温室茄子茎直径微变化与作物水分状况的关系

The relationship between the change of stem diameter and plant water content of eggplants: an experimental study

在温室条件下,采用盆栽土培和小区试验相结合的方法,以茄子(Solanummelongena,品种新乡糙青茄)为材料进行了植株茎直径微变化(膨胀或收缩)与作物体内水分状况的关系试验研究,旨在为利用茎直径微变化无损快速诊断作物水分状况提供理论依据。盆栽和小区试验均采用两因素(土壤水分梯度和作物不同生育阶段)随机区组设计,土壤水分控制下限分别取田间持水量的80%FC(Fieldwatercapacity),70%FC,60%FC和50%FC;生育阶段分别为苗期、花果期和采收期;共有4×3=12个处理组合,重复3次。结果表明:无论是在较高土壤含水量或在较低土壤含水量条件下,在晴好的天气里,茄子茎直径都是在白天收缩,傍晚、夜间复原或膨胀,而且这种微变化动态与植株体内的水分状况密切相关,不同土壤含水量条件下植株茎胀缩的幅度存在明显差异。高水分条件下,植株茎收缩幅度小,复原能力强;低水分条件下,植株茎收缩幅度大,恢复能力差。茎直径变化对环境因子水汽压差(VPD)的响应比较敏感,二者呈正相关关系,相关系数R2为0·8938。茎直径变化量(ΔSd)与叶水势(ψL)、叶片相对含水量(LRWC)呈极显著正相关关系,相关系数R2分别为0·867和0·965。这些结果显示,茎直径变化量能灵敏、实时、准确地反映植株体内的水分状况;与其它作物水分诊断方法(叶水势法,叶片相对含水量法,细胞液浓度法等)相比,茎直径微变化法可能具有简便、稳定、无损、连续监测和自动记录的优势。

A simple nondestructive method to continuously measure plant water content has long been sought in the study of both soil-water-plant relations and the impact of environment on plant growth. A number of methods have been proposed to measure plant water content, and most of these require indirect measurement of other variables, such as leaf water potential and/or leaf water content, to infer plant water content. These methods are destructive, consuming plant tissue and providing only intermittent and localized measurements. In practice, a non-destructive, frequent measure of water content of a whole plant is needed. One way to quantify the water content of a whole plant is to measure the change of stem diameter, which has proven successful for fruit trees. In this paper we experimentally investigate the responsive change of stem diameter of the eggplant to plant water content and soil moisture in a greenhouse. The experiment was conducted at Xinxiang, Henan Province, China （latitude 35.19° N） in a greenhouse of 40 m long and 8.5 m wide. It is a sub-humid area, susceptible to drought. Eggplants （Solanum melongena） were cultivated in pots and a small plot respectively, both in the greenhouse. The soil property in the pots and the plot are： organic matter 18.85g/kg, total-N 1.10g/ kg, total-P 2.22g/kg, available-N 15.61mg/kg, available-P 72.0mg/kg, available-K20 101mg/kg, soil bulk density 1.38kg/ cm^3 , and a field water capacity of 24% . The experiment was designed using a two-factor randomized-block method by taking soil moisture content and growing stages as variables. The soil moisture content was controlled at 80 %, 70 %, 60 % and 50 % of the field water capacity, and growing stages that were chosen were seedling, flowering and fruit-forming, and harvesting stages; each treatment having three replicates. The pots were weighed and watered daily to minimize soil moisture change, and the soil water content of the small plot was monitored using Time Domain Reflectrometry and drying-weight method respectively at five-day intervals. The change of stem diameter was measured continuously using a stem diameter sensor （DD-type） linked to a date logger. The measurement started when the stem diameter was large enough to hold the stem diameter sensor. The sensor was attached to the stem of each plant approximately10-15 cm above the soil surface, and the measurements were taken automatically at an interval of either 10 min or 30 min. The data stored in the data logger was downloaded to a microcomputer after three or five days. The leaf water potential was measured at hourly intervals with a pressure chamber （ZLZ-4）, each measurement was taken on two leaves. The leaf relative water content was measured with the weighing method. Transpiration rate and stomatal conductance were measured by a Portable Photosynthesis System （CIRAS-1 type）. All the measurements were made simultaneously at sunny days from 08：00 to 18：00 to minimize the diurnal variations. Air temperature, relative air humidity, net solar radiation and other atmospheric factors were taken from a standard meteorological station installed in the greenhouse during the growing season from 2002 to 2004. The results showed that on all sunny days the stem diameters shrank in the daytime and returned to their original size at nights, regardless of plant water content. The degree of shrinking and swelling of the stem diameter was closely related to plant water content and soil moisture content. Results from the small-plot experiment indicated that the change of stem diameter was positively related to vapor pressure deficit in the greenhouse with a correlation coefficient of 0. 8938. The diurnal change of stem diameter was closely related to the diurnal change of leaf water potential and relative leaf water content with correlation coefficients 0. 867 and 0.965 respectively （p = 0.01）. These results suggest that the change of stem diameter can be seen as an indicator of plant water content and hence be used as a simple non-destructive method to continuously measure plant water content.