From leaf to whole-plant water use efficiency(WUE)in complex canopies:Limitations of leaf WUE as a selection target

Plant water use efficiency(WUE) is becoming a key issue in semiarid areas, where crop production relies on the use of large volumes of water. Improving WUE is necessary for securing environmental sustainability of food production in these areas. Given that climate change predictions include increases in temperature and drought in semiarid regions,improving crop WUE is mandatory for global food production. WUE is commonly measured at the leaf level, because portable equipment for measuring leaf gas exchange rates facilitates the simultaneous measurement of photosynthesis and transpiration. However,when those measurements are compared with daily integrals or whole-plant estimates of WUE, the two sometimes do not agree. Scaling up from single-leaf to whole-plant WUE was tested in grapevines in different experiments by comparison of daily integrals of instantaneous water use efficiency [ratio between CO2assimilation(AN) and transpiration(E); AN/E] with midday AN/E measurements, showing a low correlation, being worse with increasing water stress. We sought to evaluate the importance of spatial and temporal variation in carbon and water balances at the leaf and plant levels. The leaf position(governing average light interception) in the canopy showed a marked effect on instantaneous and daily integrals of leaf WUE. Night transpiration and respiration rates were also evaluated, as well as respiration contributions to total carbon balance. Two main components were identified as filling the gap between leaf and whole plant WUE: the large effect of leaf position on daily carbon gain and water loss and the large flux of carbon losses by dark respiration. These results show that WUE evaluation among genotypes or treatments needs to be revised.

极干旱胁迫对雀麦、多年生黑麦草生长和体内水分的影响

为研究极端干旱对牧草生长的影响,选择多年生黑麦草(Lolium perenne,Lp)和雀麦(Bromus valdivianus,Bv)给予80%~85%植物有效水(Plant available water,PAW)和20%~25%PAW 2种水分处理,分析两种牧草生长及体内水分状况对干旱胁迫的响应。研究表明:80%~85%PAW充足水分下,两种牧草生物量积累、水势(Water potential,WP)、相对含水量(Relative water content,RWC)和净光合速率(Net photosynthetic rate,Pn)无明显种间差异。Bv叶片宽而重,蒸腾速率(Transpiration rate,Tr)、CO_(2)总导度(Total conductance to CO_(2),CndCO_(2))和气孔导度(Conductance to H 2O,Gs)显著高于Lp。而Lp分蘗多、叶多汁,瞬时水分利用效率是Bv的1.63倍。20%~25%PAW对两种牧草生长影响不完全一致,叶饱和重、干重和叶面积有相反变化趋势,但与充足水分相比差异不显著;Pn,Tr,CndCO_(2),Gs和RWC则极显著降低,WP极显著降低了1.60 MPa,致使枯叶占比和叶温差显著升高。总之,雀麦和多年生黑麦草生长相近,水分利用模式不同;遭受极端干旱,不同种的两种牧草耐旱机制具有一定的共性,通过增强叶片持水力、降低水分循环、减少蒸腾失水以提高牧草抗旱性。

Assessing effects of deficit irrigation techniques on water productivity of tomato for subsurface drip irrigation system

Water resources are subjected to ever-increasing supply constraints due to extensive agricultural water demand for irrigated lands.Therefore,water-saving irrigation strategies need to be explored.The present study was conducted to explore the possibilities of using regulated deficit irrigation(RDI)and partial root zone drying irrigation(PRD)methods as water-saving irrigation techniques for subsurface irrigation.The objective of this study are to assess the effects of RDI and PRD irrigation on the water productivity of vegetable crops(tomato)under SSD systems in arid climatic conditions,and to compare the responses of tomato crops to PRD,RDI,and FI under an SSD system in terms of productivity,crop quality,and the amount of water saved.The field experiment was conducted during the fall 2014-2015 and 2015-2016 seasons in an experimental field located on an educational farm owned by the Faculty of Food and Agriculture Sciences Department,King Saud University,Riyadh,Kingdom of Saudi Arabia.An area of 102.7 m^(2)(13 m×7.9 m)was allocated for the experiment to manage three treatments:RDI,PRD,and full irrigation(FI).The RDI and PRD treatments received 70%of the irrigation water volume of FI.Each was replicated three times.The most important results indicated that the soil water content(SWC)for the RDI and PRD treatments was lower than that of the FI treatments.FI had the highest stomatal conductance values(gs),while PRD had the lowest stomatal conductance values.The photosynthetic rate(A_(n))was lower under RDI and PRD compared to FI.However,there was no significant change in A_(n) between treatments for most readings taken during both time periods,which means that the water saving treatments(PRD and RDI)did not affect the net photosynthesis rate,thereby enhancing irrigation water use efficiency(IWUE)under DI treatments.The water-saving irrigation techniques decreased transpiration rate(T)compared to the FI treatment.The values of the abscisic acid(ABA)contents were higher under PRD and RDI than FI.The marketable yield under the FI treatment yielded the highest values.The fruit quality parameter results showed that the RDI and PRD treatments increased the total soluble solids,vitamin C,and titratable acidity of tomato compared to the FI treatment.Most of the minimum IWUE values were associated with FI.These results indicate the effects of deficit levels on IWUE.