * *分别表示显著性水平P<0.05,P<0.01,P<0.001
3 讨论 3.1 茎干直径微变化规律

Ortuño等认为日最大、最小茎干直径分别在日出和下午的某个时刻[1]。Intrigliolo和Castel也认为茎干直径在早晨达到最大值,在黄昏时达到最小值[22]。石羊河流域苹果树日最大最小茎干直径出现在8:00和16:00两个特定时刻,这为非连续测量确定日最大收缩量提供科学依据。

连续降雨天气条件下,果树茎干直径变化不再呈正弦曲线波动,茎干直径日最小值或最大值出现在一天起始或结束时刻,而不是出现在16:00和8:00。这可能是由于树干吸水,直径膨大,此时得到的茎干直径微变化参数不能反映植物体吸水失水过程,应进行校正。晴天和多云天气条件下茎干直径微变化规律无明显差别,说明茎干直径微变化受热胀冷缩影响较小。分析降雨或灌溉导致的茎干直径波动有以下原因:(1)降雨和灌溉使得植物体内水分状况良好,果树茎干直径显著增大;(2)降雨后果树茎干树皮受水分影响发生膨胀,随着树皮水分减少,果树茎干直径也减小,而且这种减小可以抵消茎干直径生长。这会引起茎干直径变化监测结果误差,需要进行合理校正以得到正确的茎干直径变化监测结果。

雨天天气下,茎干直径微变化峰值不明显。除了阴雨天气,日最大茎干直径(MXTD)在发芽后逐日增大;成熟采收期MXTD不再增加,甚至是逐日降低。2007和2008年,果树茎干直径在DOY 194—200 d期间停止增长,2009—2010年,在DOY 186—194 d之间茎干直径不再增长。DOY 120—186 d为果树展叶幼果期和果实膨大期前半段,这期间果树枝条叶片快速生长。

3.2 茎干直径日最大收缩量(MDS)与各环境因素关系

MDS可以反映成年苹果树体内水分状况,因此采用MDS探讨茎干直径微变化对环境因素的响应。全生育期MDS与气象因素的决定系数大小顺序为VPDmax>Tmax>Rn,这表明VPDmax是影响苹果树的MDS的主要因素。有研究表明其他气象因素,如太阳辐射[23]和空气温度[7]是与MDS最相关的因素。MDS与VPDmaxTmax相关性高表明MDS受最大需水时段内的气象条件影响大[24],Egea等认为MDS与各气象因素相关程度差异主要是果树种类不同造成的[24]。从多元线性回归模型看(表 2),果实膨大和成熟期MDS与气象因子综合相关系数高于发芽开花和展叶幼果期,这可能是果树体内储水量大,MDS的变化受气象因素的影响大[11]

ET0增加时,苹果树茎干失水增加,这会导致茎干水势下降和植物与土壤间水势梯度上升,从而MDS增大[11]。由于发芽开花期叶片较小,ET0增大未导致果树茎干过量失水,茎干收缩不明显,故MDS与ET0之间的关系不明显。不同生育阶段MDS与ET0之间的决定系数差别较大,发芽开花和展叶幼果期较小,果实膨大和成熟期较高为0.50—0.85(表 2)。研究表明,成年柠檬树(30年生)、樱桃树(2年生)、石榴树(10年生)和油桃树(7年生)的MDS与ET0之间的决定系数分别为0.68[7]、0.5—0.6[26]、0.76[26]和0.37[27],不同果树MDS与ET0的关系不仅与果树种类有关,还与土壤含水量[28]和树干液流量[29]有关。

3.3 茎干直径微变化与产量的关系

2007年DOY 150—280之间,茎干直径增大1994 μm。2008、2009和2010年茎干直径增大总量分别为4796、2152 μm和3063 μm,2007—2010年苹果产量分别为81200、37715、82067、32597 kg/hm2,果实产量越高,茎干直径年增长总量较小,果实负载量对茎干直径的增大总量有影响。从年际变化看,直径年增长量有下降趋势。Berman和DeJong的研究认为果实产量越高,茎干直径年增长量越低,单株果树产量与树干直径年增长量呈反比关系[30]。Conejero也认为果实产量与茎干直径微变化的关系密切[20]

3.4 茎干直径日最大收缩量指导灌溉方法探讨

由于茎干直径微变化受气象因素、土壤水分、树龄、耕作措施等影响较大,目前很少采用其绝对值作为灌溉标准,而是根据不同水分状况下的茎干直径微变化规律来进行精确灌溉[31]。其基本原理是以充分供水下各参数的变化为标准,根据实际的参数与充分供水下规律对比,得到实际生产中的灌溉制度。

充分供水条件下MDS主要受气象因素影响,充分灌溉下MDS的值可作为灌溉参考值,当苹果树茎干MDS持续高于水分充足条件下的MDS时,就需要进行灌溉来保证果树体内水分状况良好[17]。MDS可以充分反映植物细胞吸水膨胀、失水收缩的过程,故通过充分供水下的MDS的来指导灌溉是目前研究的热点。根据本研究结论,MDS可以由以下几种途径确定:第一,精确测定其特定时段树干直径(早晨和傍晚的最大和最小值)可以得到近似的MDS数据;第二,采用测树器实际测定MDS结果;第三,采用经验公式,根据单一因素或多因素回归模型近似计算MDS。假定充分供水下的MDS为MDSr,实际生长条件下的MDS为MDSt,则可以得到MDS的信号强度SIMDS的变化过程[1]

充分供水灌溉标准SIMDS可取为1或者小于1;依据灌溉可利用水资源状况,可取SIMDS为1.15、1.25等作为非充分灌溉的标准。一般当MDSt值连续3d超过所选阈值时进行灌溉。若需要在某阶段进行非充分灌溉,则调高这一阶段的信号强度[2]

4 结论

果树茎干直径在8:00左右达到最大值,在16:00左右达到最小值,精确测定这两个时刻茎干直径可近似得到其日最大收缩量(MDS)。MXTD呈先增长后保持稳定的季节变化规律;MDS与茎干水势关系密切,表明茎干直径微变化可以反映苹果树水分状况;MDS对VPDmaxET0响应最为明显,果实膨大和成熟期的MDS对净辐射、空气温度、水汽压差、参考作物蒸发蒸腾量响应明显高于发芽开花和展叶幼果期。综上所述,苹果树茎干直径微变化规律可以为制定苹果园的灌溉制度提供科学依据。

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