Down-regulation of photosynthesis by drought under field conditions in grapevine leaves

Abstract

The importance of both stomatal closure and reduced carboxylation efficiency on the photo- synthesis decline in response to long term water stress was previously measured in field-grown grapevines. Here we address the question of whether water stress affects the photochemical capacity of leaves, measuring gas-exchange rates and chlorophyll fluorescence under drought and moderate irrigat- ion at intervals through the summer season during three consecutive years. We conclude that usually water stress does not induce photoinhibition in field-grown grapevines, even when stomatal conductance and photosynthesis are reduced to very low values. Moreover, down-regulat- ion of photochemical reactions is low, leading to a general pattern of photosynthetic response to drought consistent in large reductions of stomatal conductance (g), followed by a consistent decrease of CO2 assimilation (A) but with a much lower effect on electron transport rate (ETR). In consequence, the intrinsic water-use efficiency (A/g) increased, as well as the ratio ETR/A. It is suggested that increased electron transport to alternative pathways, such as photorespiration, prevented further down-regulation of ETR under drought conditions. These results are in agreement with our previous reports for potted plants. However it is clear that, under field conditions with a much more slowly developed water stress, ETR reductions are more attenuated than in potted plants, reducing their incidence in carbon assimilation, which seems to be mainly regulated by stomatal closure.

Estimation of Water Stress in Grapevines Using Proximal and Remote Sensing Methods

“…In this study, we found that water deficit induced the inhibition of photosynthesis caused by decreases in stomatal conductance, as clearly observed also by Flexas [41][42][43]. All the tested cultivars activated effective photoprotective mechanisms when drought induced photosynthesis inhibition.…”

Limitations to leaf photosynthesis in field-grown grapevine under drought — metabolic and modelling approaches

“…Differences among species and in the rates of imposition of water deficits, as well as the superimposition of other environmental stresses, may also play a role in the relative importance of stomatal vs non-stomatal limitations under drought (Chaves 1991). In grapevine (Vitis vinifera L.), water stress aggravates photoinhibition of the photochemical apparatus under elevated irradiances, causing stomatal closure and downregulation of carbon assimilation (Correia et al 1990;Quick et al 1992;Rodrigues et al 1993;Chaumont et al 1997;Flexas et al 1998Flexas et al , 1999b. Non-stomatal effects have been suggested for grapevine responses to drought under field conditions, as estimated from coupled gas-exchange and fluorescence measurements (Flexas et al 1998(Flexas et al , 1999bEscalona et al 1999).…”

“…In grapevine (Vitis vinifera L.), water stress aggravates photoinhibition of the photochemical apparatus under elevated irradiances, causing stomatal closure and downregulation of carbon assimilation (Correia et al 1990;Quick et al 1992;Rodrigues et al 1993;Chaumont et al 1997;Flexas et al 1998Flexas et al , 1999b. Non-stomatal effects have been suggested for grapevine responses to drought under field conditions, as estimated from coupled gas-exchange and fluorescence measurements (Flexas et al 1998(Flexas et al , 1999bEscalona et al 1999). However, unresponsiveness of net CO 2 assimilation relative to C i suggests that the occurrence of non-stomatal effects under drought stress may be, to some degree, attributable to patchy stomatal aperture in heterobaric leaves, although these effects may be minimized when water deficits are imposed slowly (Mott and Buckley 2000).…”

Competencia entre Zea mays y Sorghum halepense por agua edáfica y su incidencia en el intercambio gaseoso foliar

“…Sin embargo, Lawlor (2002) estableció que a medida que decrece el CRA, la tasa fotosintética disminuye inicialmente debido a una caída en la conductancia estomática y luego debido a causas metabólicas (no estomáticas), ocasionada fundamentalmente por una disminución en la síntesis de ribulosa 1-5 bifosfato (RUBP). No obstante, Flexas et al (1998) y Maroco et al (2002, determinaron que en condiciones de déficit hídrico prolongadas (días a semanas), luego de generarse una merma en la tasa fotosintética por la disminución de la conductancia estomática se produciría un nuevo ajuste de esta variable a fin de modular el nivel de actividad a la concentración intercelular de CO 2 existente y al bajo nivel de crecimiento alcanzado. De este modo, dadas las tendencias visualizadas en ambas especies, es posible que en S.halepense la disminución en la tasa fotosintética haya sido debida fundamentalmente a causas estomáticas, en tanto la inhibición de la tasa fotosintética de los genotipos de Z.mays podría haberse debido a ambos tipos de limitaciones.…”